European Journal of N u c l e a r
Eur. J. Nucl. Med. 4, 211-215 (1979)
Medicine © by Springer-Verlag 1979
Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A A. G u a r i n o a n d S.K. S h u k l a Laboratorio di Chimica Nucleare, C.N.R., C.P.10, 1-00016 Monterotondo Stazione (Roma), Italy L. Castelli Istituto Regina Elena per lo Studio e la Cura dei Tumori, Viale Regina Elena 291, Roma, Italy C. C i p r i a n i a n d G.B. M a n n i Reparto di Medicina Nucleare, Ospedale S. Eugenio, Roma, Italy
Abstract. 6 7 G a - c h l o r o - 6 - m e r c a p t o p u r i n e a n d 67Gac i t r a t o - 6 - m e r c a p t o p u r i n e c o m p l e x e s have been prep a r e d a n d their d i s t r i b u t i o n in M o r r i s - h e p a t o m a - 3 9 2 4 A - b e a r i n g rats studied. The t u m o u r affinity of the gallium-67 c o m p o u n d s varies in the o r d e r : 6 7 G a - c h l o r o 6-mercaptopurine > 67Ga-citrato-6-mercaptopurine > 67Ga-citrate > 67Ga-chloride.
test has i n d i c a t e d [24] t h a t 5 7 C o - b l e o m y c i n is n o t s u p e r i o r to gallium-67 citrate. The labelling o f 6 - m e r c a p t o p u r i n e , a n i m p o r t a n t c a r c i n o s t a t i c a g e n t [11] c o n c e n t r a t i n g in t u m o u r s [1], with t e c h n e t i u m - 9 9 m , for d e v e l o p i n g a t u m o u r scint i g r a p h i c agent, led to a r a d i o p h a r m a c e u t i c a l for chol e o s c i n t i g r a p h y [8]. Since g a l l i u m itself possesses antit u m o u r activity [4] we t h o u g h t it o f interest to p r e p a r e 6 7 G a - 6 - m e r c a p t o p u r i n e c o m p l e x a n d s t u d y its p r o p erty as a t u m o u r s c a n n i n g agent. The p r e s e n t note describes s o m e p r e l i m i n a r y results o b t a i n e d with this radiopharmaceutical.
Introduction G a l l i u m - 6 7 citrate is so far the m o s t widely e m p l o y e d t u m o u r - s e e k i n g r a d i o p h a r m a c e u t i c a l [10, 15, 17, 20]. The f a c t o r s : t u m o u r , i n f l a m m a t i o n , age, sex, horm o n e status, l a c t a t i o n , p r e g n a n c y , e x p o s u r e to ionizing r a d i a t i o n o r c h e m o t h e r a p e u t i c agents, a n d the a m o u n t o f the e l e m e n t p r e s e n t in the dose a d m i n istered, which d e t e r m i n e [7] the tissue d i s t r i b u t i o n o f gallium-67, a n d its extensive u p t a k e in the liver, spleen, a n d b o w e l [9], have so far k e p t it f r o m being an ideal t u m o u r s c a n n i n g agent [10]. T h e low specific l o c a l i z a t i o n often renders the gallium-67 citrate scan i n t e r p r e t a t i o n difficult [3]. Basing on the r a t i o n a l e t h a t the labelled p r o d u c t , like the p a r e n t , will also have t u m o u r affinity, m a n y a t t e m p t s have been m a d e to d e v e l o p r a d i o p h a r m a c e u t i c a l s o f high t u m o u r specificity by r a d i o l a b e l l i n g a n t i - t u m o u r agents, which have been s h o w n to c o n c e n t r a t e to some extent in t u m o u r s a g a i n s t which they act [1, 3, 5, 12, 16, 21, 23]. The results p a r t i c u l a r l y those o f N o u e l a n d cow o r k e r s [13] a r o u s e d m u c h interest in this field a n d 5 7 C o - b l e o m y c i n was f o u n d to give the m o s t c o n s i s t e n t results [14], b u t the l o n g half-life (270 days) o f 57Co has been a serious d r a w b a c k a g a i n s t p u t t i n g the r a d i o p h a r m a c e u t i c a l in r o u t i n e use. A detailed c o m p a r a t i v e
Experimental Gallium-67 citrate, both from Philips-Duphar B.V., Petten, Holland, and from the Radiochemical Centre Ltd., Amersham, was used. Gallium-67 chloride in 0.04 M HC1 was obtained from the Radiochemical Centre Ltd., Amersham. 6-Mercaptopurine was from Merck. 67Ga-6-mercaptopurine was synthesized according to the method, with slight modifications, described by Kirschner and coworkers [11] for the preparation of other metallo-6-mercaptopurines. In order to avoid the hydrolysis of gallium-67, a solution of 6-mercaptopurine (1 rag/10 ml) in 0.04 M sodium hydroxide was added dropwise to the gallium-67 solution with shaking at room temperature. The pH of the solution was brought to 7, and the fresh solution was examined chromatographically for the formation of the complex. Chromatograms were developed with physiological saline in the manner previously described [18, 19]. Tumour affinity of the 67Ga-6-mercaptopurine was studied after intravenous injection of the freshly prepared complex solution in the tail of Morris hepatoma-3924 A-bearing ACI rats. The rats were bred in our laboratory. Morris hepatoma-3924 A was inoculated intramuscularly into the hind left leg. Rats (weighing 170 to 200 g) of the same age and sex were used. For each study a group of three tumour-bearing rats was used and the preparation of the complex and its distribution eXamined at least three times. The healthy rats of the same age and sex served as control studies. After the injection of the radiopharmaceutical each animal was
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A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A 60.000
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Fig. 1.a Radiochromatogram of 67Ga-citrate. b Radiochromatogram of 67Ga-citrato-6-mercaptopurine. Paper: HCl-washed Whatman 3 MM; Mobile Phase: physiological saline, temperature: 20 ° C
5.0 Start
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Distance in cm
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Fig. 2. a Radiochromatogram of 67Ga-chloride. b Radiochromatogram of 6VGa-chloro-6-mercaptopurine. Paper: HCl-washed Whatman 3 MM; Mobile Phase: physiological saline; temperature: 20 ° C
Fig. 3. a Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-citrate. b Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 6VGa-citrato6-mercaptopurine. Tumours: 10-days old; scintigrams 22 h post injection
kept in a separate cage. Water and laboratory chow (Mangimi Bilanciati Roma S.r.1., Roma) were available to animals ad Iibiturn. The distribution of the radiopharmaceutical was studied by whole body scanning of the rat after a light ether anaesthesia. The scintigrams were obtained with an Italelettronica scanner.
R e s u l t s and D i s c u s s i o n
Radiochromatograms of gallium-67 citrate, gallium67 c h l o r i d e a n d o f t h e c o r r e s p o n d i n g 6 - m e r c a p t o p u rine complex are shown in Figs. 1 and 2 respectively.
A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A
213
Fig. 4.a Scintigram of a healthy female rat injected with 67Gachloride, b Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloride. Tumour : 11-days old. e Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumour: 11-days old. d Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumour: 25-days old: Scintigrams 8 h post-injection
Fig. 5a-d. Scintigrams of Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumor: ll-days old. a Scintigram: 8 h post-injection, b Scintigram: 22 h post-injection. e Scintigram: 47 h post-injection, d Scintigram: 6 days postinjection
The f o r m a t i o n o f the 67Ga-6-mercaptopurine complex was concluded f r o m the difference in the Rf value o f the reaction p r o d u c t and the initial gallium67 salt. The nature of the complex did not change on aging its solution at r o o m temperature. Similar r a d i o c h r o m a t o g r a m s for fresh and aged solutions were obtained. The different Rf value of the 6-mercaptopurine complex with gallium-67 citrate and gallium67 chloride, 0.5 and 0.10 respectively, shows that the p r o d u c t s o f the two reactions are not the same. The two complexes are hereafter called 67Ga-citrato-6m e r c a p t o p u r i n e and 67Ga-chloro-6-mercaptopurine respectively.
The distribution of gallium-67 citrate and 67Gacitrato-6-mercaptopurine in rats with a 10-day old Morris hepatoma-3924 A is shown in Fig. 3a and b respectively. The t u m o u r affinity o f 67Ga-citrato-6m e r c a p t o p u r i n e was f o u n d to be slightly higher than that of gallium-67 citrate. Figure 4 a and b show the distribution o f gallium67 chloride in a healthy and a Morris hepatoma-3924 A (11-day old) bearing rats respectively. The distribution o f 6VGa-6-mercaptopurine in healthy rats is similar to that of gallium-67 chloride, and of gallium-67 citrate, i.e., mainly in the liver. The uptake of the gallium-67 chloride in the h e p a t o m a is slightly less
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A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A
mercaptopurine complex, the 67Ga-mercaptopurines have considerable tumour affinity. Work is in progress on the study of the composition of gallium-6-mercaptopurine complexes and their distribution in different organs of tumour-bearing rats. Acknowledgement. The authors wish to thank Mr. L. Damasi for the tumour transplantations.
References
Fig. 6. Scintigram of a Walker-256 carcinosarcoma-bearing male rat injected with 67Ga-chloro-6-mercaptopurine. Scintigram: 22 h post-injection
than that of the citrate. The scintigrams in Fig. 4c and d illustrate the distribution of 67Ga-chloro-6-mercaptopurine in 11 and 25-day old hepatoma-bearing rats respectively. Like gallium-67 citrate and other radiopharmaceuticals [2, 6], the 67Ga-chloro-6-mercaptopurine accumulation in recently transplanted tumours is more intense than that in the older ones. The scintigrams at different intervals of post-injection of 67Ga-chloro-6-mercaptopurine are shown in Fig. 5. Once concentrated in the tumour the complex seems to remain bound in it and with time distributes itself in it as the tumour grows. The 67 Ga-chloro-6-mercaptopurine complex was found also to concentrate to some extent in Walker256 carcinosarcoma (Fig. 6). All gallium-67 compounds were found to concentrate intensely in the liver. The tumour affinity of the gallium-67 compounds studied here varies in the order: 67Ga-chloro-6-mercaptopurine > 67Ga-citrato-6-mercaptopurine >gallium-67 citrate >gallium-67 chloride. The results reported here show that, unlike the observations of Hunt and coworkers [8] for 99mTc-6-
1. Bartosek, I., Donelli, M.G., Guaitani, A., Colombo, T., Russo, R., Garattini, S. : Differences of cyclophosphamide and 6-mercaptopurine metabolic rates in perfused liver of normal and tumour-bearing animals. Biochem. Pharmacol. 24, 289 291 (1975) 2. Edwards, C.L., Hayes, R.L.,: Scanning malignat neoplasms with gallium-67. J. Am. Med. Assoc. 212, 1182-1190 (1970) 3. Goodwin, D.A., Meares, C.F.: Radiolabeled Antitumour Agents. Semin. Nucl. Med. 6, 389-396 (1976) 4. Hart, M.M., Adamson, R.H. : Antitumour activity and toxicity of salts of inorganic group IIIa metals: aluminium, gallium, indium, and thallium. Proc. Nat. Acad. Sci. USA 68, 1623 1626 (1971) 5. Hayakawa, T., Ushio, Y., Mogami, H., Horibata, K.: The uptake, distribution and antitumour activity of bleomycin in gliomas in the mouse. Europ. J. Cancer 10, 137 142 (1974) 6. Hayes, R.L., Nelson, B., Swartzendruber, D.C., Carlton, J.E., Byrd, B.L. : Gallium-67 localization in rat and mouse tumours. Science 167, 289-290 (1970) 7. Hayes, R.L." The tissue distribution of gallium radionuclides. J. Nucl. Med. 18, 74~742 (1977) 8. Hunt, F.C., Maddalena, D.J., Yeates, M.G., : Technetium-99m6-mercaptupurine, a new radiopharmaceutical for cholescintigraphy. In: Recent advances in nuclear medicine. H. Ueda, M. Lio, S. Kato (eds.). Proceedings of the first world congress of nuclear medicine, Sept. 30-Oct. 5, 1974, pp. 869-871, Tokyo: Japan Radioisotopes Association 1974 9. Kaplan, H.S.: Hodgkin's disease: Multidisciplinary contributions to the conquest of a neoplasm. Radiology 123, 551-558 (1977) 10. Kaufman, J.H., Cedermark, B.J., Parthasarathy, K.L., Didolkar, M.S., Bakshi, S.J.: The value o f 67Ga scintigraphy in soft-tissue sarcoma and chondrosarcoma. Radiology 123, 131-134 (1977) 11. Kirschner, S., Wei, Y.K., Francis, D., Bergman, J.G.: Anticancer and potential antiviral activity of complex inorganic compounds, J. Med. Chem. 9, 369-372 (1966) 12. Milch, R.A., Rall, D.P., Tobies, J.E.: Bone localization of tetracycline. J. Natl. Cancer Inst. 19, 87-94 (1957) 13. Nouei, J.P., Renault, H., Robert, J., Jeanne, C., Wicart, L.: La bl6omycine marqu6e au Co-57, Int6r6t darts le diagnostic des tumeurs malignes et de leurs extension. Nouv. Presse M6d. 1, 95-98 (1972) 14. Nouel, J.P., Robert, J., Bertrand, A., Witz, H., Delorme, G., Renault, H., Mamo, L. : Labelled bleomycin in the diagnosis of cancer: A study containing the results of 1,000 patients. In: Recent advances in nuclear medicine, H. Ueda, M. Lio, S. Kato (eds.). Proceedings of the first world congress of nuclear medicine, Sept. 30-Oct. 5, 1974, pp. 129-133. Tokyo: Japan Radioisotopes Association 1974
A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A 15. Pinsky, S.M., Henkin, R.E.: Gallium-67 tumour scanning. Semin. Nucl. Meal. 6, 397-409 (1976) 16. Rall, D.P., Loo, T.L., Lane, M., Kelly, M.G.: Appearance and persistance of fluorescent material in tumour tissue after tetracycline administration. J. Natl. Cancer Inst. 19, 79 86 (1957) 17. Richman, S.D., Appelbaum, F., Levenson, S.M., Johnston, G.S., Ziegler, J.L. : 67Ga radionuclide imaging in Burkitt's lymphoma. Radiology 117, 639~545 (1975) 18. Shukla, S.K., Manni, G.B., Cipriani, C. : Behaviour of the pertechnetate ion in humans. J. Chromatogr. 143, 522-526 (1977) 19. Shukla, S.K., Manni, G.B., Cipriani, C.: Effect of aluminium impurities in the generator-produced pertechnetate-99m ion on thyroid scintigrams. Eur. J. Nucl. Med. 2, 137-141 (1977) 20. Silberstein, E.B., : The role of tumour imaging radiopharmaceuticals. Am. J. Med. 60, 226-237 (1976) 21. Titus, E.D., Loo, T.L., Rall, D.P.: Identification of the bone fluorophore in tetracycline-treated rabbits. Antibiot. Ann., 949-953 (1957 1958)
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22. Umezawa, H., Ishizuka, M., Mori, S., Chimura, H., Takeuchi, T. : The distribution of 3Hbleomycin in mouse tissue. J. Antibiot. 21, Ser. A, 638-642 (1968) 23. Umezawa, H., Takeuchi, T., Hori, S., Sawa, T., Ishizuka, M.: Studies on the mechanism of antitumour effect of bleomycin in squamous cell carcinoma. J. Antibiot. 25, 409 420 (1972) 24. Watanabe, K., Kawashira, K., Kamoi, I., Morita, K., Matsura, K.: Clinical evaluation of 57Co-bleomycin as a tumour localizing radiopharmaceutical: Its comparison with 67Ga-citrate. In: Recent advances in nuclear medicine (H. Ueda, M. Lio, S. Kato, eds.). Proceedings of the first world congress of nuclear medicine. Sept. 3 0 - Oct. 5, 1974, pp. 937-939. Tokyo: Japan Radioisotopes Association 1974
Received April 3, 1978
Eur. J. Nucl. Med. 4, 211-215 (1979)
Medicine © by Springer-Verlag 1979
Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A A. G u a r i n o a n d S.K. S h u k l a Laboratorio di Chimica Nucleare, C.N.R., C.P.10, 1-00016 Monterotondo Stazione (Roma), Italy L. Castelli Istituto Regina Elena per lo Studio e la Cura dei Tumori, Viale Regina Elena 291, Roma, Italy C. C i p r i a n i a n d G.B. M a n n i Reparto di Medicina Nucleare, Ospedale S. Eugenio, Roma, Italy
Abstract. 6 7 G a - c h l o r o - 6 - m e r c a p t o p u r i n e a n d 67Gac i t r a t o - 6 - m e r c a p t o p u r i n e c o m p l e x e s have been prep a r e d a n d their d i s t r i b u t i o n in M o r r i s - h e p a t o m a - 3 9 2 4 A - b e a r i n g rats studied. The t u m o u r affinity of the gallium-67 c o m p o u n d s varies in the o r d e r : 6 7 G a - c h l o r o 6-mercaptopurine > 67Ga-citrato-6-mercaptopurine > 67Ga-citrate > 67Ga-chloride.
test has i n d i c a t e d [24] t h a t 5 7 C o - b l e o m y c i n is n o t s u p e r i o r to gallium-67 citrate. The labelling o f 6 - m e r c a p t o p u r i n e , a n i m p o r t a n t c a r c i n o s t a t i c a g e n t [11] c o n c e n t r a t i n g in t u m o u r s [1], with t e c h n e t i u m - 9 9 m , for d e v e l o p i n g a t u m o u r scint i g r a p h i c agent, led to a r a d i o p h a r m a c e u t i c a l for chol e o s c i n t i g r a p h y [8]. Since g a l l i u m itself possesses antit u m o u r activity [4] we t h o u g h t it o f interest to p r e p a r e 6 7 G a - 6 - m e r c a p t o p u r i n e c o m p l e x a n d s t u d y its p r o p erty as a t u m o u r s c a n n i n g agent. The p r e s e n t note describes s o m e p r e l i m i n a r y results o b t a i n e d with this radiopharmaceutical.
Introduction G a l l i u m - 6 7 citrate is so far the m o s t widely e m p l o y e d t u m o u r - s e e k i n g r a d i o p h a r m a c e u t i c a l [10, 15, 17, 20]. The f a c t o r s : t u m o u r , i n f l a m m a t i o n , age, sex, horm o n e status, l a c t a t i o n , p r e g n a n c y , e x p o s u r e to ionizing r a d i a t i o n o r c h e m o t h e r a p e u t i c agents, a n d the a m o u n t o f the e l e m e n t p r e s e n t in the dose a d m i n istered, which d e t e r m i n e [7] the tissue d i s t r i b u t i o n o f gallium-67, a n d its extensive u p t a k e in the liver, spleen, a n d b o w e l [9], have so far k e p t it f r o m being an ideal t u m o u r s c a n n i n g agent [10]. T h e low specific l o c a l i z a t i o n often renders the gallium-67 citrate scan i n t e r p r e t a t i o n difficult [3]. Basing on the r a t i o n a l e t h a t the labelled p r o d u c t , like the p a r e n t , will also have t u m o u r affinity, m a n y a t t e m p t s have been m a d e to d e v e l o p r a d i o p h a r m a c e u t i c a l s o f high t u m o u r specificity by r a d i o l a b e l l i n g a n t i - t u m o u r agents, which have been s h o w n to c o n c e n t r a t e to some extent in t u m o u r s a g a i n s t which they act [1, 3, 5, 12, 16, 21, 23]. The results p a r t i c u l a r l y those o f N o u e l a n d cow o r k e r s [13] a r o u s e d m u c h interest in this field a n d 5 7 C o - b l e o m y c i n was f o u n d to give the m o s t c o n s i s t e n t results [14], b u t the l o n g half-life (270 days) o f 57Co has been a serious d r a w b a c k a g a i n s t p u t t i n g the r a d i o p h a r m a c e u t i c a l in r o u t i n e use. A detailed c o m p a r a t i v e
Experimental Gallium-67 citrate, both from Philips-Duphar B.V., Petten, Holland, and from the Radiochemical Centre Ltd., Amersham, was used. Gallium-67 chloride in 0.04 M HC1 was obtained from the Radiochemical Centre Ltd., Amersham. 6-Mercaptopurine was from Merck. 67Ga-6-mercaptopurine was synthesized according to the method, with slight modifications, described by Kirschner and coworkers [11] for the preparation of other metallo-6-mercaptopurines. In order to avoid the hydrolysis of gallium-67, a solution of 6-mercaptopurine (1 rag/10 ml) in 0.04 M sodium hydroxide was added dropwise to the gallium-67 solution with shaking at room temperature. The pH of the solution was brought to 7, and the fresh solution was examined chromatographically for the formation of the complex. Chromatograms were developed with physiological saline in the manner previously described [18, 19]. Tumour affinity of the 67Ga-6-mercaptopurine was studied after intravenous injection of the freshly prepared complex solution in the tail of Morris hepatoma-3924 A-bearing ACI rats. The rats were bred in our laboratory. Morris hepatoma-3924 A was inoculated intramuscularly into the hind left leg. Rats (weighing 170 to 200 g) of the same age and sex were used. For each study a group of three tumour-bearing rats was used and the preparation of the complex and its distribution eXamined at least three times. The healthy rats of the same age and sex served as control studies. After the injection of the radiopharmaceutical each animal was
0340-6997/79/0004/0211/$01.00
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A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A 60.000
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Fig. 1.a Radiochromatogram of 67Ga-citrate. b Radiochromatogram of 67Ga-citrato-6-mercaptopurine. Paper: HCl-washed Whatman 3 MM; Mobile Phase: physiological saline, temperature: 20 ° C
5.0 Start
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Fig. 2. a Radiochromatogram of 67Ga-chloride. b Radiochromatogram of 6VGa-chloro-6-mercaptopurine. Paper: HCl-washed Whatman 3 MM; Mobile Phase: physiological saline; temperature: 20 ° C
Fig. 3. a Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-citrate. b Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 6VGa-citrato6-mercaptopurine. Tumours: 10-days old; scintigrams 22 h post injection
kept in a separate cage. Water and laboratory chow (Mangimi Bilanciati Roma S.r.1., Roma) were available to animals ad Iibiturn. The distribution of the radiopharmaceutical was studied by whole body scanning of the rat after a light ether anaesthesia. The scintigrams were obtained with an Italelettronica scanner.
R e s u l t s and D i s c u s s i o n
Radiochromatograms of gallium-67 citrate, gallium67 c h l o r i d e a n d o f t h e c o r r e s p o n d i n g 6 - m e r c a p t o p u rine complex are shown in Figs. 1 and 2 respectively.
A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A
213
Fig. 4.a Scintigram of a healthy female rat injected with 67Gachloride, b Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloride. Tumour : 11-days old. e Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumour: 11-days old. d Scintigram of a Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumour: 25-days old: Scintigrams 8 h post-injection
Fig. 5a-d. Scintigrams of Morris hepatoma-3924 A-bearing female rat injected with 67Ga-chloro-6-mercaptopurine. Tumor: ll-days old. a Scintigram: 8 h post-injection, b Scintigram: 22 h post-injection. e Scintigram: 47 h post-injection, d Scintigram: 6 days postinjection
The f o r m a t i o n o f the 67Ga-6-mercaptopurine complex was concluded f r o m the difference in the Rf value o f the reaction p r o d u c t and the initial gallium67 salt. The nature of the complex did not change on aging its solution at r o o m temperature. Similar r a d i o c h r o m a t o g r a m s for fresh and aged solutions were obtained. The different Rf value of the 6-mercaptopurine complex with gallium-67 citrate and gallium67 chloride, 0.5 and 0.10 respectively, shows that the p r o d u c t s o f the two reactions are not the same. The two complexes are hereafter called 67Ga-citrato-6m e r c a p t o p u r i n e and 67Ga-chloro-6-mercaptopurine respectively.
The distribution of gallium-67 citrate and 67Gacitrato-6-mercaptopurine in rats with a 10-day old Morris hepatoma-3924 A is shown in Fig. 3a and b respectively. The t u m o u r affinity o f 67Ga-citrato-6m e r c a p t o p u r i n e was f o u n d to be slightly higher than that of gallium-67 citrate. Figure 4 a and b show the distribution o f gallium67 chloride in a healthy and a Morris hepatoma-3924 A (11-day old) bearing rats respectively. The distribution o f 6VGa-6-mercaptopurine in healthy rats is similar to that of gallium-67 chloride, and of gallium-67 citrate, i.e., mainly in the liver. The uptake of the gallium-67 chloride in the h e p a t o m a is slightly less
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A. Guarino et al. : Uptake of 67Ga-6-Mercaptopurines in Morris Hepatoma-3924 A
mercaptopurine complex, the 67Ga-mercaptopurines have considerable tumour affinity. Work is in progress on the study of the composition of gallium-6-mercaptopurine complexes and their distribution in different organs of tumour-bearing rats. Acknowledgement. The authors wish to thank Mr. L. Damasi for the tumour transplantations.
References
Fig. 6. Scintigram of a Walker-256 carcinosarcoma-bearing male rat injected with 67Ga-chloro-6-mercaptopurine. Scintigram: 22 h post-injection
than that of the citrate. The scintigrams in Fig. 4c and d illustrate the distribution of 67Ga-chloro-6-mercaptopurine in 11 and 25-day old hepatoma-bearing rats respectively. Like gallium-67 citrate and other radiopharmaceuticals [2, 6], the 67Ga-chloro-6-mercaptopurine accumulation in recently transplanted tumours is more intense than that in the older ones. The scintigrams at different intervals of post-injection of 67Ga-chloro-6-mercaptopurine are shown in Fig. 5. Once concentrated in the tumour the complex seems to remain bound in it and with time distributes itself in it as the tumour grows. The 67 Ga-chloro-6-mercaptopurine complex was found also to concentrate to some extent in Walker256 carcinosarcoma (Fig. 6). All gallium-67 compounds were found to concentrate intensely in the liver. The tumour affinity of the gallium-67 compounds studied here varies in the order: 67Ga-chloro-6-mercaptopurine > 67Ga-citrato-6-mercaptopurine >gallium-67 citrate >gallium-67 chloride. The results reported here show that, unlike the observations of Hunt and coworkers [8] for 99mTc-6-
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Received April 3, 1978
