U.S. patent number RE43,618 [Application Number 12/199,498] was granted by the patent office on 2012-08-28 for method and apparatus for destroying dividing cells.
This patent grant is currently assigned to Novocure Ltd. Invention is credited to Yoram Palti.
United States Patent |
RE43,618 |
Palti |
August 28, 2012 |
Method and apparatus for destroying dividing cells
Abstract
The present invention provides a method and apparatus for
selectively destroying dividing cells in living tissue formed of
dividing cells and non-dividing cells. The dividing cells contain
polarizable intracellular members and during late anaphase or
telophase, the dividing cells are connected to one another by a
cleavage furrow. According to the present method the living tissue
is subjected to electric field conditions sufficient to cause
movement of the polarizable intracellular members toward the
cleavage furrow in response to a non-homogenous electric field
being induced in the dividing cells. The non-homogenous electric
field produces an increased density electric field in the region of
the cleavage furrow. The movement of the polarizable intracellular
members towards the cleavage furrow causes the break down thereof
which results in destruction of the dividing cells, while the
non-dividing cells of the living tissue remain intact.
Inventors: |
Palti; Yoram (Haifa,
IL) |
Assignee: |
Novocure Ltd (St. Helier,
NJ)
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Family
ID: |
22672230 |
Appl.
No.: |
12/199,498 |
Filed: |
February 16, 2001 |
PCT
Filed: |
February 16, 2001 |
PCT No.: |
PCT/IB01/00202 |
371(c)(1),(2),(4) Date: |
October 16, 2002 |
PCT
Pub. No.: |
WO01/60994 |
PCT
Pub. Date: |
August 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60183295 |
Feb 17, 2000 |
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Reissue of: |
10204334 |
Oct 16, 2002 |
7333852 |
Feb 19, 2008 |
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Current U.S.
Class: |
607/2 |
Current CPC
Class: |
A61N
1/205 (20130101); A61N 1/326 (20130101); A61B
2018/147 (20130101); A61B 2018/00613 (20130101) |
Current International
Class: |
A61N
1/00 (20060101) |
Field of
Search: |
;607/1-3,101-103
;435/173.7,173.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 330 797 |
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Sep 1989 |
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EP |
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0330797 |
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Sep 1989 |
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EP |
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1 419 660 |
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Dec 1975 |
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GB |
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1419660 |
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Dec 1975 |
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GB |
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2 026 322 |
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Feb 1980 |
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GB |
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2026322 |
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Feb 1980 |
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GB |
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2 043 453 |
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Oct 1980 |
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GB |
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2043453 |
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Oct 1980 |
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GB |
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0160994 |
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Aug 2001 |
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WO |
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WO 01/60994 |
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Aug 2001 |
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WO |
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Other References
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Mag., Dec. 1986, p. 6-23, New York. cited by other .
Berg et al., "Electric Field Effects on Bilogical
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Science, 1987,p. 135-166,vol. 32,Phys. Science, New York. cited by
other .
Kirson et al., "Disruption of Cancer Cell Replication by
Alternating Electric Fields", Cancer Research 64, May 2004, p.
3288-3295, Haifa, Israel. cited by other .
Asbury et al., "Trapping of DNA in Nonuniform Oscillating Electric
Fields", Biophysical Journal, Feb. 1998, p. 1024-1030, vol.
74,Seattle, WA. cited by other .
Janigro et al., "Alternating current electrical stimulation
enhanced chemotherapy: a novel strategy to bypass multidrug
resistance in tumor cells", BMC Cancer, 2006, 6:72. cited by other
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Giladi et al., Microbial Growth Inhibition by Alternating Electric
Fields, Antimicrobial Agents and Chemotherapy, Oct. 2008, p.
3517-3522. cited by other .
Search Report and Written Opinion from corresponding application
PCT/US2008/002134. cited by other .
U.S. Appl. No. 10/263,329, filed Oct. 2, 2002, Palti. cited by
other .
Palti, Oct. 31, 2002, Titled: Apparatus and Method for Treating a
Tumor or the Like. cited by other .
Palti, Nov. 4, 2002, Titled: Method and Apparatus for Destroying
Tumor Cells. cited by other.
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Primary Examiner: Evanisko; George
Attorney, Agent or Firm: Proskauer
Parent Case Text
.Iadd.CROSS REFERENCE TO RELATED APPLICATIONS.Iaddend.
.Iadd.This application is a .sctn.371 national stage of
PCT/IB01/00202, filed Feb. 16, 2001, which claims the benefit of
U.S. Provisional Application 60/183,295, filed Feb. 17,
2000..Iaddend.
Claims
What is claimed is:
1. A method for selectively destroying dividing cells in living
tissue, the dividing cells having polarizable intracellular
members, the method comprising the steps of: passing a first
.Iadd.alternating .Iaddend.electric field through the living tissue
to produce a non-homogenous electric field within the dividing
cells with an increased density in a region of a cleavage furrow in
late anaphase or telophase, the non-homogenous electric field
.[.being.]. .Iadd.having a .Iaddend.sufficient .Iadd.electric field
strength .Iaddend.to move the polarizable intracellular members
toward the cleavage furrow until the intracellular members disrupt
the cleavage furrow, wherein the passing step is implemented for
one or more intervals of time that are collectively sufficient for
the disruptions of the cleavage furrow to destroy a significant
portion of the dividing cells in the living tissue, and wherein
passage of the first electric field through nondividing cells in
the living tissue leaves the nondividing cells substantially
undamaged.
2. A method according to claim 1, wherein the cleavage furrow is in
the form of a cytoplasm bridge membrane.
3. A method according to claim 1, wherein the first electric field
has a sufficient frequency so that the non-homogenous electric
field produced in the dividing cells defines electric field lines
which generally converge at a region of the cleavage furrow,
thereby defining the increased density electric field.
4. A method according to claim 1, wherein the passing step
comprises the step of: subjecting the living tissue to an
alternating electric potential at a sufficient frequency to cause
associated electric field lines to penetrate the dividing cells and
form the non-homogenous electric field within the dividing
cells.
5. A method according to claim 1, wherein the non-homogenous
electric field generates electric forces in the dividing cells
which act to pull the polarizable intracellular members toward the
increased density electric field region.
6. A method according to claim 1, wherein the polarizable
intracellular members are organelles.
7. A method according to claim 1, wherein the passing step
comprises the step of: subjecting the living tissue to a pulsating
alternating electric potential at a sufficient frequency to form
the non-homogenous electric field within the dividing cells.
8. A method according to claim 1, wherein the passing step
comprises the step of: subjecting the living tissue to an
alternating electric potential at a frequency of between about 10
kHz and about 1 MHz.
9. A method according to claim 1, wherein the dividing cells
comprise a first sub-cell and a second sub-cell with the cleavage
furrow connecting the two in late anaphase or telophase.
10. A method according to claim 1, wherein the passing step
comprises the step of: providing a first electrode; providing a
second electrode; applying an alternating electric potential across
the first and second electrodes, wherein the first and second
electrodes are disposed in a vicinity of the living tissue to be
treated.
11. A method according to claim 1 further comprising the step of:
rotating a source of the first electric field relative to the
living tissue.
12. A method according to claim 1, wherein movement of the
intracellular members toward the cleavage furrow increases pressure
being exerted on the cleavage furrow, the increased pressure
causing the region of the cleavage furrow to expand resulting in
the cleavage furrow breaking apart and causing destruction of the
dividing cells.
13. A method according to claim 1, wherein the living tissue is
subjected to the first electric field for a predetermined period of
time.
14. A method according to claim 13, wherein the predetermined
period of time is less than about 2 hours.
15. A method according to claim 1, further comprising: removing the
first electric field for a predetermined period of time; and
resubjecting the living tissue to the first electric field after
the predetermined period of time has passed.
16. A method according to claim 1, wherein the first electric field
is a substantially uniform electric field.
17. A method according to claim 1, wherein the passing step is
continued for one or more intervals of time that collectively
comprise at least two hours.
.[.18. A method for selectively destroying dividing cells in living
tissue, the dividing cells containing polarizable intracellular
members, the method comprising the step of: passing an electric
field through the living tissue to create conditions in dividing
cells in late anaphase or telophase which are sufficient to cause
displacement of the polarizable intracellular members towards a
cleavage furrow connecting the dividing cells in response to a
non-homogenous electric field being induced in the dividing cells,
wherein the passing step is continued for one or more intervals of
time that are collectively sufficient to permit the displacement of
the polarizable intracellular members to cause a break down of the
cleavage furrow which results in the destruction of a significant
portion of the dividing cells while non-dividing cells of the
living tissue remain intact..].
.[.19. A method according to claim 18, wherein the passing step
comprises the step of: subjecting the living tissue to an
alternating electric potential at a frequency of between about 10
kHz and about 1 MHz..].
.[.20. A method according to claim 18, wherein the passing step is
continued for one or more intervals of time that collectively
comprise at least two hours..].
21. A method for selectively destroying a dividing-cell organism,
the organism containing polarizable intracellular members and being
attached to one another in late anaphase or telophase with a
cleavage furrow, the method comprising the step of: passing an
.Iadd.alternating .Iaddend.electric field through the organism
.[.to create.]. .Iadd.at a frequency that induces a non-homogenous
.Iaddend.electric field .[.conditions sufficient.]. .Iadd.in the
organism during late anaphase or telophase, the alternating
electric field having a sufficient electric field strength
.Iaddend.to cause displacement of the polarizable intracellular
members towards the cleavage furrow .[.in response to a
non-homogenous electric field being induced in the organism.].
.Iadd.until the intracellular members disrupt the cleavage
furrow.Iaddend., wherein the electric field conditions are applied
for one or more intervals of time that are collectively sufficient
to permit the non-homogenous electric field produced within the
dividing cells to cause the displacement of the polarizable
intracellular members, to cause a break down of the cleavage furrow
which results in destruction of the dividing organism.
22. A method according to claim 21, wherein the passing step is
continued for one or more intervals of time that collectively
comprise at least two hours.
.Iadd.23. A method according to claim 1, wherein the alternating
electric field has a frequency of about 100 kHz and an electric
field strength of about 78 V/cm..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to selective destruction of rapidly
dividing cells and, more particularly, to a method and device for
selectively destroying dividing cells.
BACKGROUND OF THE INVENTION
It is known in the art that tumors, particularly malignant or
cancerous tumors, grow very uncontrollably compared to normal
tissue. Such expedited growth enables tumors to occupy an
ever-increasing space and to damage or destroy tissue adjacent
thereto. Furthermore, certain cancers are characterized by an
ability to transmit cancerous "seeds", including single cells or
small cell clusters (metastasises), to new locations where the
metastatic cancer cells grow into additional tumors.
The rapid growth of tumors in general, and malignant tumors in
particular, as described above, is the result of relatively
frequent cell division or multiplication of these cells compared to
normal tissue cells. The distinguishably frequent cell division of
cancer cells is the basis for the effectiveness of existing cancer
treatments, e.g., irradiation therapy and the use of various
chemo-therapeutic agents. Such treatments are based on the fact
that cells undergoing division are more sensitive to radiation and
chemo-therapeutic agents than non-dividing dells. Because tumor
cells divide much more frequently than normal cells, it is
possible, to a certain extent, to selectively damage or destroy
tumor cells by cells, it is possible, to a certain extent, to
selectively damage or destroy tumor cells by radiation therapy
and/or by chemotherapy. The actual sensitivity of cells to
radiation, therapeutic agents, etc., is also dependent on specific
characteristics of different types of normal or malignant cell
type. Thus, unfortunately, the sensitivity of tumor cells is not
sufficiently higher than that of many types of normal tissues. This
diminishes the ability to distinguish between tumor cells and
normal cells and, therefore, existing cancer treatments typically
cause significant damage to normal tissues, thus limiting the
therapeutic effectiveness of such treatments. Furthermore, the
inevitable damage to other tissue renders treatments very traumatic
to the patients and, often, patients are unable to recover from a
seemingly successful treatment. Also, certain types of tumors are
not sensitive at all to existing methods of treatment.
There are also other methods for destroying cells that do not rely
on radiation therapy or chemotherapy alone. For example, ultrasonic
and electrical methods for destroying tumor cells may be used in
addition to or instead of conventional treatments. In the typical
electrical method, electrical current is delivered to a region of
the target tissue using electrodes that are placed in contact with
the body of the patient. The applied electrical current destroys
substantially all cells in the vicinity of the target tissue. Thus,
this type of electrical method does not discriminate between
different types of cells within the target tissue and results in
the destruction of both tumor cells and normal cells.
In U.S. Pat. No. 6,043,066 ('066) to Mangano, a method and device
are presented which enable discrete objects having a conducting
inner core, surrounded by a dielectric membrane to be selectively
inactivated by electric fields via irreversible breakdown of their
dielectric membrane. One potential application for this is in the
selection and purging of certain biological cells in a suspension.
According to this patent, an electric field is applied for
targeting selected cells to cause breakdown of the dielectric
membranes of these tumor cells, while purportedly not adversely
affecting other desired subpopulations of cells. The cells are
selected on the basis of intrinsic or induced differences in a
characteristic electroporation threshold. The differences in this
threshold can depend upon a number of parameters, including the
difference in cell size.
The method of the '066 patent is therefore based on the assumption
that the electroporation threshold of tumor cells is sufficiently
distinguishable from that of normal cells because of differences in
cell size and differences in the dielectric properties of the cell
membranes. Based upon this assumption, the larger size of many
types of tumor cells makes these cells more susceptible to
electroporation and thus, it may be possible to selectively damage
only the larger tumor cell membranes by applying an appropriate
electric field. One disadvantage of this method is that the ability
to discriminate is highly dependent upon on cell type, for example,
the size difference between normal cells and tumor cells is
significant only in certain types of cells. Another drawback of
this method is that the voltages which are applied may damage some
of the normal cells and may not damage all of the tumor cells
because the differences in size and membrane dielectric properties
are largely statistical and the actual cell geometries and
dielectric properties may vary significantly.
All living organisms proliferate by cell division, including tissue
cultures, microorganisms (such as bacteria, mycoplasma, yeast,
protozoa, and other single-celled organisms), fungi, algae, plant
cells, etc. Dividing cells of organisms may be destroyed, or their
proliferation controlled, by methods that are based on the
sensitivity of the dividing cells of these organisms to certain
agents. For example, certain antibiotics stop the multiplication
process of bacteria
The process of eukaryotic cell division is called "mitosis", which
involves nine distinct phases (see Darnell et al, Molecular Cell
Biology, New York: Scientific American Books, 1986, p. 149). During
interphase, the cell replicates chromosomal DNA, which begins
condensing in early prophase. At this point, centrioles (each cell
contains 2) begin moving towards opposite poles of the cell. In
middle prophase, each chromosome is composed of duplicate
chromatids. Microtubular spindles radiate from regions adjacent to
the centrioles, which are closer to their poles. By late prophase,
the centrioles have reached the poles, and some spindle fibers
extend to the center of the cell, while others extend from the
poles to the chromatids. The cells them moves into metaphase, when
the chromosomes move toward the equator of the cell and align in
the equatorial plane. Next is early anaphase, during which time
daughter chromatids separate from each other at the equator by
moving along the spindle fibers toward a centromere at opposite
poles. The cell begins to elongate along the axis of the pole; the
pole-to-pole spindles also elongate. Late anaphase occurs when the
daughter chromosomes (as they are not called) each reach their
respective opposite poles. At this point, cytokinesis begins as the
cleavage furrow begins to form at the equator of the cell. In other
words, late anaphase is the point at which pinching of the cell
membrane begins. During telophase, cytokinesis is nearly complete
and the spindles disappear. Only a relatively narrow membrane
connection joins the two cytoplasms. Finally, the membranes
separate fully, cytokinesis is complete, and the cell returns to
interphase.
In meisosis, the cell undergoes a second division, involving
separation of sister chromosomes to opposite poles of the cell
along spindle fibers, followed by formation of a cleavage furrow
and cell division. However, this division is not preceded by
chromosome replication, yielding a haploid germ cell.
Bacteria also divide by chromosome replication, followed by cell
separation. However, the daughter chromosomes separate by
attachment to membrane components; there is no visible apparatus
that contributes to cell division as in eukaryotic cells.
What is needed in the art and has heretofore not been available is
a method of killing dividing cells that better discriminates
between dividing cells, including single-celled organisms, and
non-dividing cells and is capable of selectively destroying the
dividing cells or organisms with substantially no affect on the
non-dividing cells or organisms.
SUMMARY OF THE INVENTION
The present invention provides a new method and apparatus for
selectively destroying cells undergoing growth and division. This
includes cells, particularly tumor cells, in living tissue and
single-celled organisms. The method and apparatus of the present
invention eliminate or control the growth of such living tissue or
organisms.
A major use of the method and apparatus of the present invention is
in treatment of tumors by selective destruction of tumor cells with
substantially no affect on normal tissue cells and, thus, the
invention is described below in the context of selective
destruction of tumor cells. It should be appreciated however that,
for the purpose of the description that follows, the term "cell"
may also refer to single-celled organisms (eubacteria, bacteria,
yeast, protozoa), multi-celled organisms (fungi, algae, mold), and
plants as or parts thereof that are not normally classified as
"cells". The method of the present invention enables selective
destruction of tumor cells, or other organisms, by selective
destruction of cells undergoing division in a way that is more
effective and more accurate (e.g., more adaptable to be aimed at
specific targets) than existing methods. Further, the method of the
present invention causes minimal damage, if any, to normal tissue
and, thus, reduces or eliminates many side-effects associated with
existing selective destruction methods, such as radiation therapy
and chemotherapy. The selective destruction of dividing cells in
accordance with the method of the present invention does not depend
on the sensitivity of the cells to chemical agents or radiation.
Instead, the selective destruction of dividing cells is based on
distinguishable geometrical characteristics of cells undergoing
division, in comparison to non-dividing cells, regardless of the
cell geometry of the type of cells being treated.
In an embodiment of the present invention, cell geometry-dependent
selective destruction of living tissue is performed by inducing a
non-homogenous electric field in the cells, as described below.
It has been observed by the present inventor that, while different
cells in their non-dividing state may have different shapes, e.g.,
spherical, ellipsoidal, cylindrical, "pancake" like, etc., the
division process of practically all cells is characterized by
development of a "cleavage furrow" in late anaphase and telophase.
This cleavage furrow is a slow constriction of the cell membrane
(between the two sets of daughter chromosomes) which appears
microscopically as a growing cleft (e.g., a groove or a notch) that
gradually separates the cell into two new cells. During this
division process, there is a transient period (telophase) during
which the cell structure is basically that of two sub-cells
interconnected by a narrow "bridge" formed of the cell material.
The division process is completed when the "bridge" between the two
sub-cells is broken. The selective destruction of tumor cells in
accordance with an embodiment of the present invention utilizes
this unique geometrical feature of dividing cells, as described
below.
When a cell or a group of cells are under natural conditions or
environment, i.e., part of a living tissue, they are disposed
surrounded by a conductive environment consisting mostly of an
electrolytic inter-cellular fluid and other cells that are composed
mostly of an electrolytic intra-cellular liquid. When an electric
field is induced in the living tissue, by applying an electric
potential across the tissue, an electric field is formed in the
tissue having and the specific distribution and configuration of
the electric field lines defines the paths of electric currents in
the tissue, if currents are in fact induced in the tissue. The
distribution and configuration of the electric field is dependent
on various parameters of the tissue, including the geometry and the
electric properties of the different tissue components, and the
relative conductivities, capacities and dielectric constants (that
may be frequency dependent) of the tissue components.
For constant electric fields or alternating fields having
relatively low frequencies, the dielectric properties of the
various system components may be ignored in determining the field
distribution. Therefore, as a first approximation, the tissue
properties may be reasonably represented by the relative impedances
or conductivities of the various tissue components. Under these
conditions, the intercellular fluid and intracellular fluid both
have a relatively low impedance, while the cell membrane has a very
high impedance. Thus, under these conditions, only a fraction of
the electric field lines, or currents generated by the electric
field, may penetrate the cells. These field lines or currents may
penetrate the cell through the part of the membrane closest to the
pole generating the field or current. The currents then flow across
the cell in generally uniform pattern, in response to a generally
homogenous field inside the cell, and exit the cell through a
portion of the cell membrane closest to the other pole.
The electric current flow pattern for cells undergoing division is
very different and unique. Such cells include first and second
sub-cells, namely, an "original" cell and a newly formed cell, that
are connected by a cytoplasm "bridge" or "neck". The currents
penetrate the first sub-cell through the part of the membrane the
current source pole; however, they do not exit the first sub-cell
through a portion of its membrane closer to the opposite pole
(i.e., the current sink). Instead, the lines of current flow
converge at the neck or cytoplasm bridge, whereby the density of
the current flow lines is greatly increased. A corresponding,
"mirror image", process takes place in the second sub-cell, whereby
the current flow lines diverge to a lower density configuration as
they depart from the bridge, and finally exit the second sub-cell
from a part of its membrane closest to the current sink.
It is well known that when an object with no net electric charge is
placed in a homogeneous electric field, although the object may be
polarized, no net electric forces act upon it. However, when such
an object is placed in a non-uniform converging or diverging field,
electric forces act on it and pull it towards the higher density
electric field lines. In the case of a dividing cell, electric
forces are exerted in the direction of the cytoplasm bridge between
the two cells. Since all intracellular organelles are polarizable,
they are all forced towards the bridge between the two cells. The
field polarity is irrelevant to the direction of the force and,
therefore, an alternating electric field may be used to produce
substantially the same effect. The electric forces acting on
macromolecules or intracellular organelles and the consequent
movement of such macromolecules or intracellular organelles, in
response to a non-homogenous electric field, is known in the
art.
The movement of the cellular organelles towards the bridge disrupts
the cell structure and results in increased pressure in the
vicinity of the connecting bridge membrane. This pressure of the
organelles on the bridge membrane is expected to break the bridge
membrane and, thus, it is expected that the dividing cell will
"explode" in response to this pressure. The ability to break the
membrane and disrupt other cell structures can be enhanced by
applying a pulsating alternating electric field, rather than a
steady alternating electric field. When a pulsating electric field
is applied to the tissue, the forces exerted on the intracellular
organelles has a "hammering" effect, whereby force pulses (or
beats) are applied to the organelles numerous times per second,
enhancing the movement of organelles of different sizes and masses
towards the bridge (or neck) portion from both of the sub-cells,
thereby increasing the probability of breaking the cell membrane at
the bridge portion. The forces exerted on the intracellular
organelles also affect the organelles themselves and may collapse
or break the organelles.
It is noted, however, that for the electric field to be effective
in breaking the dividing cells, it should be properly orientated
relative to the geometry of the dividing cell. For example, a field
normal to the axis of the bridge will not be effective. Therefore,
for effectively destroying a high percentage of the dividing cells,
in accordance with the present invention, the electric potential
applied to the tumor tissue is preferably rotated relative to the
tumor tissue. Alternatively, if the electric field is applied for a
sufficiently long period of time, it is expected to eventually
affect all dividing cells, because the cells, which are not
spacially oriented, as epithelial cells, may constantly change
their orientation during the division process or with multiple
divisions. Discontinuous, e.g., periodical, application of the
electric field over longer periods of time, e.g., on and off for a
few hours, is also expected to destroy all tumor cells.
The normal cells that may be sensitive to the electric fields are
those cells that undergo relatively frequent divisions. Such cells
are present mainly in the hematopoietic system, the ovaries or
testicles, certain skin layers and embryos. In such tissues,
undesired destruction of normal cells may occur, as it does with
traditional cancer treatments like chemotherapy and radiation.
Therefore, in a preferred embodiment of the invention, the electric
field is applied selectively to avoid regions of rapidly dividing
normal cells, for example, by shielding or by localized application
of electrodes. Shielding can be performed by means of a conducting
material, such as copper, aluminum, steel, etc. Additionally or
alternatively, the field may be selectively targeted to specific
regions, e.g., by controlling the configuration of the
field-inducing electrodes. Additionally or alternatively, the field
may be controlled by active means, for example, by applying
secondary fields of opposite polarities at the areas being
protected, to cancel the effect of the primary electric field at
the protected areas.
In an embodiment of the invention, electric fields may be generated
in the body by placing metal electrodes over the desired areas,
with or without making actual contact with the skin. If fields not
associated with conductive currents are desired, the electrodes may
be electrically insulated. Localized internal fields may be
produced by introducing electrodes into the living tissue, e.g., by
insertion through body cavities or by penetrating the surface of
the body. By properly controlling the field polarities and
potentials, electric fields can be controlled and directed or
focused at a relatively high resolution so as to be effective only
in the desired regions. Additionally, physical components such as
waveguides may be used to direct the fields and to access specific
sites that are known to contain tumors.
It should be appreciated that the present invention may also be
used in applications other than treatment of tumors in a living
body. In fact, the selective destruction in accordance with the
present invention may be used in conjunction with any organisms
that proliferate by division and multiplication, for example,
tissue cultures, microorganisms such as bacteria, mycoplasma,
protozoa, fungi, algae, plant cells, etc. Such organisms divide by
the formation of a groove or cleft as described above. As the
groove or cleft deepens, a narrow bridge is formed between the two
parts of the organism, similar to the bridge formed between the
sub-cells of dividing animal cells. Since such organisms are
covered by a membrane having a relatively low electric
conductivity, similar to an animal cell membrane described above,
the electric field lines in a dividing organism converge at the
bridge connecting the two parts of the dividing organism. The
converging field lines result in electric forces that displace
polarizable elements within the dividing organism.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1E are simplified, schematic, cross-sectional,
illustrations of various stages of a cell division process;
FIGS. 2A and 2B are schematic illustrations of a non-dividing cell
being subjected to an electric field, in accordance with an
embodiment of the present invention;
FIGS. 3A, 3B and 3C are schematic illustrations of a dividing cell
being subjected to an electric field, resulting in destruction of
the cell (FIG. 3C), in accordance with an embodiment of the present
invention;
FIG. 4 is a series of sequential microphotographic frames taken
over a set period of time illustrating a typical cell division
process; and
FIG. 5 is a series of sequential microphotographic frames
illustrating a dividing cell being subjected to an electric field
according to the method of the present invention, resulting in the
cell being unable to complete the division process.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS THE INVENTION
Reference is made to FIGS. 1A-1E which schematically illustrate
various stages of a cell division process. FIG. 1A shows a cell 10
at its normal geometry, which may be generally spherical (as shown
in the drawings), ellipsoidal, cylindrical, "pancake" like, or any
other cell geometry, as is known in the art. FIGS. 1B-1D show cell
10 during different stages of its division process, which results
in the formation of two new cells 18 and 20, shown in FIG. 1E.
As shown in FIGS. 1B-1D, the division process of cell 10 is
characterized by a slowly growing cleft 12 which gradually
separates cell 10 into two units, namely, sub-cells 14 and 16,
which eventually evolve into new cells 18 and 20 (FIG. 1E). As
shown specifically in FIG. 1D, the division process is
characterized by a transient period during which the structure of
cell 10 is basically that of the two sub-cells 14 and 16
interconnected by a narrow "bridge" 22 containing cell material
(cytoplasm surrounded by cell membrane).
Reference is now made to FIGS. 2A and 2B, which schematically
illustrate non-dividing cell 10 being subjected to an electric
field produced by applying an alternating electric potential, at a
relatively low frequency and at a relatively high frequency,
respectively. Cell 10 includes intracellular organelles, e.g., a
nucleus 30. Alternating electrical potential is applied across
electrodes 28 and 32 that may be attached externally to a patient
at a predetermined region, e.g., in the vicinity of a tumor being
treated. When cell 10 is under natural conditions, i.e., part of a
living tissue, it is disposed in a conductive environment
(hereinafter referred to as: "volume conductor") consisting mostly
of electrolytic inter-cellular liquid. When an electric potential
is applied across electrode 28 and 32, some of the field lines of
the resultant electric field (or the current induced in the tissue
in response to the electric field) penetrate cell 10, while the
rest of the field lines (or induced current) flow in the
surrounding medium. The specific distribution of the electric field
lines, which is substantially consistent with the direction of
current flow in this case, depends on the geometry and the electric
properties of the system components, e.g., the relative
conductivities and dielectric constants of the system components,
that may be frequency dependent. For low frequencies, e.g.,
frequencies considerably lower than 10 kHz, the conductance
properties of the components dominate the current flow, and the
field distribution is generally as depicted in FIG. 2A. At higher
frequencies, e.g., at frequencies of between 10 kHz and 1 MHz, the
dielectric properties of the components become more significant and
eventually dominate the field distribution, resulting in field
distribution lines as depicted generally in FIG. 2B.
For constant (i.e., DC) electric fields or relatively low frequency
alternating electric fields, for example, frequencies under 10 kHz,
the dielectric properties of the various components are not
significant in determining and computing the field distribution.
Therefore, as a first approximation, with regard to the electric
field distribution, the system can be reasonably represented by the
relative impedances of its various components. Under this
approximation, the intercellular (i.e., extracellular) fluid and
the intracellular fluid have a relatively low impedance, while the
cell membrane 11 has a relatively high impedance. Thus, under low
frequency conditions, only a fraction of the electric field lines
(or currents induced by the electric field) penetrate membrane 11
of cell 10. At relatively high frequencies (e.g., 10 kHz-1 MHz), in
contrast, the impedance of membrane 11 relative to the
intercellular and intracellular fluids decreases and, thus, the
fraction of currents penetrating the cells increases significantly.
It should be noted that at very high frequencies, i.e., above 1
MHz, the membrane capacitance may short the membrane resistance
and, therefore, the total membrane resistance may become
negligible.
In any of the embodiments described above, the electric field lines
(or induced currents) penetrate cell 10 from a portion of membrane
11 closest to one of the electrodes generating the current, e.g.,
closest to positive electrode 28 (also referred to herein as
"source"). The current flow pattern across cell 10 is generally
uniform because, under the above approximation. the field induced
inside the cell is substantially homogenous. The currents exit cell
10 through a portion of membrane 11 closest to the opposite
electrode, e.g., negative electrode 32 (also referred to herein as
"sink").
The distinction between field lines and current flow may depend on
a number of factors, for example, on the frequency of the applied
electric potential and on whether electrodes 28 and 32 are
electrically insulated. For insulated electrodes applying a DC or
low frequency alternating voltage, there is practically no current
flow along the lines of the electric field. At higher frequencies,
displacement currents are induced in the tissue due to charging and
discharging of the cell membranes (which act as capacitors to a
certain extent), and such currents follow the lines of the electric
field. Fields generated by non-insulated electrodes, in contrast,
always generate some form of current flow, specifically, DC or low
frequency alternating fields generate conductive current flow along
the field lines, and high frequency alternating fields generate
both conduction and displacement currents along the field lines. It
should be appreciated, however, that movement of polarizable
intracellular organelles according to the present invention (as
described below) is not dependent on actual flow of current and,
therefore, both insulated and non-insulated electrodes may be used
efficiently in conjunction with the present invention.
Nevertheless, insulated electrodes have the advantage of lower
power consumption and causing less heating of the treated
regions.
Reference is now made to FIGS. 3A-3C which schematically illustrate
the electric current flow pattern in cell 10 during its division
process, under the influence of high frequency alternating electric
field in accordance with an embodiment of the invention. The field
lines or induced currents penetrate cell 10 through a part of the
membrane of sub-cell 16 closer to electrode 28. However, they do
not exit through the cytoplasm bridge 22 that connects sub-cell 16
with the newly formed yet still attached sub-cell 14, or through a
part of the membrane in the vicinity of bridge 22. Instead, the
electric field or current flow lines--that are relatively widely
separated in sub-cell 16--converge as they approach bridge 22 (also
referred to as "neck" 22) and, thus, the current/field line density
within neck 22 is increased dramatically. A "mirror image" process
takes place in sub-cell 14, whereby the converging field lines in
bridge 22 diverge as they approach the exit region of sub-cell
14.
It should be appreciated by persons skilled in the art that
homogenous electric fields do not exert a force on electrically
neutral objects, i.e., objects having substantially zero net
charge, although such objects may become polarized. However, under
a non-uniform, converging electric field, as shown in FIGS. 3A-3C,
electric forces are exerted on polarized objects, moving them in
the direction of the higher density electric field lines. In the
configuration of FIGS. 3A and 3B, the direction of movement of
polarized objects is towards the higher density electric filed
lines, i.e., towards the cytoplasm bridge 22 between sub-cells 14
and 16. It is known in the art that all intracellular organelles,
for example, nuclei 24 and 26 of sub-cells 14 and 16, respectively,
are polarizable and, thus, such intracellular organelles will be
electrically forced in the direction of bridge 22. Since the
movement is always from the lower density currents to the higher
density currents, regardless of the field polarity, the forces
applied by the alternating electric field to organelles such as
nuclei 24 and 26 are always in the direction of bridge 22. A
comprehensive description of such forces and the resulting movement
of macromolecules or intracellular organelles, a phenomenon
referred to as dielectrophoresis, is described extensively in the
literature, for example, in C. L. Asbury & G. van den Engh,
Biophys. J. 74, 1024-1030, 1998, the disclosure of which is
incorporated herein by reference.
The movement of organelles 24 and 26 towards bridge 22 disrupts the
structure of the dividing cell and, eventually, the pressure of the
converging organelles on bridge membrane 22 results in breakage of
cell membrane 11 at the vicinity of bridge 22, as shown
schematically in FIG. 3C. The ability to break membrane 11 at
bridge 22 and to otherwise disrupt the cell structure and
organization may be enhanced by applying a pulsating AC electric
field, rather than a steady AC field. When a pulsating field is
applied, the forces acting on organelles 24 and 26 may have a
"hammering" effect, whereby pulsed forces beat on the intracellular
organelles at a desired rhythm, e.g., a pre-selected number of
times per second. Such "hammering" is expected to enhance the
movement of intracellular organelles towards neck 22 from both sub
cells 14 and 16), thereby increasing the probability of breaking
cell membrane 11 in the vicinity of neck 22.
It is appreciated that the effectiveness of the field in causing
the desired motion of the intracellular organelles is dependent on
the orientation of the field relative to the dividing cell. For
example, a field normal to the longitudinal axis of bridge 22
(i.e., normal to that shown in the drawings) will generally not be
effective in destroying the cells. Therefore, in an embodiment of
the present invention, the alternating electric potential applied
to the tissue being treated is rotated relative to the tissue.
Additionally or alternatively, those types of cells that randomly
change the orientation of their division may be destroyed by
applying an electric field for a sufficiently long period of time,
or by repeating the application of the field periodically, e.g., in
accordance with the cell-division cycle of the cells being
destroyed, whereby the electric field lines eventually interact
with all the dividing cells at an effective orientation. It is
appreciated, however, that certain types of cells, e.g., epithelial
cells, divide generally only in a specific orientation, and
therefore, to effectively destroy such cells, the orientation of
the field should be adjusted in accordance with the division
orientation of the cells.
To demonstrate the expected effectiveness of electric fields in
destroying tumor cells, following is an exemplary analysis of the
effect of applying an electric field to a tumor which grows at a
relatively moderate rate, e.g., a tumor that doubles its volume in
6 months from 1 cm.sup.3 to 2 cm.sup.3. In such a tumor, on the
average, each cell divides every 20-30 minutes and each division is
at its cleaving stage (FIGS. 1B-1D) for approximately 10-20
minutes. Thus, for example, an electric field applied to this tumor
for a total time period of approximately two hours (which period
may be divided into any number of sub-sessions), has a high
probability of destroying practically all tumor cells, without
damaging normal (i.e., non-dividing) cells in the vicinity of the
tumor tissue. This expected result applies not only to the original
tumor tissue, but also to metastases that may appear in various
locations possessing similar qualities. Since the method of the
present invention causes substantially no damage to non-dividing
cells, this method may be used as a preventive treatment, to
eliminate tumors before they are even detectable, whereby healthy
tissue is not damage by redundant or unnecessary treatment.
It is appreciated that certain normal cells, e.g., cells in the
hematopoietic system, the ovaries or testicles, skin and embryos,
etc., undergo relative frequent divisions and, thus, may be
sensitive to the electric fields. This situation also occurs with
existing tumor treatments, such therapeutic irradiation or
chemotherapy. Therefore, in an embodiment of the present invention,
areas that include sensitive (i.e., frequently dividing) normal
cells are selectively excluded from the regions covered by the
electric fields, and/or shielded from the applied fields. Shielding
may be preformed by positioning conducting materials, such as
copper, aluminum, steel, etc., around the sensitive area to
dissipate the electrical field. Additionally or alternatively, the
field may be selectively applied to specific target regions, e.g.,
by controlling the configuration of the field-producing electrodes
28 and 30. Additionally or alternatively, the electrodes may be
inserted into the body and brought to a vicinity of the target
tissue, thereby producing a localized electric field in the
vicinity of the cells being destroyed.
In an embodiment of the invention, electric fields may be generated
in the body by placing metal electrodes over the desired areas,
with or without actual contact with the skin. By properly
controlling the field polarities and potentials, electric fields
can be controlled and directed or focused at a relatively high
resolution so as to be effective only in the desired regions.
Additionally or alternatively, physical components such as
wave-guides may be used to direct the fields and to access specific
sites that are known to contain tumors.
FIG. 4 presents a number of sequential microphotographic frames
taken over a predetermined time period showing typical cell
division when no electric field is applied. In this embodiment, the
cells are BHK (baby hamster kidney) cells. The microphotography was
taken over a 40 minute period. The cells were cultured in a
standard culture medium (DMEM). Time is given above each photograph
in terms of hours and minutes (hr:min). The photographs are
magnified 500.times. to show the cell division more clearly. An
ellipse is provided in each photograph to mark an area of interest.
Frame A shows the location of a dividing cell prior to the division
process. A non-dividing cell is normally flattened on the tissue
culture plate. In this state, the cell can not be distinguished
from the neighboring cells in the photographic frame. In frame B,
the cell can be seen as it prepares itself for division and takes
on a more spherical shape. As the cell assumes this general shape,
the cell is more clearly distinguishable from the neighboring
cells. As the division process continues, the dividing cell forms a
cleft shown in frame C and proceeds to take on an hourglass-like
shape, as shown in frame D. In frame E, the dividing cell splits
into two separate cells and the cells move away from each other in
frame F. The daughter cell begins to flatten in frame G and
eventually disappear in frame H.
FIG. 5 presents a number of sequential microphotographic frames
taken over a predetermined time period illustrating the application
of the method of the present invention. More specifically, FIG. 5
shows the arrested division of BHK cells when an electrical field
according to the present invention is applied for a limited
predetermined period of time. In this example, the microphotography
was taken over a period of 6 hours, while the electric field was
activated for the first 1 hour and 40 minutes. The cells were grown
in a standard tissue culture medium. The intensity of the electric
field was 78 V/cm and the frequency was 100 KHz. Once again, time
is given above each photographic frame in terms of hour and minute
(hr:min). In this example, the magnification is on the order of
250.times. and an ellipse is provided to mark an area of
interest.
Frame A is taken as the electric field is applied and shows a cell
in the process of dividing. The cell is bulging from the plate and
has a cleft. After almost 40 minutes, when one would expect the
division process to be complete, the cell, shown in frame B, is
maintaining its spherical shape and the cleft identified in the
discussion of FIG. 4 cannot be identified at this point. After an
additional 40 minute period, the dividing cell, as shown in frame
C, is unable to complete the division process. About 20 minutes
after the electric field is inactivated, frame D is taken. In this
frame, the dividing cell is still in its division process and has
taken on a generally hourglass-like shape. Subsequent frames E
through I (taken at 40 minute intervals) show that the cell
maintains the generally hourglass-like shape for the remainder of
the filming session (3 hours) and in unable to complete the
division process.
As used herein, the term "tumor" refers to a malignant tissue
comprising transformed cells that grow uncontrollably. Tumors
include leukemias, lymphomas, myelomas, plasmacytomas, and the
like; and solid tumors. Examples of solid tumors that can be
treated according to the invention include sarcomas and carcinomas
such as, but not limited to: fibrosarcoma, myxosarcoma,
liposarcoma, chondrosarcoma, osteogenic sarcoma, chordoma,
angiosarcoma, endotheliosarcoma, lymphangiosarcoma,
lymphangioendotheliosarcoma, synovioma, mesothelioma, Ewing's
tumor, leiomyosarcoma, rhabdomyosarcoma, colon carcinoma,
pancreatic cancer, breast cancer, ovarian cancer, prostate cancer,
squamous cell carcinoma, basal cell carcinoma, adenocarcinoma,
sweat gland carcinoma, sebaceous gland carcinoma, papillary
carcinoma, papillary adenocarcinomas, cystadenocarcinoma, medullary
carcinoma, bronchogenic carcinoma, renal cell carcinoma, hepatoma,
bile duct carcinoma, choriocarcinoma, seminoma, embryonal
carcinoma, Wilms' tumor, cervical cancer, testicular tumor, lung
carcinoma, small cell lung carcinoma, bladder carcinoma, epithelial
carcinoma, glioma, astrocytoma, medulloblastoma, craniopharyngioma,
ependymoma, pinealoma, hemangioblastoma, acoustic neuroma,
oligodendroglioma, meningioma, melanoma, neuroblastoma, and
retinoblastoma. Because each of these tumors undergoes rapid
growth, any one can be treated in accordance with the invention.
The invention is particularly advantageous for treating brain
tumors, which are difficult to treat with surgery and radiation,
and often inaccessible to chemotherapy or gene therapies. In
addition, the present invention is suitable for use in treating
skin and breast tumors because of the ease of localized treatment
provided by the present invention.
In addition, the present invention can control uncontrolled growth
associated with non-malignant or pre-malignant conditions, and
other disorders involving inappropriate cell or tissue growth by
application of an electic field in accordance with the invention to
the tissue undergoing inappropriate growth. For example, it is
contemplated that the invention is useful for the treatment of
arteriovenous (AV) malformations, particularly in intracranial
sites. The invention may also be used to treat psoriasis, a
dermatologic condition that is characterized by inflammation and
vascular proliferation; and benign prostatic hypertrophy, a
condition associated with inflammation and possibly vascular
proliferation. Treatment of other hyperproliferative disorders is
also contemplated.
Furthermore, undesirable fibroblast and endothelial cell
proliferation associated with wound healing, leading to scar and
keloid formation after surgery or injury, and restenosis after
angioplasty can be inhibited by application of an electric field in
accordance with the present invention. The non-invasive nature of
this invention makes it particularly desirable for these types of
conditions, particularly to prevent development of internal scars
and adhesions, or to inhibit restenosis of coronary, carotid, and
other important arteries.
Thus, the present invention provides an effective, simple method of
selectively destroying dividing cells, e.g., tumor cells and
parasitic organisms, while non-dividing cells or organisms are left
affected by application of the method on living tissue containing
both types of cells or organisms. Thus, unlike many of the
conventional methods, the present invention does not damage the
normal cells or organisms. In addition, the present invention does
not discriminate based upon cell type (e.g., cells having differing
sizes) and therefore may be used to treat any number of types of
sizes having a wide spectrum of characteristics, including varying
dimensions.
It will be appreciated by persons skilled in the art that the
present invention is not limited to the embodiments described thus
far with reference to the accompanying drawing. Rather the present
invention is limited only by the following claims.
* * * * *