Tazuko Tashiro

Antitumor activity of a new platinum complex, oxalato (trans-l-1,2-diaminocyclohexane)platinum (II): new experimental data

Antitumor activity of a new platinum complex, oxalato (trans-l-1,2-diaminocyclohexane) platinum (II) (l-OHP), was studied. This water-soluble platinum complex showed a more prominent life-prolonging effect on a mouse leukemia L1210 than cisplatin (DDP). By an intermittent treatment schedule cured mice were observed at the optimal dose. In addition, a subline of L1210 having a 40-fold resistance to DDP (L1210/DDP) showed lack of cross-resistance to l-OHP both in vivo and in vitro. Especially in vivo l-OHP was more active against L1210/DDP than against the original L1210, and all mice were cured at doses of 6.25 and 3.12 mg/kg. l-OHP was also effective against several mouse tumors such as P388 leukemia, B16 melanoma, Lewis lung carcinoma, colon 26 and colon 38 adenocarcinomas, and M5076 fibrosarcoma, though its antitumor spectrum was somewhat different from that of DDP. The synthesis of both DNA and RNA in L1210 cells was inhibited by about 50% with exposure to 10 microM of l-OHP for 1 h, followed by postincubation in drug-free medium for 6-24 h, while only the inhibition of DNA synthesis was observed by DDP in the same experiment. If severe toxicity is not observed in preclinical study, l-OHP expected to be a new clinically active Pt complex.

Evaluation of antitumor activity in a human breast tumor/nude mouse model with a special emphasis on treatment dose.

Eight lines of human breast tumors implanted in nude mice were treated with various antitumor agents at two different doses, maximum tolerated doses (MTD) and rational doses (RD) that were pharmacokinetically equivalent to the clinical doses; the response rates to both doses were compared. With MTD, the response rates to mitomycin C and vinblastine were 100%, and those to other agents including cyclophosphamide, nimustine (a water‐soluble nitrosourea), vincrisitine, Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH), 5‐fluorouracil (5‐FU), and methotrexate were 30%–50%, indicating high responsiveness to the former two agents. In contrast, when the RD were used, the response rates to the majority of these agents were 25%–40%, and those to vincristine and nimustine were 13% and 0%, respectively. These results agree with the reported clinical results compared with those with MTD, suggesting the importance of the use of clinically equivalent doses in the evaluation of antitumor efficacy in a human tumor/nude mouse system.

Responsiveness of human lung cancer/nude mouse to antitumor agents in a model using clinically equivalent doses

SummaryThe responses of 14 lines of human lung cancer xenografts in BALB/c-nu/nu mice to eight known antitumor agents were investigated. These xenografts consisted of four small-cell carcinomas (SCLC) and ten non-small-cell carcinomas (four large cell, three squamous cell, and three adenocarcinomas; NSCLC). The doses used in the experiments were the maximum tolerated dose (MTD) in nude mice and the “rational dose” (RD), the latter considered to be pharmacokinetically equivalent to the clinical dose. When given at MTDs, all drugs except 5-fluorouracil (5-FU) and methotrexate (MTX) were extremely effective against NSCLC as well as SCLC. The response rates of drug-sensitive SCLC to mitomycin C (MMC), ACNU, and vinblastine (VLB) were 100%, and those to Adriamycin (ADR) and vincristine (VCR) were 75%. In addition, the response rates of even drug-resistant NSCLC to MMC and VLB were 70% and 90%, respectively. In contrast, the response rates of NSCLC to RDs of the drugs were reduced to <40% and corresponded well to the respective clinical rates. In SCLC, a good correlation of experimental and clinical response rates was observed with four drugs [cyclophosphamide (CPM), ACNU, VLB, and 5-FU]. As a result, we emphasize that a more reasonable prediction of the clinical effectiveness of antitumor agents can be made by a protocol using clinically equivalent doses.

Pharmacokinetic approach to rational therapeutic doses for human tumor-bearing nude mice.

To improve clinical predictability from therapeutic results of various antitnmor agents in human tumor/nude mouse models it seems to be important to use a dose pharmacokinetically equivalent to the clinical dose. Thus, we attempted to find the dose of a given drug that can reproduce in the nude mouse a plasma level similar to that seen in human patients treated with an effective dose of the drug based on comparative pharmacokinetic studies between man and nude mouse. As a result, those of 3 alkylating agents, mitomycin C, 3‐[(4‐amino‐2‐methyl‐5‐pyrimidinyl)methyl]‐l‐(2‐chloroethyl)‐l‐nitrosourea (ACNU) and cyclophosphamide, and those of 2 antimitotic agents, vincristine and vinblastine, were estimated to be one‐fourth or one‐fifth of their maximum tolerated doses (MTDs). On the other hand, in the case of adriamycin, its MTD was approxmately equivalent to its clinical dose pharmacokinetically. In contrast, clinically equivalent doses of 2 antimetabolites tested, 5‐fluorouracil and methotrexate, were significantly greater than their MTDs; i.e., their plasma levels did not reach the effective clinical ones even when their MTDs were administered to the nude mice. These results suggest that the antitumor effects of mostv antitumor agents are over‐ or underestimated in this model when MTDs are used as a therapeutic dose, and indicate that the use of clinically equivalent doses determined pharmacokinetically isdesirable.

Responsiveness of Human Gastric Tumors Implanted in Nude Mice to Clinically Equivalent Doses of Various Antitumor Agents

To reproduce clinical effects of various antitumor agents in the human tumor/nude mouse model, we investigated the responsiveness of 11 lines of human gastric tumor xenografts to doses of the agents pharmacokinetically equivalent to the respective clinical doses, which we designated the “rational dose” (RD). We found that the response rates to mitomycin C, 3‐[(4‐amino‐2‐methyl‐5‐pyrimidinyl]methyl‐1‐[2‐chloroethyl]‐1‐nitrosourea (ACNU), adriamycin, 5‐fluorouracil were 18%, and that to vinblastine was 30%; on the other hand, those to vincristine, methotrexate, and cyclophosphamide were poor. In contrast, in our previous study using the maximum tolerated doses, response rates to mitomycin C, ACNU, and vinblastine were as high as 64–82%, and those to adriamycin and 5‐fluorouracil were 18%. When these results were compared with the clinical response rates of gastric tumors, as a whole, the results with RDs exhibited much better coincidence with the clinical data in terms of relative therapeutic potency, indicating the validity of the use of clinically equivalent doses instead of maximum tolerated doses in the human tumor model.

In vitro-in vivo correlation in anticancer drug sensitivity test using AUC-based concentrations and collagen gel droplet-embedded culture.

To improve the ability of an in vitro drug sensitivity test to predict in vivo effects, we applied a drug concentration that was pharmacokinetically equivalent to plasma levels and collagen gel droplet-embedded culture with a high cloning efficiency. We reported that the cell-killing effect of cell cycle phase-nonspecific drugs such as mitomycin C, cisplatin and Adriamycin depends on the area under the drug concentration-time curve (AUC). The plasma AUC values of these drugs were estimated after an injection into nude mice at the maximal tolerated doses (MTD). Tumor cells isolated from human tumor xenografts implanted into nude mice and cultured in collagen gel droplets were exposed to drugs under conditions that can reproduce the plasma AUC in vitro. The in vitro sensitivity to a drug was compared with the in vivo response of the same tumor treated with the MTD of the drug. When the criterion of sensitivity was taken as 50% or less of the growth inhibition (growth rate of treated group/that of control group, T/C), the correlation between the in vitro and in vivo growth inhibition of all 3 drugs tested was relatively high (86% of the true-positive rate, 82% of the true-negative rate and 83% of the correlation rate).

A new orally active antitumor 1R,2R-cyclohexanediamine-platinum(IV) complex: trans-(n-valerato)chloro(1R,2R-cyclohexanediamine) (oxalato)platinum(IV)

Purpose: The authors have previously reported that trans-bis(n-valerato)(1R,2R-cyclohexanediamine) (oxalato)platinum(IV) (C5-OHP), an oxaliplatin derivative, is an orally active antitumor agent in an intraperitoneal (i.p.) L1210 murine leukemia model. In this study, several oxaliplatin derivatives of the general formula trans-(carboxylato)chloro(1R,2R-cyclohexanediamine)(oxalato)platinum(IV) were synthesized in order to find new derivatives with greater oral activity than C5-OHP in a clinically predictive tumor model. In the formula, the carboxylate and chloride ligands are situated in axial positions. Methods: Four complexes with the axial carboxylate ligands n-butyrate, n-valerate, n-caproate or n-heptanoate were synthesized and designated C4-OHP-Cl, C5-OHP-Cl, C6-OHP-Cl and C7- OHP-Cl, respectively. The oral antitumor activity of the complexes was evaluated against the murine reticulosarcoma M5076 implanted subcutaneoulsy (s.c.) in to male BDF1 mice. The complexes were administered orally daily for 5 days in two cycles initiated on days 5 and 12 postimplantation. The physicochemical properties were examined by measuring the concentrations of the complexes in test solutions at intervals by HPLC. The pharmacokinetic behaviors of C5-OHP-Cl, C6-OHP-Cl and C5-OHP following a single oral administration were studied in non-tumor-bearing male BDF1 mice. Results: Of the complexes synthesized in this study, C5-OHP-Cl, which exhibited high activity in the i.p. L1210 model, was found to be orally active in the s.c. M5076 model while C5-OHP was not. The in vitro reduction of the complexes by ascorbate was much more rapid than that of C5-OHP, while the complexes were more stable than C5-OHP in HCl-acidic and alkaline solutions. Pharmacokinetic study showed that Cmax and AUC0–24h values of plasma total and filterable platinum of C5-OHP-Cl were four to six times greater than those of C5-OHP, indicating that C5-OHP-Cl was absorbed more than C5-OHP. Conclusion: C5-OHP-Cl was found to be a superior l-OHP derivative C5-OHP, exhibiting significant oral antitumor activity in the s.c. M5076 model. The enhanced activity of C5-OHP-Cl was considered to be due in part to increased susceptibility to reduction and increased gastrointestinal absorption. C5-OHP-Cl is a suitable candidate for further study as an oral cancer chemotherapy agent.

Synthesis and anti-tumor activity of vinyl polymers containing 5-fluorouracils attached via carbamoyl bonds to organosilicon groups

Abstract A homopolymer and several copolymers containing 5-fluorouracils (5FU)s attached via carbamoyl bonds to organosilicon groups were synthesized by means of homopolymerization and copolymerization of the corresponding vinyl monomers. For the purpose of evaluating the release behavior of 5FU in vivo, the hydrolysis of carbamoyl bonds in these polymers was investigated in vitro at 37°C in aqueous solutions with varying compositions. The release rate of 5FU from polymers showed a typical pH-dependent sigmoid. The low molecular weight homopolymer of 5-fluoro-3,4-dihydro-2,4-dioxo-N-(4,4-dimethyl-4-silahex-5-enyl)-1-(2H)-pyrimidinecarboxamide (KY-20), Poly(KY-20), and the copolymer of KY-20 with 2-hydroxyethyl methacrylate exhibited remarkably high anti-tumor activities against P-388 lymphocytic leukemia in mice in vivo (i.p./i.p.).

Evaluation of antitumor activity of navelbine (vinorelbine ditartrate) against human breast carcinoma xenografts based on its pharmacokinetics in nude mice

The In vitro antitumor activity of navelbine (NVB, KW- 2307), a newly synthesized vlnca alkaloid, was compared with that of adrlamycln (ADM) against human breast carcinomas Inoculated into nude mice at the maximum tolerated dose (MTO) and clinically equivalent dose (CED). The plasma levels of NVB after Intravenous Injection Into nude mice at doses of 1.2 and 4.8 mg/kg diminished rapidly during the early phase (0-1 h), followed by a very long shallow one. NVB was still detected 96 h after administration at a dose of 4.8 mg/kg. The pharmacokinetlc parameters of NVB In plasma Indicated that NVB extensively distributes to tissues. The CED of NVB was provisionally decided to be 4.8 mg/kg based on the comparison of AUC values at 24-oo h between human patients and nude mice. When compared by a single Injection of MTD (NVB, 16 mg/kg; ADM 12 mg/kg), NVB was effective against all four tumor lines, MC-2, MC-8, MMKY and H-31, while ADM was effective only against H- 31. On the other hand, the body weight loss by NVB was mild as compared with that by ADM, Indicating that the antitumor activity of NVB is superior to that of ADM at their MTDs. A single Injection of NVB at its CED (4.8 mg/ kg) produced a poor antitumor effect and no or little toxlclty In terms of body weight loss, as compared with those at MTD. However, when NVB was administered Intermittently at CED, It exhibited significant antitumor activity against three tumor lines. The body weight loss was still mild even on this Intermittent schedule. These results Indicate that NVB can offer antitumor activity against human breast carcinoma xenografts at its CED.

Antitumor effects of IST-622, a novel synthetic derivative of chartreusin, against murine and human tumor lines following oral administration.

The antitumor effects of 6-O-(3-ethoxypropionyl)-3′,4′-O-exo-benzylidenechartreusin (IST-622), a new synthetic derivative of chartreusin (CT), were investigated. Following oral administration, IST-622 showed marked antitumor effects against various mouse tumors such as P388 and L 1210 leukemias, B 16 melanoma, Lewis lung carcinoma, Colon 26 and Colon 38 adenocarcinomas, and M5076 reticulum-cell sarcoma. The best antitumor effects were obtained by five intermittent treatments given every 4 days. In addition, IST-622 showed a significant growth-inhibitory effect against two human tumor xenografts, a large-cell lung cancer (Lu-116) and a gastric adenocarcinoma (St-4), among the seven lines tested. IST-622, which was rapidly metabolized into 3′,4′-O-exo-benzylidenechartreusin (A-132) and not into CT in vivo or in culture medium, exhibited remarkable growth-inhibitory activity against P388 leukemia in vitro, its 50% growth-inhibitory concentration (IC50) being over 20-fold lower than that of CT. IST-622 showed an in vivo antitumor effect superior to that of authentic A-132, possibly resulting from a higher absorption ratio of IST-622 through the gastrointestinal tract. IST-622 is now under clinical phase I study in Japan.