Inhibiting PI3Kβ with AZD8186 Regulates Key Metabolic Pathways in PTEN-Null Tumors

Development of PI3Kγ selective inhibitors: the strategies and application

The γ isoform of Class I PI3Ks (PI3Kγ) is primarily found in leukocytes and is essential for the function of myeloid cells, as it regulates the migration, differentiation, and activation of myeloid-lineage immune cells. Thus, PI3Kγ has been identified as a promising drug target for the treatment of inflammation, autoimmune disease, and immuno-oncology. Due to the high incidence of serious adverse events (AEs) associated with PI3K inhibitors, in the development of PI3Kγ inhibitors, isoform selectivity was deemed crucial. In this review, an overview of the development of PI3Kγ selective inhibitors in the past years is provided. The isoform selectivity of related drugs was achieved by different strategies, including inducing a specificity pocket by a propeller-shape structure, targeting steric differences in the solvent channel, and modulating the conformation of the Asp-Phe-Gly DFG motif, which have been demonstrated feasible by several successful cases. The insights in this manuscript may provide a potential direction for rational drug design and accelerate the discovery of PI3Kγ selective inhibitors.

Development of small-molecule inhibitors that target PI3Kβ

Phosphatidylinositol-3 kinase (PI3K) β, a subtype of class I PI3Ks, has an essential role in PTEN-deficient tumors and links to thrombosis, male fertility, and Fragile X syndrome. PI3Kβ-specific targeting therapy could be an efficacious treatment for diseases highly dependent on PI3Kβ, while mitigating the severe toxicity of pan-PI3K inhibitors. Achieving selectivity can be accomplished through three primary strategies, namely, binding to the induced lipophilic pocket, targeting the unique amino acid residue of PI3Kβ, or using atropisomerism to lock conformation. In this review, we focus on advances in the development of these β-isoform-selective PI3K inhibitors, providing potential guidance for the further development of novel clinical candidates.

IGFBP2 from a novel copper metabolism-associated biomarker promoted glioma progression and response to immunotherapy

Introduction

Copper metabolism encompasses all cellular metabolic processes involving copper ions and plays a significant role in the pathogenesis of diseases, including cancer. Furthermore, copper is intricately involved in various processes related to nucleotide metabolism. However, a comprehensive analysis of copper metabolism in gliomas remains lacking despite its importance.

Methods

To address this gap, glioma patients were stratified based on the expression levels of copper metabolism-related genes. By utilizing machine learning techniques, a novel copper metabolism-associated biomarker was developed. The potential of this biomarker in prognosis, mutation analysis, and predicting immunotherapy response efficiency in gliomas was systematically investigated.

Results

Notably, IGFBP2, identified as a glioma tumor promoter, was found to promote disease progression and influence immunotherapy response. Additionally, glioma-derived IGFBP2 was observed to enhance microglial migration. High IGFBP2 expression in GBM cells facilitated macrophage interactions through the EGFR, CD63, ITGB1, and CD44 signaling pathways. Discussion: Overall, the copper metabolism-associated biomarker shows promising potential to enhance the clinical management of gliomas, offering valuable insights into disease prognosis and treatment strategies.

By using machine learning and in vitro testing, SERPINH1 functions as a novel tumorigenic and immunogenic gene and predicts immunotherapy response in osteosarcoma

Introduction

The most prevalent bone tumor with a relatively high level of aggressiveness and malignancy is osteosarcoma. The characteristics of the serpin family in osteosarcoma have not been defined.

Methods

In this study, the predictive significance of the serpin superfamily was investigated in the osteosarcoma and Gene Expression Omnibus (GEO) databases from The Cancer Genome Atlas (TCGA).

Results

It was discovered that SERPINH1 is a significant biological marker in osteosarcoma. According to the CCK-8, EdU, and Transwell assays as well as the IHC assay, SERPINH1 may promote osteosarcoma proliferation and migration. It is also more expressed in tumor samples than in healthy samples. SERPINH1 might forecast the effects of immunotherapy. Additionally, immune cells are interacted with through checkpoint, cytokine, and growth factor pathways in osteosarcomas with high SERPINH1 levels. The biological function, immunological characteristics, and treatment response (immunotherapy and chemotherapy responses) of patients with osteosarcoma were successfully predicted using a model related to SERPINH1. SERPINH1 and the SERPINH1-related score predict ferroptosis/pyroptosis/apoptosis/necroptosis in osteosarcoma.

Discussion

The SERPINH1-related score was an effective method for identifying osteosarcoma patients who would respond to immunotherapy and chemotherapy, as well as for predicting the survival outcomes of such patients.

Targeting Class I-II-III PI3Ks in Cancer Therapy: Recent Advances in Tumor Biology and Preclinical Research

Phosphatidylinositol-3-kinase (PI3K) enzymes, producing signaling phosphoinositides at plasma and intracellular membranes, are key in intracellular signaling and vesicular trafficking pathways. PI3K is a family of eight enzymes divided into three classes with various functions in physiology and largely deregulated in cancer. Here, we will review the recent evidence obtained during the last 5 years on the roles of PI3K class I, II and III isoforms in tumor biology and on the anti-tumoral action of PI3K inhibitors in preclinical cancer models. The dependency of tumors to PI3K isoforms is dictated by both genetics and context (e.g., the microenvironment). The understanding of class II/III isoforms in cancer development and progression remains scarce. Nonetheless, the limited available data are consistent and reveal that there is an interdependency between the pathways controlled by all PI3K class members in their role to promote cancer cell proliferation, survival, growth, migration and metabolism. It is unknown whether this feature contributes to partial treatment failure with isoform-selective PI3K inhibitors. Hence, a better understanding of class II/III functions to efficiently inhibit their positive and negative interactions with class I PI3Ks is needed. This research will provide the proof-of-concept to develop combination treatment strategies targeting several PI3K isoforms simultaneously.

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.

mTOR inhibition amplifies the anti-lymphoma effect of PI3Kβ/δ blockage in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is an aggressive disease that exhibits constitutive activation of phosphoinositide 3-kinase (PI3K) driven by chronic B-cell receptor signaling or PTEN deficiency. Since pan-PI3K inhibitors cause severe side effects, we investigated the anti-lymphoma efficacy of the specific PI3Kβ/δ inhibitor AZD8186. We identified a subset of DLBCL models within activated B-cell-like (ABC) and germinal center B-cell-like (GCB) DLBCL that were sensitive to AZD8186 treatment. On the molecular level, PI3Kβ/δ inhibition decreased the pro-survival NF-κB and AP-1 activity or led to downregulation of the oncogenic transcription factor MYC. In AZD8186-resistant models, we detected a feedback activation of the PI3K/AKT/mTOR pathway following PI3Kβ/δ inhibition, which limited AZD8186 efficacy. The combined treatment with AZD8186 and the mTOR inhibitor AZD2014 overcame resistance to PI3Kβ/δ inhibition and completely prevented outgrowth of lymphoma cells in vivo in cell line- and patient-derived xenograft mouse models. Collectively, our study reveals that subsets of DLBCLs are addicted to PI3Kβ/δ signaling and thus identifies a previously unappreciated role of the PI3Kβ isoform in DLBCL survival. Furthermore, our data demonstrate that combined targeting of PI3Kβ/δ and mTOR is effective in all major DLBCL subtypes supporting the evaluation of this strategy in a clinical trial setting.

Untargeted stable isotope-resolved metabolomics to assess the effect of PI3Kβ inhibition on metabolic pathway activities in a PTEN null breast cancer cell line

The combination of high-resolution LC-MS untargeted metabolomics with stable isotope-resolved tracing is a promising approach for the global exploration of metabolic pathway activities. In our established workflow we combine targeted isotopologue feature extraction with the non-targeted X¹³CMS routine. Metabolites, detected by X¹³CMS as differentially labeled between two biological conditions are subsequently integrated into the original targeted library. This strategy enables monitoring of changes in known pathways as well as the discovery of hitherto unknown metabolic alterations. Here, we demonstrate this workflow in a PTEN (phosphatase and tensin homolog) null breast cancer cell line (MDA-MB-468) exploring metabolic pathway activities in the absence and presence of the selective PI3Kβ inhibitor AZD8186. Cells were fed with [U-¹³C] glucose and treated for 1, 3, 6, and 24 h with 0.5 µM AZD8186 or vehicle, extracted by an optimized sample preparation protocol and analyzed by LC-QTOF-MS. Untargeted differential tracing of labels revealed 286 isotope-enriched features that were significantly altered between control and treatment conditions, of which 19 features could be attributed to known compounds from targeted pathways. Other 11 features were unambiguously identified based on data-dependent MS/MS spectra and reference substances. Notably, only a minority of the significantly altered features (11 and 16, respectively) were identified when preprocessing of the same data set (treatment vs. control in 24 h unlabeled samples) was performed with tools commonly used for label-free (i.e. w/o isotopic tracer) non-targeted metabolomics experiments (Profinder´s batch recursive feature extraction and XCMS). The structurally identified metabolites were integrated into the existing targeted isotopologue feature extraction workflow to enable natural abundance correction, evaluation of assay performance and assessment of drug-induced changes in pathway activities. Label incorporation was highly reproducible for the majority of isotopologues in technical replicates with a RSD below 10%. Furthermore, inter-day repeatability of a second label experiment showed strong correlation (Pearson R² > 0.99) between tracer incorporation on different days. Finally, we could identify prominent pathway activity alterations upon PI3Kβ inhibition. Besides pathways in central metabolism, known to be changed our workflow revealed additional pathways, like pyrimidine metabolism or hexosamine pathway. All pathways identified represent key metabolic processes associated with cancer metabolism and therapy.

Inhibition of MyD88 attenuates angiotensin II-induced hypertensive kidney disease via regulating renal inflammation

BACKGROUND

Kidney damage is a frequent event in the course of hypertension. Recent researches highlighted a critical role of non-hemodynamic activities of angiotensin II (Ang II) in hypertension-associated kidney fibrosis and inflammation. These activities are mediated through toll-like receptors (TLRs) but the mechanisms by which Ang II links TLRs to downstream inflammatory and fibrogenic responses is not fully known. In this study, we investigated the role of TLR adapter protein called myeloid differentiation primary-response protein-88 (MyD88) as the potential link.

METHODS

C57BL/6 mice were administered Ang II by micro-osmotic pump infusion for 4 weeks to develop nephropathy. Mice were treated with small-molecule MyD88 inhibitor LM8. In vitro, MyD88 was blocked using siRNA or LM8 in Ang II-challenged renal tubular epithelial cells.

RESULTS

We show that MyD88 is mainly located in tubular epithelial cells and Ang II increases the interaction between TLR4 and MyD88. This interaction activates MAPKs and nuclear factor-κB (NF-κB), leading to increased production of inflammatory and fibrogenic factors. Inhibition of MyD88 by siRNA or selective inhibitor LM8 supresses MyD88-TLR4 interaction, NF-κB activation, and elaboration of inflammatory cytokines and fibrosis-associated factors. These protective actions resulted in decreased renal pathological changes and preserved renal function in LM8-treated hypertensive mice, without affecting hypertension.

CONCLUSION

These results demonstrate that Ang II induces inflammation and fibrosis in renal tubular epithelial cells through MyD88 and present MyD88 as a potential point of intervention for hypertension-associated kidney disease.

Prognosis and Dissection of Immunosuppressive Microenvironment in Breast Cancer Based on Fatty Acid Metabolism-Related Signature

Fatty acid metabolism has been deciphered to augment tumorigenesis and disease progression in addition to therapy resistance via strengthened lipid synthesis, storage, and catabolism. Breast cancer is strongly associated with the biological function of fatty acid metabolism owing to the abundant presence of adipocytes in breast tissue. It has been unraveled that tumor cells exhibit considerable plasticity based on fatty acid metabolism, responding to extra-tumoral and a range of metabolic signals, in which tumor microenvironment plays a pivotal role. However, the prognostic significance of fatty acid metabolism in breast cancer remains to be further investigated. Alongside these insights, we retrieved 269 reliable fatty acid metabolism-related genes (FMGs) and identified the landscape of copy number variations and expression level among those genes. Additionally, 11 overall survival-related FMGs were clarified by univariate Cox hazards regression analysis in The Cancer Genome Atlas (TCGA) and the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) databases. Subsequently, a prognostic signature based on 6 overall survival (OS)-related FMGs was generated using Lasso Cox hazards regression analysis in TCGA dataset and was validated in two external cohorts. The correlation between the signature and several essential clinical parameters, including T, N, and PAM50 subtypes, was unveiled by comparing the accumulating signature value in various degrees. Furthermore, an optimal nomogram incorporating the signature, age, and American Joint Committee on Cancer (AJCC) stage was constructed, and the discrimination was verified by C-index, the calibration curve, and the decision curve analysis. The underlying implications for immune checkpoints inhibitors, the landscape of tumor immune microenvironment, and the predictive significance in therapy resistance to diverse strategies were depicted ultimately. In conclusion, our findings indicate the potential prognostic connotation of fatty acid metabolism in breast cancer, supporting novel insights into breast cancer patients’ prognosis and administrating effective immunotherapy.

Actionability evaluation of biliary tract cancer by genome transcriptome analysis and Asian cancer knowledgebase

INTRODUCTION

Treatment options for biliary tract cancer (BTC) are very limited. It is necessary to investigate actionable genes and candidate drugs using a sophisticated knowledgebase (KB) and characterize BTCs immunologically for evaluating the actionability of molecular and immune therapies.

MATERIALS AND METHODS

The genomic and transcriptome data of 219 patients with BTC who underwent surgery were analyzed. Actionable mutations and candidate drugs were annotated using the largest available KB of the Asian population (CancerSCAN^®). Predictive biomarkers of immune checkpoint inhibitors were analyzed using DNA and RNA sequencing data.

RESULTS

Twenty-two actionable genes and 43 candidate drugs were annotated in 74 patients (33.8%). The most frequent actionable genes were PTEN (7.3%), CDKN2A (6.8%), KRAS (6.4%). BRCA2, CDKN2A, and FGFR2 mutations were most frequently identified in case of intrahepatic cholangiocarcinoma. PTEN and CDKN2A mutations were associated with significantly shorter overall survival. PD-L1 and PD-1 expression was significantly higher in case of extrahepatic cholangiocarcinoma and T-cell-high expression. In total, 49.7% of cases were evaluated as having actionability for molecular therapy or immune checkpoint inhibitors.

CONCLUSIONS

Identifying actionable genes and candidate drugs using the KB contribute to the development of therapeutic drugs and personalized treatment for BTC.

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.

Genetic variants in the cholesterol biosynthesis pathway genes and risk of prostate cancer

Previous studies have found the relationship between cholesterol biosynthesis pathway genes and the risk or prognosis of prostate cancer (PCa), while there is no definite evidence that genetic variants in the cholesterol biosynthesis pathway gene is related to PCa risk. Consequently, we performed this study to explore the associations of single-nucleotide polymorphisms (SNPs) in the cholesterol biosynthesis pathway with PCa risk. We systematically evaluated the association of SNPs in 21 cholesterol biosynthesis pathway genes with the risk of PCa using the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial database using a logistic regression model. Gene expression data of PCa from Gene Expression Omnibus (GEO) datasets and the Cancer Genome Atlas (TCGA) database were applied for mRNA expression analysis. The TCGA database was used to perform expression quantitative trait loci (eQTL) analysis. The interaction between demographic factors and SNPs was analyzed using two-by-four tables. We found T allele of rs67415672 in HMGCS1 is a significant protective allele of PCa [adjusted odds ratio (OR) = 0.90, 95% confidence interval (CI) = 0.83-0.97, P = 4.16 × 10^-3]. Moreover, rs67415672 was an eQTL for HMGCS1 (P = 2.23 × 10^-6). The expression of HMGCS1 significantly decreased in PCa primary tumors than that in normal tissues. These findings indicated that the HMGCS1 rs67415672 might be possible functional susceptibility loci for PCa.

Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss

Background: PTEN-deficient tumors are dependent on PI3Kβ activity, making PI3Kβ a compelling target. We evaluated the efficacy of PI3Kβ inhibitor AZD8186 on tumors with PTEN loss. Results: In vitro cell viability assay and immunoblotting demonstrated that PTEN loss was significantly correlated with AZD8186 sensitivity in triple negative breast cancer (TNBC) cell lines. Colony formation assay confirmed sensitivity of PTEN-deficient cell lines to AZD8186. AZD8186 inhibited PI3K signaling in PTEN loss TNBC cells. AZD8186 in combination with paclitaxel, eribulin had synergistic effects on growth inhibition in PTEN loss cells. AZD8186 promoted apoptosis in PTEN loss cells which was synergized by paclitaxel. In vivo, AZD8186 had limited activity as a single agent, but enhanced antitumor activity when combined with paclitaxel in MDA-MB-436 and MDA-MB-468 cell-line xenografts. AZD8186 significantly enhanced antitumor efficacy of anti-PD1 antibodies in the PTEN-deficient BP murine melanoma xenograft model, but not in the PTEN-wild-type CT26 xenograft model. Methods: In vitro, cell proliferation and colony formation assays were performed to determine cell sensitivity to AZD8186. Immunoblotting was performed to assess PTEN expression and PI3K signaling activity. FACS was performed to evaluate apoptosis. In vivo, antitumor efficacy of AZD8186 and its combinations were evaluated. Conclusions: AZD8186 has single agent efficacy in PTEN-deficient TNBC cell lines in vitro, but has limited single agent efficacy in vivo. However, AZD8186 has enhanced efficacy when combined with paclitaxel and anti-PD1 in vivo. Further study is needed to determine optimal combination therapies for PTEN-deficient solid tumors.

Statin Use Is Associated with Lower Risk of PTEN-Null and Lethal Prostate Cancer

PURPOSE

Statins are associated with lower risk of aggressive prostate cancer, but lethal prostate cancer is understudied and contributing mechanisms are unclear. We prospectively examined statins and lethal prostate cancer risk in the Health Professionals Follow-up Study (HPFS), tested associations with molecular subtypes, and integrated gene expression profiling to identify putative mechanisms.

EXPERIMENTAL DESIGN

Our study included 44,126 men cancer-free in 1990, followed for prostate cancer incidence through 2014, with statin use recorded on biennial questionnaires. We used multivariable Cox regression to examine associations between statins and prostate cancer risk overall, by measures of clinically significant disease, and by ERG and PTEN status. In an exploratory analysis, age-adjusted gene set enrichment analysis identified statin-associated pathways enriched in tumor and adjacent normal prostate tissue.

RESULTS

During 24 years of follow-up, 6,305 prostate cancers were diagnosed and 801 (13%) were lethal (metastatic at diagnosis or metastatic/fatal during follow-up). Relative to never/past use, current statin use was inversely associated with risk of lethal prostate cancer [HR, 0.76; 95% confidence interval (CI), 0.60-0.96] but not overall disease. We found a strong inverse association for risk of PTEN-null cancers (HR, 0.40; 95% CI, 0.19-0.87) but not PTEN-intact cancers (HR, 1.18; 95% CI, 0.95-1.48; P heterogeneity = 0.01). Associations did not differ by ERG. Inflammation and immune pathways were enriched in normal prostate tissue of statin ever (n = 10) versus never users (n = 103).

CONCLUSIONS

Molecular tumor classification identified PTEN and inflammation/immune activation as potential mechanisms linking statins with lower lethal prostate cancer risk. These findings support a potential causal association and could inform selection of relevant biomarkers for statin clinical trials.

Discovery of 3-Oxabicyclo[4.1.0]heptane, a Non-nitrogen Containing Morpholine Isostere, and Its Application in Novel Inhibitors of the PI3K-AKT-mTOR Pathway

4-(Pyrimidin-4-yl)morpholines are privileged pharmacophores for PI3K and PIKKs inhibition by virtue of the morpholine oxygen, both forming the key hydrogen bonding interaction and conveying selectivity over the broader kinome. Key to the morpholine utility as a kinase hinge binder is its ability to adopt a coplanar conformation with an adjacent aromatic core favored by the morpholine nitrogen nonbonding pair of electrons interacting with the electron deficient pyrimidine π-system. Few selective morpholine replacements have been identified to date. Herein we describe the discovery of a potent non-nitrogen containing morpholine isostere with the ability to mimic this conformation and its application in a potent selective dual inhibitor of mTORC1 and mTORC2 (29b).

PI3Kα/δ inhibition promotes anti-tumor immunity through direct enhancement of effector CD8+ T-cell activity

PI3K inhibitors with differential selectivity to distinct PI3K isoforms have been tested extensively in clinical trials, largely to target tumor epithelial cells. PI3K signaling also regulates the immune system and inhibition of PI3Kδ modulate the tumor immune microenvironment of pre-clinical mouse tumor models by relieving T-regs-mediated immunosuppression. PI3K inhibitors as a class and PI3Kδ specifically are associated with immune-related side effects. However, the impact of mixed PI3K inhibitors in tumor immunology is under-explored. Here we examine the differential effects of AZD8835, a dual PI3Kα/δ inhibitor, specifically on the tumor immune microenvironment using syngeneic models. Continuous suppression of PI3Kα/δ was not required for anti-tumor activity, as tumor growth inhibition was potentiated by an intermittent dosing/schedule in vivo. Moreover, PI3Kα/δ inhibition delivered strong single agent anti-tumor activity, which was associated with dynamic suppression of T-regs, improved CD8⁺ T-cell activation and memory in mouse syngeneic tumor models. Strikingly, AZD8835 promoted robust CD8⁺ T-cell activation dissociated from its effect on T-regs. This was associated with enhancing effector cell viability/function. Together these data reveal novel mechanisms by which PI3Kα/δ inhibitors interact with the immune system and validate the clinical compound AZD8835 as a novel immunoncology drug, independent of effects on tumor cells. These data support further clinical investigation of PI3K pathway inhibitors as immuno-oncology agents.

The next generation of PI3K-Akt-mTOR pathway inhibitors in breast cancer cohorts

The PI3K/Akt/mTOR pathway plays a role in various oncogenic processes in breast cancer and key pathway aberrations have been identified which drive the different molecular subtypes. Early drugs developed targeting this pathway produced some clinical success but were hampered by pharmacokinetics, tolerability and efficacy problems. This created a need for new PI3K pathway-inhibiting drugs, which would produce more robust results allowing incorporation into treatment regimens for breast cancer patients. In this review, the most promising candidates from the new generation of PI3K-pathway inhibitors is explored, presenting evidence from preclinical and early clinical research, as well as ongoing trials utilising these drugs in breast cancer cohorts. The problems hindering the development of drugs targeting the PI3K pathway are examined, which have created problems for their use as monotherapies. PI3K pathway inhibitor combinations therefore remains a dynamic research area, and their role in combination with immunotherapies and epigenetic therapies is also inspected.

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.