Long-term maintenance therapy of established human small cell variant lung carcinoma implants in athymic mice with a cyclic regimen of difluoromethylornithine.
We report that cyclic p.o. administration of alpha-difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis, is an effective long-term (1-year) maintenance therapy for established implants of cultured human small cell lung carcinoma in athymic (nude) mice. Human small cell lung carcinoma cells, from a line which exhibited cell death in culture in the presence of DFMO, were inoculated into athymic mice and permitted to grow to palpable tumors (3-5-mm nodules with mean volume of 0.04 cm3). The animals were then randomized into untreated, continuous treatment and cyclic (3 weeks of 4 beginning 1 week after 8 weeks continuous) treatment groups. Treatment consisted of 3% DFMO in the drinking water (5.1 g/kg/day). The tumors in the untreated group grew to 27 cm3 by 8 weeks and the animals had a median survival of 7.6 weeks. Tumor growth was inhibited by 99% (0.3 cm3) in the continuous treatment group in comparison to untreated controls. Survival was prolonged with 93% survival at 10 weeks and a 101% increase in median survival to 15.3 weeks (P less than 0.05). The cyclic DFMO group had a 98.3% inhibition in tumor growth for longer than 1 year (0.56 cm3; P less than 0.05). Survival was also markedly prolonged compared to the untreated group with 100% survival up to 24 weeks and a median survival of 54.3 weeks (P less than 0.05). No significant toxicities were observed in the first 10 weeks of DFMO treatment even though antitumor effects were observed. With continuous DFMO treatment, the animals eventually became debilitated and developed marked weight loss and thrombocytopenia; by 20 weeks, mortality was 79%. With cyclic therapy, the animals resumed weight gain, recovered from thrombocytopenia and, at 20 weeks, had 0% mortality. By 55 weeks, mortality was 50% which, however, was not significantly different (P approximately 0.50) from mortality of a control group of nontumorous, athymic mice that had weekly body weight and skin fold measurements concurrently with the experimental, tumor-bearing animals. Thus, the observed mortality is ascribable to continuous encroachment on the normally sterile environment. These data suggest a role for DFMO in long-term therapy of sensitive human tumors such as small cell lung carcinoma, especially in patients with a low tumor burden. Furthermore, a cyclic regimen might be an important tool in maintaining clinical remissions induced by conventional combination chemotherapy.
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D018288:Carcinoma, Small Cell / Q000188:drug therapy* / Q000473:pathology; D002449:Cell Aggregation / Q000187:drug effects; D000518:Eflornithine; D005260:Female; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009952:Ornithine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use / Q000633:toxicity; D014183:Transplantation, Heterologous
D009952:Ornithine; D000518:Eflornithine