Clinical and biologic activity of the farnesyltransferase inhibitor R115777 in adults with refractory and relapsed acute leukemias: a phase 1 clinical-laboratory correlative trial

Differential co-expression network analysis elucidated genes associated with sensitivity to farnesyltransferase inhibitor and prognosis of acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease and the most common form of acute leukemia with a poor prognosis. Due to its complexity, the disease requires the identification of biomarkers for reliable prognosis. To identify potential disease genes that regulate patient prognosis, we used differential co-expression network analysis and transcriptomics data from relapsed, refractory, and previously untreated AML patients based on their response to treatment in the present study. In addition, we combined functional genomics and transcriptomics data to identify novel and therapeutically potential systems biomarkers for patients who do or do not respond to treatment. As a result, we constructed co-expression networks for response and non-response cases and identified a highly interconnected group of genes consisting of SECISBP2L, MAN1A2, PRPF31, VASP, and SNAPC1 in the response network and a group consisting of PHTF2, SLC11A2, PDLIM5, OTUB1, and KLRD1 in the non-response network, both of which showed high prognostic performance with hazard ratios of 4.12 and 3.66, respectively. Remarkably, ETS1, GATA2, AR, YBX1, and FOXP3 were found to be important transcription factors in both networks. The prognostic indicators reported here could be considered as a resource for identifying tumorigenesis and chemoresistance to farnesyltransferase inhibitor. They could help identify important research directions for the development of new prognostic and therapeutic techniques for AML.

Farnesyltransferase-inhibitors exert in vitro immunosuppressive capacity by inhibiting human B-cells

Objectives

Farnesyltransferase inhibitors (FTI), which inhibit the prenylation of Ras GTPases, were developed as anti-cancer drugs. As additional target proteins for prenylation were identified in the past, it is likely that FTI have potential value for therapeutic purposes beyond cancer. The effect of FTI on B-cells remains unclear. To address this issue, we investigated the effects of in vitro FTI treatment on effector and regulatory B-cells in healthy controls and renal transplant patients.

Methods

For this purpose, B-cells were isolated from the peripheral blood of healthy controls and renal transplant patients. Purified B-cells were stimulated via Toll-like-receptor 9 (TLR-9) in the presence or absence of FTI. Regulatory functions, such as IL-10 and Granzyme B (GrB) secretion, were assessed by flow cytometry. In addition, effector B-cell functions, such as plasma cell formation and IgG secretion, were studied.

Results

The two FTI Lonafarnib and tipifarnib both suppressed TLR-9-induced B-cell proliferation. Maturation of IL-10 producing B-cells was suppressed by FTI at high concentrations as well as induction of GrB-secreting B-cells. Plasma blast formation and IgG secretion were potently suppressed by FTI. Moreover, purified B-cells from immunosuppressed renal transplant patients were also susceptible to FTI-induced suppression of effector functions, evidenced by diminished IgG secretion.

Conclusion

FTI suppress in vitro B-cell proliferation and plasma cell formation while partially preserving IL-10 as well as GrB production of B-cells. Thus, FTI may have immunosuppressive capacity encouraging further studies to investigate the potential immunomodulatory value of this agent.

Virtual screening and biological evaluation to identify pharmaceuticals potentially causing hypertension and hypokalemia by inhibiting steroid 11β-hydroxylase

Several drugs were found after their market approval to unexpectedly inhibit adrenal 11β-hydroxylase (CYP11B1)-dependent cortisol synthesis. Known side-effects of CYP11B1 inhibition include hypertension and hypokalemia, due to a feedback activation of adrenal steroidogenesis, leading to supraphysiological concentrations of 11-deoxycortisol and 11-deoxycorticosterone that can activate the mineralocorticoid receptor. This results in potassium excretion and sodium and water retention, ultimately causing hypertension. With the risk known but usually not addressed in preclinical evaluation, this study aimed to identify drugs and drug candidates inhibiting CYP11B1. Two conceptually different virtual screening methods were combined, a pharmacophore based and an induced fit docking approach. Cell-free and cell-based CYP11B1 activity measurements revealed several inhibitors with IC50 values in the nanomolar range. Inhibitors include retinoic acid metabolism blocking agents (RAMBAs), azole antifungals, α2-adrenoceptor ligands, and a farnesyltransferase inhibitor. The active compounds share a nitrogen atom embedded in an aromatic ring system. Structure activity analysis identified the free electron pair of the nitrogen atom as a prerequisite for the drug-enzyme interaction, with its pKa value as an indicator of inhibitory potency. Another important parameter is drug lipophilicity, exemplified by etomidate. Changing its ethyl ester moiety to a more hydrophilic carboxylic acid group dramatically decreased the inhibitory potential, most likely due to less efficient cellular uptake. The presented work successfully combined different in silico and in vitro methods to identify several previously unknown CYP11B1 inhibitors. This workflow facilitates the identification of compounds that inhibit CYP11B1 and therefore pose a risk for inducing hypertension and hypokalemia.

Targeting Harvey rat sarcoma viral oncogene homolog in head and neck cancer: how to move forward?

PURPOSE OF REVIEW

Despite recent advances, treatment personalization remains an issue for recurrent metastatic head and neck squamous cell carcinoma (RM HNSCC) patients. After human papilloma virus (HPV) and programmed death ligand 1 (PDL1) expression, Harvey rat sarcoma viral oncogene homolog (HRAS) appears as an emerging target in this field. In this review, we summarize the features of HRAS -mutated HNSCC and its targeting by farnesyl transferase inhibitors.

RECENT FINDINGS

HRAS mutations define a small subgroup of RM HNSCC patients with a poor prognosis and often refractory to the standard treatments. Posttranslational processing of HRAS being dependent on farnesylation, farnesyl transferase inhibitors have been evaluated in HRAS -mutated tumors. Tipifarnib, a first in class farnesyl transferase inhibitor, has shown efficacy in phase 2 trials with HRAS -mutated tumors. Despite reported high response rates in selected population, the efficacy of Tipifarnib is inconsistent and always transient, probably because of limiting hematological toxicities leading to dose reduction and occurrence of secondary resistance mutations.

SUMMARY

Tipifarnib is the first in the class of farnesyl transferase inhibitors to show efficacy in HRAS -mutated RM HNSCC. The understanding of mechanisms of resistance will pave the way for the design of second-generation farnesyl transferases inhibitors.

Synthetic Small Molecule Modulators of Hsp70 and Hsp40 Chaperones as Promising Anticancer Agents

A class of chaperones dubbed heat shock protein 70 (Hsp70) possesses high relevance in cancer diseases due to its cooperative activity with the well-established anticancer target Hsp90. However, Hsp70 is closely connected with a smaller heat shock protein, Hsp40, forming a formidable Hsp70-Hsp40 axis in various cancers, which serves as a suitable target for anticancer drug design. This review summarizes the current state and the recent developments in the field of (semi-)synthetic small molecule inhibitors directed against Hsp70 and Hsp40. The medicinal chemistry and anticancer potential of pertinent inhibitors are discussed. Since Hsp90 inhibitors have entered clinical trials but have exhibited severe adverse effects and drug resistance formation, potent Hsp70 and Hsp40 inhibitors may play a significant role in overcoming the drawbacks of Hsp90 inhibitors and other approved anticancer drugs.

Targeting the Isoprenoid Biosynthetic Pathway in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy for which there is currently no cure. While treatment options for MM have expanded over the last two decades, all patients will eventually become resistant to current therapies. Thus, there is an urgent need for novel therapeutic strategies to treat MM. The isoprenoid biosynthetic pathway (IBP) is responsible for the post-translational modification of proteins belonging to the Ras small GTPase superfamily, such as Ras, Rho and Rab family members. Given the important roles these GTPase proteins play in various cellular processes, there is significant interest in the development of inhibitors that disturb their prenylation and consequently their activity in MM cells. Numerous preclinical studies have demonstrated that IBP inhibitors have anti-MM effects, including the induction of apoptosis in MM cells and inhibition of osteoclast activity. Some IBP inhibitors have made their way into the clinic. For instance, nitrogenous bisphosphonates are routinely prescribed for the management MM bone disease. Other IBP inhibitors, including statins and farnesyltransferase inhibitors, have been evaluated in clinical trials for MM, while there is substantial preclinical investigation into geranylgeranyl diphosphate synthase inhibitors. Here we discuss recent advances in the development of IBP inhibitors, assess their mechanism of action and evaluate their potential as anti-MM agents.

Mechanistic insight into impact of phosphorylation on the enzymatic steps of farnesyltransferase

Farnesyltransferase (FTase) is a heterodimeric enzyme, which catalyzes covalent attachment of the farnesyl group to target proteins, thus coordinating their trafficking in the cell. FTase has been demonstrated to be highly expressed in cancer and neurological diseases; hence considered as a hot target for therapeutic purposes. However, due to the nonspecific inhibition, there has been only one inhibitor that could be translated into the clinic. Importantly, it has been shown that phosphorylation of the α-subunit of FTase increases the activity of the enzyme in certain diseases. As such, understanding the impact of phosphorylation on dynamics of FTase provides a basis for targeting a specific state of the enzyme that emerges under pathological conditions. To this end, we performed 18 μs molecular dynamics (MD) simulations using complexes of (non)-phosphorylated FTase that are representatives of the farnesylation reaction. We demonstrated that phosphorylation modulated the catalytic site by rearranging interactions between farnesyl pyrophosphate (FPP)/peptide substrate, catalytic Zn2+ ion/coordinating residues and hot-spot residues at the interface of the subunits, all of which led to the stabilization of the substrate and facilitation of the release of the product, thus collectively expediting the reaction rate. Importantly, we also identified a likely allosteric pocket on the phosphorylated FTase, which might be used for specific targeting of the enzyme. To the best of our knowledge, this is the first study that systematically examines the impact of phosphorylation on the enzymatic reaction steps, hence opens up new avenues for drug discovery studies that focus on targeting phosphorylated FTase.

New Perspectives in Treating Acute Myeloid Leukemia: Driving towards a Patient-Tailored Strategy

For decades, intensive chemotherapy (IC) has been considered the best therapeutic option for treating acute myeloid leukemia (AML), with no curative option available for patients who are not eligible for IC or who have had failed IC. Over the last few years, several new drugs have enriched the therapeutic arsenal of AML treatment for both fit and unfit patients, raising new opportunities but also new challenges. These include the already approved venetoclax, the IDH1/2 inhibitors enasidenib and ivosidenib, gemtuzumab ozogamicin, the liposomal daunorubicin/cytarabine formulation CPX-351, and oral azacitidine. Venetoclax, an anti BCL2-inhibitor, in combination with hypomethylating agents (HMAs), has markedly improved the management of unfit and elderly patients from the perspective of improved quality of life and better survival. Venetoclax is currently under investigation in combination with other old and new drugs in early phase trials. Recently developed drugs with different mechanisms of action and new technologies that have already been investigated in other settings (BiTE and CAR-T cells) are currently being explored in AML, and ongoing trials should determine promising agents, more synergic combinations, and better treatment strategies. Access to new drugs and inclusion in clinical trials should be strongly encouraged to provide scientific evidence and to define the future standard of treatment in AML.

Tipifarnib as maintenance therapy did not improve disease-free survival in patients with acute myelogenous leukemia at high risk of relapse: Results of the phase III randomized E2902 trial

PURPOSE

Despite the achievement of complete remission with chemotherapy in patients with acute myeloid leukemia (AML), relapse is common and the majority of patients will die of their disease. Patients who achieve a remission after refractory or relapsed disease as well as elderly patients have a very high rate of relapse even if they achieve a complete remission. A phase 3 randomized ECOG-ACRIN-led intergroup study was conducted to determine whether post-remission therapy with the farnesyl transferase inhibitor, tipifarnib (R115777), improved the disease-free survival (DFS) of adult patients with AML in complete remission (CR), at high risk for relapse.

PATIENTS AND METHODS

Adult patients with AML in remission after salvage therapy and/or over age 60 in first remission were enrolled in this study. They were randomly assigned to treatment with tipifarnib or observation (control). The primary objective was to compare the disease-free survival (DFS) between the two arms based on intention to treat, which includes all randomized patients.

RESULTS

One hundred and forty-four patients were enrolled on the study. Median DFS was 8.9 vs 5.3 months, for tipifarnib vs observation (one-sided p = 0.026) and did not cross the pre-specified boundary to call the study positive. For the 134 eligible patients, median DFS was 10.8 vs 5.3 months for those randomized to tipifarnib vs observation (one-sided p = 0.008). Moreover in an ad hoc evaluation of all women (n = 71) median DFS was 12.1 vs 3.9 months for tipifarnib vs observation (one-sided p = 0.0004) while median OS was 26.5 vs 8.4 months respectively (one-sided p = 0.001).

CONCLUSION

This study was not able to demonstrate a benefit to tipifarnib as maintenance therapy in patients with AML in remission. While subsets of patients may indeed benefit, additional studies would be needed to elucidate that benefit which is unlikely given that other seemingly better options have since become available.

Potential of Farnesyl Transferase Inhibitors in Combination Regimens in Squamous Cell Carcinomas

Current therapies for recurrent and metastatic SCC are associated with poor outcomes, and options for later lines of treatment are limited. Insights into potential therapeutic targets, as well as mechanisms of resistance to available therapies, have begun to be elucidated, creating the basis for exploration of combination approaches to drive better patient outcomes. Tipifarnib, a farnesyl transferase inhibitor (FTI), is a small molecule drug that has demonstrated encouraging clinical activity in a genetically-defined subset of head and neck squamous cell carcinoma (HNSCC)-specifically, tumors that express a mutation in the HRAS protooncogene. More recently, bioinformatic analyses and results from patient-derived xenograft modeling indicate that HRAS pathway dependency may extend to a broader subpopulation of SCCs beyond HRAS mutants in the context of combination with agents such as cisplatin, cetuximab, or alpelisib. In addition, tipifarnib can also inactivate additional farnesylated proteins implicated in resistance to approved therapies, including immunotherapies, through a variety of distinct mechanisms, suggesting that tipifarnib could serve as an anchor for combination regimens in SCCs and other tumor types.

A phase I clinical trial to study the safety of treatment with tipifarnib combined with bortezomib in patients with advanced stages of myelodysplastic syndrome and oligoblastic acute myeloid leukemia

PURPOSE

To determine the safety of tipifarnib in combination with escalating doses of bortezomib and to determine the maximum tolerated dose in patients with untreated high-risk MDS and oligoblastic acute myeloid leukemia, who were not eligible for intensive therapy.

EXPERIMENTAL DESIGN

In a "3 + 3″ design, patients received fixed doses of tipifarnib 200 mg bid (days 1-21) and escalating doses of bortezomib (days 8, 15, 22) every 4 weeks in 4-6 cycles.

RESULTS

The combination was tolerated well by the 11 patients in this study without reaching the maximum tolerated dose. Myelosuppression was the most frequent side effect, but usually of short duration. Interestingly a complete response with or without complete count recovery was observed in three patients and three additional patients had stable disease. The median duration of overall survival was 449 days. Two patients were still alive at 4.0 and 4.3 years, including one patient in continuing CR.

CONCLUSIONS

The combination of tipifarnib and bortezomib was tolerated well and appeared to have clinical activity in patients with high-risk MDS and AML with low counts of marrow blasts. Our results warrant further evaluation in a phase II study.

Genomic landscape in acute myeloid leukemia and its implications in risk classification and targeted therapies

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy in terms of clinical features, underlying pathogenesis and treatment outcomes. Recent advances in genomic techniques have unraveled the molecular complexity of AML leukemogenesis, which in turn have led to refinement of risk stratification and personalized therapeutic strategies for patients with AML. Incorporation of prognostic and druggable genetic biomarkers into clinical practice to guide patient-specific treatment is going to be the mainstay in AML therapeutics. Since 2017 there has been an explosion of novel treatment options to tailor personalized therapy for AML patients. In the past 3 years, the U.S. Food and Drug Administration approved a total of eight drugs for the treatment of AML; most specifically target certain gene mutations, biological pathways, or surface antigen. These novel agents are especially beneficial for older patients or those with comorbidities, in whom the treatment choice is limited and the clinical outcome is very poor. How to balance efficacy and toxicity to further improve patient outcome is clinically relevant. In this review article, we give an overview of the most relevant genetic markers in AML with special focus on the therapeutic implications of these aberrations.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

Identification of tipifarnib sensitivity biomarkers in T-cell acute lymphoblastic leukemia and T-cell lymphoma

Patients diagnosed with T-cell leukemias and T-cell lymphomas (TCLs) still have a poor prognosis and an inadequate response to current therapies, highlighting the need for targeted treatments. We have analyzed the potential therapeutic value of the farnesyltransferase inhibitor, tipifarnib, in 25 TCL cell lines through the identification of genomic and/or immunohistochemical markers of tipifarnib sensitivity. More than half of the cell lines (60%) were considered to be sensitive. Tipifarnib reduced cell viability in these T-cell leukemia and TCL cell lines, induced apoptosis and modified the cell cycle. A mutational study showed TP53, NOTCH1 and DNMT3 to be mutated in 84.6%, 69.2% and 30.0% of sensitive cell lines, and in 62.5%, 0% and 0% of resistant cell lines, respectively. An immunohistochemistry study showed that p-ERK and RelB were associated as potential biomarkers of tipifarnib sensitivity and resistance, respectively. Data from RNA-seq show that tipifarnib at IC₅₀ after 72 h downregulated a great variety of pathways, including those controlling cell cycle, metabolism, and ribosomal and mitochondrial activity. This study establishes tipifarnib as a potential therapeutic option in T-cell leukemia and TCL. The mutational state of NOTCH1, p-ERK and RelB could serve as potential biomarkers of tipifarnib sensitivity and resistance.

Prediction of Apparent Oral Clearance of Small-Molecule Inhibitors in Pediatric Patients

The purpose of this study was to build regression models for the prediction of apparent oral clearance (CL/F) for small-molecule inhibitors in the pediatric population using data obtained from adults. Two approaches were taken; a simple allometric regression model which considers no interdrug or interindividual variability and an allometric regression model with mixed-effects modeling where some variability parameters are included in the model. Average CL/F values were obtained for 15 drugs at various dosages from 31 literatures (a total of 139 data sets) conducted in adults and for 15 drugs from 26 literatures (62 data sets) conducted in children. Data were randomly separated into the "modeling" or "validation" data set, and the 2 allometric regression models were applied to the modeling data set. The predictive ability of the models was examined by comparing the observed and model-predicted CL/F in children using the validation data set. The percentage root mean square error was 17.2% and 26.3% in the simple allometric regression model and the allometric regression model with mixed-effects modeling, respectively. The predictive ability of the 2 models seems acceptable, suggesting that they could be useful for predicting the CL/F of new small-molecule inhibitors and for determining adequate doses in clinical pharmacotherapy for children.

Molecular-Targeted Agents in Pancreatic Cancer

Background

Despite the acceptance of gemcitabine as the standard first-line agent for the treatment of advanced pancreatic cancer as well as the improved response rates seen with gemcitabine combinations, novel therapies are needed for this disease, which has one of the lowest survival rates. The growing understanding of the molecular basis of pancreatic cancer and the recent introduction of targeted therapeutic agents have initiated novel studies that have the potential to improve on existing treatments.

Methods

We review the rationale and the clinical studies of therapeutic agents that target some of the molecular abnormalities commonly found in pancreatic cancer.

Results

Matrix metalloproteinase inhibitors (MMPIs), farnesyltransferase inhibitors (FTIs), and tyrosine-kinase inhibitors and monoclonal antibodies against growth factors or their receptors are novel agents that have undergone phase II or III trials. Phase III studies of MMPIs, alone or in combination with gemcitabine, and phase III studies of FTIs have produced disappointing results. Other agents in earlier phases of clinical development remain promising.

Conclusions

Despite the negative studies of MMPIs and FTIs, the results of phase II trials of other drugs are encouraging. Targeted agents may improve the prognosis of pancreatic cancer.

Management of Acute Myelogenous Leukemia in the Elderly

BACKGROUND

Acute myelogenous leukemia (AML) is a hematopoietic neoplasm that primarily affects older adults. Despite scientific advances into the epidemiologic, genetic, and biological features of AML, this disease remains fatal to the majority of patients, particularly older individuals.

METHODS

We review the biologic and clinical characteristics of AML in the elderly and the treatment options that have emerged for them during the past several years.

RESULTS

Several biologic features of AML differ between older and younger individuals. Older patients often have disease that expresses multidrug resistance phenotype and cytogenetic abnormalities, which may be responsible in large part for the poor outcomes observed in older-aged subgroups. Traditional cytotoxic chemotherapy is associated with a low complete response rate and a high treatment-related mortality in older patients, which explains in part the poorer outcomes in cohorts over 60 years of age. Research into the pathophysiology of AML has revealed an abundance of intracellular signaling events that govern proliferation and survival of the malignant cell. Such discoveries have promoted recognition of new molecular and antigenic targets (eg, Flt-3 kinase, Ras, CD33 antigen) to which therapeutic development may be aimed.

CONCLUSIONS

New therapies directed against these unique targets may add to the current arsenal of antileukemic regimens and improve response rates and survival in older patients.

Targeted Therapy for Hematologic Malignancies

Background:

The introduction of monoclonal antibodies, either as native molecules or conjugated to radioisotopes or other toxins, has led to new therapeutic options for patients with hematologic malignancies. In addition, the use of small molecules against specific cell surface receptors, enzymes, and proteins has become an important strategy in the treatment of such disorders.

Methods:

The author reviewed the published clinical trials of monoclonal antibody and other targeted therapies in hematologic malignancies.

Results:

Results from several trials demonstrate a therapeutic benefit for the use of monoclonal antibodies (either native or conjugated) and other targeted therapies, used alone or in combination with standard cytotoxic chemotherapy.

Conclusions:

Targeted therapy of hematologic malignancies seems to be an effective and less toxic approach to the treatment of such disorders. Nevertheless, additional studies are needed to determine where and when such management fits into a therapeutic regimen for any given disorder, whether upfront or as salvage therapy, alone or in combination with chemotherapy (concurrent or sequential).

Farnesyltransferase Inhibitors and Their Role in the Treatment of Multiple Myeloma

BACKGROUND

Ras mutations are among the most common oncogene mutations found in multiple myeloma (MM). Patients with mutated Ras are less likely to respond to chemotherapy and have a shortened median survival. Therefore, targeting Ras farnesylation may be a valuable approach to treatment of MM. R115777 (tipifarnib) is a potent farnesyltransferase inhibitor (FTI) presently undergoing phase II/III clinical trials.

METHODS

We reviewed the preclinical and clinical experience of FTIs as antineoplastic agents and describe their potential role in the treatment of MM.

RESULTS

FTIs are a novel group of agents that selectively inhibit farnesyltransferase, an enzyme responsible for the posttranslational modification of several proteins including Ras. Since Ras is among the most commonly mutated oncogenes associated with cancer, this class of drugs has been evaluated in clinical trials in a diversity of tumors. R115777 has been evaluated in a phase II clinical trial in patients with advanced myeloma and found to be well tolerated. It induced disease stabilization in more than 60% of patients with advanced myeloma.

CONCLUSIONS

The drug selectively targets farnesyltransferase, but this effect did not correlate with disease stabilization, suggesting that these drugs may be targeting a survival pathway independent of Ras processing. Further studies will evaluate the use of FTI in maintenance therapy as well as in combination with other agents in advanced myeloma.

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

Emerging strategies for the treatment of older patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia in adults, and its incidence increases with age. Clinical outcomes in younger patients have improved over the years but, unfortunately, there is little evidence for an equivalent improvement in outcome for older patients. Approximately 50 % of older patients who are able to receive intensive chemotherapy will achieve a complete remission; however, they face a much higher relapse rate than younger patients, and survival rates for this group are low. Therefore, there is an urgent need to improve outcomes in older patients with AML. In this article, we discuss current treatment paradigms for older patients with AML including the challenges faced when determining which patients are eligible for intensive chemotherapy. We then highlight new treatments in development that may benefit this patient group. Cytotoxic agents, hypomethylating agents, molecularly targeted agents, and cell cycle kinase inhibitors are discussed, with a focus on novel agents that have achieved an advanced stage of development. Overall, the treatment of AML in older patients remains a challenge and, whenever possible, treatment should be offered in the context of clinical trials and should be planned with curative intent.

Phase II/III trial of a pre-transplant farnesyl transferase inhibitor in juvenile myelomonocytic leukemia: a report from the Children's Oncology Group

BACKGROUND

Juvenile myelomonocytic leukemia (JMML) is not durably responsive to chemotherapy, and approximately 50% of patients relapse after hematopoietic stem cell transplant (HSCT). Here we report the activity and acute toxicity of the farnesyl transferase inhibitor tipifarnib, the response rate to 13-cis retinoic acid (CRA) in combination with cytoreductive chemotherapy, and survival following HSCT in children with JMML.

PROCEDURE

Eighty-five patients with newly diagnosed JMML were enrolled on AAML0122 between 2001 and 2006. Forty-seven consented to receive tipifarnib in a phase II window before proceeding to a phase III trial of CRA in combination with fludarabine and cytarabine followed by HSCT and maintenance CRA. Thirty-eight patients enrolled only in the phase III trial.

RESULTS

Overall response rate was 51% after tipifarnib and 68% after fludarabine/cytarabine/CRA. Tipifarnib did not increase pre-transplant toxicities. Forty-six percent of the 44 patients who received protocol compliant HSCT relapsed. Five-year overall survival was 55 ± 11% and event-free survival was 41 ± 11%, with no significant difference between patients who did or did not receive tipifarnib.

CONCLUSIONS

Administration of tipifarnib in the window setting followed by HSCT in patients with newly diagnosed JMML was safe and yielded a 51% initial response rate as a single agent, but failed to reduce relapse rates or improve long-term overall survival.

Identification of novel therapeutic targets in acute leukemias with NRAS mutations using a pharmacologic approach

Oncogenic forms of NRAS are frequently associated with hematologic malignancies and other cancers, making them important therapeutic targets. Inhibition of individual downstream effector molecules (eg, RAF kinase) have been complicated by the rapid development of resistance or activation of bypass pathways. For the purpose of identifying novel targets in NRAS-transformed cells, we performed a chemical screen using mutant NRAS transformed Ba/F3 cells to identify compounds with selective cytotoxicity. One of the compounds identified, GNF-7, potently and selectively inhibited NRAS-dependent cells in preclinical models of acute myelogenous leukemia and acute lymphoblastic leukemia. Mechanistic analysis revealed that its effects were mediated in part through combined inhibition of ACK1/AKT and of mitogen-activated protein kinase kinase kinase kinase 2 (germinal center kinase). Similar to genetic synthetic lethal approaches, these results suggest that small molecule screens can be used to identity novel therapeutic targets in cells addicted to RAS oncogenes.

HMG-CoA reductase inhibitors as adjuvant treatment for hematologic malignancies: what is the current evidence?

Statins have been shown to possess properties that go beyond their lipid-lowering effects. These agents act on the mevalonate pathway and inhibit synthesis of cholesterol, geranylgeranyl pyrophosphate, and farnesyl pyrophosphate, which are necessary for posttranslational modification of the Rho, Rac, and Ras superfamily of proteins. Early phase studies have demonstrated that this modulation of cellular signaling can ultimately exert pro-apoptotic, anti-angiogenic, and immunomodulatory effects, and might even restore chemosensitivity in several hematologic cancers. Nonetheless, these promising preclinical results have not yet migrated from the bench to the bedside as their effectiveness as adjuvant agents in hematologic malignancies is currently uncertain. In the present review, we summarize the existing evidence stemming from preclinical and clinical studies pertaining to the use of statins as adjuvant therapies in hematologic malignancies, and discuss the new insights gained from the ongoing translational research.

Upregulation of IGF1R by mutant RAS in leukemia and potentiation of RAS signaling inhibitors by small-molecule inhibition of IGF1R

PURPOSE

Activating mutations in the RAS oncogene occur frequently in human leukemias. Direct targeting of RAS has proven to be challenging, although targeting of downstream RAS mediators, such as MEK, is currently being tested clinically. Given the complexity of RAS signaling, it is likely that combinations of targeted agents will be more effective than single agents.

EXPERIMENTAL DESIGN

A chemical screen using RAS-dependent leukemia cells was developed to identify compounds with unanticipated activity in the presence of an MEK inhibitor and led to identification of inhibitors of IGF1R. Results were validated using cell-based proliferation, apoptosis, cell-cycle, and gene knockdown assays; immunoprecipitation and immunoblotting; and a noninvasive in vivo bioluminescence model of acute myeloid leukemia (AML).

RESULTS

Mechanistically, IGF1R protein expression/activity was substantially increased in mutant RAS-expressing cells, and suppression of RAS led to decreases in IGF1R. Synergy between MEK and IGF1R inhibitors correlated with induction of apoptosis, inhibition of cell-cycle progression, and decreased phospho-S6 and phospho-4E-BP1. In vivo, NSG mice tail veins injected with OCI-AML3-luc+ cells showed significantly lower tumor burden following 1 week of daily oral administration of 50 mg/kg NVP-AEW541 (IGF1R inhibitor) combined with 25 mg/kg AZD6244 (MEK inhibitor), as compared with mice treated with either agent alone. Drug combination effects observed in cell-based assays were generalized to additional mutant RAS-positive neoplasms.

CONCLUSIONS

The finding that downstream inhibitors of RAS signaling and IGF1R inhibitors have synergistic activity warrants further clinical investigation of IGF1R and RAS signaling inhibition as a potential treatment strategy for RAS-driven malignancies.

Novel drugs for older patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is the second most common form of leukemia and the most frequent cause of leukemia-related deaths in the United States. The incidence of AML increases with advancing age and the prognosis for patients with AML worsens substantially with increasing age. Many older patients are ineligible for intensive treatment and require other therapeutic approaches to optimize clinical outcome. To address this treatment gap, novel agents with varying mechanisms of action targeting different cellular processes are currently in development. Hypomethylating agents (azacitidine, decitabine, SGI-110), histone deacetylase inhibitors (vorinostat, pracinostat, panobinostat), FMS-like tyrosine kinase receptor-3 inhibitors (quizartinib, sorafenib, midostaurin, crenolanib), cytotoxic agents (clofarabine, sapacitabine, vosaroxin), cell cycle inhibitors (barasertib, volasertib, rigosertib) and monoclonal antibodies (gentuzumab ozogamicin, lintuzumab-Ac225) represent some of these promising new treatments. This review provides an overview of novel agents that have either completed or are currently in ongoing phase III trials in patients with previously untreated AML for whom intensive treatment is not an option. Other potential drugs in earlier stages of development will also be addressed in this review.

Ras/Raf/MEK/ERK Pathway Activation in Childhood Acute Lymphoblastic Leukemia and Its Therapeutic Targeting

Deregulation of the Ras/Raf/MEK/extracellular signal-regulated kinase pathway is a common event in childhood acute lymphoblastic leukemia and is caused by point mutation, gene deletion, and chromosomal translocation of a vast array of gene types, highlighting its importance in leukemia biology. Pathway activation can be therapeutically exploited and may guide new therapies needed for relapsed acute lymphoblastic leukemia and other high risk subgroups.

Identification of Wee1 as a novel therapeutic target for mutant RAS-driven acute leukemia and other malignancies

Direct targeting of rat sarcoma (RAS), which is frequently mutated, has proven to be challenging, and inhibition of individual downstream RAS mediators has resulted in limited clinical efficacy. We designed a chemical screen to identify compounds capable of potentiating mammalian target of rapamycin (mTOR) inhibition in mutant RAS-positive leukemia, and identified a Wee1 inhibitor. Synergy was observed in both mutant neuroblastoma RAS viral oncogene homolog (NRAS)- and mutant kirsten RAS viral oncogene homolog (KRAS)-positive acute myelogenous leukemia (AML) cell lines and primary patient samples. The observed synergy enhanced dephosphorylation of AKT, 4E-binding protein 1 and s6 kinase, and correlated with increased apoptosis. The specificity of Wee1 as the target of MK-1775 was validated by Wee1 knockdown, as well as partial reversal of drug combination-induced apoptosis by a cyclin-dependent kinase 1 (CDK1) inhibitor. Importantly, we also extended our findings to other mutant RAS-expressing malignancies, including mutant NRAS-positive melanoma, and mutant KRAS-positive colorectal cancer, pancreatic cancer and lung cancer. We observed favorable responses with combined Wee1/mTOR inhibition in human cancer cell lines from multiple malignancies, and inhibition of tumor growth in in vivo models of mutant KRAS lung cancer and leukemia. The present study introduces for the first time Wee1 inhibition combined with mTOR inhibition as a novel therapeutic strategy for the selective treatment of mutant RAS-positive leukemia and other mutant RAS-expressing malignancies.

Four different regimens of farnesyltransferase inhibitor tipifarnib in older, untreated acute myeloid leukemia patients: North American Intergroup Phase II study SWOG S0432

We report on 348 patients ≥ 70 years (median age 78 years) with acute myeloid leukemia (>50% with secondary AML) randomized to receive either 600 mg or 300 mg of tipifarnib orally twice daily on days 1-21 or days 1-7 and 15-21, repeated every 28 days (4 treatment regimens). Responses were seen in all regimens, with overall response rate (CR + CRi + PR) highest (20%) among patients receiving tipifarnib 300 mg twice daily on days 1-21. Toxicities were acceptable. Unless predictors of response to tipifarnib are identified, further study as a single agent in this population is unwarranted.

Cloretazine for the treatment of acute myeloid leukemia

Cloretazine is a new sulfonylhydrazine alkylating agent with antileukemic activity. Phase I studies have shown myelosuppression to be the dose limiting toxicity in both solid tumors and leukemias. A large Phase II study of single agent cloretazine (600 mg/m2) confirmed its activity in patients with relapsed acute myeloid leukemia, and in elderly patients with previously untreated acute myeloid leukemia or myelodysplastic syndrome. It also confirmed the limited nonhematological toxicity, even in elderly patients. Cloretazine can be safely combined with cytarabine, and this combination regimen is currently being tested in a large Phase III study in patients with relapsed acute myeloid leukemia. Cloretazine is a promising new antileukemic agent that may be incorporated into an intensive combination regimen.

Novel therapies for patients with chronic myeloid leukemia

The most immediate issues that will have a major impact on the long-term survival of patients with chronic myeloid leukemia is the optimal use of imatinib mesylate (Gleevec, Novartis) and the development of effective therapies for those patients who are intolerant of, or become resistant to, optimal doses of this agent. Of the multiple new agents that are currently being developed for patients with chronic myeloid leukemia, most are being investigated in patients who have developed resistance to imatinib, which is a confounding factor in itself. The mechanisms of action of novel agents are diverse and they may have a variably synergistic therapeutic relationship with imatinib. The complete blockade of the intracellular pathways that are triggered by Bcr-Abl, combined with successful reversal of apoptotic and/or angiogenic abnormalities in chronic myeloid leukemia, may well lead to a cure for the majority of patients.

Novel targeted drug therapies for the treatment of childhood acute leukemia

The cure rates for childhood acute leukemia have dramatically improved to approximately 70% overal, with treatments that include intensive cytotoxic chemotherapy and, in some cases, hematopoietic stem cell transplantation. However, many children still die of their disease or of treatment-related toxicities. Even in patients that are cured, there can be significant and, not uncommonly debilitating, acute and late complications of treatment. Improved understanding of the molecular and cellular biology of leukemia and the increasing availability of high-throughput genomic techniques have facilitated the development of molecularly targeted therapies that have the potential to be more effective and less toxic than the standard approaches. In this article, we review the progress to date with agents that are showing promise in the treatment of childhood acute leukemia, including monoclonal antibodies, inhibitors of kinases and other signaling molecules (e.g., BCR-ABL, FLT3, farnesyltransferase, mTOR and γ-secretase), agents that target epigenetic regulation of gene expression (DNA methyltransferase inhibitors and histone deacetylase inhibitors) and proteasome inhibitors. For the specific agents in each of these classes, we summarize the published preclinical data and the clinical trials that have been completed, are in progress or are being planned for children with acute leukemia. Finally, we discuss potential challenges to the success of molecularly targeted therapy, including proper target identification, adequate targeting of leukemia stem cells, developing synergistic and tolerable combinations of agents and designing adequately powered clinical trials to test efficacy in molecularly defined subsets of patients.

Tanespimycin and tipifarnib exhibit synergism in inducing apoptosis in melanoma cell lines from later stages of tumor progression

Many anticancer strategies rely on efficient induction of apoptosis. The need for development of drug combinations with a strong pro-apoptotic activity is of particular interest in melanoma resistant to currently available chemotherapeutic regimes. We studied the pro-apoptotic properties of combination of tanespimycin+tipifarnib in five melanoma cell lines representing various stages of tumor progression. Our results show that in cells derived from vertical- and metastatic-phase the combination of tested drugs is strongly cytotoxic and efficient in inducing apoptosis, as evidenced by activation of caspase-9 and caspase-3 and enhanced fragmentation of DNA.

Farnesyltransferase inhibitor tipifarnib inhibits Rheb prenylation and stabilizes Bax in acute myelogenous leukemia cells

Although farnesyltransferase inhibitors have shown promising activity in relapsed lymphoma and sporadic activity in acute myelogenous leukemia, their mechanism of cytotoxicity is incompletely understood, making development of predictive biomarkers difficult. In the present study, we examined the action of tipifarnib in human acute myelogenous leukemia cell lines and clinical samples. In contrast to the Ras/MEK/ERK pathway-mediated Bim upregulation that is responsible for tipifarnib-induced killing of malignant lymphoid cells, inhibition of Rheb-induced mTOR signaling followed by dose-dependent upregulation of Bax and Puma occurred in acute myelogenous leukemia cell lines undergoing tipifarnib-induced apoptosis. Similar Bax and Puma upregulation occurred in serial bone marrow samples harvested from a subset of acute myelogenous leukemia patients during tipifarnib treatment. Expression of FTI-resistant Rheb M184L, like knockdown of Bax or Puma, diminished tipifarnib-induced killing. Further analysis demonstrated that increased Bax and Puma levels reflect protein stabilization rather than increased gene expression. In U937 cells selected for tipifarnib resistance, neither inhibition of signaling downstream of Rheb nor Bax and Puma stabilization occurred. Collectively, these results not only identify a pathway downstream from Rheb that contributes to tipifarnib cytotoxicity in human acute myelogenous leukemia cells, but also demonstrate that FTI-induced killing of lymphoid versus myeloid cells reflects distinct biochemical mechanisms downstream of different farnesylated substrates. (ClinicalTrials.gov identifier NCT00602771).

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.

The clinically relevant pharmacogenomic changes in acute myelogenous leukemia

Acute myelogenous leukemia (AML) is an extremely heterogeneous neoplasm with several clinical, pathological, genetic and molecular subtypes. Combinations of various doses and schedules of cytarabine and different anthracyclines have been the mainstay of treatment for all forms of AMLs in adult patients. Although this combination, with the addition of an occasional third agent, remains effective for treatment of some young-adult patients with de novo AML, the prognosis of AML secondary to myelodysplastic syndromes or myeloproliferative neoplasms, treatment-related AML, relapsed or refractory AML, and AML that occurs in older populations remains grim. Taken into account the heterogeneity of AML, one size does not and should not be tried to fit all. In this article, the authors review currently understood, applicable and relevant findings related to cytarabine and anthracycline drug-metabolizing enzymes and drug transporters in adult patients with AML. To provide a prime-time example of clinical applicability of pharmacogenomics in distinguishing a subset of patients with AML who might be better responders to farnesyltransferase inhibitors, the authors also reviewed findings related to a two-gene transcript signature consisting of high RASGRP1 and low APTX, the ratio of which appears to positively predict clinical response in AML patients treated with farnesyltransferase inhibitors.

New therapeutic approaches to acute myeloid leukemia

BACKGROUND

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the pathogenesis and treatment of patients with AML. Understanding the basic cellular and molecular pathogenesis of leukemic cells is vital to the development of new treatment approaches.

OBJECTIVE/METHODS

To review progress until now with agents that are showing promise in the treatment of AML, we summarize the published preclinical and clinical trials that have been completed.

RESULTS

Based on recent progress of investigations, more specifically targeted agents have been developed for the treatment of AML such as tyrosine kinase inhibitors, monoclonal antibodies, epigenetic agents, antiangiogenic agents, and farnesyl transferase inhibitors.

CONCLUSION

In the future, in addition to performing therapeutic trials of these agents, it will be important to identify other highly specific therapeutic agents based on our evolving understanding of the biology of AML.

A phase I/II study of sorafenib in combination with low dose cytarabine in elderly patients with acute myeloid leukemia or high-risk myelodysplastic syndrome from the National Cancer Institute of Canada Clinical Trials Group: trial IND.186

Sorafenib is active in patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). The National Cancer Institute of Canada (NCIC) Clinical Trials Group initiated a phase I/II study of the combination of sorafenib with cytarabine in older patients with AML or high-risk MDS who were unsuitable for intensive chemotherapy. FLT3 mutational status was determined in all patients. Twenty-one patients were enrolled (four MDS, 17 AML) with a median age of 77 years. The recommended phase II dose (RP2D) was cytarabine 10 mg bid days 1-10 and sorafenib 600 mg/day days 2-28. Dose-limiting toxicities were fatigue, sepsis and skin rash. Of 15 evaluable patients treated at the RP2D, two patients responded. The overall response rate for eligible patients was 10%. FLT3 mutations were found in only three patients. We conclude that this combination of sorafenib and cytarabine has limited activity in this unselected cohort of elderly patients with AML/MDS in which FLT3 mutations seemed underrepresented.

The Development of Novel Therapies for the Treatment of Acute Myeloid Leukemia (AML)

Acute myeloid leukemia (AML) is nearly always a fatal malignancy. For the past 40 years, the standard of care remains a combination of cytarabine and an anthracycline known as 7 + 3. This treatment regimen is troubled by both low survival rates (10% at 5 years) and deaths due to toxicity. Substantial new laboratory findings over the past decade have identified many cellular pathways that contribute to leukemogenesis. These studies have led to the development of novel agents designed to target these pathways. Here we discuss the molecular underpinnings and clinical benefits of these novel treatment strategies. Most importantly these studies demonstrate that clinical response is best achieved by stratifying each patient based on a detailed understanding of their molecular abnormalities.

Targeting oncogenic Ras signaling in hematologic malignancies

Ras proteins are critical nodes in cellular signaling that integrate inputs from activated cell surface receptors and other stimuli to modulate cell fate through a complex network of effector pathways. Oncogenic RAS mutations are found in ∼25% of human cancers and are highly prevalent in hematopoietic malignancies. Because of their structural and biochemical properties, oncogenic Ras proteins are exceedingly difficult targets for rational drug discovery, and no mechanism-based therapies exist for cancers with RAS mutations. This article reviews the properties of normal and oncogenic Ras proteins, the prevalence and likely pathogenic role of NRAS, KRAS, and NF1 mutations in hematopoietic malignancies, relevant animal models of these cancers, and implications for drug discovery. Because hematologic malignancies are experimentally tractable, they are especially valuable platforms for addressing the fundamental question of how to reverse the adverse biochemical output of oncogenic Ras in cancer.

Inhibition of protein geranylgeranylation and farnesylation protects against graft-versus-host disease via effects on CD4 effector T cells

Despite advances in immunosuppressive regimens, acute graft-versus-host disease remains a frequent complication of allogeneic hematopoietic cell transplantation. Pathogenic donor T cells are dependent on correct attachment of small GTPases to the cell membrane, mediated by farnesyl- or geranylgeranyl residues, which, therefore, constitute potential targets for graft-versus-host disease prophylaxis. A mouse model was used to study the impact of a farnesyl-transferase inhibitor and a geranylgeranyl-transferase inhibitor on acute graft-versus-host disease, anti-cytomegalovirus T-cell responses and graft-versus-leukemia activity. Treatment of mice undergoing allogeneic hematopoietic cell transplantation with farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor reduced the histological severity of graft-versus-host disease and prolonged survival significantly. Mechanistically, farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor treatment resulted in reduced alloantigen-driven expansion of CD4 T cells. In vivo treatment led to increased thymic cellularity and polyclonality of the T-cell receptor repertoire by reducing thymic graft-versus-host disease. These effects were absent when squalene production was blocked. The farnesyl-transferase inhibitor and geranylgeranyl-transferase inhibitor did not compromise CD8 function against leukemia cells or reconstitution of T cells that were subsequently responsible for anti-murine cytomegalovirus responses. In summary, we observed an immunomodulatory effect of inhibitors of farnesyl-transferase and geranylgeranyl-transferase on graft-versus-host disease, with enhanced functional immune reconstitution. In the light of the modest toxicity of farnesyl-transferase inhibitors such as tipifarnib in patients and the potent reduction of graft-versus-host disease in mice, farnesyl-transferase and geranylgeranyl-transferase inhibitors could help to reduce graft-versus-host disease significantly without having a negative impact on immune reconstitution.

Tipifarnib and tanespimycin show synergic proapoptotic activity in U937 cells

BACKGROUND

Farnesyltransferase inhibitor tipifarnib (R115777) has been used for treatment of hematological malignancies; however, its observed anticancer effect was limited. This prompted us to search for inhibitors that would show synergic, proapoptotic effect when combined with R115777. We decided to study LY294002, which inhibits PI-3 kinase, and tanespimycin (17AAG), which inhibits Hsp90--a chaperone for a number of proteins, including Akt kinase.

METHODS

The effect of drugs, used alone or in combination, was tested in U937 cells (human leukemic monocyte lymphoma), which are often used as a model for liquid tumor. The number of viable cells was evaluated with trypan blue staining, while apoptosis was assessed by presence of active caspase-3 and terminal dUTP nick-end labeling of DNA (TUNEL).

RESULTS

At concentrations in which R115777, LY294002 and 17AAG were only slowing down the proliferation rate, when used separately, the combination of R115777 + LY294002 and R115777 + 17AAG significantly reduced the number of cells and induced cellular apoptosis.

CONCLUSIONS

Our results suggest that the combination of R115777 + 17AAG could be useful in treating some of the hematological malignancies.

Acute myeloid leukaemia: optimal management and recent developments

The current treatment of patients with acute myeloid leukaemia yields poor results, with expected cure rates in the order of 30-40% depending on the biological characteristics of the leukaemic clone. Therefore, new agents and schemas are intensively studied in order to improve patients' outcomes. This review summarizes some of these new paradigms, including new questions such as which anthracycline is most effective and at what dose. High doses of daunorubicin have shown better responses in young patients and are well tolerated in elderly patients. Monoclonal antibodies are promising agents in good risk patients. Drugs blocking signalling pathways could be used in combination with chemotherapy or in maintenance with promising results. Epigenetic therapies, particularly after stem cell transplantation, are also discussed. New drugs such as clofarabine and flavopiridol are reviewed and the results of their use discussed. It is clear that many new approaches are under study and hopefully will be able to improve on the outcomes of the commonly used '7+3' regimen of an anthracycline plus cytarabine with daunorubicin, which is clearly an ineffective therapy in the majority of patients.

Multi-institutional phase 2 clinical and pharmacogenomic trial of tipifarnib plus etoposide for elderly adults with newly diagnosed acute myelogenous leukemia

Tipifarnib (T) exhibits modest activity in elderly adults with newly diagnosed acute myelogenous leukemia (AML). Based on preclinical synergy, a phase 1 trial of T plus etoposide (E) yielded 25% complete remission (CR). We selected 2 comparable dose levels for a randomized phase 2 trial in 84 adults (age range, 70-90 years; median, 76 years) who were not candidates for conventional chemotherapy. Arm A (T 600 mg twice a day × 14 days, E 100 mg days 1-3 and 8-10) and arm B (T 400 mg twice a day × 14 days, E 200 mg days 1-3 and 8-10) yielded similar CR, but arm B had greater toxicity. Total CR was 25%, day 30 death rate 7%. A 2-gene signature of high RASGRP1 and low aprataxin (APTX) expression previously predicted for T response. Assays using blasts from a subset of 40 patients treated with T plus E on this study showed that AMLs with a RASGRP1/APTX ratio of more than 5.2 had a 78% CR rate and negative predictive value 87%. This ratio did not correlate with outcome in 41 patients treated with conventional chemotherapies. The next T-based clinical trials will test the ability of the 2-gene signature to enrich for T responders prospectively. This study is registered at www.clinicaltrials.gov as #NCT00602771.