Synthesis and biological evaluation of butanoate, retinoate, and bis(2,2,2-trichloroethyl)phosphate derivatives of 5-fluoro-2 '-deoxyuridine and 2 ',5-difluoro-2 '-deoxyuridine as potential dual action anticancer prodrugs

A group of 3'-O-butanoyl, 5'-O-butanoyl, and 3',5'-di-O-butanoyl esters of 5-fluoro-2'-deoxyuridine (FDU), and 2',5-difluoro-2'-deoxyuridine (DFDU), 3 '-O-retinoyl, and 3',5'-di-O-retinoyl esters of FDU, and 5'-O-bis(2,2,2-tri choloroethyl)phosphoryl-FDU and its 3'-O-butanoyl ester, was synthesized. T hese compounds were designed to act as double prodrugs that would serve as a depot to release two active drugs that act through different mechanisms. Thus, a nucleotide derivative of FDU or DFDU could act as a competitive inh ibitor for thymidylate synthase, whereas retinoic acid and butyric acid wou ld be expected to induce cell differentiation. The in vitro anticancer acti vities for these prodrugs were determined against a panel of nine tumor typ es (leukemia, non-small cell lung, colon, CNS, melanoma, ovarian, renal, pr ostate, breast) that encompassed about 60 human tumor cell lines. Structure -activity relationships indicate that O-butanoyl esters of FDU are approxim ately equipotent to FDU, the O-butanoyl esters of DFDU are less active than FDU, and the retinoyl and bis(2,2,2-trichloroethyl)phosphate derivatives o f FDU exhibit comparable activity to FDU. In addition to their cytotoxic ef fect, 3'-O-retinoyl-FDU (12) and 3'-O-butanoyl-5'-O-bis(2,2,2-trichloroethy l)phosphoryl-FDU (16) also induced in vitro cell differentiation of promyel ocytic leukemia HL60 cells. These combined cytotoxic and cell differentiati on effects exhibited by 12 and 16 produced great morphological drug-induced granulation and neutrophil vacuolation, and more cell apoptosis, than obse rved upon exposure to either retinoic acid or sodium butanoate. Dose-escala tion studies in mice showed that 12 or 16 did not induce any acute or chron ic toxicity, change in plasma clinical chemistry parameters, or gross hista pathological changes at 60 days following an initial dosage regimen of 0.01 3 mmol/kg ip for 7-consecutive days. The in vivo growth delay response of m urine mammary EMT6 solid tumors suggests that 3'-O-retinoyl-FDU (12) delays tumor growth relative to the other prodrugs investigated, sodium butyrate, retinoic acid, FDU, or a combination of retinoic acid and FDU. These preli minary results suggest that 3'-O-retinoyl-FDU (12) warrants further in vivo investigation to determine its tissue biodistribution and pharmacokinetic parameters that would be of value in assessing its potential usefulness as an anticancer prodrug.