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Some procedures to reduce cis-platinum toxicity reduce antitumour activity
CancerTreatmentReviews(1987) 14, 389-395
Some procedures to reduce c/s-platinum toxicity reduce antitnrnour activity Steinar Aamdal,* Oystein Fodstad and Alexander Pihl Institutefor Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo 3, Norway
Introduction Cis-diamminedichloroplatinum(II) (CDDP), is one of the most potent antitumour agents in current use. However, the clinical usefulness of C D D P is limited by its pronounced nephrotoxicity. Since the dose-response curves for sensitive tumours are steep (5), treatment results might be significantly improved if drug toxicity could be reduced and higher CDDP doses could be given. However, the toxicity and antitumour activity of a drug are often closely related and it is important therefore, that before toxicity-reducing procedures are accepted for clinical use it is established that a reduction in the severity of the druginduced side-effects is not accompanied by a concurrent reduction in antitumour efficacy. Various attempts have been made to reduce C D D P nephrotoxicity. The use of hydration (4) and diuretics (6, 15) is already well established in the clinic and has indeed increased the therapeutic index of CDDP. These procedures act by reducing the concentration of CDDP species in the kidney tubules but they do not influence the drug itself. However, other procedures proposed, such as the use of hypertonic saline as the drug vehicle (11) and administration of the nucleophilic agent sodium thiosulphate (8), do interact with the drug and may interfere with its antitumour activity. Whether this is the case is difficult to assess in patients, and such studies should be carried out preclinically in experimental systems. This paper reviews animal experiments performed to test the validity of administering C D D P dissolved in hypertonic saline, and of simultaneous intravenous (i.v.) use of C D D P and thiosulphate.
Hypertonic saline and s o d i u m thiosulphate reduce CDDP toxicity It is known that CDDP is unstable in aqueous solution and that, when dissolved, it dissociates to form aquated species (14), which probably is responsible for the toxicity of CDDP (10). If the chloride ion concentration in the solvent is increased, the dissociation of C D D P is reduced (14). Thus it has been found that hypertonic NaC1 in the drug vehicle greatly reduces its lethality to mice and permits higher CDDP doses to be given (11). In agreement with this, we found that when the NaC1 concentration was increased from
* Supported by the Norwegian Cancer Society. 0305 7372/87/3&40389+07 $03.00/0
© 1987 Academic Press Limited 389
390
S. AAMDAL E T AL.
o i"I× I.
LifO 9
I
1.8
I
4.0
I
6.0
NoCI in vehicle {%) Fzgure 1. Effect of different NaCI concentrations in the vehicle on the antitumour activity of 7.5 mg/kg (O), 10
mg/kg (A) and 12.5 mg/kg (VI) i.v. CDDP against systemic Ll210 leukaemia. Groups of mice were injected i.v. with 106 tumour cells and treated on the next day. The lifespan was recorded and compared with the life span of untreated control animals. Each data point represents the mean increase in life span (ILS) for 6-22 animals.
0.9% to 4.0%, the C D D P dose given to mice could be raised by approximately 50% without enhancing its toxicity (1). Intravenously administered thiosulphate is concentrated in the kidneys and, since thiosulphate reacts with the C D D P species to form biologically inactive products (3), the nephrotoxicity of C D D P is reduced and larger doses of C D D P can be tolerated.
Effect of hypertonic saline on CDDP antitumor
activity
Litterst (11) reported that in experiments in mice, hypertonic saline as the vehicle reduced the toxicity of C D D P with retained antitumour activity. O n this basis Ozols et al. (12) introduced 'high-dose' C D D P regimens involving hypertonic NaCI for the treatment of non-seminomatous testicular cancers of poor prognosis. The assumption that hypertonic saline as vehicle does not alter the antitumour activity of C D D P was based on a single experiment with the P388 ascites tumour in which intraperitoneal (i.p.) administration of the drug (1 l), i.e. 'intratumoural' injection of the compound, was used. However, in other model systems, where the drug was given i.v., we obtained different results (2), as described below.
L 1 2 1 0 mouse leukaemia
In animals with systemic L 1210 leukaemia, increasing NaC1 concentrations in the vehicle clearly reduced the antitumour activity ofi.v, injected C D D P (Figure 1). Thus, when the NaC1 concentration was increased from 0.9% to 4%, the C D D P antitumour activity was reduced by about 50%.
T O X I C I T Y R E D U C T I O N AND EFFICACY OF C I S - P L A T I N U M
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Fzgure 2. Effect of different NaCI concentrations in the vehicle on the antitumour activity of CDDP against a human malignant melanoma xenografi (LOX) growing s.c. in athymic nude mice and under the kidney capsule in the 6-day SRC assay. In the nude mouse assay (left) the animals were treated i.v. with 6 mg/kg of CDDP every seventh day and the tumour size was measured twice weekly. Each curve represents eight animals. In the 6-day SRC assay (right) the animals were treated i.v. with 6 mg/kg of CDDP on day 1 and 2 and the tumours were measured in situ after 6 days. Each curve represents five animals.
Human tumour xenografts
The antitumour activity of C D D P given i.v. against a human malignant melanoma (LOX) (Figure 2), growing either as subcutaneous (s.c.) xenografts in nude mice or under the kidney capsule in the 6-day subrenal capsule assay, was greatly reduced by hypertonic NaC1. In fact, the CDDP dose, even when doubled, did not overcome the NaCl-induced reduction ofantitumour activity (1). Similar results were obtained with a human sarcoma xenograft (ASX) (1). It has been reported, however, that high-dose C D D P with hypertonic NaC1 in the vehicle improved the response rates and reduced the nephrotoxicity (12) in patients with advanced testicular cancer. Importantly, however, in these studies patients also received far more extensive hydration than in previous studies used for comparison. Moreover, in the new protocol an additional drug, VP16, was introduced. In view of our preclinical studies it is likely that the improved response rates may be attributed to the higher CDDP dose allowed by increased hydration and possibly to the contribution of an additional antitumour drug.
Effect o f s o d i u m t h i o s u l p h a t e o n C D D P a n t i t u m o u r a c t i v i t y Howell et al. (7) have found in animal studies that thiosulphate given i.v. inactivates C D D P that reaches the systemic circulation after i.p. administration of the drug. Intravenous thiosulphate was therefore introduced in the treatment of patients with ovarian carcinoma and other turnouts in which the CDDP was administered into the abdominal cavity (8). Recently, however, attempts have been made to treat also patients with extraperitoneal tumours by giving both CDDP and thiosulphate by the i.v. route (13). Part of the rationale was the finding that the concentration of'free', active CDDP in plasma, as measured by using high pressure liquid chromatography, was unaffected by the presence ofthiosulphate
392
S. AAMDAL E T AL.
I
I
I
0
400
800
Thiosulphote (mg/kg bodyweight) Figure 3. Effect of thiosulphate on the antitumour activity of CDDP against systemic L1210 leukaemia. The animals were treated i.v. either with 5 mg/kg (0) or 10 mg/kg (A) of CDDP and with increasing doses of thiosulphate as indicated, and the lifespan was recorded. Each data point represents the mean ILS for eight animals.
9o
~, 70
5o
\
,o
IO
20
310
CDDP(mg/kgbody weight)
Figure 4. Effect of increasing CDDP doses together with a fixed dose of thiosulphate on the ILS of Ll210 leukaemic mice. Groups of animals were treated i.v. with 800 mg/kg of thiosulphate and immediately thereafter with i.v. CDDP doses as indicated ( . ) . One group of animals was treated i.v. with 10 mg/kg of CDDP in the absence of thiosulphate (A). Each data point represents the mean ILS for eight animals.
(8, 13). Since the effect o f this t o x i c i t y - r e d u c i n g p r o c e d u r e on the a n t i t u m o u r a c t i v i t y was not m e a s u r e d , we h a v e s t u d i e d this q u e s t i o n in several e x p e r i m e n t a l systems. L 1 2 1 0 mouse leukaemia
I n m i c e w i t h systemic L 1 2 1 0 l e u k a e m i a , the C D D P a n t i t u m o u r a c t i v i t y was s t r o n g l y i n h i b i t e d by i.v. t h i o s u l p h a t e ( F i g u r e 3). I n a n i m a l s r e c e i v i n g 10 m g / k g o f C D D P a n d 800 m g / k g of s o d i u m t h i o s u l p h a t e , the C D D P a n t i t u m o u r a c t i v i t y was r e d u c e d to t h a t o b t a i n e d w i t h 5 m g / k g o f C D D P w i t h o u t t h i o s u l p h a t e . E v e n if the C D D P dose was i n c r e a s e d to 20 m g / k g , the a n t i t u m o u r a c t i v i t y o f C D D P in the p r e s e n c e o f 800 m g / k g o f t h i o s u l p h a t e was not raised a b o v e t h a t o b t a i n e d by 10 m g / k g o f C D D P w i t h o u t t h i o s u l p h a t e ( F i g u r e 4).
TOXICITY REDUCTION AND EFFICACY OF CIS-PLATINUM
393
8 05
O
~5
It 15 19 rime after implantation (days) Figure 5. Effect of increasing doses of thiosulphate on the antitumour activity of CDDP against s.c. growing C3H mammary carcinoma in mice. The i.v. CDDP dose was 8 mg/kg. Each data point represents the mean tumour diameter difference for six animals. A, CDDP alone; A, CDDP + 200 mg/kg of S20~- ; U1, CDDP + 450 mg/kg of $2O2 ; m, CDDP + 800 mg/kg of $2O2 ; O, untreated controls.
10
20 30 40 Time after implantation (daysl
Figure 6. Effect of thiosulphate on the growth inhibiting effect of CDDP against an s.c. growing human sarcoma xenograft (MHMX). The animals were treaed i.v. every seventh day and the tumour size was measured twice weekly. The CDDP dose was 6 mg/kg and the thiosulphate dose was 400 mg/kg. Each data point represents the mean tumour diameter difference for eight animals. A, CDDP alone; alia, CDDP + $20~- ; 0 , untreated controls. Solid murine tumours I n a n i m a l s w i t h s.c. g r o w i n g L e w i s l u n g c a r c i n o m a a n d C 3 H m a m m a r y c a r c i n o m a ( F i g u r e 5), it w a s f o u n d t h a t t h e C D D P a n t i t u m o u r a c t i v i t y w a s a l m o s t a b o l i s h e d b y s i m u l t a n e o u s i.v. a d m i n i s t r a t i o n o f t h i o s u l p h a t e .
Human sarcoma xenograft I n a t h y m i c n u d e m i c e c a r r y i n g a s.c. g r o w i n g h u m a n s a r c o m a ( M H M X ) x e n o g r a f t , t h e t h i o s u l p h a t e t r e a t m e n t also s i g n i f i c a n t l y r e d u c e d t h e a n t i t u m o u r effect o f C D D P ( F i g u r e
6). The
apparent
inconsistency
between
our
results a n d
the
pharmacological
studies
394
S. AAMDAL E T AL.
mentioned above (8, 13), may possibly be explained by recent studies in rabbits showing that the biological activity of the 'free' CDDP, measured by a biological assay, is clearly reduced in the presence of sodium thiosulphate (9). In agreement with this, and with the results obtained in the tumour models, no responders were observed in the group of patients treated by this procedure (13).
Conclusion Recent results in our laboratory have confirmed, in animal systems, that administration of CDDP in hypertonic saline solution and thiosulphate given concurrently with CDDP reduce significantly the toxicity of the drug. The mechanism of action is probably that the hypertonic saline reduces the amount of aquated, reactive CDDP species in the plasma and that sodium thiosulphate binds covalently to form inactive products of CCDP species. We have found, however, in murine and human tumour models, that the antitumour activity of the drug was reduced to about the same extent as the toxicity. The increase in CDDP doses made possible by the toxicity-reducing procedures did not fully compensate for the reduction in antitumour activity. It is concluded that hypertonic saline in the drug vehicle and sodium thiosulphate injections do not increase the therapeutic index of i.v. administered CCDP.
Acknowledgements The authors wish to thank Torill Groth, Marianne Isaksen and Unni Ronning for excellent technical assistance. We also want to thank Eva Skaar for typing the manuscript.
References 1. Aamdal, S., Fodstad, O., Kaalhus, O. & Pihl, A. (1984) Reduced antineoplastic activity in mice ofcisplatin administered with high salt concentration in the vehicle. J N C 1 7 3 : 7 4 3 752. 2. Aamdal, S., Fodstad, O., Storeng, R. & Pihl, A. (1986) Reduced antitumour activity of cis-platin after concurrent intravenous administration of thiosulfate. Proc. Am. Ass. Cancer Res. 1157. 3. Burchenal, J. H., Kalaher, K., Dew, K., Lokys, L. & Gale, G. (1978) Studies of cross-resistance, synergistic combinations and blocking of activity of platinum derlvates. Biochimie (Paris) 60:961 965. 4. Charry, K. K., Highby, D.J., Henderson, E. S. & Swinerton, K. D. (1977) Phase I study of high-dose cisdichlorodiammineplatinum (II) with forced diuresis. Cancer Treat. Rep. 61:367 370. 5. Frei, E. I I I & Canellos, G. P. (1980) Dose: A critical factor in cancer chemotherapy. Am. J. Med. 69: 585 594. 6. Hayes, D. M., Cvitkovic, E., Golbey, R. B., Scheiner, E., Helson, L. & Krakoff, I. H. (1977) High dose cisplatinum diamminedichloride: amelioration of renal toxicity ofmannitol diuresis. Cancer39:1372 1381. 7. Howell, S. B. & Taetle, R. (1980) EfFect ofsodiuna thiosulfate on cis-dichlorodiammineplatinum (II) toxicity and antitumor activity in LI210 leukemia. Cancer Treat. Rep. 64:611 616. 8. Howell, S. B., Pfeifle, C. L., Wung, W. E., Olshen, R. A., Lucas, W. E., Yon, J. L. & Green, M. (1982) Intraperitoneal cisplatin with systemic thiosulfate protection. Ann. Intern Med. 97:845-85 l. 9. Iwamoto, Y., Kawano, T., Ishizawa, M., Aoki, K., Kuroiwa, T. & Baba, T. (1985) Inactivation of cisdiamminedichloroplatinum (I1) in blood and protection of its toxicity by sodium thiosulfate in rabbits. Cancer Chemother. Pharmacol. 15:228 232. 10. Kohl, H. K., Friedman, M. E., Melius, P., Mora, E. C. & McAuliff, C. A. (1979) Enhanced inhibition of
TOXICITY REDUCTION AND EFFICACY OF C I S - P L A T I N U M
1l.
12. 13. 14. 15.
395
both cellular protein synthesis and malate dehydrogenase by aged aquoplatinum(II) complexes. Chem. Biol. Interact. 24: 209-215. Litterst, C.L. (•98•)A•tera••nsinthet•xi•ity•fcis-dich••r•diamminep•atinum-IIandintissue••ca•izati•n of platinum as a function of NaCI concentration in the vehicle of administration. Toxicol. Appl. Pharmacol. 61:99 108. Ozols, R. F., Corden, B. J., Jacob, J., Wesley, M. N., Ostchega, Y. & Young, R. C. (1984) High-dose cisplatin in hypertonic saline. Ann. Intern. Med. 100: 19-24. Pfeifle, C. E., Howell, S. B., Felthouse, R. D., Woliver, T. B. S., Andrews, P. A., Markman, M. & Murphy, M. P. (1985) High-dose cisplatin with sodium thiosulfate protection. J. Clin. Oncol. 3: 237-244. Rosenberg, B. (1979) Anticanceractivityofcis-dichlorodiammineplatinum(II) and some relevant chemistry. Cancer Treat. Rep. 63: 1433-1438. Ward, J. M., Grabin, M. E., Berlin, E. & Young, D. M. (1977) Brief communication: Prevention of renal failure in rats receiving cis-diamminedichloroplatiniam (II) by administration of furosemide. Cancer Res. 37: 1238 1240.
Some procedures to reduce c/s-platinum toxicity reduce antitnrnour activity Steinar Aamdal,* Oystein Fodstad and Alexander Pihl Institutefor Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo 3, Norway
Introduction Cis-diamminedichloroplatinum(II) (CDDP), is one of the most potent antitumour agents in current use. However, the clinical usefulness of C D D P is limited by its pronounced nephrotoxicity. Since the dose-response curves for sensitive tumours are steep (5), treatment results might be significantly improved if drug toxicity could be reduced and higher CDDP doses could be given. However, the toxicity and antitumour activity of a drug are often closely related and it is important therefore, that before toxicity-reducing procedures are accepted for clinical use it is established that a reduction in the severity of the druginduced side-effects is not accompanied by a concurrent reduction in antitumour efficacy. Various attempts have been made to reduce C D D P nephrotoxicity. The use of hydration (4) and diuretics (6, 15) is already well established in the clinic and has indeed increased the therapeutic index of CDDP. These procedures act by reducing the concentration of CDDP species in the kidney tubules but they do not influence the drug itself. However, other procedures proposed, such as the use of hypertonic saline as the drug vehicle (11) and administration of the nucleophilic agent sodium thiosulphate (8), do interact with the drug and may interfere with its antitumour activity. Whether this is the case is difficult to assess in patients, and such studies should be carried out preclinically in experimental systems. This paper reviews animal experiments performed to test the validity of administering C D D P dissolved in hypertonic saline, and of simultaneous intravenous (i.v.) use of C D D P and thiosulphate.
Hypertonic saline and s o d i u m thiosulphate reduce CDDP toxicity It is known that CDDP is unstable in aqueous solution and that, when dissolved, it dissociates to form aquated species (14), which probably is responsible for the toxicity of CDDP (10). If the chloride ion concentration in the solvent is increased, the dissociation of C D D P is reduced (14). Thus it has been found that hypertonic NaC1 in the drug vehicle greatly reduces its lethality to mice and permits higher CDDP doses to be given (11). In agreement with this, we found that when the NaC1 concentration was increased from
* Supported by the Norwegian Cancer Society. 0305 7372/87/3&40389+07 $03.00/0
© 1987 Academic Press Limited 389
390
S. AAMDAL E T AL.
o i"I× I.
LifO 9
I
1.8
I
4.0
I
6.0
NoCI in vehicle {%) Fzgure 1. Effect of different NaCI concentrations in the vehicle on the antitumour activity of 7.5 mg/kg (O), 10
mg/kg (A) and 12.5 mg/kg (VI) i.v. CDDP against systemic Ll210 leukaemia. Groups of mice were injected i.v. with 106 tumour cells and treated on the next day. The lifespan was recorded and compared with the life span of untreated control animals. Each data point represents the mean increase in life span (ILS) for 6-22 animals.
0.9% to 4.0%, the C D D P dose given to mice could be raised by approximately 50% without enhancing its toxicity (1). Intravenously administered thiosulphate is concentrated in the kidneys and, since thiosulphate reacts with the C D D P species to form biologically inactive products (3), the nephrotoxicity of C D D P is reduced and larger doses of C D D P can be tolerated.
Effect of hypertonic saline on CDDP antitumor
activity
Litterst (11) reported that in experiments in mice, hypertonic saline as the vehicle reduced the toxicity of C D D P with retained antitumour activity. O n this basis Ozols et al. (12) introduced 'high-dose' C D D P regimens involving hypertonic NaCI for the treatment of non-seminomatous testicular cancers of poor prognosis. The assumption that hypertonic saline as vehicle does not alter the antitumour activity of C D D P was based on a single experiment with the P388 ascites tumour in which intraperitoneal (i.p.) administration of the drug (1 l), i.e. 'intratumoural' injection of the compound, was used. However, in other model systems, where the drug was given i.v., we obtained different results (2), as described below.
L 1 2 1 0 mouse leukaemia
In animals with systemic L 1210 leukaemia, increasing NaC1 concentrations in the vehicle clearly reduced the antitumour activity ofi.v, injected C D D P (Figure 1). Thus, when the NaC1 concentration was increased from 0.9% to 4%, the C D D P antitumour activity was reduced by about 50%.
T O X I C I T Y R E D U C T I O N AND EFFICACY OF C I S - P L A T I N U M
14 '
'
"~~1~ ®~
'
////~ ' SC'-NUDE '
i/
6.0%NaC)~/ /~-~
t
i a,/!
' 13
,
,
23
/~
SRC-ASSAY
~
l
33
t
43
~ ,
~
391
Ctr 20
6.0( Nal
~ o.l, ,
r-Q.
(I~Q o.
t
Time after implantation
(days)
Fzgure 2. Effect of different NaCI concentrations in the vehicle on the antitumour activity of CDDP against a human malignant melanoma xenografi (LOX) growing s.c. in athymic nude mice and under the kidney capsule in the 6-day SRC assay. In the nude mouse assay (left) the animals were treated i.v. with 6 mg/kg of CDDP every seventh day and the tumour size was measured twice weekly. Each curve represents eight animals. In the 6-day SRC assay (right) the animals were treated i.v. with 6 mg/kg of CDDP on day 1 and 2 and the tumours were measured in situ after 6 days. Each curve represents five animals.
Human tumour xenografts
The antitumour activity of C D D P given i.v. against a human malignant melanoma (LOX) (Figure 2), growing either as subcutaneous (s.c.) xenografts in nude mice or under the kidney capsule in the 6-day subrenal capsule assay, was greatly reduced by hypertonic NaC1. In fact, the CDDP dose, even when doubled, did not overcome the NaCl-induced reduction ofantitumour activity (1). Similar results were obtained with a human sarcoma xenograft (ASX) (1). It has been reported, however, that high-dose C D D P with hypertonic NaC1 in the vehicle improved the response rates and reduced the nephrotoxicity (12) in patients with advanced testicular cancer. Importantly, however, in these studies patients also received far more extensive hydration than in previous studies used for comparison. Moreover, in the new protocol an additional drug, VP16, was introduced. In view of our preclinical studies it is likely that the improved response rates may be attributed to the higher CDDP dose allowed by increased hydration and possibly to the contribution of an additional antitumour drug.
Effect o f s o d i u m t h i o s u l p h a t e o n C D D P a n t i t u m o u r a c t i v i t y Howell et al. (7) have found in animal studies that thiosulphate given i.v. inactivates C D D P that reaches the systemic circulation after i.p. administration of the drug. Intravenous thiosulphate was therefore introduced in the treatment of patients with ovarian carcinoma and other turnouts in which the CDDP was administered into the abdominal cavity (8). Recently, however, attempts have been made to treat also patients with extraperitoneal tumours by giving both CDDP and thiosulphate by the i.v. route (13). Part of the rationale was the finding that the concentration of'free', active CDDP in plasma, as measured by using high pressure liquid chromatography, was unaffected by the presence ofthiosulphate
392
S. AAMDAL E T AL.
I
I
I
0
400
800
Thiosulphote (mg/kg bodyweight) Figure 3. Effect of thiosulphate on the antitumour activity of CDDP against systemic L1210 leukaemia. The animals were treated i.v. either with 5 mg/kg (0) or 10 mg/kg (A) of CDDP and with increasing doses of thiosulphate as indicated, and the lifespan was recorded. Each data point represents the mean ILS for eight animals.
9o
~, 70
5o
\
,o
IO
20
310
CDDP(mg/kgbody weight)
Figure 4. Effect of increasing CDDP doses together with a fixed dose of thiosulphate on the ILS of Ll210 leukaemic mice. Groups of animals were treated i.v. with 800 mg/kg of thiosulphate and immediately thereafter with i.v. CDDP doses as indicated ( . ) . One group of animals was treated i.v. with 10 mg/kg of CDDP in the absence of thiosulphate (A). Each data point represents the mean ILS for eight animals.
(8, 13). Since the effect o f this t o x i c i t y - r e d u c i n g p r o c e d u r e on the a n t i t u m o u r a c t i v i t y was not m e a s u r e d , we h a v e s t u d i e d this q u e s t i o n in several e x p e r i m e n t a l systems. L 1 2 1 0 mouse leukaemia
I n m i c e w i t h systemic L 1 2 1 0 l e u k a e m i a , the C D D P a n t i t u m o u r a c t i v i t y was s t r o n g l y i n h i b i t e d by i.v. t h i o s u l p h a t e ( F i g u r e 3). I n a n i m a l s r e c e i v i n g 10 m g / k g o f C D D P a n d 800 m g / k g of s o d i u m t h i o s u l p h a t e , the C D D P a n t i t u m o u r a c t i v i t y was r e d u c e d to t h a t o b t a i n e d w i t h 5 m g / k g o f C D D P w i t h o u t t h i o s u l p h a t e . E v e n if the C D D P dose was i n c r e a s e d to 20 m g / k g , the a n t i t u m o u r a c t i v i t y o f C D D P in the p r e s e n c e o f 800 m g / k g o f t h i o s u l p h a t e was not raised a b o v e t h a t o b t a i n e d by 10 m g / k g o f C D D P w i t h o u t t h i o s u l p h a t e ( F i g u r e 4).
TOXICITY REDUCTION AND EFFICACY OF CIS-PLATINUM
393
8 05
O
~5
It 15 19 rime after implantation (days) Figure 5. Effect of increasing doses of thiosulphate on the antitumour activity of CDDP against s.c. growing C3H mammary carcinoma in mice. The i.v. CDDP dose was 8 mg/kg. Each data point represents the mean tumour diameter difference for six animals. A, CDDP alone; A, CDDP + 200 mg/kg of S20~- ; U1, CDDP + 450 mg/kg of $2O2 ; m, CDDP + 800 mg/kg of $2O2 ; O, untreated controls.
10
20 30 40 Time after implantation (daysl
Figure 6. Effect of thiosulphate on the growth inhibiting effect of CDDP against an s.c. growing human sarcoma xenograft (MHMX). The animals were treaed i.v. every seventh day and the tumour size was measured twice weekly. The CDDP dose was 6 mg/kg and the thiosulphate dose was 400 mg/kg. Each data point represents the mean tumour diameter difference for eight animals. A, CDDP alone; alia, CDDP + $20~- ; 0 , untreated controls. Solid murine tumours I n a n i m a l s w i t h s.c. g r o w i n g L e w i s l u n g c a r c i n o m a a n d C 3 H m a m m a r y c a r c i n o m a ( F i g u r e 5), it w a s f o u n d t h a t t h e C D D P a n t i t u m o u r a c t i v i t y w a s a l m o s t a b o l i s h e d b y s i m u l t a n e o u s i.v. a d m i n i s t r a t i o n o f t h i o s u l p h a t e .
Human sarcoma xenograft I n a t h y m i c n u d e m i c e c a r r y i n g a s.c. g r o w i n g h u m a n s a r c o m a ( M H M X ) x e n o g r a f t , t h e t h i o s u l p h a t e t r e a t m e n t also s i g n i f i c a n t l y r e d u c e d t h e a n t i t u m o u r effect o f C D D P ( F i g u r e
6). The
apparent
inconsistency
between
our
results a n d
the
pharmacological
studies
394
S. AAMDAL E T AL.
mentioned above (8, 13), may possibly be explained by recent studies in rabbits showing that the biological activity of the 'free' CDDP, measured by a biological assay, is clearly reduced in the presence of sodium thiosulphate (9). In agreement with this, and with the results obtained in the tumour models, no responders were observed in the group of patients treated by this procedure (13).
Conclusion Recent results in our laboratory have confirmed, in animal systems, that administration of CDDP in hypertonic saline solution and thiosulphate given concurrently with CDDP reduce significantly the toxicity of the drug. The mechanism of action is probably that the hypertonic saline reduces the amount of aquated, reactive CDDP species in the plasma and that sodium thiosulphate binds covalently to form inactive products of CCDP species. We have found, however, in murine and human tumour models, that the antitumour activity of the drug was reduced to about the same extent as the toxicity. The increase in CDDP doses made possible by the toxicity-reducing procedures did not fully compensate for the reduction in antitumour activity. It is concluded that hypertonic saline in the drug vehicle and sodium thiosulphate injections do not increase the therapeutic index of i.v. administered CCDP.
Acknowledgements The authors wish to thank Torill Groth, Marianne Isaksen and Unni Ronning for excellent technical assistance. We also want to thank Eva Skaar for typing the manuscript.
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