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In response to environmental cues that promote IP3 (inositol 1,4,5-trisphosphate) generation, IP3 receptors (IP3Rs) located on the endoplasmic reticulum allow the 'quasisynaptical' feeding of calcium to the mitochondria to promote oxidative phosphorylation. However, persistent Ca release results in mitochondrial Ca overload and consequent apoptosis. Among the three mammalian IP3Rs, IP3R3 appears to be the major player in Ca -dependent apoptosis. Here we show that the F-box protein FBXL2 (the receptor subunit of one of 69 human SCF (SKP1, CUL1, F-box protein) ubiquitin ligase complexes) binds IP3R3 and targets it for ubiquitin-, p97- and proteasome-mediated degradation to limit Ca influx into mitochondria. FBXL2-knockdown cells and FBXL2-insensitive IP3R3 mutant knock-in clones display increased cytosolic Ca release from the endoplasmic reticulum and sensitization to Ca -dependent apoptotic stimuli. The phosphatase and tensin homologue (PTEN) gene is frequently mutated or lost in human tumours and syndromes that predispose individuals to cancer. We found that PTEN competes with FBXL2 for IP3R3 binding, and the FBXL2-dependent degradation of IP3R3 is accelerated in Pten mouse embryonic fibroblasts and PTEN-null cancer cells. Reconstitution of PTEN-null cells with either wild-type PTEN or a catalytically dead mutant stabilizes IP3R3 and induces persistent Ca mobilization and apoptosis. IP3R3 and PTEN protein levels directly correlate in human prostate cancer. Both in cell culture and xenograft models, a non-degradable IP3R3 mutant sensitizes tumour cells with low or no PTEN expression to photodynamic therapy, which is based on the ability of photosensitizer drugs to cause Ca -dependent cytotoxicity after irradiation with visible light. Similarly, disruption of FBXL2 localization with GGTi-2418, a geranylgeranyl transferase inhibitor, sensitizes xenotransplanted tumours to photodynamic therapy. In summary, we identify a novel molecular mechanism that limits mitochondrial Ca overload to prevent cell death. Notably, we provide proof-of-principle that inhibiting IP3R3 degradation in PTEN-deregulated cancers represents a valid therapeutic strategy.

PTEN, a known tumour suppressor, inhibits the FXBL2-dependent degradation of IP3R3, an IP3 receptor, thus augmenting IP3R3-mediated calcium release from the endoplasmic reticulum to mitochondria and inducing apoptosis; inhibiting FXBL2 sensitizes PTEN-deficient tumours to photodynamic therapy. Assisted apoptosis in cancer cells Resistance to apoptosis is a feature of cancer cells and contributes to their endurance. Calcium overload in the mitochondria is a pro-apoptotic stimulus. This report dissects a pathway that controls endoplasmic reticulum (ER) calcium release to the mitochondria. The IP3 ER membrane receptor IP3R promotes ER calcium release. It is targeted for degradation by FXBL2, which limits calcium flux to mitochondria. Interestingly, the tumour suppressor PTEN competes with FXBL2 for IP3R binding. In the absence of PTEN, IP3R degradation is increased, limiting calcium-flux-induced apoptosis. Restoring IP3R levels could enhance the effects of apoptosis-inducing cancer therapies. In response to environmental cues that promote IP3 (inositol 1,4,5-trisphosphate) generation, IP3 receptors (IP3Rs) located on the endoplasmic reticulum allow the ‘quasisynaptical’ feeding of calcium to the mitochondria to promote oxidative phosphorylation 1 . However, persistent Ca 2+ release results in mitochondrial Ca 2+ overload and consequent apoptosis 2 . Among the three mammalian IP3Rs, IP3R3 appears to be the major player in Ca 2+ -dependent apoptosis. Here we show that the F-box protein FBXL2 (the receptor subunit of one of 69 human SCF (SKP1, CUL1, F-box protein) ubiquitin ligase complexes 3 ) binds IP3R3 and targets it for ubiquitin-, p97- and proteasome-mediated degradation to limit Ca 2+ influx into mitochondria. FBXL2-knockdown cells and FBXL2-insensitive IP3R3 mutant knock-in clones display increased cytosolic Ca 2+ release from the endoplasmic reticulum and sensitization to Ca 2+ -dependent apoptotic stimuli. The phosphatase and tensin homologue ( PTEN ) gene is frequently mutated or lost in human tumours and syndromes that predispose individuals to cancer 4 . We found that PTEN competes with FBXL2 for IP3R3 binding, and the FBXL2-dependent degradation of IP3R3 is accelerated in Pten −/− mouse embryonic fibroblasts and PTEN -null cancer cells. Reconstitution of PTEN -null cells with either wild-type PTEN or a catalytically dead mutant stabilizes IP3R3 and induces persistent Ca 2+ mobilization and apoptosis. IP3R3 and PTEN protein levels directly correlate in human prostate cancer. Both in cell culture and xenograft models, a non-degradable IP3R3 mutant sensitizes tumour cells with low or no PTEN expression to photodynamic therapy, which is based on the ability of photosensitizer drugs to cause Ca 2+ -dependent cytotoxicity after irradiation with visible light 5 , 6 . Similarly, disruption of FBXL2 localization with GGTi-2418, a geranylgeranyl transferase inhibitor 7 , sensitizes xenotransplanted tumours to photodynamic therapy. In summary, we identify a novel molecular mechanism that limits mitochondrial Ca 2+ overload to prevent cell death. Notably, we provide proof-of-principle that inhibiting IP3R3 degradation in PTEN-deregulated cancers represents a valid therapeutic strategy.

The AKT/PKB kinase is a key signaling component of one of the most frequently activated pathways in cancer and is a major target of cancer drug development. Most studies have focused on its activation by Receptor Tyrosine Kinase (RTK) mediated Phosphatidylinositol-3-OH kinase (PI3K) activation or loss of Phosphatase and Tensin homolog (PTEN). We have uncovered that growth factors binding to RTKs lead to activation of a non-receptor tyrosine kinase, Ack1 (also known as ACK or TNK2), which directly phosphorylates AKT at an evolutionarily conserved tyrosine 176 in the kinase domain. Tyr176-phosphorylated AKT localizes to the plasma membrane and promotes Thr308/Ser473-phosphorylation leading to AKT activation. Mice expressing activated Ack1 specifically in the prostate exhibit AKT Tyr176-phosphorylation and develop murine prostatic intraepithelial neoplasia (mPINs). Further, expression levels of Tyr176-phosphorylated-AKT and Tyr284-phosphorylated-Ack1 were positively correlated with the severity of disease progression, and inversely correlated with the survival of breast cancer patients. Thus, RTK/Ack1/AKT pathway provides a novel target for drug discovery.

Key Points Post-translational modifications with the lipids farnesyl or geranylgeranyl (together referred to as prenyl) are catalysed by farnesyltransferase (FT) or geranylgeranyltransferase 1 (GGT1) and are required for the cellular localization, function and cancer-causing activities of some proteins. Among the hundreds of proteins that are estimated to be prenylated most are either exclusively farnesylated (for example, HRAS and RAS homologue enriched in brain (RHEB)) or geranylgeranylated (for example, RHOA, RHOC, RALA and RALB); some are both farnesylated and geranylgeranylated (RHOB), and others are naturally farnesylated but become geranylgeranylated when FT is inhibited (for example, KRAS and NRAS). These and other important observations prompted the design and development of inhibitors of FT (FTIs) and GGT1 (GGTIs) as potential anticancer drugs. Several FTIs have been tested clinically but only one GGTI has recently entered clinical trials. Further validation of FT and GGT1 as anticancer drug targets was recently provided by genetic mouse models: conditional loss of FT and/or GGT1 hampers mutant KRAS-induced tumorigenesis and extends the lifespan of mice. FTI treatment results in the reversal of several hallmarks of cancer, including mitotic arrest at prometaphase, induction of apoptosis, inhibition of anchorage-dependent and anchorage-independent growth, invasion, angiogenesis and tumour growth, as well as induction of tumour regression in animal models. These effects seem to be mediated by interference with aberrant signal transduction pathways such as RAF–MEK–ERK, PI3K–AKT, and other oncogenic and survival pathways. GGTI treatment also results in the reversal of the cancer hallmarks mentioned above except that they block cells in the G1 phase of the cell cycle, and this seems to be owing to their ability to induce the accumulation of the cyclin-dependent kinase (CDK) inhibitors p21 and p27 and to inhibit CDKs and induce hypophosphorylation of RB. GGTI treatment also decreases the levels of phospho-AKT and survivin, and this seems to mediate their ability to induce apoptosis. Although in preclinical models FTIs are highly effective as antitumour agents, in clinical trials limited efficacy was observed. This is primarily due to poor patient selection. This in turn is due to our lack of understanding of the mechanism of action of FTIs. In the future, a major effort must be dedicated to identifying the prenylated proteins the inhibition of which is responsible for the antitumour effects of PTIs. This will be of great value not only for enhancing our understanding of the mechanism of action of FTIs and GGTIs, but also for selecting patients whose tumours are addicted to specific prenylated proteins and who are more likely to respond to these agents. Recent advances in techniques to characterize the human prenylome are likely to accelerate achieving these crucial goals in the prenylation field. It was hoped that targeting protein prenylation would inhibit the oncogenic signalling of RAS family members. However, preclinical and clinical trials of prenyltransferase inhibitors have conflicting results. This Review discusses why these differences might occur and the future of targeting prenylation. Protein farnesylation and geranylgeranylation, together referred to as prenylation, are lipid post-translational modifications that are required for the transforming activity of many oncogenic proteins, including some RAS family members. This observation prompted the development of inhibitors of farnesyltransferase (FT) and geranylgeranyltransferase 1 (GGT1) as potential anticancer drugs. In this Review, we discuss the mechanisms by which FT and GGT1 inhibitors (FTIs and GGTIs, respectively) affect signal transduction pathways, cell cycle progression, proliferation and cell survival. In contrast to their preclinical efficacy, only a small subset of patients responds to FTIs. Identifying tumours that depend on farnesylation for survival remains a challenge, and strategies to overcome this are discussed. One GGTI has recently entered the clinic, and the safety and efficacy of GGTIs await results from clinical trials.

Mutant KRas is a significant driver of human oncogenesis and confers resistance to therapy, underscoring the need to develop approaches that disable mutant KRas-driven tumors. Because targeting KRas directly has proven difficult, identifying vulnerabilities specific for mutant KRas tumors is an important alternative approach. Here we show that glycogen synthase kinase 3 (GSK3) is required for the in vitro and in vivo growth and survival of human mutant KRas-dependent tumors but is dispensable for mutant KRas-independent tumors. Further, inhibiting phosphorylation of GSK3 substrates c-Myc on T58 and β-catenin on S33/S37/T41 and their subsequent upregulation contribute to the antitumor activity of GSK3 inhibition. Importantly, GSK3 blockade inhibits the in vivo growth of G12D, G12V, and G12C mutant KRas primary and metastatic patient-derived xenografts from pancreatic cancer patients who progressed on chemo- and radiation therapies. This discovery opens new avenues to target mutant KRas-dependent cancers. Direct targeting of mutant KRas is challenging and alternative approaches are needed. Here they show glycogen synthase kinase 3 (GSK3) to be required for the growth and survival of human mutant KRas-dependent tumors but dispensable for mutant KRas-independent tumors and show GSK3 inhibition to inhibit in vivo growth of Kras mutant patient-derived pancreatic tumors.

The relative contribution of intrinsic genetic factors and extrinsic environmental ones to cancer aetiology and natural history is a lengthy and debated issue. Gene–environment interactions (G x E) arise when the combined presence of both a germline genetic variant and a known environmental factor modulates the risk of disease more than either one alone. A panel of experts discussed our current understanding of cancer aetiology, known examples of G × E interactions in cancer, and the expanded concept of G × E interactions to include somatic cancer mutations and iatrogenic environmental factors such as anti-cancer treatment. Specific genetic polymorphisms and genetic mutations increase susceptibility to certain carcinogens and may be targeted in the near future for prevention and treatment of cancer patients with novel molecularly based therapies. There was general consensus that a better understanding of the complexity and numerosity of G × E interactions, supported by adequate technological, epidemiological, modelling and statistical resources, will further promote our understanding of cancer and lead to novel preventive and therapeutic approaches.

Cerebral cavernous malformations (CCMs) are common vascular anomalies that develop in the central nervous system and, more rarely, the retina. The lesions can cause headache, seizures, focal neurological deficits, and hemorrhagic stroke. Symptomatic lesions are treated according to their presentation; however, targeted pharmacological therapies that improve the outcome of CCM disease are currently lacking. We performed a high-throughput screen to identify Food and Drug Administration-approved drugs or other bioactive compounds that could effectively suppress hyperproliferation of mouse brain primary astrocytes deficient for CCM3. We demonstrate that fluvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase and the N-bisphosphonate zoledronic acid monohydrate, an inhibitor of protein prenylation, act synergistically to reverse outcomes of CCM3 loss in cultured mouse primary astrocytes and in Drosophila glial cells in vivo. Further, the two drugs effectively attenuate neural and vascular deficits in chronic and acute mouse models of CCM3 loss in vivo, significantly reducing lesion burden and extending longevity. Sustained inhibition of the mevalonate pathway represents a potential pharmacological treatment option and suggests advantages of combination therapy for CCM disease.

Allergic disease is a common and symptomatically heterogeneous group of inflammatory disorders marked by overactive Th2 and mast cell (MC) responses along with eosinophil infiltration. Treatment options require continual assessment due to breakthrough symptoms on standard regimens. One approach to improved therapy is drug repurposing. Our lab previously showed that cholesterol-lowering statin drugs can suppress IgE-mediated mast cell function by inhibiting protein isoprenylation, a pathway using cholesterol biosynthesis intermediates. Additionally, mast cells are activated by the alarmin IL-33, released by epithelial cells after contact with cellular stressors. We hypothesized that IL-33-mediated mast cell function can be inhibited by disrupting isoprenylation via statins or the dual farnesyltransferase (FT) geranylgeranyltransferase-1 inhibitor, FGTI-2734. We used IL-33 to stimulate mast cells and eosinophils and inhibited their function using simvastatin and FGTI-2734. Using primary mast cells and eosinophils, we measured cytokine production by ELISA and qPCR. Flow cytometry and western blots were used to measure phosphorylation of IL-33 signaling components, and eosinophil migration. Human mast cells were assessed by ELISA for cytokine inhibition. Lastly, a murine model of IL-33 induced peritonitis was used to assess the effects of isoprenylation inhibition on eosinophil and neutrophil influx. We show simvastatin and FGTI-2734 suppressed IL-33-mediated cytokine protein and mRNA production in primary murine mast cells from the C57BL/6 strain. Simvastatin effects were lost on mast cells from the 129/SvJ strain and were inconsistent among primary human mast cells. In contrast, FGTI-2734 inhibited IL-33-induced cytokine production by mast cells on the 129/SvJ strain and among human donors. Simvastatin and FGTI-2734 also inhibited IL-33-induced cytokine production and chemokine-induced migration of C57BL/6 primary eosinophils. Simvastatin and FGTI-2734 had no effect on expression of the IL-33 receptor, ST2, suggesting that inhibition occurs at a step in IL-33 signaling. Importantly, FGTI-2734 significantly reduced eosinophil and neutrophil influx in a model of IL-33-induced peritonitis, whereas simvastatin had no effect. These findings indicate that targeting FT and GGT-1 is a viable target in IL-33-induced inflammation.

All cancer cells reprogram metabolism to support aberrant growth. Here, we report that cancer cells employ and depend on imbalanced and dynamic heme metabolic pathways, to accumulate heme intermediates, that is, porphyrins. We coined this essential metabolic rewiring “porphyrin overdrive” and determined that it is cancer-essential and cancer-specific. Among the major drivers are genes encoding mid-step enzymes governing the production of heme intermediates. CRISPR/Cas9 editing to engineer leukemia cell lines with impaired heme biosynthetic steps confirmed our whole-genome data analyses that porphyrin overdrive is linked to oncogenic states and cellular differentiation. Although porphyrin overdrive is absent in differentiated cells or somatic stem cells, it is present in patient-derived tumor progenitor cells, demonstrated by single-cell RNAseq, and in early embryogenesis. In conclusion, we identified a dependence of cancer cells on non-homeostatic heme metabolism, and we targeted this cancer metabolic vulnerability with a novel “bait-and-kill” strategy to eradicate malignant cells.

BackgroundGeranylgeranyltransferase I (GGTase I) catalyzes geranylgeranylation, a modification required for the function of many oncogenic RAS-related proteins. GGTI-2418 is a peptidomimetic small molecule inhibitor of GGTase I.ObjectiveThe aim of this study was to establish the maximum tolerated dose of GGTI-2418 in patients with advanced solid tumors.Patients and MethodsThis was a phase I, open-label, dose-escalation study conducted in two US centers (University of Pennsylvania and Indiana University) in adults with treatment-refractory advanced solid tumors. An accelerated dose-escalation schema was used across eight dose levels, from 120 to 2060 mg/m2, administered on days 1–5 of each 21-day cycle.ResultsFourteen patients were enrolled in the dose-escalation cohort. No dose-limiting toxicities were observed, and 2060 mg/m2 was determined to be the maximum tolerated dose. The only potential drug-related grade 3 or 4 toxicities were elevated bilirubin and alkaline phosphatase in a single patient with concurrent malignant biliary obstruction. No objective responses were observed. Four of thirteen evaluable patients had stable disease for up to 6.7 months. The study was terminated prior to dose expansion based on a sponsor decision. Pharmacokinetic analysis demonstrated a mean terminal half-life of 1.1 h.ConclusionsGGTI2418 was safe and tolerable at all tested dose levels with some evidence of disease stability. Due to rapid elimination, dosing of GGTI2418 in this study may have been inadequate to achieve optimal inhibition of its target, GGTase I.