Murine pharmacokinetics of 6-aminonicotinamide (NSC 21206), a novel biochemical modulating agent

The pyridine nucleotide 6-aminonicotinamide (6AN) was shown recently to sen sitize a number of human tumor cell lines to cisplatin in vitro. The presen t studies were undertaken to compare the drug concentrations and length of exposure required for this sensitization in vitro with the drug exposure th at could be achieved in mice in vivo. Human K562 leukemia cells and A549 lu ng cancer cells were incubated with 6AN for various lengths of time, expose d to cisplatin for 1-2 hr, and assayed for Pt-DNA adducts as well as the ab ility to form colonies. K562 cells displayed progressive increases in Pt-DN A adducts and cisplatin sensitivity during the first 10 hr of 6AN exposure. An 18-hr 6AN exposure was likewise more effective than a 6 hr 6AN exposure in sensitizing A549 cells to cisplatin. HPLC analysis of 6AN and its metab olite, 6-amino NAD(+), permitted assessment of exposures achieved in vivo a fter i.v. administration of 10 mg/kg of 6AN to CD2F(1), mice. 6AN reached p eak serum concentrations of 80-90 mu M and was cleared rapidly, with T-1/2 alpha and T-1/2 beta Values of 7.4 and 31.3 min, respectively. Bioavailabil ity was 80-100% with identical plasma pharmacokinetics after i.p. administr ation. At least 25% of the 6AN was excreted unchanged in the urine. The met abolite 6-amino-NAD(+) was detected in perchloric acid extracts of brain, l iver, kidney, and spleen, but not in serum. Efforts to prolong systemic 6AN exposure by administering multiple i.p. doses or using osmotic pumps resul ted in lethal toxicity. These results demonstrated that 6AN exposures requi red to sensitize tumor cells to cisplatin in vitro are difficult to achieve in vivo. (C) 1999 Elsevier Science Inc.