Enzymatic reactivity and anti-tumor activity of 1-(beta-D-arabinofuranosyl)-2-thiocytosine derivatives.

Sixteen derivatives of 1-(beta-D-arabinofuranosyl)-2-thiocytosine (araSC), including five 5'-esters, three 3'-esters, five N4-amides and three 5'-phosphodiesters, were synthesized and their reactivity to mouse tissue homogenates, including plasma, liver and intestine, and antitumor activity in mice bearing P388 cells were measured. The ester derivatives had a potent effect on the enzyme systems while the amide and phosphodiester derivatives were less active. The reactivity of ester derivatives was highly dependent on their chemical structure. The reactivity of amides and phosphodiester derivatives on mouse plasma and intestinal homogenate was also dependent on the chemical structure, although their action on intestinal enzymes was very similar. Two of eight ester derivatives showed considerable antitumor activity in vivo, although they also showed serious toxicity indicated by a weight loss in the mice. Four out of five amides and two out of three phosphodiesters showed antitumor activity, and two were highly effective (>200% in T/C, the ratio of the mean survival time of the treated group to that of the control group) with only a very slight weight loss.