Synthesis and evaluation of a series of 3,5-disubstituted benzisoxazole-4,7-diones. Potent radiosensitizers in vitro.

A series of 3,5-disubstituted-2,1-benzisoxazole-4,7-diones was synthesized and evaluated as radiosensitizers both in vitro and in vivo. These compounds were designed as non-nitro electron-affinic agents in an effort to alleviate some of the toxicities seen with the 2-nitroimidazole radiosensitizers evaluated in the clinic. Several compounds in this series were potent radiosensitizers in vitro, with sensitizer enhancement ratios of 2.0-2.3 at concentrations less than 0.5 mM. Compounds with potent in vitro activity were also evaluated in vivo. However, none of these compounds showed radiosensitizing activity in vivo. The reduction potentials of these compounds were determined by cyclic voltammetry and compared to other electron-affinic radiosensitizers. In general, the reduction potentials of this series of compounds was slightly more positive than the 2-nitroimidazoles, but they fell within the range postulated as acceptable to yield in vivo activity. The results suggest that factors other than reduction potential may be responsible for the lack of in vivo radiosensitizing activity observed for this class of radiosensitizers.

Pyrazoloacridines, a new class of anticancer agents with selectivity against solid tumors in vitro.

A series of 2-aminoalkyl-5-nitropyrazolo[3,4,5-kl]acridines (pyrazoloacridines) was evaluated in vitro for activity against a panel of human tumor cell lines of breast, colon, or lung origin. Several pyrazoloacridines were found to possess solid tumor selectivity relative to their activity against murine leukemia L1210 cells as well as human lymphoblastoid cells. The superior compounds in this regard were also found to exhibit excellent activity against primary human tumors in stem cell clonogenic assays. In addition, many of the compounds tested were found to be selectively cytotoxic to hypoxic relative to oxic HCT-8 colon adenocarcinoma cells, a property that may be a consequence of the potentially reducible 5-nitro function. A number of pyrazoloacridines were also found to exhibit potency against noncycling Chinese hamster ovary cells comparable to that observed against actively dividing cultures. Consistent with their favorable activity against nondividing cells, further testing of the pyrazoloacridines revealed that generally less drug is required to inhibit RNA synthesis than DNA synthesis in L1210 cells. Collectively these data indicate that the pyrazoloacridines represent a novel class of antitumor agents which warrant further preclinical evaluation for their potential clinical usefulness in the treatment of solid tumors.

Bacterial DNA reactivity of the novel antitumor antibiotics PD 114,759 and PD 115,028 (veractamycins A and B).

The novel antitumor antibiotics PD 114,759 and PD 115,028 were evaluated for their ability to cause repairable DNA damage and the induction of SOS functions in bacterial systems. PD 114,759 and PD 115,028 were preferentially toxic to DNA repair-defective Escherichia coli WP100 uvrA recA in comparison to wild-type E. coli WP2 at concentrations of 10 approximately 30 micrograms/ml in agar diffusion assays. Both compounds were inducers of cell filamentation and prophage lambda (two E. coli SOS functions) at concentrations of 0.1 approximately 1 microgram/ml. In addition, the ability of PD 114,759 and PD 115,028 to retain their filamentation-inducing effects under both aerobic conditions and anaerobic conditions suggests that a bioreductive, rather than an oxygen-requiring, mechanism is involved in the DNA-reactive effects of these agents.

Antimycotic effects of the novel antitumor agents fostriecin (CI-920), PD 113,270 and PD 113,271.

The novel fermentation products fostriecin and analogs PD 113,270 and PD 113,271 are structurally related polyene lactone phosphates that have antitumor activity in vitro and in vivo. They have no antibacterial effects, but they were inhibitory to yeasts (agar diffusion method) with MICs of 3 approximately 300 micrograms/ml. Fostriecin or its analogs were active vs. 29 of 46 yeast species (11 genera). Ten of 12 cultures of Candida sp. were not sensitive to any of the analogs, while 11 of 14 cultures of Saccharomyces sp. were inhibited by one or more of the agents. Sensitivity patterns were of three types: Twelve cultures were sensitive only to PD 113,270; fostriecin and PD 113,271 (but not PD 113,270) were active vs. 7 cultures; and 9 cultures were sensitive to all three compounds. Dephosphorylation of the compounds resulted in the loss of antimycotic effects. Activity vs. the yeasts was related to studies of uptake and activity against cancer cells.

The Escherichia coli K-12 SOS chromotest agar spot test for simple, rapid detection of genotoxic agents.

The Escherichia coli K-12 SOS chromotest is a colorimetric (beta-galactosidase induction) system for detecting genotoxic chemicals as agents which induce filamentation in response to DNA damage. The chromotest was modified from a liquid suspension assay to a simple, convenient agar spot test, which was performed in the manner of a related colorimetric prophage induction assay (BIA). Chromotest agar dishes yielded optimal results after 16-18 h incubation, presumably because of the agar growth characteristics of tester strain PQ37. Of 44 tested chemicals, nitro aromatics, cytotoxic/antitumor agents, polycyclic hydrocarbons and aflatoxins showed good activity. Alkylating agents such as MNNG and MMS were active only at high concentrations. Compounds active in both the chromotest and BIA were active at 10-100-fold lower concentrations in the chromotest. The chromotest appeared to be less effective than the Salmonella Ames mutagenicity test in the detection of diverse classes of chemical carcinogens. The chromotest may be a useful alternative to the BIA in the study of particular classes of genotoxic compounds.