2',3'-Dideoxyadenosine is selectively toxic for TdT-positive cells

Abstract

The 2′,3′-dideoxynucleosides (ddNs) are currently undergoing clinical evaluation as antiretroviral agents in HIV-infected individuals. When phosphorylated, the ddNs (ddNTPs) function as chain-terminating substrate analogues with reverse transcriptase, thereby inhibiting HIV replication. These nucleoside analogues can also inhibit, by chain- terminating additions, the primitive lymphoid DNA polymerase, terminal deoxynucleotidyl transferase (TdT). To determine the effect of possible intracellular chain-terminating additions of ddNMPs by TdT, we exposed a series of TdT-positive and TdT-negative cell lines to 2′,3′- dideoxyadenosine (ddA), a representative ddN. At ddA concentrations 25- fold higher than required for inhibition of HIV replication, progressive dose-related cytotoxicity was observed in the TdT-positive cell lines. This was accentuated by the adenosine deaminase inhibitor Coformycin (CF), presumably by enhancing the intracellular generation of ddATP from ddA. A central role of TdT in mediating the ddA/CF cytotoxicity was suggested by studies in a pre-B-cell line rendered TdT positive by infection with a TdT cDNA-containing retroviral vector. After a 48-hour continuous exposure period to 250 mumol/L ddA and 30 mumol/L CF, 30% cell death was observed in the TdT-negative parental line, whereas 90% cell death was observed in the TdT-positive daughter line. Exposure of fresh TdT-positive leukemic cells to ddA/CF for 72 hours ex vivo resulted in cytotoxicity (six cases of acute lymphocytic leukemia [ALL]) while not affecting TdT-negative acute leukemic cells (six cases). We conclude that ddA/CF selectively damages TdT-positive cells, presumably by chain-terminating additions of ddAMP, and that this may have therapeutic relevance in TdT-positive malignant disease.

A Non-natural Nucleoside with Combined Therapeutic and Diagnostic Activities against Leukemia

“…6,7 The ability of TdT to randomly incorporate dNTPs promotes immunological diversity during an immune response. 8 Indeed, TdT activity increases antigen receptor diversity by facilitating the generation of ∼10 14 different immunoglobulins and ∼10 18 unique T cell antigen receptors that are required to neutralize potential antigens. 9,10 TdT is also noteworthy for its role in cancer as it is overexpressed in acute lymphocytic leukemia (ALL) and acute myelocytic leukemia (AML).…”

“…One noteworthy example is the nucleoside analogue cordycepin (3′-deoxyadenosine) (Figure A) that lacks a 3′-OH and thus terminates DNA synthesis after its incorporation into DNA. This analogue produces cytotoxic effects against TdT-positive leukemia, especially when combined with the adenosine deaminase inhibitor, deoxycoformycin. , Unfortunately, cordycepin is not a truly selective TdT inhibitor as it is also utilized by template-dependent DNA polymerases involved in chromosomal DNA synthesis . The ability of these polymerases to incorporate but not elongate cordycepin terminates DNA synthesis in both cancerous and healthy cells.…”