Largomycin FII chromophore component 4, a new pluramycin antibiotic.

The chromophore of the antitumor chromoprotein largomycin FII is a mixture of components belonging to the pluramycin class of antitumor antibiotics. Against most organisms tested, component 4 exhibited activity equal to or greater than the major chromophore components pluramycin A and deacetylpluramycin A. Data obtained from UV, IR, 1H and 13C NMR, and from fast atom bombardment mass spectrometry were used to determine the structure of component 4 as epoxykidamycin, a new member of the pluramycin class.

Structure and properties of major largomycin FII chromophore components.

Largomycin FII, a protein antitumor antibiotic of molecular weight 29,300 daltons, contains a chromophore that is separable under mild denaturing conditions. The chromophore complex was found to be considerably less stable than the holoprotein towards light and heat, suggesting a protective effect of the protein on the chromophore. Separation of the chromophore into several components was achieved using high performance liquid chromatography, and the biological activity of the isolated components was determined. Data gathered from UV, IR, proton and carbon NMR, and fast atom bombardment mass spectrometry indicated that all the chromophore components belong to the pluramycin class of antitumor agents. Pluramycin A and deacetylpluramycin A were found to be the two major components.

Activation of antitumor agent gilvocarcins by visible light.

Gilvocarcins that are antitumor agents are activated by low doses of visible light to induce bacteriophage lambda in Escherichia coli. This result is dependent on interaction with DNA. Gilvocarcin M, an analog without antitumor activity, failed to induce the prophage after light exposure, thus demonstrating a correlation between photosensitizing and antitumor activities. These results raise several possibilities regarding the mode of action of gilvocarcins as antitumor agents in vivo, involving light or enzymatic activating systems, which could be exploited in human cancer therapy.

Genetic and biochemical factors affecting the induction of bacteriophage lambda by N-nitroso compounds.

As part of our effort to validate a biochemical (prophage) induction assay (BIA) as a screening test for carcinogens, we have tested more than 100 N-nitroso compounds. An enzyme, beta-galactosidase, is induced as an indirect consequence of DNA damage to the host, as part of the 'SOS' response. Besides the obvious practical importance of detecting this class of carcinogen, there is the question of the mechanism by which these compounds work. Mutagenesis by one compound, N-methyl-N'-nitro-N-nitrosoguanidine, is known to proceed by both SOS (recA)-dependent and SOS-independent pathways. Mispairing due to O6 alkylation of guanine is thought to be responsible for the SOS-independent pathway; however, there has been little consideration of recA-dependent functions, of which phage induction is one. Although nitrosamides could be detected as phage inducers in our assay, N-nitrosamines in the presence of rat liver 9 000 X g supernatant usually gave no response. We found that the use of several mutant strains, particularly a lexA mutant, in combination with hamster liver 9 000 X g supernatant, allowed us to detect most N-nitrosamines reasonably well, in either a spot test or a quantitative tube assay. Induction in a lexA strain was most unexpected, since this mutation usually diminishes the expression of SOS functions induced by ultra-violet light. Because the genetic and biochemical conditions that favour phage induction are different from those that favour mutagenesis, it seems likely that the lesions in DNA leading to the two biological end-points are different.