Akiko Tohgo

DJ-927, a novel oral taxane, overcomes P-glycoprotein-mediated multidrug resistance in vitro and in vivo.

DJ‐927 is a novel taxane, which was selected for high solubility, non‐neurotoxicity, oral bioavailability, and potent antitumor activity. In this study, we compared the in vitro and in vivo efficacy of DJ‐927 with those of paclitaxel and docetaxel. DJ‐927 exhibited stronger cytotoxicity than paclitaxel and docetaxel in various tumor cell lines, especially against P‐glycoprotein (P‐gp)‐expressing cells. The cytotoxicity of DJ‐927, unlike those of other taxanes, was not affected by the P‐gp expression level in tumor cells, or by the co‐presence of a P‐gp modulator. When intracellular accumulation of the three compounds was compared, intracellular amounts of DJ‐927 were much higher than those of paclitaxel or docetaxel, particularly in P‐gp‐positive cells. In vivo, DJ‐927 showed potent antitumor effects against two human solid tumors in male BALB/c‐nu/nu mice, and yielded significant life‐prolongation in a murine liver metastasis model with male C57BL/6 mice, in which neither paclitaxel nor docetaxel was effective. The results demonstrate the superior efficacy of orally administered DJ‐927 over intravenously administered paclitaxel or docetaxel against P‐gp‐expressing tumors, probably due to higher intracellular accumulation. A phase I clinical trials of DJ‐927 is currently ongoing in the US. (Cancer Sci 2003; 94: 459–466)

Potent and broad antitumor effects of DX-8951f, a water-soluble camptothecin derivative, against various human tumors xenografted in nude mice

Purpose: We have previously reported that DX-8951f, a water-soluble and nonprodrug camptothecin (CPT) derivative, exhibits both high in vitro potency against a series of 32 malignant cell lines and significant topoisomerase I inhibition. The purpose of this study was to evaluate the therapeutic efficacy of DX-8951f against human tumor xenografts in nude mice and to compare its activity with those of CPT-11 and other current CPT derivatives. Methods: The antitumor activity of DX-8951f against xenografts of several different types of human tumors was determined in nude mice using a schedule in which DX-8951f was administered intravenously every 4th day for a total of four injections. Results: Against both gastric adenocarcinoma SC-6 and its CPT-11-resistant variant, SC-6/CPT-11, DX-8951f demonstrated superior antitumor activity and antitumor activity over a broader range of doses than did CPT-11, SK&F104864 (hycamtin, topotecan) and GG-211 (GI147211). DX-8951f at 75 mg/kg was effective (growth inhibition rate IR≧58%) against 15 of 16 lines of human cancers examined (6 colon cancers, 5 lung cancers, 2 breast cancers, 1 renal cancer and the above 2 gastric cancers), and exhibited excellent antitumor activity (IR≧80%) against 14 of these lines. CPT-11 exhibited antitumor activity with IR values of 58% and higher against 11 lines and IR values of 80% and higher against only eight of the same 16 human tumors. DX-8951f was effective in inhibiting the growth of an SN-38-resistant tumor and some P-glycoprotein-expressing tumors, but CPT-11 was not. Conclusions: DX-8951f exhibited potent antitumor activity against various types of human tumor xenografts. Its in vivo antitumor effects were superior to those of current camptothecin analogs against certain tumors.

DX-8951f, a water-soluble camptothecin analog, exhibits potent antitumor activity against a human lung cancer cell line and its SN-38-resistant variant.

We previously reported that DX‐8951f, a novel water‐soluble camptothecin analog, significantly inhibits the growth of various human and murine tumors in vitro and in vivo. The antitumor effects and topoisomerase I inhibitory activity of DX‐8951f are stronger than those of other current camptothecin analogs. In this study, we established an SN‐38‐resistant cell line, PC‐6/SN2‐5, from the human oat cell carcinoma PC‐6 cell line by a stepwise selection system, investigated the mechanism of resistance of this cell line and then compared the antitumor activity of camptothecin analogs against the cell line. PC‐6/SN2‐5 cells were resistant to SN‐38 (32‐fold) and SK&F104864 (topotecan; 14‐fold), but barely resistant to CPT‐11 (3‐fold) and DX‐8951f (2‐fold). Topoisomerase I protein levels and topoisomerase I activities of parental cells were similar to those of resistant cells. Determination of the cellular drug concentration by either flow cytometric analysis or the high‐performance liquid chromatography method confirmed that the cellular accumulation of SN‐38 and topotecan was significantly reduced in PC‐6/SN2‐5 cells, whereas that of DX‐8951f was only slightly reduced. Furthermore, DX‐895lf stabilized the cleavable complex formations in intact PC‐6/SN2‐5 cells as well as in parental cells, but SN‐38 and topotecan did not in the resistant cells. Our data suggest that PC‐6/SN2‐5 cells may have acquired resistance to camptothecin analogs by a decrease in intracellular drug accumulation and that DX‐8951f may have the potency to overcome such a type of resistance mechanism induced by camptothecin compounds. Int. J. Cancer 72:680–686, 1997.

Growth inhibitory effect of a new camptothecin analog, DX-8951f, on various drug-resistant sublines including BCRP-mediated camptothecin derivative-resistant variants derived from the human lung cancer cell line PC-6

DX-8951f, a new water-soluble camptothecin (CPT) derivative, has been reported to show potent antitumor effects against various tumors in vitro and in vivo. We further evaluated the cytotoxic effect of DX-8951f against eight drug-resistant sublines derived by stepwise exposure of human oat cell carcinoma PC-6 to various drugs. In paclitaxel-, adriamycin-, vincristine- and etoposide-resistant cells, overexpression of P-glycoprotein (P-gp) and a correlative reduction in drug accumulation and typical drug-sensitivity pattern were confirmed. The etoposide-resistant line with the highest P-gp level was cross-resistant also to SN-38, CPT-11 and topotecan (TPT), but not to 9-aminocamptothecin (9-AC), CPT and DX-8951f. SN-38- and CPT-11-resistant cells, of which topoisomerase I activities and levels were similar to those of the parent cells, showed cross-resistance clearly to TPT, 9-AC and mitoxantrone, but hardly to DX-8951f. In these two resistant sublines, the intracellular topotecan level was significantly lower than that in parental PC-6 and the reduced accumulation was found to be mediated by breast cancer resistant protein (BCRP). The cisplatin-resistant variant, which had a 2-fold increase in glutathione content, showed no cross-resistance and the 5-fluorouracil-resistant variant, which had a 50% decrease in glutathione content, exhibited collateral sensitivity to most of the other anticancer agents including DX-8951f. We concluded that DX-8951f showed a potent cytotoxic effect on various types of drug-resistant cells.

Antitumor Effect of DX‐8951, a Novel Camptothecin Analog, on Human Pancreatic Tumor Cells and Their CPT‐11‐resistant Variants Cultured in vitro and Xenografted into Nude Mice

DX‐8951 is a novel water‐soluble derivative of camptothecin. We evaluated the effects of DX‐8951 on the growth of several pancreatic tumor cell lines in vitro and in vivo. In vitro cytotoxic activity of DX‐8951 against SUIT‐2 and KP‐1N cells, as indicated by IC50 value, was several times more potent than that of SN‐38, an active metabolite of CPT‐11, and dozens of times more potent than that of SK&F104864 (topotecan). DX‐8951 also showed the greatest cytotoxicity against CPT‐11‐resis‐tant variants, SUIT‐2/CPT‐11 and KP‐1N/CPT‐11 cells, and the cross‐resistance of these cells to DX‐8951 was lower than that to SN‐38 and SK&F104864. Topoisomerase 1 inhibitory activity of DX‐8951 was about three‐fold stronger than that of SN‐38, as measured in crude nuclear extract obtained from SUIT‐2 cells. DX‐8951 induced DNA fragmentation, a specific feature of apoptosis, in SUIT‐2 cells more effectively than SN‐38. DX‐8951 exhibited potent antitumor effects against SUIT‐2 in a solid tumor model and in a liver metastasis model, in which tumor cells were xenografted sub‐cutaneously and intrasplenically, respectively, into nude mice. The in vivo effects were closely similar to or somewhat superior to those of CPT‐11, DX‐8951 also showed significant antitumor effects against SUIT‐2/CPT‐11 solid tumors, against which CPT‐11 had no effect. These results suggest that, on the basis of its strong antitumor activity and effectiveness against CPT‐11‐resistant tumors, DX‐8951 may be a useful therapeutic agent in the treatment of human cancer. The potent cytotoxicity of DX‐8951 may result from strong inhibition of topoisomerase I, which may then trigger apoptotic cell death.

Antitumour activity of DX-8951f: a new camptothecin derivative.

DX-8951f is a water-soluble camptothecin analogue with a unique hexacyclic structure. Compared to other current camptothecin derivatives, DX-8951f is the most effective topoisomerase I (topo I) inhibitor and has the most potent cytotoxic activity against various tumour cell lines in vitro. Of particular interest is DX-8951fs significant effect on certain tumour cell lines resistant to other camptothecin derivatives, as well as on multi-drug resistant variants that overexpress P-glycoprotein. In addition, in in vivo xenograft systems using nude mice, DX-8951f strongly inhibits the growth of human solid tumours, including resistant tumours. Its antitumour effects and resulting life prolongation in tumour-bearing mice have also been confirmed in several metastasis models. DX-8951f provides greater therapeutic efficacy and broader effective dose ranges using multiple injections than with a bolus injection and simple intermittent applications. The in vivo effects of the compound are superior to those of CPT-11 and SK&F104864, suggesting that DX-8951f is a promising therapeutic agent for the treatment of cancer patients. Phase I clinical trials are ongoing in Europe, the USA and Japan.

Excretion Into Gastrointestinal Tract of Irinotecan Lactone and Carboxylate Forms and Their Pharmacodynamics in Rodents

AbstractPurpose. To investigate the excretion of irinotecan hydrochloride (CPT-11) and its active metabolite, SN-38, into the gastrointestinal lumen via the biliary and/or intestinal membrane route after dosing with lactone and carboxylate forms of CPT-11, and to evaluate the toxic and antitumor effects of the two forms. Methods. The excretions of CPT-11 and SN-38 were investigated by the in situ perfusion technique using rats. The incidence of delayed diarrhea was evaluated after i.v. dosing (60 mg/kg) with CPT-11 lactone and carboxylate forms for 4 days. Antitumor activity and changes in body weight were investigated in mice with Meth A tumors. Results. The excretion of CPT-11 into bile was greater in dosing with CPT-11 carboxylate than that with its lactone form, whereas the exsorption across intestinal membrane was greater in dosing with CPT-11 lactone than that with its carboxylate form. Dosing with CPT-11 lactone dose-dependently inhibited the increase in tumor weights in Meth A tumor mice, whereas the dosing with its carboxylate form reduced the antitumor effect. Conclusions. The decreased antitumor effect caused by dosing with the CPT-11 carboxylate form could be due to less accumulation in the tissue including tumor cells resulting from the rapid elimination of the form in the body.

Significant antitumor effect of a synthetic lipid A analogue, DT-5461, on murine syngeneic tumor models

SummaryThe antitumor effect of a synthetic lipid A analogue, DT-5461, was investigated using syngeneic tumor models in mice. Intravenous injection of DT-5461 into mice transplanted with solid tumors of MethA fibrosarcoma, MH134 hepatoma, MM46 mammary carcinoma, Lewis lung carcinoma (3LL), and colon adenocarcinomas 26 and 38 resulted in significant reductions in the weight of all tumors except Colon 26, with marked hemorrhagic necrosis of tumor tissues. Efficacy was almost equal to that of anEscherichia coli-type synthetic lipid A (compound 506), and also to those of some chemotherapeutics including Adriamycin, mitomycin C, fluorouracil and cisplatin. Furthermore, DT-5461 was more effective than other immunotherapeutics, including picibanil (OK-432) and lentinan. However, its antitumor effects were inferior to those of Adriamycin or OK-432 against the malignant ascites caused by intraperitoneal inoculation with MethA or with MH134 cells; life span was not prolonged by either intraperitoneal or intravenous administration. In addition, although DT-5461 showed direct inhibitory effects on the in vitro growth of MethA or MH134, these were much weaker than those of Adriamycin. These findings clearly indicated that DT-5461 with systemic administration is a highly effective antitumor agent on solid tumors, and suggest that the antitumor effect of DT-5461 with potent necrotizing activity might derive from indirect mechanisms related to the activation of host immune systems and not to the weak direct cytotoxicity.

Antitumor effect of DT-5461a, a synthetic low-toxicity lipid a analog, involves endogenous tumor necrosis factor induction subsequent to macrophage activation

We previously showed that the synthetic lipid A derivative DT-5461a exhibited significant antitumor effects against various murine solid tumors, probably via activation of host immune systems. To clarify the participation of the macrophage-stimulating effect of DT-5461a in the antitumor mechanisms, we studied the ability of this compound to induce cytostatic macrophages and TNF production in murine systems. Cytostatic macrophages were induced by treatment with DT-5461a either in vitro or in vivo. DT-5461a also induced TNF production by resident peritoneal macrophages or spleen cells obtained from untreated mice. When spleen cells prepared from DT-5461a-treated mice were re-stimulated in vitro with DT-5461a, no TNF was produced by cells obtained at 1 day after the treatment. This may be due to transient refractoriness of macrophages to the compound, since the response to re-stimulation with DT-5461a recovered in cells obtained at 3 or 5 days after treatment. Moreover, while the serum TNF production and antitumor effects by DT-5461a decreased on daily administration, they were elicited by intermittent administration at intervals of 3 days or more. This suggests that the antitumor effects of DT-5461a depend on the TNF-producing activity of macrophages. These results indicate that DT-5461a possesses significant macrophage-stimulating activity, and that macrophages so activated mediate the DT-5461a-induced augmentation of host response against solid tumors.

Anticancer drugs that induce cancer-associated cachectic syndromes.

Cachexia – a wasting condition – seriously impairs the quality of life of patients with advanced cancer. Previous studies have shown that several inflammatory cytokines mediate the development of cancer-associated cachexia. Experimentally, cachexia-like symptoms can be induced in tumor-bearing mice and treatment of such mice with chemotherapeutic agents reverses cachexia as a result of its therapeutic action. Nonetheless, cancer chemotherapy occasionally induces anorexia as an adverse reaction. For example, treatment with antitubulin taxanes reduces body weight in tumor-bearing mice more than healthy mice, even when the agents significantly reduce tumor growth. However, the complex relationship between cancer cachexia and the effects of anticancer drugs remains to be elucidated. This review outlines what is known about the development of cachectic reactions, especially in tumor-bearing mice, that occur during treatment with anticancer agents and highlights the clinical relevance of the information.