ENHANCED INCORPORATION OF 1-BETA-D-ARABINOFURANOSYLCYTOSINE BY PRETREATMENT WITH ETOPOSIDE

We examined the effects of timing of administration of etoposide on cy tosine arabinoside (ara-C) incorporation into DNA in L1210 ascites tum or. At 1 hr after injection of ara-C, 3-hr and 6-hr pretreatments with 15 mg/kg of etoposide increased ara-C incorporation to more than 200% as compared to that of ara-C given alone. Simultaneous administration of etoposide, however, decreased ara-C incorporation to 33% of that o f ara-C alone. These results might explain the previously reported seq uence dependency of the antitumor effect of etoposide and ara-C.