THE SPECIFIC EFFECTS OF 8-METHOXYPSORALEN PHOTOADDUCTS ON CELL-GROWTH- HPLC ANALYSIS OF MONOADDUCT AND CROSS-LINK FORMATION IN CELLS EXPOSED TO SPLIT-DOSE TREATMENT

The effects of 8-methoxypsoralen (8-MOP) monoadducts and crosslinks on growth and viability of mastocytoma cells were investigated. To induc e monoadduct formation (4',5'-monoadducts and 3,4-monoadducts), the ce lls were incubated with 8-MOP (1 mug ml-1) and exposed to 419 nm radia tion, resulting in the formation of more than 96% monoadducts. After w ashing and resuspension, the cells were exposed to a small dose of lon g-wavelength UV radiation (UVA, 2 J cm-2) to convert monoadducts into crosslinks. Similar adduct levels were obtained after either 8-MOP plu s visible light treatment or 8-MOP plus split-dose protocol. Cells tre ated with 419 nm light resumed normal growth rates more rapidly than c ells which also received the UVA dose. High performance liquid chromat ography (HPLC) analysis of DNA obtained from each group of cells showe d that the UVA step resulted in an increase in crosslinks from 3.2% af ter 419 nm radiation to 56.5% after UVA irradiation.