methylnitronitrosoguanidine and tiazofurin

Antineoplastic activity of tiazofurin (Tz) and selenazofurin (Se) depends on their conversion to substances which are analogs of NAD. NAD performs pleiotropic and essential cellular functions, both as a cofactor in oxidation-reduction reactions and as a substrate for poly- and mono-ADP-ribosylation reactions. The therapeutic potential of modulating intracellular NAD levels and activity of NAD-dependent enzymes by concomitant administration of conventional anticancer agents merits further research. Our aim was to investigate the cytotoxic effects of Tz and Se in hematopoietic cells and to test their ability to potentiate the effects of DNA strand-disrupting agents.. THP-1, a cell line, derived from human acute monoblastic leukemia, was used. CLL lymphocytes were obtained from 8 patients with CLL.. The WST-l test was used to detect the function of NAD(P)-dependent dehydrogenases after exposure of THP-1 cells to Tz or Se. Cytotoxicity of Tz, Se, MNNG and chlorambucil was assessed using the membrane permeability assay (PI test).. THP-1 cells were sensitive to cytotoxic effects of Tz and Se, with IC50 values of 2.5 x 10(-5) M for Tz and 2 x 10(-6) M for Se, as determined with the WST-1 test; 10 microM Se induced cell membrane disruption in more than 20% of THP-1 cells 48 hours after commencement of treatment, whereas the same concentration of Tz failed to increase membrane permeability. Pretreatment of THP-1 cells with 0.5 - 1.5 microM Se had no effect on the time course of cell death, induced by treatment with the DNA-damaging agent 1-methyl-3-nitro-1 - nitrosoguanidinium (MNNG) for 36 hours. However, when incubation of THP-1 cells with MNNG was prolonged (72 hours) without changing the incubation medium, pretreatment with Se had the following effects: the relative number of cells that died spontaneously decreased, and the cytotoxicity of MNNG was diminished. This effect was also demonstrated ex vivo in 6 of 8 cases of CLL, treated with MNNG and chlorambucil.. Contrary to other investigations, we here demonstrate that preincubation with Se may partially protect cells from cell death induced by the alkylating agents MNNG and chlorambucil in the THP-1 cell line and in CLL lymphocytes presumably by affecting spontaneous cell death.

Topics: Antineoplastic Agents; Cell Death; Cell Line; Cell Survival; Chlorambucil; Dose-Response Relationship, Drug; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Leukemia, Monocytic, Acute; Methylnitronitrosoguanidine; Organoselenium Compounds; Ribavirin; Ribonucleosides

Poly(ADP-ribose) polymerase (PADPRP), which uses NAD to synthesize ADP-ribose polymers, is activated by DNA strand breaks and mediates cellular responses to DNA damage. The consequences of low cellular NAD levels in a cell line deficient in nicotinamide mononucleotide adenylyltransferase (NMNAT), an enzyme essential for NAD biosynthesis, were investigated by assessing NAD metabolism and DNA repair after treatment with alkylating agents. A tiazofurin-resistant L1210 cell line (TZR) was isolated. NAD levels were approximately 5933 and 3375 pmol mg(-1) protein for parental (wild type, WT) and TZR cells respectively, and NMNAT levels were reduced by > 95%. TZR cells were more sensitive to temozolomide (TM) and 1-methyl-3-nitro-1-nitroso-guanidine (MNNG), particularly at concentrations that caused > 50% NAD depletion. TM and MNNG treatment decreased NAD levels in both cell lines, but took longer to return to control levels in TZR cells. For example, MNNG (5 microM), depleted NAD levels at 6 h to approximately 4512 (WT) and 1442 (TZR) pmol mg(-1) protein; however, NAD levels had returned to control levels by 8 h in WT cells, but were not restored by 16 h in TZR cells. Both cell lines were equisensitive to the growth-inhibitory effects of NU1025 per se (IC50 370 microM). Co-exposure of the cell lines to TM (100 microM) with increasing concentrations of NU1025 led to a synergistic enhancement of cytotoxicity, with IC50 values for NU1025 decreasing to 17 +/- 4 microM (TZR) and 37 +/- 6 microM (WT). A similar enhanced sensitivity to NU1025 (approximately 2.7-fold) was obtained when TZR cells were co-exposed to MNNG + NU1025. TM-induced DNA strand breaks were increased by co-incubation with NU1025, and again the TZR cell line showed increased sensitivity to NU1025. There were no significant changes in NMNAT activity in response to MNNG treatment over 24 h, either in the presence or in the absence of NU1025. These data demonstrate that modest decreases in cellular NAD levels can sensitize cells to alkylating agents and PADPRP inhibitors.

Topics: Animals; Antineoplastic Agents; Carcinogens; Cell Division; Dacarbazine; DNA Repair; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Leukemia L1210; Methylnitronitrosoguanidine; Mice; NAD; Nicotinamide-Nucleotide Adenylyltransferase; Ribavirin; Temozolomide