Chlorodeoxyadenosine and arabinosylcytosine in patients with acute myelogenous leukemia: pharmacokinetic, pharmacodynamic, and molecular interactions

Abstract

The effectiveness of arabinosylcytosine (ara-C) for the treatment of acute myelogenous leukemia (AML) depends on the formation of its active metabolite, the triphosphate of ara-C (ara-CTP). Using biochemical modulation strategies to increase the accumulation of ara-CTP in leukemia blasts, a clinical protocol was designed combining 2- chlorodeoxyadenosine (CdA), an inhibitor of ribonucleotide reductase, and ara-C for adults with AML. The protocol stipulated an infusion of 1 g/m2 of ara-C over 2 hours on day 1. A continuous infusion of CdA (12 mg/m2/d) begun 24 hours later and continued for 5 days. Identical doses of ara-C were administered on days 3, 4, 5, and 6. Pharmacokinetic and pharmacodynamic interactions between CdA and ara-C during therapy were investigated. To complement these studies, molecular actions of the triphosphate of ara-C and CdA on DNA extension by human DNA polymerase alpha in an in vitro model system was conducted. In the circulating leukemia blasts of 7 of the 9 patients studied, ara-CTP pharmacokinetics showed a median 40% increase in the rate of ara-CTP accumulation after 24 hours of CdA infusion. The ex vivo effect of CdA on accumulation of ara-CTP in AML blasts was similar to that during therapy except that the enhancement was less. The DNA synthetic capacity of the circulating blasts was inhibited to a greater extent by administration of CdA and ara-C in combination than by either one alone. Additionally the lowered level of DNA synthesis was maintained until the next infusion of ara-C. Endogenous levels of deoxynucleotides increased 24 hours after ara-C infusion. Administration of CdA in general lowered the concentrations of all dNTPs. DNA pol alpha incorporated CdATP and ara-CTP with high affinity in a DNA primer extending over an oligonucleotide template of defined sequence. Human DNA polymerase alpha extended DNA primers terminated by CdA monophosphate (CdAMP) at its 3′-end by incorporating ara-C monophosphate (ara-CMP). The tandem incorporation of CdAMP and ara-CMP resulted in nearly complete inhibition of DNA primer extension. The insertion of two analogs in sequence, inhibition of ribonucleotide reductase, and the metabolic potentiation of ara-CTP by CdA infusion may be responsible for sustained inhibition of DNA synthesis in the circulating leukemia blasts during therapy with this combination regimen.

Phase II Study of Venetoclax Added to Cladribine Plus Low-Dose Cytarabine Alternating With 5-Azacitidine in Older Patients With Newly Diagnosed Acute Myeloid Leukemia

“…7 The combination of another nucleoside analog such as fludarabine or cladribine (CLAD) with cytarabine maximizes intracellular concentrations of ara-cytosine triphosphate providing synergistic antileukemic activity. 8,9 To exploit this synergy, we previously studied a lowerintensity regimen combining LDAC with CLAD (CLAD/ LDAC) in a phase II study. 10 Among 118 patients, with a median age of 69 years, the CR/CRi rate was 68%, median OS was 13.8 months, and 4-week mortality was 1%.…”

Venetoclax in combination with nucleoside analogs in acute myelogenous leukemia

“…Cladribine has modest activity as a single agent. Similar to fludarabine, pretreatment with cladribine enhanced intracellular cytarabine accumulation in leukemic blasts by as much as 50–65% [33,34]. Cladribine, but not fludarabine improved efficacy of 7 + 3 induction in a randomized phase 3 study [35].…”

Cladribine, Cytarabine, and Etoposide-Based Regimens Are Safe and Tolerable In Relapsed and Refractory Acute Myeloid Leukemia Patients

“…Additionally, purine analogs (e.g., fludarabine, cladribine, clofarabine) have shown to be beneficial in AML, providing time sequential synergistic effect by delaying cytarabine metabolism via dephosphorylation and thus potentiates its activity in AML [3, 4]. Regimens like FLAG +/− Ida (fludarabine, cytarabine, G-CSF, idarubicin) and CLAG +/−M (cladribine, cytarabine, G-CSF, mitoxantrone) utilize this concept and are commonly used in the R/R setting.…”