Photocarcinogenesis in mice by 4,4',6 trimethylangelicin plus UVA radiation

The carcinogenic effect of a new monofunctional psoralen 4,4',6-trimethylangelicin (TMA) plus UVA radiation was examined in C3H/HeN mice and compared with that of the parent compound angelicin. TMA carcinogenic effects were also compared with the previously reported effects of 8-methoxypsoralen. Using 2 different doses of TMA (25 micrograms and 250 micrograms) combined with 1 J/cm2 of UVA radiation, we found that 42% and 52% of the mice (respectively) developed tumors on the treated site. A dose of angelicin (215 micrograms) equimolar to the highest dose of TMA combined with 1 J/cm2 of UVA radiation produced tumors in 28% of the mice (P greater than 0.05). All tumors were squamous cell carcinomas. No metastases were found in any of the mice. We conclude that, although TMA + UVA radiation is carcinogenic in mice, it seems to be an equally active, but less phototoxic and less carcinogenic psoralen than 8-methoxypsoralen. The parent compound angelicin is not significantly less carcinogenic, and its clinical efficacy is poor.