ADP-ribose Polymerase Inhibitors Research Articles

Effect of adriamycin and hyperthermia on the sedimentation of nucleoids from L1210 cells.

We report on the individual and combined effects of adriamycin (ADR) and hyperthermia (HYP) on the sedimentation behavior of L1210 mouse leukemia cell nucleoids in neutral sucrose gradients. Nucleoid sedimentation profiles obtained from cells incubated with ADR (1-10 microM; 30 min; 37 degrees C) exhibited an increased sedimentation rate associated with an increased protein content of these subnuclear units. Exposure of cells to HYP (1-3 h; 42 degrees C) produced similar results. Simultaneous exposure of L1210 cells to conditions of HYP and ADR which resulted in minimal changes in nucleoid sedimentation when used singly, produced an enhanced effect. A similar enhancement was observed with other intercalating antineoplastic agents believed to exert their effect, at least partially, via free radicals (daunorubicin, amsacrine, bisantrene, mitoxantrone). However, enhancement with HYP was not observed with (a) the classic intercalating agent, ethidium bromide; (b) non-intercalating DNA-breaking agents (bleomycin, lithocholic acid, etoposide); (c) inhibitors of poly (ADP-ribose) polymerase (m-methoxybenzamide, benzamide); or (d) non-intercalating antineoplastic agents capable of causing free radical formation (bleomycin). The results suggest that DNA intercalating agents capable of initiating free radical processes may show an enhanced toxicity with simultaneous HYP treatment, and that the nucleoid assay may be a means of screening agents with these biological properties for potential clinical usefulness in combination with HYP.

Elevation of polycyclic aromatic hydrocarbon-inducible aryl hydrocarbon hydroxylase activity in rat hepatocytes in primary culture by inhibitors of poly(ADP-ribose) polymerase

Induction of aryl hydrocarbon hydroxylase (AHH) activity was studied in primary cultures of rat hepatocytes. AHH activity was induced by treatment with benz[a]anthracene and combined treatment with cycloheximide for an initial short period during the induction enhanced benz[a]anthracene-inducible AHH activity. The enhancement was correlated to amounts of cytochrome P-450 RNA, indicating that cycloheximide treatment increased transcription of benz[a]anthracene-inducible cytochrome P-450 gene species. 3-Methoxybenzamide and 3-aminobenzamide, known to be physiologically specific inhibitors for poly(ADP-ribose) polymerase, but not the structurally related non-inhibitor, 3-aminobenzoic acid, also increased benz[a]anthracene-induced AHH activity. In addition, 3-methoxybenzamide was found to further increase the enhancing effects of cycloheximide on benz[a]anthracene induction of AHH. The effects of poly(ADP-ribose) polymerase inhibitors were not mediated by reduction of cyclic nucleotide phosphodiesterase activity. This was in clear contrast to the situation with the xanthine derivative, aminophylline, which also brought about a similar enhancement of AHH induction by benz[a]anthracene. The results suggest the participation of poly(ADP-ribose) in the regulation of expression of benz[a]anthracene-inducible cytochrome P-450 genes.

Delayed repair of DNA single-strand breaks does not increase cytogenetic damage.

DNA damage and cytogenetic effects of ionizing radiation were investigated in Chinese hamster ovary (CHO) cells and unstimulated human peripheral blood lymphocytes. DNA damage and repair were analysed by alkaline elution under conditions that predominantly measured DNA single-strand breaks (ssb). X-radiation (2.5 Gy) induced ssb in both CHO cells and unstimulated lymphocytes, and the breaks were repaired within 30 and 90 min, respectively. This rapid repair was delayed by the poly(ADP-ribose) polymerase inhibitor, 3-aminobenzamide (3AB). The cytogenetic effects of the 3AB-induced delay in DNA repair were examined by analysing sister chromatid exchange (SCE) frequency in CHO cells and fragmentation of prematurely condensed chromosomes (PCC) in unstimulated human lymphocytes after 2.5 Gy of X-rays. Although 3AB delayed the rejoining of DNA ssb, this delay did not result in increased cytogenetic damage manifested as either SCE or fragmentation of PCC. These results indicate that the rapidly rejoining DNA ssb are not important in the production of chromosome damage.