Apoptotic and genotoxic effects of a methyl sulfonate ester that selectively generates N3-methyladenine and poly(ADP-ribose) polymerase inhibitors in normal peripheral blood lymphocytes.
Selective N3-adenine methylation represents a novel strategy for tumors with a phenotype of poor responsiveness to a number of anticancer agents currently used in the clinic. Resistance to N3-methyladenine-inducing agents, such as MeOSO(2)(CH(2))(2)-lexitropsin (Me-Lex), is due to high levels of N-methylpurine glycosylase (MPG). However, tumor cells with high MPG activity can be rendered susceptible to Me-Lex using poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors.


OBJECTIVE
To evaluate the potential toxicity of Me-Lex, used as single agent or combined with PARP-1 inhibitors, in normal peripheral blood lymphocytes (PBL).


METHODS
PBL either resting or activated with phytohemagglutinin (PHA), obtained from healthy donors, were treated with graded concentrations of Me-Lex with or without PARP-1 inhibitor (3-aminobenzamide, AB, or NU1025, NU). MPG activity, apoptosis and sister chromatid exchanges (SCE) were evaluated.


RESULTS
(a) Me-Lex was cytotoxic mainly in PHA-activated PBL with low MPG activity; (b) combined treatment with Me-Lex and AB induced apoptotic effects as early as 24 h after drug exposure both in non-stimulated and PHA-activated PBL. When concentrations of PARP-1 inhibitors (25 microM NU and 4 m M AB) that produced a twofold increase in Me-Lex cytotoxicity in tumor cells were compared, NU induced a less-pronounced increase in apoptosis in PBL treated with Me-Lex; (c) Me-Lex at concentrations that allowed cytogenetic analysis did not induce a significant number of SCE; (d) PARP-1 inhibitors provoked a dose-dependent increase in SCE, but 25 microM NU was devoid of genotoxic effects and did not significantly increase SCE in PBL treated with Me-Lex.


CONCLUSIONS
Me-Lex showed preferential cytotoxicity against mitogen-activated PBL. Our results also indicated that for each PARP-1 inhibitor it is necessary to define the concentration devoid of genotoxic effects in normal cells, but still capable of enhancing the efficacy of DNA-damaging agents in tumor cells.
Tentori
Lucio
L
Department of Neuroscience, University of Rome Tor Vergata, Via Montpellier 1, 00133 Rome, Italy.
Portarena
Ilaria
I
Vernole
Patrizia
P
Gold
Barry
B
Graziani
Grazia
G
D000477:Alkylating Agents / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000633:toxicity*; D005434:Flow Cytometry; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation / Q000187:drug effects; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D009153:Mutagens / Q000633:toxicity*; D009429:Netropsin / Q000031:analogs & derivatives* / Q000633:toxicity*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D012016:Reference Values; D014407:Tumor Cells, Cultured
D000477:Alkylating Agents; D004791:Enzyme Inhibitors; D009153:Mutagens; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C110963:methyl lexitropsin; D009429:Netropsin