The relative sensitivity of peripheral blood T-lymphocyte colony forming cells and bone marrow CFU-GM to deoxyadenosine and 2'deoxycoformycin

Pentostatin and purine analogs for indolent lymphoid malignancies

Pentostatin has been shown to be active in a variety of B- and T-cell malignancies. The drug is a tight inhibitor of adenosine deaminase, a key degradative enzyme of purine metabolism present in all human tissues, with the highest levels found in the lymphoid system. Early clinical trials indicated that this agent was highly active in acute lymphoblastic leukemias with high intracellular adenosine deaminase levels. Relatively high doses of the drug were needed, which was associated with severe adverse events. Through the efforts of a few investigators, better tolerated, low-dose regimens have been shown to be extremely active in lymphoproliferative diseases with very low intracellular adenosine deaminase levels such as hairy cell leukemia, B- and T-cell chronic leukemias, T-cell cutaneous lymphomas and low-grade non-Hodgkin lymphomas. Clinical as well as experimental data have indicated that this drug induces lymphocyte-specific cytotoxicity, and myelosuppressive adverse events have been minimal. Although all the purine analogs have shown similar activity, the advantage of pentostatin is the relatively specific cytotoxicity against lymphocytes, which permits treatment even in patients with severe cytopenias. Although no direct comparisons of the purine analogs have been performed, pentostatin may be preferred due to this property.

Selective toxicity of purine nucleosides to human leukaemic cells

The in vitro cytotoxicity of various purine nucleosides and purine enzyme inhibitors, alone or in combination, and of the alkylating agent mafosfamide (Asta Z7557), incubated for 4 and 24 h have been studied in 17 leukaemic cell lines and normal bone marrow (BM). The purine nucleosides and their analogues included: 2'chlorodeoxyadenosine (CdA), 2'deoxyadenosine (AdR), 3'deoxyadenosine (3'AdR) (cordycepin), adenosine (AR), adenine arabinoside (Ara-A), deoxyguanosine (GdR) and guanine arabinoside (Ara-G). Purine enzyme inhibitors included 2-deoxycoformycin (dCF) and 8-aminoguanosine (8-AG). Cytotoxicity was based on inhibition of (i) incorporation of 3H-leucine into cell proteins and (ii) colony forming units--granulocytic/monocytic (CFU-GM) and for mixed cell colonies (CFU-GEMM). Marked and selective inhibition of T-cell growth was shown by the combinations dCF with either AdR or Ara-A, 8-AG and GdR and by CdA or Ara-G alone; these compounds even at high concentrations produced only partial inhibition of the growth of normal bone marrow CFU-GM and CFU-GEMM except for CdA which completely inhibited the formation of CFU-GEMM colonies. The combination dCF + cordycepin and alkylating agent mafosfamide were, however, toxic to all the cell lines at the concentrations employed, as well as to CFU-GM and CFU-GEMM. The high therapeutic index of some of the purine nucleosides with a relatively short exposure time makes them candidates for selective in vitro removal of residual neoplastic cells in autologous bone marrow transplantation (ABMT) for T-ALL.

Inability of poly-ADP-ribosylation inhibitors to protect peripheral blood lymphocytes from the toxic effects of ADA inhibition

We have evaluated the effectiveness of two inhibitors of poly-ADP-ribosylation, nicotinamide and 3-aminobenzamide as rescue agents in resting and PHA-stimulated lymphocytes damaged by the combination of deoxycoformycin (dCF) plus deoxyadenosine (dAdo). Incubation with dCF (10(-5)M) and dAdo (10(-4)M) for 18 hours, inhibited protein and RNA synthesis in unstimulated lymphocytes and impaired the ability of the cells to respond to PHA stimulation or to give rise to T-cell colonies in methyl-cellulose. Predominantly dead cells using trypan blue exclusion were observed at day 4, in both unstimulated and PHA-stimulated lymphocytes, whether or not the drugs were removed at 18 hours. The number of viable cells at day 4 increased from 13.7% to 41.1% with the addition of 5 mM nicotinamide, and to 28.8% with 5 mM 3-aminobenzamide added with dCF and dAdo. Although nicotinamide was able to prevent a fall in NAD concentration for 24h (but not for 48h) and to reduce the fall of cell ATP concentration, the inhibition by dCF and dAdo of protein synthesis, RNA synthesis, ability of cells to form colonies or to respond to PHA was not reversed. We conclude that inhibition of NAD utilisation by inhibiting ADP-ribosylation with nicotinamide or 3-aminobenzamide does not protect cells in vitro from deoxyadenosine toxicity with ADA inhibition and is not likely to give significant clinical benefit in ADA deficiency.

Clinical consequences of 2'-deoxycoformycin treatment in patients with refractory adult T-cell leukaemia

Five patients from the Kyushu area in Japan with adult T-cell leukaemia (ATL) refractory to conventional chemotherapeutic agents were treated with 5 mg/m2 of the adenosine deaminase inhibitor, 2'-deoxycoformycin (DCF), intravenously (i.v.) for 3 consecutive days, followed by 5 mg/m2 i.v. weekly. Two patients showed a good response, and three were resistant to DCF. One patient with ATL receiving DCF had a continuous remission without further therapy. Another patient in the terminal stage received three daily injections of 7.5 mg of DCF. The most prominent change was the drop in the leucocyte count. The cell count fell from 116.4 X 10(9)/l to 2.0 X 10(9)/l on day 7. The only adverse effects of DCF therapy were gastrointestinal toxicity, nausea and vomiting. These results suggest that DCF may be a valuable drug for treating refractory ATL.