In vitro and in vivo studies of a promising antileukemic thymidine analogue, 5-hydroxymethyl-2' deoxyuridine.

The toxicity and metabolism of a thymidine analogue, 5-hydroxymethyl-2'-deoxyuridine (5HmdUrd) were studied with human leukemia cells (HL-60) and with human platelets. 3 X 10(-5) M 5HmdUrd caused a 50% inhibition in the proliferation of HL-60 cells. The compound was hydrolyzed to 5-hydroxymethyluracil (5HmUra) by the enzyme thymidine phosphorylase (EC 2.4.2.4) present in leukemia cells; this catabolic product was non-toxic. The catabolism of 5HmdUrd by human platelet thymidine phosphorylase could be inhibited by 6-aminothymine. The toxicity of 5HmdUrd was effectively reversed by deoxycytidine and 5HmdUrd increased the incorporation of deoxycytidine into dCTP and DNA several fold. The two latter phenomena are explicable in terms of a feedback action to ribonucleotide reductase, resulting in deoxycytidylate starvation, which is a known effect of excess thymidine. We report here also our preliminary observations that 5HmdUrd is active against mouse leukemia in vivo.

5-Hydroxymethyl-2'-deoxyuridine. Cytotoxicity and DNA incorporation studied by using a novel [2-14C]-derivative with normal and leukemic human hematopoietic cells.

5-Hydroxymethyl-2'-deoxyuridine is a biologically active thymidine analogue. This investigation was aimed at characterizing the cytotoxicity of 5-hydroxymethyl-2'-deoxyuridine and its incorporation into DNA. Fifty percent inhibition of cellular proliferation, assessed by incorporation of [U-14C]-L-leucine in vitro, was caused by 1.7-5.8 X 10(-5) incorporation of [U-14C]-L-leucine in vitro, was caused by 1.7-5.8 X 10(-5) M 5-hydroxymethyl-2'-deoxyuridine in seven human leukemia cell lines. Higher concentrations of 5-hydroxymethyl-2'-deoxyuridine, i.e. 6-8 X 10(-5) M, were required for a comparable inhibition in human PHA-stimulated peripheral blood lymphocytes. A new synthesis procedure for [2-14C]5-hydroxymethyl-2'-deoxyuridine was developed. The net incorporation of [2-14C]5-hydroxymethyl-2'-deoxyuridine into DNA of hematopoietic cells was low. The possibility of a repair mechanism for 5-hydroxymethyluracil bound to DNA is discussed.