Profound toxicity of deoxyadenosine and 2-chlorodeoxyadenosine toward human monocytes in vitro and in vivo

Phase II study of 2-chlorodeoxyadenosine plus idarubicin for children with acute myeloid leukaemia in first relapse: a paediatric oncology group study

Relapse remains the leading cause of death in patients with acute myeloid leukaemia (AML). Relatively few new chemotherapy agents have been proven to be effective in this population. We report on a Phase 2 clinical trial using the novel combination of 2-chlorodeoxyadenosine (2-CDA) (8 mg/m² per d x 5 d) plus idarubicin (Ida) (10 mg/m² per d x 3 d). The study involved 109 paediatric patients with AML at first relapse, of whom 104 were available for analysis. The overall response rate was 51% (complete response [CR] + partial response) with a CR rate of 46%. 2-year event-free survival (EFS) and overall survival (OS) were 20% and 26%. The only significant variable in determining response, EFS and OS was duration of initial remission, with patients who had an initial remission >1 year having much worse outcomes overall (response rate 74% vs. 25%, EFS 8% vs. 37% and OS of 16% vs. 39%, P < 0.01 for all). There was an acceptable toxicity profile with one neurological event and no cardiac events observed. The most common grade 3-4 toxicities observed were neutropenia (59%) and thrombocytopenia (68%). This study demonstrated that the novel combination of 2-CDA/Ida was effective and should be considered for incorporation in front line therapy for children with AML.

Treatment of advanced mycosis fungoides/Sézary syndrome with fludarabine and potential adjunctive benefit to subsequent extracorporeal photochemotherapy

BACKGROUND

Purine analogues [fludarabine monophosphate (FAMP); deoxycoformycin and 2-chlorodeoxyadenosine) and extracorporeal photochemotherapy (ECP) have been suggested to be active agents in advanced cutaneous T-cell lymphoma (CTCL) patients.

OBJECTIVES

To explore further the clinical efficacy and safety of FAMP monochemotherapy in advanced CTCL and to evaluate if the sequential association of ECP to FAMP in selected patients may improve the response rate (RR) and/or lengthen the remission duration.

PATIENTS AND METHODS

Forty-four CTCL patients [17 Sézary syndrome (SS); 26 mycosis fungoides (MF), stage IIB-IV or with peripheral blood involvement; one MF associated with lymphomatoid papulosis (LyP)] were enrolled in this pilot cohort study. All the patients received FAMP 25 mg m(-2) 5 days monthly; 19 patients (43.2%) underwent ECP after FAMP was discontinued. The majority of patients with erythrodermic CTCL or peripheral blood involvement underwent the combined FAMP-ECP schedule.

RESULTS

After a median follow-up of 4.2 years, the overall FAMP RR was 29.5% (13/44); a higher RR was obtained in SS (35.3%) than in MF patients (25.9%). According to the treatment group, the RR of the FAMP-ECP group (63.2%) was significantly higher than that of the FAMP monotherapy group (24%; P=0.021). No statistically significant difference was found in time-to-progression (TTP) or survival by therapy group, even if the TTP of the patients treated with the FAMP-ECP combination therapy was higher (median 13 vs. 7 months). A decrease or a normalization in the CD4+CD26- circulating subset was observed in responding patients, paralleling the reduction in the circulating Sézary cells.

CONCLUSIONS

FAMP confirms its clinical activity as a single agent in SS; conversely, FAMP results do not compare favourably with other therapeutic approaches for advanced stage MF patients. The sequential association of ECP after FAMP seems to increase the RR, even if future randomized studies are needed to confirm these results.

The Antileukemia Drug 2-Chloro-2′-deoxyadenosine: An Intrinsic Transcriptional Antagonist

The nucleoside analog 2-chloro-2'-deoxyadenosine (CldAdo; cladribine) is effective in the treatment of hairy cell leukemia and chronic lymphocytic leukemia. CldAdo is phosphorylated and incorporated into cellular DNA but is not an absolute chain terminator. We demonstrated by in vitro gel-shift assays that binding interactions of the human TATA box-binding protein (TBP) were disrupted on 2-chlorodeoxyadenosine monophosphate (CldAMP)-substituted TATA box consensus sequences. We hypothesized that human RNA polymerase II (pol II) transcriptional processes would therefore be affected by 2-chlorodeoxyadenosine triphosphate (CldATP) incorporation into a promoter TATA element. Double-stranded DNA templates containing the adenovirus major late promoter and coding sequences were enzymatically synthesized as control or with site-specific CldAMP residues, incubated with HeLa extract, and the synthesis of radiolabeled 44-base transcripts was assessed. With increasing amounts of HeLa extract, CldAMP substitution for dAMP within the TATA box decreased in vitro pol II transcription by approximately 35% compared with control substrates. Time-course studies showed that transcript production increased in a linear fashion on control substrates. In contrast, transcription on CldAMP-substituted TATA sequences reached a plateau after 20 min. Furthermore, CldAMP-substituted promoter sequences trapped or sequestered TBP, preventing its dissociation from DNA and subsequent binding to additional TATA elements to reinitiate transcription. CldAdo thus represents the first example of a nucleoside analog that acts as a transcriptional antagonist. CldATP incorporation into gene regulatory sequences may provide a novel strategy to modulate specific protein/DNA interactions.

2 chlorodeoxyadenosine activity and cross resistance patterns in primary cultures of human hematologic neoplasms

2-Chlorodeoxyadenosine (2-CDA) is an adenosine deaminase resistant analogue of deoxyadenosine which has shown clinical activity in human hematologic neoplasms. The exact mode of action of this drug remains the subject of investigation. We applied the Differential Staining Cytotoxicity (DiSC) assay to 50 human tumour specimens obtained from patients with a variety of hematologic malignancies to characterise the activity spectrum of 2-CDA. We evaluated the disease-specific activity of this agent in vitro and compared its relative cytotoxicity with that of other antineoplastic agents in current clinical use. Comparisons were conducted against nitrogen mustard, doxorubicin, vincristine and cytosine arabinoside. Our results indicate that 2-CDA has activity in myeloid and many lymphoid neoplasms but that multiple myeloma specimens reveal significant resistance. Cross resistance studies reveal a correlation between 2-CDA and the alkylator nitrogen mustard but no correlation between 2-CDA and doxorubicin, vincristine nor cytosine arabinoside. The results suggest 2-CDA activity in many human hematologic neoplasms with the clear exception of multiple myeloma and further suggest a relationship between this agent and alkylators of the mustard class. The DiSC assay may provide useful insights in the pre-clinical evaluation of new antineoplastic drugs and may help to elucidate drug activities and mechanisms of action.

Metabolism and action of purine nucleoside analogs

Recent investigations have identified many new purine nucleoside analogs that act as antimetabolites. This article focuses on the metabolism and mechanisms of action of tiazofurin, 3-deazaguanosine, neplanocin A, arabinosyladenine in combination with inhibitors of adenosine deaminase, arabinosyl-2-fluoroadenine, and 2-chloro-2'-deoxyadenosine, drugs that are either currently being evaluated in clinical trials or are close to that stage. The diverse metabolic requirements for activation, unique mechanisms of action, and differential biological activities of these compounds are characterized and evaluated for prospective therapeutic application.