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Summary Forty-nine ovarian tumours were examined for loss of heterozygosity (LOH) on chromosome 5 using eight microsatellite markers spanning both arms, including one at the APC locus. LOH on Sq was a frequent event, detectable in 23 of 49 (47%) tumours, whereas 5p LOH was detected in only 1 of 22 tumours (5%). Six tumours showed partial LOH on 5q, enabling the candidate region to be localised to a 22 cM region proximal to APC, flanked by D5S424 and D5S644. An association was found between 5q LOH and TP53 mutation, with 18 of 23 (78%) tumours with LOH on Sq also harbouring a TP53 mutation. LOH on Sq was observed in 6 of 18 (33%) stage I tumours, suggesting that it may be an early event in the molecular pathogenesis of certain ovarian carcinomas.

Caffeine inhibits the G2 checkpoint activated by DNA damage and enhances the toxicity of DNAdamaging agents towards p53-defective cancer cells. The relationship between structure and G2 checkpoint inhibition was determined for 56 caffeine analogs. Replacement of the methyl group at position 3 or 7 resulted in loss of activity, while replacement at position 1 by ethyl or propyl increased activity slightly. 8-Substituted caffeines retained activity, but were relatively insoluble. The structure-activity profile did not resemble those for other known pharmacological activities of caffeine. The active analogs also potentiated the killing of p53-defective cells by ionizing radiation, but none was as effective as caffeine.

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