Farnesyltransferase Inhibitors Research Articles

A phase 1/2 trial to evaluate the safety and antitumor activity of tipifarnib and alpelisib for patients with PIK3CA-mutated/amplified and/or HRAS-overexpressing recurrent/metastatic head and neck squamous cell carcinoma.

TPS6104 Background: Understanding connections between key cellular pathways is particularly important when selecting combinatorial cancer therapies. HRAS preferentially activates PI3K 5-fold more efficiently than KRAS, while KRAS is a more efficient activator of RAF (Yan et al. 1998). Further, mutant HRAS is insufficient for oncogenic transformation if it is unable to recruit PI3K in preclinical models (Gupta et al. 2007). Conversely, mutant PI3K requires RAS to drive tumor growth (Zhao and Vogt 2008). HRAS mutation/overexpression and PIK3CA mutations/amplifications account for up to 50% of head and neck squamous cell carcinoma (HNSCC). Recognition of these interdependencies was the basis for the evaluation of HNSCC PDX models which demonstrated additive or synergistic anti-tumor effects that confirmed the codependency of these pathways, thus providing robust rationale for investigating combined pathway inhibition in the clinic. The KURRENT trial is enrolling patients with HRAS and/or PIK3CA-dependent tumors who will receive combination treatment with tipifarnib (a potent and selective inhibitor of farnesyltransferase, a critical enzyme for HRAS activity) and alpelisib, a PI3K inhibitor. Methods: The KURRENT trial (KO-TIP-013, NCT04809233) is an ongoing multicenter, open-label, 2-cohort, phase 1/2 trial designed to evaluate the safety of the combination of tipifarnib and alpelisib, determine the recommended combination dose(s) regimen, and evaluate preliminary anti-tumor activity in patients with recurrent/metastatic (R/M) HNSCC whose tumors are dependent upon HRAS and/or PIK3CA signaling. The trial will enroll 40 HNSCC patients; 20 each into two biomarker defined cohorts (Cohort 1; PIK3CA; Cohort 2; HRAS). Participants must have documented treatment failure from at least one prior therapy in the R/M setting and have measurable disease by RECIST v1.1. At the starting dose level, participants will receive tipifarnib at 300 mg twice daily on days 1-7 and 15-21 and alpelisib 200 mg each morning continuously during a 28-day cycle. The trial will use an adaptive dose escalation design (based on a Bayesian logistic regression model) to characterize safety, tolerability, and clinical activity of the combination to identify the Optimal Biologically Active Dose (OBAD) while maintaining a dose limiting toxicity (DLT) rate < 33%. No formal interim analysis is planned as the model-based dose escalation process requires decisions based on real-time evaluation of aggregate toxicity and efficacy data. All observed/available data among each cohort will be evaluated before choosing the combination dose for a subsequent cohort. Enrollment into the PIK3CA cohort began in October 2021. Clinical trial information: NCT04809233.

HRAS Q61L Mutation as a Possible Target for Non-Small Cell Lung Cancer: Case Series and Review of Literature

Introduction: Assessment of actionable gene mutations and oncogene fusions have made a paradigm shift in treatment strategies of non-small cell lung cancer (NSCLC). HRAS mutations involved around 0.2–0.8% of NSCLC patients, mostly on codon 61. For these patients, few data are available regarding clinical characteristics and response to therapies. Methods: Next-Generation Sequencing (NGS) done routinely at Nantes University Hospital was used to identify HRAS molecular alterations in NSCLC patients. We identified and described four HRAS p.GlnQ61Leu mutated patients. Literature of previously HRAS-mutant NSCLC cases was reviewed, and available data in solid tumour with the most advanced H-Ras specific inhibitor, tipifarnib, were presented. Results: Of 1614 patients diagnosed with advanced NSCLC from January 2018 to December 2020, four (0.25%) had HRAS p.Gln61Leu mutation. Three of them died during the first-line systemic therapy. Furthermore, three additional cases were identified in literature. All cases were current or former smokers, most of them had pleural or pericardial effusion at diagnosis. Conclusions: The clinical course of patients with HRAS-mutant NSCLC remains unclear. Furthers cases should be identified in order to clarify prognosis and response to therapies. Tipifarnib, a farnesyl transferase inhibitor, is a promising candidate to target HRAS-mutant tumours and should be explored in NSCLC patients.

Therapeutic Options in Neuro-Oncology.

One of the biggest challenges in neuro-oncology is understanding the complexity of central nervous system tumors, such as gliomas, in order to develop suitable therapeutics. Conventional therapies in malignant gliomas reconcile surgery and radiotherapy with the use of chemotherapeutic options such as temozolomide, chloroethyl nitrosoureas and the combination therapy of procarbazine, lomustine and vincristine. With the unraveling of deregulated cancer cell signaling pathways, targeted therapies have been developed. The most affected signaling pathways in glioma cells involve tyrosine kinase receptors and their downstream pathways, such as the phosphatidylinositol 3-kinases (PI3K/AKT/mTOR) and mitogen-activated protein kinase pathways (MAPK). MAPK pathway inhibitors include farnesyl transferase inhibitors, Ras kinase inhibitors and mitogen-activated protein extracellular regulated kinase (MEK) inhibitors, while PI3K/AKT/mTOR pathway inhibitors are divided into pan-inhibitors, PI3K/mTOR dual inhibitors and AKT inhibitors. The relevance of the immune system in carcinogenesis has led to the development of immunotherapy, through vaccination, blocking of immune checkpoints, oncolytic viruses, and adoptive immunotherapy using chimeric antigen receptor T cells. In this article we provide a comprehensive review of the signaling pathways underlying malignant transformation, the therapies currently used in the treatment of malignant gliomas and further explore therapies under development, including several ongoing clinical trials.

Selected Articles from This Issue

Despite the proven benefits of antibody-based therapies for HER2-amplified cancers, there remains an urgent need for novel therapeutic approaches to combat acquired and innate drug resistance. Here, O'Brien and colleagues demonstrate that tucatinib, a small molecule inhibitor of HER2, has selective activity in HER2-driven cancers. Tucatinib showed single agent and combined efficacy with trastuzumab and inhibitors of CDK4/6 in cell line xenograft models. The selective nature of tucatinib make it an ideal combination partner for HER2-based therapies. Data presented here provide insight into the optimal patient selection and combination strategies for the expanded clinical development of tucatinib.Head and neck squamous cell carcinoma (HNSCC) is a common cancer with limited treatment options. Recent clinical trials in patients with HRAS-mutant HNSCC have shown the efficacy of tipifarnib, a farnesyl transferase inhibitor (FTI) that blocks a required posttranslational modification of HRAS and other proteins. Here, Javaid and colleagues have validated HRAS as a key therapeutic target of tipifarnib and identified multiple signaling pathways that could cause treatment resistance. Combining FTI with an ERK inhibitor blocked compensatory signaling changes, enhancing the efficacy of FTI and showing that this combination could be a promising treatment strategy for patients with HRAS-mutant HNSCC.Pancreatic ductal adenocarcinoma (PDAC) is the most RAS-addicted of all cancers and development of anti-RAS therapies is a major priority. RRSP-DTB is an engineered biologic with specific RAS proteolytic activity. Vidimar and colleagues conducted a study to assess in vitro RAS degradation and in vivo activity of RRSP-DTB in RAS-driven PDAC models. As a single agent, RRSP-DTB effectively degraded RAS in cells and engaged RAS in mice leading to nearly complete regression of PDAC patient-derived xenografts without development of resistance. These results support further study of RRSP-DTB as an unprecedented RAS biodegrader for RAS-addicted tumors.Clinical outcomes in FLT3-mutant acute myeloid leukemia (AML) remain exceedingly poor due to FLT3 tyrosine kinase inhibitor (TKI) resistance. FF-10101 is the first covalent FLT3 inhibitor and recently completed phase I clinical evaluation. Here, Ferng and colleagues profile FF-10101 against a panel of FLT3 TKI resistance-mutations and off-target resistance mechanisms. FF-10101 suppresses all clinically described on-target mutations but not those that compromise covalent binding to FLT3. FF-10101 also exhibits activity in an in vitro model of cytokine-driven TKI resistance. Thus, FF-10101 shows the potential to benefit AML patients already treated with existing FLT3 TKIs or patients harboring certain FLT3 mutations.

Loss of isoprenylation significantly reduces IgE mediated mast cell activation

Abstract Allergic disease is the 6th leading cause of chronic illness in the US and accounts for billions of dollars in healthcare costs annually. Mast cells are tissue resident innate immune cells linked to allergic disease and activated by IgE and other ligands. Upon activation they release histamine, cytokines, chemokines, proteases, and lipid mediators evoking allergic symptoms. New ways of targeting mast cells could greatly benefit allergic disease therapy. Previous findings showed repurposing of statin drugs, such as Fluvastatin, reduced allergic symptoms in vitro and in vivo. We found that Fluvastatin suppresses IgE-mediated mast cell activation by inhibiting isoprenylation of proteins. However, statin effects were dependent on genetic background. To avert genetic background dependency, we tested the hypothesis that a dual farnesyl and geranylgeranyl transferase inhibitor (FGTI 2734) would suppress allergic disease withoutgenetic background limitations. We show that FGTI 2734 reduced IgE-mediated degranulation and cytokine production by bone marrow derived mast cells from multiple genetic backgrounds. Similarly, FGTI 2734 also suppressed IgE-mediated anaphylaxis on multiple genetic backgrounds. These in vivo effects extended to an allergic asthma model, in which FGTI 2734 inhibited pulmonary inflammation. Finally, we show that FGTI-2734 can significantly reduce IgE-induced cytokine production from human skin mast cells. These data show that dual farnesyl and geranylgeranyl transferase inhibitors may be an effective therapeutic treatment for mast cell-associated diseases. Supported by NIH (1RO1AI101153)

Targeting farnesylation as a novel therapeutic approach in HRAS-mutant rhabdomyosarcoma

Activating RAS mutations are found in a subset of fusion-negative rhabdomyosarcoma (RMS), and therapeutic strategies to directly target RAS in these tumors have been investigated, without clinical success to date. A potential strategy to inhibit oncogenic RAS activity is the disruption of RAS prenylation, an obligate step for RAS membrane localization and effector pathway signaling, through inhibition of farnesyltransferase (FTase). Of the major RAS family members, HRAS is uniquely dependent on FTase for prenylation, whereas NRAS and KRAS can utilize geranylgeranyl transferase as a bypass prenylation mechanism. Tumors driven by oncogenic HRAS may therefore be uniquely sensitive to FTase inhibition. To investigate the mutation-specific effects of FTase inhibition in RMS we utilized tipifarnib, a potent and selective FTase inhibitor, in in vitro and in vivo models of RMS genomically characterized for RAS mutation status. Tipifarnib reduced HRAS processing, and plasma membrane localization leading to decreased GTP-bound HRAS and decreased signaling through RAS effector pathways. In HRAS-mutant cell lines, tipifarnib reduced two-dimensional and three-dimensional cell growth, and in vivo treatment with tipifarnib resulted in tumor growth inhibition exclusively in HRAS-mutant RMS xenografts. Our data suggest that small molecule inhibition of FTase is active in HRAS-driven RMS and may represent an effective therapeutic strategy for a genomically-defined subset of patients with RMS.

Small extracellular vesicles induce resistance to anti-GD2 immunotherapy unveiling tipifarnib as an adjunct to neuroblastoma immunotherapy

BackgroundAnti-GD2 monoclonal antibody immunotherapy has significantly improved the overall survival rate for high-risk neuroblastoma patients. However, 40% of patients fail to respond or develop resistance to treatment, and the molecular...

Rheb regulates nuclear mTORC1 activity independent of farnesylation

The small GTPase Ras homolog enriched in brain (Rheb) plays a critical role in activating the mechanistic target of rapamycin complex 1 (mTORC1), a signaling hub that regulates various cellular functions. We recently observed nuclear mTORC1 activity, raising an intriguing question as to how Rheb, which is known to be farnesylated and localized to intracellular membranes, regulates nuclear mTORC1. In this study, we found that active Rheb is present in the nucleus and required for nuclear mTORC1 activity. We showed that inhibition of farnesyltransferase reduced cytosolic, but not nuclear, mTORC1 activity. Furthermore, a farnesylation-deficient Rheb mutant, with preferential nuclear localization and specific lysosome tethering, enables nuclear and cytosolic mTORC1 activities, respectively. These data suggest that non-farnesylated Rheb is capable of interacting with and activating mTORC1, providing mechanistic insights into the molecular functioning of Rheb as well as regulation of the recently observed, active pool of nuclear mTORC1.

Lonafarnib Inhibits Farnesyltransferase via Suppressing ERK Signaling Pathway to Prevent Osteoclastogenesis in Titanium Particle-Induced Osteolysis.

Wear debris after total joint arthroplasty can attract the recruitment of macrophages, which release pro-inflammatory substances, triggering the activation of osteoclasts, thereby leading to periprosthetic osteolysis (PPOL) and aseptic loosening. However, the development of pharmacological strategies targeting osteoclasts to prevent periprosthetic osteolysis has not been fruitful. In this study, we worked toward researching the effects and mechanisms of a farnesyltransferase (FTase) inhibitor Lonafarnib (Lon) on receptor activator of nuclear factor κB (NF-κB) ligand (RANKL)-induced osteoclastogenesis and bone resorption, as well as the impacts of Lon on titanium particle-induced osteolysis. To investigate the impacts of Lon on bone resorption and osteoclastogenesis in vitro, bone marrow macrophages were incubated and stimulated with RANKL and macrophage colony-stimulating factor (M-CSF). The influence of Lon on osteolysis prevention in vivo was examined utilizing a titanium particle-induced mouse calvarial osteolysis model. The osteoclast-relevant genes expression was explored by real-time quantitative PCR. Immunofluorescence was used to detect intracellular localization of nuclear factor of activated T cells 1 (NFATc1). SiRNA silence assay was applied to examine the influence of FTase on osteoclasts activation. Related signaling pathways, including NFATc1 signaling, NF-κB, mitogen-activated protein kinases pathways were identified by western blot assay. Lon was illustrated to suppress bone resorptive function and osteoclastogenesis in vitro, and it also reduced the production of pro-inflammatory substances and prevented titanium particle-induced osteolysis in vivo. Lon decreased the expression of osteoclast-relevant genes and suppressed NFATc1 nuclear translocation and auto-amplification. Mechanistically, Lon dampened FTase, and inhibition of FTase reduced osteoclast formation by suppressing ERK signaling. Lon is a promising treatment option for osteoclast-related osteolysis diseases including periprosthetic osteolysis by targeted inhibition of FTase through suppressing ERK signaling.

Concurrent Inhibition of ERK and Farnesyltransferase Suppresses the Growth of HRAS Mutant Head and Neck Squamous Cell Carcinoma.

Human papilloma virus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) is a common cancer worldwide with an unmet need for more effective, less toxic treatments. Currently, both the disease and the treatment of HNSCC cause significant mortality and morbidity. Targeted therapies hold new promise for patients with HPV-negative status whose tumors harbor oncogenic HRAS mutations. Recent promising clinical results have renewed interest in the development of farnesyltransferase inhibitors (FTIs) as a therapeutic strategy for HRAS-mutant cancers. With the advent of clinical evaluation of the FTI tipifarnib for the treatment of HRAS-mutant HNSCC, we investigated the activity of tipifarnib and inhibitors of HRAS effector signaling in HRAS-mutant HNSCC cell lines. First, we validated that HRAS is a cancer driver in HRAS-mutant HNSCC lines. Second, we showed that treatment with the FTI tipifarnib largely phenocopied HRAS silencing, supporting HRAS as a key target of FTI antitumor activity. Third, we performed reverse-phase protein array analyses to profile FTI treatment-induced changes in global signaling, and conducted CRISPR/Cas9 genetic loss-of-function screens to identify previously unreported genes and pathways that modulate sensitivity to tipifarnib. Fourth, we determined that concurrent inhibition of HRAS effector signaling (ERK, PI3K, mTORC1) increased sensitivity to tipifarnib treatment, in part by overcoming tipifarnib-induced compensatory signaling. We also determined that ERK inhibition could block tipifarnib-induced epithelial-to-mesenchymal transition, providing a potential basis for the effectiveness of this combination. Our results support future investigations of these and other combination treatments for HRAS mutant HNSCC.

Abolishing the prelamin A ZMPSTE24 cleavage site leads to progeroid phenotypes with near-normal longevity in mice.

Prelamin A is a farnesylated precursor of lamin A, a nuclear lamina protein. Accumulation of the farnesylated prelamin A variant progerin, with an internal deletion including its processing site, causes Hutchinson-Gilford progeria syndrome. Loss-of-function mutations in ZMPSTE24, which encodes the prelamin A processing enzyme, lead to accumulation of full-length farnesylated prelamin A and cause related progeroid disorders. Some data suggest that prelamin A also accumulates with physiological aging. Zmpste24-/- mice die young, at ∼20 wk. Because ZMPSTE24 has functions in addition to prelamin A processing, we generated a mouse model to examine effects solely due to the presence of permanently farnesylated prelamin A. These mice have an L648R amino acid substitution in prelamin A that blocks ZMPSTE24-catalyzed processing to lamin A. The LmnaL648R/L648R mice express only prelamin and no mature protein. Notably, nearly all survive to 65 to 70 wk, with ∼40% of male and 75% of female LmnaL648R/L648R mice having near-normal lifespans of 90 wk (almost 2 y). Starting at ∼10 wk of age, LmnaL648R/L648R mice of both sexes have lower body masses than controls. By ∼20 to 30 wk of age, they exhibit detectable cranial, mandibular, and dental defects similar to those observed in Zmpste24-/- mice and have decreased vertebral bone density compared to age- and sex-matched controls. Cultured embryonic fibroblasts from LmnaL648R/L648R mice have aberrant nuclear morphology that is reversible by treatment with a protein farnesyltransferase inhibitor. These novel mice provide a model to study the effects of farnesylated prelamin A during physiological aging.

A Farnesyltransferase Inhibitor Restores Cognitive Deficits in Tsc2+/- Mice through Inhibition of Rheb1.

Tuberous sclerosis complex (TSC) is caused by mutations in Tsc1 or Tsc2, whose gene products inhibit the small G-protein Rheb1. Rheb1 activates mTORC1, which may cause refractory epilepsy, intellectual disability, and autism. The mTORC1 inhibitors have been used for TSC patients with intractable epilepsy. However, its effectiveness for cognitive symptoms remains unclear. We found a new signaling pathway for synapse formation through Rheb1 activation, but not mTORC1. Here, we show that treatment with the farnesyltransferase inhibitor lonafarnib increased unfarnesylated (inactive) Rheb1 levels and restored synaptic abnormalities in cultured Tsc2+/- neurons, whereas rapamycin did not enhance spine synapse formation. Lonafarnib treatment also restored the plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in cultured Tsc2+/- neurons. Lonafarnib action was partly dependent on the Rheb1 reduction with syntenin. Oral administration of lonafarnib increased unfarnesylated protein levels without affecting mTORC1 and MAP (mitogen-activated protein (MAP)) kinase signaling, and restored dendritic spine morphology in the hippocampi of male Tsc2+/- mice. In addition, lonafarnib treatment ameliorated contextual memory impairments and restored memory-related Arc expression in male Tsc2+/- mice in vivo Heterozygous Rheb1 knockout in male Tsc2+/- mice reproduced the results observed with pharmacological treatment. These results suggest that the Rheb1 activation may be responsible for synaptic abnormalities and memory impairments in Tsc2+/- mice, and its inhibition by lonafarnib could provide insight into potential treatment options for TSC-associated neuropsychiatric disorders.SIGNIFICANCE STATEMENT Tuberous sclerosis complex (TSC) is an autosomal-dominant disease that causes neuropsychiatric symptoms, including intractable epilepsy, intellectual disability (ID) and autism. No pharmacological treatment for ID has been reported so far. To develop a pharmacological treatment for ID, we investigated the mechanism of TSC and found that Rheb1 activation is responsible for synaptic abnormalities in TSC neurons. To inhibit Rheb1 function, we used the farnesyltransferase inhibitor lonafarnib, because farnesylation of Rheb1 is required for its activation. Lonafarnib treatment increased inactive Rheb1 and recovered proper synapse formation and plasticity-related Arc (activity-regulated cytoskeleton-associated protein) expression in TSC neurons. Furthermore, in vivo lonafarnib treatment restored contextual memory and Arc induction in TSC mice. Together, Rheb1 inhibition by lonafarnib could provide insight into potential treatments for TSC-associated ID.

FNTB Promoter Polymorphisms Are Independent Predictors of Survival in Patients with Triple Negative Breast Cancer.

Simple SummaryIn breast cancer, the promising efficacy of farnesyltransferase inhibitors (FTIs) in preclinical studies is in contrast to only limited effects in clinical trials. Therefore, this study focussed on the clinical relevance of polymorphisms in FNTB, the gene encoding the catalytically active β-subunit of farnesyltransferase, in early breast cancer. This is the first study on breast cancer suggesting that FNTB promoter polymorphisms are independent prognostic biomarkers, particularly in patients with early triple negative breast cancer (TNBC), and possibly modulate FNTB transcriptional activity. Taken together, we describe for the first time, a link between FNTB promoter polymorphism and the prognosis of breast cancer patients. We propose that FNTB genotyping, which is easily possible from a single blood drawing, may allow independent prognostic stratification, particularly in TNBC, in order to identify patients with a high risk of recurrence and poor prognosis. Ultimately, our results encourage further prospective evaluations of the role of FNTB promoter polymorphisms in predicting response to FTIs, particularly in TNBC patients.In breast cancer, the promising efficacy of farnesyltransferase inhibitors (FTIs) in preclinical studies is in contrast to only limited effects in clinical Phase II–III trials. The objective of this study was to explore the clinical relevance of farnesyltransferase β-subunit (FNTB) single nucleotide promoter polymorphisms (FNTB-173 6G > 5G (rs3215788), -609 G > C (rs11623866) and -179 T > A (rs192403314)) in early breast cancer. FNTB genotyping was performed by pyrosequencing in 797 patients from a prospective multicentre observational PiA trial (NCT 01592825). In the total cohort, the FNTB-173 6G > 5G polymorphism was an independent predictor of RFI (HR = 0.568; 95% CI = 0.339–0.949, p = 0.031), OS (HR = 0.629; 95% CI = 0.403–0.980, p = 0.040) and BCSS (HR = 0.433; 95% CI = 0.213–0.882; p = 0.021), whereas the FNTB-609 G > C polymorphism was an independent predictor of RFI (HR = 0.453; 95% CI = 0.226–0.910, p = 0.026) and BCSS (HR = 0.227; 95% CI = 0.075–0.687, p = 0.009). Subtype analysis revealed the independent prognostic relevance of FNTB promoter polymorphisms, particularly in TNBC but not in luminal or HER2-positive intrinsic subtypes. Finally, we used electrophoretic mobility shift assays (EMSAs) to confirm in vitro that the polymorphism FNTB-173 6G > 5G resulted in the differential binding of nuclear proteins from five different breast cancer cell lines. This is the first study on breast cancer suggesting that FNTB promoter polymorphisms (i) are independent prognostic biomarkers, particularly in patients with early TNBC, and (ii) could modulate FNTB’s transcriptional activity.

Loss of hepatitis D virus infectivity upon farnesyl transferase inhibitor treatment associates with increasing RNA editing rates revealed by a new RT-ddPCR method

Chronic hepatitis D is the most severe form of chronic viral hepatitis and to date, efficient therapeutic approaches against hepatitis D virus (HDV) are limited. Among the antiviral molecules currently tested in clinical trials, the farnesyl transferase inhibitor (FTI) Lonafarnib inhibits the prenylation of the large delta antigen (L-HDAg), blocking virus assembly. Given the importance of L-HDAg in the virus life cycle, we hypothesized that Lonafarnib treatment may have side effects on virus replication. Here, we setup an innovative method for the quantification of HDV RNA allowing the independent quantification of edited and non-edited versions of the HDV genome upon infection. We demonstrated that FTI treatment of HBV/HDV co-infected dHepaRG or primary human hepatocytes leads to an accumulation of intracellular HDV RNAs and a marked increase in the levels of edited RNAs non only within the infected cells but also in the viral particles that are produced. Interestingly, these viral particles were less infectious, probably due to an enrichment in edited genomes that are packaged, leading to unproductive infection given the absence of S-HDAg synthesis after viral entry. Taken together, we setup an innovative quantification method allowing the investigation of RNA editing during HDV infection in a simple, fast, clinically-relevant assay and demonstrated for the first time the dual antiviral activity of FTI on HDV infection.

Drug targeting opportunities en route to Ras nanoclusters.

Disruption of the native membrane organization of Ras by the farnesyltransferase inhibitor tipifarnib in the late 1990s constituted the first indirect approach to drug target Ras. Since then, our understanding of how dynamically Ras shuttles between subcellular locations has changed significantly. Ras proteins have to arrive at the plasma membrane for efficient MAPK-signal propagation. On the plasma membrane Ras proteins are organized into isoform specific proteo-lipid assemblies called nanocluster. Recent evidence suggests that Ras nanocluster have a specific lipid composition, which supports the recruitment of effectors such as Raf. Conversely, effectors possess lipid-recognition motifs, which appear to serve as co-incidence detectors for the lipid domain of a given Ras isoform. Evidence suggests that dimeric Raf proteins then co-assemble dimeric Ras in an immobile complex, thus forming the minimal unit of an active nanocluster. Here we review established and novel trafficking chaperones and trafficking factors of Ras, along with the set of lipid and protein modulators of Ras nanoclustering. We highlight drug targeting approaches and opportunities against these determinants of functional Ras membrane organization. Finally, we reflect on implications for Ras signaling in polarized cells, such as epithelia, which are a common origin of tumorigenesis.

CXCL12 in Pancreatic Cancer: Its Function and Potential as a Therapeutic Drug Target.

Simple SummaryPancreatic cancer is a challenging disease to treat effectively. Fibroblasts associated with pancreatic cancer contribute to disease progression by secreting factors that enhance tumor cell survival and help tumor cells avoid detection by the immune system. This overview focuses on a chemokine, CXCL12, produced by cancer-associated fibroblasts and how CXCL12 signaling enhances pancreatic cancer progression by contributing to various hallmarks of cancer including, but not limited to, tumor growth and evasion of immune response. These pro-oncogenic functions of CXCL12 make it an attractive target in pancreatic cancer. We discuss the different approaches in development to therapeutically target CXCL12 and finally propose a novel approach, the use of the farnesyl transferase inhibitor tipifarnib to inhibit CXCL12 expression in pancreatic fibroblasts.Pancreatic ductal adenocarcinoma (PDAC) is a disease with limited therapeutic options and dismal long-term survival. The unique tumor environment of PDAC, consisting of desmoplastic stroma, immune suppressive cells, and activated fibroblasts, contributes to its resistance to therapy. Activated fibroblasts (cancer-associated fibroblasts and pancreatic stellate cells) secrete chemokines and growth factors that support PDAC growth, spread, chemoresistance, and immune evasion. In this review, we focus on one such chemokine, CXCL12, secreted by the cancer-associated fibroblasts and discuss its contribution to several of the classical hallmarks of PDAC and other tumors. We review the various therapeutic approaches in development to target CXCL12 signaling in PDAC. Finally, we propose an unconventional use of tipifarnib, a farnesyl transferase inhibitor, to inhibit CXCL12 production in PDAC.

Cardiac decompensation and promiscuous prenylation of small GTPases in cardiomyocytes in response to local mevalonate pathway disruption.

Investigations of major mevalonate pathway enzymes have demonstrated the importance of local isoprenoid synthesis in cardiac homeostasis. Farnesyl diphosphate synthase (FPPS) synthesizes isoprenoid precursors needed for cholesterol biosynthesis and protein prenylation. Wang, Zhang, Chen et al, in a recently published article in The Journal of Pathology, elegantly elucidated the pathological outcomes of FPPS deficiency in cardiomyocytes, which paradoxically resulted in increased prenylation of the small GTPases Ras and Rheb. Cardiomyocyte FPPS depletion caused severe dilated cardiomyopathy that was associated with enhanced GTP-loading and abundance of Ras and Rheb in lipidated protein-enriched cardiac fractions and robust activation of downstream hypertrophic ERK1/2 and mTOR signaling pathways. Cardiomyopathy and activation of ERK1/2 and mTOR caused by loss of FPPS were ameliorated by inhibition of farnesyltransferase, suggesting that impairment of FPPS activity results in promiscuous activation of Ras and Rheb through non-canonical actions of farnesyltransferase. Here, we discuss the findings and adaptive signaling mechanisms in response to disruption of local cardiomyocyte mevalonate pathway activity, highlighting how alteration in a key branch point in the mevalonate pathway affects cardiac biology and function and perturbs protein prenylation, which might unveil novel strategies and intricacies of targeting the mevalonate pathway to treat cardiovascular diseases. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Superinfection of other hepatitis viruses on top of chronic hepatitis B: The more, the worse

Superinfection of other hepatitis viruses on top of chronic hepatitis B: The more, the worse

The Lonafarnib target, Rhes, is uniquely dysregulated in tauopathies: A human postmortem study

AbstractBackgroundThe farnesyltransferase inhibitor, Lonafarnib, is capable of reducing tau lesions and associated atrophy in tauopathy models through activity on the Ras GTPase, Rhes (Hernandez I et al., 2019). While hinting at a role of Rhes in tau proteinopathic etiology, it is unclear how Rhes activity changes in human tauopathies or other neurodegenerative diseases. As these models reflect rare, familial forms of tauopathy, we sought to detect evidence of Rhes changes in human sporadic tauopathy versus FTLD‐TDP and synucleinopathies.MethodAllocortical and neocortical sections from postmortem cases (Table 1) representing five different tauopathies, FTLD‐TDP, Lewy body disease, and healthy controls (HC) were immunohistochemically stained for Rhes, proteinopathic lesions (i.e. PHF‐1 positive tau inclusions, phospho‐TDP‐43, or α‐synuclein), and NeuN. Single‐nucleus RNA‐sequencing (snRNA‐seq) was also performed in a separate cohort representing HC and early AD.Result40 cases were examined in this study (Table 1). Rhes is widespread in cortical neurons, as detected by immunohistochemical staining and snRNA‐seq (Figure 1). In tauopathies, neurons either present Rhes as diffuse or punctiform, or feature an absence of Rhes (Figure 2). Accordingly, we classified neurons as Rhes type Diffuse, Punctiform, or Absent. The proportion of neurons with PHF‐1 positive tau inclusions significantly differ between the three neuronal Rhes phenotypes (p < 0.0001) with the majority of Absent type neurons harboring PHF‐1 positive tau inclusions and Diffuse type neurons mostly devoid of PHF‐1 positive tau inclusions (Figure 3, Table 2). Punctiform and Absent type neurons were not detected in neurons with phospho‐TDP‐43 inclusions or α‐synuclein inclusions (Figure 4).ConclusionGiven the distribution of PHF‐1 positive tau inclusions across different Rhes‐deliniated neuronal phenotypes, we propose a model by which Rhes takes on a punctiform phenotype then is ultimately cleared from neurons with tau lesions. This postmortem study in humans, together with in vivo and in vitro work done in familial tauopathy models, suggests the presence of a causal relationship between Rhes clearance and tau proteinopathic lesions, but not phospho‐TDP‐43 or α‐synuclein inclusions. As such, Rhes cellular phenotype represents a novel postmortem hallmark of tauopathy and supports to application of Lonafarnib to the treatment of tauopathies.

Bacteria Are New Targets for Inhibitors of Human Farnesyltransferase.

Farnesyltransferase inhibitors (FTIs) are focus for the treatment of several diseases, particularly in the field of cancer therapy. Their potential, however, goes even further, as a number of studies have evaluated FTIs for the treatment of infectious diseases such as malaria, African sleeping sickness, leishmaniosis, and hepatitis D virus infection. Little is known about protein prenylation mechanisms in human pathogens. However, disruption of IspA, a gene encoding the geranyltranstransferase of Staphylococcus aureus (S. aureus) leads to reprogramming of cellular behavior as well as impaired growth and decreased resistance to cell wall-targeting antibiotics. We used an agar well diffusion assay and a time kill assay and determined the minimum inhibitory concentrations of the FTIs lonafarnib and tipifarnib. Additionally, we conducted cell viability assays. We aimed to characterize the effect of these FTIs on S. aureus, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis (S. epidermidis), Escherichia coli (E. coli), Enterococcus faecium (E. faecium), Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa (P. aeruginosa), and Streptococcus pneumoniae (S. pneumoniae). Both the FTIs lonafarnib and tipifarnib were capable of inhibiting the growth of the Gram-positive bacteria S. aureus, MRSA, S. epidermidis, and S. pneumoniae, whereas no effect was observed on Gram-negative bacteria. The analysis of the impact of lonafarnib and tipifarnib on common human pathogens might lead to novel insights into their defense mechanisms and therefore provide new therapeutic targets for antibiotic-resistant bacterial infections.