Activating Mutations in PIK3CB Confer Resistance to PI3K Inhibition and Define a Novel Oncogenic Role for p110β

Integrative modeling uncovers p21-driven drug resistance and prioritizes therapies for PIK3CA-mutant breast cancer

Utility of PI3Kα inhibitors like BYL719 is limited by the acquisition of genetic and non-genetic mechanisms of resistance which cause disease recurrence. Several combination therapies based on PI3K inhibition have been proposed, but a way to systematically prioritize them for breast cancer treatment is still missing. By integrating published and in-house studies, we have developed in silico models that quantitatively capture dynamics of PI3K signaling at the network-level under a BYL719-sensitive versus BYL719 resistant-cell state. Computational predictions show that signal rewiring to alternative components of the PI3K pathway promote resistance to BYL719 and identify PDK1 as the most effective co-target with PI3Kα rescuing sensitivity of resistant cells to BYL719. To explore whether PI3K pathway-independent mechanisms further contribute to BYL719 resistance, we performed phosphoproteomics and found that selection of high levels of the cell cycle regulator p21 unexpectedly promoted drug resistance in T47D cells. Functionally, high p21 levels favored repair of BYL719-induced DNA damage and bypass of the associated cellular senescence. Importantly, targeted inhibition of the check-point inhibitor CHK1 with MK-8776 effectively caused death of p21-high T47D cells, thus establishing a new vulnerability of BYL719-resistant breast cancer cells. Together, our integrated studies uncover hidden molecular mediators causing resistance to PI3Kα inhibition and provide a framework to prioritize combination therapies for PI3K-mutant breast cancer.

MYC is a clinically significant driver of mTOR inhibitor resistance in breast cancer

Targeting the PI3K-AKT-mTOR pathway is a promising therapeutic strategy for breast cancer treatment. However, low response rates and development of resistance to PI3K-AKT-mTOR inhibitors remain major clinical challenges. Here, we show that MYC activation drives resistance to mTOR inhibitors (mTORi) in breast cancer. Multiomic profiling of mouse invasive lobular carcinoma (ILC) tumors revealed recurrent Myc amplifications in tumors that acquired resistance to the mTORi AZD8055. MYC activation was associated with biological processes linked to mTORi response and counteracted mTORi-induced translation inhibition by promoting translation of ribosomal proteins. In vitro and in vivo induction of MYC conferred mTORi resistance in mouse and human breast cancer models. Conversely, AZD8055-resistant ILC cells depended on MYC, as demonstrated by the synergistic effects of mTORi and MYCi combination treatment. Notably, MYC status was significantly associated with poor response to everolimus therapy in metastatic breast cancer patients. Thus, MYC is a clinically relevant driver of mTORi resistance that may stratify breast cancer patients for mTOR-targeted therapies.

PI3K/AKT/mTOR signaling transduction pathway and targeted therapies in cancer

The PI3K/AKT/mTOR (PAM) signaling pathway is a highly conserved signal transduction network in eukaryotic cells that promotes cell survival, cell growth, and cell cycle progression. Growth factor signalling to transcription factors in the PAM axis is highly regulated by multiple cross-interactions with several other signaling pathways, and dysregulation of signal transduction can predispose to cancer development. The PAM axis is the most frequently activated signaling pathway in human cancer and is often implicated in resistance to anticancer therapies. Dysfunction of components of this pathway such as hyperactivity of PI3K, loss of function of PTEN, and gain-of-function of AKT, are notorious drivers of treatment resistance and disease progression in cancer. In this review we highlight the major dysregulations in the PAM signaling pathway in cancer, and discuss the results of PI3K, AKT and mTOR inhibitors as monotherapy and in co-administation with other antineoplastic agents in clinical trials as a strategy for overcoming treatment resistance. Finally, the major mechanisms of resistance to PAM signaling targeted therapies, including PAM signaling in immunology and immunotherapies are also discussed.

PI3K/AKT/mTOR pathway mediated-cell cycle dysregulation contribute to malignant proliferation of mouse spermatogonia induced by microcystin-leucine arginine

Environmental cyanotoxin exposure may be a trigger of testicular cancer. Activation of PI3K/AKT/mTOR signaling pathway is the critical molecular event in testicular carcinogenesis. As a widespread cyanotoxin, microcystin-leucine arginine (MC-LR) is known to induce cell malignant transformation and tumorigenesis. However, the effects of MC-LR on the regulatory mechanism of PI3K/AKT/mTOR pathway in seminoma, the most common testicular tumor, are unknown. In this study, mouse spermatogonia cell line (GC-1) and nude mice were used to investigate the effects and mechanisms of MC-LR on the malignant transformation of spermatogonia by nude mouse tumorigenesis assay, cell migration invasion assay, western blot, and cell cycle assay, and so forth. The results showed that, after continuous exposure to environmentally relevant concentrations of MC-LR (20 nM) for 35 generations, the proliferation, migration, and invasion abilities of GC-1 cells were increased by 120%, 340%, and 370%, respectively. In nude mice, MC-LR-treated GC-1 cells formed tumors with significantly greater volume (0.998 ± 0.768 cm³ ) and weight (0.637 ± 0.406 g) than the control group (0.067 ± 0.039 cm³ ; 0.094 ± 0.087 g) (P < .05). Furthermore, PI3K inhibitor Wortmannin inhibited the PI3K/AKT/mTOR pathway and its downstream proteins (c-MYC, CDK4, CCND1, and MMP14) activated by MC-LR. Blocking PI3K alleviated MC-LR-induced cell cycle disorder and malignant proliferation, migration and invasive of GC-1 cells. Altogether, our findings suggest that MC-LR can induce malignant transformation of mouse spermatogonia, and the PI3K/AKT/mTOR pathway-mediated cell cycle dysregulation may be an important target for malignant proliferation. This study provides clues to further reveal the etiology and pathogenesis of seminoma.

Development and safety of PI3K inhibitors in cancer

The phosphatidylinositol 3-kinase (PI3K) signalling pathway regulates cell survival, proliferation, migration, metabolism and other vital cellular life processes. In addition, activation of the PI3K signalling pathway is important for cancer development. As a result, a variety of PI3K inhibitors have been clinically developed to treat malignancies. Although several PI3K inhibitors have received approval from the Food and Drug Administration (FDA) for significant antitumour activity, frequent and severe adverse effects have greatly limited their clinical application. These toxicities are mostly on-target and immune-mediated; nevertheless, the underlying mechanisms are still unclear. Current management usually involves intervention through symptomatic treatment, with discontinuation if toxicity persists. Therefore, it is necessary to comprehensively understand these adverse events and ensure the clinical safety application of PI3K inhibitors by establishing the most effective management guidelines, appropriate intermittent dosing regimens and new combination administration. Here, the focus is on the development of PI3K inhibitors in cancer therapy, with particular emphasis on isoform-specific PI3K inhibitors. The most common adverse effects of PI3K inhibitors are also covered, as well as potential mechanisms and management approaches.

PI3K/AKT/mTOR-Targeted Therapy for Breast Cancer

Phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB/AKT) and mechanistic target of rapamycin (mTOR) (PAM) pathways play important roles in breast tumorigenesis and confer worse prognosis in breast cancer patients. The inhibitors targeting three key nodes of these pathways, PI3K, AKT and mTOR, are continuously developed. For breast cancer patients to truly benefit from PAM pathway inhibitors, it is necessary to clarify the frequency and mechanism of abnormal alterations in the PAM pathway in different breast cancer subtypes, and further explore reliable biomarkers to identify the appropriate population for precision therapy. Some PI3K and mTOR inhibitors have been approved by regulatory authorities for the treatment of specific breast cancer patient populations, and many new-generation PI3K/mTOR inhibitors and AKT isoform inhibitors have also been shown to have good prospects for cancer therapy. This review summarizes the changes in the PAM signaling pathway in different subtypes of breast cancer, and the latest research progress about the biomarkers and clinical application of PAM-targeted inhibitors.

PIK3CB promotes oesophageal cancer proliferation through the PI3K/AKT/mTOR signalling axis

PIK3CB is abnormally expressed in various carcinomas and affects the proliferation, invasion and drug resistance of cancer cells. However, its role in oesophageal squamous cell carcinoma (ESCC) is still unclear. In this study, PIK3CB was found to be highly expressed in ESCC tissues and cells and positively correlated with the poor prognosis of ESCC. Silencing PIK3CB inhibited the proliferation of ESCC cells, arrested the cell cycle, and promoted apoptosis. Mechanistic studies showed that the tumour-promoting effect of PIK3CB was achieved through PI3K/AKT/mTOR signalling pathway activation. Moreover, the high PIK3CB expression level in ESCC may be closely associated with the hypomethylation status of the gene promoter. In conclusion, PIK3CB promotes ESCC by activating the PI3K/AKT/mTOR signalling axis. PIK3CB may be a potential target in ESCC.

The expression and prognostic significance of PIK3CB in lung adenocarcinoma

OBJECTIVE

The aim of this study was to explore the expression and prognostic significance of PIK3CB in lung adenocarcinoma (LUAD) and to analyse the possible molecular mechanism that promotes LUAD development.

METHODS

Differences of PIK3CB expression at transcriptional level between LUAD and normal tissues were analysed with the Timer and UALCAN databases. Then, immunohistochemical staining was performed to investigate PIK3CB expression at the protein level, and relationships between PIK3CB and clinical characteristics were accessed. Univariate and multivariate Cox regression were performed to identify the independent prognostic risk factors for LUAD. Genetic alterations were analysed using the cBioPortal database. The main coexpressed genes and enrichment pathways of PIK3CB were estimated with the LinkedOmics database.

RESULTS

Compared with normal tissues, PIK3CB was higherly expressed in LUAD at the transcriptional level and protein level, respectively. PIK3CB expression was closely related to prognosis of LUAD patients, and PIK3CB protein expression was associated with lymph node metastasis and pathological differentiation, but not related to sex, age, pleural invasion, vascular invasion, tumour site, tumour size or clinical stage. PIK3CB and tumour size were independent risk factors for LUAD patients. The expression of PIK3CB was negatively correlated with AKT1 and AKT2, but there was no significant correlation with AKT3, and strong positive correlations with ARMC8, DNAJC13 and PIK3R4. The main enrichment pathways of PIK3CB and related genes included adherens junctions and the phosphatidylinositol signalling pathways, ErbB signalling pathways, Hedgehog signalling pathways, and C-type lectin receptor signalling pathways. Therefore, we hypothesized that PIK3CB expression did not promote LUAD development through the classical PI3K/AKT pathway.

CONCLUSION

High PIK3CB expression was associated with the development of LUAD and worse prognosis. PIK3CB was an independent risk factor for LUAD patients. Therefore, this study provides a reliable reference for the prognostic assessment and targeted therapy for LUAD patients.

PIP3 abundance overcomes PI3K signaling selectivity in invadopodia

PI3Kβ is required for invadopodia-mediated matrix degradation by breast cancer cells. Invadopodia maturation requires GPCR activation of PI3Kβ and its coupling to SHIP2 to produce PI(3,4)P2 . We now test whether selectivity for PI3Kβ is preserved under conditions of mutational increases in PI3K activity. In breast cancer cells where PI3Kβ is inhibited, short-chain diC8-PIP3  rescues gelatin degradation in a SHIP2-dependent manner; rescue by diC8-PI(3,4)P2  is SHIP2-independent. Surprisingly, the expression of either activated PI3Kβ or PI3Kα mutants rescued the effects of PI3Kβ inhibition. In both cases, gelatin degradation was SHIP2-dependent. These data confirm the requirement for PIP3 conversion to PI(3,4)P2 for invadopodia function and suggest that selectivity for distinct PI3K isotypes may be obviated by mutational activation of the PI3K pathway.

Silencing ESRP1 expression promotes caspase-independent cell death via nuclear translocation of AIF in colon cancer cells

Epithelial splicing regulatory protein 1 (ESRP1) is overexpressed in the majority of cancer types, while downregulated in a few cancers, thus it has emerged as a tumorigenic or a tumor suppressor depending on disease context and cell type. Moreover, the underlying molecular mechanism of ESRP1 is poorly understood in cancer progression. Here, we initially analyzed Clinical Proteomic Tumor Analysis Consortium (CPTAC), colon tissue microarray, and colon cancer cells to evaluate the ESRP1 expression levels in colorectal cancer subtypes. The association between the expression of ESRP1 and cell death signaling pathways was evaluated in colon cancer cells. Furthermore, silencing ESRP1 was performed to detect the relation between ESRP1 and apoptosis-inducing factor (AIF). Subsequently, translocation of AIF and apoptosis were analyzed by immunofluorescence assay and FACS, respectively. ESRP1 is found to be expressed at high levels in the early stage, and gradually decreases with the increasing colorectal cancer stage, wherein epithelial cell to mesenchymal cell transition (EMT) occurs during cancer progression. Moreover, ESRP1 silencing in HCT116 colorectal cancer cells reveals the translocation of the caspase-independent cell death marker AIF to the nucleus, thereby enhancing the DNA damage response, which inevitably induces cancer cell death. Our results demonstrate that silencing ESRP1 in colorectal cancer cells promotes HCT116 cell death by inducing caspase-independent cell death via regulation of CD44 alternative splicing. Collectively, our findings provide an insight into ESRP1 as a therapeutic target in colon cancer.

Attacking the PI3K/Akt/mTOR signaling pathway for targeted therapeutic treatment in human cancer

Cancer is the second leading cause of human death globally. PI3K/Akt/mTOR signaling is one of the most frequently dysregulated signaling pathways observed in cancer patients that plays crucial roles in promoting tumor initiation, progression and therapy responses. This is largely due to that PI3K/Akt/mTOR signaling is indispensable for many cellular biological processes, including cell growth, metastasis, survival, metabolism, and others. As such, small molecule inhibitors targeting major kinase components of the PI3K/Akt/mTOR signaling pathway have drawn extensive attention and been developed and evaluated in preclinical models and clinical trials. Targeting a single kinase component within this signaling usually causes growth arrest rather than apoptosis associated with toxicity-induced adverse effects in patients. Combination therapies including PI3K/Akt/mTOR inhibitors show improved patient response and clinical outcome, albeit developed resistance has been reported. In this review, we focus on revealing the mechanisms leading to the hyperactivation of PI3K/Akt/mTOR signaling in cancer and summarizing efforts for developing PI3K/Akt/mTOR inhibitors as either mono-therapy or combination therapy in different cancer settings. We hope that this review will facilitate further understanding of the regulatory mechanisms governing dysregulation of PI3K/Akt/mTOR oncogenic signaling in cancer and provide insights into possible future directions for targeted therapeutic regimen for cancer treatment, by developing new agents, drug delivery systems, or combination regimen to target the PI3K/Akt/mTOR signaling pathway. This information will also provide effective patient stratification strategy to improve the patient response and clinical outcome for cancer patients with deregulated PI3K/Akt/mTOR signaling.

Identification and Kinetic Characterization of Serum- and Glucocorticoid-Regulated Kinase Inhibitors Using a Fluorescence Polarization-Based Assay

The serum- and glucocorticoid-regulated kinase (SGK) family consists of three isoforms (SGK1, SGK2, and SGK3) that have been implicated in the regulation of tumor growth, metastasis, autophagy, and epithelial ion transport. SGK1 and SGK3 play essential roles in protein kinase B (AKT or PKB)-independent phosphoinositide 3-kinases (PI3K)-mediated tumorigenesis, as evidenced by the significantly elevated expression levels of SGK1 and SGK3 in many cancers, including prostate cancer, colorectal carcinoma, estrogen-dependent breast cancer, and glioblastoma. Therefore, SGK is a potential target for anticancer therapy. A small kinase-focused library comprising 160 compounds was screened against SGK1 using a fluorescence polarization-based kinase assay that yielded a Z'-factor of 0.82. Among the 39 compounds obtained as initial hits in a primary screen, 12 compounds contained the thiazolidine-2,4-dione scaffold. The inhibitory mechanisms of the most potent hit, KMU010402, were further investigated using kinetic analyses, followed by determination of the inhibition constants for SGK1, SGK2, and SGK3. Molecular modeling was used to propose a potential binding mode of KMU010402 to SGK1.

The Role of PI3K Inhibition in the Treatment of Breast Cancer, Alone or Combined With Immune Checkpoint Inhibitors

Dysregulation of phosphoinositide 3-kinase (PI3K) signaling is highly implicated in tumorigenesis, disease progression, and the development of resistance to the current standard of care treatments in breast cancer patients. This review discusses the role of PI3K pathway in breast cancer and evaluates the clinical development of PI3K inhibitors in both early and metastatic breast cancer settings. Further, this review examines the evidence for the potential synergistic benefit for the combination treatment of PI3K inhibition and immunotherapy in breast cancer treatment.

PI3K inhibition in breast cancer: Identifying and overcoming different flavors of resistance

The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is commonly deregulated in many human tumors, including breast cancer. Somatic mutations of the PI3K alpha catalytic subunit (PIK3CA) are the most common cause of pathway hyperactivation. Hence, several PI3K inhibitors have been investigated with one of them, alpelisib, recently approved for the treatment of endocrine sensitive, PIK3CA mutated, metastatic breast cancer. Unfortunately, all patients receiving a PI3K inhibitor eventually develop resistance to these compounds. Mechanisms of resistance include oncogenic PI3K alterations, pathway reactivation through upstream or downstream effectors and enhancement of parallel pro-survival pathways. We review the prognostic and predictive role of PI3K alterations in breast cancer, focusing on resistance to PI3K inhibitors and on biomarkers with potential clinical relevance. We also discuss combination strategies that may overcome resistance to PI3K inhibitors, thus increasing the efficacy of these drugs in breast cancer.

Organismal roles for the PI3Kα and β isoforms: their specificity, redundancy or cooperation is context-dependent

PI3Ks are important lipid kinases that produce phosphoinositides phosphorylated in position 3 of the inositol ring. There are three classes of PI3Ks: class I PI3Ks produce PIP3 at plasma membrane level. Although D. melanogaster and C. elegans have only one form of class I PI3K, vertebrates have four class I PI3Ks called isoforms despite being encoded by four different genes. Hence, duplication of these genes coincides with the acquisition of coordinated multi-organ development. Of the class I PI3Ks, PI3Kα and PI3Kβ, encoded by PIK3CA and PIK3CB, are ubiquitously expressed. They present similar putative protein domains and share PI(4,5)P2 lipid substrate specificity. Fifteen years after publication of their first isoform-selective pharmacological inhibitors and genetically engineered mouse models (GEMMs) that mimic their complete and specific pharmacological inhibition, we review the knowledge gathered in relation to the redundant and selective roles of PI3Kα and PI3Kβ. Recent data suggest that, further to their redundancy, they cooperate for the integration of organ-specific and context-specific signal cues, to orchestrate organ development, physiology, and disease. This knowledge reinforces the importance of isoform-selective inhibitors in clinical settings.

Circulating tumour DNA in B-cell lymphomas: current state and future prospects

Circulating tumour DNA (ctDNA) is a highly versatile analyte and an emerging biomarker for detection of tumour-specific sequences in lymphoid malignancies. Since ctDNA is derived from tumour cells throughout the body, it overcomes fundamental limitations of tissue biopsies by capturing the complete molecular profile of tumours, including those from inaccessible anatomic locations. Assays for ctDNA are minimally invasive and serial sampling monitors the effectiveness of therapy and identifies minimal residual disease below the detection limit of standard imaging scans. Dynamic changes in ctDNA levels measure real-time tumour kinetics, and early reductions in ctDNA during treatment correlate with clinical outcomes in multiple B-cell lymphomas. After therapy, ctDNA can effectively discriminate between patients who achieved a complete molecular remission from those with residual treatment-resistant disease. Serial monitoring of ctDNA after therapy can detect early molecular relapse and identify drug-resistant clones that harbour targetable mutations. In order for ctDNA to reach its full potential, the standardization and harmonization of the optimal pre-analytical and analytical techniques for B-cell lymphomas is a critically necessary requirement. Prospective validation of ctDNA within clinical studies is also required to determine its clinical utility as an adjunctive decision-making tool.

Alpelisib in the treatment of metastatic HR+ breast cancer with PIK3CA mutations

Since the US FDA approval of everolimus/exemestane in July 2012, and of the first CDK 4/6 inhibitor, palbociclib, combined with endocrine treatment in February 2015, a third class of therapeutic compounds, the PI3K inhibitors, has been introduced to the arsenal of targeted therapies overcoming endocrine resistance in hormone receptor-positive metastatic breast cancer. Alpelisib (PIQRAY®) is the first of these novel agents yielding promising clinical results, giving an impetus to further development of tailored endocrine anticancer treatments. Herein, we review its pharmacodynamic and pharmacokinetic properties, safety and efficacy data, as well as Phase III SOLAR-1 trial, prompting FDA approval of alpelisib in hormone receptor-positive metastatic breast cancer harboring PIK3CA mutations. Furthermore, implications for clinical use and current research will also be discussed.

Targeted inhibition of cooperative mutation- and therapy-induced AKT activation in AML effectively enhances response to chemotherapy

Most AML patients exhibit mutational activation of the PI3K/AKT signaling pathway, which promotes downstream effects including growth, survival, DNA repair, and resistance to chemotherapy. Herein we demonstrate that the inv(16)/KIT^D816Y AML mouse model exhibits constitutive activation of PI3K/AKT signaling, which was enhanced by chemotherapy-induced DNA damage through DNA-PK-dependent AKT phosphorylation. Strikingly, inhibitors of either PI3K or DNA-PK markedly reduced chemotherapy-induced AKT phosphorylation and signaling leading to increased DNA damage and apoptosis of inv(16)/KIT^D816Y AML cells in response to chemotherapy. Consistently, combinations of chemotherapy and PI3K or DNA-PK inhibitors synergistically inhibited growth and survival of clonogenic AML cells without substantially inhibiting normal clonogenic bone marrow cells. Moreover, treatment of inv(16)/KIT^D816Y AML mice with combinations of chemotherapy and PI3K or DNA-PK inhibitors significantly prolonged survival compared to untreated/single-treated mice. Mechanistically, our findings implicate that constitutive activation of PI3K/AKT signaling driven by mutant KIT, and potentially other mutational activators such as FLT3 and RAS, cooperates with chemotherapy-induced DNA-PK-dependent activation of AKT to promote survival, DNA repair, and chemotherapy resistance in AML. Hence, our study provides a rationale to select AML patients exhibiting constitutive PI3K/AKT activation for simultaneous treatment with chemotherapy and inhibitors of DNA-PK and PI3K to improve chemotherapy response and clinical outcome.

Personalized cancer therapy prioritization based on driver alteration co-occurrence patterns

Identification of actionable genomic vulnerabilities is key to precision oncology. Utilizing a large-scale drug screening in patient-derived xenografts, we uncover driver gene alteration connections, derive driver co-occurrence (DCO) networks, and relate these to drug sensitivity. Our collection of 53 drug-response predictors attains an average balanced accuracy of 58% in a cross-validation setting, rising to 66% for a subset of high-confidence predictions. We experimentally validated 12 out of 14 predictions in mice and adapted our strategy to obtain drug-response models from patients’ progression-free survival data. Our strategy reveals links between oncogenic alterations, increasing the clinical impact of genomic profiling.

Biology, pathology, and therapeutic targeting of RAS

RAS was identified as a human oncogene in the early 1980s and subsequently found to be mutated in nearly 30% of all human cancers. More importantly, RAS plays a central role in driving tumor development and maintenance. Despite decades of effort, there remain no FDA approved drugs that directly inhibit RAS. The prevalence of RAS mutations in cancer and the lack of effective anti-RAS therapies stem from RAS' core role in growth factor signaling, unique structural features, and biochemistry. However, recent advances have brought promising new drugs to clinical trials and shone a ray of hope in the field. Here, we will exposit the details of RAS biology that illustrate its key role in cell signaling and shed light on the difficulties in therapeutically targeting RAS. Furthermore, past and current efforts to develop RAS inhibitors will be discussed in depth.

New Mechanisms of mTOR Pathway Activation in KIT-mutant Malignant GISTs

A great majority of gastrointestinal stromal tumors (GISTs) are primarily driven by gain-of-function KIT receptor tyrosine kinase mutations that subsequently lead to activation of phosphatidiylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway, a downstream effector of KIT signaling. KIT tyrosine kinase inhibitor, imatinib mesylate, has been successfully used for the treatment of primary, advanced, and disseminated GISTs. Recently, activation of mTOR pathway independent of KIT signaling was demonstrated in imatinib mesylate naïve malignant GISTs and treatment-resistant metastatic tumors. This activation was attributed to oncogenic mutations in PIK3CA encoding PI3K 110α subunit, or to the inactivation of PTEN tumor suppressor, a potent mTOR negative regulator. In this study, mTOR pathway genes were evaluated in 14 imatinib mesylate naïve, KIT-mutant, malignant small intestinal GISTs using next-generation sequencing. Mutations were detected in 3 (21%) of 14 analyzed tumors: (1) c.3200A>T substitution in PIK3CB encoding PI3K 110β subunit, (2) c.1040A>G substitution in tuberous sclerosis complex (TSC2) encoding tuberin, mTOR down-regulator (3) c.6625C>G substitution in mTOR. At the protein level, these changes were predicted to cause, respectively, PIK3CB p.D1067V, TSC2 p.K347R, and mTOR p.L2209V mutations. Previously reported "in vitro" experiments with mouse 3T3 fibroblasts demonstrated oncogenic potential of PIK3CB p.D1067V and mTOR p.L2209V mutants; whereas, PolyPhen-2 software analysis predicted TSC2 p.K347R mutation to likely have a damaging impact on tuberin function. The results of this and previous studies indicate diversity of genetic changes leading to activation of PI3K-AKT-TSC-mTOR pathway in malignant GISTs. Extensive genotyping of the genes involved in mTOR pathway demonstrates common alterations that need to be considered in targeted treatment.

Lipid metabolic reprogramming as an emerging mechanism of resistance to kinase inhibitors in breast cancer

Breast cancer is one of the leading causes of death in women in the United States. In general, patients with breast cancer undergo surgical resection of the tumor and/or receive drug treatment to kill or suppress the growth of cancer cells. In this regard, small molecule kinase inhibitors serve as an important class of drugs used in clinical and research settings. However, the development of resistance to these compounds, in particular HER2 and CDK4/6 inhibitors, often limits durable clinical responses to therapy. Emerging evidence indicates that PI3K/AKT/mTOR pathway hyperactivation is one of the most prominent mechanisms of resistance to many small molecule inhibitors as it bypasses upstream growth factor receptor inhibition. Importantly, the PI3K/AKT/mTOR pathway also plays a pertinent role in regulating various aspects of cancer metabolism. Recent studies from our lab and others have demonstrated that altered lipid metabolism mediates the development of acquired drug resistance to HER2-targeted therapies in breast cancer, raising an interesting link between reprogrammed kinase signaling and lipid metabolism. It appears that, upon development of resistance to HER2 inhibitors, breast cancer cells rewire lipid metabolism to somehow circumvent the inhibition of kinase signaling. Here, we review various mechanisms of resistance observed for kinase inhibitors and discuss lipid metabolism as a potential therapeutic target to overcome acquired drug resistance.

PI3K/AKT/β-Catenin Signaling Regulates Vestigial-Like 1 Which Predicts Poor Prognosis and Enhances Malignant Phenotype in Gastric Cancer

Although gastric cancer is a common cause of cancer mortality worldwide, its biological heterogeneity limits the available therapeutic options. Therefore, identifying novel therapeutic targets for developing effective targeted therapy of gastric cancer is a pressing need. Here, we investigate molecular function and regulatory mechanisms of Vestigial-like 1 (VGLL1) in gastric cancer. Microarray analysis of 556 gastric cancer tissues revealed that VGLL1 was a prognostic biomarker that correlated with PI3KCA and PI3KCB. VGLL1 regulates the proliferation of gastric cancer cells, as shown in live cell imaging, sphere formation, and in vivo xenograft model. Tail vein injection of NUGC3 cells expressing shVGLL1 resulted in less lung metastasis occurring when compared to the control. In contrast, larger metastatic lesions in lung and liver were detected in the VGLL1-overexpressing NUGC3 cell xenograft excision mouse model. Importantly, VGLL1 expression is transcriptionally regulated by the PI3K-AKT-β-catenin pathway. Subsequently, MMP9, a key molecule in gastric cancer, was explored as one of target genes that were transcribed by VGLL1-TEAD4 complex, a component of the transcription factor. Taken together, PI3K/AKT/β-catenin signaling regulates the transcription of VGLL1, which promotes the proliferation and metastasis in gastric cancer. This finding suggests VGLL1 as a novel prognostic biomarker and a potential therapeutic target.

Challenges for the Clinical Development of PI3K Inhibitors: Strategies to Improve Their Impact in Solid Tumors

The PI3K pathway is mutated and aberrantly activated in many cancers and plays a central role in tumor cell proliferation and survival, making it a rational therapeutic target. Until recently, however, results from clinical trials with PI3K inhibitors in solid tumors have been largely disappointing. Here, we describe several factors that have limited the success of these agents, including the weak driver oncogenic activity of mutant PI3K, suboptimal patient selection in trials, drug-related toxicities, feedback upregulation of compensatory mechanisms when PI3K is blocked, increased insulin production upon PI3Kα inhibition, lack of mutant-specific inhibitors, and a relative scarcity of studies using combinations with PI3K antagonists. We also suggest strategies to improve the impact of these agents in solid tumors. Despite these challenges, we are optimistic that isoform-specific PI3K inhibitors, particularly in combination with other agents, may be valuable in treating appropriately selected patients with PI3K-dependent tumors. SIGNIFICANCE: Despite the modest clinical activity of PI3K inhibitors in solid tumors, there is an increasing understanding of the factors that may have limited their success. Strategies to ameliorate drug-related toxicities, use of rational combinations with PI3K antagonists, development of mutant-selective PI3K inhibitors, and better patient selection should improve the success of these targeted agents against solid tumors.

PI3Kβ-A Versatile Transducer for GPCR, RTK, and Small GTPase Signaling

The phosphoinositide 3-kinase (PI3K) family includes eight distinct catalytic subunits and seven regulatory subunits. Only two PI3Ks are directly regulated downstream from G protein-coupled receptors (GPCRs): the class I enzymes PI3Kβ and PI3Kγ. Both enzymes produce phosphatidylinositol 3,4,5-trisposphate in vivo and are regulated by both heterotrimeric G proteins and small GTPases from the Ras or Rho families. However, PI3Kβ is also regulated by direct interactions with receptor tyrosine kinases (RTKs) and their tyrosine phosphorylated substrates, and similar to the class II and III PI3Ks, it binds activated Rab5. The unusually complex regulation of PI3Kβ by small and trimeric G proteins and RTKs leads to a rich landscape of signaling responses at the cellular and organismic levels. This review focuses first on the regulation of PI3Kβ activity in vitro and in cells, and then summarizes the biology of PI3Kβ signaling in distinct tissues and in human disease.

Targeting PI3K in cancer: mechanisms and advances in clinical trials

Phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling is one of the most important intracellular pathways, which can be considered as a master regulator for cancer. Enormous efforts have been dedicated to the development of drugs targeting PI3K signaling, many of which are currently employed in clinical trials evaluation, and it is becoming increasingly clear that PI3K inhibitors are effective in inhibiting tumor progression. PI3K inhibitors are subdivided into dual PI3K/mTOR inhibitors, pan-PI3K inhibitors and isoform-specific inhibitors. In this review, we performed a critical review to summarize the role of the PI3K pathway in tumor development, recent PI3K inhibitors development based on clinical trials, and the mechanisms of resistance to PI3K inhibition.

Autophagy Inhibition to Augment mTOR Inhibition: a Phase I/II Trial of Everolimus and Hydroxychloroquine in Patients with Previously Treated Renal Cell Carcinoma

PURPOSE

Everolimus inhibits the mTOR, activating cytoprotective autophagy. Hydroxychloroquine inhibits autophagy. On the basis of preclinical data demonstrating synergistic cytotoxicity when mTOR inhibitors are combined with an autophagy inhibitor, we launched a clinical trial of combined everolimus and hydroxychloroquine, to determine its safety and activity in patients with clear-cell renal cell carcinoma (ccRCC).

PATIENTS AND METHODS

Three centers conducted a phase I/II trial of everolimus 10 mg daily and hydroxychloroquine in patients with advanced ccRCC. The objectives were to determine the MTD of hydroxychloroquine with daily everolimus, and to estimate the rate of 6-month progression-free survival (PFS) in patients with ccRCC receiving everolimus/hydroxychloroquine after 1-3 prior treatment regimens. Correlative studies to identify patient subpopulations that achieved the most benefit included population pharmacokinetics, measurement of autophagosomes by electron microscopy, and next-generation tumor sequencing.

RESULTS

No dose-limiting toxicity was observed in the phase I trial. The recommended phase II dose of hydroxychloroquine 600 mg twice daily with everolimus was identified. Disease control [stable disease + partial response (PR)] occurred in 22 of 33 (67%) evaluable patients. PR was observed in 2 of 33 patients (6%). PFS ≥ 6 months was achieved in 15 of 33 (45%) of patients who achieved disease control.

CONCLUSIONS

Combined hydroxychloroquine 600 mg twice daily with 10 mg daily everolimus was tolerable. The primary endpoint of >40% 6-month PFS rate was met. Hydroxychloroquine is a tolerable autophagy inhibitor in future RCC or other trials.

Class I Phosphoinositide 3-Kinase PIK3CA/p110α and PIK3CB/p110β Isoforms in Endometrial Cancer

The phosphoinositide 3-kinase (PI3K) signalling pathway is highly dysregulated in cancer, leading to elevated PI3K signalling and altered cellular processes that contribute to tumour development. The pathway is normally orchestrated by class I PI3K enzymes and negatively regulated by the phosphatase and tensin homologue, PTEN. Endometrial carcinomas harbour frequent alterations in components of the pathway, including changes in gene copy number and mutations, in particular in the oncogene PIK3CA, the gene encoding the PI3K catalytic subunit p110α, and the tumour suppressor PTEN. PIK3CB, encoding the other ubiquitously expressed class I isoform p110β, is less frequently altered but the few mutations identified to date are oncogenic. This isoform has received more research interest in recent years, particularly since PTEN-deficient tumours were found to be reliant on p110β activity to sustain transformation. In this review, we describe the current understanding of the common and distinct biochemical properties of the p110α and p110β isoforms, summarise their mutations and highlight how they are targeted in clinical trials in endometrial cancer.

MaxMIF: A New Method for Identifying Cancer Driver Genes through Effective Data Integration

Identification of a few cancer driver mutation genes from a much larger number of passenger mutation genes in cancer samples remains a highly challenging task. Here, a novel method for distinguishing the driver genes from the passenger genes by effective integration of somatic mutation data and molecular interaction data using a maximal mutational impact function (MaxMIF) is presented. When evaluated on six somatic mutation datasets of Pan-Cancer and 19 datasets of different cancer types from TCGA, MaxMIF almost always significantly outperforms all the existing state-of-the-art methods in terms of predictive accuracy, sensitivity, and specificity. It recovers about 30% more known cancer genes in 500 top-ranked candidate genes than the best among the other tools evaluated. MaxMIF is also highly robust to data perturbation. Intriguingly, MaxMIF is able to identify potential cancer driver genes, with strong experimental data support. Therefore, MaxMIF can be very useful for identifying or prioritizing cancer driver genes in the increasing number of available cancer genomic data.

Combined Inhibition of PI3Kβ and mTOR Inhibits Growth of PTEN-null Tumors

Loss of the tumor suppressor PTEN confers a tumor cell dependency on the PI3Kβ isoform. Achieving maximal inhibition of tumor growth through PI3K pathway inhibition requires sustained inhibition of PI3K signaling; however, efficacy is often limited by suboptimal inhibition or reactivation of the pathway. To select combinations that deliver comprehensive suppression of PI3K signaling in PTEN-null tumors, the PI3Kβ inhibitor AZD8186 was combined with inhibitors of kinases implicated in pathway reactivation in an extended cell proliferation assay. Inhibiting PI3Kβ and mTOR gave the most effective antiproliferative effects across a panel of PTEN-null tumor cell lines. The combination of AZD8186 and the mTOR inhibitor vistusertib was also effective in vivo controlling growth of PTEN-null tumor models of TNBC, prostate, and renal cancers. In vitro, the combination resulted in increased suppression of pNDRG1, p4EBP1, as well as HMGCS1 with reduced pNDRG1 and p4EBP1 more closely associated with effective suppression of proliferation. In vivo biomarker analysis revealed that the monotherapy and combination treatment consistently reduced similar biomarkers, while combination increased nuclear translocation of the transcription factor FOXO3 and reduction in glucose uptake. These data suggest that combining the PI3Kβ inhibitor AZD8186 and vistusertib has potential to be an effective combination treatment for PTEN-null tumors. Mol Cancer Ther; 17(11); 2309-19. ©2018 AACR.

[Clinical Significance and Mechanism of PI3K p110β Overexpression in Non-small Cell Lung Cancer]

BACKGROUND

Phosphatidylinositide 3-kinases (PI3K) pathway is one of the most important pathway in cells, which plays an important role in proliferation, growth, differentiation and mobility of cells. The aberrant activation of PI3K pathway was exsited in 50%-70% cases of non-small cell lung cancer (NSCLC). As the key point in PI3K pathway, expression of PI3K plays a critical role in activity of the pathway, which is closely related with the initiation and development of NSCLC, furthermore with the response of tumor to target treatment. Our study is to analyze the clinical significance and mechanism of PI3K p110β overexpression in NSCLC.

METHODS

Expression of p110β and other proteins in PI3K pathway were detected by immunohistochemistry in 170 cases of NSCLC. Correlation between expression of p110β and clinicopathological characteristics of patients as well as expression of other proteins in PI3K pathway was analyzed.

RESULTS

In 170 NSCLC, overexpression of p110β was found in 41.8% of cases. Correlation between overexpression of p110β and Ki 67 index was significant (P=0.040). No significant difference of p110 expression were observed among different cohorts of gender, age, smoking status, classification, grade and stage (P>0.05). Correlation between expression of p110β and other proteins in PI3K pathway was various, positively correlated with PTEN loss (P<0.001) and negatively correlated with mutant EGFR (P=0.022), while not correlated with P-Akt (Ser473), HER2, ALK, ROS1 and wild type EGFR (P>0.05).

CONCLUSIONS

Overexpression of p110β is frequently detected in NSCLC. It is closely related with PTEN loss NSCLC, which shows that it plays an important role in maintaining and developing of tumors driven by PTEN loss. It initiates the proliferation of tumor cells in NSCLC without phosphorylating Akt. PIK3CB mutation is not the major cause of overexpression of p110β. Dysregulation of receptor tyrosine kinases (RTKs) doesn't show potential of increasing p110β level in cancer tissue, furthermore the expression of p110β in tumors with EGFR mutation is lower than in tumors without EGFR mutation.

RNA-Seq of Circulating Tumor Cells in Stage II-III Breast Cancer

BACKGROUND

We characterized the whole transcriptome of circulating tumor cells (CTCs) in stage II-III breast cancer to evaluate correlations with primary tumor biology.

METHODS

CTCs were isolated from peripheral blood (PB) via immunomagnetic enrichment followed by fluorescence-activated cell sorting (IE/FACS). CTCs, PB, and fresh tumors were profiled using RNA-seq. Formalin-fixed, paraffin-embedded (FFPE) tumors were subjected to RNA-seq and NanoString PAM50 assays with risk of recurrence (ROR) scores.

RESULTS

CTCs were detected in 29/33 (88%) patients. We selected 21 cases to attempt RNA-seq (median number of CTCs = 9). Sixteen CTC samples yielded results that passed quality-control metrics, and these samples had a median of 4,311,255 uniquely mapped reads (less than PB or tumors). Intrinsic subtype predicted by comparing estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) versus PAM50 for FFPE tumors was 85% concordant. However, CTC RNA-seq subtype assessed by the PAM50 classification genes was highly discordant, both with the subtype predicted by ER/PR/HER2 and by PAM50 tumors. Two patients died of metastatic disease, both of whom had high ROR scores and high CTC counts. We identified significant genes, canonical pathways, upstream regulators, and molecular interaction networks comparing CTCs by various clinical factors. We also identified a 75-gene signature with highest expression in CTCs and tumors taken together that was prognostic in The Cancer Genome Atlas and Molecular Taxonomy of Breast Cancer International Consortium datasets.

CONCLUSION

It is feasible to use RNA-seq of CTCs in non-metastatic patients to discover novel tumor biology characteristics.

Phosphatidyl inositol-3 kinase (PIK3CA) E545K mutation confers cisplatin resistance and a migratory phenotype in cervical cancer cells

The phosphatidylinositol-3 kinase (PI3K)/Akt/mTOR signaling pathway is activated in many human cancers. Previously, we reported that patients with early stage cervical cancer whose tumours harbour PIK3CA exon 9 or 20 mutations have worse overall survival in response to treatment with radiation and cisplatin than patients with wild-type PIK3CA. The purpose of this study was to determine whether PIK3CA-E545K mutation renders cervical cancer cells more resistant to cisplatin and/or radiation, and whether PI3K inhibition reverses the phenotype. We found that CaSki cells that are heterozygous for the PIK3CA-E545K mutation are more resistant to cisplatin or cisplatin plus radiation than either HeLa or SiHa cells that express only wild-type PIK3CA. Similarly, HeLa cells engineered to stably express PIK3CA-E545K were more resistant to cisplatin or cisplatin plus radiation than cells expressing only wild-type PIK3CA or with PIK3CA depleted. Cells expressing the PIK3CA-E545K mutation also had constitutive PI3K pathway activation and increased cellular migration and each of these phenotypes was reversed by treatment with the PI3K inhibitor GDC-0941/Pictilisib. Our results suggests that cervical cancer patients whose tumours are positive for the PIK3CA-E545K mutation may benefit from PI3K inhibitor therapy in concert with standard cisplatin and radiation therapy.

Phosphorylation of PI3K regulatory subunit p85 contributes to resistance against PI3K inhibitors in radioresistant head and neck cancer

OBJECTIVES

PI3K/Akt/mTOR pathway is commonly activated in most cancers and is correlated with resistance to anticancer therapies such as radiotherapy. Therefore, PI3K is an attractive target for treating PI3K-associated cancers.

MATERIAL AND METHODS

We investigated the basal expression and the expression after treatment of PI3K inhibitor or Src inhibitor of PI3K/Akt pathway-related proteins in AMC-HN3, AMC-HN3R, HN30 and HN31 cells by performing immunoblotting analysis. The sensitivity to PI3K inhibitors or Src inhibitor was analyzed by MTT assay and clonogenic assay. To determine the antitumoral activity of combination treatment with PI3K inhibitor and Src inhibitor, we used using xenograft mouse model.

RESULTS

We found that PI3K regulatory subunit p85 was predominantly phosphorylated in radioresistant head and neck cancer cell line (HN31), which showed resistance to PI3K inhibitors. Next, we investigated mechanism through which PI3K p85 phosphorylation modulated response to PI3K inhibitors. Of note, constitutive activation of Src was found in HN31 cells and upon PI3K inhibitor treatment, restoration of p-Src was occurred. Src inhibitor improved the efficacy of PI3K inhibitor treatment and suppressed the reactivation of both Src and PI3K p85 in HN31 cells. Furthermore, downregulation of PI3K p85 expression by using a specific siRNA suppressed Src phosphorylation.

CONCLUSIONS

Together, our results imply the novel role of the PI3K regulatory subunit p85 in the development of resistance to PI3K inhibitors and suggest the presence of a regulatory loop between PI3K p85 and Src in radioresistant head and neck cancers with constitutively active PI3K/Akt pathway.

Functional characterization of a novel somatic oncogenic mutation of PIK3CB

Class I phosphoinositide 3-kinase (PI3K) enzymes have attracted considerable attention as drug targets in cancer therapy over the last 20 years. The signaling pathway triggered by class I PI3Ks is dysregulated in a range of tumor types, impacting cell proliferation, survival and apoptosis. Frequent oncogenic mutations of PIK3CA have previously been discovered. In contrast, reports of PIK3CB mutations have been limited; however, in most cases, those that have been identified have been shown to be activating and oncogenic. The functional characterization of a PIK3CB catalytic domain mutant, p110β^E1051K, first discovered by others in castrate-resistant prostate cancer (mCRPC), is outlined in this report; our data suggest that p110β^E1051K is a gain-of-function mutation, driving PI3K signaling, tumorigenic cell growth and migration. Tumor cells expressing p110β^E1051K are sensitive to p110β inhibition; its characterization as an oncogenic driver adds to the rationale for targeting p110β and indicates a continuing need to further develop specific PI3K inhibitors for clinical development in cancer therapy.

The Role of Class IA Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunits in Glioblastoma

Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) plays a critical role in the pathogenesis of cancer including glioblastoma, the most common and aggressive form of brain cancer. Targeting the PI3K pathway to treat glioblastoma has been tested in the clinic with modest effect. In light of the recent finding that PI3K catalytic subunits (PIK3CA/p110α, PIK3CB/p110β, PIK3CD/p110δ, and PIK3CG/p110γ) are not functionally redundant, it is imperative to determine whether these subunits play divergent roles in glioblastoma and whether selectively targeting PI3K catalytic subunits represents a novel and effective strategy to tackle PI3K signaling. This article summarizes recent advances in understanding the role of PI3K catalytic subunits in glioblastoma and discusses the possibility of selective blockade of one PI3K catalytic subunit as a treatment option for glioblastoma.

High-depth sequencing of paired primary and metastatic tumours: Implications for personalised medicine

BACKGROUND

Next-generation sequencing of large panel of genes had been associated with clinical benefit in a significant proportion of patients with advanced cancer. However, the molecular profile of the primary tumour from the initial surgical specimen might significantly differ from the molecular profile in a tumour sample obtained from a biopsy of a metastatic site.

PATIENTS AND METHODS

We compare the genetic profile of primary tumours and paired metastases by using a large panel of cancer genes. Training and validation set including a total of 152 primary and metastatic tumour pairs were sequenced (up to 429 genes) focussing on variants described in the Catalogue of Somatic Mutations in Cancer (COSMIC).

RESULTS

Training and validation set including a total of 152 primary and metastatic tumour pairs were sequenced focussing on variants described in COSMIC. Agreement rate between the couples of primary and metastasis on COSMIC variants was 65% (24/37) and 43% (49/115) in the training and validation cohort, respectively. That rose to 74% (20/27) and 58% (42/73) when focussing on targetable mutations. In five cases, the discordance was related to appearance of secondary resistance mutation, giving a targetable refined agreement rate of 67% (67/100).

CONCLUSION

Up to 40% of paired primary tumour/metastases have discordant molecular profile. Liquid biopsies may overcome, in the near future, the limits of tumour tissue genotyping.

The PI3K Pathway in Human Disease

Phosphoinositide 3-kinase (PI3K) activity is stimulated by diverse oncogenes and growth factor receptors, and elevated PI3K signaling is considered a hallmark of cancer. Many PI3K pathway-targeted therapies have been tested in oncology trials, resulting in regulatory approval of one isoform-selective inhibitor (idelalisib) for treatment of certain blood cancers and a variety of other agents at different stages of development. In parallel to PI3K research by cancer biologists, investigations in other fields have uncovered exciting and often unpredicted roles for PI3K catalytic and regulatory subunits in normal cell function and in disease. Many of these functions impinge upon oncology by influencing the efficacy and toxicity of PI3K-targeted therapies. Here we provide a perspective on the roles of class I PI3Ks in the regulation of cellular metabolism and in immune system functions, two topics closely intertwined with cancer biology. We also discuss recent progress developing PI3K-targeted therapies for treatment of cancer and other diseases.

Targeting the mTOR pathway in breast cancer

Mechanistic target of rapamycin controls cell growth, metabolism, and aging in response to nutrients, cellular energy stage, and growth factors. In cancers including breast cancer, mechanistic target of rapamycin is frequently upregulated. Blocking mechanistic target of rapamycin with rapamycin, first-generation and second-generation mechanistic target of rapamycin inhibitors, called rapalogs, have shown potent reduction of breast cancer tumor growth in preclinical models and clinical trials. In this review, we summarize the fundamental role of the mechanistic target of rapamycin pathway in driving breast tumors. Moreover, we also review key molecules involved with aberrant mechanistic target of rapamycin pathway activation in breast cancer and current efforts to target these components for therapeutic gain. Further development of predictive biomarkers will be useful in the selection of patients who will benefit from inhibition of the mechanistic target of rapamycin pathway.

A First-Time-in-Human Study of GSK2636771, a Phosphoinositide 3 Kinase Beta-Selective Inhibitor, in Patients with Advanced Solid Tumors

Background: The PI3K/protein kinase B (AKT) pathway is commonly activated in several tumor types. Selective targeting of p110β could result in successful pathway inhibition while avoiding the on- and off-target effects of pan-PI3K inhibitors. GSK2636771 is a potent, orally bioavailable, adenosine triphosphate-competitive, selective inhibitor of PI3Kβ.Methods: We evaluated the safety, pharmacokinetics, pharmacodynamics and antitumor activity of GSK2636771 to define the recommended phase II dose (RP2D). During the dose-selection and dose-escalation stages (parts 1 and 2), patients with PTEN-deficient advanced solid tumors received escalating doses of GSK2636771 (25-500 mg once daily) using a modified 3+3 design to determine the RP2D; tumor type-specific expansion cohorts (part 3) were implemented to further assess tumor responses at the RP2D.Results: A total of 65 patients were enrolled; dose-limiting toxicities were hypophosphatemia and hypocalcemia. Adverse events included diarrhea (48%), nausea (40%), and vomiting (31%). Single- and repeat-dose exposure increased generally dose proportionally. GSK2636771 400 mg once daily was the RP2D. Phospho/total AKT ratio decreased with GSK2636771 in tumor and surrogate tissue. A castrate-resistant prostate cancer (CRPC) patient harboring PIK3CB amplification had a partial response for over a year; an additional 10 patients derived durable (≥24 weeks) clinical benefit, including two other patients with CRPC with PIK3CB alterations (≥34 weeks). GSK2636771 400 mg once daily orally induced sufficient exposure and target inhibition with a manageable safety profile.Conclusions: Genomic aberrations of PIK3CB may be associated with clinical benefit from GSK2636771. Clin Cancer Res; 23(19); 5981-92. ©2017 AACR.

PI3Kδ inhibitor idelalisib in combination with BTK inhibitor ONO/GS-4059 in diffuse large B cell lymphoma with acquired resistance to PI3Kδ and BTK inhibitors

Activated B-cell-like diffuse large B-cell lymphoma relies on B-cell receptor signaling to drive proliferation and survival. Downstream of the B-cell receptor, the key signaling kinases Bruton’s tyrosine kinase and phosphoinositide 3-kinase δ offer opportunities for therapeutic intervention by agents such as ibrutinib, ONO/GS-4059, and idelalisib. Combination therapy with such targeted agents could provide enhanced efficacy due to complimentary mechanisms of action. In this study, we describe both the additive interaction of and resistance mechanisms to idelalisib and ONO/GS-4059 in a model of activated B-cell-like diffuse large B-cell lymphoma. Significant tumor regression was observed with a combination of PI3Kδ and Bruton’s tyrosine kinase inhibitors in the mouse TMD8 xenograft. Acquired resistance to idelalisib in the TMD8 cell line occurred by loss of phosphatase and tensin homolog and phosphoinositide 3-kinase pathway upregulation, but not by mutation of PIK3CD. Sensitivity to idelalisib could be restored by combining idelalisib and ONO/GS-4059. Further evaluation of targeted inhibitors revealed that the combination of idelalisib and the phosphoinositide-dependent kinase-1 inhibitor GSK2334470 or the AKT inhibitor MK-2206 could partially overcome resistance. Characterization of acquired Bruton’s tyrosine kinase inhibitor resistance revealed a novel tumor necrosis factor alpha induced protein 3 mutation (TNFAIP3 Q143*), which led to a loss of A20 protein, and increased p-IκBα. The combination of idelalisib and ONO/GS-4059 partially restored sensitivity in this resistant line. Additionally, a mutation in Bruton’s tyrosine kinase at C481F was identified as a mechanism of resistance. The combination activity observed with idelalisib and ONO/GS-4059, taken together with the ability to overcome resistance, could lead to a new therapeutic option in activated B-cell-like diffuse large B-cell lymphoma. A clinical trial is currently underway to evaluate the combination of idelalisib and ONO/GS-4059 (NCT02457598).

Phosphoproteome Profiling Reveals Molecular Mechanisms of Growth-Factor-Mediated Kinase Inhibitor Resistance in EGFR-Overexpressing Cancer Cells

Although substantial progress has been made regarding the use of molecularly targeted cancer therapies, resistance almost invariably develops and presents a major clinical challenge. The tumor microenvironment can rescue cancer cells from kinase inhibitors by growth-factor-mediated induction of pro-survival pathways. Here we show that epidermal growth factor receptor (EGFR) inhibition by Gefitinib is counteracted by growth factors, notably FGF2, and we assessed the global molecular consequences of this resistance at the proteome and phosphoproteome level in A431 cells. Tandem mass tag peptide labeling and quantitative mass spectrometry allowed the identification and quantification of 22 000 phosphopeptides and 8800 proteins in biological triplicates without missing values. The data show that FGF2 protects the cells from the antiproliferative effect of Gefitinib and largely prevents reprogramming of the proteome and phosphoproteome. Simultaneous EGFR/FGFR or EGFR/GSG2 (Haspin) inhibition overcomes this resistance, and the phosphoproteomic experiments further prioritized the RAS/MEK/ERK as well as the PI3K/mTOR axis for combination treatment. Consequently, the MEK inhibitor Trametinib prevented FGF2-mediated survival of EGFR inhibitor-resistant cells when used in combination with Gefitinib. Surprisingly, the PI3K/mTOR inhibitor Omipalisib reversed resistance mediated by all four growth factors tested, making it an interesting candidate for mitigating the effects of the tumor microenvironment.