Carboxyimamidate, a low-molecular-weight polyelectrolyte with antitumor properties and low toxicity

Synthesis of poly(maleimide-co-2-ethylacrylic acid) and its properties of suppressing metastasis and growth of carcinoma

A series of copolymers is prepared using maleimide and 2-ethylacrylic acid as comonomer. This kind of copolymer shows low toxicity (LD50: 601-798 mg/kg) and significant curative effect on Lewis lung carcinoma and S180.

Application of chemical immunomodulators to the treatment of cancer and AIDS

A number of potential advantages, development of promising new agents, and the discovery of synergy with cytokines or cell products continue to spur research into the application of chemical immunomodulators for the treatment of cancer and AIDS. In preclinical in vitro and in vivo systems, chemical immunomodulators definitely modulate the immune system and have therapeutic efficacy. Although clinical trials have shown the ability of these agents to modulate the human immune system, thus far chemical immunomodulators have generally not fulfilled the therapeutic promise generated in animal models for the treatment of human diseases. While the discrepancy in results between animal models and human trials is obvious, the basis is not apparent. Species differences in elimination kinetics, presentation of active drug at the site of action, and the development of tachyphylaxis have been postulated as reasons for the minimal activity of these agents in humans. In addition, the use of investigational techniques established for cytotoxic agents may not be appropriate for immunomodulators. As with any immunomodulator, determining an optimal immunostimulatory dose and schedule and applying the therapy to patients with minimal tumor burden would perhaps be more appropriate than use of a maximally tolerated dose in patients with advanced disease. A dose-immunological effect relationship has recently been demonstrated for levamisole at doses higher than those used for many years in levamisole trials (99). While research and clinical investigation have identified several potentially useful chemical immunomodulators, the elementary understanding of the biochemical mechanisms involved in immunoregulation remains basic. Future research must elucidate these mechanisms, particularly in humans, to maximize the benefits of chemical immunomodulators as single agents or combined with cytotoxic chemotherapeutic agents, surgery, radiation therapy, other immunomodulators, and antiviral agents.

Phase II trial of carbetimer in metastatic melanoma

A phase II study of the synthetic polyelectrolyte Carbetimer 6500 mg/m2 i.v. daily for five days every 21-day cycle was conducted in patients with metastatic melanoma. No responses were seen in 18 evaluable patients. Two patients had stable disease for five months. Toxicity was generally manageable and included mild hyperphosphatemia, mild proteinuria, fatigue, pain at the injection site, and nausea. Carbetimer is inactive in metastatic melanoma at this dose and schedule.

Phase I trial of a 5-day course of carbetimer

Carbetimer (carboxyimamidate) is a low molecular weight derivative of ethylene/maleic anhydride polymer. This compound has demonstrated antitumor activity against several animal models with a daily x 5 schedule appearing most effective. A phase I clinical study of the daily x 5 schedule repeated every 28 days was therefore performed. Forty-one evaluable patients received 66 evaluable cycles of Carbetimer at daily doses ranging from 100-11,000 mg/m2. Hypercalcemia was the dose limiting toxicity with both patients at the 11,000 mg/m2 daily dose level and one patient who received 6 cycles of drug at the 4200 mg/m2 dose level developing severe hypercalcemia not explained by the underlying malignancy. Mild nausea, concentration and rate dependent arm pain at the site of infusion, proteinuria, and coagulopathy were also seen. Calcium balance studies revealed hypercalciuria, suggesting increased mobilization of calcium rather than renal retention. In vitro coagulation studies revealed concentration dependent prolongation of the partial thromboplastin time and thrombin time. No complete or partial responses were seen. However mixed response or biochemical response (reduction in serum lactic dehydrogenase) were seen in 5 patients with melanoma or renal cancer. Due to unacceptable toxicity at the 11,000 mg/m2 daily dose level, Carbetimer 8500 mg/m2 is the recommended dose for a 5-day treatment schedule every 28 days. Special attention should be directed toward possible activity against melanoma and renal cancer.

Phase I clinical trial with carbetimer

Carbetimer, a low molecular weight polymer derived from ethylene and maleic anhydride, belongs to a class of chemical compounds different from previously available anticancer agents. It has shown moderate antitumor activity against the Madison 109, Lewis lung, colon 26 and M5076 ovarian carcinomas. In the human tumor stem cell assay, antitumor activity was seen against carcinomas of the breast, ovary, lung, colon and kidney. A total of 26 patients with solid tumors were entered into this trial; carbetimer was given on 5 consecutive days as a 1-2-h intravenous infusion. The dose was escalated from 1.08 to 11 g/m2/day. The drug did not induce the usual side-effects of chemotherapy: leukopenia, thrombocytopenia, alopecia and mucositis were minimal or totally absent. Gastrointestinal toxicity was limited to mild to moderate nausea and vomiting; these were observed at all dose levels and required antimetics in only two patients. The major side-effects of carbetimer consisted of hypercalcemia and neurotoxicity. Hypercalcemia was dose- and treatment duration-dependent. The precise mechanism of hypercalcemia is presently under investigation, but remains unclear. Neurotoxicity was observed only after prolonged therapy; two patients, who received cumulative doses higher than 250 g/m2, developed a peripheral neuropathy with paresthesia, decrease in sensory perception and motor weakness. One patient recovered completely; the other patient improved slightly before developing fatal brain metastases. Two patients with malignant melanoma exhibited major antitumor response; both were previously treated; after excellent partial responses to carbetimer, both were operated on and one is presently disease-free 2 1/2 years after completion of therapy with carbetimer. In conclusion, carbetimer is a new compound with an unusual pattern of side-effects and interesting antitumor activity against malignant melanoma. Its antitumor activity is presently being investigated in phase II trials.