Enhanced radiation lethality in partially synchronized solid mouse tumors.

We studied the combined effects of local irradiation on in vivo partially synchronized solid mouse tumors. Syngeneic fibrosarcoma cells were transplanted s.c. into the thighs of C3H/He mice. When the tumors grew to 179 cu mm in volume, 1-beta-D-arabinofuranosylcytosine (ara-C) was repeatedly injected i.p. followed by a single injection of vinblastine sulfate at 5 hr after the end of the ara-C treatment. The mitotic indexes increased from 4% in control to 22 to 23% at 5 hr after the ara-C treatment, and the level continued for another 5 hr. Further treatment with vinblastine sulfate after the ara-C injections resulted in more effective accumulation of mitotic cells, i.e., 30% at the sixth hr. The tumor was locally irradiated with a single dose of 3000 rads of gamma-rays at the maximum level of mitotic index. The results indicated a synergistic inhibition of tumor growth and an 84% prolongation of the 50% survival day beyond that of the nontreated control mice.