Farnesyl transferase inhibitors: a novel targeted tnerapy for cancer

Recent Developments in Targeting RAS Downstream Effectors for RAS-Driven Cancer Therapy

Aberrant activity of oncogenic rat sarcoma virus (RAS) protein promotes tumor growth and progression. RAS-driven cancers comprise more than 30% of all human cancers and are refractory to frontline treatment strategies. Since direct targeting of RAS has proven challenging, efforts have been centered on the exploration of inhibitors for RAS downstream effector kinases. Two major RAS downstream signaling pathways, including the Raf/MEK/Erk cascade and the phosphatidylinositol-3-kinase (PI3K) pathway, have become compelling targets for RAS-driven cancer therapy. However, the main drawback in the blockade of a single RAS effector is the multiple levels of crosstalk and compensatory mechanisms between these two pathways that contribute to drug resistance against monotherapies. A growing body of evidence reveals that the sequential or synergistic inhibition of multiple RAS effectors is a more convenient route for the efficacy of cancer therapy. Herein, we revisit the recent developments and discuss the most promising modalities targeting canonical RAS downstream effectors for the treatment of RAS-driven cancers.

Colony-stimulating factor 3 signaling in colon and rectal cancers: Immune response and CMS classification in TCGA data

Colorectal cancer is the 2nd leading cause of cancer-related deaths in the world. The mechanisms underlying CRC development, progression, and resistance to treatment are complex and not fully understood. The immune response in the tumor microenvironment has been shown to play a significant role in many cancers, including colorectal cancer. Colony-stimulating factor 3 (CSF3) has been associated with changes to the immune environment in colorectal cancer animal models. We hypothesized that CSF3 signaling would correlate with pro-tumor tumor microenvironment changes associated with immune infiltrate and response. We utilized publicly available datasets to guide future mechanistic studies of the role CSF3 and its receptor (CSF3R) play in colorectal cancer development and progression. Here, we use bioinformatics data and mRNA from patients with colon (n = 242) or rectal (n = 92) cancers, obtained from The Cancer Genome Atlas Firehose Legacy dataset. We examined correlations of CSF3 and CSF3R expression with patient demographics, tumor stage and consensus molecular subtype classification. Gene expression correlations, cell type enrichment, Estimation of STromal and Immune cells in MAlignant Tumor tissues using Expression data scores and Gene Ontology were used to analyze expression of receptor and ligand, tumor microenvironment infiltration of immune cells, and alterations in biological pathways. We found that CSF3 and CSF3R expression is highest in consensus molecular subtype 1 and consensus molecular subtype 4. Ligand and receptor expression are also correlated with changes in T cell and macrophage signatures. CSF3R significantly correlates with a large number of genes that are associated with poor colorectal cancer prognosis.

Targeting KRAS mutant cancers by preventing signaling transduction in the MAPK pathway

KRAS genes are the most commonly mutated oncogenes in cancer. Unfortunately, effective therapeutic strategies for targeting KRAS mutant cancers have proven to be difficult to obtain. A key reason for this setback is due to the lack of success direct KRAS mutant inhibitors have received. Researchers have turned their efforts away from targeting the KRAS nucleotide-binding site directly and towards targeting other areas of the MAPK signaling pathway to block KRAS function. Researchers found that inhibiting enzymes and protein-protein interactions involved in the MAPK signaling pathway inhibit the activation of KRAS mutant therefore can lead to a potential therapeutic for KRAS mutated cancers. Throughout the past two decades, various indirect inhibitors have been designed and tested. EGFR and MEK inhibitors have presented with less success; however, significant advances have been made when targeting the plasma membrane localization process and the allosteric site of KRAS mutant. Farnesyltransferase and allosteric inhibitors have both advanced to human clinical trials. This comprehensive review presents the most recent developments of direct and indirect KRAS mutant inhibitors. This review summarizes published data on the inhibitory and anti-cancer activity of compounds that target KRAS activation as well as highlights the most promising strategies for targeting KRAS mutant cancers.

How to make an undruggable enzyme druggable: lessons from ras proteins

Significant advances have been made toward discovering allosteric inhibitors for challenging drug targets such as the Ras family of membrane-associated signaling proteins. Malfunction of Ras proteins due to somatic mutations is associated with up to a quarter of all human cancers. Computational techniques have played critical roles in identifying and characterizing allosteric ligand-binding sites on these proteins, and to screen ligand libraries against those sites. These efforts, combined with a wide range of biophysical, structural, biochemical and cell biological experiments, are beginning to yield promising inhibitors to treat malignancies associated with mutated Ras proteins. In this chapter, we discuss some of these developments and how the lessons learned from Ras might be applied to similar other challenging drug targets.

Berberine as Source of Antiproliferative Hybrid Compounds: In Vitro Antiproliferative Activity and Quantitative Structure-activity Relationship

BACKGROUND

Despite advances for cancer treatment, it still remains a major worldwide public health problem. Compounds derived from natural sources are important alternatives to combat this mortal disease. Berberine is an isoquinoline alkaloid with a wide variety of pharmacological properties, including antiproliferative activity. Previously, we have found that fatty acids also show antiproliferative activity against cancer cell lines..

OBJECTIVE

To combine berberine and fatty acids, or carboxylic acids, in order to improve their antiproliferative properties.

METHODS

We synthetized six new hybrid derivatives through a simple methylenedioxy group-cleavage method followed by the reaction with fatty acids, or carboxylic acids. The structure of the compounds was elucidated by IR, NMR and HRMS. The in vitro antiproliferative activity against four human cancer cell lines (HeLa, A-549, PC-3 and LS-180) and one normal cell line (ARPE-19), was evaluated by the MTT method. Chemical structures were drawn using SPARTAN '08 software and the conformational analysis was carried out with a molecular mechanic level of theory and the SYBIL force field. All molecular structures were subjected to geometrical optimization at the semi-empirical method PM3. Molecular descriptors were calculated using DRAGON 5.4 and SPARTAN ´08 programs.

RESULTS

The geranic acid and berberine hybrid compound (6) improved the antiproliferative activity shown by natural berberine, even more than the 16- to 18-carbon atoms fatty acids. Compound 6 showed IC50 values of 2.40 ± 0.60, 1.5 ± 0.24, 5.85 ± 1.07 and 5.44 ± 0.24 μM, against HeLa, A-549, PC-3 and LS-180 human cancer cell lines, respectively. Using this information, we performed a quantitative structure-activity relationship (QSAR) of the hybrid molecules and found that the molecular descriptors associated with the antiproliferative activity are: hydrophobic constant associated with substituents (π(A) = 6.5), molecular volume descriptor (CPKvolume≈ 700 Å3), EHOMO, number of rotatable bonds (RBN) and number of 6-membered rings (nR06).

CONCLUSION

The methylendioxy and methoxyl groups in berberine are important for the antiproliferative activity shown by its derivatives. Better results in antiproliferative activity were obtained in compound 6 with the prenyl moiety. The QSAR indicates that the molecular descriptors which associated positively with the antiproliferative activity are: hydrophobic constant associated with substituents (π(A) = 6.5), molecular volume descriptor (CPKvolume≈ 700 Å3) and EHOMO. This research gave the basis for the design and preparation of new, easily afforded molecules derived from berberine and carboxylic acids, with improved antiproliferative activity.

The microRNA-200 family acts as an oncogene in colorectal cancer by inhibiting the tumor suppressor RASSF2

This study aimed to determine whether manipulation of the microRNA-200 (miR-200) family could influence colon adenocarcinoma cell behavior. The miR-200 family has a significant role in tumor suppression and functions as an oncogene. In vitro studies on gain and loss of function with small interfering RNA demonstrated that the miR-200 family could regulate RASSF2 expression. Knockdown of the miR-200 family in the HT-29 colon cancer cell line increased KRAS expression but decreased signaling in the MAPK/ERK signaling pathway through reduced ERK phosphorylation. Increased expression of the miR-200 family in the CCD-841 colon epithelium cell line increased KRAS expression and led to increased signaling in the MAPK/ERK signaling pathway but increased ERK phosphorylation. Functionally, knockdown of the miR-200 family led to decreased cell proliferation in the HT-29 cells; therefore, increased miR-200 family expression could increase cell proliferation in the CCD-841 cell line. The present study included a large paired miR array dataset (n=632), in which the miR-200 family was significantly found to be increased in colon cancer when compared with normal adjacent colon epithelium. In a miR-seq dataset (n=199), the study found that miR-200 family expression was increased in localized colon cancer compared with metastatic disease. Decreased expression was associated with poorer overall survival. The miR-200 family directly targeted RASSF2 and was inversely correlated with RASSF2 expression (n=199, all P<0.001). Despite the well-defined role of the miR-200 family in tumor suppression, the present findings demonstrated a novel function of the miR-200 family in tumor proliferation.

Reversal of Resistance in Targeted Therapy of Metastatic Melanoma: Lessons Learned from Vemurafenib (BRAFV600E-Specific Inhibitor)

Malignant melanoma is the most aggressive form of skin cancer and has a very low survival rate. Over 50% of melanomas harbor various BRAF mutations with the most common being the V600E. BRAF^V600E mutation that causes constitutive activation of the MAPK pathway leading to drug-, immune-resistance, apoptosis evasion, proliferation, survival, and metastasis of melanomas. The ATP competitive BRAF^V600E selective inhibitor, vemurafenib, has shown dramatic success in clinical trials; promoting tumor regression and an increase in overall survival of patients with metastatic melanoma. Regrettably, vemurafenib-resistance develops over an average of six months, which renders melanomas resistant to other therapeutic strategies. Elucidation of the underlying mechanism(s) of acquisition of vemurafenib-resistance and design of novel approaches to override resistance is the subject of intense clinical and basic research. In this review, we summarize recent developments in therapeutic approaches and clinical investigations on melanomas with BRAF^V600E mutation to establish a new platform for the treatment of melanoma.

The discovery of a novel compound with potent antitumor activity: virtual screening, synthesis, biological evaluation and preliminary mechanism study

Farnesyltransferase has been regarded as a promising drug target against cancer as it is critical for membrane association of several signal transduction proteins. In this study, a novel farnesyltransferase inhibitor (IMB-1406) was identified through virtual screening. It exhibits stronger potency (IC₅₀s: 6.92–8.99 μM) than Sunitinib against all of the tested cancer cell lines. Preliminary studies on mechanism reveal that IMB-1406 induces apoptosis in HepG2 cells by arresting the cell cycle at the S phase, altering anti- and pro-apoptotic proteins leading to mitochondrial dysfunction and activation of caspase-3. This anti-tumor effect is most probably related to the inhibition of farnesyltransferase as indicated by molecular docking. Overall, IMB-1406 is a novel lead compound with potent antitumor activity and deserves further structural modifications.

Endpoint of cancer treatment: targeted therapies

Nowadays there are several limitations in cancer treatment. One of these is the use of conventional medicines which not only target cancer cells and thus also cause high toxicity precluding effective treatment. Recent elucidation of mechanisms that cause cancer has led to discovery of novel key molecules and pathways which have have become successful targets for the treatments that eliminate only cancer cells. These so-called targeted therapies offer new hope for millions of cancer patients, as briefly reveiwed here focusing on different types of agents, like PARP, CDK, tyrosine kinase, farnysyl transferase and proteasome inhibitors, monoclonal antibodies and antiangiogenic agents.

Assessing the efficacy of molecularly targeted agents on cell line-based platforms by using system identification

Background

Molecularly targeted agents (MTAs) are increasingly used for cancer treatment, the goal being to improve the efficacy and selectivity of cancer treatment by developing agents that block the growth of cancer cells by interfering with specific targeted molecules needed for carcinogenesis and tumor growth. This approach differs from traditional cytotoxic anticancer drugs. The lack of specificity of cytotoxic drugs allows a relatively straightforward approach in preclinical and clinical studies, where the optimal dose has usually been defined as the "maximum tolerated dose" (MTD). This toxicity-based dosing approach is founded on the assumption that the therapeutic anticancer effect and toxic effects of the drug increase in parallel as the dose is escalated. On the contrary, most MTAs are expected to be more selective and less toxic than cytotoxic drugs. Consequently, the maximum therapeutic effect may be achieved at a "biologically effective dose" (BED) well below the MTD. Hence, dosing study for MTAs should be different from cytotoxic drugs. Enhanced efforts to molecularly characterize the drug efficacy for MTAs in preclinical models will be valuable for successfully designing dosing regimens for clinical trials.

Results

A novel preclinical model combining experimental methods and theoretical analysis is proposed to investigate the mechanism of action and identify pharmacodynamic characteristics of the drug. Instead of fixed time point analysis of the drug exposure to drug effect, the time course of drug effect for different doses is quantitatively studied on cell line-based platforms using system identification, where tumor cells' responses to drugs through the use of fluorescent reporters are sampled over a time course. Results show that drug effect is time-varying and higher dosages induce faster and stronger responses as expected. However, the drug efficacy change along different dosages is not linear; on the contrary, there exist certain thresholds. This kind of preclinical study can provide valuable suggestions about dosing regimens for the in vivo experimental stage to increase productivity.

Phase I study of lonafarnib (SCH66336) in combination with trastuzumab plus paclitaxel in Her2/neu overexpressing breast cancer: EORTC study 16023

PURPOSE

This phase I study was performed to determine the maximum tolerated dose (MTD), dose-limiting toxicities (DLT), safety profile, recommended dose for phase II studies, the pharmacokinetics, and antitumor activity of the combination of lonafarnib (farnesyl transferase inhibitor), trastuzumab, and paclitaxel in Her2-positive advanced breast cancer.

METHODS

Twenty-three patients with Her2-overexpressing breast cancer received in the first cycle paclitaxel and trastuzumab and from cycle 2 onwards lonafarnib which was added to the combination. Dose-limiting toxicity (DLT) was determined during the second cycle.

RESULTS

The MTD and the recommended dose for phase II trials are lonafarnib: 250 mg/day [125 mg/bi-daily (BID)] continuously, paclitaxel: 175 mg/m² 3-h infusion every 3 weeks, and trastuzumab: 4 mg/kg loading dose and 2 mg/kg/week thereafter. The most frequently observed adverse events starting from cycle 1 onwards were alopecia, myalgia, sensory neuropathy, fatigue, arthralgia, leukocytopenia, and neutropenia. From cycle 2 onwards, additional adverse events appeared, such as diarrhea, nausea, dyspepsia, vomiting, and allergy. The mean systemic exposures of both lonafarnib and paclitaxel through all dose levels were higher in the regimen with all three study medications but with no statistically significant difference. Preliminary antitumor activity (CR + PR) was observed in 58% of all patients.

CONCLUSION

Lonafarnib can be safely combined and tolerated with full doses of paclitaxel and trastuzumab in Her2-positive advanced breast cancer patients. Promising preliminary antitumor activity warrants further evaluation of lonafarnib in combination with paclitaxel and trastuzumab in Her2-positive breast cancer.

Targeting the Cellular Signaling: BRAF Inhibition and Beyond for the Treatment of Metastatic Malignant Melanoma

Although advances in cytotoxic treatments have been obtained in several neoplasias, in metastatic melanoma there was no drug able to significantly change the natural history of the disease in the last 30 years. In the last decade, translational research identified important mechanisms in malignant transformation, invasion, and progression. Signaling pathways can be abnormally activated by oncogenes. The identification of oncogenic mutated kinases implicated in this process provides an opportunity for new target therapies. The melanoma dependence on BRAF-mutated kinase allowed the development of inhibitors that produced major responses in clinical trials. This is the beginning of a novel class of drugs in metastatic melanoma; the identification of the transduction signaling networking and other “druggable” kinases is in active research. In this paper, we discuss the ongoing research on cellular signaling inhibition, resistance mechanisms, and strategies to overcome treatment failure.

Spatiotemporal regulation of small GTPases as revealed by probes based on the principle of Förster Resonance Energy Transfer (FRET): Implications for signaling and pharmacology

Low molecular weight ("small") GTPases are key regulators of a number of signaling cascades. Each GTPase is regulated by numerous guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs), and each GTPase binds to numerous effector proteins in a GTP-dependent manner. In many instances, individual regulators activate more than one GTPase, and each effector binds to one or more GTPases belonging to the same family. To untangle these complex networks, probes based on the principle of Förster resonance energy transfer (FRET) are widely used. Here, we provide an overview of the probes based on FRET and examples of discoveries achieved with them. In the process, we attempt to delineate the merits, current limitations, and future applications of this technique to pharmacological studies.

A new era: melanoma genetics and therapeutics

We have recently witnessed an explosion in our understanding of melanoma. Knowledge of the molecular basis of melanoma and the successes of targeted therapies have pushed melanoma care to the precipice of a new era. Identification of significant pathways and oncogenes has translated to the development of targeted therapies, some of which have produced major clinical responses. In this review, we provide an overview of selected key pathways and melanoma oncogenes as well as the targeted agents and therapeutic approaches whose successes suggest the promise of a new era in melanoma and cancer therapy. Despite these advances, the conversion of transient remissions to stable cures remains a vital challenge. Continued progress towards a better understanding about the complexity and redundancy responsible for melanoma progression may provide direction for anti-cancer drug development.

Molecular mechanisms of metastasis in prostate cancer

Prostate cancer (PCa) preferentially metastasizes to the bone marrow stroma of the axial skeleton. This activity is the principal cause of PCa morbidity and mortality. The exact mechanism of PCa metastasis is currently unknown, although considerable progress has been made in determining the key players in this process. In this review, we present the current understanding of the molecular processes driving PCa metastasis to the bone.

Drug delivery in acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia was among the first malignancies to be cured by drug therapy alone, but overall survival rates remain unsatisfactory and have changed little over the past 20 years. Conventional chemotherapeutic regimens, which almost invariably include cytarabine and anthracyclines, are untargeted, and more specific therapies are needed.

OBJECTIVE

We have chosen acute myeloid leukemia as a disease prototype to review established and novel targeted approaches in leukemia treatment.

METHODS

Our selection of the reviewed literature focused on drug delivery aspects.

CONCLUSION

While the toxicity profile of chemotherapeutics has been improved by liposomal formulations and antibody conjugation for leukemia-directed uptake, their efficacy has probably not changed significantly. Drugs with an alternative mode of action, including kinase inhibitors, hold great promise. Further improvements may result from the characterization of novel acute myeloid leukemia (AML) cell surface receptors and of leukemic stem cells, as well as from the design of leukemia-targeted gene therapy vectors.

Molecular pathogenesis and therapeutic targets in epithelial ovarian cancer

Ovarian cancer, the most aggressive gynecologic cancer, is the foremost cause of death from gynecologic malignancies in the developed world. Two primary reasons explain its aggressive behavior: most patients present with advanced disease at diagnosis, and die of recurrences from disease that has become resistant to conventional chemotherapies. In this paper on epithelial ovarian cancer (EOC), we will review molecular alterations associated with the few precursor lesions identified to date, followed by the more commonly recognized processes of de novo carcinogenesis, metastasis, and the development of chemoresistance. We will propose a unifying model of ovarian epithelial tumorigenesis that takes into account various hypotheses. We will also review novel approaches to overcome the major problem of chemoresistance in ovarian cancer. Finally, we will discuss advances and new challenges in the development of mouse model systems to investigate EOC precursor lesions, progression, metastasis, and chemoresistance.

Recent discoveries in the genetics of melanoma and their therapeutic implications

The incidence of cutaneous malignant melanoma, tumors arising from melanocytes, has increased markedly over the past few years in many countries. Although early melanoma is curable through surgical excision, the prognosis of advanced melanoma is very poor, this tumor being resistant to current therapies. Thus there is a need for new therapies to improve the treatment of advanced melanoma. This review provides an overview of recent discoveries in the genetics of melanoma which could offer new therapeutic opportunities.

Expression of the human phosphatases of regenerating liver (PRLs) in colonic adenocarcinoma and its correlation with lymph node metastasis

BACKGROUND

Human phosphatases of regenerating liver (PRLs) can induce cell growth, differentiation, and malignant transformation. In this study, we used specific polyclonal antibodies against PRLs to investigate their expression in colonic adenocarcinomas and its correlation with patient gender, age, tumor differentiation, localization, invasion, and metastasis.

MATERIALS AND METHODS

The polyclonal antibodies against PRL-1, PRL-2, and PRL-3 were produced and purified. The expression of PRLs in human colorectal carcinoma cell lines (SW480 and SW620) was examined by Western blotting. We also examined their expression in normal and pathologic tissues from the human colon. The tissues included 49 primary colonic adenocarcinomas, 14 cases with lymph node metastases, 15 colonic adenomas, and 12 normal colon samples. Hematoxylin and eosin staining, immunohistochemistry, and semiquantitative morphological analysis were used to evaluate the sections.

RESULTS

PRLs were widely expressed in SW480 and SW620. PRL-1, PRL-2, and PRL-3 were expressed, respectively, in 16, 10, and 16% of primary colonic adenocarcinomas. In contrast, PRLs were strongly expressed in all lymph node metastases. There were no significant correlations between the expression of PRLs and patient gender, age, tumor differentiation, depth of invasion, or localization of tumor within the different sections of the colon. PRLs were not expressed in normal colon tissues or in colonic adenomas. PRLs were mainly expressed in the cytoplasm and at the cytoplasmic membranes of the colonic adenocarcinoma cells as well as in the endothelial cells and the surrounding smooth muscle cells of larger vessels in the lymph node metastases.

CONCLUSION

Colonic adenocarcinoma cells have the ability to produce PRLs, which may relate to the lymph node metastasis of colonic adenocarcinoma.

The emerging role of targeted therapy for hematologic malignancies: update on bortezomib and tipifarnib

As therapy for hematologic malignancy evolves, new regimens and novel agents that target specific cellular processes allow a more optimistic prognosis for many patients. Bortezomib and tipifarnib are two new, targeted treatments for hematologic malignancies. Bortezomib, a proteasome inhibitor, has shown impressive efficacy in patients with relapsed multiple myeloma and as initial treatment, including before autologous stem cell transplantation. It has been studied as monotherapy and in combination with standard treatments such as dexamethasone, and with newer agents such as the immunomodulators thalidomide and lenalidomide; response is encouraging, even in patients who have relapsed after previously receiving components of a regimen as single agents. Bortezomib is generally well tolerated, including in combination with novel and conventional agents. Tipifarnib is a specific inhibitor of farnesyltransferase. Clinical trials in patients with high-risk acute leukemias and myelodysplastic syndromes have demonstrated good efficacy with tipifarnib. Continued investigation with these new, targeted treatments will further define their use as treatment options in patients with hematologic cancer.

Farnesyltransferase Inhibitor, Manumycin A, Prevents Atherosclerosis Development and Reduces Oxidative Stress in Apolipoprotein E-Deficient Mice

OBJECTIVE

Statins are presumed to exert their antiatherogenic effects in part via lipid-lowering-independent mechanisms. Inhibition of protein farnesylation and/or geranylgeranylation by statins has been postulated to contribute to the lipid-lowering-independent effects. However, a role for protein farnesylation in atherogenesis has not yet been studied. Therefore, we examined the effects of farnesyltransferase inhibitor, manumycin A, on the development of atherosclerosis in apolipoprotein E (apoE)-deficient mice fed a high-fat diet.

METHODS AND RESULTS

Manumycin A treatment for 22 weeks decreased Ras activity, and reduced fatty streak lesion size at the aortic sinus to 43% of that in vehicle-treated apoE-deficient mice (P<0.05), while plasma total cholesterol was unaltered. Moreover, manumycin A reduced alpha-smooth muscle actin-positive area to 29% of that in vehicle-treated apoE-deficient mice (P<0.01). The prevention of atherogenesis by manumycin A was accompanied by amelioration of oxidative stress, as judged by reduced ex vivo superoxide production and nitrotyrosine immunoreactivity.

CONCLUSIONS

These results indicate that the inhibition of farnesyltransferase prevents the development of mature atherosclerosis with concomitant alleviation of oxidative stress in apoE-deficient mice. The present data highlight farnesyltransferase as a potential molecular target for preventive and/or therapeutic intervention against atherosclerosis.

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.

Cytotoxic farnesyl glycosides from Pittosporum pancheri

Bioassay guided purification of the ethanolic extract of the bark of New Caledonian Pittosporum pancheri Brongn. and Gris (Pittosporaceae) led to the isolation and characterization of two new farnesyl monoglycosides, pancherins A and B. The structure of these compounds were determined on the basis of spectroscopic studies. The new compounds displayed a significant activity in the in vitro cytotoxic assay against KB cancer cell line, and pancherin A inhibits weakly farnesyl protein transferase.

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.

Rho2 is a target of the farnesyltransferase Cpp1 and acts upstream of Pmk1 mitogen-activated protein kinase signaling in fission yeast

We have previously demonstrated that knockout of the calcineurin gene or inhibition of calcineurin activity by immunosuppressants resulted in hypersensitivity to Cl- in fission yeast. We also demonstrated that knockout of the components of the Pmk1 mitogen-activated protein kinase (MAPK) pathway, such as Pmk1 or Pek1 complemented the hypersensitivity to Cl-. Using this interaction between calcineurin and Pmk1 MAPK, here we developed a genetic screen that aims to identify new regulators of the Pmk1 signaling and isolated vic (viable in the presence of immunosuppressant and chloride ion) mutants. One of the mutants, vic1-1, carried a missense mutation in the cpp1+ gene encoding a beta subunit of the protein farnesyltransferase, which caused an amino acid substitution of aspartate 155 of Cpp1 to asparagine (Cpp1(D155N)). Analysis of the mutant strain revealed that Rho2 is a novel target of Cpp1. Moreover, Cpp1 and Rho2 act upstream of Pck2-Pmk1 MAPK signaling pathway, thereby resulting in the vic phenotype upon their mutations. Interestingly, compared with other substrates of Cpp1, defects of Rho2 function were more phenotypically manifested by the Cpp1(D155N) mutation. Together, our results demonstrate that Cpp1 is a key component of the Pck2-Pmk1 signaling through the spatial control of the small GTPase Rho2.

Chemotherapy and targeted therapy combinations in advanced melanoma

For three decades, clinical trials with chemotherapy in melanoma have failed to show superiority of any one regimen over another. Dacarbazine remains the only "standard" agent. With response rates of <10% and median progression-free survival of 2 months or less in contemporary trials, there is a need to improve systemic therapy. Combination chemotherapy is associated with higher response rates than single-agent therapy but this has not translated into improved survival. An increasing number of potential therapeutic targets have been identified. For some, pharmacologic inhibitors are available, including sorafenib for BRAF, farnesyltransferase inhibitors for NRAS, PD-0325901 for mitogen-activated protein kinase/extracellular signal-regulated kinase kinase, rapamycin analogues for mammalian target of rapamycin, and agents that inhibit either vascular endothelial growth factor or its receptors. Several multitargeted kinase inhibitors have potency against the fibroblast growth factor receptor, c-kit, and platelet-derived growth factor receptor. Small-molecule inhibitors of c-met and Akt are in preclinical development. Another class of agents indirectly affect aberrant signaling, including inhibitors of chaperones and proteasomes. Several targeted agents seem to enhance the cytotoxicity of chemotherapy in preclinical models. The mechanism by which signaling inhibition might synergize with chemotherapy requires more study so that rational combinations move forward. Very few targeted agents have been studied rigorously in this fashion.

Novel therapeutic agents in ovarian cancer

AIMS

Epithelial ovarian cancer is responsible for 4% of all cancer deaths in women, and the five-year overall survival of patients with advanced disease is 30-40%. Treatment currently comprises a combination of surgery and chemotherapy with carboplatin and paclitaxel. The main reason for treatment failure is that the majority of patients present with advanced disease, and current drugs are unable to effect a cure even in chemosensitive patients. This article systematically reviews novel therapeutic strategies that have been evaluated in patients with ovarian cancer in the last 5 years.

METHODS

Pubmed (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed) and American Society of Clinical Oncology Annual conference abstracts were searched using the terms "(phase I OR phase II OR phase III OR phase 1 OR phase 2 OR phase 3) AND (ovary OR ovarian) AND (cancer OR carcinoma)" from January 2000 to May 2005 to identify studies for potential inclusion in this review. Reviews of novel therapies in ovarian cancer were also used to identify additional clinical trials.

FINDINGS

A wide range of therapeutic strategies are currently being evaluated in ovarian cancer. These include novel cytotoxics, small molecule inhibitors, monoclonal antibodies, gene therapy and immuno-therapy strategies. The rationale for the development of these agents includes enhancement of efficacy by targeting novel biological pathways, re-sensitisation to existing drugs, simplification of drug administration and/or reduction of drug-toxicity.

CONCLUSIONS

Current developments have the potential to result in substantial improvements in the outlook for women with ovarian cancer.

Is tailored therapy feasible in oncology?

Tailored therapy aims to cure a patient who suffers from a specific disease with an effective and safe drug, based on the complex interactions among patient's characteristics, disease physiopathology and drug metabolism. Genomic and proteomic technologies represent promising new useful tools to understand cancer biology and molecular basis of interindividual differences of anticancer drugs efficacy. Genomic profiling seems to be able to re-classifying cancer into new molecular and prognostic homogeneous subgroups. By individual polymorphisms it is possible to identify the patients at higher risk for severe toxicity from those that may gain benefit from a particular treatment. The clinical use of targeted therapy is hampered by several questions, including: optimal biological dose, availability of surrogate biomarkers predictive of activity, schedule of administration, tumor histotype and stage to treat and modalities of combination with chemo/radiotherapy. In addition, further efforts are needed to improve the reliability of genomic and proteomic technologies. These unsolved issues presently make tailored therapy an open challenge.

Pharmacogenetics for individualized cancer chemotherapy

The same doses of medication cause considerable heterogeneity in efficacy and toxicity across human populations. Genetic factors are thought to represent important determinants of drug efficacy and toxicity. Pharmacogenetics focuses on the prediction of the response of tumor and normal tissue to standard therapy by genetic profiling and, thereby, to select the most appropriate medication at optimal doses for each individual patient. In the present review, we discuss the relevance of single nucleotide polymorphisms (SNP) in genes, whose gene products act upstream of the actual drug target sites, that is, drug transporters and drug metabolizing phase I and II enzymes, or downstream of them, that is, apoptosis-regulating genes and chemokines. SNPs in relevant genes, which encode for proteins that interact with anticancer drugs, were also considered, that is, enzymes of DNA biosynthesis and metabolism, DNA repair enzymes, and proteins of the mitotic spindle. A significant body of evidence supports the concept of predicting drug efficacy and toxicity by SNP genotyping. As the efficacy of cancer chemotherapy, as well as the drug-related toxicity in normal tissues is multifactorial in nature, sophisticated approaches such as genome-wide linkage analyses and integrate drug pathway profiling may improve the predictive power compared with genotyping of single genes. The implementation of pharmacogenetics into clinical routine diagnostics including genotype-based recommendations for treatment decisions and risk assessment for practitioners represents a challenge for the future.

Antitumor activity of orally bioavailable farnesyltransferase inhibitor, ABT-100, is mediated by antiproliferative, proapoptotic, and antiangiogenic effects in xenograft models

PURPOSE

To evaluate the preclinical pharmacokinetics, antitumor efficacy, and mechanism of action of a novel orally active farnesyltransferase inhibitor, ABT-100.

EXPERIMENTAL DESIGN

In vitro sensitivity of a panel of human cell lines was determined using proliferation and clonogenic assays. In vivo efficacy of ABT-100 was evaluated in xenograft models (flank or orthotopic) by assessing angiogenesis, proliferation, and apoptosis in correlation with pharmacokinetics. Efficacy of the racemate of ABT-100 (A-367074) was also compared with R115777 (tipifarnib).

RESULTS

ABT-100 inhibited proliferation of cells in vitro carrying oncogenic H-Ras (EJ-1 bladder; IC(50) 2.2 nmol/L), Ki-Ras (DLD-1 colon, MDA-MB-231 breast, HCT-116 colon, and MiaPaCa-2 pancreatic; IC(50) range, 3.8-9.2 nmol/L), and wild-type Ras (PC-3 and DU-145; IC(50), 70 and 818 nmol/L, respectively) as well as clonogenic potential. ABT-100 shows 70% to 80% oral bioavailability in mice. ABT-100 regressed EJ-1 tumors (2-12.5 mg/kg/d s.c., every day for 21 days) and showed significant efficacy in DLD-1, LX-1, MiaPaCa-2, or PC-3 tumor-bearing mice (6.25-50 mg/kg/d s.c. once daily or twice daily orally). A-367074 showed equivalent efficacy to R115777 given at approximately one-fourth the total dose of R115777 for a shorter duration (EJ-1 and LX-1). Antitumor activity was associated with decreased cell proliferation (Ki-67), increased apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling), and decreased angiogenesis. A reduction in tumor angiogenic cytokine levels (vascular endothelial growth factor, basic fibroblast growth factor, and interleukin-8) correlated with a reduction in tumor vascularity (CD31).

CONCLUSIONS

Overall, ABT-100 has an acceptable pharmacokinetic profile, is well tolerated, and possesses broad-spectrum antitumor activity against a series of xenograft models similar to farnesyltransferase inhibitors in clinical development; therefore, it is an attractive candidate for clinical evaluation.

Human T-lymphotropic virus type 1 mitochondrion-localizing protein p13II sensitizes Jurkat T cells to Ras-mediated apoptosis

Human T-lymphotropic virus type 1 (HTLV-1) is the etiological agent of adult T-cell leukemia. In addition to typical retroviral structural and enzymatic gene products, HTLV-1 encodes unique regulatory and accessory proteins, including a singly spliced pX open reading frame II (ORF II) product, p13(II). We have demonstrated that proviral clones of HTLV-1 which are mutated in pX ORF II fail to obtain typical proviral loads and antibody responses in a rabbit animal model. p13(II) localizes to mitochondria and reduces cell growth and tumorigenicity in mice, but its function in human lymphocytes remains undetermined. For this study, we analyzed the functional properties of Jurkat T cells expressing p13(II), using both transient and stable expression vectors. Our data indicate that p13(II)-expressing Jurkat T cells are sensitive to caspase-dependent, ceramide- and FasL-induced apoptosis. p13(II)-expressing Jurkat T cells also exhibited reduced proliferation when cultured at a high density. Furthermore, preincubation of the p13(II)-expressing cells with a farnesyl transferase inhibitor, which blocks the posttranslational modification of Ras, markedly reduced FasL-induced apoptosis, indicating the participation of the Ras pathway in p13(II)'s influence on lymphocyte survival. Our data are the first to demonstrate that p13(II) alters Ras-mediated apoptosis in T lymphocytes, and they reveal a potential mechanism by which HTLV-1 alters lymphocyte proliferation.

Induction of cytotoxicity in human lung adenocarcinoma cells by 6-O-carboxypropyl-alpha-tocotrienol, a redox-silent derivative of alpha-tocotrienol

Tocotrienols are one of the most potent anticancer agents of all natural compounds and the anticancer property may be related to the inactivation of Ras family molecules. The anticancer potential of tocotrienols, however, is weakened due to its short elimination half life in vivo. To overcome the disadvantage and reinforce the anticancer activity in tocotrienols, we synthesized a redox-silent analogue of alpha-tocotrienol (T3), 6-O-carboxypropyl-alpha-tocotrienol (T3E). We estimated the possibility of T3E as a new anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras gene. T3E showed cytotoxicity against A549 cells, a human lung adenocarcinoma cell line with a ras gene mutation, in a dose-dependent manner (0-40 microM), whereas T3 and a redox-silent analogue of alpha-tocopherol (T), 6-O-carboxypropyl-alpha-tocopherol (TE), showed much less cytotoxicity in cells within 40 microM. T3E cytotoxicity was based on the accumulation of cells in the G1-phase of the cell-cycle and the subsequent induction of apoptosis. Similar to this event, 24-hr treatment of A549 cells with 40 microM T3E caused the inhibition of Ras farnesylation, and a marked decrease in the levels of cyclin D required for G1/S progression in the cell-cycle and Bcl-xL, a key anti-apoptotic molecule. Moreover, the T3E-dependent inhibition of RhoA geranyl-geranylation is an inducing factor for the occurrence of apoptosis in A549 cells. Our results suggest that T3E suppresses Ras and RhoA prenylation, leading to negative growth control against A549 cells. In conclusion, a redox-silent analogue of T3, T3E may be a new candidate as an anticancer agent against lung adenocarcinoma showing poor prognosis based on the mutation of ras genes.

The MAPK signalling pathways and colorectal cancer

There are three major subfamilies of mitogen-activated protein kinases (MAPK): the extracellular-signal-regulated kinases (ERK MAPK); the c-jun N-terminal kinase or stress-activated protein kinases (JNK or SAPK); and MAPK14. The ERK MAPK pathway is one of the most important for cell proliferation. The MAPK pathways are located downstream of many growth-factor receptors, including that for epidermal growth factor. Overexpression and activation of this receptor are commonly detected in colorectal cancer, and several lines of evidence indicate that overexpression and activation of ERK MAPK play an important part in progression of this cancer. ERK MAPK could be a molecular target for treatment of the disorder. This review focuses on the ERK MAPK signal-transduction pathway, the consequences of its dysregulation in colorectal cancer, and its potential as an approach to cancer treatment. Future challenges for the assessment of these targeted agents in the clinic are also presented.

Therapy of breast cancer with molecular targeting agents

Invasive breast cancer is a heterogeneous disease sustained by intercorrelated and complex growth pathways. Classically, human breast carcinoma has been classified for therapeutic purposes in two distinct categories: one hormone-correlated, the other hormone-uncorrelated. However, the recent advancements of the technology applied to molecular biology by genomic and proteomic analyses have suggested that many more factors are involved in breast cancer growth and progression and that some clusters of these distinguish subgroups of patients at different prognosis. The knowledge of the diversities between tumor and normal tissue of origin is the key to identify novel targets for new selective therapeutic strategies. In fact, the principal goal of molecular-targeted therapy is the suppression of the transformed phenotype minimally affecting normal cells. This review focuses on the molecular targeting compounds directed against the known molecular pathways involved in breast cancer such as: type I growth factors (HER-2/neu; epidermal growth factor receptor [EGFR]), angiogenesis, cyclooxigenase-2 (COX-2) and farnesylation. Presently, trastuzumab is the first agent approved for therapy of HER-2/neu overexpressing tumors. Several other compounds directed against different targets have entered clinical evaluation and the preliminary results are here presented and commented. The major challenges on the clinical development of targeted therapy include the proper selection of patients, the identification of the optimal dosage and schedule of administration, the combinations with conventional treatments and the more appropriate therapeutic strategy.

Design, synthesis, and evaluation of potent and selective benzoyleneurea-based inhibitors of protein geranylgeranyltransferase-I

A series of novel protein geranylgeranyltransferase-I (PGGTase-I) inhibitors based on a benzoyleneurea scaffold has been synthesized. Using a benzoyleneurea scaffold as a mimetic for the central dipeptide (AA), we have developed CAAX peptidomimetic inhibitors that selectively block the activity of PGGTase-I over the closely related enzyme protein farnesyltransferase. In this new class of PGGTase-I inhibitors, compound (6c) with X=L-phenylalanine, displayed the highest inhibition activity against PGGTase-I with an IC50 value of 170 nM. The inhibitors described in this study represent novel and promising leads for the development of potent and selective inhibitors of mammalian PGGTase-I for potential application as antitumor agents.

Unraveling the mechanism of the farnesyltransferase enzyme

Farnesyltransferase enzyme (FTase) is currently one of the most fascinating targets in cancer research. Studies in other areas, namely in the fight against parasites and viruses, have also led to very promising results. However, in spite of the thrilling achievements in the development of farnesyltransferase inhibitors (FTIs) over the past few years, the farnesylation mechanism remains, to some degree, a mystery. This review tries to shed some light on this puzzling enzyme by analyzing seven key mechanistic dilemmas, based on recent studies that have dramatically changed the way this enzyme is currently perceived.

Spectroscopic study of fluorescent peptides for prenyl transferase assays

A study of the prenyl transferase reactions was performed by fluorescence using rat brain cytosol fractions as an enzyme source. Four dansylated peptides corresponding to the C-terminal sequence of Ras isoforms were synthesised. The effects of different detergents on the farnesylation or geranylgeranylation of the four peptides were evaluated. Dose-dependent effects of dodecyl-maltoside, a non-ionic detergent, on the farnesyl transferase or geranylgeranyl transferase activities were observed with all peptide substrates. Additionally, the effect of temperature was investigated and these assays were applied to determine Michaelis-Menten constants (K(m)) of the substrates: dansyl-GCVLS (1.8 microM), dansyl-GCVVM (3.2 microM), dansyl-CVIM (3.4 microM) and dansyl-GCVLL (8.4 microM) and FPP (22.6 microM) for FTase activity. Using GGPP as co-substrate, GGTase activity was measured with K(m) values superior to 50 microM for all the three substrate dansyl-GCVLS, dansyl-GCVVM, or dansyl-CVIM, whereas values of 7.6 and 5.4 microM were calculated for the dansyl-GCVLL sequence and GGPP co-substrate, respectively. IC50 values of selective prenyl transferase inhibitors, B-581, FTI 276 and GGTI 287 have been measured to 34, 0.8 and 18 nM, respectively, using dansyl-GCVLS as substrate (FTase inhibition). When dansyl-GCVLL is used as substrate (GGTase inhibition) the IC50 values are 5100, 75 and 5 nM for B-581, FTI 276 and GGTI 287, respectively. Then, this developed method allowed to evaluate the selectivity of all the three inhibitors tested.

Potent and Selective Farnesyl Transferase Inhibitors

We recently described a novel series of CA(1)A(2)X peptidomimetics as farnesyl transferase inhibitors (FTIs). These compounds possess an N-(4-piperidinyl)benzamide scaffold mimicking A(1)A(2) residue. Extensive exploration of structure--activity relationships revealed that replacement of cysteine by substituted benzylimidazoles provided nanomolar FTIs with in vitro activities (18e, IC(50) = 4.60 nM on isolated enzyme, EC(50) = 20.0 nM for growth inhibition on a tumor cell line). The molecular docking of 18e and 19e in the active site of the enzyme provided details of key interactions with the protein and showed that the methionine or phenylalanine residue fits into the aryl binding site.

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.

Molecular therapy in pancreatic adenocarcinoma

Pancreatic cancer is one of the commonest causes of death from cancer. Despite therapy with surgery, conventional chemotherapy, and radiation, 5-year survival for patients with this diagnosis remains poor. However, advances in the molecular understanding of this malignant disease over the past 5 years might lead to new treatment strategies. Strategies of gene therapy, antiangiogenic treatments, immunotherapy, and signal-transduction inhibition are in preclinical development. This review presents an overview of molecular therapy in pancreatic cancer.