PI3Kα Inhibitor BYL719 Research Articles

Integrated genomic and transcriptomic analysis reveals the activation of PI3K signaling pathway in HPV-independent cervical cancers

BackgroundHPV-independent cervical cancers (HPV-ind CCs) are uncommon with worse prognosis and poorly understood. This study investigated the molecular characteristics of HPV-ind CCs, aiming to explore new strategies for HPV-ind CCs.MethodsHPV status of 1010 cervical cancer patients were detected by RT-PCR, PCR and RNA-sequencing (RNA-seq). Whole exome sequencing (WES) and RNA-seq were performed in identified HPV-ind CCs. The efficacy of PI3Kα inhibitor BYL719 in HPV-ind CCs was evaluated in cell lines, patient-derived organoids (PDOs) and patient-derived xenografts (PDXs).ResultsTwenty-five CCs were identified as HPV-ind, which were more common seen in older, adenocarcinoma patients and exhibited poorer prognosis as well as higher tumor mutation burden compared to HPV-associated CCs. HPV-ind CCs were featured with highly activated PI3K/AKT signaling pathway, particularly, PIK3CA being the most predominant genomic alteration (36%). BYL719 demonstrated superior tumor suppression in vitro and in vivo. Furthermore, HPV-ind CCs were classified into two subtypes according to distinct prognosis by gene expression profiles, the metabolism subtype and immune subtype.ConclusionsThis study reveals the prevalence, clinicopathology, and molecular features of HPV-ind CCs and emphasizes the importance of PIK3CA mutations and PI3K pathway activation in tumorigenesis, which suggests the potential significance of PI3Kα inhibitors in HPV-ind CC patients.

Upregulation of PIK3IP1 monitors the anti-cancer activity of PI3Kα inhibitors in gastric cancer cells

Gastric cancer remains one of the most malignant cancers in the world. The target-based drugs approved by FDA for gastric cancer treatment include only three targets and benefit a small portion of gastric cancer patients. PIK3CA, a confirmed oncogene, mutates in 7–25% gastric cancer patients. PI3Kα inhibitor BYL719 has been approved for treating specific breast cancer. However, there is no comprehensive study about PI3Kα inhibitor in gastric cancer. In this study, we found pharmacological inhibition or knockdown of PI3Kα effectively inhibited the proliferation of partial gastric cancer cells. Then, we systematically explored the potential biomarkers for predicting or monitoring treatment response according to previous reports and found that basal expression of several receptor tyrosine kinases were related with the sensitivity of gastric cancer cells to BYL719. Next, RNA-seq technique was utilized and showed that BYL719 inhibited Myc targets V2 gene set in sensitive gastric cancer cells, and western blotting further verified that c-Myc was only inhibited in sensitive gastric cancer cells. More importantly, we firstly found BYL719 significantly elevated the expression of PIK3IP1 in sensitive gastric cancer cells, which was also observed in NCI-N87 cell derived xenograft mice models. Meanwhile, knockdown of PIK3IP1 partially rescued the cell growth inhibited by BYL719 in sensitive gastric cancer cells, suggesting the important role of PIK3IP1 in the antitumor activity of BYL719. In conclusion, our study provides biological evidence that PI3Kα is a promising target in specific gastric cancer and the elevation of PIK3IP1 could supply as a biomarker that monitoring treatment response.

Combination therapy with BYL719 and LEE011 is synergistic and causes a greater suppression of p-S6 in triple negative breast cancer

A third of patients with triple negative breast cancer (TNBC) have relapsed disease within 2–5 years from initial diagnosis, leaving an unmet need for therapeutic targets. TNBC frequently harbors alterations of the PI3K/AKT/mTOR pathway, but single agent PI3K/AKT/mTOR inhibitors have not shown marked efficacy. In this study, we investigated a strategy to improve efficacy of PI3K-α inhibitor BYL719 (alpelisib) in TNBC. While BYL719 is effective at inhibiting cell proliferation in T47D, a triple positive cell line, it had limited activity in TNBC. This may be partially due to persistent phosphorylation of RB, and incomplete inhibition of p-S6 in TNBC, since the inhibitory effect of BYL719 on p-RB and p-S6 was significantly reduced in TNBC compared to T47D cells. Addition of the CDK4/6 inhibitor LEE011 to BYL719 caused a simultaneous reduction of p-RB and p-S6, and a more complete inhibition of p-S6, leading to decreased expression of the pro-survival protein MCL-1, an induction of apoptosis, and an enhanced reduction of tumor growth in a PDX model of TNBC. These findings suggest that inhibition of p-RB and p-S6 is important for an effective response to the treatment of TNBC, and provides a strong rationale for clinical development of combination therapy with BYL719 and LEE011 for treatment of metastatic TNBC with intact RB.Presentation: This study was presented in part as an abstract at the 2016 San Antonio Breast Cancer Symposium (P3-03-15) and the 2018 Cancer Research and Targeted Therapy in London.

Novel cell line models to study mechanisms and overcoming strategies of proteasome inhibitor resistance in multiple myeloma

Experimental data on resistance mechanisms of multiple myeloma (MM) to ixazomib (IXA), a second-generation proteasome inhibitor (PI), are currently lacking. We generated MM cell lines with a 10-fold higher resistance to IXA as their sensitive counterparts, and observed cross-resistance towards the PIs carfilzomib (CFZ) and bortezomib (BTZ). Analyses of the IXA-binding proteasome subunits PSMB5 and PSMB1 show increased PSMB5 expression and activity in all IXA-resistant MM cells, and upregulated PSMB1 expression in IXA-resistant AMO1 cells. In addition, sequence analysis of PSMB5 revealed a p.Thr21Ala mutation in IXA-resistant MM1.S cells, and a p.Ala50Val mutation in IXA-resistant L363 cells, whereas IXA-resistant AMO1 cells lack PSMB5 mutations. IXA-resistant cells retain their sensitivity to therapeutic agents that mediate cytotoxic effects via induction of proteotoxic stress. Induction of ER stress and apoptosis by the p97 inhibitor CB-5083 was strongly enhanced in combination with the PI3Kα inhibitor BYL-719 or the HDAC inhibitor panobinostat suggesting potential therapeutic strategies to circumvent IXA resistance in MM. Taken together, our newly established IXA-resistant cell lines provide first insights into resistance mechanisms and overcoming treatment strategies, and represent suitable models to further study IXA resistance in MM.

Inhibition of BTF3 sensitizes luminal breast cancer cells to PI3Kα inhibition through the transcriptional regulation of ERα

Selective phosphatidylinositol 3 kinase (PI3K) inhibitors are being actively tested in clinical trials for ERα-positive (ER+) breast cancer due to the presence of activating PIK3CA mutations. However, recent studies have revealed that increased ERα transcriptional activity limits the efficacy of PI3K inhibitor monotherapy for ER + breast cancers. Herein, we report the identification of BTF3 as an oncogenic transcription factor that regulates ERα expression in luminal breast cancers. Our TCGA analysis reveals high expression levels of BTF3 in luminal/ER + breast cancer and cell line models harboring ERα overexpression. Concordantly, BTF3 expression is highly and strongly associated with ESR1 expression in multiple breast cancer cohorts. We further show that BTF3 promotes the proliferation, survival and migration of ER + breast cancer cells by modulating ESR1 expression and ERα-dependent transcription. Moreover, BTF3 knockdown sensitizes ER + breast cancer cells to the PI3Kα inhibitor BYL-719 in both in vitro and in vivo models. Together, our findings highlight a novel role of BTF3 in modulation of ERα-dependent transcriptional activity and its potential as a predictive marker for the response to PI3K-targeted therapy in ER + breast cancer.

Abstract 3933: Circadian timing regimen for alpelisib (NVP-BYL719), a selective inhibitor of the class Ia PI3K isoform alpha to maximize therapeutic index

Abstract The gene encoding for the catalytic subunit of the phosphatidylinositol-3-kinase (PI3K), p110a (PIK3CA) is the most frequently mutated kinase in cancer. This discovery triggered the development of small molecule anti-PI3K inhibitors, such as NVP-BYL719. However, the PI3K / Akt signaling pathway plays not only an important role in promoting cell growth, proliferation and survival but also in regulating glucose homeostasis by directly mediating insulin-stimulated glucose uptake into insulin sensitive tissues (adipocytes and muscles). NVP-BYL719 (a selective inhibitor of the class Ia PI3K isoform alpha) given in the morning is facing on-target tolerability challenge (hyperglycemia) in clinical trials limiting the dose being administered to patient (1). As glucose metabolism is highly impacted by circadian rhythms in patients and rodents, we have decided to adopt an integrative circadian-timing approach in our pre-clinical models to interrogate the benefit of morning vs evening dosing for BYL719. By using a newly developed radio-telemetry technology (2), we were able to record in real time and 'around-the-clock' blood glucose levels in stress-free, freely moving rats dosed with NVP-BYL719 at different regimens. The dynamic profile of hyperglycemia observed after active or inactive period dosing of NVP-BYL719 (50 mg/kg qd p.o.) were similar. Dosing before the inactive phase (10 a.m.) allowed blood glucose to normalize in between 2 doses, which could not be achieved when dosing before the active phase (5 p.m.). After treatment discontinuation a significant hyperglycemia remained for a period up to 12h in the group dosed before the active phase (5 p.m.). Circadian “evening” NVP-BYL719 dosing is associated with a better control of glycaemia. Clinically this could potentially translate to better compliance and longer time on treatment hence better efficacy for patient. Based on these findings we could recommend optimized treatment schedules for future combination experiments in the clinic with NVP-BYL719. 1) Juric et al, “Phase I study of the PI3Kα Inhibitor BYL719, as a Single Agent in Patients with Advanced Solid Tumors (AST)”, Annals of Oncology (2014), 25 (Supp. 4) 2) Brockway et al, “Fully Implantable Arterial Blood Glucose Device for Metabolic Research Applications in Rats for Two Months”, J Diabetes Sci Technol (2015), 9(4):771-81 Citation Format: Christian R. Schnell, Thomas Ferrat, Daniel Wyss, Walter Tinetto, Sonja Tobler, Christine Fritsch, Michael Jensen. Circadian timing regimen for alpelisib (NVP-BYL719), a selective inhibitor of the class Ia PI3K isoform alpha to maximize therapeutic index [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3933.

The role of GSK3 and its reversal with GSK3 antagonism in everolimus resistance.

Pancreatic neuroendocrine tumors (panNETs) are often inoperable at diagnosis. The mTORC1 inhibitor everolimus has been approved for the treatment of advanced NETs. However, the regular development of resistance to everolimus limits its clinical efficacy. We established two independent everolimus-resistant panNET (BON1) cell lines (BON1 RR1, BON1 RR2) to find potential mechanisms of resistance. After 24 weeks of permanent exposure to 10 nM everolimus, BON1 RR1 and BON1 RR2 showed stable resistance with cellular survival rates of 96.70% (IC50 = 5200 nM) and 92.30% (IC50 = 2500 nM), respectively. The control cell line showed sensitivity to 10 nM everolimus with cellular survival declining to 54.70% (IC50 = 34 nM). Both resistant cell lines did not regain sensitivity over time and showed persistent stable resistance after a drug holiday of 13 weeks. The mechanisms of resistance in our cell line model included morphological adaptations, G1 cell cycle arrest associated with reduced CDK1(cdc2) expression and decreased autophagy. Cellular migration potential was increased and indirectly linked to c-Met activation. GSK3 was over-activated in association with reduced baseline IRS-1 protein levels. Specific GSK3 inhibition strongly decreased BON1 RR1/RR2 cell survival. The combination of everolimus with the PI3Kα inhibitor BYL719 re-established everolimus sensitivity through GSK3 inhibition and restoration of autophagy. We suggest that GSK3 over-activation combined with decreased baseline IRS-1 protein levels and decreased autophagy may be a crucial feature of everolimus resistance, and hence, a possible therapeutic target.

Phosphatidylinositol 3-kinase β and δ isoforms play key roles in metastasis of prostate cancer DU145 cells.

Metastasis is the main cause of the lethality of prostate cancer. Class I phosphatidylinositol 3-kinases (PI3Ks), which contain 4 isoforms, α, β, δ, and γ, are known to play important roles in cell growth, migration, invasion, and so on. However, the respective role of each PI3K isoform in cancer cell migration and invasion remains unknown. In a study that aimed to elucidate the respective role of the 4 PI3K isoforms, we investigated the change in migratory and invasive ability of DU145 cells after treatment with each PI3K isoform-specific inhibitor. Both migration and invasion of DU145 cells were potently blocked by each of the PI3Kβ inhibitors (GSK2636771 and TGX221) and PI3Kδ inhibitors (CAL101 and IC87114) while not obviously affected by PI3Kα inhibitor BYL719 or PI3Kγ inhibitor AS252424. Furthermore, knocking down PI3Kβ or PI3Kδ isoform led to a significant decrease in migration of DU145. The results suggest that PI3Kβ and PI3Kδ play key roles in prostate cancer cell migration, while PI3Kα and PI3Kγ might be redundant. Oral administration of GSK2636771 (100 mg/kg) and CAL101 (30 mg/kg) inhibited tumor growth in bone, an experimental model by intratibia injection of DU145 cells, with improved bone structure and bone mineral density analyzed by micro-computed tomography. Tissue staining indicated reduction of metastatic DU145 cells and osteoclasts in the bones of GSK2636771- and CAL101-treated mice compared to the untreated group. In summary, our results indicated the distinct roles of 4 PI3K isoforms in the migration of prostate cancer DU145 cells, and they demonstrated the in vitro and in vivo antimetastatic effect of PI3K-isoform specific inhibitors, most of which are in clinical trials.-Zhang, Z., Liu, J., Wang, Y., Tan, X., Zhao, W., Xing, X., Qiu, Y., Wang, R., Jin, M., Fan, G., Zhang, P., Zhong, Y., Kong, D. Phosphatidylinositol 3-kinase β and δ isoforms play key roles in metastasis of prostate cancer DU145 cells.

Abstract PR04: HER3 crosstalk with HPV16-E6E7 is a feedback resistance mechanism to PI3K-targeted therapies in head and neck cancer

Abstract Human papillomavirus (HPV) 16 plays an etiologic role in a growing subset of head and neck squamous cell carcinoma (HNSCC), where viral expression of the E6 and E7 oncoproteins is necessary for tumor growth and maintenance. Although patients with HPV(+) tumors have a more favorable prognosis, there are currently no HPV-selective therapies. Accumulating evidence indicates that HPV oncoproteins can activate the Phosphoinositol-3-Kinase (PI3K) pathway, which contributes to transformation. Furthermore, PI3K is genomically activated by PIK3CA mutation or amplification in a disproportionately high number of HPV(+) tumors as compared to HPV(-) tumors. Based on this knowledge, we investigated the efficacy of PI3K-targeted therapies in preclinical models of HPV(+) HNSCC. Our results indicate that HPV(+) preclinical models were less sensitive to the PI3K inhibitors BYL719, BKM120, and BEZ235 as compared with HPV(-) models. Sensitivity of HPV(+) cell lines to PI3K inhibitors was increased upon knockdown of the E6 and E7 oncoproteins. Reciprocally, overexpression of E6 and E7 in HPV(-) cells rendered them resistant to PI3K-targeted therapies. Proteomic analyses indicated that treatment of HPV(+) cell lines and patient-derived xenografts (PDXs) with the PI3Kα inhibitor BYL719 induced expression of the receptor tyrosine kinase HER3, as well as E6 and E7. HER3 was found to regulate the abundance of E6 and E7 in the HPV(+) models. Targeting HER3 with siRNAs or the monoclonal antibody, KTN3379, blocked the increase in E6 and E7 protein levels following BYL719 treatment, and enhanced the efficacy of PI3K inhibitors in HPV(+) cell line and PDX models. Taken together, these results suggest that crosstalk between HER3 and HPV16-E6E7 can limit the efficacy of PI3K inhibitors, and that co-targeting HER3 and PI3K may be an effective therapeutic strategy in HPV(+) tumors. This abstract is also being presented as Poster 67. Citation Format: Toni M. Brand, Stefan Hartmann, Neil E. Bhola, Hua Li, Yan Zeng, Rachel O'Keefe, Max V. Ranall, Sourav Bandyopadhyay, Margaret Soucheray, Danielle L. Swaney, Nevan Krogan, Carolyn Kemp, Umamaheswar Duvvuri, Daniel E. Johnson, Michelle A. Ozbun, Julie E. Bauman, Jennifer R. Grandis. HER3 crosstalk with HPV16-E6E7 is a feedback resistance mechanism to PI3K-targeted therapies in head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr PR04.

The selective PI3Kα inhibitor BYL719 as a novel therapeutic option for neuroendocrine tumors: Results from multiple cell line models

Background/AimsThe therapeutic options for metastatic neuroendocrine tumors (NETs) are limited. As PI3K signaling is often activated in NETs, we have assessed the effects of selective PI3Kp110α inhibition by the novel agent BYL719 on cell viability, colony formation, apoptosis, cell cycle, signaling pathways, differentiation and secretion in pancreatic (BON-1, QGP-1) and pulmonary (H727) NET cell lines.MethodsCell viability was investigated by WST-1 assay, colony formation by clonogenic assay, apoptosis by caspase3/7 assay, the cell cycle by FACS, cell signaling by Western blot analysis, expression of chromogranin A and somatostatin receptors 1/2/5 by RT-qPCR, and chromogranin A secretion by ELISA.ResultsBYL719 dose-dependently decreased cell viability and colony formation with the highest sensitivity in BON-1, followed by H727, and lowest sensitivity in QGP-1 cells. BYL719 induced apoptosis and G0/G1 cell cycle arrest associated with increased p27 expression. Western blots showed inhibition of PI3K downstream targets to a varying degree in the different cell lines, but IGF1R activation. The most sensitive BON-1 cells displayed a significant, and H727 cells a non-significant, GSK3 inhibition after BYL719 treatment, but these effects do not appear to be mediated through the IGF1R. In contrast, the most resistant QGP-1 cells showed no GSK3 inhibition, but a modest activation, which would partially counteract the other anti-proliferative effects. Accordingly, BYL719 enhanced neuroendocrine differentiation with the strongest effect in BON-1, followed by H727 cells indicated by induction of chromogranin A and somatostatin receptor 1/2 mRNA-synthesis, but not in QGP-1 cells. In BON-1 and QGP-1 cells, the BYL719/everolimus combination was synergistic through simultaneous AKT/mTORC1 inhibition, and significantly increased somatostatin receptor 2 transcription compared to each drug separately.ConclusionOur results suggest that the agent BYL719 could be a novel therapeutic approach to the treatment of NETs that may sensitize NET cells to somatostatin analogs, and that if there is resistance to its action this may be overcome by combination with everolimus.

Abstract 4038: Exploring optimal targeted combination therapies with neratinib for HER2+ breast cancer

Abstract Activation by amplification or overexpression of the proto-oncogene HER2 (also known as ERBB2) is associated with the development and progression of breast cancer. Neratinib is a novel, irreversible, pan-HER tyrosine kinase inhibitor which selectively inhibits EGFR, HER2 and HER4. In this preclinical study, we explored the efficacy of neratinib in combination with other clinically relevant targeted agents for optimal treatment of HER2-positive breast cancer in in vitro and in vivo models. Western blot (WB) analysis of a panel of breast cancer cell lines showed that BT-474, SKBR-3, and HCC-1954 cells displayed elevated HER2 expression levels (here denoted as HER2+), while MDA-MB-361, MDA-MB-453, and CAMA-1 breast cancer cells expressed relatively lower HER2 expression levels. Interestingly, neratinib inhibition positively correlated with HER2 expression levels as assessed by cell survival assays. The IC50 of neratinib in the HER2+ cell lines was in the 3.6 - 113nM range. Consistent with the in vitro data, treatment of a HER2+ breast cancer PDX model with neratinib single agent (p.o. 5 days/week) led to a significant dose-dependent tumor growth inhibition with tumor regressions observed at a low dose of 10 mg/kg (p<0.0001). The activity of neratinib in combination with other targeted agents was then evaluated in vitro in the HER2+ breast tumor cell lines using a Chou-Talalay method. Neratinib showed synergistic anti-proliferative activity in combination with the PI3Kα inhibitor BYL719 in all the HER2+ cell lines tested. By contrast, synergy with mTOR inhibitors (everolimus and TAK228) and with the MEK inhibitor trametinib was only observed in BT-474 and HCC-1954 cells. HCC-1954 cells had the best response to neratinib combinations among all HER2+ cell lines tested, with combination index values <0.5. Immunoblot analysis demonstrated that neratinib treatment displayed complete inhibition of HER2 phosphorylation in these cells. Substantial inhibition of downstream signaling pathways following single agent neratinib treatment was evident by reduced phosphorylation levels of AKT, S6K1, S6, 4EBP1, ERK1/2 and MEK1/2. Consistently with the cell viability data, the combination of neratinib with PI3K/Akt/mTOR and MAPK inhibitors showed a synergy on signaling blockage in these two downstream pathways respectively. Taken together this data shows that neratinib has efficacy as single agent in preclinical models of HER2+ breast tumors and its anti-proliferative activity in vitro was enhanced when combined with PI3K/Akt/mTOR and MAPK pathway inhibitors. Further studies of neratinib-based combination treatments are underway in HER2+ breast cancer xenograft and PDX models to further corroborate these findings. Citation Format: Ming Zhao, Stephen Scott, Kurt Evans, Erkan Yuca, Rashmi Murthy, Francesca Avogadri-Connors, Richard Cutler, Alshad S. Lalani, Sarina Piha-Paul, Funda Meric-Bernstam. Exploring optimal targeted combination therapies with neratinib for HER2+ breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4038. doi:10.1158/1538-7445.AM2017-4038

Integration of Receptor Tyrosine Kinases Determines Sensitivity to PI3Kα-selective Inhibitors in Breast Cancer.

PI3Kα-selective inhibitor BYL719 is currently in phase II/III clinical trial for the treatment of breast cancer, but highly variable response has been observed among patients. We sought to discover predictive biomarker for the efficacy of BYL719 by dissecting the proliferative signaling pathway mediated by PI3K in breast cancer. BYL719 concurrently inhibited the phosphorylation of AKT and ERK in PIK3CA-mutated human breast cancer cells. PI3K-regulated ERK phosphorylation was independent of canonical PDK1/AKT/mTOR pathway, while it was associated with RAF/MEK. Hyper-activation of EGFR or RAS abrogated inhibition of ERK phosphorylation by BYL719. Furthermore, hyper-activation of receptor tyrosine kinases (RTKs) including EGFR, c-MET, FGFR and HER3 but not IGF-1R restored ERK phosphorylation and cell viability suppressed by BYL719, suggesting the discriminative functions of RTKs in cell signaling and proliferation. By profiling 22 breast cancer cell lines, we found that BYL719 was more potent in cell lines where phosphorylation of both AKT and ERK was attenuated than those where only AKT phosphorylation was inhibited. The potency of BYL719 was further found to be significantly correlated with the expression profile of RTKs in breast cancer cells. Specifically, overexpression of EGFR, c-MET and/or FGFR1 forecasted resistance, while overexpression of IGF-1R and/or HER2 predicted sensitivity to BYL719 in breast cancer cells. Similar correlation between BYL719 efficacy and expression profile of RTKs was found in patient-derived xenograft models of breast cancer. Thus, inhibition of ERK phosphorylation by PI3Kα inhibitor BYL719 contributes to its antitumor efficacy and is determined by the converged signaling from RTKs. The expression profile of RTKs in breast cancer tissue could be potentially developed as a predictive biomarker for the efficacy of PI3Kα inhibitors.

Abstract CT232: SU2C Phase Ib study of the PI3K-alpha inhibitor BYL719 (alpelisib) with letrozole in ER+/HER2-metastatic breast cancer

Abstract Background: Mutations in PIK3CA, the gene encoding the p110α subunit of PI3K, have been associated with antiestrogen resistance in ER+ BC. In general, antiestrogen-resistant cancers retain ER and responsiveness to estradiol. This suggests that treatment of ER+ BC with PI3K inhibitors should also include antiestrogens. Methods: We conducted a phase Ib 3+3 dose escalation trial of letrozole (2.5 mg/day) with the PI3Kα inhibitor BYL719 in post-menopausal patients (pts) with ER+/HER2- metastatic breast cancer (MBC) refractory to previous endocrine therapy. BYL719 doses ranged from 300-400 mg/daily. Treatment continued until unacceptable toxicity or disease progression. Disease was assessed every 2 months. PIK3CA mutation status was determined by SNaPshot or targeted next generation sequencing (NGS) in all patients’ tumors. Results: Twenty-six pts were accrued; all patients were refractory to endocrine therapies in the metastatic setting, 18 had prior aromatase inhibitor (AI) therapy in their first or second-line MBC treatment. Median age was 53 years (31-72); 76% of pts had bone and 61% had visceral metastases; 50% of pts had a somatic PIK3CA hotspot mutation. Toxicities are summarized in Table 1. Rash was the dose limiting toxicity* at 350 mg/day. Of the 5 pts with a partial response, 3 (60%) had a PI3KCA mutation, 6/9 pts (67%) that were on treatment for ≥6 months; 3/6 pts (50%) that were on treatment for ≥12 months and 4/6 pts (67%) that are still on study (range 11 - 19 months) had a PI3KCA mutation. Discussion: The combination of letrozole/ BYL719 is safe and tolerable in pts with AI-refractory ER+/HER2-negative MBC. The MTD and recommended dose for phase II trials of BYL719 in combination with letrozole was 300 mg/day. Rash and hyperglycemia were observed at this dose, suggesting drug-induced inhibition of PI3K. Pts with PIK3CA-mutant tumors appeared to derive better clinical benefit, although activity of the combination was also seen in patients with PIK3CA-wild type cancers. Additional NGS of >300 cancer genes and their correlation with clinical response will be updated at the meeting. Clinical trial information: NCT01791478. Adverse Events (% by Grade)Toxicity300 mg (N = 20)300 mg (N = 20)350 mg (N = 6)350 mg (N = 6)% by Grade% by Grade% Total% by Grade% by Grade% Total2323Hyperglycemia181256202070Diarrhea12128110050Fatigue2504330080Rash180431020*40Nausea0062101060Vomiting00250030Anorexia602510040Dysgeusia00180050 Citation Format: Ingrid A. Mayer, Vandana Abramson, Justin Balko, Melinda Sanders, Dejan Juric, David Solit, Yisheng Li, Lewis Cantley, Eric Winer, Carlos Arteaga. SU2C Phase Ib study of the PI3K-alpha inhibitor BYL719 (alpelisib) with letrozole in ER+/HER2-metastatic breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT232. doi:10.1158/1538-7445.AM2015-CT232

Abstract CT330: Phase I study of PI3Kα inhibitor BYL719 + aromatase inhibitor (AI) in patients (pts) with hormone receptor-positive (HR+) metastatic breast cancer (MBC)

Abstract Background: Phosphatidylinositol 3-kinase (PI3K) hyperactivation contributes to endocrine therapy resistance. An α-selective PI3K inhibitor (BYL719) added to hormonal therapy may overcome this resistance. We conducted a phase I study to evaluate the safety and determine preliminary efficacy of BYL719 and an AI in pts with HR+ MBC. Methods: This 3+3 dose-escalation trial added oral BYL719 to letrozole (L) or exemestane (E) at standard doses using daily (Arm A: L; Arm B: E) and then intermittent dosing (Arm C: L + BYL719 every other week; Arm D: E + BYL719 on 5 of 7 days weekly). Pts with HR+ MBC, any or no PIK3CA mutation, and already on L/E were eligible. Endpoints were dose-limiting toxicity (DLT), tolerability (CTCAE 4.0), and efficacy. Paired tumor biopsies and serial plasma collection facilitated genomic, proteomic, and cell-free (cfDNA) correlatives. Results: 32 patients (Arm A/B: n = 7/7; Arm C/D: n = 9/9) received a mean of 99 days (range: 6-473d) of BYL719 + L or E. All were evaluable for toxicity; 25 (Arm A/B: 5/5; Arm C/D: 7/8) were evaluable for response. Median (M) age was 58.5 (30-83). M number of prior MBC therapies was 3 (1-12). PIK3CA status was mutant(MT)/wild-type(WT)/unknown in 8/5/1 pts on Arms A+B and 17/1/0 on Arms C+D. During dose escalation on Arms A+B, 14 pts received BYL719 doses up to 300mg/d, where 4 pts had 5 distinct DLTs: maculopapular rash (N = 3), hyperglycemia (N = 1), abdominal pain (N = 1). 8 week (w) best response on continuous dosing arms (n = 10 evaluable pts) was 1 PR (pt heavily pre-treated, including prior L, MBC to liver, Arm A, completed 10C); 7 SD (included -29.9%, -19%, -12%), and 2 POD. Due to toxicity, enrollment to these arms was halted prior to MTD determination. The protocol was amended to include 2 intermittent dosing arms. 3 DLTs were seen: Arm C, grade (G)3 rash, G1 fever and hypotension with >7d therapy hold; Arm D, G3 rash. Toxicities (Arms C+D, all cohorts, n = 18) included G≥4: hyperglycemia (n = 1, while pt on corticosteroids); G3: rash (n = 4); G1/2: mucositis (n = 9), hyperglycemia (n = 8), and anorexia (n = 5). MTD determinations are pending with evaluation of 350mg BYL719 5d on, 2d off ongoing on Arm D. On Arm C, of 7 evaluable pts, best response was SD in 3 pts (28w, 12w, 8+w in 1 pt each) and POD in 4 pts. On Arm D, of 8 evaluable pts, best response is SD in 6 pts (28+w, 16+w in 1 pt each; 20w, 8+w in 2 pts each), and POD in 2 pts. Using serial cfDNA analysis, PIK3CA mutant allele fraction declined with SD and PR and increased in pts with POD. Correlative studies including genomics and proteomics are ongoing. Conclusions: BYL719 with L or E is an active combination. Skin toxicity warranted evaluation of alternate schedules. A 5d on, 2d off schedule of BYL719 + exemestane appears tolerable and may allow for higher doses than daily administration, with MTD determination pending. Further safety, efficacy, and correlative data will be presented. Citation Format: Payal D. Shah, Mary E. Moynahan, Shanu Modi, Nicola Hamilton, Betty Ann Caravella, Stephen Zamora, Chau Dang, Theresa Gilewski, Tiffany Traina, Elizabeth Comen, Steven M. Sugarman, Gabriella D'Andrea, Diana Lake, Shari Goldfarb, Sujata Patil, Anne Covey, Michael Berger, Mario Lacouture, Larry Norton, Clifford A. Hudis, Jose Baselga, Sarat Chandarlapaty, Maura Dickler. Phase I study of PI3Kα inhibitor BYL719 + aromatase inhibitor (AI) in patients (pts) with hormone receptor-positive (HR+) metastatic breast cancer (MBC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr CT330. doi:10.1158/1538-7445.AM2015-CT330

Abstract PD5-3: Phase I trial: PI3Kα inhibitor BYL719 plus aromatase inhibitor (AI) for patients with hormone receptor-positive (HR+) metastatic breast cancer (MBC)

Abstract Background: Phosphatidylinositol 3-kinase (PI3K) hyperactivation plays a role in endocrine therapy resistance. Adding an α-selective PI3K inhibitor (BYL719) to hormonal therapy may therefore overcome resistance in HR+ MBC. We report results from a phase I study to evaluate the safety and preliminary efficacy of BYL719 plus an AI in patients (pts) with HR+ MBC. Methods: This 3+3 dose-escalation trial studied daily oral BYL719 added to standard dose letrozole (L, Arm A) or exemestane (E, Arm B), and later examined intermittent dosing (Arm C, L + BYL719 every other week; Arm D, E + BYL719 on 5 of 7 days weekly). Pts with HR+ MBC, any/no PIK3CA mutation, and on L/E were eligible. A cycle (C) was 28 days (d). Endpoints were dose-limiting toxicity (DLT), tolerability (CTCAE 4.0), and efficacy (RECIST v1.1). Paired tumor biopsies were performed for genomic and proteomic correlatives. Serial plasma was collected to quantify cell-free (cf) DNA and mutant allele fraction. Results: 14 pts (median (M) age: 55 (30-69) yrs), 7 each on Arms A and B, received a M of 76d (6-312+) of BYL719 + L or E. All were evaluable for toxicity, 10 for response. PIK3CA status was mutant(MT)/wild-type(WT)/unknown in 8/5/1 pts. M number of prior MBC therapies was 2 (1-12) in Arm A, 6 (2-14) in Arm B. Arms had similar toxicities. On Arm A, BYL719 was given at 300mg daily (DL0) to 3 pts who completed the 28d DLT period. 2 pts had 3 distinct DLTs: maculopapular rash (N=1), hyperglycemia (N=1), abdominal pain (N=1). Dose was de-escalated (DL-1=250mg) with no DLT in 3 enrolled pts. On Arm B, DL0, 1 pt experienced DLT (maculopapular rash) of 3 initially enrolled pts. Arm B expansion at DL0 had 1 additional pt with DLT (rash). Clinically significant, treatment-related toxicities included grade (G)≥4: none; G3: maculopapular rash (N=8, including 1 pt treated at DL-1), hyperglycemia (N=1) and G1/2: fatigue (N=7), nausea (N=7), and hyperglycemia (N=6). Toxicity required 6 dose reductions in 4pts and discontinuation in 2 pts. M duration on study for PIK3CA MT vs. WT was 169.5d vs. 69.5d, respectively. In pts with PIK3CA–MT MBC evaluable for response (n=7), 6 had clinical benefit: 1 PR (pt heavily pre-treated, including prior L, MBC to liver, Arm A, now C10+ after DLT); SD (n=5, included -29.9%, -19%, -12%), and POD (n=1). In pts with PIK3CA-WT MBC evaluable for response (n=3), 2 had SD (no changes ≥+/-5%) and 1 had POD. Serial cfDNA analysis in 4 pts with SD or PR demonstrated a decrease of >90% in the PIK3CA mutant allele fraction on treatment. Due to toxicity seen with continuous BYL719, the study was amended to explore intermittent dosing schedules (Arm C, L; Arm D, E; DL0=250mg), with 5 pts enrolled, 3 of whom have completed the DLT period with no DLTs, and 1 pt with G3 rash. Correlative studies including serial cf DNA collection from these pts is ongoing. Conclusions: Continuously dosed BYL719 with L or E shows promising antitumor activity. Skin toxicity warranted evaluation of alternative schedules. Mutant allele fraction may be an early predictor of response and may serve as a pharmacodynamic marker during intermittent treatment. Safety, efficacy, and correlative data from study Arm C and Arm D will also be presented. Citation Format: Payal D Shah, Mary Ellen Moynahan, Shanu Modi, Betty Ann Caravella, Farrah M Datko, Stephen Zamora, Elizabeth Comen, Theresa Gilewski, Steven M Sugarman, Gabriella D'Andrea, Diana E Lake, Shari B Goldfarb, Sujata Patil, Anne Covey, Michael F Berger, Mario E Lacouture, Larry Norton, Clifford A Hudis, Jose Baselga, Sarat Chandarlapaty, Maura N Dickler. Phase I trial: PI3Kα inhibitor BYL719 plus aromatase inhibitor (AI) for patients with hormone receptor-positive (HR+) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr PD5-3.

Abstract PD5-5: Phase I study of the PI3Kα inhibitor BYL719 plus fulvestrant in patients with PIK3CA-altered and wild type ER+/HER2- locally advanced or metastatic breast cancer

Abstract Background: BYL719 selectively inhibits the α-isoform of Class I PI3K. PI3Kα is encoded by PIK3CA, a frequently altered gene in human cancers. Preclinical data indicate BYL719 may be more effective in patients (pts) with PIK3CA-altered tumors; however there are data to suggest that PIK3CA-wild-type (wt) tumors may also be sensitive to BYL719. Here, we present updated data from the Phase I study of BYL719 + fulvestrant in pts with PIK3CA-altered or -wt ER+/HER2– locally advanced/metastatic breast cancer (BC) (NCT01219699). Methods: Adult women with PIK3CA-altered (mutation or amplification) ER+/HER2– BC received continuous oral BYL719 (300–400 mg/day; 28-day cycles) + fixed-dose fulvestrant (500 mg every 4 weeks, plus an additional dose 2 weeks after first dose) during dose escalation and expansion. Pts with PIK3CA-wt ER+/HER2– BC were enrolled into the dose expansion to receive BYL719 400 mg/day + fulvestrant. A Bayesian logistic regression model with overdose control guided dose escalation. Primary objective: to determine the maximum tolerated dose (MTD) and/or recommended phase II dose (RP2D) of BYL719 in combination with fulvestrant, which was declared previously as 400 mg/day. An expansion cohort at the MTD assessed safety (CTCAE v4.0), tolerability, pharmacokinetics (PK), and preliminary efficacy (RECIST v1.0). Results: As of May 2, 2014, 64 pts (PIK3CA-altered n=41; PIK3CA-wt n=16; PIK3CA status unknown/pending n=7) received BYL719 300–400 mg/day + fulvestrant. Median number of prior antineoplastic therapies: 5 (range: 1–12) for pts with PIK3CA-altered tumors and 5 (range: 4–16) for pts with PIK3CA-wt tumors. Prior fulvestrant treatment: 19 (46%) and 7 (44%) pts with PIK3CA-altered and -wt tumors, respectively. Overall, the most common (≥25%) adverse events (AEs; all grades/all doses) suspected to be study drug-related were hyperglycemia (41%), diarrhea (34%), nausea (30%), and vomiting (25%). The most common (>10%) study drug-related Grade 3/4 AEs (all doses) were maculopapular rash (14%) and hyperglycemia (13%). Preliminary antitumor activity was observed in this trial. At data cut-off, partial responses (PRs) were observed in 2 patients with PIK3CA-altered tumors evaluable for response (2/33, 6%), but no PRs were observed in the 15 evaluable patients with PIK3CA-wt tumors. Duration of exposure was >16 weeks in 24 (59%) patients with PIK3CA-altered tumors and in 5 (31%) patients with PIK3CA-wt tumors. PK and exposure of BYL719 + fulvestrant was similar to that observed with single-agent BYL719 at the same dose levels. At data cut-off, treatment was ongoing in 20 (49%) and 2 (13%) pts with PIK3CA-altered and -wt tumors, respectively. Conclusions: BYL719 + fulvestrant demonstrated a favorable safety profile in pts with PIK3CA-altered and -wt ER+/HER2– BC, with mostly on-target effects (i.e. hyperglycemia, rash). Preliminary clinical activity was seen in pts with PIK3CA-altered and -wt tumors, but confirmed PRs were only observed in pts with PIK3CA-altered tumors. The low number of pts with PIK3CA-wt tumors limits further conclusion. Citation Format: Filip Janku, Dejan Juric, Javier Cortes, Hope Rugo, Howard A Burris, Martin Schuler, Barbara Deschler-Baier, Mark R Middleton, Marta Gil-Martin, Jordan Berlin, Eric Winer, Douglas Bootle, Lars Blumenstein, David Demanse, Christina Coughlin, Cornelia Quadt, José Baselga. Phase I study of the PI3Kα inhibitor BYL719 plus fulvestrant in patients with PIK3CA-altered and wild type ER+/HER2- locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr PD5-5.

AXL Mediates Resistance to PI3Kα Inhibition by Activating the EGFR/PKC/mTOR Axis in Head and Neck and Esophageal Squamous Cell Carcinomas

Phosphoinositide-3-kinase (PI3K)-α inhibitors have shown clinical activity in squamous cell carcinomas (SCCs) of head and neck (H&N) bearing PIK3CA mutations or amplification. Studying models of therapeutic resistance, we have observed that SCC cells that become refractory to PI3Kα inhibition maintain PI3K-independent activation of the mammalian target of rapamycin (mTOR). This persistent mTOR activation is mediated by the tyrosine kinase receptor AXL. AXL is overexpressed in resistant tumors from both laboratory models and patients treated with the PI3Kα inhibitor BYL719. AXL dimerizes with and phosphorylates epidermal growth factor receptor (EGFR), resulting in activation of phospholipase Cγ (PLCγ)-protein kinase C (PKC), which, in turn, activates mTOR. Combined treatment with PI3Kα and either EGFR, AXL, or PKC inhibitors reverts this resistance.

Combined Inhibition of Phosphatidylinositol 3-Kinase (PI3K) Isoform α and δ By the Pan-Class I PI3K Inhibitor SAR245409 (XL765) in Primary Chronic Lymphocytic Leukemia Cells Blocks Survival, Adhesion and Proliferation

CLL cells are highly dependent on B- cell receptor (BCR) signaling and on stimuli from the microenvironment for survival and proliferation. New drugs targeting PI3K downstream of BCR signaling have emerged as promising treatment options for patients with CLL. Among four PI3K catalytic subunits, the PI3Kd isoform is crucial for downstream BCR signaling, but the relative importance of the PI3Kα isoform in CLL is less clear. Impressive clinical activity of idelalisib in CLL and indolent NHL patients was recently reported. Idelalisib, a PI3Kd specific inhibitor, inhibits chemotaxis and adhesion of leukemia cells, resulting in rapid lymphocytosis followed by a decrease in lymphadenopathy. However, idelalisib has no direct impact on leukemic cell survival [1], raising the potential risk of residual clones responsible for the development of resistance. In this study, we evaluated the impact of a pan-class I PI3K inhibitor (SAR245409/XL765), a PI3Kα-specific inhibitor (BYL719) and a PI3Kd specific inhibitor (idelalisib) on PI3K/mTOR signaling, apoptosis, cell adhesion, CD40-induced survival and proliferation in primary patient derived leukemic cells.Phosphorylation of the downstream effector of mTOR, S6RP, was completely blocked by SAR245409 but not by BYL719 or idelalisib. SAR245409 induced apoptosis in unstimulated CLL cells (IC50= 0.86µM) in contrast to BYL719 or idelalisib (IC50 >10µM), demonstrating that targeting multiple PI3K isoforms is required to completely block the PI3K/Akt/mTOR pathway (table 1). Importantly, SAR245409 also induced apoptosis in p53 or ATM dysfunctional CLL samples. SAR245409, as well as idelalisib, and in contrast to BYL719 completely inhibited BCR-mediated adhesion to fibronectin [2]. Similarly, SAR245409 inhibited CD40L-mediated survival [3], and induced upregulation of the pro-apoptotic protein BIM. All 3 PI3K inhibitors inhibited CD40 ligation + IL-21-mediated CLL proliferation [4].This study revealed that the pan-class I PI3K inhibitor SAR245409 is more cytotoxic to primary CLL cells than PI3Kα or PI3Kd specific inhibitors. Furthermore, combined inhibition of PI3Kα and d can block signaling pathways that are critical for CLL survival, adhesion and proliferation in the LN microenvironment (see table 1). This work provides a rationale for the evaluation of SAR245409 in CLL patients either as monotherapy or in combination therapies.[1] Hoellenriegel et al. The phospoinositide 3′-kinase delta inhibitor, CAL-101, inhibits B-cell receptor signaling and chemokine networks in chronic lymphocytic leukemia. Blood 2011;(118):3603-3612[2] de Rooij et al. The clinically active BTK inhibitor PCI-32765 targets B-cell receptor- and chemokine-controlled adhesion and migration in chronic lymphocytic leukemia. Blood 2012;(119):2590-2594.[3] Smit et al. Differential Noxa/Mcl-1 balance in peripheral versus lymph node chronic lymphocitic leukemia cells correlates with survival capacity. Blood 2007;(109):1660-1668.[4] Pascutti et al. IL-21 and CD40L signals from autologous T cells can induce antigen-independent proliferation of CLL cells. Blood 2013;(122):3010-3019.Table 1The effect of the PI3Kd inhibitor idelalisib, PI3Kα inhibitor BYL719 or pan PI3K inhibitor SAR245409 on CLL cells in functional assaysPI3Kd inhibitorPI3Kα inhibitorpan PI3K inhibitorCytotoxicity (IC50)1>10µM>10µM0.86µMInhibition of adhesion248%**21%43%**ActivationInhibition of CD40L-induced survival314%0%54%*Inhibition of CD40L+IL21 induced proliferation447%*35%*51%*1 CLL cells were incubated with 0.001-10 μM idelalisib (n=18), BYL719 (n=6) or SAR245409 (n=28) for 48 hours. Viability was assessed by DiOC6/PI staining.2 CLLcells pretreated with 1 µM idelalisib, BYL719, or SAR245409 were stimulated with α-IgM and allowed to adhere to fibronectin-coated surfaces (n=5). 3 CLL cells were cultured on fibroblast expressing CD40L in the absence or presence of 1 µM of idelalisib, BYL719, or SAR245409 for 3 days. Apoptosis was assessed by DiOC6/PI staining (n=8).4 CFSE labelledCLL cells were cultured on fibroblast expressing CD40L with IL-21 and co-treated with 1 µM idelalisib, BYL719, or SAR245409. After 4 days, CFSE was measured by FACS (n=11)2-4 The one sample T test was used to determine the significance of differences between means of treated samples and normalized values of untreated samples (100%). * p <0,05;** p<0,01 DisclosuresEgile:Sanofi: Employment. Kersten:Sanofi: Research Funding. Kater:Sanofi: Research Funding.

Abstract LB-327: Loss of PTEN leads to clinical resistance to the PI3Kα inhibitor BYL719 and provides evidence of convergent evolution under selective therapeutic pressure

Abstract Activating mutations of PIK3CA, the gene encoding the p110α subunit of PI3K, are frequent in breast cancer and selective inhibitors of this enzyme have shown promising clinical activity in breast tumors harboring these mutations. We studied the case of a patient with metastatic breast cancer harboring a PIK3CA mutation that was treated in a clinical trial with BYL719, a highly selective PI3Kα inhibitor. The treatment resulted in a robust partial response that lasted 7 months followed by rapid progression and death. A rapid autopsy was performed with collection of tissue samples from 16 different metastatic sites. We compared by whole genome and exome sequencing the original primary tumor, a rapidly progressing lung metastasis and a periaortic lesion that was still responding to BYL719 at time of death. Besides several common alterations, PTEN loss and a missense mutation were detected only in the lung metastasis. Using targeted exome sequencing we analyzed all the other available samples. Strikingly, we observed a consistent loss in PTEN (via different mechanisms such as deletion, splice site mutation and frameshift mutations) in all the lesions refractory to BYL719 but not in the responding ones. In every case, the loss of PTEN was also documented by lack of protein expression by immunohistochemistry (IHC). Finally, we were able to build a dendrogram showing the phylogenetic evolution of the lesions and the evolutionary convergence of the PTEN alterations. To validate PTEN loss as a possible mechanism of acquired resistance to selective PI3Kα inhibition, we generated doxycycline-inducible PTEN shRNA stable clones starting from three different BYL719-sensitive cell lines. In all the studied models, induction of PTEN shRNA resulted in resistance to BYL719. Since PTEN deficient genetic models have been shown to rely on the β subunit of the PI3K holoenzyme, we tested whether the concomitant inhibition of both p110α and p110β was sufficient to revert the resistant phenotype. BKM120 (a pan-PI3K inhibitor) or the addition of AZD6482 (p110β inhibitor) to BYL719 re-sensitized the cells to BYL719. To expand our findings in vivo, we generated a patient-derived xenograft (PDX) model from a PTEN-null non-responding lesion (lung). Consistently, this PDX model was refractory to the antitumor activity of BYL719 but conserved sensitivity to BKM120 or the combination of AZD6482 and BYL719. In both cases, IHC analysis revealed a decrease in PI3K/AKT downstream effectors pPRAS40 (246) and pS6 (240/4) staining with BKM120 or AZD6482+BYL719, but not with BYL719 alone. Preliminary analyses of other samples collected from patients treated with BYL719 suggest that PTEN loss is a relatively frequent event upon therapy progression. Taken together, the different mechanisms that inactivate PTEN in the tumor treated with BYL719 can be explained by convergent phenotypic evolution in a heterogeneous tumor and highlight the importance of PTEN and PI3Kβ in acquired resistance to PI3Kα inhibitors. Citation Format: Pau Castel, Dejan Juric, Helen Won, Benjamin Ainscough, Haley Ellis, Saya Ebbesen, Malachi Griffith, Obi Griffith, Iyer Gopakumar, Dennis Sgroi, Steven Isakoff, Elaine Mardis, David Solit, Scott Lowe, Cornelia Quadt, Malte Peters, Michael Berger, Maurizio Scaltriti, José Baselga. Loss of PTEN leads to clinical resistance to the PI3Kα inhibitor BYL719 and provides evidence of convergent evolution under selective therapeutic pressure. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-327. doi:10.1158/1538-7445.AM2014-LB-327

Dual targeting of RAF-MEK-ERK and PI3K-AKT-mTOR pathways in RAS-mutant cancers: Preclinical insights and institutional experience from a clinical trial of binimetinib (MEK162) plus BYL719.

e13559 Background: Current development is focused on agents targeting the RAF-MEK-ERK and PI3K-AKT-mTOR pathways. Combinations of these agents may address causes of de novo resistance. Identifying patients (pts) most likely to benefit from these combinations is important. Methods: A panel of 20 cell lines (5 BRAFM, 5 KRASM, 5 PIK3CAM and 5 BRAF/PIK3CA/KRASWT) were exposed to MEK and/or AKT inhibitors and evaluated for inhibition of pathway signaling and cell growth. Inhibition of signaling output of the RAF-MEK-ERK (p-ERK) and PI3K-AKT-mTOR (p-S6) pathways was quantified by ELISA. Growth inhibition was determined using sulforhodamine B assay. Based on the results of preclinical experiments, at our center we prioritized enrolling pts with RAS mutant tumors (including ovarian cancer and non-small cell lung cancer [NSCLC]) into an ongoing phase 1b clinical trial (CMEK162X2109) evaluating the combination of MEK inhibitor binimetinib (MEK162) and the PI3K-α inhibitor BYL719 in pts with RAS and RAF mutant tumor...