Antitumor effects of three platinum complexes, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)-platinum (II) monohydrate (DWA2114R), cis-diammine-(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) and cis-diamminedichloroplatinum(II) (CDDP), in mice.

(-)-(R)-2-Aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +)platinum(II) monohydrate (DWA2114R), cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) and cis-diamminedichloroplatinum(II) (CDDP) were compared for their antitumor effects and nephrotoxicity-inducing activities at the same dosage (1/8, 1/4, 1/3, 1/2, 2/3 or 3/4 of the LD10 or LD10) on the basis of their intravenous lethal doses in mice. DWA2114R was effective against murine tumor lines, Colon 26 and Colon 38 carcinomas, M5076 ovarian sarcoma and P388 L1210 leukemias, implanted subcutaneously (s.c.). Triple injection every other day of DWA2114R was more effective than a single injection at each sublethal dose. The antitumor effects of DWA2114R against these tumors were more effective than or were similar to those of CBDCA and CDDP. The antitumor effect against CDDP-resistant L1210 leukemia implanted s.c. was only observed in the treatment of DWA2114R, but not in CBDCA and CDDP. No excellent antitumor effects of three platinum complexes were observed against Lewis lung carcinoma and B16 melanoma implanted s.c. even at triple injection every other day, and no effect was obtained against Meth-A fibrosarcoma under similar conditions. While the treatment of CDDP showed marked increases in levels of blood urea nitrogen and of urinary protein and sugar at effective doses in the antitumor evaluations, the treatment of DWA2114R as well as CBDCA showed no increase in these parameters. These results indicate that DWA2114R represents a desirable second generation antitumor platinum complex.     

Toxicological and tumoricidal evaluations of a new platinum complex, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato+ ++)platinum( II) monohydrate, in rats

The toxicities and antitumor activity of a new anticancer platinum compound, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +) platinum(II) monohydrate (DWA2114R), were examined in rats by single intravenous injection in comparison with those of cis-diammine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) and cis-diamminedichloroplatinum(II) (CDDP). The lethal dose (LD) of DWA2114R (100 mg/kg) or CBDCA (80 mg/kg) caused a slight decrease in body weight (less than 10%) and no significant change in the levels of blood urea nitrogen and urinary sugar and protein. In contrast, a sub-LD level of CDDP (8 mg/kg) seriously decreased body weight (20%) and markedly elevated the levels of these nephrotoxicity parameters. Monitoring the numbers of peripheral blood cells for 3 weeks after the drug injection revealed that all three drugs showed severe thrombocytopenia, moderate leukopenia and slight anemia. However, CBDCA induced the most severe thrombocytopenia among these drugs. The number of platelets was reduced by 60% in rats injected with a half LD of CBDCA. A moderate reduction in platelet count (35-43%) was caused by an equitoxic dose of DWA2114R or CDDP, but abated about 3 days faster than that caused by CBDCA. Interestingly, only CDDP caused an irreversible anemia. Each drug showed a potent antitumor activity at weakly toxic doses against Walker 256 carcinosarcoma transplanted intramuscularly into rats. These results indicate that DWA2114R could be a promising new platinum anticancer agent with an improved toxicity profile.     

Toxicological and Tumoricidal Evaluations of a New Platinum Complex, (–)-(R)-2-Aminomethy lpyrrolidine (1,1-cyclobutanedicarboxylato) platinum (II) Monohydrate, in Rats

The toxicities and antitumor activity of a new anticancer platinum compound, (-)-( R )-2-amino-methylpyrrolidine(l,l-cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114R), were examined in rats by single intravenous injection in comparison with those of cis -diammine(1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) and cis diamminedichloroplatinum(II) (CDDP). The lethal dose (LD) of DWA2114R (100 mg/kg) or CBDCA (80 mg/kg) caused a slight decrease in body weight <10%) and no significant change in the levels of blood urea nitrogen and urinary sugar and protein. In contrast, a sub-LD level of CDDP (8 mg/kg) seriously decreased body weight (20%) and markedly elevated the levels of these nephrotoxicity parameters. Monitoring the numbers of peripheral blood cells for 3 weeks after the drug injection revealed that all three drugs showed severe thrombocytopenia, moderate leukopenia and slight anemia. However, CBDCA induced the most severe thrombocytopenia among these drugs. The number of platelets was reduced by 60% in rats injected with a half LD of CBDCA. A moderate reduction in platelet count (35–43%) was caused by an equitoxic dose of DWA2114R or CDDP, but abated about 3 days faster than that caused by CBDCA. Interestingly, only CDDP caused an irreversible anemia. Each drug showed a potent antitumor activity at weakly toxic doses against Walker 256 carcinosarcoma transplanted intramuscularly into rats. These results indicate that DWA2114R could be a promising new platinum anticancer agent with an improved toxicity profile.     

Antitumor activity and cellular accumulation of a new platinum complex, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platinum( II) monohydrate, in cisplatin-sensitive and -resistant murine P388 leukemia cells.

We have examined the cytotoxicity and accumulation of (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +)platinum(II) monohydrate (DWA2114R) in parent and cisplatin-resistant mouse P388 leukemia cells (P388 and P388/DDP), in comparison with those of cisplatin (CDDP) and carboplatin (CBDCA). The degrees of resistance to CDDP and CBDCA, expressed as the ratio of IC50 for P388/DDP cells to IC50 for P388 cells, were 75-33 and 100-27, respectively, under the conditions of 2-24 h exposure to each drug at a density of 10(6) cells/ml. The corresponding values (25-7) for DWA2114R were relatively low. Accumulations of CDDP and CBDCA were reduced in P388/DDP cells; however, no reduction in accumulation of DWA2114R was observed at various exposure periods and concentrations of the drugs. The accumulations of CDDP in P388 and P388/DDP cells at drug concentrations corresponding to the IC50 values for drug exposure periods of 2-24 h were 0.41-0.97 and 13.1-33.7 ng Pt/10(7) cells, respectively, suggesting that an intracellular mechanism of resistance against CDDP could be activated in P388/DDP cells. P388/DDP cells also showed relatively low resistance to DWA2114R via this mechanism in comparison with CDDP and CBDCA. From the relationship between structure and activity of several Pt-complexes, these different properties of DWA2114R compared with CDDP and CBDCA could be due not only to the differences in carrier ligand structure but also to the properties of the whole molecule associated with the carrier ligand and leaving group.     

Accumulation of cis-diamminedichloroplatinum (II) and its analogues in sensitive and resistant human ovarian carcinoma cells.

Human ovarian carcinoma cell line (NOS2), established from a patient with serous cystadenocarcinoma of the ovary, has been exposed to a stepwise increase in cis-diamminedichloroplatinum (II) (CDDP) concentration to produce a CDDP-resistant cell line NOS2CR) as an experimental model for resistance to CDDP. NOS2CR cells showed a 7-fold resistance to CDDP and a lesser degree of cross-resistance to diammine (1,1-cyclobutanedicarboxylato)-platinum (II) (CBDCA) and (-)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato) platinum (II) (DWA2114R). In the absence of CDDP, cross-resistance to DWA2114R was reduced to the original level by 2 months, although 83% resistance to CDDP remained up to 6 months. To investigate CDDP-resistant mechanisms, alterations in the intracellular accumulation of CDDP and analogues were assayed by atomic absorption. In both NOS2 and NOS2CR cells, accumulation of CDDP increased linearly with time and was concentration-dependent. NOS2CR cells demonstrated 71, 52 and 12% reduction in accumulation of CDDP, CBDCA, and DWA2114R, respectively. These reductions did not seem to be due to P-glycoprotein, because expression of multidrug-resistant 1 gene was not detected in either NOS2 or NOS2CR cells. These studies indicate that the mechanisms of resistance to CDDP and analogues in NOS2CR cells are related in the main to reduced intracellular accumulation of drugs. DWA2114R might be helpful to treat CDDP-resistant and recurrent tumors which were treated by CDDP.     

Establishment and Characterization of Acquired Resistance to Platinum Anticancer Drugs in Human Ovarian Carcinoma Cells

To investigate differences in resistance to cis -diamminedichloroplatinum(II) (CDDP) and diammine (1,1-cyclobutanecarboxylato)platinum(II) (CBDCA), and their newly developed derivative, ((—)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato)platinum (II)) (DWA2114R), four types of resistant cell lines were established from a parental cell line (NOS2) of a serous cystadeno-carcinoma of the ovary. The cross-resistance of CDDP-resistant cells (NOS2CR1 and NOS2CR2) to DWA2114R was slight (only 25% of the resistance to CDDP), and no cross-resistance was observed to anticancer drugs other than the CDDP derivative, except to camptothecin (CPT-11) in the case of NOS2CR2 cells. The cross-resistance of CBDCA-resistant cells (NOS2CBR) to DWA2114R was slight (only about 1/3 of the resistance to CBDCA), and no cross-resistance was observed among anticancer drugs other than the CDDP derivative. On the other hand, DWA2114R-resistant cells (NOS2DR) showed a high cross-resistance to CDDP, CBDCA, etoposide (VP-16), and CPT-11. Intracellular accumulations of CDDP and CBDCA were markedly reduced in NOS2CR1, NOS2CR2, and NOS2CBR cells compared to those in NOS2 cells, but were reduced only slightly in NOS2DR cells. Intracellular accumulation of DWA2114R was reduced somewhat in the four types of resistant cells. Glutathione S-transferase activity was not increased in any of the four types of resistant cells, and intracellular GSH concentration was increased only in NOS2CR2 cells (by 2.6 fold). From these results, we consider that the resistance mechanisms against CDDP and CDBCA are similar, and reduction of intracellular drug accumulations is a significant factor. Resistance to DWA2114R differed from resistance to CDDP and CBDCA in both cross-resistance spectrum and resistance mechanism, indicating that reduction in intracellular drug accumulation is not the major resistance mechanism.     

Potent antitumour activity of (-)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114R) against advanced L1210 leukaemia in mice.

The time dependency of the antitumour activity of (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +)platinum(II) monohydrate (DWA2114R) was examined in mice inoculated i.p. with 10(5) mouse L1210 leukaemia cells. The increase in life span was greater in mice treated with 72 mg kg-1 DWA2114R on the 6th day following tumour inoculation than in mice treated at earlier times. Such superior effects against advanced L1210 were also seen with cis-diammine (1,1-cyclobutanedicarboxylato)platinum(II) (CBDCA) but not seen with the parent compound, cis-diamminedichloroplatinum(II) (CDDP) or other antitumour agents devoid of platinum. After the injection of DWA2114R on day 6, most of the ascites tumour cells accumulated in the S and G2/M phases of the cell cycle and the total cell number markedly decreased from 10(8) to less than 10(6). On the other hand, only a temporary G1 arrest and a less than 50% reduction of the cell number were induced after a similar treatment on day 3. Interestingly, the superiority of DWA2114R for advanced L1210 was lost in athymic nude mice and mice depleted of T cells by anti-thymocyte antisera. In addition, mice cured of advanced L1210 specifically rejected re-inoculated L1210 cells. These results indicate that the superior antitumour activity against advanced L1210 is unique to DWA2114R among the agents tested (except for CBDCA) and is caused by both an increased drug susceptibility of tumour cells and a drug-induced antitumour effect mediated by T cells of the host mice.     

Antitumor Activity and Cellular Accumulation of a New Platinum Complex, (—)-(R)-2-Aminomethylpyrrolidine(1,l-cyclobutanedicarboxylato)platinum(II) Monohydrate, in Cisplatin-sensitive and -resistant Murine P388 Leukemia Cells

We have examined the cytotoxicity and accumulation of (—)-(U)-2-aminomethylpyrrolidine(1,l-cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114R) in parent and cisplatin-resistant mouse P388 leukemia cells (P388 and P388/DDP), in comparison with those of cisplatin (CDDP) and carboplatin (CBDCA). The degrees of resistance to CDDP and CBDCA, expressed as the ratio of IC₅₀for P388/DDP celts to IC₅₀ for P388 cells, were 75–33 and 100-27, respectively, under the conditions of 2–24 h exposure to each drug at a density of 10⁶ cells/ml. The corresponding values (25–7) for DWA2114R were relatively low. Accumulations of CDDP and CBDCA were reduced in P388/DDP cells; however, no reduction in accumulation of DWA2114R was observed at various exposure periods and concentrations of the drugs. The accumulations of CDDP in P388 and P388/DDP cells at drug concentrations corresponding to the IC₅₀ values for drug exposure periods of 2–24 h were 0.41–0.97 and 13.1–33.7 ng Pt/10⁷ cells, respectively, suggesting that an intracellular mechanism of resistance against CDDP could be activated in P388/DDP cells. P388/DDP cells also showed relatively low resistance to DWA2114R via this mechanism in comparison with CDDP and CBDCA. From the relationship between structure and activity of several Pt-complexes, these different properties of DWA2114R compared with CDDP and CBDCA could be due not only to the differences in carrier ligand structure but also to the properties of the whole molecule associated with the carrier ligand and leaving group.     

Antitumor activity of a new platinum complex (R)-(-)-2-aminomethylpyrrolidine (1,1-cyclobutane dicarboxylato) platinum (II) (DWA2114R) by its serial administration

Antitumor activity of a newly synthesized platinum complex, DWA2114R, by the serial administration was examined and compared with that of cis-diammine-1,1-cyclobutane dicarboxylato platinum (II) (CBDCA). In mice transplanted s.c. with tumor, the serial i.p. administration resulted in the increases of both maximal tolerated dose (MTD) and growth inhibitory ratio (GIR) of DWA2114R than single administration. Such increases in MTD and GIR were also shown by CBDCA, but the degree of these increases, such as the ratio of MTD or GIR by the serial administration compared to that at the single administration, was higher in DWA2114R than CBDCA. GIR of DWA2114R by the serial administration was higher than that of CBDCA at the doses to induce the same toxicity which was estimated by body weight loss. In addition, in the experiment using ascites tumor-bearing mice, better antitumor activity of DWA2114R was shown by the elongation of survival time. These results indicate that the cumulative toxicity of DWA2114R is lower than that of CBDCA, which causes the therapeutic advantages of DWA2114R in the serial administration.     

Antitumor activity of a new platinum complex, 2-aminomethyl-pyrrolidine (1, 1-cyclobutanedicarboxylato) platinum (II)

One hundred cis-diamminedichloroplatinum (II) (CDDP) analogs have been evaluated for antitumor activity in male CDF1 mice subcutaneously (s.c.) implanted with tumor fragments of Colon 26 carcinoma. Among the complexes tested, 2-aminomethyl-pyrrolidine (1, 1-cyclobutanedicarboxylato) platinum (II) (DWA 2114) had the best antitumor effect. The mice intraperitoneally (i.p.) injected with DWA 2114 at a dose of 40 mg/kg/day on days 4, 6 and 8 after inoculation showed a 97% growth inhibitory ratio (GIR) on day 14 compared to the non-treated control mice. We evaluated the inhibitory effects of DWA 2114 on other tumors, such as Colon 38 carcinoma, Ca 755 mammary adenocarcinoma and L1210 leukemia, and found that it also had antitumor effects on various kinds of tumors. The nephrotoxicity-inducing activity of DWA 2114 and CDDP was evaluated in normal BDF1 mice, as indicated by changes in blood urea nitrogen (BUN) at almost the maximum tolerated dose (MTD) (DWA 2114: 100 mg/kg, CDDP: 12 mg/kg). DWA 2114 had no effect on BUN levels, while CDDP elevated BUN levels. These results indicate that DWA 2114 represents a second generation platinum antitumor complex.     

Comparison of the antitumour effects and nephrotoxicity-inducing activities of two new platinum complexes, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato+ ++)-platinum (II) monohydrate, and its enantiomeric isomer.

New platinum complexes, (-)-(R)-2-aminomethylpyrrolidine(1,1- cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114R) and its enantiomeric isomer, (+)-(S)-2-aminomethylpyrrolidine(1,1- cyclobutanedicarboxylato)platinum(II) monohydrate (DWA2114S), were compared in their antitumour effects and nephrotoxicity-inducing activities. Both compounds were effective against the murine tumours L1210 and Colon 26 by i.p. injection of 20-100 mg kg-1. While DWA2114S showed marked increases in blood urea nitrogen (BUN) and urinary protein and sugar in BDF1 mice treated i.p. at the maximum tolerated dose, DWA2114R showed no increases in these parameters. To clarify the difference of nephrotoxicity between the isomers, tissue distribution was examined. Renal Pt concentration in DWA2114S-treated mice was more than 5-fold higher compared with that in DWA2114R-treated mice 2h after i.p. injection of 80 mg kg-1. However, there were no such marked differences in the lung, liver, heart, spleen and plasma. The low content of Pt in the kidneys of DWA2114R-treated mice could explain its lower nephrotoxicity. The in vitro experiments for uptake of the drugs into the cultured normal rat kidney cells and fresh splenocytes revealed that the Pt amount in the cells treated with DWA2114S, especially in the kidney cells, was much higher than DWA2114R.     

Combination therapy of a new platinum complex, DWA2114R with various antitumor agents against mouse tumors in vivo]

In vivo antitumor activity of (-)-(R)-2-aminomethylpyrrolidine (1, 1-cyclobutanedicarboxylato) platinum (II) monohydrate (DWA2114R) in combination with various antitumor agents was examined using mouse leukemia P388, Meth-A fibrosarcoma and M5076 reticulum cell sarcoma. The combination treatment of DWA2114R with cyclophosphamide, 5-fluorouracil, adriamycin, etoposide or vindesine showed synergistic effects on the prolongation of survival time of mice bearing P388. Among these combinations, combination of DWA2114R with adriamycin or vindesine showed a good synergism. In the combination treatment with vindesine against Meth-A which is not so sensitive to platinum agent, DWA2114R showed a synergistic or additive effect, but cis-diamminedichloroplatinum (II) (CDDP) showed subadditive. Three-drug combination of DWA2114R or CDDP with cyclophosphamide and adriamycin was examined in mice inoculated i.p. or s.c. with M5076. In both models, the combination of DWA2114R was more active than that of CDDP at the dose less than 1/16-fold of the dose of CDDP which is the ratio of two drugs in clinical trial.     

Effect of treatment schedule of an antitumor platinum complex, DWA2114R, on the antitumor activity]

Effects of treatment schedule of (-)-(R)-2-aminomethylpyrrolidine (1,1-cyclobutanedicarboxylato) platinum (II) monohydrate, DWA2114R, on the antitumor activity against murine colon adenocarcinoma (Colon 26) and Lewis lung carcinoma (3LL) were examined. Colon 26 or 3LL tumors were transplanted s.c. into the flank and subsequently DW A2114R was given i.v. by single or multiple injections. The tumor weight was determined on days 14 or 25 and the antitumor effect was evaluated by GIR%. Although the total dose of DWA2114R was identical in both schedules, single injection was superior to multiple. Effect of treatment schedule of cis-dichlorodiammine-platinum (II), CDDP, and cis-diammine (1, 1-cyclobutanedicarboxylato) platinum (II), CBDCA, on the antitumor activities were the same as in case of DWA 2114R, i.e., single injection was superior to multiple.     

A new anticancer platinum compound, (-)-(R)-2-aminomethyl-pyrrolidine(1,1-cyclobutanedicarboxylato) platinum(II): DNA interstrand crosslinking, repair and lethal effects in normal human, Fanconi's anaemia and xeroderma pigmentosum cells.

Interstrand cross-linking, repair and lethal effects of (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato++ +) platinum(II) (DWA2114R) were studied in normal human. Fanconi''s anaemia (FA) and xeroderma pigmentosum group A (XPA) cells. Interstrand crosslinking by DWA2114R was slower than that by cisplatin (CDDP), since DWA2114R produced mainly Pt(II)-monoadducts after 1 h treatment, followed by progressive interstrand crosslinking to a maximum 5 h post-incubation, while CDDP induced rapidly interstrand crosslinks in approximately 70% DNA during the 1 h treatment, followed by a approximately 30% residual increase. At the maximum rate, DWA2114R was 18 times less interstrand-crosslinking than CDDP on the 1 mM basis. FA cells were specifically defective in the first half-excision of DWA2114R and CDDP-induced Pt(II) interstrand crosslinks, but XPA cells were as proficient as normal cells (t1/2 = 5-7 h). On the contrary, XPA cells were deficient in excision repair of intrastrand crosslinks, but FA cells were normal. In clonogenic survival curves of all types of cells, mean lethal doses (Do) of DWA2114R were an order of magnitude greater than those of CDDP. FA cells were most (3.5 times) sensitive (Do = 25.1 +/- 0.96 microM) and XPA cells were 1.9 times more sensitive (Do = 47.1 +/- 0.17 microM) to DWA2114R than normal cells (Do = 87.6 +/- 5.65 microM). DWA2114R and carboplatin with a cyclobutanedicarboxylato group exhibited almost similar lethal effects on each of normal, FA and XPA strains. FA (Do = 3.44 +/- 0.44 microM) and XPA cells (Do = 3.84 +/- 0.17 microM) were similarly 3-fold more sensitive to CDDP than normal (Do = 9.97 +/- 0.15 microM). On the basis of a single lethal hit (Do), thus DWA2114R and carboplatin effectively killed more FA cells defective in interstrand crosslink repair than XPA cells defective in intrastrand crosslink repair.     

In vitro and in vivo antineoplastic activity of a new platinum antineoplastic agent, (R)-(-)-1,1-cyclobutanedicarboxylate (2-aminomethylpyrrolidine)-platinum (II) (DWA2114R) on freshly separated human tumor cells and human tumor xenografts transplanted in nude mice--a comparison with cis-diammine-dichloroplatinum (CDDP)

The in vitro antimetabolic effect of a newly synthesized platinum antineoplastic agent, DWA2114R, on 72 fresh human tumors was compared with that of cis-platinum (CDDP). DWA2114R is reported to have a lower nephrotoxicity than CDDP, but is as strong an inhibitor of DNA synthesis as CDDP. In vitro IC50 was assessed in 10 tumors; the IC50 of DWA2114R ranged between 9.2 and 107 microM (mean +/- S.D., 45.9 +/- 36.6) and that of CDDP ranged between 0.9 and 40 microM (18.3 +/- 15.1). DWA2114R had an antitumor spectrum similar to that of CDDP. Primary esophageal and pancreatic cancers were sensitive to DWA2114R, and cells separated from malignant effusion or metastatic lymph nodes were more sensitive than those from primary lesions. Nude mice were transplanted with 3 kinds of human tumor xenografts (esophageal, pancreatic and bile duct cancer lines), and were then treated with CDDP or DWA2114R at 4 times the clinical doses. CDDP significantly inhibited the growth of all the 3 lines, and DWA2114R inhibited the growth of 2 of the lines. The effect of DWA2114R on body weight was smaller than that of CDDP. These results suggest that DWA2114R may be less potent than CDDP but may be useful as a new platinum antineoplastic agent with lower grade of side effects than CDDP.     

Antitumor activity of cis-malonato[(4R,5R)-4,5-bis(aminomethy1)-2-isopropyl-1,3-dioxolanelplatinum(II), a new platinum analogue,as an anticancer agent

 The in vitro and in vivo antitumor activity of a new antitumor platinum complex, cis-malonato[(4R, 5R)-4, 5-bis(aminomethyl)-2-isopropyl-1,3-dioxolane]platinum(II) (SKI 2053R, NSC D644591), were evaluated and compared with those of cisplatin (CDDP) and carboplatin (CBDCA) using murine tumors. SKI 2053R was highly active in vitro against both L1210 murine leukemia and its CDDP-resistant subline, L1210/DDP; the relative resistances were 20.0-, 14.5-, and 2.7-fold for CDDP, CBDCA, and SKI 2053R, respectively. SKI 2053R showed activity comparable with or superior to either CDDP or CBDCA in mice implanted with L1210. In mice implanted with L1210/DDP, as compared with CBDCA, SKI 2053R showed high values for the percentage of treated survivors relative to controls and for numbers of cured mice, whereas CDDP had virtually no activity. In mice implanted with P388, all three drugs were highly active, but the intensity of activity was shown to be ranked in the following order: SKI 2053R > CDDP > CBDCA. The antitumor activity of SKI 2053R against Lewis lung carcinoma was comparable with that of both CDDP and CBDCA. The antitumor activity of SKI 2053R was further investigated against two human tumor xenografts, KATO III (stomach adenocarcinoma) and WiDr (colon adenocarcinoma), implanted s.c. in nude mice and was compared with that of CDDP. In SKI 2053R-treated groups, the time required for a mean tumor weight of 1,000 mg was 33.1 days in KATO III xenografts and 35.0 days in WiDr xenografts as compared with 30.2 and 27.2 days in CDDP-treated groups, respectively. SKI 2053R achieved growth-inhibition rates comparable with those of CDDP against KATO III (65% versus 59%) and WiDr xenografts (64% versus 54%) on day 35. These results indicate that SKI 2053R is an attractive candidate for further development as a clinically useful anticancer drug. Received: 7 June 1994 / Accepted: 27 September 1994     

Sequence-dependent termination of mammalian DNA polymerase reaction by a new platinum compound, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato)-2-plati num(II) monohydrate)

We examined the mechanism of the inhibition of DNA synthesis by a new platinum compound, (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato+ ++)-2-platinum(II) monohydrate (DWA-2114R), a derivative of the antitumor drug cis-diamminedichloroplatinum(II) (CDDP), using prokaryotic and eukaryotic DNA polymerases. Preincubating activated DNA with CDDP or DWA-2114R reduced its template activity for prokaryotic and eukaryotic DNA polymerases in a dose-dependent manner. DWA2114R required six times greater drug concentration and two times longer incubation time to show the same decrease of the template activity compared to CDDP. Treatment of primed pUC118 ssDNA templates with the two drugs followed by second-strand synthesis by prokaryotic and eukaryotic DNA polymerases revealed that DWA2114R bound to DNA in a similar manner to CDDP and these adducts blocked DNA elongation by DNA polymerases of eukaryotes as well as of prokaryotes. With these two drugs, the elongations by E. coli DNA polymerase I (Klenow fragment), T7 DNA polymerase and calf thymus DNA polymerase alpha were strongly arrested at guanine-guanine sequences (GG). Stop bands were also observed at adenine-guanine sequences (AG) guanine-adenine-guanine sequences (GAG) and mono-guanine sequence (G). Calf testis DNA polymerase beta was also arrested efficiently at AG, GAG and G, but much more weakly at GG. This pattern was common to DWA2114R and CDDP.     

Antitumor activity and toxicity of KB-5424 R, a newly developed antitumor platinum compound

KB-5424 (ab-(3-aminopyrrolidine)-cd-[glycolato (2-)-0, 0'] platinum (II) is a newly developed antitumor platinum compound which was synthesized at Kanebo Institute for Cancer Research. When the antitumor activity of KB-5424 was evaluated using several rodent tumors, no significant differences were observed between the antitumor activities of KB-5424, cisplatin (CDDP) and DWA-2114 R (DWA). KB-5424 was divided into two kinds of optical isomers, KB-5424 R and KB-5424 S, of which antitumor activity was compared each other. The maximum increased life span (ILSmax) on L 1210 of KB-5424 R was almost equal to that of CDDP and better than those of KB-5424 S and carboplatin (CBDCA). The antitumor activity of KB-5424 R on a human tumor xenograft MX-1 was almost identical to those of CDDP and CBDCA and better than that of DWA. Since the nephrotoxicity of KB-5424 R was significantly reduced comparing with CDDP, this newly developed antitumor platinum compound was thought to be a promising agent for the clinical application.     

Synergistic Enhancement of Cisplatin Cytotoxicity by SN-38, an Active Metabolite of CPT-11, for Cisplatin-resistant HeLa Cells

A cisplatin ( cis -diamininedichloroplatinuin(II); CDDP)-resistant HeLa cell line (HeLa/CDDP cells), which showed more than 8-fold resistance to CDDF compared to the parent cells, was newly established for this study. HeLa/CDDP cells accumulated 50% less platinum than the parent cells. There was no difference in intracellular glutathione (GSH) content between the parent and HeLa/ CDDP cells. The dose modification factor by DL-buthionine-S, R-sulfoximine (BSO) pretreatment was similar in both cell lines. HeLa/CDDP cells had cross-resistance to diammine (l, l-cyclobutanedicarboxylato)platinum(II) (CBDCA), ( cis -diammine (glycolato)platinum (254-S), but not to (-)-(R)-2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platinum(II) (DWA2114R), adriamycin, or VP-16. HeLa/CDDP cells showed a collateral sensitivity to 7-ethyl-10-hydroxycampto-thecin (SN-38), an active metabolite of 7-ethyl-10-[4-(l-piperidino)-l-piperidino]carbonyloxycamptothecin (CPT-11). Furthermore, isobologram analysis indicated synergistic interaction of CDDP and SN-38 only for HeLa/CDDP cells. The present study suggests that combination therapy with CDDP and CPT-11 may he potentially useful in the treatment of some patients with CDDP-resistant cancer.     

Sequence-dependent Termination of Mammalian DNA Polymerase Reaction by a New Platinum Compound, (–)-(R)-2-Aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato)-2-platinum(II) Monohydrate

We examined the mechanisms of the inhibition of DNA synthesis by a new platinum compound, (-)-( R )-2-aminomethylpyrrolidine(1,1-cyclobutane-dicarboxylato)-2-platinum(II) monohydrate (DWA-2114R), a derivative of the antitumor drug cis- diamminedichloroplatinum(II) (CDDP), using prokaryotic and eukaryotic DNA polymerases. Preincubating activated DNA with CDDP or DWA-2114R reduced its template activity for prokaryotic and eukaryotic DNA polymerases in a dose-dependent manner. DWA2114R required six times greater drug concentration and two times longer incubation time to show the same decrease of the template activity compared to CDDP. Treatment of primed pUC118 ssDNA templates with the two drugs followed by second-strand synthesis by prokaryotic and eukaryotic DNA polymerases revealed that DWA2114R bound to DNA in a similar manner to CDDP and these adducts blocked DNA elongation by DNA polymerases of eukaryotes as well as of prokaryotes. With these two drugs, the elongations by E. coli DNA polymerase I (Klenow fragment), T7 DNA polymerase and calf thymus DNA polymerase α were strongly arrested at guanine-guanine sequences (GG). Stop bands were also observed at adenine-guanine sequences (AG) guanine-adenine-guanine sequences (GAG) and mono-guanine sequence (G). Calf testis DNA polymerase β was also arrested efficiently at AG, GAG and G, but much more weakly at GG. This pattern was common to DWA2114R and CDDP.