rhizoxin and Melanoma

Rhizoxin is a new anti-tumour agent isolated from the pathogenic fungus Rhizopus chinensis. It has shown broad activity against murine tumour models and is also active against vinca alkaloid-resistant cells. The purpose of our studies was to determine the clinical activity of this compound in patients with advanced breast cancer and melanoma. Based on the results of a phase I study, 2.0 mg m-2 was administered as intravenous infusion over 5 min every 21 days. Nineteen patients were entered into the breast cancer phase II trial and received a total of 50 courses (median 2, range 1-6). Of these, dose reductions were performed in three courses because of leucopenia or stomatitis (1.5 mg m-2, one course; 1.45 mg m-2, two courses). Twenty-six patients were entered into the melanoma trial and received a total of 70 courses (median 2, range 1-12). No dose reductions were required. All patients were eligible for toxicity. Haematological toxicity included neutropenia CTC grade 3 (29/120 courses, 24.2%) and grade 4 (11/20 courses, 9.2%). Only drug-related CTC grade 1 thrombocytopenia was observed. Non-haematological toxicity included alopecia in all patients after two courses of treatment as well as CTC grade 3/4 stomatitis and asthenia. In the breast cancer study, one patient achieved a more than 50% tumour reduction after six cycles but was progressing after 6 weeks. Another patient showed a partial remission after the first course but was taken off the study because of CTC grade 3 skin toxicity. One patient was not evaluable for response (early death). No objective remissions were observed in 15 evaluable patients. In melanoma, no objective remissions were observed. We conclude that rhizoxin can be safely administered at 2.0 mg m-2 every 3 weeks. However, it has little activity in patients with advanced breast cancer and melanoma.

Topics: Adult; Aged; Antibiotics, Antineoplastic; Breast Neoplasms; Female; Hematopoiesis; Humans; Lactones; Macrolides; Male; Melanoma; Middle Aged

Rhizoxin is a macrocyclic lactone compound that binds to tubulin and inhibits microtubule assembly. Rhizoxin demonstrated preclinical anti-tumour activity against a variety of human tumour cell lines and xenograft models. Phase I evaluation found a maximum tolerated rhizoxin dose of 2.6 mg m-2, with reversible, but dose-limiting, mucositis, leucopenia and diarrhoea. Clinical trials were then initiated by the EORTC ECSG in melanoma, breast, head and neck, and non-small-cell lung cancers with the recommended phase II rhizoxin dose of 2 mg m-2. Pharmacological studies were instituted with the phase II trials to complement the limited pharmacokinetic data available from the phase I trial. Blood samples were obtained from 69 of 103 eligible patients enrolled in phase II rhizoxin studies, and these were evaluable for pharmacokinetic analysis in 36 patients. Plasma rhizoxin concentrations were determined by high-performance liquid chromatography (HPLC), and post-distribution pharmacokinetic parameters were estimated by a one-compartment model. Rhizoxin was rapidly eliminated from plasma, with a median systemic clearance of 8.41 min-1 m-2 and an elimination half-life of 10.4 min. Rhizoxin area under the concentration-time curve (AUC) was higher in patients obtaining a partial response or stable disease than in those with progressive disease (median 314 vs 222 ng ml-1 min; P = 0.03). As predicted from previous studies, haematological and gastrointestinal toxicity was observed, but could not be shown to be related to rhizoxin AUC. This study demonstrated the rapid and variable elimination of rhizoxin from the systemic circulation. The presence of pharmacodynamic relationships and the low level of systemic toxicity suggest that future trials of rhizoxin with alternative dosage or treatment schedules are warranted.

Topics: Antibiotics, Antineoplastic; Area Under Curve; Breast Neoplasms; Carcinoma, Non-Small-Cell Lung; Female; Head and Neck Neoplasms; Humans; Injections, Intravenous; Lactones; Lung Neoplasms; Macrolides; Male; Melanoma; Treatment Outcome

Rhizoxin, isolated from a plant pathogenic fungus which causes rice seedling blight, inhibits the mitosis of the tumor cells in a manner similar to that of Vinca alkaloids as revealed by morphological study and flow cytometry analysis. This new 16-membered macrocyclic lactone showed similar chemotherapeutic effects to those of vincristine against L1210 and P388 leukemia-bearing mice. The drug is also effective against B16 melanoma inoculated i.p. or s.c. Rhizoxin, in contrast to the ansamacrolide, maytansine, was effective against human and murine tumor cells resistant to vincristine and Adriamycin in vitro and in vivo. A maximum 60% increase in life span was obtained in mice inoculated with P388 leukemia resistant to vincristine. Rhizoxin showed greater cytotoxicity in cultured tumor cells than did vincristine. Rhizoxin seems to bear consideration for further development as a new chemotherapeutic agent.

Topics: Animals; Antibiotics, Antineoplastic; Cell Cycle; Cells, Cultured; Drug Resistance; Female; Lactones; Leukemia L1210; Leukemia P388; Leukemia, Experimental; Macrolides; Maytansine; Melanoma; Mice; Microscopy, Electron, Scanning