A phase I study of tipifarnib combined with conventional induction and consolidation therapy for previously untreated patients with acute myeloid leukemia aged 60 years and over

miR-126 Regulates Distinct Self-Renewal Outcomes in Normal and Malignant Hematopoietic Stem Cells

To investigate miRNA function in human acute myeloid leukemia (AML) stem cells (LSC), we generated a prognostic LSC-associated miRNA signature derived from functionally validated subpopulations of AML samples. For one signature miRNA, miR-126, high bioactivity aggregated all in vivo patient sample LSC activity into a single sorted population, tightly coupling miR-126 expression to LSC function. Through functional studies, miR-126 was found to restrain cell cycle progression, prevent differentiation, and increase self-renewal of primary LSC in vivo. Compared with prior results showing miR-126 regulation of normal hematopoietic stem cell (HSC) cycling, these functional stem effects are opposite between LSC and HSC. Combined transcriptome and proteome analysis demonstrates that miR-126 targets the PI3K/AKT/MTOR signaling pathway, preserving LSC quiescence and promoting chemotherapy resistance.

Small molecule inhibitors in acute myeloid leukemia: from the bench to the clinic

Many patients with acute myeloid leukemia will eventually develop refractory or relapsed disease. In the absence of standard therapy for this population, there is currently an urgent unmet need for novel therapeutic agents. Targeted therapy with small molecule inhibitors represents a new therapeutic intervention that has been successful for the treatment of multiple tumors (e.g., gastrointestinal stromal tumors, chronic myelogenous leukemia). Hence, there has been great interest in generating selective small molecule inhibitors targeting critical pathways of proliferation and survival in acute myeloid leukemia. This review highlights a selective group of intriguing therapeutic agents and their presumed targets in both preclinical models and in early human clinical trials.

Tipifarnib-mediated suppression of T-bet-dependent signaling pathways

Large granular lymphocyte (LGL) leukemia is a chronic lymphoproliferative disease in which T-bet [T-box transcription factor 21 gene (tbx21)] overexpression may play a pathogenic role. T-bet orchestrates the differentiation of mature peripheral T-cells into interferon-γ (IFN-γ) and tumor necrosis factor-α producing CD4+ T-helper type I (Th1) and CD8+ T cytotoxic cells that are necessary for antiviral responses. When IL-12 is produced by antigen-presenting cells, T-bet expression is induced, causing direct stimulation of ifng gene transcription while simultaneously acting as a transcriptional repressor of the IL4 gene, which then leads to Th1 dominance and T-helper type 2 differentiation blockade. Additionally, T-bet has been shown to regulate histone acetylation of the ifng promoter and enhancer to loosen condensed DNA, creating greater accessibility for other transcription factor binding, which further amplifies IFNγ production. We found that treatment with a farnesyltransferase inhibitor tipifarnib reduced Th1 cytokines in LGL leukemia patient T-cells and blocked T-bet protein expression and IL-12 responsiveness in T-cells from healthy donors. The mechanism of suppression was based on modulation of histone acetylation of the ifng gene, which culminated in Th1 blockade.

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.

A phase I clinical-pharmacodynamic study of the farnesyltransferase inhibitor tipifarnib in combination with the proteasome inhibitor bortezomib in advanced acute leukemias

PURPOSE

To determine the safety, target inhibition, and signals of clinical activity of tipifarnib in combination with bortezomib in patients with advanced acute leukemias.

EXPERIMENTAL DESIGN

In a "3 + 3" design, patients received escalating doses of tipifarnib (days 1-14) and bortezomib (days 1, 4, 8, 11) every 3 weeks until maximum tolerated dose was reached. Peripheral blood mononuclear cells (PBMC) were collected at days 1, 8, and 22 for measurement of chymotrypsin-like and farnesyltransferase activity. Purified bone marrow leukemic blasts were collected at baseline and at day 8 for measurement of NF-κB activity.

RESULTS

The combination was well-tolerated, and maximum tolerated dose was not reached. Dose-limiting toxicities included diarrhea, fatigue, and sensorimotor neuropathy. Chymotrypsin-like and farnesyltransferase activity within PBMCs were decreased in a majority of patients at day 8. NF-κB activity within leukemic blasts was decreased in a majority of patients at day 8. Complete response with incomplete count recovery was observed in 2 patients, and additional 5 patients had stable disease.

CONCLUSIONS

Tipifarnib and bortezomib combination in patients with advanced leukemias was well-tolerated, demonstrated relevant target inhibition, and was associated with signals of clinical activity in patients with advanced and refractory acute leukemias. Future studies of this combination may be warranted in more selected groups of patients in whom these molecular targets are of particular importance.

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.

Suppression of farnesyltransferase activity in acute myeloid leukemia and myelodysplastic syndrome: current understanding and recommended use of tipifarnib

IMPORTANCE OF THE FIELD

Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) incidence in the United States increases with age. Given the progressive ageing of the general population, incidence of these diseases is likely to continue to rise in the future. There is an acute need for therapeutic developments because of the poor prognosis of these diseases. Since the knowledge of molecular genetics in AML and MDS has expanded recently, targeted therapeutics should offer an exciting new frontier for advancement. Of all the targeted inhibitors developed, tipifarnib represents one of the few compounds with some activity as a single agent.

AREAS COVERED IN THIS REVIEW

Described in this review are the molecular targets of tipifarnib, safety and tolerability of the drug, chemistry, and clinical efficacy in AML.

WHAT THE READER WILL GAIN

The reader will gain a thorough understanding of tipifarnib as it relates to the current and future use of the drug in AML.

TAKE HOME MESSAGE

The future of tipifarnib, along with other molecularly-targeted drugs, lies in achieving a better understanding of leukemia biology and harnessing the activity of this agent using predictive biomarkers for improved patient selection.

Erucylphosphohomocholine, the first intravenously applicable alkylphosphocholine, is cytotoxic to acute myelogenous leukemia cells through JNK- and PP2A-dependent mechanisms

Alkylphospholipids and alkylphosphocholines (APCs) are promising antitumor agents, which target the plasma membrane and affect multiple signal transduction networks. We investigated the therapeutic potential of erucylphosphohomocholine (ErPC3), the first intravenously applicable APC, in human acute myelogenous leukemia (AML) cells. ErPC3 was tested on AML cell lines, as well as AML primary cells. At short (6-12 h) incubation times, the drug blocked cells in G2/M phase of the cell cycle, whereas, at longer incubation times, it decreased survival and induced cell death by apoptosis. ErPC3 caused JNK 1/2 activation as well as ERK 1/2 dephosphorylation. Pharmacological inhibition of caspase-3 or a JNK 1/2 inhibitor peptide markedly reduced ErPC3 cytotoxicity. Protein phosphatase 2A downregulation by siRNA opposed ERK 1/2 dephosphorylation and blunted the cytotoxic effect of ErPC3. ErPC3 was cytotoxic to AML primary cells and reduced the clonogenic activity of CD34(+) leukemic cells. ErPC3 induced a significant apoptosis in the compartment (CD34(+) CD38(Low/Neg) CD123(+)) enriched in putative leukemia-initiating cells. This conclusion was supported by ErPC3 cytotoxicity on AML blasts showing high aldehyde dehydrogenase activity and on the side population of AML cell lines and blasts. These findings indicate that ErPC3 might be a promising therapeutic agent for the treatment of AML patients.

Tipifarnib and etoposide for older AML patients: from bench to bedside

In this issue of Blood, Karp and colleagues describe preclinical and clinical effects of the combination of tipifarnib with etoposide. The study represents an admirable example of successful translation of in vitro data to a phase 1 clinical trial.

Induction therapy for elderly patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is a disease of older adults. Efforts to intensify therapy along traditional avenues have failed to yield improved results. There remains significant clinical equipoise as to how to "induce" patients and whether or not 7+3-style regimens improve outcomes over low-dose cytarabine. What is certain is that even in those not receiving active therapy, AML is an exceptionally morbid disease. Diverse interventions are being explored in the management of older patients with AML and the currently available data will be reviewed.