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

We examined the effects of timing of administration of etoposide on cytosine arab-inoside (ara-C) incorporation into DNA in L1210 ascites tumor. 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 of ara-C alone. These results might explain the previously reported sequence dependency of the antitumor effect of etoposide and ara-C.