Effect of administration of sodium cyanate and melphalan on the lifespan of P388 tumor-bearing CD2F1 mice.

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Sodium cyanate (NaOCN) at a dose of 250 mg/kg was shown to decrease protein synthesis in P388 leukemia tumor cells to approximately 52% of control values at 2 h and 32% at 5 h after NaOCN administration, without a corresponding decrease in various normal tissues of the tumor-bearing CD2Fl mice. CD2Fl mice that had received P388 tumor cells IP 1 day prior to drug administration underwent various schedules of treatment with NaOCN and melphalan (MLN). NaOCN (200 mg/kg or 250 mg/kg) administered IP has no significant antitumor activity (increased mean lifespan [ILS] less than 20%). The simultaneous IP administration of NaOCN (250 mg/kg) plus MLN (15 mg/kg) resulted in a significantly greater antitumor activity (approximately 265% of control, with 21 of 30 animals being long-term survivors) than MLN (15 mg/kg) alone (approximately 156% of control, with 11 of 30 animals being long-term survivors). This synergism was not observed when MLN was administered 4 h after NaOCN administration. The synergistic activity of MLN with NaOCN does not appear to be secondary to alterations in the absorption from the peritoneal cavity into the systemic circulation as determined by 3H2O. NaOCN does not increase the intracellular concentration of [chloroethyl-14C]MLN into P388 cells. The mechanism of the synergistic antitumor activity of simultaneous IP administration of NaOCN and MLN is unknown.