ACTINIUM-225 COMPLEXES AND CONJUGATES FOR RADIOIMMUNOTHERAPY

COMPLEXES ET CONJUGAT D'ACTINIUM-225 POUR RADIO-IMMUNOTHERAPIE

English Abstract

Actinium-225 (225Ac) complexes with functionalized chelants of the formula (I)
wherein: each Q is independently hydrogen or (CHR5)pCO2R; Q1 is hydrogen or
(CHR5)wCO2R; each R independently is hydrogen, benzyl or C1-C4 alkyl; with the
proviso that at least two of the sum of Q and Q1 must be other than hydrogen;
each R5 independently is hydrogen; C1-C4 alkyl or (C1-C2 alkyl)phenyl; X and Y
are each independently hydrogen or may be taken with an adjacent X and Y to
form an additional carbon-carbon bond; n is 0 or 1; m is an integer from 0 to
10 inclusive; p is 1 or 2; r is 0 or 1; w is 0 or 1; with the proviso that n
is only 1 when X and/or Y form an additional carbon to carbon bond, and the
sum of r and w is 0 or 1; L is a linker/spacer group covalently bonded to, and
replaces one hydrogen atom of one of the carbon atoms to which it is joined,
said linker/spacer group being represented by the formula (1) wherein s is an
integer of 0 or 1; t is an integer of 0 to 20 inclusive; R1 is an
electrophilic or nucleophilic moiety which allows for covalent attachment to
an antibody or fragment thereof, or synthetic linker which can be attached to
an antibody or fragment thereof, or precursor thereof; and Cyc represents a
cyclic aliphatic moiety, aromatic moiety, aliphatic heterocyclic moiety, or
aromatic heterocyclic moiety, each of said moieties optionally substituted
with one or more groups which do not interfere with binding to an antibody or
antibody fragment; with the proviso that when s, t, m, r, and n are 0, then R1
is other than carboxyl; their pharmaceutically acceptable salts, their
conjugates and the use thereof for radioimmunotherapy is disclosed.

French Abstract

Cette invention a trait à des complexes d'actinium-225 (?225¿Ac) possédant des chelatants fonctionnalisés correspondant à la formule (I). Dans cette formule, chaque Q représente, de manière indépendante, un hydrogène ou (CHR?5¿)¿p?CO¿2?R, Q?1¿ représente un hydrogène ou (CHR?5¿)¿w?CO¿2?R, chaque R représente, de manière indépendante, un hydrogène, un benzyle ou un alkyle porteur de 1 à 4 atomes de carbone, à la condition qu'au moins deux éléments formés par la somme de Q et de Q?1¿ représentent un autre atome que celui de l'hydrogène, chaque R?5¿ représente, de manière indépendante un hydrogène, un alkyle porteur de 1 à 4 atomes de carbone ou un (C¿1?-C¿2? alkyl)phényle, X et Y représentent, chacun de manière indépendante, un hydrogène ou peuvent, pris avec un X et un Y adjacents, former une liaison supplémentaire carbone-carbone, la valeur de n est 0 ou 1, m représente un nombre entier dont la valeur est comprise entre 0 et 10 inclus, la valeur de p est 1 ou 2, celle de r est 0 ou 1, celle de w est 0 ou 1, à la condition que la valeur de n ne soit que 1 lorsque X et/ou Y constituent une liaison supplémentaire carbone-carbone et que la somme de r et de w s'échelonne entre 0 et 1, L représente un groupe lieur/séparateur lié de façon covalente à un atome d'hydrogène de l'un des atomes de carbone auquel il est relié et remplace celui-ci, ce groupe lieur/séparateur correspondant à la formule (1), dans laquelle S représente un nombre entier d'une valeur s'échelonnant de 0 à 1, t représente un nombre entier d'une valeur s'échelonnant de 0 à 20 inclus, R?1¿ représente un fragment électrophile ou nucléophile permettant un rattachement covalent à un anticorps ou à un fragment de celui-ci ou bien un lieur de synthèse pouvant être rattaché à un anticorps ou à un fragment ou à un précurseur de celui-ci, Cyc représente un fragment aliphatique cyclique, un fragment aromatique, un fragment aliphatique hétérocyclique ou un fragment aromatique hétérocyclique, chacun desdits fragments étant éventuellement substitués par un ou plusieurs groupes n'interférant pas avec la liaison à un anticorps ou à un fragment d'anticorps, à la condition que, lorsque la valeur de s, t, m, r, et de n est 0, R?1¿ représente autre chose qu'un carboxyle. Cette invention, qui porte également sur les sels acceptables du point de vue pharmaceutique, ainsi que sur les conjugats de ces complexes, concerne, de surcroît, l'utilisation qui en est faite en matière de radio-immunothérapie.

Claims

CLAIMS:
1. An 225Ac complex comprising a functionalized
chelant compound of the formula I
<IMG>
wherein:
each Q is independently hydrogen or (CHR5)p CO2R;
Q1 is hydrogen or (CHR5)w CO2R;
each R independently is hydrogen, benzyl or C1-C4
alkyl; with the proviso that at least two of the sum
of Q and Q1 must be other than hydrogen;
each R5 independently is hydrogen; C1-C4 alkyl or (C1-
C2 alkyl)phenyl;
X and Y are each independently hydrogen or may be
taken with an adjacent X and Y to form an additional
carbon-carbon bond;
n is 0 or 1;
m is an integer from 0 to 10 inclusive;
p is 1 or 2;
r is 0 or 1;
w is 0 or 1;
with the proviso that n is only 1 when X and/or Y form an
additional carbon to carbon bond, and the sum of r and w
is 0 or 1;
L is a linker/spacer group covalently bonded to, and
replaces one hydrogen atom of one of the carbon atoms
to which it is joined, said linker/spacer group being
represented by the formula
24

<IMG>
wherein
s is an integer of 0 or 1;
t is an integer of 0 to 20 inclusive;
R1 is an electrophilic or nucleophilic moiety which
allows for covalent attachment to an antibody or
fragment thereof, or synthetic linker which can be
attached to an antibody or fragment thereof, or
precursor thereof; and
Cyc represents a cyclic aliphatic moiety, aromatic
moiety, aliphatic heterocyclic moiety, or aromatic
heterocyclic moiety, each of said moieties optionally
substituted with one or more groups which do not
interfere with binding to an antibody or antibody
fragment;
with the proviso that when s, t, m, r, and n are 0,
then R1 is other than carboxyl; or
a pharmaceutically acceptable salt thereof; complexed
with 225Ac.
2. The 225Ac complex of Claim 1 wherein the
functionalized chelant is a compound of formula II

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least two of Q must be other than
hydrogen
each R independently is hydrogen, benzyl or C1-C4
alkyl;
m is integer from 0 to 5 inclusive;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
3. The 225Ac complex of Claim 1 wherein the
functionalized chelant is a compound of formula III
26

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR;
Q1 is hydrogen or (CHR5)w CO2R; with the proviso that at
least two the sum of Q and Q1 must be other than
hydrogen and one Q is hydrogen;
each R independently is hydrogen, benzyl or C1-C9
alkyl;
m is integer from 0 to 5 inclusive;
w is 0 or 1;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C9
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
zhiusetuicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R 2 and R9 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
4. The 225Ac complex of Claim 1 wherein the
fuctionalized chelant is a compound of formula IV
27

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least one Q must be other than
hydrogen;
each R independently is hydrogen, benzyl or C1-C9
alkyl;
m is integer from 0 to 5 inclusive;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C9 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
5. The 225Ac complex of Claim 1 wherein the
functionalized chelant compound is 1-[(2-methoxy-5-
isothiocyanatophenyl)-carboxymethyl]-4,7,10-triscarboxy-
methyl-1,4,7,10-tetraazacyclododecane (MeO-DOTA-NCS).
28

6. An 225Ac conjugate comprising a functionalized
chelant compound of the formula I
<IMG>
wherein:
each Q is independently hydrogen or (CHR5)p CO2R;
Q1 is hydrogen or (CHR5)w CO2R;
each R independently is hydrogen, benzyl or C1-C4
alkyl; with the proviso that at least two of the sum
of Q and Q1 must be other than hydrogen;
each R5 independently is hydrogen; C1-C4 alkyl or (C1-
C2 alkyl)phenyl;
X and Y are each independently hydrogen or may be
taken with an adjacent X and Y to form an additional
carbon-carbon bond;
n is 0 or 1;
m is an integer from 0 to 10 inclusive;
p is 1 or 2;
r is 0 or 1;
w is 0 or 1;
with the proviso that n is only 1 when X and/or Y
form an additional carbon-carbon bond, and the sum of
r and w is 0 or 1;
L is a linker/spacer group covalently bonded to, and
replaces one hydrogen atom of one of the carbon atoms
to which it is joined, said linker/spacer group being
represented by the formula
29

<IMG>
wherein
s is an integer of 0 or 1;
t is an integer of 0 to 20 inclusive;
R1 is an electrophilic or nucleophilic moiety which
allows for covalent attachment to an antibody or
fragment thereof, or synthetic linker which can be
attached to an antibody or fragment thereof, or
precursor thereof; and
Cyc represents a cyclic aliphatic moiety, aromatic
moiety, aliphatic heterocyclic moiety, or aromatic
heterocyclic moiety, each of said moieties optionally
substituted with one or more groups which do not
interfere with binding to an antibody or antibody
fragment;
with the proviso that when s, t, m, r, and n are 0,
then R1 is other than carboxyl; or
pharmaceutically acceptable salt thereof;
complexed with 225Ac; and covalently attached to a
biological molecule.
7. The 225Ac conjugate of Claim 6 wherein the
functionalized chelant is a compound of formula II

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least two of Q must be other than
hydrogen
each R independently is hydrogen, benzyl or C1-C9
alkyl;
m is integer from 0 to 5 inclusive;
0 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C9
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C9 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogens or
a pharmaceutically acceptable salt thereof.
8. The 225Ac conjugate of Claim 6 wherein the
functionalized chelant is a compound of formula III
31

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR;
Q1 is hydrogen or (CHR5)w CO2R; with the proviso that at
least two the sum of Q and Q1 must be other than
hydrogen and one Q is hydrogen;
each R independently is hydrogen, benzyl or C1-C9
alkyl;
m is integer from 0 to 5 inclusive;
w is 0 or 1;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R9 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
9. The 225 Ac conjugate of Claim 6 wherein the
functionalized chelant is a compound of formula IV
32

<IMG>
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least one Q must be other than
hydrogen;
each R independently is hydrogen, benzyl or C1-C4
alkyl;
m is integer from 0 to 5 inclusive;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
10. The 225Ac conjugate of Claim 6 wherein the
functionalized chelant compound is 1-{(2-methoxy-5-
isothiocyanatophenyl)-carboxymethyl]-4,7,10-triscarboxy-
methyl-1,4,7,10-tetraazacyclododecane (MeO-DOTA-NCS).
33

11. The 225Ac conjugate of any one of Claims 6 to 10
wherein the biological molecule is an antibody or antibody
fragment.
12. The 225Ac conjugate of any one of Claims 6 to 10
wherein the biological molecule is selected from the group
of antibodies consisting of NuM195, CC-49, CC-49 F(ab')2r
CC-83, and CC-83 F(ab')2.
13. The 225Ac conjugate of Claim 6 wherein the
functionalized chelant compound of the conjugate is 1-[(2-
methoxy-5-isothiocyanatophenyl)-carboxymethyl]-4,7,10-
triscarboxy-methyl-1,4,7,10-tetraazacyclododecane and the
biological molecule is selected from the group of
antibodies consisting of HuM195, CC-49, CC-49 F(ab')2, CC-
83, and CC-83 F(ab')2.
14. The 225Ac conjugate of Claim 13 wherein the
functionalized chelant compound of the conjugate is 1-[(2-
methoxy-5-isothiocyanatophenyl)-carboxymethyl]-4,7,10-
triscarboxy-methyl-1,4,7,10-tetraazacyclododecane and the
biological molecule is HuM195 antibody.
15. A pharmaceutical formulation comprising the 225Ac
conjugate of any one of Claims 6 to 10 with a
pharmaceutically acceptale carrier.
16. A pharmaceutical formulation comprising the 225 Ac
conjugate of Claim 12 with a pharmaceutically acceptable
carrier.
17. A pharmaceutical formulation comprising the 225Ac
conjugate of Claim 13 or Claim 14 with a pharmaceutically
acceptable carrier.
34

18. Use, in the manufacture of a medicament for the therapeutic
treatment of a mammal having cancer, of a therapeutically effective amount of
the
pharmaceutical formulation of Claim 15.
19. Use, in the manufacture of a medicament for the therapeutic
treatment of a mammal having cancer, of a therapeutically effective amount of
the
pharmaceutical formulation of Claim 16.
20. Use, in the manufacture of a medicament for the therapeutic
treatment of a mammal having cancer, of a therapeutically effective amount of
the
pharmaceutical formulation of Claim 17.
21. Use, for the therapeutic treatment of a mammal having cancer, of a
therapeutically effective amount of the pharmaceutical formulation of Claim
15.
22. Use, for the therapeutic treatment of a mammal having cancer, of a
therapeutically effective amount of the pharmaceutical formulation of Claim
16.
23. Use, for the therapeutic treatment of a mammal having cancer, of a
therapeutically effective amount of the pharmaceutical formulation of Claim
17.
24. The pharmaceutical formulation according to Claim 15 for use in the
therapeutic treatment of a mammal having cancer.
25. The pharmaceutical formulation according to Claim 16 for use in the
therapeutic treatment of a mammal having cancer.
26. The pharmaceutical formulation according to Claim 17 for use in the
therapeutic treatment of a mammal having cancer.

Description

CA 02381123 2002-01-31
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ACTINIUM-225 COMPLEXES AND CONJUGATES FOR
RADIOIMMUNOTHERAPY
FIELD OF THE INVENTION
This invention relates to actinium-225 (225Ac)
complexes with fuctionalized chelants, their conjugates
and their use for radioimmunotherapy.
BACKGROUND OF THE INVENTION
The use of radionuclides complexed with suitable
chelants, as well as their conjugates (that is, such
complexes covalently attached to a biologically active
carrier, for example, protein) for diagnosis of cancer
and/or therapeutic treatment of cancer in mammals is
known. These biochemically engineered molecules provide
the tumor specificity and the radioisotope provides potent
cytotoxicity. See, for example, U.S. Patent Nos.
4,897,254; 5,342,925; 5,435,990; 5,652,361; 5,696,239; and
5,756,065.
It has been recognized that antibody-targeted alpha
particles would allow extraordinary potent, single cell-
specific killing with minimal toxicity to normal cells or
the patient. The use of alpha particles as an alternative
to more traditional classes of radiation is derived from
the particle's kinetic characteristics and the radioactive
half-life of their source isotope, as well as from the
properties of the target-selective carrier moiety for the
source isotope. The use of alpha emitting radionuclides
is highly desirable for the following reasons: (a) a
single atom can kill a cell making them hundreds to
thousands of times more potent than even the most potent
toxins or drugs; (b) the range of alpha particles is only
about 50 microns, ,so that adjacent tissues are not harmed;
(c) the chelated atoms on humanized antibodies are
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unlikely to be immunogenic and can be repeatedly dosed;
(d) the radioactive atoms decay to harmless stable atoms;
(e) killing can occur from inside or outside of the cell;
(f) killing is by apoptosis and by double stranded DNA
breaks and repair is not likely.
Specific cytotoxic effects of "alpha particle-
emitting radioimmunoconjugates" have been demonstrated in
several experimental systems. Specific in vitro cell-
killing has been demonstrated against a human epidermoid
cell line using 23-3 Bi- and 225 Ac-containing
immunoconjugates, see, for example, Kaspersen et al,
Nuclear Medicine Communications, Vol. 15, pp. 468-476
(1995). Efficient and specific cell kill by the 212Bi-
labeled anti-Tac (CD25) monoclonal antibody has been
demonstrated against an adult T-cell leukemia cell line in
vitro, see, for example, R. W. Kozak et al, Proc. Natl.
Acad. Sci. USA, Vol. 83, pp. 474-478 (1986). In other
experiments, mice inoculated intraperitoneally with the
murine tumor line EL-4 were cured of their ascites after
intraperitoneal injection of 150 Ci of a 212Bi-labeled
antibody conjugate, see, for example, R. M. Macklis et al,
Science, Vol. 240, pp. 1024-1026 (1988).
Potential for use of 225Ac in radiotherapy of cancer
has also been recognized due to its favorable properties.
This isotope decays with a radioactive half-life of 10
days into a cascade of short-lived alpha and beta-emitting
isotopes. See, for example, M. W. Geerlings et al,
Nuclear Medicine Communications, Vol. 14, pp. 121-125
(1993) and Kaspersen et al, Nuclear Medicine
Communications, Vol. 15, pp. 468-476 (1995). However, the
use of 225Ac in radioimmunotherapy has been hampered due to
its toxicity and lack of a suitable carrier which will
deliver it to the targeted cells.
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In an effort to reduce the toxicity of 225Ac, numerous
chelating agents such as, for example, 1,4,7,10-tetra-
azacyclododecane-1,4,7,10-tetraacetic acid (DOTA),
diethylenetriaminepentaacetic acid (DTPA), ethylene-
diaminetetracetic acid (EDTA), 1,4,7,10,13-pentaazacyclo-
pentadecane-1,4,7,10,13-pentaacetic acid (PEPA), and
1,4,7,10,13,16-hexaazacyclohexadecane-1,4,7,10,13,16-
hexaacetic acid (HEHA) have been complexed with 225Ac and
evaluated in vivo for toxicity and stability. However,
the toxicity of these complexes has proved to be still
substantial.
G. J. Beyer et al, Isotoperpraxis, Vol. 26, pp. 111-
114 (1990), has evaluated the in vivo uptake of 225Ac-
citrate and compared it to 169Yb-citrate. This study has
found that 225Ac-citrate had more efficient blood
clearance, greater liver uptake, and lower bone uptake
than 169Yb-citrate .
G. J. Beyer et al, Nucl. Med. & Biol., Vol. 24, pp.
367-372 (1997), has evaluated EDTMP (ethylenediaminetetra-
methylenephosphonic acid) as a chelant for 225Ac. The
study has found that EDTMP, depending on its
concentration, reduces the liver uptake. However, the
liver uptake of 225Ac-EDTMP is still substantial and
excretion of 225Ac-EDTMP is poor. The study has also
suggested that greater efficacy in endoradionuclide
therapy of bone metastasis can be expected with the use of
225Ac-EDTMP due to the alpha-radiation.
K. A. Deal et al, J. Med. Chem., Vol 42, pp. 298-2992
(1999), has evaluated biodistribution of a number of 225Ac
chelates. It has been observed that the structure of the
chelant has dramatic effect on biodistribution of 225Ac.
HEHA (1,4,7,10,13,16-hexaazacyclohexadecane-
1,4,7,10,13,16-hexaacetic acid) was the largest
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CA 02381123 2002-01-31
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macrocyclic chelant. 225Ac readily formed a complex with
HEHA. Exceptional in vivo stability and reduced toxicity
has been observed for 225Ac-HEHA. This has been attributed
to the large size and macrocyclic effect of HEHA.
Although various chelating agents were suggested and
evaluated as carriers for 225Ac, up to now 225Ac has not
been successfully chelated to an antibody and no
successful therapeutic use of 225Ac in animals or humans
has been reported presumably due to its inherent toxicity
and/or stability problems of its complexes.
It would be desirable to provide complexes comprising
225Ac and functionalized chelants which are kinetically and
thermodynamically inert for use in therapeutic
applications.
It would also be desirable to provide conjugates of
such 225Ac complexes with a biological molecule. The
biological molecule in these conjugates would provide the
tumor specificity and the 225Ac isotope would provide
potent cytotoxicity.
Another desirable property of these conjugates
includes physiological compatibility which would permit
the 225Ac complex, if separated from its targeting,
conjugated biological molecule in vivo, to be soluble in
physiological fluids and thus be rapidly eliminated from
the body.
SUMMARY OF THE INVENTION
The present invention is directed to 225Ac complexes
and their conjugates with a biological molecule. The 225Ac
compelexes and conjugates of the present invention are
4

CA 02381123 2002-01-31
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useful for the treatment of cancer in mammals, especially
humans.
More specifically, the present invention is directed
to 225Ac complexes comprising a functionalized chelant
compound of the formula (I):
Q I
4X I rN~
L C (CH2)nC-(CH2r-N N-Q
Y m I (,NJ
Q
wherein:
each Q is independently hydrogen or (CHR5)pC02R;
Q1 is hydrogen or (CHR5) WC02R;
each R independently is hydrogen, benzyl or C1-C4
alkyl; with the proviso that at least two of the sum
of Q and Q1 must be other than hydrogen;
each R5 independently is hydrogen; C1-C4 alkyl or (C1-
C2 alkyl)phenyl;
X and Y are each independently hydrogen or may be
taken with an adjacent X and Y to form an additional
carbon-carbon bond;
n is 0 or 1;
m is an integer from 0 to 10 inclusive;
p is 1 or 2;
r is 0 or 1;
w is 0 or 1;
with the proviso that n is only 1 when X and/or Y
form an additional carbon-carbon bond, and the sum of
r and w is 0 or 1;
L is a linker/spacer group covalently bonded to, and
replaces one hydrogen atom of one of the carbon atoms
5

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to which it is joined, said linker/spacer group being
represented by the formula
R
CYc (CH2)t
S
wherein
s is an integer of 0 or 1;
t is an integer of 0 to 20 inclusive;
R' is an electrophilic or nucleophilic moiety which
allows for covalent attachment to an antibody or
fragment of thereof, or synthetic linker which can be
attached to an antibody or fragment thereof, or
precursor thereof; and
Cyc represents a cyclic aliphatic moiety, aromatic
moiety, aliphatic heterocyclic moiety, or aromatic
heterocyclic moiety, each of said moieties optionally
substituted with one or more groups which do not
ineterfere with binding to a biologically active
carrier;
with the proviso that when s, t, m, r, and n are 0,
then R1 is other than carboxyl;
or pharmaceutically acceptable salt thereof;
complexed with 225Ac.
The present invention is also directed to a conjugate
comprising the aforementioned 225Ac complex covalently
attached to a biological molecule.
The present invention also includes formulations
having the conjugates of this invention and a
pharmaceutically acceptable carrier, especially
6

CA 02381123 2010-11-05
52839-1
formulations where the pharmaceutically acceptable carrier
is a liquid.
The present invention is also directed to a method of
therapeutic treatment of a mammal having cancer which
comprises administering to said mammal a therapeutically
affective amount of the formulation of this invention.
Surprisingly, the 225Ac complexes and conjugates of
this invention are relatively stable (that is, do not
easily dissociate) and some display rapid clearance from
the whole body and some non-target organs, such as liver
and kidney. Additionally, the alpha-particles emitting
225Ac complexes and conjugates of this invention are
expected to have several advantages over beta particle-
emitting cytotoxic agents including higher energy and r'
potent emissions, less hazardous waste, expected lower
effective dose, the potential for outpatient treatment,
better retention at the target sites, and higher target to
non-target radiation ratios.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1. 225Ac In-Vitro Cell Kill
7

CA 02381123 2009-09-24
52839-1
DETAILED DESCRIPTION OF THE INVENTION
As used herein, the term "225Ac complex" refers to a functionalized
chelant compound of formula I complexed with 225Ac radionuclide.
As used herein, the term "225Ac conjugate" refers to 225Ac complex of
the present invention that is covalently attached to a biological molecule.
As used herein, the term "mammal" means animals that nurish their
young with milk secreted by mammary glands, preferably humans.
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As used herein, the term "biological molecule" refers
to any protein, antibody, antibody fragment, hormone,
peptide, growth factor, antigen, hapten or any other
carrier which functions in this invention to recognize a
specific biological target site. Antibody and antibody
fragment refers to any polyclonal, monoclonal, chimeric,
human, mammalian, single chains, dimeric and tetrameric
antibody or antibody fragment. Such biological molecule,
when attached to a functionalized complex, serves to carry
the attached 225Ac ion to specific targeted tissues. The
term "antibody" refers to any polyclonal, monoclonal,
chimeric antibody or heteroantibody. Preferably the
antibodies used in the 225Ac conjugates of the present
invention are monoclonal antibodies having high
specificity for the desired cancer cells. Antibodies used
in the present invention may be directed against, for
example, cancer, tumors, leukemias, autoimune disorders
involving cells of the immune system, normal cells that
need to be ablated such as bone marrow and prostate
tissue, virus infected cells including HIV, mycoplasma,
differentiation and other cell membrane antigens, patogen
surface antigens and any biologically active molecules.
Some examples of antibodies are HuM195 (anti-CD33), CC-11,
CC-46,CC-49, CC-49 F(ab')2, CC-83, CC-83 F(ab')2r and
B72.3. Particularly preferred antibody for use in the
practice of the present invention is HuM195. Antibody
fragment includes Fab fragments and F(ab')2 fragments, and
any portion of an antibody having specificity toward a
desired epitope or epitopes. The antibodies which may be
used in the 225Ac conjugates of the present invention can
be prepared by techniques well known in the art. Highly
specific monoclonal antibodies can be produced by
hybridization techniques well known in the art, see, for
example, Kohler and Milstein, Nature, 256, 495-497 (1975);
and Eur. J. Immunol., 511-519 (1976).
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As used herein, "pharmaceutically acceptable salt"
means any salt of a compound of formula (I) which is
sufficiently non-toxic to be useful in therapy of mammals.
Representative of those salts, which are formed by
standard reactions, from both organic and inorganic
sources include, for example, sulfuric, hydrochloric,
phosphoric, acetic, succinic, citric, lactic, maleic,
fumaric, palmitic, cholic, palmoic, mucic, glutamic,
d-camphoric, glutaric, glycolic, phthalic, tartaric,
formic, lauric, steric, salicylic, methanesulfonic,
bensenesulfonic, sorbic, picric, benzoic, cinnamic and
other suitable acids. Also included are salts formed by
standard reactions from both organic and inorganic sources
such as ammonium, alkali metal ions, alkaline earth metal
ions, and other similar ions. Preferred are the salts of
the compounds of formula I where the salt is potassium,
sodium, ammonium, or mixtures thereof.
As used herein, the term "therapeutically effective
amount" means an amount of the 225Ac conjugate that
produces a therapeutic effect on the disease treated. The
therapeutically effective amount will vary depending on
the mammal, the 225Ac conjugate and the method of its
administration (for example, oral or parenteral). A
person of ordinary skill in the art can determine the
therapeutically effective amount of the 225Ac conjugate.
In the practice of the present invention the 225Ac
conjugate may be administered per se or as a component of
a pharmaceutically acceptable formulation.
Thus, the present invention may be practiced with the
225Ac conjugate being provided in pharmaceutical
formulation, both for veterinary and for human medical
use. Such pharmaceutical formulations comprise the active
agent (the 225Ac conjugate) together with a physiologically
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acceptable carrier, excipient or vehicle therefore. The
carrier(s) must be physiologically acceptable in the sense
of being compatible with the other ingredient(s) in the
formulation and not unsuitably deleterious to the
recipient thereof. The 225Ac conjugate is provided in a
therapeutically effective amount, as described above, and
in a quantity appropriate to achieve the desired dose.
The formulations include those suitable for
parenteral (including subcutaneous, intramuscular,
intraperitoneal, and intravenous), oral, rectal, topical,
nasal, or ophthalmic administration. Formulations may be
prepared by any methods well known in the art of pharmacy.
Such methods 'include the step of bringing the 225Ac
conjugate into association with a carrier, excipient or
vehicle therefore. In general, the formulation may be
prepared by uniformly and intimately bringing the 225Ac
conjugate into association with a liquid carrier, a finely
divided solid carrier, or both, and then, if necessary,
shaping the product into desired formulation. In
addition, the formulations of this invention may further
include one or more accessory ingredient(s) selected from
diluents, buffers, binders, disintegrants, surface active
agents, thickeners, lubricants, preservatives, and the
like. In addition, a treatment regime might include
pretreatment with non-radioactive carrier.
Injectable formulations of the present invention may
be either in suspensions or solution form. In the
preparation of suitable formulations it will be recognized
that, in general, the water solubility of the salt is
greater than the acid form. In soliution form the complex
(or when desired the separate components) is dissolved in
a physiologically acceptable carrier. Such carriers
comprise a suitable solvent, preservatives such as free
radical quenching agents, for example, ascorbic acid,

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benzyl alcohol or any other suitable molecule, if needed,
and buffers. Useful solvents include, for example, water,
aqueous alcohols, glycols, and phosphonate or carbonate
esters. Such aqueous solutions contain no more than 50
percent of the organic solvent by volume.
Injectable suspensions are compositions of the
present invention that require a liquid suspending
medium, with or without adjuvants, as a carier. The
suspending medium can be, for example, aqueous
polyvinylpyrrolidone, inert oils such as vegetable oils or
highly refined mineral oils, polyols, or aqueous
carboxymethylcellulose. Suitable physiologically
acceptable adjuvants, if necessary to keep the complex in
suspension, may be chosen from among thickeners such as
carboxymethylcellulose, polyvinylpyrrolidone, gelatin, and
the alginates. Many surfactants are also useful as
suspending agents, for example, lecithin, alkylphenol,
polyethyleneoxide adducts, naphthalenesulfonates,
alkylbenzenesulfonates, and polyoxyethylene sorbitane
esters.
In the context of the present invention the terms
"functionalized chelant" and "bifunctional chelant" are
used interchangeably and refer to compounds which have the
dual functionality of sequestering metal ions plus the
ability to covalently bind a biological molecule having
specificity for tumor cell epitopes or antigens. Such
compounds are of great utility for therapeutic and
diagnostic applications when they are, for example,
complexed with radioactive metal ions and covalently
attached to a specific antibody. These types of complexes
have been used to carry radioactive metals to tumor cells
which are targeted by the specificity of the attached
antibody [see, for example, Mears et al., Anal. Biochem.
11

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142, 68-74 (1984); Krejcarek et al., Biochem. And Biophys.
Res. Comm. 77, 581-585 (1977)].
The functionalized chelant compounds of formula (I)
useful in the practice of the present invention are known
in the art. See, for example, U.S. Patent Nos. 5,435,990
and 5,652,361.
Compounds of formula I where: R is hydrogen or
methyl; n is 0; m is 0 through 5; r is 0; and L is a
moiety of formula A:
A
R2 R3
RI
wherein:
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2CO2H, hydroxy and hydrogen; and
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof; are
preferred functionalized chelants.
Preferred functionalized chelant compounds of formula
I include also those compounds where Q1 is hydrogen and L
is represented by formula A as shown by formula II:
12

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R 3 Q II
2 1$ N
R (CH2)m C-N N-Q
4 H vIj
R
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least two of Q must be other than
hydrogen
each R independently is hydrogen benzyl or C1-C4
alkyl;
m is integer from 0 to 5 inclusive;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen;
or
a pharmaceutically acceptable salt thereof.
Additional preferred functionalized chelant compounds
of formula I include those compounds where at least one Q
is hydrogen and are represented by formula III:
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3 Q III
_ R Q N
2 1
R (CH2)m C-(N N-Q
4 H ",
R
wherein:
each Q independently is hydrogen or CHR5COOR;
Q1 is hydrogen or (CHR5)wCO2R; with the proviso that at
least two the sum of Q and Q1 must be other than
hydrogen and one Q is hydrogen;
each R independently is hydrogen benzyl or C1-C4
alkyl;
m is integer from 0 to 5 inclusive;
w is 0 or 1;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
Other preferred functionalized chelant compounds of
formula I include compounds where Q1 is CO2R (w=0) and are
represented by formula IV:
14

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R3 Q Iv
R2 (CH2)m C N N-Q
4 H NJ
R Q
wherein:
each Q independently is hydrogen or CHR5COOR; with the
proviso that at least one Q must be other than
hydrogen;
each R independently is hydrogen benzyl or C1-C4
alkyl;
m is integer from 0 to 5 inclusive;
R2 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
R3 is selected from the group consisting of C1-C4
alkoxy, -OCH2COOH, hydroxy and hydrogen;
R4 is selected from the group consisting of hydrogen,
nitro, amino, isothiocyanato, semicarbazido,
thiosemicarbazido, carboxyl, bromoacetamido and
maleimido;
each R5 independently is hydrogen or C1-C4 alkyl;
with the proviso that R2 and R4 cannot both be
hydrogen but one of R2 and R4 must be hydrogen; or
a pharmaceutically acceptable salt thereof.
The functionalized chelants of formula I useful in
the practice of the present invention can be prepared by
known methods. General synthetic approach to a twelve-
membered macrocyclic, bifunctional chelant of the present
invention as represented by formula I involves
monofuctionalization of a free-base macrocycle (for

CA 02381123 2009-09-24
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example, 1,4,7,10-tetraazacyclododecane) at only one of
the nitrogen atoms with an appropriate electrophile (for
example, any appropriately substituted alpha-
halocarboxylic acid ester). This electrophile must
possess a suitable linker moiety which would allow
covalent attachment of bifunctional ligand to a biological
mole ml a. Various synthetic routes to functionalized
chelants of formula I have been described U.S. Patent Nos.
5,435,990 and 5,652,361õ
The method of obtaining 225Ac radionuclide is not
critical to the present invention. For example, 225Ac can
be prepared in a cyclotron. 225Ac can be obtained in pure
form from Department of Energy (DOE), U.S.A., and
Institute for Transuranium Elements (ITU), Karlsruhe,
Germany.
The Z25Ac conjugates of the present invention can be
prepared by first forming the complex and then binding the
biological molecule. Thus, the process involves preparing
or obtaining the ligand, forming the complex with 225Ac and
then adding the biological molecule. Alternatively, the
process may involve first conjugation of the ligand to the
biological molecule and then the formation of the complex
with Z25Ac. Any suitable process that results in the
formation of the 225Ac conjugates of this invention is
within the scope of the p.rnsent invention.
In the following examples, the following terms and
conditions were used unless otherwise specified.
Glossary of Terms
Ab = antibody;
BFC = bifunctional chelant;
16

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DOTA = 1,4,7,10 tetraazacyclododecane-1,4,7,10-
tetraacetic acid;
MeO-DOTA-NCS = 1-[(2-methoxy-5-isothiocyanato-
phenyl)-carboxymethyl]-4,7,10-triscarboxy-
methyl-1,4,7,10-tetraazacyclododecane;
TMAA = tetramethyl ammonium acetate buffer;
Sephadex C-25 resin is a cation exchange resin, sold
by Pharmacia Inc.;
EDTA = ethylenediaminetetraacetic acid;
DTPA = diethylenetriaminepentaacetic acid;
TETA = 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-
tetraacetic acid;
DOTPA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-
tetrapropionic acid;
TETPA = 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-
tetrapropionic acid;
DOTMP = 1,4,6,10-tetraazacyclodecane-1,4,7,10-
tetramethylenephosphonic acid.
General Experimental
Method of preparation of 225Ac conjugates: The
preparation of 225Ac conjugates involved two steps. First,
the 225Ac complex was prepared by mixing a solution of the
functionalized chelant compound of formula I with the
solution of 225Ac at pH of about 5-6 in a suitable buffer.
The complex formation was tested using cation exchange
chromatography. Then, the conjugation of the 225Ac complex
to a biological molecule (suitably an antibody) was
carried out at the pH of about 8.5 in the presence of a
suitable buffer. The antibody and the antibody 225Ac
complex conjugates were then separated from the
unconjugated low molecular weight materials using gel
filtration chromatography. The fraction of radioactivity
associated with the antibody was then determined.
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The y emission counting was performed using a 3-inch x
3-inch NaI well crystal utilizing the y emission of 225Ac
decay product 221Fr (half-life of 4.8 min.) at 218 KeV.
Counting was carried out half an hour after sample
preparation.
Method for determining yield and stability of 225Ac
complexes and conjugates thereof: Instant Thin Layer
Chromatography (ITLC) was utilized with either a 10 mM
EDTA or 10 mM NaOH/9% NaCl solvent systems using ITLC SG
strips (sold by Gelman Sciences company) to assess the
complexation and conjugation efficiency of the DOTA-based
bifunctional 225Ac conjugate with HuM195 antibody.
The following examples are provided to further
illustrate the present invention, and should not be
construed as limiting thereof.
Example 1: Preparation of 225Ac-MeO-DOTA-NCS Complex
An aqueous solution of MeO-DOTA-NCS (35 p1; 0.31
mg/ml) was mixed with the 225Ac chloride solution (35 pl;
1.65 pCi/pl,) in 0.1M HC1. The pH was adjusted to about 5
using the TMAA buffer (130 p1 , 0.2 M, pH about 6).
Reaction mixture was incubated at about 50 C for one hour.
Complex formation was checked by cation exchange
chromatography employing the Sephadex C-25 resin and it
was determined that 99 percent of 225Ac was complexed.
Example 2: Preparation of 225Ac-HuM195 Conjugate
HuM195 antibody solution (20 pl, 5 mg/ml) was added
to the 225Ac complex solution (200 pl) prepared as
described in Example 1. The pH was adjusted to about 8.5
using a NaHCO3 buffer (85 p1, 0.1 M, pH=8.7). The molar
ratios of the reactants used were as follows: MeO-DOTA-
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NCS / 225Ac = 6549; MeO-DOTA-NCS / HuM195 = 24; and HuM195
/ 225Ac = 275. After 30 minutes incubation at 20 C the
protein and the small molecular weight components of the
solution were separated by gel filtration chromatography
using the Econo-Pack 10 DG gel filtration column. The
extent of coupling was determined by y emission counting.
It was determined that 7.3 percent of the 225Ac complex was
coupled to HuM195 antibody.
Example 3: Conjugation of Antibodies HuM195 (anti-
CD33) and B4 (anti-CD19) to MeO-DOTA-NCS
mg of HuM195 (or B4) monoclonal antibody solution
was mixed with 0.05 M HEPES containing EDTA at about pH 8
15 and dialysed against 0.05 M HEPES buffer for 24 hours in
an Amicon stirred cell dialysis unit to remove any metal
ions associated with antibodies. A MeO-DOTA-NCS solution
containing 3.38 mg of MeO-DOTA-NCS was added and allowed
to conjugate with the antibody at room temperature for 24
20 hours. Then the reaction mixture was dialysed against a
NaAc / NaCl buffer solution at about pH 7.0 for 24 hours
to remove any unreacted MeO-DOTA-NCS. The immunoconjugate
was recovered from the stirred cell and characterized
using a size exclusion high pressure liquid chromatography
(HPLC). This was compared to the native HuM195 or B4.
Antibody concentration was determined by UV-absorption at
280 nM.
The immunoconjugates could be labeled readily with
In showing success of the conjugation reaction. For
example, approximately 400 pCi of 111In in 200 pl of 0.2 M
HC1 was mixed with 29 pl of ammonium acetate (3M) and 9 p1
of 1-ascorbic acid (150 mg/ml) to adjust the pH to 5.0 and
then 0.5 mg of HuM195-MeO-DOTA-NCS immunoconjugate was
added. The reaction was allowed to progress at 37 C for 60
minutes. An 87% reaction yield was obtained.
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Example 4: Labeling of HuM195-MeO-DOTA
Immunoconj ugate with 225Ac
200 pCi of 225Ac in 0.2 M HC1 was mixed with 700 pl
metal free water and then buffered with 93 pl of NH4Ac at
about pH 6.5. Each of four 200 pl aliquots was mixed with
0 mg, 0.1 mg, 0.5 mg, 1 mg of HuM195-MeO-DOTA (prepared as
in Example 3), respectively. The reaction tubes were
placed into a 37 C water bath. The 225Ac incorporation was
monitored by TLC developed in 10 mM EDTA solvent at 3
hours. The 225Ac incorporation (percentage of activity
remaining at origin) data are given in Table 1 below for
the various antibody concentrations and Ab:Ac ratios.
Table 1: 225Ac Incorporation at 3 hr for three different
concentrations of the antibody
Antibody (pM) 1.6 8.1 16.1
Ab to Ac Ratio 174 870 1740
% Incorporation 7.1 23.1 51.8
Example 5: Stability of 225Ac-HuM195-MeO-DOTA
The three 225Ac-HuM195-MeO-DOTA solutions from Example
4 were combined and challenged with 20 pl of 10 mM DTPA to
remove unbounded metals. 100 pl of 1-ascorbic acid (150
mg/ml) was added as a radioprotection agent. The solution
was purified through a 10-DG desalting column (Bio-Rad
company) to separate 225Ac-HuM195-MeO-DOTA from unreacted
225Ac (in DTPA form). The purified 225Ac-HuM195-MeO-DOTA
was subjected to a stability study in human serum.
The purified 225Ac-HuM195-MeO-DOTA was assessed for
stability in different media such as 1% and 25% albumin
(human) and 1% and 25% human serum at 37 C. Overall
stability half-lives of 225Ac-HuM195-MeO-DOTA in either

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albumin (human) at 4 C or human serum at 37 C exceeded
150 days.
Example 6: 225Ac-HuM195-MeO-DOTA In-Vitro Cell Kill
A cell-based immunoreactivity study (binding of labeled
antibody to antigen excess) has shown that 225Ac labeled
HuM195 antibody (225Ac-HuM195-MeO-DOTA) is still
immunoreactive (N70%). The potency and specificity of 225Ac-
HuM195-MeO-DOTA was then evaluated in-vitro as a function of
specific activity and activity concentration on antigen
positive and negative cell lines. The LD50 in a 5-day assay
was -0.3 nCi/ml at a specific activity of 0.035 Ci/g which
is 3 log more potent than the similar 213Bi alpha emitting
agent with much high specific activity (see Nikula et al, J
Nuci Med 1999; 40, 166-176). These data (derived from 3H-
thymidine incorporation) are plotted below in Figure 1. The
LD50 in a 2-day assay is about 1.4 nCi/ml for positive cell
line and about 28 nCi/ml for negative cell line which
demonstrates the specificity. Internalization of isotope
into target cells was also demonstrated and more than 50%
was internalized in the target cells in 5 hours which is
crucial to control the fate of daughter isotopes. This
preliminary study suggests that 225Ac-HuMI95-MeO-DOTA
conjugates are useful clinically as a way to target alpha
particles to kill cells.
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Example 7: In Vivo Biodistribution
The in vivo biodistribution of free 225Ac acetate,
22SAc-DOTA and 2`5Ac-HuM195-MeO-DOTA was studied in nu/nu
mice by intraperitoneal injection of approximately 2 pCi
of 225Ac of each compound in 400 pl. It was demonstrated
that a different pattern of distribution existed (see
Table 2 below) for the three agents. The 225Ac-DOTA was
excreted very quickly and most activity was cleared in
less than 40 minutes. 225Ac in acetate was held up in the
liver and bone but cleared from blood. The 22'Ac-HuM195-
MeO-DOTA has longer blood circulation time and less bone
ptake over the period of 5 days. These data indicated
225Ac-HuM195-MeO-DOTA is stable in vivo.
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Table 2. Summary of the 22-'Ac Biodistribution (% dose/g) in nu/nu Mice
225Ac Acetate 225Ac-DOTA 225Ac-HuM195-
DOTAHuM195-
McO-DOTA
Average 1 d 2d 5d 40 min 2 h 18 h 1 d 2d 5d
Blood 0.1 0.2 0.0 3.0 1.8 1.1 10.1 10.2 4.5
Kidneys 3.8 3.2 2.8 4.9 3.5 3.1 4.6 5.2 4.6
Liver 46.6 43.1 68.5 4.5 4.6 5.8 8.8 10.0 20.7
Bone 13.3 12.0 17.1 3.9 4.2 4.9 3.8 4.1 5.3
23