Received for publication March 31, 2005.
Revised May 2, 2005.
Accepted for publication May 18, 2005.

Diketo hexenoic acid (DKHA) derivatives are novel selective non-nucleoside inhibitors of mammalian terminal deoxynucleotidyl transferases, with potent cytotoxic effect against leukemic cells

Abstract

Mammalian terminal deoxyribonucleotidyl transferase (TDT) catalyzes the non-template-directed polymerization of deoxyribonucleoside triphosphates and has a key role in V(D)J recombination during lymphocyte and repertoire development. Over 90% of leukemic cells in acute lymphocytic leukemia and approximately 30% of leukemic cells in the chronic myelogenous leukemia crisis show elevated TDT activity. This finding is connected to a poor prognosis and response to chemotherapy and reduced survival time. On the other hand, recent data indicated that TDT is not the only terminal deoxyribonucleotidyl transferase in mammalian cells. Its close relative, DNA polymerase can synthesise DNA both in a template dependent (polymerase) and template-independent (terminal deoxyribonucleotidyl transferase) fashion. DNA polymerase might be involved in the nonhomologous end joning (NHEJ) recombinational repair pathway of DNA double strand breaks. In this work we report the characterisation of the mechanism of action of three diketo hexenoic acid (DKHA) derivatives, which proved to be extremely selective for the terminal deoxyribonucleotidyl transferase activity of DNA polymerase lambda and TDT. They appear to be the first non-nucleoside specific inhibitors of mammalian terminal transferases reported so far. Moreover, the DKHA analog RDS2119 was not toxic towards HeLa cells (CC₅₀ > 100 µM), whereas it showed significant cytotoxicity against the TDT⁺ leukemia cell line MOLT-4 (CC₅₀ = 14.9 µM), thus having the potential to be further developed as a novel antitumor agent.

Key words: Thermodynamic and kinetic processes and modeling, DNA damage and repair, Protein targets, Mechanisms of cell killing/apoptosis