U.S. patent application number 15/401452 was filed with the patent office on 2017-04-27 for method of selecting phosphate binder and its uses thereof.
The applicant listed for this patent is Panion & BF Biotech, Inc.. Invention is credited to Keith CHAN.
Application Number | 20170112876 15/401452 |
Document ID | / |
Family ID | 38327902 |
Filed Date | 2017-04-27 |
United States Patent
Application |
20170112876 |
Kind Code |
A1 |
CHAN; Keith |
April 27, 2017 |
METHOD OF SELECTING PHOSPHATE BINDER AND ITS USES THEREOF
Abstract
A method of selecting or determining a candidate compound
suitable for use as a phosphate binder is disclosed. The candidate
compound includes ferric compounds, ferric compound complexes, and
their derivatives, salts, analogs, and metabolites. The
effectiveness of the candidate compound as a phosphate binder is
evaluated by a method, comprising measuring and correlating
reduction of phosphate concentration in solution and reduction of
phosphate absorption in cells.
Inventors: |
CHAN; Keith; (Rockville,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panion & BF Biotech, Inc. |
Taipei |
|
TW |
|
|
Family ID: |
38327902 |
Appl. No.: |
15/401452 |
Filed: |
January 9, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14594469 |
Jan 12, 2015 |
9539284 |
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15401452 |
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12162247 |
Jul 25, 2008 |
8932648 |
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PCT/US2007/002158 |
Jan 26, 2007 |
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14594469 |
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60763735 |
Jan 30, 2006 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61K 31/555 20130101;
G01N 33/84 20130101; G01N 2500/10 20130101; A61K 33/26 20130101;
G01N 33/502 20130101; G01N 2800/347 20130101 |
International
Class: |
A61K 33/26 20060101
A61K033/26; G01N 33/50 20060101 G01N033/50; A61K 31/555 20060101
A61K031/555; G01N 33/84 20060101 G01N033/84 |
Claims
1-34. (canceled)
35. A method to determine whether a candidate compound is capable
of binding phosphate, comprising the steps of: a) contacting the
candidate compound with phosphate in a variety of buffers or
solutions, and measuring the reduction of phosphate concentration;
b) contacting the candidate compound with phosphate in a solution
containing Caco-2 cells, and measuring the reduction of phosphate
absorption in said cells as compared to the absence of said
compound; and wherein a candidate compound that reduces both the
phosphate concentration in the absence of Caco-2 cells, and
phosphate absorption in the Caco-2 cells is a phosphate binder.
36. The method of claim 35, wherein the buffers or solutions are
simulated gastrointestinal fluids.
37. The method of claim 35, wherein ferric citrate is used as a
standard for a phosphate binder.
38. The method of claim 35, wherein measuring reduction of
phosphate concentration in a variety of buffers or solutions
comprises determining the Langmuir adsorption isotherm in said
buffers or solutions.
39. The method of claim 35, wherein measuring reduction of
phosphate concentration or phosphate absorption comprises
equilibrium binding experiments or kinetic experiments.
40. A method for preventing, treating or stabilizing phosphate
imbalance in a subject, comprising administrating to said subject
an amount of ferric trimaltol effective for preventing, treating or
stabilizing phosphate imbalance.
41. The method of claim 40, wherein the amount of ferric trimaltol
is 3-6 grams per day.
42. The method of claim 40, wherein the subject suffers from
hyperphosphatemia.
43. The method of claim 40, wherein the subject suffers from
metabolic acidosis.
44. The method of claim 40, wherein the subject is a chronic kidney
disease patient.
45. A method for preventing, treating or stabilizing phosphate
imbalance in a subject, comprising administrating to said subject
an amount of ferric bicarbonate effective for preventing, treating
or stabilizing phosphate imbalance.
46. The method of claim 45, wherein the amount of ferric
bicarbonate is 3-6 grams per day.
47. The method of claim 45, wherein the subject suffers from
hyperphosphatemia.
48. The method of claim 45, wherein the subject suffers from
metabolic acidosis.
49. The method of claim 45, wherein the subject is a chronic kidney
disease patient.
50. A method for preventing, treating or stabilizing phosphate
imbalance in a subject, comprising administrating to said subject
an amount of ferric carbonate effective for preventing, treating or
stabilizing phosphate imbalance.
51. The method of claim 50, wherein the amount of ferric carbonate
is 3-6 grams per day.
52. The method of claim 50, wherein the subject suffers from
hyperphosphatemia.
53. The method of claim 50, wherein the subject suffers from
metabolic acidosis.
54. The method of claim 50, wherein the subject is a chronic kidney
disease patient.
Description
[0001] This application is a division of U.S. Ser. No. 12/162,247,
filed Jul. 25, 2008, which is a National Stage of International
Application NO. PCT/US2007/002158, filed Jan. 26, 2007, which
claims the benefit of U.S. Ser. No. 60/763,735, filed Jan. 30,
2006. The disclosure of the preceding applications is hereby
incorporated by reference in its entirety into this
application.
[0002] Throughout this application, various references or
publications are cited. Disclosures of these references or
publications in their entireties are hereby incorporated by
reference into this application in order to more fully describe the
state of the art to which this invention pertains.
BACKGROUND OF THE INVENTION
[0003] Hyperphosphatemia is a serious and chronic medical condition
in end-stage renal diseases. Although it is possible to increase
the elimination of phosphate from the plasma in dialysis patient,
this approach is severely limited by the fact that transfer of
phosphate from the blood cells into plasma is the rate-limiting
step (Pohlmeier and Vienken, Phosphate removal and hemodialysis
conditions. Kidney Int. Suppl. 78:S190-194 (2001)). Therefore, a
more promising route of treating phosphate overload is to decrease
the absorption of phosphate. Phosphate is transported into the
intestinal cells via a phosphate-sodium co-transporter, and
transported across the basolateral membrane into the blood via a
yet to be identified pathway (Murer et. al., Molecular aspects in
the regulation of renal inorganic phosphate reabsorption: the type
IIa sodium/inorganic phosphate co-transporter as the key player.
Curr. Opin. Nephrol. Hypertens. 10:555-561 (2001)). The
phosphate-sodium cotransporter is stimulated by
1.25-dihydroxycholecalciferol, an active metabolite of vitamin D,
but the mechanism of this action is not entirely clear. Because
phosphate is taken up by carrier-mediated pathways, the rate of
absorption may not increase linearly with the concentration.
[0004] Presently, the therapy for managing phosphate absorption is
through the use of precipitation agents such as aluminum, calcium
(Malluche et.al., Hyperphosphatemia: pharmacologic intervention
yesterday, today and tomorrow. Clin. Nephrol. 54:309-317 (2000))
and other heavy metal ions such as lanthanum, and a polymer-like
materials such as sevelamer HCl, (a non-aluminum, non-calcium
containing hydrogel or Renagel.RTM.) (Gallieni et. al., Sevelamer
reduces calcium load and maintains a low calcium-phosphorus ion
product in dialysis patients. J Nephrol. 14:176-183 (2001)). These
agents have been shown to be beneficial but better agents are yet
to be developed, because the available drugs are only partially
effective.
SUMMARY OF THE INVENTION
[0005] A brief summary of the invention is presented. Some
simplifications and omission may be made in the following summary,
which is intended to highlight and introduce some aspects of the
present invention, but not to limit its scope. Detailed
descriptions of a preferred exemplary embodiment adequate to allow
those of ordinary skill in the art to make and use the invention
concepts will follow in later sections.
[0006] This invention provides a method to determine whether a
candidate compound is capable of binding phosphate, comprising the
steps of measuring reduction of phosphate concentration in solution
and reduction of phosphate absorption in cells. In one embodiment,
the present invention provides a method of selecting a candidate
compound capable of reducing phosphate absorption by 75%.
[0007] This invention also provides a dietary phosphate binder
determined or identified according to the method described
above.
[0008] This invention also provides a pharmaceutical composition
comprising an effective amount of a compound determined to be a
phosphate binder by the method described above and a
pharmaceutically acceptable carrier.
[0009] This invention also provides a method for preventing,
treating as stabilizing a subject who has phosphate imbalance,
comprising administrating to said subject a compound determined to
be a phosphate binder by the method described above.
DETAILED DESCRIPTION OF THE INVENTION
[0010] This invention provides a method of determining whether a
candidate compound, such as a ferric compound, is capable of
binding phosphate. Candidate compound includes, but is not limited
to, PBF1681 (Panion and BF Biotech, Inc., Taiwan) and other ferric
compounds, their salts, compounds, metabolites, or derivates.
PBF1681, disclosed in U.S. Ser. No. 11/206,981, filed Aug. 18,
2005, and in WO 2004/07444, filed Feb. 18, 2004, is a dietary
phosphate binder which has shown efficacy in treating
hyperphosphatemia. U.S. Ser. No. 11/206,981 and WO 2004/07444 are
hereby incorporated by reference in their entireties.
[0011] The method of determining whether a candidate compound is a
potential dietary phosphate binder comprises: contacting the
candidate compound with phosphate under conditions permitting
binding of the candidate compound with phosphate; measuring
reduction of phosphate concentration in the presence of the
candidate compound in a variety of buffer or solution; contacting
the candidate compound with Caco-2 cells in a phosphate solution;
measuring reduction of phosphate absorption in the cell; and
correlating reduction of phosphate concentration in solution with
reduction of phosphate absorption in the Caco-2 cells, wherein
direct correlation of phosphate reduction indicates that the
candidate compound is a phosphate binder.
[0012] In general, ferric citrate is used as a standard for a
phosphate binder in the above method. In one embodiment, the buffer
or solution used in the above method is simulated gastrointestinal
fluids. Preferably, measuring reduction of phosphate concentration
in a variety of buffer or solution comprises determining Langmuir
adsorption isotherm in said buffer or solution. Furthermore,
measuring reduction of phosphate concentration or phosphate
absorption may comprise equilibrium binding experiments or kinetic
experiments.
[0013] Completing the above steps has shown that ferric citrate and
PBF1681 is a phosphate binder that was not previously known. An
effective amount of a candidate compound identified by the above
method (e.g. ferric citrate) in combination with a pharmaceutically
acceptable carrier will comprise a pharmaceutical composition.
[0014] A "pharmaceutically acceptable carrier" means any of the
standard pharmaceutical carriers. Examples of suitable carriers are
well known in the art and may include, but are not limited to, any
of the standard pharmaceutical carriers like phosphate buffered
saline solutions, phosphate buffered saline containing Polysorb 80,
water, emulsions such as oil/water emulsion, and various types of
wetting agents. Other carriers may also include sterile solutions,
tablets, coated tablets, and capsules.
[0015] Typically such carriers contain excipients like starch,
milk, sugar, certain types of clay, gelatin, stearic acid or salts
thereof, magnesium or calcium stearate, talc, vegetable fats or
oils, gums, glycols, or other known excipients. Such carriers may
also include flavor and color additives or other ingredients.
Compositions comprising such carriers are formulated by well known
conventional methods.
[0016] This invention also provides a method for preventing,
treating or stabilizing a subject (e.g. a mammal or a human) that
have a phosphate imbalance, comprising administering to said
subject a phosphate binder identified by the above method. In
general, one of ordinary skill in the art would be able to readily
determine the dose and route of administering the phosphate binder
identified by the method described herein. In one embodiment, the
phosphate binder is ferric trimaltol, ferric bicarbonate, or ferric
carbonate. Ferric trimaltol has been shown to be capable of
correcting iron deficiency (Harvey et al., Ferric trimaltol
corrects iron deficiency anaemia in patients intolerant of iron.
Aliment. Pharmacol. Ther. 12:845-848 (1998)), whereas ferric
carbonate and ferric bicarbonate can be used as arsenic or hydrogen
sulfide removal media (U.S. Pat. Nos. 6,849,187; 5,948,269;
6,849,187; 5,948,269). However, these three ferric compounds have
not been previously reported as phosphate binders.
[0017] This invention also provides use of a compound determined to
be a phosphate binder by the method described herein in preparation
of a medicament for treating a subject having phosphate imbalance.
In one embodiment, the phosphate binder is ferric trimaltol, ferric
bicarbonate, or ferric carbonate.
[0018] The invention being generally described, will be more
readily understood by reference to the following examples which are
included merely for purposes of illustration of certain aspects and
embodiments of the present invention, and are not intended to limit
the invention.
EXAMPLE 1
Potential Ferric Compound Suitable as Dietary Phosphate Binder
[0019] Ideally, a ferric compound, salt or complex suitable for use
as a dietary phosphate binder should have the following
properties:
[0020] A. Ability to control hyperphosphatemia by binding dietary
phosphate via the mechanism of reducing dietary phosphate
absorption.
[0021] B. Ability to correct metabolic acidosis in renal
failure.
[0022] C. Appropriate dissolution profile and availability of
ferric ion to bind to dietary phosphate in the GI tract but with
minimal systemic absorption of ferric either as ionic form or as
salt form into the body.
[0023] D. The cationic form of the ferric compounds, salts or
complex should be non-toxic to patient with chronic kidney disease
and should not lead to concentration so high that cause side effect
(Note: the estimated effective dose of PBF1681 (Panion and BF
Biotech, Inc., Taiwan) is in the range of around 3-6 gm per day,
which is equivalent to 116-174 mg of available ferric ion to bind
with dietary phosphate).
[0024] E. Since relatively high oral dose (equivalent to 116-174 g
of Ferric ion) is required to bind to the dietary phosphate, the GI
irritation potential for the ferric compound and salt would be
another criterion to be considered.
[0025] The criteria for selecting candidate compounds which have
potential as a dietary phosphate binder is provided below. Method
of evaluating candidate ferric compounds, and their salts,
derivatives, analogs, metabolites, to determine their effectiveness
as a dietary phosphate binder is provided in Example 2.
Criteria for Selecting Phosphate Binders
[0026] 1. The anion groups of the potential compounds should be
non-toxic to patients with chronic kidney disease and should not
lead to concentration so high that cause side effects. Anion groups
such as ammonium, nitrate, sulfate, and etc should be avoided.
[0027] 2. Appropriate solubility of potential ferric compounds in
the GI tract condition. Compound should be with appropriate
solubility to release ferric ion. Anion groups such as fatty acids
with low solubility should be avoided.
[0028] 3. Appropriate equivalence of ferric ion per gram of
compound. The potential ferric compound should contain enough
ferric ions to effectively bind with dietary phosphate. For
example, PBF1681 contains 114 mg of ferric ion per capsule (500
mg). Compounds with ferric content less than 57 mg are
excluded.
[0029] 4. Metabolic acidosis is also a common problem in chronic
kidney disease patients. Normal body pH range is between 6.0-7.5.
The pKa of the anion group should be within the range. Acetic anion
groups should be avoided.
[0030] The ferric compounds which satisfy the above criteria are:
ferric trimaltol, ferric citrate, ferric bicarbonate, and ferric
carbonate. The ferric content in the ferric trimaltol is the lowest
among the four (65 mg Fe3+/500 mg compound). For ferric carbonate,
the pKa of the carbonate group is beyond the normal body pH range
(pKa=10.3). Ferric citrate and ferric bicarbonate are the ideal
compounds with high ferric content and may ameliorate the acidosis
problem in chronic kidney disease patients. See Table 2 below for a
list of ferric compounds as potential phosphate binder, and a list
of excluded compounds. Other compounds suitable for use as a
dietary phosphate binder can be readily selected or determined by a
person of ordinary skill in the art following the teaching of this
invention. The potential of ferric compounds as dietary phosphate
can be evaluated following the procedures described in Example
2.
[0031] Other ferric complex compounds suitable for use as a dietary
phosphate binder can be readily selected or determined by a person
of ordinary skill in the art following the teaching of this
invention. An example of a suitable ferric complex compound is Iron
Dextran which has been used for treating anemia. More recently,
Ferrlecit.RTM. (sodium ferric gluconate complex in sucrose
injection) was approved for the treatment of iron deficiency
anemia. Of course, both Iron Dextran and sodium ferric gluconate
complex are used to treat systemic disease and are not used as oral
dietary phosphate binder. However, the potential of ferric complex
compounds as dietary phosphate can be evaluated following the
procedures described in Example 2.
TABLE-US-00001 TABLE 2 Ferric Compound List (excluding ammonium,
nitrate, sulfate, and etc are excluded.) Fe.sup.3+ content per pKa
of Compound Molecular Formula MW 500 mg compound anionic group Note
& Consideration Potential ferric compounds as phosphate binders
after selection ferric trimaltol Fe(C6H5O3)3 431 65 Not found Low
Fe.sup.3+ content ferric citrate FeC6H4O7 245 114 pKa = 6.4 *
ferric bicarbonate Fe(CHO3)3 239 117 pKa = 6.3 * ferric carbonate
Fe2(CO3)3 292 191 pKa = 10.3 pKa > 7.5 (normal body pH range)
Ferric compounds that are excluded * ferric oleate Fe(C18H33O2)3
899 31 Not found Fe.sup.3+ < 1/2 PBF1681 ferric gluconate
Fe(C6H11O7)3 641 44 pKa = 12.64 Fe.sup.3+ < 1/2 PBF1681 * ferric
histidinate Fe(C6H8N3O2)3 518 54 pKa = 1.8 Fe.sup.3+ < 1/2
PBF1681 ferric octoate Fe(C8H15O2)3 485 58 Not found Fe.sup.3+ <
1/2 PBF1681 * ferric aspartate Fe(C4H6NO4)3 452 62 pKa = 1.99 May
deteriorate acidosis (pKa < 6) * ferric picolinate Fe(C6H4NO2)3
422 66 pKa = 3.98 May deteriorate acidosis (pKa < 6) ferric
acetylacetonate Fe(C5H8O2)3 356 78 Not found Toxic ferric choline
citrate FeC11H24NO8+ 354 79 Not found Fatty acid with solubility
concerns ferric EDTA FeC10H13N2O8 345 81 Not found Sally concerns
if consuming in large dose ferric HEDTA FeC10H15N2O7 331 85 Not
found Sally concerns if consuming in large dose * ferric
triglycinate Fe(C2H4NO2)3 278 100 pKa = 2.35 May deteriorate
acidosis (pKa < 6) * ferric malate Fe2(C4H4O5)3 508 110 pKa =
3.4 May deteriorate acidosis (pKa < 6) ferric acetate
Fe(C2H3O2)3 233 120 pKa = 4.8 May deteriorate acidosis (pKa < 6)
ferric ascorbate FeC6H7O6+2 230 121 pKa = 4.04 May deteriorate
acidosis (pKa < 6) * ferric fumarate Fe2(C4H2O4)3 448 125 pKa =
3.02 May deteriorate acidosis (pKa < 6) ferric oxalate
Fe2(C2O4)3 393 142 pKa = 1.25 Toxic ferric formate Fe(CHO2)3 190
147 pKa = 3.75 May deteriorate acidosis (pKa < 6) * ferric
tartrate Fe(C4H5O6)3 503 56 pKa1 = 2.98 May deteriorate acidosis
(pKa < 6) Fe2(C4H4O6)3 556 100 pKa2 = 4.34 May deteriorate
acidosis (pKa < 6) * ferric succinate Fe(C4H5O4)3 407 69 pKa1 =
4.21 May deteriorate acidosis (pKa < 6) Fe2(C4H4O4)3 460 122
pKa2 = 5.64 May deteriorate acidosis (pKa < 6)
EXAMPLE 2
System for Evaluating Absorption of Phosphates In Vitro
[0032] Hyperphosphatemia has been shown to be associated with
increased risk of mortality in hemodialysis patients and increased
cardiovascular risk. The normalization of phosphate level in the
plasma is very important for managing patients suffering from
severe renal disease. Because absorption of phosphate from the food
exceeds the elimination through a hemodialysis treatment, a chronic
phosphate overload exists for the majority of hemodialysis
patients.
[0033] A methodology for determining how the absorption of
phosphate can be reduced by decreasing the amount of phosphate
available for absorption (and/or amount of phosphate absorption),
comprises the following phases:
[0034] Phase I. Establish an in vitro method to measure phosphate
concentration in solution in the presence of various candidate
compounds and to determine how amounts of phosphate in solution may
be reduced in the presence of the candidate compounds.
[0035] Phase I further comprises:
[0036] 1. Determining how method(s) reported in the literature
measure unbound inorganic phosphate (free and potentially
absorbable), for example, using a kit from Sigma, can be adapted
for determination of free and unbound inorganic phosphates.
Determining if method utilized in measuring phosphate in vivo can
be indirectly transferred to estimating phosphate concentration
from colloidal solution (or suspension) and polymer solution
(suspension). Determining the effects of pH and buffers (e.g.,
simulated gastric fluid) on the measurement of phosphate.
Establishing a method such that the linear response range will be
from 10-0.1 mM. Normally, the plasma phosphate concentration in
human is 1 mM, and patients with severe renal diseases may have
level triple the normal phosphate concentration. Because of the
need to separate soluble phosphate from colloidal particles and
polymers, equilibrium dialysis will be employed. Therefore, the
concentration of phosphate measured will be equilibrium
concentrations. This method of measuring concentration will be
verified with high speed (100,000.times. g) centrifuge whenever
possible.
[0037] 2. Characterizing the potentials of candidate compounds in
reducing phosphate concentrations in vitro. Determining the
Langmuir adsorption isotherm for each tested compound in several
buffers. Salts, calcium citrate and magnesium chloride will be
used; two polymers, sevelamer and a positively charged polymer
hydrogel; two colloidal solutions, aluminum oxide and lanthanum
oxide; and three negative control, sodium chloride, a negatively
charged hydrogel, and a negatively charged colloidal solution.
[0038] Phase II. Evaluate the potentials of various candidate
compounds/agents in reducing the concentration of phosphate in a
variety of buffer and simulated gastrointestinal fluids.
[0039] Phase II further comprises:
[0040] 1. Measuring and ranking the potentials of candidate
compounds/agents in reducing phosphate concentrations against the
standard substrates used in phase I.
[0041] 2. Evaluating the effectiveness of the method established in
Phase I in selecting compounds with potential to decrease soluble
phosphate in a solution.
[0042] Phase III. Determine and verify potential of model
substrates in reducing the absorption of phosphates in the Caco-2
model.
[0043] Phase III further comprises:
[0044] 1. Correlating the amount of phosphate in solution with
amount of phosphate absorbed in the Caco-2 model in the absence or
presence of selected candidate compounds with distinctive ability
to change the phosphate concentration in a solution. Only pH values
and conditions shown to be effective in reducing phosphate
concentration will be use in this aim to reduce the number of
studies necessary.
[0045] 2. Determining which mode of decreasing phosphate
concentrations will translate better into decreasing phosphate
absorption in the Caco-2 model. Theoretically, those compounds that
produced the most precipitation are expected to cause the largest
decrease in phosphate absorption. However, this may be confounded
by factors such as equilibrium constants. If phosphate could be
adsorbed and deadsorbed rapidly by a compound, that compound may be
effective in reducing phosphate concentration in an equilibrium
system, but may not be the best in a dynamic system such as Caco-2,
where concentration of phosphate will change with time.
EXAMPLE 3
In Vitro Equilibrium Binding and Kinetic Studies
Determine the Common Phosphate Content in the Diet of a
Population
[0046] For example, the phosphate content in a Normal American Diet
is determined (from literature). This information will be used as
the amounts of phosphate expected in the normal diet intake of a
given population from each meal. Various amounts, such as 1.times.,
2.times., 4.times., etc., will be used in the in vitro equilibrium
and kinetic studies. Various binding agents will then be tested for
its equilibrium binding and kinetics to phosphate. Assuming that
the phosphate will either bind to the binding agents as precipitate
or entrapped into the polymer type of binding agents, one can
measure either the disappearing of phosphate or binding agents
before or after physical removal of precipitates or complex.
Analytical method to determine phosphate or binding agents will be
considered and priority will be give to measuring phosphate
first.
Media Used in These Studies
[0047] The following media may be considered in the studies
(provided in increasing complicity): water, simulated gastric fluid
with and without enzyme, simulated intestinal fluid with and
without enzyme, and the possibility of adding bile and fatty acids.
Note: SGF and SIF may already contain phosphate. Additional
phosphate from diet will be added to the media.
In vitro Equilibrium Binding Experiments
[0048] This experiment will be conducted under conditions of
constant time and varying concentrations of binding agents. The
volume of the test medium should be constant at 250 ml. All
experiments should be carried out at 37 degree C.
In vitro Kinetic Experiments
[0049] This experiment will be conducted under constant
concentration of binding agents with varying times of observation.
At least three constant concentrations of binding agents should be
used.
Feasibility and Establishment of the Testing System
[0050] The feasibility of equilibrium binding and kinetic
experiments will be evaluated and validated using standard binding
agents such as salts of aluminum, calcium, lanthanum, and
polymer-like materials such as Sevelamer HCl. After the model is
established, various binding agents may be tested in the
system.
Protocol for Testing Various Binding Agents
[0051] Once the test system has been established, a standard
protocol will be established in evaluating various binding agents
for their capacity and kinetics in binding phosphate in vitro. At
this stage, Ca citrate and Sevelamer may be used as positive
controls.
Data Treatment and Analysis
[0052] Monomolecular adsorption of adsorbate (phosphate) molecules
from solution, at constant temperature, on to an adsorbent (binding
agent) can be described by Langmuir-type equation, as follows:
[0053] X/m=(k1 k2 Ceq)/(1+k1 Ceq)
[0054] Or Ceq/(x/m)=[1/(k1 k2)]+[Ceq/k2], where
[0055] Ceq=concentration of the adsorbate (phosphate) remaining in
the solution at equilibrium;
[0056] x=the amount of adsorbate bound to the adsorbent (binding
agent); and
[0057] m=the amount of adosrbent used.
[0058] The constant, k1, is defined as the adsorption coefficient
or affinity constant and is related to the magnitude of the forces
involved in the binding process. [0059] The Langmuir-capacity
constant, k2, indicates the apparent maximum amount of adsorbate
that can be adsorbed per unit weight of adsorbent. The k1 and k2
constants can be obtained by plotting Ceq/(x/m) versus Ceq
Data and Parameters to be Reported
[0060] Six observations with mean +/- SD for the following
parameters should be obtained and reported for both the test and
reference products: [0061] Percent binding of adsorbate at each
concentration; [0062] Micromoles (or amounts) of adsorbate bound at
each concentration; [0063] Affinity constant k1 and capacity
constant k2; [0064] Coefficient of determination, r2, when linear
regression is used to determine k1 and k2.
* * * * *