The pharmacokinetics and pharmacodynamics of the novel clinical candidate 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (
CNDAC) were investigated in human lymphoblastoid CCRF-CEM cells and human myeloblastic
leukemia ML-1 cells. Formation of
CNDAC 5'-mono-, di-, and
triphosphate (CNDACTP) was concentration-dependent;
nucleotide accumulation was greater in the lymphoid cells than in the myeloid cells. The
nucleotides were eliminated with linear kinetics from both lines, but were retained more effectively by the ML-1 cells.
DNA synthesis was selectively inhibited by a 4-hr treatment with
CNDAC in CCRF-CEM and ML-1 cells; the IC(50) values were 1 and 0.8 microM, respectively. Evaluation of the polymerization reaction of a primer on an M13mp19(+) template by human
DNA polymerase alpha indicated that CNDACTP was incorporated effectively (K(m) = 0.22 microM) opposite a complementary
dGMP in the template strand. CNDACTP competed with the normal substrate,
dCTP, for incorporation, and the two
nucleotides showed similar substrate efficiencies (V(max)/K(m):
dCTP = 0.91; CNDACTP = 0.77). Primer extension was potently inhibited by
CNDAC triphosphate (K(i) = 23 nM); once the analog had been incorporated, further extension was not observed in vitro, suggesting that primers containing a 3'-terminal
nucleotide analog were high K(m) substrates for polymerase alpha. Thus, the ability of human
leukemia cells to effectively accumulate and retain CNDACTP, coupled with the favorable kinetics of competition for incorporation into
DNA, and the relatively strong ability of the analog to terminate further extension, are likely to contribute to the cytotoxic action of
CNDAC.