Isoprenoid addition to Ras protein is the critical modification for its membrane association and transforming activity

Regulation of protein prenylation

Prenyltransferases (PTases) are known to play a role in embryonic development, normal tissue homeostasis and cancer by posttranslationally modifying proteins involved in these processes. They are being discussed as potential drug targets in an increasing number of diseases, ranging from Alzheimer's disease to malaria. Protein prenylation and the development of specific PTase inhibitors (PTIs) have been subject to intense research in recent decades. Recently, the FDA approved lonafarnib, a specific farnesyltransferase inhibitor that acts directly on protein prenylation; and bempedoic acid, an ATP citrate lyase inhibitor that might alter intracellular isoprenoid composition, the relative concentrations of which can exert a decisive influence on protein prenylation. Both drugs represent the first approved agent in their respective substance class. Furthermore, an overwhelming number of processes and proteins that regulate protein prenylation have been identified over the years, many of which have been proposed as molecular targets for pharmacotherapy in their own right. However, certain aspects of protein prenylation, such as the regulation of PTase gene expression or the modulation of PTase activity by phosphorylation, have attracted less attention, despite their reported influence on tumor cell proliferation. Here, we want to summarize the advances regarding our understanding of the regulation of protein prenylation and the potential implications for drug development. Additionally, we want to suggest new lines of investigation that encompass the search for regulatory elements for PTases, especially at the genetic and epigenetic levels.

Multiple Strategies to Develop Small Molecular KRAS Directly Bound Inhibitors

KRAS gene mutation is widespread in tumors and plays an important role in various malignancies. Targeting KRAS mutations is regarded as the "holy grail" of targeted cancer therapies. Recently, multiple strategies, including covalent binding strategy, targeted protein degradation strategy, targeting protein and protein interaction strategy, salt bridge strategy, and multivalent strategy, have been adopted to develop KRAS direct inhibitors for anti-cancer therapy. Various KRAS-directed inhibitors have been developed, including the FDA-approved drugs sotorasib and adagrasib, KRAS-G12D inhibitor MRTX1133, and KRAS-G12V inhibitor JAB-23000, etc. The different strategies greatly promote the development of KRAS inhibitors. Herein, the strategies are summarized, which would shed light on the drug discovery for both KRAS and other "undruggable" targets.

The Genus Chrysosporium: A Potential Producer of Natural Products

Chrysosporium, a genus of ascomycete fungi in the family Onygenaceae, has the ability to produce abundant new bioactive natural products, providing a structural foundation in drug development. This review includes the sources, distribution, biological activities and structural characteristics of the compounds isolated from Chrysosporium from 1984 to 2021. The results show that 66% of the compounds isolated from Chrysosporium are new natural products. More than half of the Chrysosporium-isolated compounds are from marine-derived Chrysosporium. The chemical structures of Chrysosporium-derived compounds have different skeletons, which are concentrated in alkaloids, polyketides, and lactones. Eighty percent of the natural products isolated from Chrysosporium have been found to have various biological activities, including cytotoxic, antibacterial, antifungal and enzyme-inhibitory activities. These results demonstrate the potential of Chrysosporium for producing new bioactive secondary metabolites, which can be used as the structural basis for developing new drugs.

Drugging KRAS: current perspectives and state-of-art review

After decades of efforts, we have recently made progress into targeting KRAS mutations in several malignancies. Known as the ‘holy grail’ of targeted cancer therapies, KRAS is the most frequently mutated oncogene in human malignancies. Under normal conditions, KRAS shuttles between the GDP-bound ‘off’ state and the GTP-bound ‘on’ state. Mutant KRAS is constitutively activated and leads to persistent downstream signaling and oncogenesis. In 2013, improved understanding of KRAS biology and newer drug designing technologies led to the crucial discovery of a cysteine drug-binding pocket in GDP-bound mutant KRAS G12C protein. Covalent inhibitors that block mutant KRAS G12C were successfully developed and sotorasib was the first KRAS G12C inhibitor to be approved, with several more in the pipeline. Simultaneously, effects of KRAS mutations on tumour microenvironment were also discovered, partly owing to the universal use of immune checkpoint inhibitors. In this review, we discuss the discovery, biology, and function of KRAS in human malignancies. We also discuss the relationship between KRAS mutations and the tumour microenvironment, and therapeutic strategies to target KRAS. Finally, we review the current clinical evidence and ongoing clinical trials of novel agents targeting KRAS and shine light on resistance pathways known so far.

Gene Expression over Time during Cell Transformation Due to Non-Genotoxic Carcinogen Treatment of Bhas 42 Cells

The Bhas 42 cell transformation assay (Bhas 42 CTA) is the first Organization for Economic Cooperation and Development (OECD)-certificated method used as a specific tool for the detection of the cell-transformation potential of tumor-promoting compounds, including non-genotoxic carcinogens (NGTxCs), as separate from genotoxic carcinogens. This assay offers the great advantage of enabling the phenotypic detection of oncotransformation. A key benefit of using the Bhas 42 CTA in the study of the cell-transformation mechanisms of tumor-promoting compounds, including non-genotoxic carcinogens, is that the cell-transformation potential of the chemical can be detected directly without treatment with a tumor-initiating compound since Bhas 42 cell line was established by transfecting the v-Ha-ras gene into a mouse fibroblast cloned cell line. Here, we analyzed the gene expression over time, using DNA microarrays, in Bhas 42 cells treated with the tumor-promoting compound 12-O-tetradecanoylphorbol-13-acetate (TPA), and NGTxC, with a total of three repeat experiments. This is the first paper to report on gene expression over time during the process of cell transformation with only a tumor-promoting compound. Pathways that were activated or inactivated during the process of cell transformation in the Bhas 42 cells treated with TPA were related not only directly to RAS but also to various pathways in the hallmarks of cancer.

RNF141 interacts with KRAS to promote colorectal cancer progression

RING finger proteins (RNFs) play a critical role in cancer initiation and progression. RNF141 is a member of RNFs family; however, its clinical significance, roles, and mechanism in colorectal cancer (CRC) remain poorly understood. Here, we examined the expression of RNF141 in 64 pairs of CRC and adjacent normal tissues by real-time PCR, Western blot, and immunohistochemical analysis. We found that there was more expression of RNF141 in CRC tissue compared with its adjacent normal tissue and high RNF141 expression associated with T stage. In vivo and in vitro functional experiments were conducted and revealed the oncogenic role of RNF141 in CRC. RNF141 knockdown suppressed proliferation, arrested the cell cycle in the G1 phase, inhibited migration, invasion and HUVEC tube formation but promoted apoptosis, whereas RNF141 overexpression exerted the opposite effects in CRC cells. The subcutaneous xenograft models showed that RNF141 knockdown reduced tumor growth, but its overexpression promoted tumor growth. Mechanistically, liquid chromatography-tandem mass spectrometry indicated RNF141 interacted with KRAS, which was confirmed by Co-immunoprecipitation, Immunofluorescence assay. Further analysis with bimolecular fluorescence complementation (BiFC) and Glutathione-S-transferase (GST) pull-down assays showed that RNF141 could directly bind to KRAS. Importantly, the upregulation of RNF141 increased GTP-bound KRAS, but its knockdown resulted in a reduction accordingly. Next, we demonstrated that RNF141 induced KRAS activation via increasing its enrichment on the plasma membrane not altering total KRAS expression, which was facilitated by the interaction with LYPLA1. Moreover, KRAS silencing partially abolished the effect of RNF141 on cell proliferation and apoptosis. In addition, our findings presented that RNF141 functioned as an oncogene by upregulating KRAS activity in a manner of promoting KRAS enrichment on the plasma membrane in CRC.

Targeting KRAS in pancreatic cancer: new drugs on the horizon

Kirsten Rat Sarcoma (KRAS) is a master oncogene involved in cellular proliferation and survival and is the most commonly mutated oncogene in all cancers. Activating KRAS mutations are present in over 90% of pancreatic ductal adenocarcinoma (PDAC) cases and are implicated in tumor initiation and progression. Although KRAS is a critical oncogene, and therefore an important therapeutic target, its therapeutic inhibition has been very challenging, and only recently specific mutant KRAS inhibitors have been discovered. In this review, we discuss the activation of KRAS signaling and the role of mutant KRAS in PDAC development. KRAS has long been considered undruggable, and many drug discovery efforts which focused on indirect targeting have been unsuccessful. We discuss the various efforts for therapeutic targeting of KRAS. Further, we explore the reasons behind these obstacles, novel successful approaches to target mutant KRAS including G12C mutation as well as the mechanisms of resistance.

Post-translational modification of KRAS: potential targets for cancer therapy

Aberrant activation of the RAS superfamily is one of the critical factors in carcinogenesis. Among them, KRAS is the most frequently mutated one which has inspired extensive studies for developing approaches to intervention. Although the cognition toward KRAS remains far from complete, mounting evidence suggests that a variety of post-translational modifications regulate its activation and localization. In this review, we summarize the regulatory mode of post-translational modifications on KRAS including prenylation, post-prenylation, palmitoylation, ubiquitination, phosphorylation, SUMOylation, acetylation, nitrosylation, etc. We also highlight the recent studies targeting these modifications having exhibited potent anti-tumor activities.

Zebrafish as a Model for the Study of Lipid-Lowering Drug-Induced Myopathies

Drug-induced myopathies are classified as acquired myopathies caused by exogenous factors. These pathological conditions develop in patients without muscle disease and are triggered by a variety of medicaments, including lipid-lowering drugs (LLDs) such as statins, fibrates, and ezetimibe. Here we summarise the current knowledge gained via studies conducted using various models, such as cell lines and mammalian models, and compare them with the results obtained in zebrafish (Danio rerio) studies. Zebrafish have proven to be an excellent research tool for studying dyslipidaemias as a model of these pathological conditions. This system enables in-vivo characterization of drug and gene candidates to further the understanding of disease aetiology and develop new therapeutic strategies. Our review also considers important environmental issues arising from the indiscriminate use of LLDs worldwide. The widespread use and importance of drugs such as statins and fibrates justify the need for the meticulous study of their mechanism of action and the side effects they cause.

A membrane-associated metalloprotease of Schistosoma japonicum structurally related to the FACE-1/Ste24p protease family

The CaaX proteases are closely related in the post-translational modification of many membrane-bound or secreted proteins and play a key role in the activation or stabilization of these molecules belonging to the CAAX family. In this study, a full-length cDNA putatively encoding a FACE-1/Ste24p CaaX protease (type I) of the Schistosoma japonicum was isolated. The cDNA, named SjSte24p, composed of 1646 bp and encoded 473 amino acids with predicted Mr/pI as 54.77 kDa/8.04. SjSte24p is a monoexonic gene constantly expressed in the parasite from cercariae to adult stages. It contained the characteristic of CaaX protease topology, including seven trans-membrane domains and a metallo-protease segment with a zinc-binding motif (HEXXH). SjSte24p shared a considerable degree of sequence identity with the type I CaaX proteases. A phylogenetic analysis showed that this protein family is tightly conserved from fungi to vertebrates. The expressed recombinant SjSte24p protein showed a proteolytic activity, which was inhibited by EDTA. Its activity was increased at low doses of the Zn²⁺ (0.001-0.01 mM); but was reversibly down-regulated at high doses (>0.1 mM). The native SjSte24p appeared to function in insoluble from. The protein was mainly localized in the tegument on the surface of adult worms. These results indicated that the SjSte24p is a practical zinc-dependent metalloprotease, which belongs to the FACE-1/Ste24p protease family.

Mechanisms of statin-associated skeletal muscle-associated symptoms

Statins lower the serum low-density lipoprotein cholesterol and prevent cardiovascular events by inhibiting 3-hydroxy-3-methyl-glutaryl-CoA reductase. Although the safety of statins is documented, many patients ingesting statins may suffer from skeletal muscle-associated symptoms (SAMS). Importantly, SAMS are a common reason for stopping the treatment with statins. Statin-associated muscular symptoms include fatigue, weakness and pain, possibly accompanied by elevated serum creatine kinase activity. The most severe muscular adverse reaction is the potentially fatal rhabdomyolysis. The frequency of SAMS is variable but in up to 30% of the patients ingesting statins, depending on the population treated and the statin used. The mechanisms leading to SAMS are currently not completely clarified. Over the last 15 years, several research articles focused on statin-induced mitochondrial dysfunction as a reason for SAMS. Statins can impair the function of the mitochondrial respiratory chain, thereby reducing ATP and increasing ROS production. This can induce mitochondrial membrane permeability transition, release of cytochrome c into the cytosol and induce apoptosis. In parallel, statins inhibit activation of Akt, mainly due to reduced function of mTORC2, which may be related to mitochondrial dysfunction. Mitochondrial dysfunction by statins is also responsible for activation of AMPK, which is associated with impaired activation of mTORC1. Reduced activation of mTORC1 leads to increased skeletal muscle protein degradation, impaired protein synthesis and stimulation of apoptosis. In this paper, we discuss some of the different hypotheses how statins affect skeletal muscle in more detail, focusing particularly on those related to mitochondrial dysfunction and the impairment of the Akt/mTOR pathway.

Biochemical significance of limonene and its metabolites: future prospects for designing and developing highly potent anticancer drugs

Monocyclic monoterpenes have been recognized as useful pharmacological ingredients due to their ability to treat numerous diseases. Limonene and perillyl alcohol as well as their metabolites (especially perillic acid and its methyl ester) possess bioactivities such as antitumor, antiviral, anti-inflammatory, and antibacterial agents. These therapeutic properties have been well documented. Based on the aforementioned biological properties of limonene and its metabolites, their structural modification and development into effective drugs could be rewarding. However, utilization of these monocyclic monoterpenes as scaffolds for the design and developments of more effective chemoprotective agents has not received the needed attention by medicinal scientists. Recently, some derivatives of limonene metabolites have been synthesized. Nonetheless, there have been no thorough studies on their pharmacokinetic and pharmacodynamic properties as well as their inhibition against isoprenylation enzymes. In this review, recent research progress in the biochemical significance of limonene and its metabolites was summarized with emphasis on their antitumor effects. Future prospects of these bioactive monoterpenes for drug design and development are also highlighted.

Mechanistic regulation of epithelial-to-mesenchymal transition through RAS signaling pathway and therapeutic implications in human cancer

RAS effector signaling instead of being simple, unidirectional and linear cascade, is actually recognized as highly complex and dynamic signaling network. RAF-MEK-ERK cascade, being at the center of complex signaling network, links to multiple scaffold proteins through feed forward and feedback mechanisms and dynamically regulate tumor initiation and progression. Three isoforms of Ras harbor mutations in a cell and tissue specific manner. Besides mutations, their epigenetic silencing also attributes them to exhibit oncogenic activities. Recent evidences support the functions of RAS oncoproteins in the acquisition of tumor cells with Epithelial-to-mesenchymal transition (EMT) features/ epithelial plasticity, enhanced metastatic potential and poor patient survival. Google Scholar electronic databases and PubMed were searched for original papers and reviews available till date to collect information on stimulation of EMT core inducers in a Ras driven cancer and their regulation in metastatic spread. Improved understanding of the mechanistic basis of regulatory interactions of microRNAs (miRs) and EMT by reprogramming the expression of targets in Ras activated cancer, may help in designing effective anticancer therapies. Apparent lack of adverse events associated with the delivery of miRs and tissue response make 'drug target miRNA' an ideal therapeutic tool to achieve progression free clinical response.

KRAS-mutation status dependent effect of zoledronic acid in human non-small cell cancer preclinical models

Background

In non-small cell lung cancer (NSCLC) KRAS-mutant status is a negative prognostic and predictive factor. Nitrogen-containing bisphosphonates inhibit prenylation of small G-proteins (e.g. Ras, Rac, Rho) and thus may affect proliferation and migration. In our preclinical work, we investigated the effect of an aminobisphosphonate compound (zoledronic acid) on mutant and wild type KRAS-expressing human NSCLC cell lines.

Results

We confirmed that zoledronic acid was unable to inhibit the prenylation of mutant K-Ras unlike in the case of wild type K-Ras. In case of in vitro proliferation, the KRAS-mutant human NSCLC cell lines showed resistance to zoledronic acid wild-type KRAS-cells proved to be sensitive. Combinatory application of zoledronic acid enhanced the cytostatic effect of cisplatin. Zoledronic acid did not induce significant apoptosis. In xenograft model, zoledronic acid significantly reduced the weight of wild type KRAS-EGFR-expressing xenograft tumor by decreasing the proliferative capacity. Futhermore, zoledronic acid induced VEGF expression and improved in vivo tumor vascularization.

Materials and methods

Membrane association of K-Ras was examined by Western-blot. In vitro cell viability, apoptotic cell death and migration were measured in NSCLC lines with different molecular background. The in vivo effect of zoledronic acid was investigated in a SCID mouse subcutaneous xenograft model.

Conclusions

The in vitro and in vivo inhibitory effect of zoledronic acid was based on the blockade of cell cycle in wild type KRAS-expressing human NSCLC cells. The zoledronic acid induced vascularization supported in vivo cytostatic effect. Our preclinical investigation suggests that patients with wild type KRAS-expressing NSCLC could potentially benefit from aminobisphosphonate therapy.

Molecular processes involved in B cell acute lymphoblastic leukaemia

B cell leukaemia is one of the most frequent malignancies in the paediatric population, but also affects a significant proportion of adults in developed countries. The majority of infant and paediatric cases initiate the process of leukaemogenesis during foetal development (in utero) through the formation of a chromosomal translocation or the acquisition/deletion of genetic material (hyperdiploidy or hypodiploidy, respectively). This first genetic insult is the major determinant for the prognosis and therapeutic outcome of patients. B cell leukaemia in adults displays similar molecular features as its paediatric counterpart. However, since this disease is highly represented in the infant and paediatric population, this review will focus on this demographic group and summarise the biological, clinical and epidemiological knowledge on B cell acute lymphoblastic leukaemia of four well characterised subtypes: t(4;11) MLL-AF4, t(12;21) ETV6-RUNX1, t(1;19) E2A-PBX1 and t(9;22) BCR-ABL1.

A phase II study of tipifarnib and gemcitabine in metastatic breast cancer

Background Tipifarnib is an orally active, competitive inhibitor of farnesyltransferase which has shown encouraging signs of activity either alone or when combined with other agents. Clinical studies of tipifarnib in combination with anti-estrogen therapy have yielded disappointing results. In contrast, tipifarnib appears to be synergistic in combination with anthracycline based chemotherapy. Here we report the results of the first prospective phase II trial evaluating the efficacy of the novel combination of tipifarnib and gemcitabine in the treatment of metastatic breast cancer. Patients and Methods 30 postmenopausal women with metastatic breast cancer were treated on a 21-day cycle with tipifarnib 300 mg PO twice daily from days 1 through 14. Gemcitabine was administered intravenously at a dose of 1000 mg/m² on days 1 and 8. Patients were treated until disease progression or unacceptable toxicity. Results There was one complete response and four partial responses yielding an objective response rate of 16.7%. Median progression-free survival and overall survival was 2.5 months (95% confidence interval: 1.6-5.7 months) and 13.1 months (95% confidence interval: 9.1-20.6 months), respectively. 40% of patients experienced grade 4 neutropenia in this study. Conclusion The combination of tipifarnib and gemcitabine is not well tolerated with high rates of myelosuppression and is not more effective than gemcitabine monotherapy in the treatment of metastatic breast cancer.

Pyruvate dehydrogenase kinase 4 exhibits a novel role in the activation of mutant KRAS, regulating cell growth in lung and colorectal tumour cells

RAS signalling is involved in the control of several metabolic pathways including glycolysis, mitochondrial respiration and glutamine metabolism. Importantly, we have found here that loss of PDHK4, a key regulator of the pyruvate dehydrogenase complex, caused a profound cell growth inhibition in tumour cells harbouring KRAS mutations. Using isogenic cells and a panel of colorectal and lung cell lines we demonstrated that KRAS mutant cells showed a dependency on PDHK4 whereas KRAS wild-type cells were significantly resistant to PDHK4 knockdown. We have found that PDHK4 plays a role in the post-translational regulation of mutant KRAS activity. Depletion of PDHK4 causes disruption of KRAS cellular localization, a reduction in KRAS activity which, in turn, results in reduced MAPK signalling. Interestingly, PDHK4 and KRAS depletion resulted in a similar metabolic phenotype consisting of a reduction of glucose and fatty acid oxidation. Moreover, stable expression of PDHK4 increased localization of activated KRAS at the plasma membrane and induced tumour cell growth in vitro and in vivo. Taken together these data support a model where PDHK4 regulates KRAS signalling and its tumorigenic properties and suggest that inhibition of PDHK4 could represent a novel therapeutic strategy to target KRAS mutant colorectal and lung cancers.

Overexpression of RASD1 inhibits glioma cell migration/invasion and inactivates the AKT/mTOR signaling pathway

The RAS signaling pathway is hyperactive in malignant glioma due to overexpression and/or increased activity. A previous study identified that RASD1, a member of the RAS superfamily of small G-proteins, is a significantly dysregulated gene in oligodendroglial tumors that responded to chemotherapy. However, the role and mechanism of RASD1 in the progression of human glioma remain largely unknown. In the present study, by analyzing a public genomics database, we found that high levels of RASD1 predicted good survival of astrocytoma patients. We thus established lentivirus-mediated RASD1-overexpressing glioma cells and found that overexpressing RASD1 had no significant effects on glioma cell proliferation. However, the overexpression of RASD1 inhibited glioma cell migration and invasion. In the intracranial glioma xenograft model, the overexpression of RASD1 significantly reduced the number of tumor cells invading into the surrounding tissues without affecting the tumor size. An intracellular signaling array revealed that the phosphorylation of both AKT and the S6 ribosomal protein significantly decreased with RASD1 overexpression in glioma cells. Interestingly, RASD1 protein levels were significantly higher in grade II and grade III astrocytoma tissues than in nontumorous brain tissues. These findings suggest that the upregulation of RASD1 in glioma tissues may play an inhibitory role in tumor expansion, possibly through inactivating the AKT/mTOR signaling pathway.

Gamma-tocotrienol reverses multidrug resistance of breast cancer cells with a mechanism distinct from that of atorvastatin

In addition to its antioxidant properties, γ-tocotrienol also has the ability to inhibit HMG-CoA reductase, which is the key enzyme in the mevalonate pathway for cholesterol biosynthesis. Statins, the competitive inhibitors of HMG-CoA reductase, display potent anticancer activity and reversal ability of multidrug resistance in a variety of tumor cells, which is believed to be due to their inhibition of HMG-CoA reductase. Here, we determined the role of the mevalonate pathway in γ-tocotrienol-mediated reversal of multidrug resistance in cancer cells. We found both γ-tocotrienol and atorvastatin effectively reversed multidrug resistance of MCF-7/Adr and markedly inhibited the intracellular levels of FPP and GGPP. Exogenous addition of mevalonate or FPP and GGPP almost completely prevented the reversal ability of atorvastatin but only partly attenuated the reversal effect of γ-tocotrienol on doxorubicin resistance. In addition, γ-tocotrienol actively inhibited the expression of P-gp and increased the accumulation of doxorubicin in cells, which led to the enhanced G2/M arrest and cell apoptosis. Taken together, γ-tocotrienol reversed the multidrug resistance of MCF-7/Adr with a mechanism distinct from that of atorvastatin. Instead of the mevalonate pathway, the inhibition of P-gp expression is a potential mechanism by which γ-tocotrienol reverses multidrug resistance in MCF-7/Adr.

Ataxia-telangiectasia mutated interactor regulates head and neck cancer metastasis via KRas expression

OBJECTIVES

Relapse is the most serious problem affecting the morbidity and mortality rates of patients with head and neck squamous cell carcinoma (HNSCC). Although HNSCC has been studied for several decades, the exact mechanism of cancer recurrence remains unclear.

MATERIALS AND METHODS

ataxia-telangiectasia mutated interactor (ATMIN) messenger RNA(mRNA) expression was detected in HNSCC samples by quantitative RT-PCR, and was analyzed with patients' clinical outcomes by Kaplan-Meier analyses. The ectopic ATMIN expression or ATMIN silencing on invasion ability was evaluated in HNSCC cell lines. Lymph node metastasis ability was investigated by buccal orthotopic implantation in vivo. All statistical tests were two-sided.

RESULTS

ATMIN mRNA expression was positively correlated with patients' clinical outcomes. ATMIN blockage reduced invasion, migration, and metastasis abilities both in vitro and in vivo. Evidence from a buccal orthotopic implantation mice model showed that silenced ATMIN expression prolongs mice survival and reduced lymph node metastasis. In high-throughput microarray and bioinformative analyses, KRas was identified as a crucial downstream effector in ATMIN-mediated HNSCC metastasis and was positively associated with patients' clinical stages and ATMIN mRNA expression.

CONCLUSIONS

The role of ATMIN and its regulatory mechanisms in HNSCC progression are reported for the first time. The study results improve our understanding of the ATMIN-KRas axis leading to HNSCC migration or invasion and metastasis and facilitates the identification of possible therapy targets of downstream genes for designing effective therapeutic strategies in personalized medicine.

Side Chain Cyclized Aromatic Amino Acids: Great Tools as Local Constraints in Peptide and Peptidomimetic Design

Constraining the conformation of flexible peptides is a proven strategy to increase potency, selectivity, and metabolic stability. The focus has mostly been on constraining the backbone dihedral angles; however, the correct orientation of the amino acid side chains (χ-space) that constitute the peptide pharmacophore is equally important. Control of χ-space utilizes conformationally constrained amino acids that favor, disfavor, or exclude the gauche (-), the gauche (+), or the trans conformation. In this review we focus on cyclic aromatic amino acids in which the side chain is connected to the peptide backbone to provide control of χ¹- and χ²-space. The manifold applications for cyclized analogues of the aromatic amino acids Phe, Tyr, Trp, and His within peptide medicinal chemistry are showcased herein with examples of enzyme inhibitors and ligands for G protein-coupled receptors.

Breast Cancer: A Molecular and Redox Snapshot

SIGNIFICANCE

Breast cancer is a unique disease characterized by heterogeneous cell populations causing roadblocks in therapeutic medicine, owing to its complex etiology and primeval understanding of the biology behind its genesis, progression, and sustenance. Globocan statistics indicate over 1.7 million new breast cancer diagnoses in 2012, accounting for 25% of all cancer morbidities.

RECENT ADVANCES

Despite these dismal statistics, the introduction of molecular gene signature platforms, progressive therapeutic approaches in diagnosis, and management of breast cancer has led to more effective treatment strategies and control measures concurrent with an equally reassuring decline in the mortality rate.

CRITICAL ISSUES

However, an enormous body of research in this area is requisite as high mortality associated with metastatic and/or drug refractory tumors continues to present a therapeutic challenge. Despite advances in systemic chemotherapy, the median survival of patients harboring metastatic breast cancers continues to be below 2 years.

FUTURE DIRECTIONS

Hence, a massive effort to scrutinize and evaluate chemotherapeutics on the basis of the molecular classification of these cancers is undertaken with the objective to devise more attractive and feasible approaches to treat breast cancers and improve patients' quality of life. This review aims to summarize the current understanding of the biology of breast cancer as well as challenges faced in combating breast cancer, with special emphasis on the current battery of treatment strategies. We will also try and gain perspective from recent encounters on novel findings responsible for the progression and metastatic transformation of breast cancer cells in an endeavor to develop more targeted treatment options. Antioxid. Redox Signal. 25, 337-370.

Could drugs inhibiting the mevalonate pathway also target cancer stem cells?

Understanding the connection between metabolic pathways and cancer is very important for the development of new therapeutic approaches based on regulatory enzymes in pathways associated with tumorigenesis. The mevalonate cascade and its rate-liming enzyme HMG CoA-reductase has recently drawn the attention of cancer researchers because strong evidences arising mostly from epidemiologic studies, show that it could promote transformation. Hence, these studies pinpoint HMG CoA-reductase as a candidate proto-oncogene. Several recent epidemiological studies, in different populations, have proven that statins are beneficial for the treatment-outcome of various cancers, and may improve common cancer therapy strategies involving alkylating agents, and antimetabolites. Cancer stem cells/cancer initiating cells (CSC) are key to cancer progression and metastasis. Therefore, in the current review we address the different effects of statins on cancer stem cells. The mevalonate cascade is among the most pleiotropic, and highly interconnected signaling pathways. Through G-protein-coupled receptors (GRCP), it integrates extra-, and intracellular signals. The mevalonate pathway is implicated in cell stemness, cell proliferation, and organ size regulation through the Hippo pathway (e.g. Yap/Taz signaling axis). This pathway is a prime preventive target through the administration of statins for the prophylaxis of obesity-related cardiovascular diseases. Its prominent role in regulation of cell growth and stemness also invokes its role in cancer development and progression. The mevalonate pathway affects cancer metastasis in several ways by: (i) affecting epithelial-to-mesenchymal transition (EMT), (ii) affecting remodeling of the cytoskeleton as well as cell motility, (iii) affecting cell polarity (non-canonical Wnt/planar pathway), and (iv) modulation of mesenchymal-to-epithelial transition (MET). Herein we provide an overview of the mevalonate signaling network. We then briefly highlight diverse functions of various elements of this mevalonate pathway. We further discuss in detail the role of elements of the mevalonate cascade in stemness, carcinogenesis, cancer progression, metastasis and maintenance of cancer stem cells.

Rasd1, a small G protein with a big role in the hypothalamic response to neuronal activation

Background

Rasd1 is a member of the Ras family of monomeric G proteins that was first identified as a dexamethasone inducible gene in the pituitary corticotroph cell line AtT20. Using microarrays we previously identified increased Rasd1 mRNA expression in the rat supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus in response to increased plasma osmolality provoked by fluid deprivation and salt loading. RASD1 has been shown to inhibit adenylyl cyclase activity in vitro resulting in the inhibition of the cAMP-PKA-CREB signaling pathway. Therefore, we tested the hypothesis that RASD1 may inhibit cAMP stimulated gene expression in the brain.

Results

We show that Rasd1 is expressed in vasopressin neurons of the PVN and SON, within which mRNA levels are induced by hyperosmotic cues. Dexamethasone treatment of AtT20 cells decreased forskolin stimulation of c-Fos, Nr4a1 and phosphorylated CREB expression, effects that were mimicked by overexpression of Rasd1, and inhibited by knockdown of Rasd1. These effects were dependent upon isoprenylation, as both farnesyltransferase inhibitor FTI-277 and CAAX box deletion prevented Rasd1 inhibition of cAMP-induced gene expression. Injection of lentiviral vector into rat SON expressing Rasd1 diminished, whereas CAAX mutant increased, cAMP inducible genes in response to osmotic stress.

Conclusions

We have identified two mechanisms of Rasd1 induction in the hypothalamus, one by elevated glucocorticoids in response to stress, and one in response to increased plasma osmolality resulting from osmotic stress. We propose that the abundance of RASD1 in vasopressin expressing neurons, based on its inhibitory actions on CREB phosphorylation, is an important mechanism for controlling the transcriptional responses to stressors in both the PVN and SON. These effects likely occur through modulation of cAMP-PKA-CREB signaling pathway in the brain.

Unraveling the Catalytic Pathway of Metalloenzyme Farnesyltransferase through QM/MM Computation

The protein farnesyltransferase (FTase) is a Zn(2+)-metalloenzyme that catalyzes the farnesylation reaction, i.e., the transfer of the 15-carbon atom farnesyl group from farnesyl diphosphate (FPP) to a specific cysteine of protein substrates. Oncogenic Ras proteins, which are among the FTase substrates, are observed in about 20-30% of human cancer cells. Thus, FTase represents a target for anticancer drug design. Herein, we present a classical force-field-based and quantum mechanics/molecular mechanics (QM/MM) computational study of the FTase reaction mechanism. Our findings offer a detailed picture of the FTase catalytic pathway, describing structural features and the energetics of its saddle points. A moderate dissociation of the diphosphate group from the FPP is observed during the nucleophilic attack of the zinc-bound thiolate. At the transition state, a resonance structure is observed, which indicates the formation of a metastable carbocation. However, no stable intermediate is found along the reaction pathway. Thus, the reaction occurs via an associative mechanism with dissociative character, in agreement with the mechanism proposed by Fierke et al. ( Biochemistry 2000, 39, 2593-2602 and Biochemistry 2003, 42, 9741-9748 ). Moreover, a fluorine-substituted FPP analogue (CF3-FPP) is used to investigate the inhibitory effect of fluorine, which in turn provides additional agreement with experimental data.

Vitamin D and S-farnesylthiosalicylic acid have a synergistic effect on hepatic stellate cells proliferation

BACKGROUND

Hepatic stellate cells (HSCs) have a key role in the formation of hepatic fibrosis. The active form of vitamin D, 1,25(OH)2D3, has been found to have antiproliferative and antifibrotic effects in various tissues including liver. Farnesylthiosalicylic acid (FTS), a novel Ras antagonist, was also found to inhibit hepatic fibrosis.

AIMS

The purpose of this study was to examine the antiproliferative and antifibrotic effects of the combined treatment of 1,25(OH)2D3 and FTS on primary cultured HSCs.

METHODS

Primary HSCs, isolated from rat's livers, were treated with 1,25(OH)2D3, FTS or a combination of both. Proliferation was assessed by bromodeoxyuridine. Expression of p-ERK, ERK, Ras-GTP, total-Ras, CyclinD1 and fibrotic markers was measured by western blotting analysis and real-time PCR. Cytotoxicity was assessed by lactate dehydrogenase method.

RESULTS

The combined treatment inhibited HSCs proliferation by threefold. The effect was synergistic and non-cytotoxic. In concordance, the combined treatment suppressed CyclinD1 expression by ~2-fold, whereas 1,25(OH)2D3 or FTS alone showed a significantly lower inhibitory effect. The effect of the combined treatment on CyclinD1 expression was mediated via Ras-GTP and p-ERK signal transduction pathway. The effect on fibrotic markers showed that 1,25(OH)2D3 decreased collagen Iα1 expression by ~40%, FTS by ~50% and the combined treatment by ~60%. 1,25(OH)2D3 inhibited tissue inhibitor of metalloproteinases-1 (TIMP-1) expression by 20%. FTS alone or 1,25(OH)2D3 + FTS inhibited TIMP-1 expression by 60%. FTS inhibited transforming growth factor-β (TGF-β) expression by 25%, while 1,25(OH)2D3 had no effect.

CONCLUSION

Although the combination of 1,25(OH)2D3 and FTS did not demonstrate an additive antifibrotic effect, it showed a synergistic antiproliferative effect on primary HSCs. Therefore, the combined treatment may have a potential therapeutic value in the initiation of fibrotic process.

Antroquinonol blocks Ras and Rho signaling via the inhibition of protein isoprenyltransferase activity in cancer cells

Antroquinonol is the smallest anticancer molecule isolated from Antrodia camphorata thus far. The ubiquinone-like structure of Antroquinonol exhibits a broad spectrum of activity against malignancies in vivo and in vitro. However, the mechanism of action of Antroquinonol remains unclear. Here, we provide evidence that Antroquinonol plays a role in the inhibition of Ras and Ras-related small GTP-binding protein functions through the inhibition of protein isoprenyl transferase activity in cancer cells. Using cell line-based assays, we found that the inactive forms of Ras and Rho proteins were significantly elevated after treatment with Antroquinonol. We also demonstrated that Antroquinonol binds directly to farnesyltransferase and geranylgeranyltransferase-I, which are key enzymes involved in activation of Ras-related proteins, and inhibits enzymes activities in vitro. Furthermore, a molecular docking analysis illustrated that the isoprenoid moiety of Antroquinonol binds along the hydrophobic cavity of farnesyltransferase similar to its natural substrate, farnesyl pyrophosphate. In contrast, the ring structure of Antroquinonol lies adjacent to the Ras-CAAX motif-binding site on farnesyltransferase. The molecular docking study also showed a reasonable correlation with the IC50 values of Antroquinonol analogues. We also found that the levels of LC3B-II and the autophagosome-associated LC3 form were also significantly increased in H838 after Antroquinonol administration. In conclusion, Antroquinonol inhibited Ras and Ras-related GTP-binding protein activation through inhibition of protein isoprenyl transferase activity, leading to activation of autophagy and associated mode of cell death in cancer cells.

Functional thyrotropin receptor expression in the ventricle and the effects on ventricular BNP secretion

Elevated thyrotropin (TSH) and hypercholesterolemia commonly coexist in patients with subclinical hypothyroidism, which can cause and aggravate heart disease. However, it is unclear whether TSH has a direct effect on cardiac function. To determine the expression of the thyrotropin receptor (TSHR) and the effects of TSH on ventricular function, we analyzed the ventricular tissues and thyroid glands from normal rats and mice and the H9c2 cardiomyocyte cell line. The results revealed that TSHR was expressed at the transcriptional and protein levels by PCR, immunoblotting, immunohistochemistry and immunofluorescence. The mRNA levels of β-MHC and the expression of pCREB and HMGCR in the ventricle were significantly lower in Tshr (-/-) mice than in wild-type (WT) mice (p < 0.05), but serum NT-proBNP levels were similar between WT and Tshr (-/-) mice. After synchronization, H9c2 cells were stimulated with several concentrations of TSH for various time periods. TSH up-regulated β-MHC mRNA expression in H9c2 cells. Cyclic adenosine monophosphate (cAMP) production and downstream signaling, such as pCREB and HMGCR expression and NT-proBNP secretion, increased in dose- and time-dependent manners. The TSH-stimulated effects were suppressed by an adenylyl cyclase inhibitor, a protein kinase A (PKA) inhibitor and HMGCR inhibitors (all p < 0.05). The data indicate functional TSHR is expressed in ventricular myocytes and mediates TSH-induced BNP secretion and HMGCR up-regulation through the cAMP/PKA/pCREB signaling pathway. Our findings suggest a potentially novel pathophysiological role of TSH in heart failure-associated hypothyroidism.

A functional screen reveals an extensive layer of transcriptional and splicing control underlying RAS/MAPK signaling in Drosophila

A global RNAi screening approach in Drosophila cells identifies a large group of transcription and splicing factors that modulate RAS/MAPK signaling by altering the expression of MAPK.

The small GTPase RAS is among the most prevalent oncogenes. The evolutionarily conserved RAF-MEK-MAPK module that lies downstream of RAS is one of the main conduits through which RAS transmits proliferative signals in normal and cancer cells. Genetic and biochemical studies conducted over the last two decades uncovered a small set of factors regulating RAS/MAPK signaling. Interestingly, most of these were found to control RAF activation, thus suggesting a central regulatory role for this event. Whether additional factors are required at this level or further downstream remains an open question. To obtain a comprehensive view of the elements functionally linked to the RAS/MAPK cascade, we used a quantitative assay in Drosophila S2 cells to conduct a genome-wide RNAi screen for factors impacting RAS-mediated MAPK activation. The screen led to the identification of 101 validated hits, including most of the previously known factors associated to this pathway. Epistasis experiments were then carried out on individual candidates to determine their position relative to core pathway components. While this revealed several new factors acting at different steps along the pathway—including a new protein complex modulating RAF activation—we found that most hits unexpectedly work downstream of MEK and specifically influence MAPK expression. These hits mainly consist of constitutive splicing factors and thereby suggest that splicing plays a specific role in establishing MAPK levels. We further characterized two representative members of this group and surprisingly found that they act by regulating mapk alternative splicing. This study provides an unprecedented assessment of the factors modulating RAS/MAPK signaling in Drosophila. In addition, it suggests that pathway output does not solely rely on classical signaling events, such as those controlling RAF activation, but also on the regulation of MAPK levels. Finally, it indicates that core splicing components can also specifically impact alternative splicing.

The RAS/MAPK pathway is a cornerstone of the cell proliferation signaling apparatus. It has a notable involvement in cancer as mutations in the components of the pathway are associated with aberrant proliferation. Previous work has focused predominantly on post-translational regulation of RAS/MAPK signaling such that a large and intricate network of factors is now known to act on core pathway components. However, regulation at the pre-translational level has not been examined nearly as extensively and is comparatively poorly understood. In this study, we used an unbiased and global screening approach to survey the Drosophila genome—using Drosophila cultured cells—for novel regulators of this pathway. Surprisingly, a majority of our hits were associated to either transcription or mRNA splicing. We used a series of secondary screening assays to determine which part of the RAS/MAPK pathway these candidates target. We found that these factors were not equally distributed along the pathway, but rather converged predominantly on mapk mRNA expression and processing. Our findings raise the intriguing possibility that regulation of mapk transcript production is a key step for a diverse set of regulatory inputs, and may play an important part in RAS/MAPK signaling dynamics.

Nutrient sensing and signaling in the yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae has been a favorite organism for pioneering studies on nutrient-sensing and signaling mechanisms. Many specific nutrient responses have been elucidated in great detail. This has led to important new concepts and insight into nutrient-controlled cellular regulation. Major highlights include the central role of the Snf1 protein kinase in the glucose repression pathway, galactose induction, the discovery of a G-protein-coupled receptor system, and role of Ras in glucose-induced cAMP signaling, the role of the protein synthesis initiation machinery in general control of nitrogen metabolism, the cyclin-controlled protein kinase Pho85 in phosphate regulation, nitrogen catabolite repression and the nitrogen-sensing target of rapamycin pathway, and the discovery of transporter-like proteins acting as nutrient sensors. In addition, a number of cellular targets, like carbohydrate stores, stress tolerance, and ribosomal gene expression, are controlled by the presence of multiple nutrients. The protein kinase A signaling pathway plays a major role in this general nutrient response. It has led to the discovery of nutrient transceptors (transporter receptors) as nutrient sensors. Major shortcomings in our knowledge are the relationship between rapid and steady-state nutrient signaling, the role of metabolic intermediates in intracellular nutrient sensing, and the identity of the nutrient sensors controlling cellular growth.

Recent progress in developing small molecule inhibitors designed to interfere with ras membrane association: toward inhibiting K-Ras and N-Ras functions

K-Ras and N-Ras are mutated in a wide range of human cancers, thus making these proteins attractive targets of anticancer drug development. However, no effective compounds have been obtained so far. One of the approaches taken to inhibit the function of K-Ras and N-Ras is to interfere with their membrane association. Various attempts have been taken. In the first example, we examine the approach conceived in early 1990s to inhibit protein prenylation that is required for their membrane association. The initial premise that the inhibition of Ras farnesylation leads to the inhibition of Ras was not realized, mainly due to alternative prenylation of K-Ras and N-Ras proteins. This led to the idea that the combined inhibition of FTase and GGTase-I can block membrane association of K-Ras and N-Ras. Dual specificity inhibitors of FTase and GGTase-I (DPIs) were also developed. These compounds were tested in preclinical and clinical studies. It appears that sufficiently high concentration of the drug to inhibit K-Ras was not achieved in previous attempts. In addition, dose-limiting toxicity has been observed and this was primarily ascribed to GGTase-I inhibition. Strategies to confer cancer targeting capabilities to the inhibitors may overcome the dose-limiting toxicity. In the second approach, postprenylation events were exploited. This led to the development of various inhibitors including the ICMT inhibitors. Finally, recent identification of compounds that inhibit the interaction between K-Ras and PDE-δ is discussed.

Gene of the month: KRAS

This is a general overview of KRAS, its structure and role in pertinent cancers. Also its role in determining adjuvant therapy is discussed.

Targeted agents and systemic therapy in hepatocellular carcinoma

Cytotoxic chemotherapy, hormonal agents, and immunotherapy have been tested in hepatocellular cancer (HCC) with marginal efficacy to date. Recent insights into the molecular pathogenesis of HCC have identified several aberrant signaling pathways that have served as targets for novel therapeutic agents. These discoveries have been translated into the clinical realm with the use of the antiangiogenic and the Raf kinase inhibitor, sorafenib, and have revealed the potential of targeted agents to produce clinically meaningful survival benefits in patients with advanced HCC. Efforts continue in the quest to improve the outcome of HCC patients through the development and evaluation of other targeted agents, and to better understand the interactions between the underlying disease biology and response to therapy. Several pathways are now implicated in hepatocarcinogenesis and agents that target these pathways continue to be developed.

Approaches to Ras signaling modulation and treatment of Ras-dependent disorders: a patent review (2007--present)

INTRODUCTION

Ras proteins are small GTPases molecular switches that cycle through two alternative conformational states, a GDP-bound inactive state and a GTP-bound active state. In the active state, Ras proteins interact with and modulate the activity of several downstream effectors regulating key cellular processes including proliferation, differentiation, survival, senescence, migration and metabolism. Activating mutations of RAS genes and of genes encoding Ras signaling members have a great incidence in proliferative disorders, such as cancer, immune and inflammatory diseases and developmental syndromes. Therefore, Ras and Ras signaling represent important clinical targets for the design and development of pharmaceutically active agents, including anticancer agents.

AREAS COVERED

The authors summarize methods available to down-regulate the Ras pathway and review recent patents covering Ras signaling modulators, as well as methods designed to kill specifically cancer cells bearing activated RAS oncogene.

EXPERT OPINION

Targeted therapy approach based on direct targeting of molecules specifically altered in Ras-dependent diseases is pursued with molecules that down-regulate expression or inhibit the biological function of mutant Ras or Ras signaling members. The low success rate in a clinical setting of molecules targeting activated members of the Ras pathway may require development of novel approaches, including combined and synthetic lethal therapies.

Preclinical metabolism of LB42908, a novel farnesyl transferase inhibitor, and its effects on the cytochrome P450 isozyme activities

Metabolism of LB42908, a novel farnesyl transferase inhibitor, was investigated for preclinical development. In vitro hepatic metabolism of LB42908 gave rise to at least 9 metabolites via phase I biotransformation pathways, which were characterized by HPLC-UV, LC-MS, and LC-MS/MS analyses. N-Dealkylation was shown to be a major phase I metabolic pathway. Species-specific in vitro metabolism of LB42908 was studied in liver fractions of rat, dog, monkey, and human. Order of metabolic stability is human≈dog>rat≈monkey in both S9 and microsomal fractions. Tissue-specific metabolism of LB42908 in various tissue homogenates of rats demonstrated that the liver was the major organ responsible for phase I metabolism of LB42908. The results from both qualitative and quantitative metabolism studies such as metabolic profiling and metabolic clearance indicated that dog would be the animal model of choice for preclinical toxicology studies. In addition, LB42908 was a potent CYP3A4 inhibitor in human liver microsomes and induced the activities of several CYP isozymes, implying that it has the potential for drug-drug interactions. Repeated dosing of LB42908 in rats did not significantly affect its own metabolism, indicating that long-term administration of LB42908 would not alter its pharmacokinetic profiles.

Ras oncogenes in oral cancer: the past 20 years

Oral squamous cell carcinoma (OSCC) of head and neck is associated with high morbidity and mortality in both Western and Asian countries. Several risk factors for the development of oral cancer are very well established, including tobacco chewing, betel quid, smoking, alcohol drinking and human papilloma virus (HPV) infection. Apart from these risk factors, many genetic factors such as oncogenes, tumor suppressor genes and regulatory genes are identified to involve in oral carcinogenesis with these risk factors dependent and independent manner. Ras is one of the most frequently genetically deregulated oncogene in oral cancer. In this review, we analyze the past 22years of literature on genetic alterations such as mutations and amplifications of the isoforms of the ras oncogene in oral cancer. Further, we addressed the isoform-specific role of the ras in oral carcinogenesis. We also discussed how targeting the Akt and MEK, downstream effectors of the PI3K/Akt and MAPK pathways, respectively, would probably pave the possible molecular therapeutic target for the ras driven tumorigenesis in oral cancer. Analysis of these ras isoforms may critically enlighten specific role of a particular ras isoform in oral carcinogenesis, enhance prognosis and pave the way for isoform-specific molecular targeted therapy in OSCC.

Sodium butyrate inhibits the self-renewal capacity of endometrial tumor side-population cells by inducing a DNA damage response

We previously isolated side-population (SP) cells from a human endometrial cancer cell line, Hec1, and determined that Hec1-SP cells have cancer stem-like cell features. In this study, we isolated SP cells and non-SP (NSP) cells derived from a rat endometrial cell line expressing human [(12)Val] KRAS (RK12V cells) and determined the SP phenotype. RK12V-SP cells showed self-renewal capacity, the potential to develop into stromal cells, reduced expression levels of differentiation markers, long-term proliferating capacity in cultures, and enhanced tumorigenicity, indicating that RK12V-SP cells have cancer stem-like cell features. RK12V-SP cells also display higher resistance to conventional chemotherapeutic drugs. In contrast, treatment with a histone deacetylases (HDAC) inhibitor, sodium butyrate (NaB), reduced self-renewal capacity and completely suppressed colony formation of RK12V-SP cells in a soft agar. The levels of intracellular reactive oxygen species (ROS) and the number of γH2AX foci were increased by NaB treatment of both RK12V-SP cells and RK12V-NSP cells. The expression levels of γH2AX, p21, p27, and phospho-p38 mitogen-activated protein kinase were enhanced in RK12V-SP cells compared with RK12V-NSP cells. These results imply that treatment with NaB induced production of intracellular ROS and DNA damage in both RK12V-SP and RK12V-NSP cells. Following NaB treatment, DNA damage response signals were enhanced more in RK12V-SP cells than in RK12V-NSP cells. This is the first article on an inhibitory effect of NaB on proliferation of endometrial cancer stem-like cells. HDAC inhibitors may represent an attractive antitumor therapy based upon their inhibitory effects on cancer stem-like cells.

Farnesyl transferase expression determines clinical response to the docetaxel-lonafarnib combination in patients with advanced malignancies

BACKGROUND

Lonafarnib (LNF) is a protein farnesyl transferase (FTase) inhibitor that has shown synergistic activity with taxanes in preclinical models and early stage clinical trials. Preclinical findings suggested tubulin acetylation and FTase expression levels may be important determinants of drug sensitivity that would help identify patient populations more likely to benefit from this regimen. This pilot study evaluated the biological effects of LNF and docetaxel (DTX) combination therapy in refractory solid tumors by comparing pretreatment and post-treatment tumor biopsies.

METHODS

Patients with histologically confirmed locally advanced or metastatic solid malignancies refractory to standard therapies or with no effective therapies available were eligible. Patients were randomized to 1 of 4 dosing cohorts: 1) 30 mg/m², 100 mg; 2) 36 mg/m², 100 mg; 3) 30 mg/m², 150 mg; or 4) 36 mg/m², 150 mg of DTX intravenously weekly, LNF orally twice daily, respectively.

RESULTS

Of the 38 patients enrolled, 36 were treated, and 29 were evaluable for toxicity and response assessment. The combination of LNF and DTX was tolerated in all cohorts with the exception of a 28% incidence of grade 3/4 diarrhea, which was manageable with aggressive antidiarrheal regimens. Seven patients derived clinically meaningful benefit from this combination treatment; these patients had significantly lower basal FTase-beta mRNA expression levels than the mean study population level (P < .05). Correlation of clinical benefit with tubulin acetylation content as well as basal acetyl-tubulin content were evaluated. However, no significant correlation was found.

CONCLUSIONS

Despite the small number of patients, these findings support our preclinical mechanistic studies and warrant further clinical investigations using FTase-beta mRNA expression as a potential predictive biomarker to select for an enriched patient population to study the effects of taxane and FTase inhibitor combination therapies.

Ras Isoprenylation and pAkt Inhibition by Zoledronic Acid and Fluvastatin Enhances Paclitaxel Activity in T24 Bladder Cancer Cells

Background

Bisphosphonates interfere with the mevalonate pathway and inhibit the prenylation of small GTP-binding proteins such as ras and rap. We hypothesized that zoledronic acid would synergistically inhibit T24 bladder cancer cell growth in combination with fluvastatin and paclitaxel.

Methods

Increasing doses of fluvastatin, zoledronic acid, and paclitaxel were investigated as single agents and in combination, and synergistic interactions were evaluated by the Chou-Talalay method. Western blots were used to assess effects on signal transduction pathways.

Results

Growth of T24 was significantly inhibited with IC₅₀ values of 2.67 ± 0.61 μM for fluvastatin and 5.35 ± 1.35 μM for zoledronic acid after 72 hours treatment. Geranylgeranyl pyrophosphate and farnesyl pyrophosphate was able to block, in part, this inhibitory activity. The combinations of zoledronic acid and paclitaxel, zoledronic acid and fluvastatin, and fluvastatin and paclitaxel were all synergistic. Both fluvastatin and zoledronic acid inhibited Ras and Rap prenylation, and the phosphorylation of ERK1/2 and AKT. The degree of inhibition of phosphorylation of these key signaling transduction pathways appears to closely correlate with their synergistic interactions.

Conclusions

Zoledronic acid enhances fluvastatin and paclitaxel activity against T24 in a synergistic manner and this is mediated largely by inhibition of both the Ras/Raf/MEK/ERK and PI3K/AKT signaling pathways via isoprenylation inhibition.