In vivo and in vitro anticancer activity of the structurally novel and highly potent antibiotic CI-940 and its hydroxy analog (PD 114,721)

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Abstract
CI-940, PD 114,721, and PD 118,607 are structurally novel antibiotics, which were isolated from fermentation beers of a previously unknown actinomycete. They are highly lipophilic acids characterized by unsaturated lactone and branched, polyunsaturated aliphatic sidechain moieties. All three agents demonstrated significant cytotoxic activity in vitro against a number of human and mouse tumour lines which encompassed a wide range of tissue types. CI-940 retained full activity in vitro against lines of P388 leukemia that are resistant to Adriamycin, amsacrine, and mitoxantrone. Activity was confirmed for both CI-940 and PD 114,721 against a number of murine experimental tumor systems in vivo, which included the P388 and L1210 leukemias and also B16 melanoma, Ridgway osteogenic and M5076 sarcomas, and mammary adenocarcinoma 16/C. PD 118,607 was also highly active against B16 melanoma. All three agents demonstrated anticancer activity at very low dosages compared with current clinically useful anticancer agents. No significant activity was seen against the MX-1 human mammary xenograft or pancreas 02 tumor models. The primary target for host toxicity of CI-940 and PD 114,721 appeared to be gastrointestinal in nature. Neither CI-940 nor PD 114,721 caused delayed lethality when given either IP or IV. In schedule studies, the toxicities of both CI-940 and PD 114,721 were moderately dependent on the regimen used, with total maximum tolerated dosages for intermittent (q4dx2), daily (qdx5), and divided daily (q4hx3, qdx5) dosing schedules of 1, 0.25, and 0.12 mg/kg, respectively. CI-940 is being developed for clinical trial on the basis of its potent activity against seven different tumor models, its novel structure, and its apparently novel mechanism of action.