Novel Derivatives of 5-Fluorouridine and 5-Fluorouracil Having Potent Antitumor and Lower Immunosuppressive Activities

We studied the biological activities of several 5-fluorouridine (5-FUR) and 5-fluorouracil (5-FU) derivatives to find novel antitumor drugs with lower immunosuppressive effects. We examined 5-FUR and 5-FU derivatives acylated with (2-n-propyl-n-pentanoyl)glycine (KN-539). Among the examined compounds, we found satisfactory activities in a derivative of 5-FUR, 2'', 3'', 5''-tris-O-[N-(2-n-propyl-n-pentanoyl)glycyl]-5-fluorouridine (UK-21), and a derivative of 5-FU, 1-{6-[N-(2-n-propyl-n-pent anoyl)glycyl]amino-n-hexylcarbamoyl}-5 -fluorouracil (UK-25). UK-21 (0.05-0.2 mmole/kg, p.o., 10 days) and UK-25 (0.1-0.4 mmole/kg, p.o., 10 days) suppressed Meth A and E.L.4 tumor growths in the corresponding syngeneic hosts (BALB/c mice and C57BL/6 mice, respectively) without decreasing body weight and blood leukocyte count. UK-21 and UK-25 suppressed the proliferation of KB tumor cells in vitro (IC50: 3.0 × 10-11 M and 4.4 × 10-7 M, respectively) at concentrations almost equivalent to those of 5-FUR and 5-FU, respectively. These results suggest that UK-21 and UK-25 express their antitumor activity as 5-FUR and 5-FU, respectively. Neither UK-21 nor UK-25 suppressed thymus weight and humoral antibody production against sheep red blood cells (SRBC) in ddY mice, although 1-(2-tetrahydrofuryl)-5-fluorouracil (FT-207) and 5-FU suppressed them in their respective therapeutic dose ranges for tumors. Thus, UK-21 and UK-25 are expected to develop into anticancer drugs with lower immunotoxicological effects.