Farnesyl protein transferase inhibitors and other therapies targeting the Ras signal transduction pathway

Targeted Therapies for the Neurofibromatoses

Over the past several years, management of the tumors associated with the neurofibromatoses has been recognized to often require approaches that are distinct from their spontaneous counterparts. Focus has shifted to therapy aimed at minimizing symptoms given the risks of persistent, multiple tumors and new tumor growth. In this review, we will highlight the translation of preclinical data to therapeutic trials for patients with neurofibromatosis, particularly neurofibromatosis type 1 and neurofibromatosis type 2. Successful inhibition of MEK for patients with neurofibromatosis type 1 and progressive optic pathway gliomas or plexiform neurofibromas has been a significant advancement in patient care. Similar success for the malignant NF1 tumors, such as high-grade gliomas and malignant peripheral nerve sheath tumors, has not yet been achieved; nor has significant progress been made for patients with either neurofibromatosis type 2 or schwannomatosis, although efforts are ongoing.

Lovastatin and perillyl alcohol inhibit glioma cell invasion, migration, and proliferation--impact of Ras-/Rho-prenylation

Alterations in small GTPase mediated signal transduction pathways have emerged as a central step in the molecular pathogenesis of glioblastoma (GBM), the most common malignant brain tumor in adults. Farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) are derived from mevalonate, whose production is catalyzed by 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase. Prenylation by FPP and GGPP is required for membrane insertion and oncogenic function of Ras- and Rho-proteins, within the stimulation of the Ras-Raf-MEK-ERK pathway. A straightforward prediction from HMG-CoA reductase inhibitor studies is that statins decrease FPP and GGPP levels and diminish ERK signaling ensuring less proliferation and migration of cancer cells. Perillyl alcohol (POH), a naturally occurring monoterpene inhibits prenyltransferases and is able to inhibit cancer cell growth, but the underlying mechanism is still unclear. We here report that lovastatin (LOV) and POH impair the regulation of the mevalonate- and the Ras-Raf-MEK-ERK pathway in U87 and U343 glioblastoma cells. Both compounds affected the post-translational modification of H-Ras and Rac1. While LOV diminished the substrates of the transferase reaction that catalyze prenylation, POH inhibited the enzymes itself. Our data highlight the impact of isoprenoids for post-translational modification of small GTPases promoting proliferation, migration and invasion capabilities in glioma cells.

Phase 2 randomized, flexible crossover, double-blinded, placebo-controlled trial of the farnesyltransferase inhibitor tipifarnib in children and young adults with neurofibromatosis type 1 and progressive plexiform neurofibromas

BACKGROUND

RAS is dysregulated in neurofibromatosis type 1 (NF1) related plexiform neurofibromas (PNs). The activity of tipifarnib, which blocks RAS signaling by inhibiting its farnesylation, was tested in children and young adults with NF1 and progressive PNs.

METHODS

Patients aged 3-25 years with NF1-related PNs and imaging evidence of tumor progression were randomized in a double-blinded fashion to receive tipifarnib (200 mg/m(2) orally every 12 h) or placebo (phase A) and crossed over to the opposite treatment arm at the time of tumor progression (phase B). PN volumes were measured with MRI, and progression was defined as ≥20% volume increase. Time to progression (TTP) in phase A was the primary endpoint, and the trial was powered to detect whether tipifarnib doubled TTP compared with placebo. Toxicity, response, and quality of life were also monitored.

RESULTS

Sixty-two patients were enrolled. Tipifarnib and placebo were well tolerated. On phase A, the median TTP was 10.6 months on the placebo arm and 19.2 months on the tipifarnib arm (P = .12; 1-sided). Quality of life improved significantly compared with baseline on the tipifarnib arm but not on the placebo arm. Volumetric tumor measurement detected tumor progression earlier than conventional 2-dimensional (WHO) and 1-dimensional (RECIST) methods.

CONCLUSIONS

Tipifarnib was well tolerated but did not significantly prolong TTP of PNs compared with placebo. The randomized, flexible crossover design and volumetric PN assessment provided a feasible and efficient means of assessing the efficacy of tipifarnib. The placebo arm serves as an historical control group for phase 2 single-arm trials directed at progressive PNs.

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.

Phase 1 trial and pharmacokinetic study of the farnesyl transferase inhibitor tipifarnib in children and adolescents with refractory leukemias: a report from the Children's Oncology Group

BACKGROUND

The objectives of this trial were to define the toxicity profile, dose, pharmacokinetics, and pharmacodynamics of the farnesyl transferase (FTase) inhibitor, tipifarnib, in children and adolescents with hematological malignancies.

PROCEDURE

Tipifarnib was administered twice daily for 21 days, repeated every 28 days starting at a dose of 300 mg/m(2) /dose. Pharmacokinetic sampling was performed for 36 hr after the first dose and leukemic blasts were collected pre-treatment and at steady state for determination of FTase activity.

RESULTS

Of 29 patients enrolled, 18 were fully evaluable for toxicity, and 23 for response; 26 had pharmacokinetic and pharmacodynamic sampling. The recommended dose is 300 mg/m(2) /dose and toxicities included skin rash, mucositis, nausea, vomiting, and diarrhea. Neurotoxicity, which was dose-limiting in adults at doses exceeding 600 mg/dose, was infrequent and mild. The plasma pharmacokinetics of tipifarnib were highly variable but comparable to adults with acute leukemia and children with solid tumors. The median apparent clearance of tipifarnib was 630 ml/min/m(2) and the median half-life was 4.7 hr. At steady state on 300 mg/m(2) /dose, FTase activity was inhibited by 82% in leukemic blasts. No objective responses were observed.

CONCLUSIONS

Oral tipifarnib is well tolerated in children with leukemia on a twice daily for 2 days schedule at 300 mg/m(2) /dose.

Propiconazole induces alterations in the hepatic metabolome of mice: relevance to propiconazole-induced hepatocarcinogenesis

Propiconazole is a mouse hepatotumorigenic fungicide and has been the subject of recent investigations into its carcinogenic mechanism of action. The goals of this study were (1) to identify metabolomic changes induced in the liver by increasing doses of propiconazole in mice, (2) to interpret these results with key previously reported biochemical, transcriptomic, and proteomic findings obtained from mouse liver under the same treatment conditions, and (3) to relate these alterations to those associated with the carcinogenesis process. Propiconazole was administered to male CD-1 mice in the feed for 4 days with six mice per feed level (500, 1250, and 2500 ppm). The 2500 ppm dose level had previously been shown to induce both adenocarcinomas and adenomas in mouse liver after a 2-year continuous feed regimen. Endogenous biochemicals were profiled using liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry methods and 261 were detected. The most populous biochemical class detected was lipids, followed by amino acids and then carbohydrates. Nucleotides, cofactors and vitamins, energy, peptides, and xenobiotics were also represented. Of the biochemicals detected, 159 were significantly altered by at least one dose of propiconazole and many showed strong dose responses. Many alterations in the levels of biochemicals were found in the glycogen metabolism, glycolysis, lipolysis, carnitine, and the tricarboxylic acid cycle pathways Several groups of metabolomic responses were ascribed to the metabolism and clearance of propiconazole: glucuronate, glutathione, and cysteine pathways. Groups of metabolic responses supported previous hypotheses on key events that can lead to propiconazole-induced tumorigenesis: oxidative stress and increases in the cholesterol biosynthesis pathway. Groups of metabolomic responses identified biomarkers associated with neoplasia: increases in glycolysis and increases in the levels of spermidine, sarcosine, and pseudouridine. These results extended the companion transcriptomic and proteomic studies and provided a more complete understanding of propiconazole's effects in mouse liver.

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.

Farnesyl Transferase Inhibitors Enhance Death Receptor Signals and Induce Apoptosis in Multiple Myeloma Cells

Multiple myeloma is an incurable plasma cell malignancy in which Ras may be constitutively active either via interleukin-6 (IL-6) receptor signaling or by mutation. Inactivation of Ras may be achieved with farnesyl transferase (FTase) inhibitors a class of drugs which have shown promise in clinical trials particularly in patients with acute leukemia. This report investigates the efficacy of two distinct classes of FTase inhibitors in diverse myeloma cell lines and primary isolates. While Ras signaling has traditionally been linked to myeloma cell growth, we found that these compounds also potently triggered cell death. Death induced by perillic acid (PA) was caspase dependent without evidence of death receptor activation. Apoptosis was associated with mitochondrial membrane depolarization and activation of caspase-9 and 3 but proceeded despite over-expression of Bcl-XL a known correlate of relapsed and chemorefractory myeloma. In addition, Fas ligand and TRAIL mediated apoptosis was potentiated in death receptor resistant (U266) and sensitive (RPMI 8226/S) cell lines. Of clinical relevance, the FTase inhibitor R115777 induced cell death in myeloma lines at doses observed in clinical trials. Furthermore, both R115777 and PA induced cell death in primary isolates with relative specificity. Taken together these preclinical data provide evidence that FTase inhibitors may be an effective therapeutic modality for the treatment of multiple myeloma.

Clinical Activity of Farnesyl Transferase Inhibitors in Hematologic Malignancies: Possible Mechanisms of Action

Farnesyl transferase inhibitors (FTIs) are a novel class of anti-cancer agents that competitively inhibit farnesyl protein transferase (FTase). Initially developed to inhibit the prenylation necessary for Ras activation, their mechanism of action seems to be more complex, involving other proteins unrelated to Ras. FTIs have been developed and tested across a wide range of human cancers. At least 3 agents within this family have been investigated in hematologic malignancies. These are tipifarnib (R115777, Zarnestra), lonafarnib (SCH66336, Sarasar), both of which are orally administered, and BMS-214662, which is given intravenously. Preliminary results from clinical trials demonstrate enzyme target inhibition, a favorable toxicity profile and promising efficacy. Ongoing studies will better determine their mechanism of action and the role of combination with other agents, defining their place in the therapeutic arsenal of hematologic disorders.

Current and emerging strategies for the management of acute myeloid leukemia in the elderly

Acute myeloid leukemia (AML) accounts for approximately 80% of acute leukemias diagnosed in adults. The elderly are disproportionately affected by AML, as 35% of newly diagnosed patients are aged >or=75 and the median age at diagnosis is 67. Elderly individuals also respond less well to standard chemotherapy than do younger individuals, as reflected by lower complete remission and relapse-free survival rates in major clinical trials. A higher prevalence of comorbid conditions as well as the unique biological features of elderly AML patients account for the relatively poor response to therapy observed in this population. Compared with AML in younger individuals, for example, AML in the elderly more often emerges from a preceding myelodysplastic syndrome and is more frequently associated with poor-prognosis karyotypes such as 5q- or 7q-. The introduction of novel therapies over the past decade has already altered the treatment paradigm of elderly individuals with AML. The first of these to emerge was gemtuzumab ozogamicin. Other agents are currently under evaluation in clinical trials, including inhibitors of multidrug resistance, farnesyltransferase inhibitors, novel nucleoside analogues, and inhibitors of the FMS-like tyrosine kinase-3. This review describes the biological features of AML in the elderly and summarizes both the current and emerging strategies for the treatment of this disease in older individuals.

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.

The farnesyltransferase inhibitor R115777 (ZARNESTRA) enhances the pro-apoptotic activity of interferon-alpha through the inhibition of multiple survival pathways

Interferon alpha (IFNalpha) induces an EGF-Ras-->Raf-1-->Erk dependent survival pathway counteracting apoptosis induced by the cytokine. In this paper we have evaluated the effects of the combination between farnesyl-transferase inhibitor (FTI) R115777 and IFNalpha on the growth inhibition and apoptosis of cancer cells. Simultaneous exposure to R115777 and IFNalpha produced synergistic both antiproliferative and proapoptotic effects. In these experimental conditions, IFNalpha and R115777 completely antagonized the increased activity of both Ras and Erk-1/2 induced by IFNalpha and strongly reduced Akt activity. Furthermore, treatment with R115777 in combination with IFNalpha regimen induced tumor growth delay on established KB cell xenografts in nude mice, while the single agents were almost inactive. R115777 was again able to antagonize the Ras-dependent survival pathway induced by IFNalpha also in vivo. Raf-1, one of the downstream targets of Ras, has been reported to activate bcl-2 through displacement and/or phosphorylation of Bad. We have found that IFNalpha induced mitochondrial localization of Raf-1 that was antagonized by R115777. Moreover, IFNalpha increased Raf-1/bcl-2 immuno-conjugate formation and intracellular co-localization and enhanced phosphorylation of Bad at Ser 112 and again R115777 counteracted all these effects. Moreover, the use of plasmids encoding for dominant negative or dominant positive Raf-1 antagonized and potentiated, respectively, the co-immunoprecipitation between Raf-1 and bcl-2. In conclusion, FTI R115777 strongly potentiates the antitumor activity of IFNalpha both in vitro and in vivo through the inhibition of different survival pathways that are dependent from isoprenylation of intracellular proteins such as ras.

Development of farnesyltransferase inhibitors for clinical cancer therapy: focus on hematologic malignancies

Farnesyltransferase inhibitors (FTIs) target and inhibit the peptide prenylating enzyme farnesyltransferase. This new class of signal transduction inhibitors is being tested clinically in diverse malignancies, with encouraging results in hematololgic malignancies and breast cancer in particuarl. Critical questions have yet to be answered, for example, optimal dose and schedule, disease subgroups most likely to respond, and appropriate combinations with standard cytotoxics and new biologics. Gene profiling studies of malignant target cells obtained during FTI clinical trials will help to identify patients who are likely to respond to FTIs and to develop mechanisms for overcoming FTI resistance. Clinical trials and correlative laboratory studies in progress and under development will define the optimal roles of FTIs in cancer patients.

Farnesyltransferase inihibitors in hematologic malignancies

Farnesyltransferase inhibitors (FTIs) inhibit certain cellular signal transduction pathways, and are being evaluated for activity in hematologic malignancies. Tipifarnib and lonafarnib are orally available FTIs that are active against a variety of targets and inhibit several pathways involved in the pathogenesis of hematologic malignancies. FTIs have demonstrated activity in a variety of hematologic diseases, including acute myeloid leukemia, myelodysplastic syndrome, chronic myeloid leukemia, and multiple myeloma. This article reviews the clinical experience with tipifarnib and lonafarnib in the treatment of hematologic malignancies.

R115777 (Zarnestra)/Zoledronic acid (Zometa) cooperation on inhibition of prostate cancer proliferation is paralleled by Erk/Akt inactivation and reduced Bcl-2 and bad phosphorylation

Zoledronic acid (ZOL) has proved activity in bone metastases from prostate cancer through inhibition of mevalonate pathway and of prenylation of intracellular proteins. We have reported that ZOL synergizes with R115777 farnesyltransferase inhibitor (FTI, Zarnestra) in inducing apoptosis and growth inhibition on epidermoid cancer cells. Here, we have studied the effects of the combination of these agents in prostate adenocarcinoma models and, specifically, on androgen-independent (PC3 and DU145) and -dependent (LNCaP) prostate cancer cell lines. We have found that ZOL and R115777 were synergistic in inducing both growth inhibition and apoptosis in prostate adenocarcinoma cells. These effects were paralleled by disruption of Ras-->Erk and Akt survival pathways, consequent decreased phosphorylation of both mitochondrial bcl-2 and bad proteins, and caspase activation. Finally, ZOL/R115777 combination induced cooperative effects also in vivo on tumor growth inhibition of prostate cancer xenografts in nude mice with a significant survival increase. These effects were paralleled by enhanced apoptosis and inactivation of both Erk and Akt. In conclusions, the combination between ZOL and FTI leads to enhanced anti-tumor activity in human prostate adenocarcinoma cells likely through a more efficacious inhibition of ras-dependent survival pathways and consequent bcl-related proteins-dependent apoptosis.

Impact on farnesyltransferase inhibition of 4-chlorophenyl moiety replacement in the Zarnestra® series

Based on the structure of R115777 (tipifarnib, Zarnestra), a series of farnesyltransferase inhibitors have been synthesized by modification of the 2-quinolinone motif and transposition of the 4-chlorophenyl ring to the imidazole or its replacement by 5-membered rings. This has yielded a novel series of potent farnesyltransferase inhibitors.

Clinical activity of tipifarnib in hematologic malignancies

Farnesyltransferase inhibitors are a novel class of anticancer agents that competitively inhibit farnesyltransferase. Initially developed to inhibit the farnesylation that is necessary for Ras activation, their mechanism of action seems to be more complex, involving other proteins unrelated to Ras. Of the four classes of farnesyltransferase inhibitors, at least three agents have been investigated in hematologic malignancies. Tipifarnib (R-115777), an orally administered non-peptidomimetic farnesyltransferase inhibitor, has shown promising clinical activity. Preliminary results from clinical trials demonstrate enzyme target inhibition, an acceptable toxicity profile and promising evidence of clinical activity. Ongoing studies will better determine the mechanism of action of tipifarnib and the role of combination with other agents, defining its place in the therapeutic arsenal of hematologic disorders.

The farnesyl transferase inhibitor, tipifarnib, is a potent inhibitor of the MDR1 gene product, P-glycoprotein, and demonstrates significant cytotoxic synergism against human leukemia cell lines

Farnesyl transferase inhibitors (FTIs) target signal-transduction pathways responsible for the proliferation and survival of hematologic malignancies, including acute myelogenous leukemias (AML). Lonafarnib has been shown to be a potent inhibitor of Pgp-mediated drug efflux. On the basis of these findings, we examined the Pgp-inhibitory properties of tipifarnib and assessed its activity when combined with anthracyclines. The effects of tipifarnib on cell proliferation, induction of apoptosis and inhibition of Pgp-mediated anthracycline efflux were analyzed in two human leukemia cell lines overexpressing Pgp (CCRF-CEM and KG1a). Measurement of residual daunorubicin (DNR)-mediated fluorescence after incubation with DNR and tipifarnib demonstrated that tipifarnib significantly inhibited DNR efflux in CCRF-CEM with an IC(50) value less than 0.5 microM. Proliferation and apoptosis assays after exposure to DNR in the presence or absence of tipifarnib demonstrated synergistic inhibition of cellular proliferation, and induction of apoptosis with the combination of tipifarnib and DNR. Similar data was obtained with an enantiomer of tipifarnib that possesses no FTI activity. Incubation with tipifarnib and DNR did not interfere with inhibition of the post-translational processing of HDJ-2. These data suggest that tipifarnib possesses Pgp-inhibitory activity in addition to its FTI activity. In high risk and refractory patients these properties may be exploited as a dual targeting mechanism in the therapy of AML.

Targeting Treatment in AML

Currently available chemotherapy has probably reached the limits of its potential in treating acute myeloid leukemia (AML). In considering the next steps it is appropriate to exploit on the one hand knowledge of the molecular, immunophenotypic and biological characteristics of the disease and on the other the biology of the patient. The aim is to move towards a more targeted approach.

Immunophenotyping has defined an adequate target (CD33) for antibody-directed treatment, although this is not leukemia specific. Monotherapy has produced important response rates in relapsed disease but it is unlikely to displace conventional chemotherapy. Several randomized trials of antibody directed chemotherapy in combination with chemotherapy nearing completion will establish the usefulness of this approach. In most patients a leukemia-specific immunophenotype can be characterized that can be used to monitor treatment. Minimal residual disease (MRD) detection in morphological remission can detect patients at high risk of relapse, as can a limited number of molecular markers. The clinical value of intervening at the time of MRD detection is not clear. Among the increasing molecular abnormalities described in AML, FLT-3 mutations appear the most attractive for therapeutic intervention. Several phase 2 studies have shown limited efficacy, and randomized trials in combination are underway. Other mechanisms that can be specifically targeted include farnesylation, methylation status, and histone deacelylation. Newer knowledge about the immunophenotypic and biological characteristics of the leukemic stem cell population has opened opportunities to develop treatments that exploit characteristics of the leukemic stem cells that differ from the normal stem cell. Some of these initiatives are now discussed.

A phase 2 study of the farnesyltransferase inhibitor tipifarnib in poor-risk and elderly patients with previously untreated acute myelogenous leukemia

Outcomes for older adults with acute myelogenous leukemia (AML) are poor due to both disease and host-related factors. In this phase 2 study, we tested the oral farnesyltransferase inhibitor tipifarnib in 158 older adults with previously untreated, poor-risk AML. The median age was 74 years, and a majority of patients had antecedent myelodysplastic syndrome. Complete remission (CR) was achieved in 22 patients (14%); partial remission or hematologic improvement occurred in 15 patients, for an overall response rate of 23%. The median duration of CR was 7.3 months and the median survival of complete responders was 18 months. Adverse karyotype, age 75 years or older, and poor performance status correlated negatively with survival. Early death in the absence of progressive disease was rare, and drug-related nonhematologic serious adverse events were observed in 74 patients (47%). Inhibition of farnesylation of the surrogate protein HDJ-2 occurred in the large majority of marrow samples tested. Baseline levels of phosphorylated mitogen-activated protein kinase and AKT did not correlate with clinical response. Tipifarnib is active and well tolerated in older adults with poor-risk AML and may impart a survival advantage in those patients who experience a clinical response.

Cellular signaling molecules as therapeutic targets in glioblastoma multiforme

Despite recent advances in operative techniques, chemotherapy, and radiotherapy, the prognosis in patients with glioblastoma multiforme (GBM) remains poor; the majority die within a year of diagnosis. Although often effective at reducing mass effect and tumor burden, surgical debulking and cytotoxic therapies have never demonstrated an unequivocally significant benefit in treating patients with GBM. This shortcoming has led to the development of molecules that target specific steps in the transduction pathways of high-grade glioma cells. In this article the authors review various cellular and extracellular signaling pathways that may prove promising in the treatment of patients with malignant glioma.

Effect of a farnesyl transferase inhibitor (R115777) on ductal carcinoma in situ of the breast in a human xenograft model and on breast and ovarian cancer cell growth in vitro and in vivo

Introduction

The ras pathway is essential for cell growth and proliferation. The effects of R115777, a farnesyl transferase inhibitor, were investigated in cancer cell lines expressing varying levels of growth factor receptors and with differing ras status. Effects on tumour xenografts and human ductal carcinoma in situ (DCIS) of the breast in a xenograft mouse model were also tested.

Method

In vitro, the concentrations required to reduce cell numbers by 50% (50% inhibitory concentration) were established (MDA-MB231, MCF-7, MCF-7/HER2-18, BT-474, SK-BR3 and SKOV3). Human DCIS was implanted in nude mice or, in separate experiments, cultured cells were injected (MDA-MB231, MCF-7/HER2-18, SKOV3) and allowed to form tumours. Proliferation and apoptosis were determined by immunohistochemistry in xenografts and cell tumours.

Results

The 50% inhibitory concentrations varied a hundred-fold, from 39 nmol/l (± 26 nmol/l) for SKBR3 to 5.9 μmol/l(± 0.8 μmol/l) for MDA-MB231. In MCF-7/HER2-18 and SKOV3 cells the levels of tumour growth inhibition were approximately 85% and 40%, respectively. There was a significant decrease in the cell turnover index (CTI; proliferation/apoptosis). In MDA-MB 231 with activated k-ras no inhibition was observed. In treated DCIS xenografts proliferation decreased and apoptosis increased. The CTI ratio between the start and 1 and 2 weeks of treatment were 1.99 and 1.50, respectively, for controls and 0.85 (P = 0.005) and 0.75 (P = 0.08) for treated xenografts.

Conclusion

Treatment with the farnesyl transferase inhibitor reduced cell growth in vitro and cell tumour growth in vivo. In DCIS treatment resulted in a reduced CTI. R115777 is a promising treatment for breast cancer but the relation between effect and growth factor receptor and ras status has to be established.

Phase I trial and pharmacokinetic study of the farnesyltransferase inhibitor tipifarnib in children with refractory solid tumors or neurofibromatosis type I and plexiform neurofibromas

PURPOSE

This pediatric phase I trial of tipifarnib determined the maximum-tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of tipifarnib in children with refractory solid tumors and neurofibromatosis type 1 (NF1) -related plexiform neurofibromas.

PATIENTS AND METHODS

Tipifarnib was administered twice daily for 21 days, repeated every 28 days starting at 150 mg/m2/dose (n = 4), with escalations to 200 (n = 12), 275 (n = 12), and 375 (n = 6) mg/m2/dose. The MTD was also evaluated on a chronic continuous dosing schedule (n = 6). Pharmacokinetic sampling was performed for 36 hours after the first dose and peripheral-blood mononuclear cells (PBMCs) were collected at baseline and steady state for determination of farnesyl protein transferase (FTase) activity and HDJ-2 farnesylation.

RESULTS

Twenty-three solid tumor and 17 NF1 patients were assessable for toxicity. The MTD was 200 mg/m2/dose, and dose-limiting toxicities on cycle 1 were myelosuppression, rash, nausea, vomiting, and diarrhea. The 200 mg/m2/dose was also tolerable on the continuous dosing schedule. Cumulative toxicity was not observed in the 17 NF1 patients who received a median of 10 cycles (range, 1 to 32 cycles). The plasma pharmacokinetics of tipifarnib were highly variable but not age dependent. At steady state on 200 mg/m2/dose, FTase activity was 30% compared with baseline, and farnesylation of HDJ-2 was inhibited in PBMCs.

CONCLUSION

Oral tipifarnib is well tolerated in children receiving the drug twice daily for 21 days and a continuous dosing schedule at 200 mg/m2/dose, which is equivalent to the MTD in adults. The pharmacokinetic profile of tipifarnib in children is similar to that in adults, and at the MTD, FTase is inhibited in PBMC in vivo.

Novel targeted therapies to overcome imatinib mesylate resistance in chronic myeloid leukemia (CML)

Imatinib mesylate (Gleevec) was developed as the first molecularly targeted therapy that specifically inhibits the BCR-ABL tyrosine kinase activity in patients with Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML). Due to its excellent hematologic and cytogenetic responses, particularly in patients with chronic phase CML, imatinib has moved towards first-line treatment for newly diagnosed CML. Nevertheless, resistance to the drug has been frequently reported and is attributed to the fact that transformation of hematopoietic stem cells by BCR-ABL is associated with genomic instability. Point mutations within the ABL tyrosine kinase of the BCR-ABL oncoprotein are the major cause of resistance, though overexpression of the BCR-ABL protein and novel acquired cytogenetic aberrations have also been reported. A variety of strategies derived from structural studies of the ABL-imatinib complex have been developed, resulting in the design of novel ABL inhibitors, including AMN107, BMS-354825, ON012380 and others. The major goal of these efforts is to create new drugs that are more potent than imatinib and/or more effective against imatinib-resistant BCR-ABL clones. Some of these drugs have already been successfully tested in preclinical studies where they show promising results. Additional approaches are geared towards targeting the expression or stability of the BCR-ABL kinase itself or targeting signaling pathways that are chronically activated and required for transformation. In this review, we will discuss the underlying mechanisms of resistance to imatinib and novel targeted approaches to overcome imatinib resistance in CML.

Enhanced FTase activity achieved via piperazine interaction with catalytic zinc

Benzocycloheptapyridine tricyclic compounds with piperazine or substituted piperidine moieties extending either from the 5- or 6-position of the tricyclic bridgehead exhibited enhanced FTase activity: this resulted from favorable binding of the ligand nitrogen with the catalytic zinc found in the FTase. A single isomer at C-11 with piperazine adduct extending from the 6-position, compound 24, exhibited excellent FTase activity with IC50 = 0.007 microM, soft agar IC50 = 72 nM, and Rat AUC(PO, 10 mpk) = 4.0 microM x h. X-ray of (-)-[8-chloro-6-(1-piperazinyl)-1H-benzo[5,6]]cyclohepta[1,2-b]pyridine-11-yl]-1-(methylsulfonyl)piperidine 24 bound to Ftase revealed favorable interaction between piperazine nitrogen and catalytic zinc atom.

Development of the farnesyltransferase inhibitor tipifarnib for therapy of hematologic malignancies

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 doing so, interdict multiple pathways involved in proliferation and survival of diverse malignant cell types. Tipifarnib is an orally bioavailable, nonpeptidomimetic methylquinolone FTI that is being tested clinically in diverse hematologic malignancies, in particular myeloid malignancies and myeloma. FTI therapy is accompanied by a relatively low toxicity profile, thereby providing an important alternative to traditional cytotoxic approaches for elderly patients who are not likely to tolerate or even benefit from aggressive chemotherapy. Current laboratory and clinical studies continue to define the determinants of FTI antitumor activity and resistance. The full development of FTIs for the therapy of hematologic malignancies will require the design and testing of rational combinations of cytotoxic, biologic and immunomodulatory agents in the laboratory and the clinic.

Synthesis, biodistribution and effects of farnesyltransferase inhibitor therapy on tumour uptake in mice of 99mTc labelled epidermal growth factor

OBJECTIVE

The goal of this study was to develop a 99mTc labelled human epidermal growth factor (hEGF) for the in-vivo prediction of cancer cell response to farnesyltransferase inhibitor (FTI) therapy. This is based on the observation that internalization of EGF receptors is inhibited by FTIs.

METHODS

We describe the radiolabelling of 99mTc-hEGF using the hydrazinonicotinamide (HYNIC) linker. Binding characteristics of 99mTc-HYNIC-hEGF to the EGF receptor are explored using an in-vitro binding assay. Biodistribution data of the compound in mice and tumour uptake in LoVo tumour bearing athymic mice before and after farnesyltransferase inhibitor therapy are presented.

RESULTS

No colloid formation was observed. Binding parameters and LoVo tumour uptake of 99mTc-HYNIC-hEGF did not differ significantly from directly labelled 123I-hEGF values. However, the biodistribution data of the 99mTc-HYNIC-hEGF showed higher uptake in liver and intestines and decreased stomach uptake compared to its 123I analogue. Eight hours after farnesyltransferase inhibitor therapy with R115777, LoVo tumour uptake of 99mTc-HYNIC-hEGF decreased significantly, as shown using planar gamma scintigraphy (the ratio tumour vs. thigh dropped from 2.54+/-0.83 to 0.99+/-0.18). These data confirm the results obtained using 123I-hEGF.

CONCLUSION

These data suggest that 99mTc-HYNIC-hEGF is a promising and selective new radiotracer for in-vivo monitoring of the EGF receptor with SPECT. Moreover, 99mTc-HYNIC-hEGF is a possible tool for early therapy response prediction of farnesyltransferase inhibitors.

Bridgehead modification of trihalocycloheptabenzopyridine leads to a potent farnesyl protein transferase inhibitor with improved oral metabolic stability

Modification of the ethano bridge of the core structure of the antitumor agent, SARASAR (SCH66336) with concomitant introduction of a sulfonamide moiety off the distal piperidine afforded inhibitor 9-(S-), a compound with greatly improved PK profile. Other compounds with enhanced FPTase inhibitory activity were obtained as exemplified by amide 10-(S-) and urea 11-(S-): these compounds demonstrated activity in picomolar range.

Dose-Ranging Pharmacodynamic Study of Tipifarnib (R115777) in Patients With Relapsed and Refractory Hematologic Malignancies

Purpose

Tipifarnib, an orally bioavailable inhibitor of farnesyl transferase, has activity in hematologic malignancies, but the dose required to achieve the proposed biologic end point, inhibition of farnesylation, is unknown.

Patients and Methods

The impact on post-translational farnesylation was assessed in 42 patients with refractory hematologic malignancies and bone marrow involvement. Tipifarnib was taken orally for 21 days of a 28-day cycle. For cycle 1, patients were randomly assigned to one of four dose levels: 100 mg bid, 200 mg bid, 300 mg bid, and 600 mg bid. In cycle 1, peripheral blood and bone marrow mononuclear cells were analyzed for inhibition of HDJ2 prenylation by Western blot analysis at baseline and on day 21.

Results

Twenty-three patients were assessable for analysis of HDJ2 prenylation before and after therapy. Inhibition of farnesylation was noted at all dose levels, although the highest level of inhibition was noted at the 300-mg-bid dose. The inhibition of farnesylation in the peripheral blood correlated with the inhibition in the bone marrow (r = 0.62). Of the 26 patients assessable for clinical activity after cycle 1, three patients had a significant decrease in total blasts count (acute myeloid leukemia in two patients, and chronic myelogenous leukemia in one patient). The inhibition of farnesylation was greater in the three responders than the nonresponders (P = .03).

Conclusion

Farnesylation as measured by HDJ2 analysis was inhibited at all dose levels administered. Clinical activity may correlate with the degree of farnesylation inhibition, rather than dose of tipifarnib, and escalation beyond 300 mg bid might not result in additional clinical activity.

Farnesyl protein transferase inhibitors targeting the catalytic zinc for enhanced binding

Successful efforts to make farnesyl transferase (FT) inhibitors with appropriately tethered ligands designed to interact with a catalytic zinc that exist in the enzyme have been realized. Thus, by introducing either a pyridylmethylamino or propylaminolimidazole amide moieties off the 2-position of the piperidine ring, FT inhibitors with activities in the picomolar range have been achieved as exemplified by compounds 12a and 12b. An X-ray structure of 11b bound to FT shows the enhanced activity is a result of interacting with the active-site zinc.

The farnesyl transferase inhibitor R115777 (Zarnestra) synergistically enhances growth inhibition and apoptosis induced on epidermoid cancer cells by Zoledronic acid (Zometa) and Pamidronate

Pamidronate (PAM) and zoledronic acid (ZOL) are aminobisphosphonates (BPs) able to affect the isoprenylation of intracellular small G proteins. We have investigated the antitumor activity of BPs and R115777 farnesyl transferase inhibitor (FTI) against epidermoid cancer cells. In human epidermoid head and neck KB and lung H1355 cancer cells, 48 h exposure to PAM and ZOL induced growth inhibition (IC(50) 25 and 10 microM, respectively) and apoptosis and abolished the proliferative and antiapoptotic stimuli induced by epidermal growth factor (EGF). In these experimental conditions, ZOL induced apoptosis through the activation of caspase 3 and a clear fragmentation of PARP was also demonstrated. A strong decrease of basal ras activity and an antagonism on its stimulation by EGF was recorded in the tumor cells exposed to BPs. These effects were paralleled by impaired activation of the survival enzymes extracellular signal regulated kinase 1 and 2 (Erk-1/2) and Akt that were not restored by EGF. Conversely, farnesol induced a recovery of ras activity and antagonized the proapoptotic effects induced by BPs. The combined treatment with BPs and R115777 resulted in a strong synergism both in growth inhibition and apoptosis in KB and H1355 cells. The synergistic activity between the drugs allowed BPs to produce tumor cell growth inhibition and apoptosis at in vivo achievable concentrations (0.1 micromolar for both drugs). Moreover, the combination was highly effective in the inhibition of ras, Erk and Akt activity, while farnesol again antagonized these effects. In conclusion, the combination of BPs and FTI leads to enhanced antitumor activity at clinically achievable drug concentrations that resides in the inhibition of farnesylation-dependent survival pathways and warrants further studies for clinical translation.

Investigation of the effect of the farnesyl protein transferase inhibitor R115777 on isoprenylation and intracellular signalling by the prostacyclin receptor

The human (h) and mouse (m) prostacyclin receptors (IPs) undergo isoprenylation through attachment of a C-15 farnesyl moiety within their conserved carboxyl terminal -CSLC sequences. Herein, the effects of a novel farnesyl transferase inhibitor R115777 on signalling by the hIP and mIP, overexpressed in human embryonic kidney 293 cells, and by the hIP endogenously expressed in human erythroleukaemia cells were investigated. R115777 significantly impaired IP-mediated cyclic AMP generation (IC(50) 0.37-0.60 nm) and intracellular calcium ([Ca(2+)](i)) mobilization (IC(50) 37-65 nm), but had no effect on signalling by the control nonisoprenylated beta(2) adrenergic receptor or the alpha or beta isoforms of the human thromboxane A(2) receptor (TP). Additionally, R115777 significantly reduced IP-mediated cross-desensitization of signalling by the TP alpha, but not by the TP beta, isoform of the human TP and impaired the farnesylation-dependent processing of the chaperone HDJ-2 protein (IC(50) 4.5 nm). Furthermore, R115777 fully impaired isoprenylation of both the Ha-Ras(WT) and Ha-Ras(CSLC) in vitro and in whole cells confirming that, unlike N-Ras and Ki-Ras, the -CSLC motif associated with the IP cannot support alternative geranylgeranylation in the presence of R115777 and does not act as a substrate for geranylgeranyl transferase 1 in vitro or in whole cells. In conclusion, these data confirm that R115777 potently impairs IP isoprenylation and signalling, and suggest that clinically it may not only target Ras proteins but may also disrupt IP isoprenylation, events which could impact on physiologic processes in which prostacyclin and its receptor are implicated.

New drugs for treatment of multiple myeloma

Multiple myeloma (MM) is a disease of plasma cells that has fatal consequences. New insights into the biology of MM have identified molecular mechanisms that hold promise as therapeutic targets. Laboratory and preclinical studies have shown that intracellular regulatory proteins and functional interactions between MM cells and the bone-marrow microenvironment have a pivotal role in the growth, survival, drug resistance, and malignant progression of MM cells. New agents associated with molecular targets have prompted clinical investigators to design new treatment strategies initially for advanced MM and later for newly diagnosed MM, with encouraging preliminary results. Here, we discuss the mechanisms of action of these new rational drugs and the preliminary clinical outcomes of a new treatment regimen for MM.

Bone microenvironment-related growth factors modulate differentially the anticancer actions of zoledronic acid and doxorubicin on PC-3 prostate cancer cells

OBJECTIVES

We analyzed the actions of zoledronic acid (10-250 microM) and doxorubicin (10-250 nM) on PC-3 prostate cancer cells using both continuous (48-96 hr) and pulsatile exposures (15 min/day for up to three consecutive days).

RESULTS

The proliferation of PC-3 cells was inhibited by either continuous or pulsatile exposures of zoledronic acid in a dose-dependent manner. In contrast, pulsatile exposures of doxorubicin failed to inhibit the growth of PC-3 cells. In addition, the inhibition of PC-3 cells by zoledronic acid was partially neutralized by exogenous administration of geranylgeranyl pyrophosphate (GGPP), however, not by farnesyl pyrophosphate (FPP). Furthermore, exogenous administration of transforming growth factor beta 1 (TGF-beta1), interleukin 6 (IL-6), basic fibroblast growth factor (bFGF), and more potently, insulin-like growth factor 1 (IGF-1) inhibited the doxorubicin-induced apoptosis of PC-3 cells. Under identical experimental conditions, these growth factors failed to alter the cytotoxicity of PC-3 cells induced by zoledronic acid.

CONCLUSIONS

These data suggest that (i) repetitive and pulsatile (15 min/day) exposure to zoledronic acid inhibited the growth of PC-3 cells, (ii) this anticancer action of zoledronic acid was partially mediated by the attenuation of GGPP production, and (iii) bone microenvironment-related growth factors do not alter the anticancer actions of zoledronic acid on PC-3 cells.

Substituted azoloquinolines and -quinazolines as new potent farnesyl protein transferase inhibitors

A series of (4-chlorophenyl)-alpha-(1-methyl-1H-imidazol-5-yl)azoloquinolines and -quinazolines was prepared. These compounds displayed potent Farnesyl Protein Transferase inhibitory activity and tetrazolo[1,5-a]quinazolines are promising agents for oral in vivo inhibition.

Farnesyltransferase inhibitors in hematologic malignancies: new horizons in therapy

Farnesyltransferase inhibitors (FTIs) are small-molecule inhibitors that selectively inhibit farnesylation of a number of intracellular substrate proteins such as Ras. Preclinical work has revealed their ability to effectively inhibit tumor growth across a wide range of malignant phenotypes. Many hematologic malignancies appear to be reasonable disease targets, in that they express relevant biologic targets, such as Ras, mitogen-activated protein kinase (MAPK), AKT, and others that may depend on farnesyl protein transferase (FTase) activity to promote proliferation and survival. A host of phase 1 trials have been recently launched to assess the applicability of FTIs in hematologic malignancies, many of which demonstrate effective enzyme target inhibition, low toxicity, and some clinical responses. As a result, phase 2 trials have been initiated in a variety of hematologic malignancies and disease settings to further validate clinical activity and to identify downstream signal transduction targets that may be modified by these agents. It is anticipated that these studies will serve to define the optimal roles of FTIs in patients with hematologic malignancies and provide insight into effective methods by which to combine FTIs with other agents.

4-Methyl-1,2,4-triazol-3-yl heterocycle as an alternative to the 1-methylimidazol-5-yl moiety in the Farnesyltransferase inhibitor ZARNESTRA ™

Replacement of the 1-methylimidazol-5-yl moiety in the farnesyltransferase inhibitor ZARNESTRA series by a 4-methyl-1,2,4-triazol-3-yl group gave us compounds with similar structure-activity relationship profiles showing that this triazole is potentially a good surrogate to imidazole for farnesyltransferase inhibition.

Signal transduction--directed cancer treatments

The pathogenic mechanisms giving rise to cancer frequently involve altered signal transduction pathways. Therefore therapeutic agents that directly address signal transduction molecules are being explored as cancer treatments. Inhibitors of protein tyrosine and threonine kinases including STI-571, ZD-1839, OSI-774, and flavopiridol are ATP-site antagonists that have completed initial phase I and phase II evaluations. Herceptin and C225 are monoclonal antibodies also directed against signaling targets. Numerous other kinase antagonists are in clinical evaluation, including UCN-01 and PD184352. Alternative strategies to downmodulate kinase-driven signaling include 17-allyl-amino-17-demethoxygeldanamycin and rapamycin derivatives, and phospholipase-directed signaling may be modulated by alkylphospholipids. Farnesyltransferase inhibitors were originally developed as inhibitors of ras-driven signals but may have activity by affecting other or additional targets. Signal transduction will remain a fertile basis for suggesting cancer treatments of the future, the evaluation of which should include monitoring effects of the drugs on their intended target signaling molecules in preclinical and early clinical studies.

Primary and Secondary Prevention of Non–Small-Cell Lung Cancer: The SPORE Trials of Lung Cancer Prevention

The aims of chemoprevention in lung cancer are to prevent the appearance of disease (primary prevention) and to stop or reverse the progression of premalignant lesions (secondary prevention). Until recently, there was little hope that these goals could be attained. However, the results achieved with tamoxifen in the prevention of breast cancer, and the emergence of new therapies specifically targeted to molecules involved in the pathogenesis of lung cancer have set the stage for investigation of these agents for chemoprevention of lung cancer. Two of these new molecular targeted agents are gefitinib, an inhibitor of epidermal growth factor receptor-tyrosine kinase activity, and tipifarnib (R115777, Zarnestra ), an inhibitor of the farnesyltransferase enzyme, which is required for the proper localization and function of the ras oncogene. Tumor responses and disease stabilization have been achieved with both agents in clinical trials. In the Iressa Dose Evaluation in Advanced Lung Cancer (IDEAL)-1 and IDEAL-2 phase II trials, gefitinib was demonstrated to be effective for disease control in patients with advanced non-small-cell lung cancer. The SPORE (Specialized Program of Research Excellence) Trials of Lung Cancer Prevention (STOP) are 2 parallel studies that will investigate the potential effectiveness of gefitinib and tipifarnib in preventing the appearance and progression of premalignant lesions in former or current smokers with a history of smoking-related cancer. These trials should provide information not only about the potential role of gefitinib and tipifarnib in lung cancer chemoprevention, but also about the molecular changes that underlie tumorigenesis and that may serve as markers of disease progression. The STOP trial objectives are to evaluate the effect of gefitinib and tipifarnib on histologic and biologic parameters in patients with evidence of sputum atypia, to evaluate various parameters as potential predictors of the effectiveness of these agents, and to evaluate the tolerability of these agents over a 6-month course of treatment. Histologic response, defined as prevention of appearance or progression of premalignant lesions, is the primary endpoint of these trials. New targeted molecular therapies such as gefitinib and tipifarnib may offer the opportunity to make chemoprevention a viable treatment modality in lung cancer as well as in other human solid tumors.

Farnesyl transferase inhibitors in myeloid malignancies

Farnesyl transferase inhibitors (FTIs) are a novel class of anti-cancer agents that competitively inhibit farnesyl protein transferase (FPT), and are currently being developed and tested across a wide range of human cancers. Hematologic malignancies, particularly those of myeloid origin, are reasonable disease targets in that they likely overexpress relevant biologic targets, such as Ras, mitogen-activated protein kinase (MAPK), or AKT, that depend upon FPT activity to promote proliferation and survival. Phase I clinical trials using FTIs in acute myelogenous leukemia (AML) and other myeloid malignancies have been performed, demonstrating enzyme target inhibition, low toxicity, and promising response rates. These findings have prompted further development in phase II trials, in order to clarify the response rate and to identify the actual downstream signal transduction targets that may be modified by these agents. It is anticipated that such information will ultimately define the optimal roles of FTIs in patients with AML and other myeloid disorders, facilitate the incorporation of FTIs into current therapeutic strategies for myeloid malignancies, and provide insight into effective methods of combining FTIs with other signal transduction inhibitors.

Effects of the farnesyl transferase inhibitor R115777 on normal and leukemic hematopoiesis

Patients with acute myelogenous leukemia or myelodysplastic syndrome may respond to farnesyl transferase inhibitors (FTIs) with partial or complete response rates noted in about 30% of such patients. FTIs prevent the attachment of a lipid farnesyl moiety to dependent proteins prior to their insertion into the plasma membrane and thereby prevent activity of these prenylation-dependent proteins, but their mechanism of tumor suppression remains unknown. Many patients receiving FTIs do experience myelosuppression. In this work, the in vitro effects of the FTI, R115777 on normal and leukemic hematopoiesis have been examined as have its effects on apoptosis induction and cell cycle profile in both leukemic blasts and normal CD34+ cells. R115777 was inhibitory to normal CD34+ cell proliferation and to leukemic blast cells, but did not affect long-term culture initiating cell frequency nor NOD-SCID reconstituting capacity. No induction of apoptosis or cell cycle changes were noted in AML blasts. These data suggest that myelosuppression with R115777 occurs largely at the intermediate to late progenitor stage of hematopoiesis and that cyclic use might avoid long-term marrow suppression.

Drug development in pancreatic cancer: finally, biology begets therapy

Pancreatic cancer is rarely curable, and only 5% of patients achieve long-term survival. The vast majority of patients present with metastatic or unresectable disease. Standard chemotherapy with gemcitabine provides clinical benefit to only a small minority of patients. Thus, the development and investigation of new therapies is clearly needed. As knowledge of the underlying biology of pancreatic cancer has increased, targeted therapies based upon preclinical laboratory work have been developed, and are entering clinical trials. Some of these agents lack traditional dose-limiting toxicities (DLTs) at biologically active doses, and therefore clinical evaluation may not follow traditional guidelines for cytotoxic drug development. This article focuses on targeted therapies currently undergoing clinical evaluation in pancreatic cancer. Classes of therapeutics reviewed include those targeting tumor-microenvironment interactions (matrix metalloproteinase inhibitors, vascular endothelial growth-factor blockade), signal transduction (e.g., farnesyltransferase inhibitors), growth-factor receptors (epidermal growth-factor receptor blockade, Her-2/neu, gastrin), and vaccine approaches. Currently, there is a renewed optimism that the clinical application of biologic understanding will lead to an improved outcome for patients with pancreatic cancer.

Farnesyltransferase Inhibitors in Acute Myeloid Leukemia and Myelodysplastic Syndromes

Farnesyltransferase inhibitors were initially developed as Ras inhibitors as they inhibit the prenylation necessary for Ras activation. It is clear now that their mechanism of action is more complex and probably involves other proteins unrelated to Ras. At least 3 drugs within this family have been investigated in acute myeloid leukemia, myelodysplastic syndromes, and other leukemias. These are tipifarnib (R115777, Zarnestra), lonafarnib (SCH66336, Sarasar), and BMS-214662. The first 2 are administered orally, whereas BMS-214662 is given intravenously. These drugs are at different stages of development, and design of treatment schedules and methodology of the available studies are very different. Although most of the information is still preliminary, these agents have demonstrated clear evidence of clinical activity in these diseases and very favorable toxicity profiles. Several studies are still ongoing to better define the efficacy of these agents in the treatment of leukemias, as well as to determine the best schedules, the role of combination with other agents, and the role of these agents in different settings, such as the management of minimal residual disease. It is very possible that these agents will soon find their way to the ranks of established agents for the management of myeloid malignancies

5-imidazolyl-quinolinones, -quinazolinones and -benzo-azepinones as farnesyltransferase inhibitors

The evaluation of structure-activity relationships associated with the modification of the R115777 quinolinone ring moiety displaying potent in vitro inhibiting activity is described.

Discovery of potent imidazole and cyanophenyl containing farnesyltransferase inhibitors with improved oral bioavailability

A pyridyl moiety was introduced into a previously developed series of farnesyltransferase inhibitors containing imidazole and cyanophenyl (such as 4), resulting in potent inhibitors with improved pharmacokinetics.

Phase II study of the farnesyl transferase inhibitor R115777 in patients with advanced non-small-cell lung cancer

PURPOSE

This phase II study was undertaken to define the efficacy and pharmacodynamics of R115777, a farnesyl transferase inhibitor, in the first-line treatment of patients with advanced non-small-cell lung cancer.

PATIENTS AND METHODS

Forty-four patients with measurable stage IIIB (pleural effusion) or stage IV disease received 193 courses of treatment (median, 2.0; range, 1 to 22) with R115777 300 mg administered orally twice daily for 21 of every 28 days. Buccal mucosa samples and peripheral blood mononuclear cells (PBMCs) were collected before and after 8 days of treatment to evaluate inhibition of farnesyl transferase in vivo.

RESULTS

No objective complete or partial responses were documented. Seven patients (16%; 95% confidence interval [CI], 8% to 31%) had disease stabilization for greater than 6 months. Median survival was 7.7 months (95% CI, 6.5 to 10.5) and time to progression was 2.7 months (95% CI, 1.9 to 3.1). The most severe toxicity was neutropenia (9% grade 3, 7% grade 4) and the most common toxicities were anemia (50% grade 1 or 2, 5% grade 3) and anorexia (50% grade 1 or 2, 2% grade 3). Mild peripheral neuropathy occurred in 25% of patients. Evidence of farnesyl transferase inhibition was documented in 83% of patients.

CONCLUSION

Single-agent R115777 was well tolerated in patients with advanced NSCLC, but demonstrated minimal clinical activity. Inhibition of farnesylation in vivo was consistently documented. On the basis of promising results of farnesyl transferase inhibitor combinations with standard chemotherapy agents, future studies of this agent in NSCLC should be in combination with systemic chemotherapy.