tetrahydrouridine and Lymphoma

One mechanism by which lymphoid malignancies resist standard apoptosis-intending (cytotoxic) treatments is genetic attenuation of the p53/p16-CDKN2A apoptosis axis. Depletion of the epigenetic protein DNA methyltransferase 1 (DNMT1) using the deoxycytidine analog decitabine is a validated approach to cytoreduce malignancy independent of p53/p16. In vivo decitabine activity, however, is restricted by rapid catabolism by cytidine deaminase (CDA). We, therefore, combined decitabine with the CDA-inhibitor tetrahydrouridine and conducted a pilot clinical trial in patients with relapsed lymphoid malignancies: the doses of tetrahydrouridine/decitabine used (∼10/0.2 mg/kg orally (PO) 2×/week) were selected for the molecular pharmacodynamic objective of non-cytotoxic, S-phase dependent, DNMT1-depletion, guided by previous Phase 1 studies. Patients with relapsed/refractory B- or T-cell malignancies (n = 7) were treated for up to 18 weeks. Neutropenia without concurrent thrombocytopenia is an expected toxicity of DNMT1-depletion and occurred in all patients (Grade 3/4). Subjective and objective clinical improvements occurred in 4 of 7 patients, but these responses were lost upon treatment interruptions and reductions to manage neutropenia. We thus performed parallel experiments in a preclinical in vivo model of lymphoma to identify regimen refinements that might sustain DNMT1-targeting in malignant cells but limit neutropenia. We found that timed-alternation of decitabine with the related molecule 5-azacytidine, and combination with inhibitors of CDA and de novo pyrimidine synthesis could leverage feedback responses of pyrimidine metabolism to substantially increase lymphoma cytoreduction but with less neutropenia. In sum, regimen innovations beyond incorporation of a CDA-inhibitor are needed to sustain decitabine DNMT1-targeting and efficacy against chemo-resistant lymphoid malignancy. Such potential solutions were explored in preclinical in vivo studies.

Topics: Antimetabolites, Antineoplastic; Azacitidine; Decitabine; Epigenesis, Genetic; Humans; Lymphoma; Pilot Projects; Tetrahydrouridine

In conventional clinical use, cytosine arabinoside (ara-C) is rapidly deaminated by pyrimidine nucleoside deaminase to the nontoxic compound uracil arabinoside. Tetrahydrouridine (THU) effectively inhibits this enzymatic degradation but is by itself nontoxic. This study demonstrates that concomitant administration of THU markedly increases the myelosuppressive potency of ara-C. When 25 or 50 mg/kg of THU iv and 0.1--0.2 mg/kg of ara-C iv are given daily x 5 days, they produce moderate-to-severe leukopenia and mild-to-moderate thrombocytopenia. A dose of 25 mg/kg of THU with 0.1 mg/kg of ara-C iv daily x 5 days appears appropriate for phase II studies; it produces myelosuppression equivalent to that produced by 3 mg/kg/day x 5 days of ara-C alone. No toxicity occurred with this combination that would not have been expected from ara-C given alone in an equitoxic dose. Although THU and ara-C produced a reduction in peripheral blood and bone marrow blast cells in eight of nine patients with acute leukemia, bone marrow remission did not occur in any of these heavily pretreated patients.

Topics: Bone Marrow; Clinical Trials as Topic; Cytarabine; Drug Evaluation; Drug Synergism; Drug Therapy, Combination; Humans; Leukemia; Lymphoma; Middle Aged; Neoplasms; Nucleoside Deaminases; Pyrimidine Nucleosides; Tetrahydrouridine; Uridine