Clofarabine for the treatment of acute lymphoblastic leukemia

Clofarabine added to intensive treatment in adult patients with newly diagnosed ALL: the HOVON-100 trial

Clofarabine (CLO) is a nucleoside analogue with efficacy in relapsed/refractory acute lymphoblastic leukemia (ALL). This randomized phase III study aimed to evaluate whether CLO added to induction and consolidation would improve outcome in adults with newly diagnosed ALL. Treatment for younger (18-40 years) patients consisted of a pediatric inspired protocol and for older patients (41-70 years) of a semi-intensive protocol was used. 340 patients were randomized. After a median follow up of 70 months, 5-year EFS was 50% and 53% for arm A and B (CLO arm). For patients ≤40 years, EFS was 58% vs 65% in arm A vs B, while in patients >40 years EFS was 43% in both arms. CR rate was 89% in both arms and similar in younger and older patients. Minimal residual disease (MRD) was assessed in 200 patients (60%). Fifty-four of 76 evaluable patients (71%) were MRD negative after consolidation 1 in arm A vs 75/81 (93%) in arm B (p=0.001). Seventy (42%) patients proceeded to allogeneic hematopoietic stem cell transplantation in both arms. Five years OS was similar in both arms, 60% vs 61%. Among patients achieving CR, relapse rates were 28% and 24%, and non-relapse mortality was 16% vs 17% after CR. CLO treated patients experienced more serious adverse events, more infections, and more often went off-protocol. This was most pronounced in older patients. We conclude that, despite a higher rate of MRD-negativity, addition of CLO does not improve outcome in adults with ALL, which might be due to increased toxicity. The trial is registered at www.trialregister.nl as NTR2004.

Effectiveness and Safety of Clofarabine Monotherapy or Combination Treatment in Relapsed/Refractory Childhood Acute Lymphoblastic Leukemia: A Pragmatic, Non-interventional Study in Korea

Purpose

Effectiveness and safety of clofarabine (one of the treatment mainstays in pediatric patients with relapsed/refractory acute lymphoblastic leukemia [ALL]) was assessed in Korean pediatric patients with ALL to facilitate conditional coverage with evidence development.

Materials and Methods

In this multicenter, prospective, observational study, patients receiving clofarabine as mono/combination therapy were followed up every 4–6 weeks for 6 months or until hematopoietic stem cell transplantation (HSCT). Response rates, survival outcomes, and adverse events were assessed.

Results

Sixty patients (2–26 years old; 65% B-cell ALL, received prior ≥ 2 regimen, 68.3% refractory to previous regimen) were enrolled and treated with at least one dose of clofarabine; of whom 26 (43.3%) completed 6 months of follow-up after the last dose of clofarabine. Fifty-eight patients (96.7%) received clofarabine combination therapy. Overall remission rate (complete remission [CR] or CR without platelet recovery [CRp]) was 45.0% (27/60; 95% confidence interval [CI], 32.4 to 57.6) and the overall response rate (CR, CRp, or partial remission [PR]) was 46.7% (28/60; 95% CI, 34.0 to 59.3), with 11 (18.3%), 16 (26.7%), and one (1.7%) patients achieving CR, CRp, and PR, respectively. The median time to remission was 5.1 weeks (95% CI, 4.7 to 6.1). Median duration of remission was 16.6 weeks (range, 2.0 to 167.6 weeks). Sixteen patients (26.7%) proceeded to HSCT. There were 24 deaths; 14 due to treatment-emergent adverse events.

Conclusion

Remission with clofarabine was observed in approximately half of the study patients who had overall expected safety profile; however, there was no favorable long-term survival outcome in this study.

Versatile synthesis and biological evaluation of novel 3'-fluorinated purine nucleosides

A unified synthetic strategy accessing novel 3'-fluorinated purine nucleoside derivatives and their biological evaluation were achieved. Novel 3'-fluorinated analogues were constructed from a common 3'-deoxy-3'-fluororibofuranose intermediate. Employing Suzuki and Stille cross-coupling reactions, fifteen 3'-fluororibose purine nucleosides 1-15 and eight 3'-fluororibose 2-chloro/2-aminopurine nucleosides 16-23 with various substituents at position 6 of the purine ring were efficiently synthesized. Furthermore, 3'-fluorine analogs of natural products nebularine and 6-methylpurine riboside were constructed via our convergent synthetic strategy. Synthesized nucleosides were tested against HT116 (colon cancer) and 143B (osteosarcoma cancer) tumor cell lines. We have demonstrated 3'-fluorine purine nucleoside analogues display potent tumor cell growth inhibition activity at sub- or low micromolar concentration.

Clinical Characteristics and Treatment of Langerhans Cell Histiocytosis

Langerhans cell histiocytosis (LCH) is a disease caused by clonal proliferation of CD1a+/CD207+ cells that is characterized by a spectrum of varying degrees of organ involvement and dysfunction. Treatment of LCH is risk adapted; patients with single lesions may respond well to local treatment, whereas patients with multi-system disease and risk-organ involvement require more intensive therapy. Although survival for patients without organ dysfunction is excellent, mortality rates for patients with organ dysfunction may reach 30% to 40%. For patients with low-risk disease, although cure is almost universal, disease reactivation rates are in excess of 30%.

Clofarabine salvage therapy in refractory multifocal histiocytic disorders, including Langerhans cell histiocytosis, juvenile xanthogranuloma and Rosai-Dorfman disease

BACKGROUND

Existing therapies for recurrent or refractory histiocytoses, including Langerhans cell histiocytosis (LCH), juvenile xanthogranuloma (JXG), and Rosai-Dorfman disease (RDD), have limited effectiveness. We report our experience with using clofarabine as therapy in children with recurrent or refractory histiocytic disorders, including LCH (11 patients), systemic JXG (4 patients), and RDD (3 patients).

METHODS

Patients treated with clofarabine for LCH, JXG, or RDD by Texas Children's Hospital physicians or collaborators between May 2011 and January 2013 were reviewed for response and toxicity.

RESULTS

Patients were treated with a median of three chemotherapeutic regimens prior to clofarabine. Clofarabine was typically administered at 25 mg/m(2) /day for 5 days. Cycles were administered every 28 days for a median of six cycles (range: 2-8 cycles). Seventeen of 18 patients are alive. All surviving patients showed demonstrable improvement after two to four cycles of therapy, with 11 (61%) complete responses, 4 (22%) partial responses, and 2 patients still receiving therapy. Five patients experienced disease recurrence, but three of these subsequently achieved complete remission. All patients with JXG and RDD had complete or partial response at conclusion of therapy. Side effects included neutropenia in all patients. Recurring but sporadic toxicities included prolonged neutropenia, severe vomiting, and bacterial infections.

CONCLUSION

Clofarabine has activity against LCH, JXG, and RDD in heavily pretreated patients, but prospective multi-center trials are warranted to determine long-term efficacy, optimal dosing, and late toxicity of clofarabine in this population.

Clofarabine salvage therapy for refractory high-risk langerhans cell histiocytosis

Pediatric patients with refractory multisystem Langerhans cell histiocytosis (LCH) have a poor prognosis despite aggressive chemotherapy. Salvage therapy with cytarabine and cladribine has shown promise as an effective treatment but is associated with significant toxicity. A previous report described two patients with refractory LCH who had a rapid response to single-agent clofarabine with minimal toxicity. In this report, we describe four children with refractory, risk-organ-positive LCH who were treated with clofarabine and provide follow-up for the two previously reported cases. The results support development of a formal trial evaluating clofarabine as front-line salvage for refractory LCH.

Investigation of reactions postulated to occur during inhibition of ribonucleotide reductases by 2'-azido-2'-deoxynucleotides

Model 3'-azido-3'-deoxynucleosides with thiol or vicinal dithiol substituents at C2' or C5' were synthesized to study reactions postulated to occur during inhibition of ribonucleotide reductases by 2'-azido-2'-deoxynucleotides. Esterification of 5'-(tert-butyldiphenylsilyl)-3'-azido-3'-deoxyadenosine and 3'-azido-3'-deoxythymidine (AZT) with 2,3-S-isopropylidene-2,3-dimercaptopropanoic acid or N-Boc-S-trityl-L-cysteine and deprotection gave 3'-azido-3'-deoxy-2'-O-(2,3-dimercaptopropanoyl or cysteinyl)adenosine and the 3'-azido-3'-deoxy-5'-O-(2,3-dimercaptopropanoyl or cysteinyl)thymidine analogs. Density functional calculations predicted that intramolecular reactions between generated thiyl radicals and an azido group on such model compounds would be exothermic by 33.6-41.2 kcal/mol and have low energy barriers of 10.4-13.5 kcal/mol. Reduction of the azido group occurred to give 3'-amino-3'-deoxythymidine, which was postulated to occur with thiyl radicals generated by treatment of 3'-azido-3'-deoxy-5'-O-(2,3-dimercaptopropanoyl)thymidine with 2,2'-azobis-(2-methyl-2-propionamidine) dihydrochloride. Gamma radiolysis of N(2)O-saturated aqueous solutions of AZT and cysteine produced 3'-amino-3'-deoxythymidine and thymine most likely by both radical and ionic processes.

Treating refractory leukemias in childhood, role of clofarabine

Approximately 4000 children and adolescents under the age of 20 years develop acute leukemia per year in the US. Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. Despite impressive improvements in outcome, relapsed ALL is the fourth most common pediatric malignancy. Therapy for relapsed ALL remains unsatisfactory, and the majority of relapse patients still succumb to leukemia. Between one-third and one-half of patients with acute myelogenous leukemia (AML) relapse, and no standard therapy is recognized for patients with relapsed and/or refractory AML. Novel therapeutic agents are needed to improve the cure rate for relapsed ALL and AML. Clofarabine is a next-generation nucleoside analog, designed to incorporate the best features and improve the therapeutic index of cladribine and fludarabine. Clofarabine inhibits both DNA polymerase and ribonucleotide reductase, leading to impaired DNA synthesis and repair, and directly induces apoptosis. Phase I and II single-agent trials in children have shown that clofarabine is safe and active in both myeloid and lymphoid relapsed/refractory acute leukemias. Clofarabine has been approved by the FDA for pediatric patients with relapsed/refractory ALL after at least 2 prior therapeutic attempts. Rational combinations of clofarabine with other active agents in refractory leukemias are currently under investigation.

Sugar-modified derivatives of cytostatic 6-(het)aryl-7-deazapurine nucleosides: 2′-C-methylribonucleosides, arabinonucleosides and 2′-deoxy-2′-fluoroarabinonucleosides

A series of novel sugar-modified derivatives of cytostatic 6-hetaryl-7-deazapurine ribonucleosides: 2′-C-methylribonucleosides, arabinonucleosides and 2′-deoxy-2′-fluoroarabinonucleosides bearing an alkyl, aryl and hetaryl group in position 6 were prepared by palladium catalyzed cross-coupling reactions of corresponding (protected) 6-chloro-(7-fluoro)-7-deazapurine nucleosides with (het)arylboronic, hetarylstannanes and trimethylaluminium eventually followed by deprotection. Key intermediate 6-chloro-7-deazapurine 2′-C-methyl-β-D-ribofuranoside was prepared via a stereoselective nucleobase anion glycosylation with toluoyl-protected 1,2-anhydro-2-C-methylribofuranose. The 1,2-anhydro sugar was synthesized in 3 steps starting from readily available 2-C-methylribonolactone. The 6-chloro-7-deazapurine arabinofuranoside intermediate was obtained by epimerization from 3′,5′-protected 6-chloro-7-deazapurine ribofuranoside via 2′-hydroxyl oxidation followed by reduction. None of the prepared compounds showed any considerable cytostatic or antiviral activity.

Defining the course and prognosis of adults with acute lymphocytic leukemia in first salvage after induction failure or short first remission duration

BACKGROUND

Results from salvage therapy in adult patients with acute lymphocytic leukemia (ALL) are wide-ranging and depend on several disease and patient characteristics. The objectives of this study were to define the prognosis for adult patients with ALL after first salvage through multivariate analyses of patient and disease characteristics.

METHODS

Adults with ALL who had primary resistance to frontline therapy or who had a disease recurrence after a first complete response (CR) duration <1 year were analyzed. Multivariate analyses for subsequent CR and survival were conducted.

RESULTS

Seventy-five of 245 patients (31%) achieved CR. The median CR duration was 5 months, the median survival was 4.7 months. In multivariate analysis, independent poor prognostic factors for not achieving CR were age >55 years, bone marrow blasts ≥20%, and platelet count <75 × 10(9) /L. Variables that were associated independently with shorter survival were age >55 years, bone marrow blasts ≥20%, platelet count <75 × 10(9) /L, albumin level <3 g/L, and lactic dehydrogenase level ≥1000 IU/L. Patients who had ≥3 of the 5 adverse factors (45%) had a median survival of 2 to 3 months and CR rates of 8% to 15%. Achieving CR was associated independently with improved survival in a landmark multivariate analysis (P < .0001; hazard ratio, 0.40; 95% confidence interval, 0.03-0.72).

CONCLUSIONS

The current analyses identified a subset of adults patients ALL in first salvage for whom standard therapies were associated with an extremely poor outcome. The results also confirmed the importance of achieving CR to attain improved survival.

Novel therapies for relapsed acute lymphoblastic leukemia

The outcome of salvage therapy for relapsed acute lymphoblastic leukemia (ALL) remains poor. Salvage therapy mimics regimens with activity in newly diagnosed ALL. Novel strategies under investigation as monotherapy or in combination with chemotherapy improve the treatment of relapsed disease. For some ALL subsets, specific therapies are indicated. The addition of targeted therapy in Philadelphia chromo some-positive ALL has improved responses in relapsed patients without resistance to available tyrosine kinase inhibitors. Nelarabine demonstrates activity as monotherapy in T-cell ALL and is approved by the US Food and Drug Administration. Clofarabine, a second-generation purine analogue approved in pediatric leukemia, has shown activity in adult acute leukemias including ALL and acute myeloid leukemia. The role of pegaspargase in adult ALL requires further investigation. The benefit of matched related-donor allogeneic stem cell transplantation is significant for standard-risk ALL but not for high-risk ALL. Development of new drugs and agents tailored to subset-specific cytogenetic-molecular characteristics remains vital to success in treating adult ALL.

Use of clofarabine for acute childhood leukemia

A second-generation of purine nucleoside analogs, starting with clofarabine, has been developed in the course of the search for new therapeutic agents for acute childhood leukemia, especially for refractory or relapsed disease. Clofarabine is a hybrid of fludarabine and cladribine, and has shown to have antileukemic activity in acute lymphoblastic leukemia as well as in myeloid disorders. As the only new antileukemic chemotherapeutic agent to enter clinical use in the last 10 years, clofarabine was approved as an orphan drug with the primary indication of use in pediatric patients. Toxicity has been tolerable in a heavily pretreated patient population, and clofarabine has been demonstrated to be safe, both as a single agent and in combination therapies. Liver dysfunction has been the most frequently observed adverse event, but this is generally reversible. Numerous Phase I and II trials have recently been conducted, and are still ongoing in an effort to find the optimal role for clofarabine in various treatment strategies. Concomitant use of clofarabine, cytarabine, and etoposide was confirmed to be safe and effective in two independent trials. Based on the promising results when used as a salvage regimen, clofarabine is now being investigated for its potential to become part of frontline protocols.

Emerging therapy for the treatment of acute lymphoblastic leukemia

IMPORTANCE OF THE FIELD

Over the last few decades, advances in acute lymphoblastic leukemia (ALL) therapy have led to long-term survival rates of > 80% in children; however, comparable rates have yet to be achieved in adults, and a large majority of patients relapse from their disease.

AREAS COVERED IN THIS REVIEW

The review describes historical therapy and advancements in ALL treatment over the past few decades, while providing a concise review of the future direction of ALL therapy. Literature was collected through peer reviewed journals and the Pharmaprojects drug profile for ALL.

WHAT THE READER WILL GAIN

Current information regarding prognostic factors for relapse, salvage therapy options and emerging drugs are provided in the review.

TAKE HOME MESSAGE

Development of new drugs with novel mechanisms, unique formulations of existing medications, as well as manipulation of current combinations of drugs remain vital to the success in adult ALL.

Outcome of adults with acute lymphocytic leukemia in second or subsequent complete remission

The outcome of adults with acute lymphocytic leukemia (ALL) who achieve a complete response (CR) on salvage therapy is thought to be poor, but not previously analyzed. To define the course of adult ALL post CR on salvage therapy and the effects of pretreatment factors on prognosis. One hundred seventy-two adults with ALL who achieved a second or third CR on salvage therapy were reviewed. Prognostic factors affecting survival were analyzed by multivariate analysis. The median survival post achieving CR for the entire group was 10 months. The estimated 1-year survival rate was 42%. Forty-three patients underwent stem cell transplant in subsequent CR: their median survival was 12 months and the 3-year survival rate was 25%. Independent poor prognostic factors for survival were age  > 55 years, duration of first CR < 12 months, and lactate dehydrogenase levels > 1000 IU/L. This analysis defines the outcome of adult ALL in CR post salvage therapy and the prognostic factors influencing survival. These results could be used in assessing the efficacy of new treatments aimed at improving CR durations and survival post salvage therapy.

Outcome of adults with acute lymphocytic leukemia after second salvage therapy

BACKGROUND

The outcome of adults with acute lymphocytic leukemia (ALL) who undergo second salvage therapy has been characterized poorly. This is important with regard to investigational approaches aimed at helping this subset of patients. The objectives of the current study were to predict outcomes and determine the prognostic factors associated with second salvage therapy in patients with ALL.

METHODS

In this study, 288 patients were analyzed who received second salvage therapy for ALL at the authors' institution.

RESULTS

Overall, 53 patients (18%) achieved a complete response (CR). The median remission duration was 7 months and the median survival was 3 months. In multivariate analysis, prognostic factors that were associated independently with achieving CR were duration of first CR and platelet count. Patients with a first CR <36 months and platelet counts <50 x 10(9)/L had an expected CR rate of 7%. In multivariate analysis, prognostic factors that were associated independently with survival were duration of first CR, percentage bone marrow blasts, platelet count, and albumin level. The expected 12-month survival rates for patients with 0 or 1, 2, 3, or 4 adverse factors were 33%, 14%, 8%, and 0%, respectively. A repeat multivariate analysis using landmark assessment at 6 weeks selected achievement of CR as adding significantly to the survival benefit (P = .0001; hazard ratio, 0.51). Only 22 patients (8%) were able to undergo allogeneic stem cell transplantation as second salvage therapy, and their 1-year survival rate was 18%.

CONCLUSIONS

The outcome of adults with ALL undergoing second salvage therapy is poor. Novel effective therapies against ALL are needed in this subset of patients.

Clofarabine in refractory Langerhans cell histiocytosis

Patients with multi-system Langerhans cell histiocytosis (LCH) who progress on frontline therapy have a dismal outcome. Responses to cladribine have been reported in relapsed LCH, but there are no well defined salvage regimens for LCH is refractory to therapy. The next generation deoxyadenosine analog, clofarabine, has demonstrated activity in patients with leukemia that is refractory to salvage regimens, including other nucleotide congeners; however, no experience exist on the use of clofarabine in LCH. In this report we describe significant single agent activity of clofarabine in disseminated LCH refractory to salvage regimens, including cladribine.

Three new drugs for acute lymphoblastic leukemia: nelarabine, clofarabine, and forodesine

The search for more effective and safer anti-leukemia therapies has led to the identification of several new agents that show activity against specific types of acute lymphoblastic leukemia (ALL). Recently, three novel purine nucleoside analogues (nelarabine, clofarabine, and forodesine) have shown promising activity in patients with relapsed or refractory ALL. Of these, nelarabine has shown clinically meaningful benefit in patients with T-cell ALL, with overall response rates ranging from 33% to 60%, the induction of durable complete remissions, and an overall 1-year survival rate of 28% in adults. Clofarabine has also shown promising clinical activity in pediatric patients, with an overall response rate of 30%, and some patients are able to proceed to allogeneic hematopoietic cell transplantation. Forodesine is the most recent novel agent, with a unique mechanism that has shown single-agent activity in relapsed and refractory T- and B-cell leukemias and cutaneous lymphomas. Although clinical experience is limited, treatment-related toxicities appear to be mild. The rationale, pharmacology, and clinical experience to date with these agents in the treatment of patients with refractory acute leukemia are reviewed, with a highlight on ALL.

Clofarabine acts as radiosensitizer in vitro and in vivo by interfering with DNA damage response

PURPOSE

Combination treatment with radiotherapy and chemotherapy has emerged as the dominant form of cancer adjuvant regimens in recent years. Clofarabine, a newly approved drug for pediatric leukemia, is a second-generation purine nucleoside analogue that can block DNA synthesis and inhibit DNA repair. Therefore, we hypothesized that clofarabine could work synergistically with radiotherapy to increase the tumor cell response.

METHODS AND MATERIALS

The effects of clofarabine on radiosensitivity have been established in several tumor cell lines in vitro and in vivo using colony-forming assays and tumor xenografts. The effect of clofarabine on the DNA damage response was also studied in vitro by measuring gamma-H2AX focus formation.

RESULTS

Clonogenic survival was significantly reduced in irradiated cells treated with clofarabine, demonstrating the strong radiosensitizing effect of clofarabine. Furthermore, clofarabine displayed a radiosensitizing effect that was greater than gemcitabine or 5-fluorouracil. We also found that low doses of clofarabine can prolong the presence of radiation-induced gamma-H2AX nuclear focus formation, and high doses of clofarabine can induce DNA double-strand breaks, suggesting that clofarabine can interfere with DNA damage response pathways. In addition, clofarabine-induced radiosensitization was also established in vivo using a colorectal cancer model, DLD-1, in athymic nude mice. When combined with fractionated radiotherapy, a moderate dose of clofarabine led to a significant increase in tumor growth inhibition.

CONCLUSION

Clofarabine acts as a powerful radiosensitizer both in vitro and in vivo by interfering with the DNA damage response.