A phase II trial of tipifarnib in myelofibrosis: primary, post-polycythemia vera and post-essential thrombocythemia

Emerging treatments for classical myeloproliferative neoplasms

There has been a major revolution in the management of patients with myeloproliferative neoplasms (MPN), and in particular those with myelofibrosis and extensive splenomegaly and symptomatic burden, after the introduction of the JAK1 and JAK2 inhibitor ruxolitinib. The drug also has been approved as second-line therapy for polycythemia vera (PV). However, the therapeutic armamentarium for MPN is still largely inadequate for coping with patients' major unmet needs, which include normalization of life span (myelofibrosis and some patients with PV), reduction of cardiovascular complications (mainly PV and essential thrombocythemia), prevention of hematological progression, and improved quality of life (all MPN). In fact, none of the available drugs has shown clear evidence of disease-modifying activity, even if some patients treated with interferon and ruxolitinib showed reduction of mutated allele burden, and ruxolitinib might extend survival of patients with higher-risk myelofibrosis. Raised awareness of the molecular abnormalities and cellular pathways involved in the pathogenesis of MPN is facilitating the development of clinical trials with novel target drugs, either alone or in combination with ruxolitinib. Although for most of these molecules a convincing preclinical rationale was provided, the results of early phase 1 and 2 clinical trials have been quite disappointing to date, and toxicities sometimes have been limiting. In this review, we critically illustrate the current landscape of novel therapies that are under evaluation for patients with MPN on the basis of current guidelines, patient risk stratification criteria, and previous experience, looking ahead to the chance of a cure for these disorders.

Therapeutic benefit of decitabine, a hypomethylating agent, in patients with high-risk primary myelofibrosis and myeloproliferative neoplasm in accelerated or blastic/acute myeloid leukemia phase

Myeloproliferative neoplasm (MPN) transformed to acute myeloid leukemia (MPN-AML), MPN in accelerated phase (MPN-AP), and high-risk primary myelofibrosis (PMF) are associated with a poor response to therapy and very short survival. Several reports have suggested clinical activity of hypomethylating agents in these patients. We conducted a retrospective study of 21 patients with MPN-AML, 13 with MPN-AP and 11 with DIPSS-plus high-risk PMF treated with decitabine at our institution over the last 7 years and evaluated their clinical outcomes. Six patients (29%) with MPN-AML responded to decitabine (3 CR, 2 CRi, and 1 PR); median response duration was 7 months. The median overall survival (OS) was significantly higher in those who responded (10.5 vs 4 months). Among patients with MPN-AP, 8 patients (62%) benefited; the median response duration was 6.5 months. The median OS was 11.8 months in responders vs 4.7 months in non-responders. Among patients with DIPSS-plus high-risk PMF, 9 (82%) benefited; the median response duration was 9 months. The median OS was 32 months in responders vs 16.3 months in non-responders. Decitabine is a viable therapeutic option for patients with MPN-AML, MP-AP and high-risk PMF. Prospective clinical studies combining decitabine with other clinically active agents are needed to improve overall outcome.

Janus kinase-1 and Janus kinase-2 inhibitors for treating myelofibrosis

BACKGROUND

Myelofibrosis is a bone marrow disorder characterized by excessive production of reticulin and collagen fiber deposition caused by hematological and non-hematological disorders. The prognosis of myelofibrosis is poor and treatment is mainly palliative. Janus kinase inhibitors are a novel strategy to treat people with myelofibrosis.

OBJECTIVES

To determine the clinical benefits and harms of Janus kinase-1 and Janus kinase-2 inhibitors for treating myelofibrosis secondary to hematological or non-hematological conditions.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, the Cochrane Library 2014, Issue 11), Ovid MEDLINE (from 1946 to 13 November 2014), EMBASE (from 1980 to 12 January 2013), and LILACS (from 1982 to 20 November 2014). We searched WHO International Clinical Trials Registry Platform and The metaRegister of Controlled Trials. We also searched for conference proceedings of the American Society of Hematology (from 2009 to October 2013), European Hematology Association (from 2009 to October 2013), American Society of Clinical Oncology (from 2009 to October 2013), and European Society of Medical Oncology (from 2009 to October 2013). We included searches in FDA, European Medicines Agency, and Epistemonikos. We handsearched the references of all identified included trials, and relevant review articles. We did not apply any language restrictions. Two review authors independently screened search results.

SELECTION CRITERIA

We included randomized clinical trials comparing Janus kinase-1 and Janus kinase-2 inhibitors with placebo or other treatments. Both previously treated and treatment naive patients were included.

DATA COLLECTION AND ANALYSIS

We used the hazard ratio (HR) and 95% confidence interval (95% CI) for overall survival, progression-free survival and leukemia-free survival, risk ratio (RR) and 95% CI for reduction in spleen size and adverse events binary data, and standardized mean differences (SMD) and 95% CI for continuous data (health-related quality of life). Two review authors independently extracted data and assessed the risk of bias of included trials. Primary outcomes were overall survival, progression-free survival and adverse events.

MAIN RESULTS

We included two trials involving 528 participants, comparing ruxolitinib with placebo or best available therapy (BAT). As the two included trials had different comparators we did not pool the data. The confidence in the results estimates of these trials was low due to the bias in their design, and their limited sample sizes that resulted in imprecise results.There is low quality evidence for the effect of ruxolitinib on survival when compared with placebo at 51 weeks of follow-up (HR 0.51, 95% CI 0.27 to 0.98) and compared with BAT at 48 weeks of follow-up (HR 0.70, 95% CI 0.20 to 2.47). Similarly there was very low quality evidence for the effect of ruxolitinib on progression free survival compared with BAT (HR 0.81, 95% CI 0.47 to 1.39).There is low quality evidence for the effect of ruxolitinib in terms of quality of life. Compared with placebo, the drug achieved a greater proportion of patients with a significant reduction of symptom scores (RR 8.82, 95% CI 4.40 to 17.69), and treated patients with ruxolitinib obtained greater MFSAF scores at the end of follow-up (MD -87.90, 95% CI -139.58 to -36.22). An additional trial showed significant differences in EORTC QLQ-C30 scores when compared ruxolitinib with best available therapy (MD 7.60, 95% CI 0.35 to 14.85).The effect of ruxolitinib on reduction in the spleen size of participants compared with placebo or BAT was uncertain (versus placebo: RR 64.58, 95% CI 9.08 to 459.56, low quality evidence; versus BAT: RR 41.78, 95% CI 2.61 to 669.75, low quality evidence).There is low quality evidence for the effect of the drug compared with placebo on anemia (RR 2.35, 95% CI 1.62 to 3.41), neutropenia (RR 3.57, 95% CI 1.02 to 12.55) and thrombocytopenia (RR 9.74, 95% CI 2.32 to 40.96). Ruxolitinib did not result in differences versus BAT in the risk of anemia (RR 1.35, 95% CI 0.91 to 1.99, low quality evidence) or thrombocytopenia (RR 1.20; 95% CI 0.44 to 3.28, low quality evidence). The risk of non-hematologic grade 3 or 4 adverse events (including fatigue, arthralgia, nausea, diarrhea, extremity pain and pyrexia) was similar when ruxolitinib was compared with placebo or BAT. The rate of neutropenia comparing ruxolitinib with standard medical treatment was not reported by the trial.

AUTHORS' CONCLUSIONS

Currently, there is insufficient evidence to allow any conclusions regarding the efficacy and safety of ruxolitinib for treating myelofibrosis. The findings of this Cochrane review should be interpreted with caution as they are based on trials sponsored by industry, and include a small number of patients. Unless powered randomized clinical trials provide strong evidence of a treatment effect, and the trade-off between potential benefits and harms is established, clinicians should be cautious when administering ruxolitinib for treating patients with myelofibrosis.

Targeting mutant KRAS for anticancer therapeutics: a review of novel small molecule modulators

The RAS proteins play a role in cell differentiation, proliferation, and survival. Aberrant RAS signaling has been found to play a role in 30% of all cancers. KRAS, a key member of the RAS protein family, is an attractive cancer target, as frequent point mutations in the KRAS gene render the protein constitutively active. A number of attempts have been made to target aberrant KRAS signaling by identifying small molecule compounds that (1) are synthetic lethal to mutant KRAS, (2) block KRAS/GEF interactions, (3) inhibit downstream KRAS effectors, or (4) inhibit the post-translational processing of RAS proteins. In addition, inhibition of novel targets outside the main KRAS signaling pathway, specifically the cell cycle related kinase PLK1, has been shown have an effect in cells that harbor mutant KRAS. Herein we review the use of various high-throughput screening assays utilized to identify new small-molecule compounds capable of targeting mutant KRAS-driven cancers.

Novel therapies in the classical BCR–ABL-negative myeloproliferative neoplasms

SUMMARY Myeloproliferative neoplasms (MPN) are clonal stem cell disorders that include essential thrombocytosis, polycythemia vera and myelofibrosis. Effective therapy is challenging owing to the heterogeneity of the disease; however, recent advances in our understanding of MPN pathogenesis have led to the evaluation of novel therapies, each with its own distinct contribution and side-effect profile. This review summarizes promising approaches to the treatment of MPN, aiming to improve upon the currently used conventional therapies.

Phase II study of the farnesyltransferase inhibitor R115777 in advanced melanoma (CALGB 500104)

Background

Multiple farnesylated proteins are involved in signal transduction in cancer. Farnesyltransferase inhibitors (FTIs) have been developed as a strategy to inhibit the function of these proteins. As FTIs inhibit proliferation of melanoma cell lines, we undertook a study to assess the impact of a FTI in advanced melanoma. As farnesylated proteins are also important for T cell activation, measurement of effects on T cell function was also pursued.

Methods

A 3-stage trial design was developed with a maximum of 40 patients and early stopping if there were no responders in the first 14, or fewer than 2 responders in the first 28 patients. Eligibility included performance status of 0–1, no prior chemotherapy, at most 1 prior immunotherapy, no brain metastases, and presence of at least 2 cutaneous lesions amenable to biopsy. R115777 was administered twice per day for 21 days of a 28-day cycle. Patients were evaluated every 2 cycles by RECIST. Blood and tumor were analyzed pre-treatment and during week 7.

Results

Fourteen patients were enrolled. Two patients had grade 3 toxicities, which included myelosuppression, nausea/vomiting, elevated BUN, and anorexia. There were no clinical responses. All patients analyzed showed potent inhibition of FT activity (85-98%) in tumor tissue; inhibition of phosphorylated ERK and Akt was also observed. T cells showed evidence of FT inhibition and diminished IFN-γ production.

Conclusions

Despite potent target inhibition, R115777 showed no evidence of clinical activity in this cohort of melanoma patients. Inhibition of T cell function by FTIs has potential clinical implications.

Clinicaltrials.gov number NCT00060125

Tipifarnib in the treatment of newly diagnosed acute myelogenous leukemia

Farnesyltransferase inhibitors (FTIs) represent a new class of signal transduction inhibitors that block the processing of cellular polypeptides that have cysteine terminal residues and, by so doing, interdict multiple pathways involved in proliferation and survival of diverse malignant cell types. Tipifarnib is an orally bioavailable, nonpeptidomimetic methylquinolone FTI that has exhibited clinical activity in patients with myeloid malignancies including elderly adults with acute myelogenous leukemia (AML) who are not candidates for traditional cytotoxic chemotherapy, patients with high-risk myelodysplasia, myeloproliferative disorders, and imatinib-resistant chronic myelogenous leukemia. Because of its relatively low toxicity profile, tipifarnib provides an important alternative to traditional cytotoxic approaches for elderly patients who are not likely to tolerate or even benefit from aggressive chemotherapy. In this review, we will focus on the clinical development of tipifarnib for treatment of newly diagnosed AML, both as induction therapy for elderly adults with poor-risk AML and as maintenance therapy following achievement of first complete remission following induction and consolidation therapies for poor-risk AML. As with all other malignancies, the optimal approach is likely to lie in rational combinations of tipifarnib with cytotoxic, biologic and/or immunomodulatory agents with non-cross-resistant mechanisms of action. Gene expression profiling has identified networks of differentially expressed genes and gene combinations capable of predicting response to single agent tipifarnib. The clinical and correlative laboratory trials in progress and under development will provide the critical foundations for defining the optimal roles of tipifarnib and in patients with AMl and other hematologic malignancies.

Multi-institutional phase 2 study of the farnesyltransferase inhibitor tipifarnib (R115777) in patients with relapsed and refractory lymphomas

A phase 2 study of the oral farnesyltransferase inhibitor tipifarnib was conducted in 93 adult patients with relapsed or refractory lymphoma. Patients received tipifarnib 300 mg twice daily on days 1-21 of each 28-day cycle. The median number of prior therapies was 5 (range, 1-17). For the aggressive B-cell, indolent B-cell, and T-cell and Hodgkin lymphoma (HL/T) groups, the response rates were 17% (7/42), 7% (1/15), and 31% (11/36), respectively. Of the 19 responders, 7 were diffuse large B-cell non-Hodgkin lymphoma (NHL), 7 T-cell NHL, 1 follicular grade 2, and 4 HL. The median response duration for the 19 responders was 7.2 months (mean, 15.8 months; range, 1.8-62), and 5 patients in the HL/T group are still receiving treatment at 29-64+ months. The grade 3/4 toxicities observed were fatigue and reversible myelosuppression. Correlative studies suggest that Bim and Bcl-2 should be examined as potential predictors of response in future studies. These results indicate that tipifarnib has activity in lymphoma, particularly in heavily pretreated HL/T types, with little activity in follicular NHL. In view of its excellent toxicity profile and novel mechanism of action, further studies in combination with other agents appear warranted. This trial is registered at www.clinicaltrials.gov as #NCT00082888.

Inhibition of the Ras/Raf/MEK/ERK and RET kinase pathways with the combination of the multikinase inhibitor sorafenib and the farnesyltransferase inhibitor tipifarnib in medullary and differentiated thyroid malignancies

PURPOSE

Ras/Raf/MAPK kinase/ERK and rearranged in transformation (RET) kinase pathways are important in thyroid cancer. We tested sorafenib, a B-Raf, RET, and vascular endothelial growth factor receptor kinase inhibitor, combined with tipifarnib, a farnesyltransferase inhibitor that inactivates Ras and other farnesylated proteins.

PATIENTS AND METHODS

We treated 35 patients with differentiated thyroid cancer (DTC) and medullary thyroid cancer (MTC) in a phase I trial. Sorafenib and tipifarnib were given for 21 d with 7 d rest in each 28-d cycle.

RESULTS

We enrolled 22 patients with metastatic DTC (16 papillary, five follicular, and one poorly differentiated) and 13 patients with MTC, of whom 15 with DTC and 10 with MTC reached first restaging. When tissue was available, eight of 15 DTC patients (53%) had B-Raf mutations; eight of 13 MTC (61.5%) patients had RET mutations. MTC partial response rate was 38% (five of 13) (duration = 9+, 12, 13, 16+, and 34+ months), stable disease of at least 6 months was 31% (four of 13). The DTC partial response rate was 4.5% (one of 22), and stable disease of at least 6 months was 36% (eight of 22). Median progression-free survival for all 35 patients was 18 months (95% confidence interval, 14.6 to not reached months). Median overall survival has not been reached, with a median follow-up of 24 months with 80% overall survival. Grade 1-2 toxicities were mainly rash, fatigue, and diarrhea. The most common grade 3-4 toxicities were rash, rise in amylase/lipase, and fatigue.

CONCLUSIONS

Inhibiting the Ras/Raf/MAPK kinase/ERK and RET kinase pathways with sorafenib and tipifarnib is well tolerated and active against thyroid cancer.

Deactylase inhibition in myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are clonal haemopoietic progenitor cell disorders characterized by the proliferation of one or more of the haemopoietic lineages (myeloid, erythroid and/or megakaryocytic). The MPNs include eight haematological disorders: chronic myelogenous leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), systemic mastocytosis (SM), chronic eosinophilic leukemia, not otherwise specified (CEL, NOS), chronic neutrophilic leukemia (CNL), and unclassifiable MPN (MPN, U). Therapeutic interventions for MPNs include the use of tyrosine kinase inhibitors (TKIs) for BCR-ABL1(+) CML and JAK2 inhibitors for PV, ET and PMF. Histone deacetylase inhibitors (HDACi) are a novel class of drugs capable of altering the acetylation status of both histone and non-histone proteins, thereby affecting a repertoire of cellular functions in neoplastic cells including proliferation, differentiation, immune responses, angiogenesis and survival. Preliminary studies indicate that HDACi when used in combination with tyrosine kinase or JAK2 inhibitors may overcome resistance to the latter agents and enhance the pro-apoptotic effects on MPN cells. This review provides a review of pre-clinical and clinical studies that have explored the use of HDACi as potential therapeutics for MPNs.

A phase 1-2 study of a farnesyltransferase inhibitor, tipifarnib, combined with idarubicin and cytarabine for patients with newly diagnosed acute myeloid leukemia and high-risk myelodysplastic syndrome

BACKGROUND

The authors conducted a phase 1/2 study of tipifarnib in combination with idarubicin and cytarabine (IA) in 95 patients with previously untreated acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome.

METHODS

Induction consisted of idarubicin 12 mg/m(2) a day on days 1-3, cytarabine 1.5 g/m(2) intravenously continuously daily on days 1-4 (days 1-3 if age ≥60 years), and tipifarnib, with the first cohort (n = 6) receiving 200 mg orally twice a day and all others receiving 300 mg twice a day for 21 days every 28 days. Consolidation consisted of 5 courses of idarubicin 8 mg/m(2) a day on days 1-2, cytarabine 0.75 g/m(2) a day on days 1-3, and tipifarnib 300 mg twice a day for 14 days every 4-6 weeks. Maintenance with tipifarnib 300 mg twice a day for 21 days every 4-6 weeks was continued for 6 months.

RESULTS

With a median follow-up of 33 months, 61 patients achieved complete remission (CR) (64%), and 9 achieved complete remission with incomplete platelet recovery (CRp) (9%). The median duration of CR was not reached. Median overall survival was 17 months. The most common grade 3 adverse events were gastrointestinal toxicities, liver dysfunction, and skin rash. Compared with historical IA, IA and tipifarnib showed a better CR duration (P = .04) and a trend toward a higher CR rate in patients with chromosome 5/7 abnormalities.

CONCLUSIONS

The combination of IA and tipifarnib is safe and active. Further studies exploring different dosages and schedules are warranted, particularly in patients with poor-risk AML.

Recent advances in diagnosis and treatment of chronic myeloproliferative neoplasms

The Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) have recently been the focus of tremendous advances in basic knowledge of disease pathophysiology following the recognition of mutations in JAK2 and MPL. These discoveries also led to refinement of the criteria employed for diagnosis. The prognostic roles of the JAK2 V617F mutation and of leukocytosis as independent risk factors for thrombosis, which represents the leading cause of death in patients with polycythemia vera and essential thrombocythemia, are supported by retrospective studies. A new risk stratification approach to the patient with primary myelofibrosis allows clinicians to distinguish categories of patients with significantly different expected survival. Finally, new drugs are currently being tested for MPNs, and molecular discoveries could ultimately lead to the development of a specific targeted therapy. Overall, significant advances in diagnosis, prognostication, and treatment have taken place in the last couple of years in the field of MPNs.

Therapy of myelofibrosis (excluding JAK2 inhibitors)

Myelofibrosis shows a progressive clinical course and usually a poor, lethal prognosis. Allogeneic transplantation is an effective, potentially curable treatment approach although only a minority of patients may currently benefit from it. New effective treatment strategies are becoming available for this disease, including not only JAK2 inhibitors, but also other innovative drugs, targeting more general oncogenic mechanisms and the epigenetic control of cell proliferation and differentiation.

Phase I trial of a combination of the multikinase inhibitor sorafenib and the farnesyltransferase inhibitor tipifarnib in advanced malignancies

PURPOSE

We evaluated the safety, maximum tolerated dose, pharmacokinetics, and biological effects of the combination of the Raf-1, RET, KIT, platelet-derived growth factor receptor, and vascular endothelial growth factor receptor 2 kinase inhibitor sorafenib and the farnesyltransferase inhibitor tipifarnib.

EXPERIMENTAL DESIGN

A standard 3 + 3 phase I dose-escalation design was used with a 28-day cycle (sorafenib daily and tipifarnib for 21 days, by mouth).

RESULTS

Fifty patients were treated; 43 reached restaging evaluation after cycle 2. The most common side effects were grade 1 to 2 rash, hyperglycemia, and diarrhea. Dose-limiting toxicity was rash, and the recommended phase II dose is sorafenib 400 mg p.o. qam/200 mg p.o. qpm and tipifarnib p.o. 100 mg bd. Despite the low doses of tipifarnib, one quarter of patients had > or =50% reduction in farnesyltransferase levels. Interestingly, six of eight patients with medullary thyroid cancer had durable stable disease (n = 3) or partial remissions (n = 3), lasting 12 to 26+ months. Five of the six responders had available tissue, and RET gene mutations were identified in them. Prolonged (> or =6 months) stable disease was also seen in nine patients as follows: papillary thyroid cancer (n = 4; 18+ to 27+ months), adrenocortical cancer (n = 2; 7 and 11 months), and one each of melanoma (platelet-derived growth factor receptor mutation positive; 14 months), renal (6 months), and pancreatic cancer (6 months).

CONCLUSIONS

Our study shows that the combination of tipifarnib and sorafenib is well tolerated. Activity was seen, especially in patients with medullary thyroid cancer, a tumor characterized by RET mutations.

Novel strategies for patients with chronic myeloproliferative disorders

PURPOSE OF REVIEW

This review focuses on new strategies for unmet clinical needs and on new targeted therapies in classical Philadelphia-negative myeloproliferative neoplasms.

RECENT FINDINGS

Meta-analyses in essential thrombocythemia documented Janus kinase 2 (JAK2) V617F as being associated with increased risk of thrombosis. New studies reinforced the evidence of leukocytosis as an independent risk factor for thrombosis in polycythemia vera and essential thrombocythemia. In a phase II trial of pegylated interferon-alpha2a in polycythemia vera patients, a decrease of JAK2 mutant expression to undetectable levels was demonstrated. New trials documented that 5-azacytidine and bortezomib have negligible effect in primary myelofibrosis, whereas thalidomide and tipifarnib produce 22 and 44% response, respectively. In primary myelofibrosis, the JAK2 inhibitor, INCB018424, resulted in a rapid and marked reduction in splenomegaly and a clinical improvement, with a modest effect on JAK2 V617F burden.

SUMMARY

Treating low-risk essential thrombocythemia and polycythemia vera patients presenting with leukocytosis or JAK2 V617F mutation in order to prevent thrombosis deserves a prospective validation. Pursuing clonal remission in polycythemia vera by interferon needs new evidence. Tipifarnib may be added to conventional therapeutic instruments for symptomatic primary myelofibrosis. The results of anti-JAK2-targeted therapies are encouraging as regards symptoms reduction but not clonal remission.

Active oral regimen for elderly adults with newly diagnosed acute myelogenous leukemia: a preclinical and phase 1 trial of the farnesyltransferase inhibitor tipifarnib (R115777, Zarnestra) combined with etoposide

The farnesyltransferase inhibitor tipifarnib exhibits modest activity against acute myelogenous leukemia. To build on these results, we examined the effect of combining tipifarnib with other agents. Tipifarnib inhibited signaling downstream of the farnesylated small G protein Rheb and synergistically enhanced etoposide-induced antiproliferative effects in lymphohematopoietic cell lines and acute myelogenous leukemia isolates. We subsequently conducted a phase 1 trial of tipifarnib plus etoposide in adults over 70 years of age who were not candidates for conventional therapy. A total of 84 patients (median age, 77 years) received 224 cycles of oral tipifarnib (300-600 mg twice daily for 14 or 21 days) plus oral etoposide (100-200 mg daily on days 1-3 and 8-10). Dose-limiting toxicities occurred with 21-day tipifarnib. Complete remissions were achieved in 16 of 54 (30%) receiving 14-day tipifarnib versus 5 of 30 (17%) receiving 21-day tipifarnib. Complete remissions occurred in 50% of two 14-day tipifarnib cohorts: 3A (tipifarnib 600, etoposide 100) and 8A (tipifarnib 400, etoposide 200). In vivo, tipifarnib plus etoposide decreased ribosomal S6 protein phosphorylation and increased histone H2AX phosphorylation and apoptosis. Tipifarnib plus etoposide is a promising orally bioavailable regimen that warrants further evaluation in elderly adults who are not candidates for conventional induction chemotherapy. These clinical studies are registered at www.clinicaltrials.gov as #NCT00112853.

Phase II trial of tipifarnib as maintenance therapy in first complete remission in adults with acute myelogenous leukemia and poor-risk features

PURPOSE

Acute myelogenous leukemia (AML) does not have a high cure rate, particularly in patients with poor-risk features. Such patients might benefit from additional therapy in complete remission (CR). Tipifarnib is an oral farnesyltransferase inhibitor with activity in AML. We conducted a phase II trial of maintenance tipifarnib monotherapy for 48 adults with poor-risk AML in first CR.

EXPERIMENTAL DESIGN

Tipifarnib 400 mg twice daily for 14 of 21 days was initiated after recovery from consolidation chemotherapy, for a maximum of 16 cycles (48 weeks).

RESULTS

Twenty (42%) patients completed 16 cycles, 24 (50%) were removed from study for relapse, and 4 (8%) discontinued drug prematurely for intolerance. Nonhematologic toxicities were rare, but tipifarnib dose was reduced in 58% for myelosuppression. Median disease-free survival (DFS) was 13.5 months (range, 3.5-59+ months), with 30% having DFS >2 years. Comparison of CR durations for 25 patients who received two-cycle timed sequential therapy followed by tipifarnib maintenance with 23 historically similar patients who did not receive tipifarnib showed that tipifarnib was associated with DFS prolongation for patients with secondary AML and adverse cytogenetics.

CONCLUSIONS

This study suggests that some patients with poor-risk AML, including patients with secondary AML and adverse cytogenetics, may benefit from tipifarnib maintenance therapy. Future studies are warranted to examine alternative tipifarnib dosing and continuation beyond 16 cycles.

Ceramide signaling in cancer and stem cells

Most of the previous work on the sphingolipid ceramide has been devoted to its function as an apoptosis inducer. Recent studies, however, have shown that in stem cells, ceramide has additional nonapoptotic functions. In this article, ceramide signaling will be reviewed in light of 'systems interface biology': as an interconnection of sphingolipid metabolism, membrane biophysics and cell signaling. The focus will be on the metabolic interconversion of ceramide and sphingomyelin or sphingosine-1-phosphate. Lipid rafts and sphingolipid-induced protein scaffolds will be discussed as a membrane interface for lipid-controlled cell signaling. Ceramide/sphingomyelin and ceramide/sphingosine-1-phosphate-interdependent cell-signaling pathways are significant for the regulation of cell polarity, apoptosis and/or proliferation, and as novel pharmacologic targets in cancer and stem cells.

Low JAK2V617F allele burden in primary myelofibrosis, compared to either a higher allele burden or unmutated status, is associated with inferior overall and leukemia-free survival

The clinical relevance of JAK2V617F allele burden in primary myelofibrosis (PMF) has not been previously studied. Bone marrow-derived DNA from 199 patients with PMF was subjected to qualitative (n=199) and quantitative (n=129) analysis for V617F. Mutational frequency was 58% and median mutant allele burden ratio in V617F-positive patients was 29% (range, 1-74%). Multivariable analysis identified older age, platelet count > or =100 x 10(9) l(-1) and peripheral blood blast percentage <3% as being associated with a positive mutational status. The mere presence of the mutation did not affect the incidence of thrombosis (P=0.78), overall survival (P=0.22) or leukemia-free survival (P=0.5). The 129 patients with allele burden information were divided into four groups: V617F-negative (n=53) and V617F-positive with mutant allele burden in the lower quartile (n=19), middle quartiles (n=38) or upper quartile (n=19) range. Kaplan-Meier plots revealed significantly shortened overall (P=0.0008) and leukemia-free (P=0.01) survival for the lower quartile, but not for upper quartile allele burden group; independent prognostic relevance was validated by multivariable analysis. We conclude that low V617F allele burden in PMF might indicate the presence of an overriding V617F-negative clone that confers a more aggressive disease phenotype.

From palliation to epigenetic therapy in myelofibrosis

Myelofibrosis shows a progressive clinical course and usually a poor, lethal prognosis. The molecular pathogenesis of this disease largely remains to be fully understood but the identification of the JAK2V617F mutation in more than half of patients was a major improvement in our understanding of the disease biology and may represent the first biologic marker useful for risk stratification, independently from conventional clinical predictors. After many elusive efforts, new effective treatment strategies are becoming available for this disease. Allogeneic transplantation following reduced-intensity conditioning programs, at least in some patients, may induce not only a hematologic response but also a molecular remission, thus supporting the hope of a possible, definitive eradication of the disease. Moreover, new innovative drugs, targeting either the JAK2V617F mutation or more general oncogenic mechanisms, may provide widely applicable, effective treatments to many patients for whom allogeneic transplantation is not feasible.