Comparison of biochemical, molecular biological, and chemosensitivity data obtained from screening a large number of cell lines (e.g., the NCI tumor cell line panel) may facilitate investigation of factors influencing drug antitumor activity. The knowledge gained may be of value in the development of new anticancer agents or in the selection of patients to receive specific therapies.

No abstract

3-amino-1,2,4-benzotriazine-1,4-di-N-oxide (tirapazamine, WIN 59075, SR 4233, NSC 130181) has entered phase 1 clinical trials as a bioreductive hypoxic cell cytotoxin because of its novel structure and impressive selective cytotoxicity towards hypoxic cells. Understanding the enzymology and underlying mechanism of oxidative and reductive DNA damage may allow more optimal development and use of this agent and contribute to the rational design of new bioreductive drugs. Here we provide unambiguous evidence that WIN 59075 undergoes one-electron reduction by purified rat liver NADPH:cytochrome P450 oxidoreductase to generate single- and double-strand breaks in plasmid DNA. The DNA damage caused may be important for the therapeutic toxicity of the drug. Enzyme kinetic parameters for this oxidoreductase reaction are in the range 1.01-1.61 mM for Km and 4416-5099 nmol/min/mg for Vmax. The relative levels of expression and cellular localization of target tumour NADPH:cytochrome P450 oxidoreductase may contribute to the therapeutic selectivity of WIN 59075.

No abstract

There is evidence that one critically short telomere may be recognized as DNA damage and, as a consequence, induce a p53/p21WAF- and p16INK4A-dependent G1 cell cycle checkpoint to cause senescence. Additionally, senescence via a p53- and p16(INK4A)-dependent mechanism can be induced by the over- or under-stimulation of certain signalling pathways that are involved in cancer. Central to this alternative senescence mechanism is the p14ARF protein, which connects oncogene activation, but not DNA damage, to p53 activation and senescence. We find that immortal keratinocytes almost invariably have dysfunctional p53 and p16 and have high levels of telomerase, but very often express a wild-type p14(ARF). Furthermore, when normal keratinocytes senesce they show a striking elevation of p16 protein, but not of p14(ARF) or its downstream targets p53 and p21(WAF). These results suggest that p16, rather than p14(ARF), is the more important gene in human keratinocyte senescence, but do not exclude a co-operative role for p14(ARF), perhaps in the induction of senescence by activated oncogenes in neoplasia. Regardless of mechanism, these results suggest that replicative senescence acts as a barrier to human cancer development.