Phosphatidylinositol 3-kinase Alpha Research Articles

Intact regulation of G1/S transition renders esophageal squamous cell carcinoma sensitive to PI3Kα inhibitors

Phosphatidylinositol 3-kinase alpha (PI3Kα) inhibitors are currently evaluated for the therapy of esophageal squamous cell carcinoma (ESCC). It is of great importance to identify potential biomarkers to predict or monitor the efficacy of PI3Kα inhibitors in an aim to improve the clinical responsive rate in ESCC. Here, ESCC PDXs with CCND1 amplification were found to be more sensitive to CYH33, a novel PI3Kα-selective inhibitor currently in clinical trials for the treatment of advanced solid tumors including ESCC. Elevated level of cyclin D1, p21 and Rb was found in CYH33-sensitive ESCC cells compared to those in resistant cells. CYH33 significantly arrested sensitive cells but not resistant cells at G1 phase, which was associated with accumulation of p21 and suppression of Rb phosphorylation by CDK4/6 and CDK2. Hypo-phosphorylation of Rb attenuated the transcriptional activation of SKP2 by E2F1, which in turn hindered SKP2-mediated degradation of p21 and reinforced accumulation of p21. Moreover, CDK4/6 inhibitors sensitized resistant ESCC cells and PDXs to CYH33. These findings provided mechanistic rationale to evaluate PI3Kα inhibitors in ESCC patients harboring amplified CCND1 and the combined regimen with CDK4/6 inhibitors in ESCC with proficient Rb.

Structure optimization, synthesis, and biological evaluation of 6-(2-amino-1H-benzo[d]imidazole-6-yl)-quinazolin-4(3H)-one derivatives as potential multi-targeted anticancer agents via Aurora A/ PI3K/BRD4 inhibition

Aurora A (Aurora kinase A), a critical regulator of cell mitosis, is frequently overexpressed in many malignant cancers, and has been considered as a promising drug target for cancer therapy. Likewise, Phosphatidylinositol 3-kinase alpha (PI3Kα) is also regarded as one of the most important targets in cancer therapy by mediating the cell growth and angiogenesis of various human cancers. In addition, Bromodomain-containing protein 4 (BRD4) modulates oncogene expressions of Myc, Aurora kinase and various RTKs. Recently, accumulating evidences indicated that hyperactivated or abnormally expressed Aurora A, PI3Kα or BRD4 are closely associated with drug resistance and poor prognosis of non-small cell lung cancer (NSCLC). Hence, simultaneous inhibition of Aurora A, PI3Kα, and BRD4 is expected to be a new strategy for NSCLC therapy. In this study, we performed further structure optimization of 6-(2-amino-1H-benzo[d]imidazole-6-yl)-quinazolin-4(3H) -one based on previous study to obtain a series of derivatives for discovering potential Aurora A, PI3Kα and BRD4 multi-targeted inhibitors. MTT assay showed that most of the newly synthesized compounds exhibited an evident anticancer activity against the NSCLC cells. Among them, the IC50 values of the most potent compound 9a were 0.83, 0.26 and 1.02 μM against A549, HCC827 and H1975 cells, respectively. In addition, 9a markedly inhibited the Aurora A and PI3Kα kinase activities with IC50 values of 10.19 nM and 13.12 nM. Compound 9a induced G2/M phase arrests and apoptosis of HCC827 cells by simultaneous inhibition of Aurora A/PI3K/ BRD4 signaling pathways. Collectively, our studies suggested that 9a might be a potential multi-targeted inhibitor for NSCLC therapy.

ODP173 Control of Alpelisib-Induced Hyperglycemia With DPP4- Inhibitors as add on to Metformin and Insulin

Abstract Context Alpelisib is an oral phosphatidylinositol-3-kinase alpha (PI3Ka) inhibitor approved in 2019 for treatment of ER/PR+, HER2-negative advanced breast cancer. The main side effect of PI3Ka inhibition is hyperglycemia. Case A 38 year-old woman was started on alpelisib and fulvestrant therapy for Stage IV bilateral breast carcinoma (ER+, PR+, HER2-negative) with multiple distant metastases. She had previously received multiple courses of systemic therapy with palbociclib, letrozole, and everolimus, in combination with fulvestrant. She was lean (BMI 20.6 kg/m 2), had a prior history of GDM only requiring diet control, and pre-existing pre-diabetes, with a baseline FPG of 5.6 mmol/L and HbA1c of 5.9%. She developed hyperglycemia after 2 months of Alpelisib 200 mg OD (FPG 138.6 mg/dL; HbA1c 5.8%) and was started on metformin 500 mg BD. Glucose levels remained under control (fasting BG of 108-126 mg/dL) until alpelisib dose was increased to 300 mg OD. Within 6 weeks of dose increment, her fasting BG markedly increased to 324 mg/dL and HbA1c to 10%. Metformin dose was increased to 1000 mg BD, linagliptin 5 mg OD and isophane insulin at 8 units once daily, was introduced in addition to lifestyle modifications. Due to the side effects resulting in diarrhea, alpelisib was discontinued temporarily for 3 weeks before subsequent reintroduction and titration to a maximum tolerable dose of 200 mg OD. Glycemic control subsequently improved with metformin, linagliptin and titration of insulin to 14units daily, with HbA1c reduction to 6. 0% and fasting BG of 84.6 mg/dL, without any hypoglycemia. Oncological assessment showed disease response, with smaller primary tumour and stable metastatic lesions. Discussion The PI3K/AKT pathway plays a central role in cellular growth and glucose metabolism. This pathway is a potent target of anticancer therapy. In physiological glucose homeostasis, postprandial insulin secretion activates the PI3Ka pathway, subsequently upregulating glucose transporters for cellular uptake and utilization of glucose. In the phase III clinical trial (SOLAR-1), the incidence of alpelisib-induced hyperglycemia was 63.7%, and was treated with insulin sensitizers such as metformin and pioglitazone. Subsequent case series have reported effective glycemic control using very low calorie diet (VLCD), SGLT2-inhibitors and insulin therapy 1 . In our patient, linagliptin, was chosen as an adjunct therapy in addition to metformin due to its mechanism of action that address insulin resistance and favourable safety profile. We also note that the severity of alpelisib side effects appeared to be dose-dependent, as seen in the clinical trial. Conclusion We demonstrated effective control of alpelisib-induced hyperglycemia using DPP4-inhibitors as an option, in combination with metformin and insulin.

Vitamin E TPGS-Poloxamer Nanoparticles Entrapping a Novel PI3Kα Inhibitor Potentiate Its Activity against Breast Cancer Cell Lines.

N-(2-fluorphenyl)-6-chloro-4-hydroxy-2-quinolone-3-carboxamide (R19) is a newly synthesized phosphatidylinositol 3-kinase alpha (PI3Kα) inhibitor with promising activity against cancer cells. The purpose of this study was to develop a polymeric nanoparticle (NP) formulation for R19 to address its poor aqueous solubility and to facilitate its future administration in preclinical and clinical settings. NPs were prepared by nanoprecipitation using two polymers: D-α-tocopheryl polyethylene glycol 1000 succinate (vitamin E TPGS) and the poloxamer Pluronic P123 in different ratios. Physicochemical characterization of the NPs revealed them to be around 100 nm in size with high monodispersity, a spherical morphology, and an almost neutral surface charge. The NPs achieved ~60% drug loading efficiency and sustained release of R19 for up to 96 h, with excellent colloidal stability in serum-containing cell culture media. NPs containing TPGS enhanced R19’s potency against MCF-7 and MDA-MB-231 breast cancer cells in vitro, with half-maximal inhibitory concentrations (IC50) ranging between 1.8 and 4.3 µM compared to free R19, which had an IC50 of 14.7–17.0 µM. The NPs also demonstrated low cytotoxicity against human dermal fibroblasts and more significant induction of apoptosis compared to the free drug, which was correlated with their cellular uptake efficiency. Our findings present a biocompatible NP formulation for the delivery of a cancer-targeted PI3Kα inhibitor, R19, which can further enhance its potency for the treatment of breast cancer and potentially other cancer types.

PIK3CA Mutations Drive Therapeutic Resistance in Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer.

The phosphatidylinositol 3-kinase (PI3K) pathway is an intracellular pathway activated in response to progrowth signaling, such as human epidermal growth factor receptor 2 (HER2) and other kinases. Abnormal activation of PI3K has long been recognized as one of the main oncogenic drivers in breast cancer, including HER2-positive (HER2+) subtype. Somatic activating mutations in the gene encoding PI3K alpha catalytic subunit (PIK3CA) are present in approximately 30% of early-stage HER2+ tumors and drive therapeutic resistance to multiple HER2-targeted agents. Here, we review currently available agents targeting PI3K, discuss their potential role in HER2+ breast cancer, and provide an overview of ongoing trials of PI3K inhibitors in HER2+ disease. Additionally, we review the landscape of PIK3CA mutational testing and highlight the gaps in knowledge that could present potential barriers in the effective application of PI3K inhibitors for treatment of HER2+ breast cancer.

Abstract P1-18-08: Effect of duration of prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) therapy (≤6 mo or >6 mo) on alpelisib benefit in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), PIK3CA-mutated advanced breast cancer (ABC) from BYLieve

Abstract Introduction: PIK3CA (encoding phosphatidylinositol 3-kinase alpha [PI3Kα]) is a driver oncogene mutated (mut) in ~40% of HR+, HER2- ABCs, leading to endocrine therapy (ET) resistance and poor prognosis. Alpelisib (ALP) is the first oral α-selective PI3K inhibitor and degrader approved in this patient (pt) population. Primary analyses of Cohorts A and B from BYLieve, an ongoing Phase II noncomparative study, demonstrated efficacy and a consistent safety profile of ALP + ET (fulvestrant [FUL] or letrozole [LET]) in pts with PIK3CA-mut, HR+, HER2- ABC in the post CDK4/6i setting. Post hoc analyses of ALP benefit in pts with centrally confirmed PIK3CA mut, based on median duration of prior CDK4/6i, supported the efficacy of ALP + ET in CDK4/6i-resistant, HR+, HER2- ABC. Here we assessed whether those who achieved a short duration of disease control (6-month [mo] cutoff), with prior CDK4/6i + ET received clinical benefit with ALP + ET. Methods: In Cohorts A and B, pts with PIK3CA-mut, HR+, HER2- ABC had received CDK4/6i + aromatase inhibitor (AI) or FUL, respectively, as immediate prior therapy (majority in first line). Pts in Cohort A received ALP 300 mg PO QD + FUL 500 mg IM Q28D + C1D15; pts in Cohort B received ALP 300 mg PO QD + LET 2.5 mg PO QD. Within each cohort, pts were divided based on duration of prior CDK4/6i therapy (≤6 mo or >6 mo), and the association of progression-free survival (PFS) with this covariate was analyzed using a stratified log-rank test and Cox Proportional Hazards model. A 6-mo cutoff was selected based on the ESO-ESMO ABC5 cutoff for primary ET resistance, as current guidelines do not specify cutoffs for CDK4/6i resistance. This analysis is based on the PFS endpoint and included pts for whom duration of prior CDK4/6i therapy was known. Results: Of the 121 pts in Cohort A with centrally confirmed PIK3CA-mut disease (modified full analysis set, mFAS), 120 had duration of prior CDK4/6i available; 26 had CDK4/6i for ≤6 mo and 94 for >6 mo, with similar demographics/disease characteristics between subgroups. The hazard ratio (HR) of median PFS (mPFS) between the ≤6-mo group and >6-mo group was 0.50 (95% confidence interval [CI], 0.27-0.94), indicating a lower risk of progression in the ≤6-mo group, with mPFS 10.0 mo (95% CI, 5.55-not estimable) and 6.0 mo (95% CI, 5.16-8.31), respectively. Grade ≥3 adverse events (AEs) were experienced by 67.5% (n=85) of all pts (safety set) in Cohort A and by 76.9% (n=20)/65.0% (n=65) in the ≤6-mo/>6-mo subgroups, respectively. Of the 115 pts in Cohort B with centrally confirmed PIK3CA-mut disease (mFAS), 113 had duration of prior CDK4/6i available; 31 had CDK4/6i for ≤6 mo and 82 for >6 mo, with similar demographics/disease characteristics between subgroups. The HR of mPFS between the ≤6-mo and >6-mo groups was 0.76 (95% CI, 0.47-1.23), with the wide CI indicating no difference in risk of progression between subgroups, and mPFS was 5.9 mo (95% CI, 3.55-10.97) and 5.6 mo (95% CI, 3.68-7.10), respectively. Grade ≥3 AEs were experienced by 69.9% (n=86) of all pts (safety set) in Cohort B and by 63.6% (n=21)/72.2% (n=65) in the ≤6-mo/>6-mo subgroups, respectively. Conclusions: This demonstrates that pts with PIK3CA-mut, HR+, HER2- ABC who achieved ≤6-mo duration of disease control with prior CDK4/6i had a numerically longer PFS in Cohort A, and almost the same clinical efficacy in Cohort B, to ALP + ET vs pts with >6-mo duration of disease control, with a comparable safety profile. This confirms targeting PI3Kα with ALP provides clinical benefit in pts with CDK4/6i-resistant ABC, including early progressors, and supports consideration of ALP + ET as an immediate next-line option in this setting, possibly delaying chemotherapy. Citation Format: Stephen Chia, Eva M Ciruelos, Hope S Rugo, Florence Lerebours, Manuel Ruiz-Borrego, Pamela Drullinsky, Aleix Prat, Thomas Bachelot, Nicholas Turner, Ennan Gu, Christina Arce, Murat Akdere, Dejan Juric. Effect of duration of prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) therapy (≤6 mo or >6 mo) on alpelisib benefit in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), PIK3CA-mutated advanced breast cancer (ABC) from BYLieve [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-08.

RP-3500: A Novel, Potent, and Selective ATR Inhibitor that is Effective in Preclinical Models as a Monotherapy and in Combination with PARP Inhibitors.

Ataxia telangiectasia and Rad3-related (ATR) kinase protects genome integrity during DNA replication. RP-3500 is a novel, orally bioavailable clinical-stage ATR kinase inhibitor (NCT04497116). RP-3500 is highly potent with IC50 values of 1.0 and 0.33 nmol/L in biochemical and cell-based assays, respectively. RP-3500 is highly selective for ATR with 30-fold selectivity over mammalian target of rapamycin (mTOR) and more than 2,000-fold selectivity over ataxia telangiectasia mutated (ATM), DNA-dependent protein kinase (DNA-PK), and phosphatidylinositol 3-kinase alpha (PI3Kα) kinases. In vivo, RP-3500 treatment results in potent single-agent efficacy and/or tumor regression in multiple xenograft models at minimum effective doses (MED) of 5 to 7 mg/kg once daily. Pharmacodynamic assessments validate target engagement, with dose-proportional tumor inhibition of phosphorylated checkpoint kinase 1 (pCHK1) (IC80 = 18.6 nmol/L) and induction of phosphorylated H2A.X variant histone (γH2AX), phosphorylated DNA-PK catalytic subunit (pDNA-PKcs), and phosphorylated KRAB-associated protein 1 (pKAP1). RP-3500 exposure at MED indicates that circulating free plasma levels above the in vivo tumor IC80 for 10 to 12 hours are sufficient for efficacy on a continuous schedule. However, short-duration intermittent (weekly 3 days on/4 days off) dosing schedules as monotherapy or given concomitantly with reduced doses of olaparib or niraparib, maximize tumor growth inhibition while minimizing the impact on red blood cell depletion, emphasizing the reversible nature of erythroid toxicity with RP-3500 and demonstrating superior efficacy compared with sequential treatment. These results provide a strong preclinical rationale to support ongoing clinical investigation of the novel ATR inhibitor, RP-3500, on an intermittent schedule as a monotherapy and in combination with PARP inhibitors as a potential means of maximizing clinical benefit.

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.

Identification of novel potential PI3Kα inhibitors for cancer therapy

Phosphatidylinositol 3-kinase alpha (PI3Kα) is among the most important PI3K isoforms and has been associated with multiple human cancers. Therefore, PI3Kα has garnered considerable attention as a viable target for anticancer drug discovery, and thus the identification and development of highly potent inhibitors of this isoform has become an important line of research. Here, structure-based virtual screening, bioassays, and molecular dynamics simulations were performed to discover novel potential PI3Kα inhibitors. TCM-N1 (ZINC13382850) was identified as a possible PI3Kα inhibitor. Particularly, fluorescence quenching assays determined that the binding affinity of the aforementioned compound was superior to that of a reference ligand (BYL719; i.e. a known PI3Kα inhibitor). Moreover, enzymatic activity and cell proliferation inhibition assays indicated that TCM-N1 possessed a moderate inhibition activity against PI3Kα and a relatively high anti-tumor proliferation ability in gastric, colorectal, and cervical cancer cells. The binding model and related thermodynamic parameters further demonstrated that TCM-N1 was tightly embedded into the ATP-binding pocket via hydrogen bonds, van der Waals interactions, and hydrophobic interactions. Therefore, this study provides promising insights into the development and design of more potent PI3Kα-inhibiting analogs. Communicated by Ramaswamy H. Sarma

Abstract P3-11-23: GDC-0077 is a selective PI3K alpha inhibitor with robust efficacy in PIK3CA mutant hormone-positive breast cancer models

Abstract The phosphatidylinositol 3kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway is a major regulator of tumor cell growth, proliferation and survival. Hotspot mutations of PIK3CA are common in all subtypes of breast cancer with a prevalence of approximately 30%. GDC-0077 is a potent ATP-competitive inhibitor of PI3K alpha (IC50 = 0.038 ± 0.003 nM), thereby inhibiting the phosphorylation of membranebound PIP2 to PIP3. Biochemically, GDC-0077 is more than 300fold selective over the other Class I PI3K isoforms, beta, delta, and gamma, and more than 2000-fold more selective over PI3K class II and III family members. Importantly, GDC-0077 is more selective for mutant versus wild-type PI3K alpha in cell-based assays. Mechanism of action studies indicate that GDC-0077 treatment leads to degradation of the mutant PI3K alpha protein in a proteasome dependent fashion, without changing WT PI3K alpha levels. Drug treatment results in sustained reduction of PI3K pathway biomarkers pAkt and pPRAS40, inhibition of cell proliferation, and increased apoptosis in human PIK3CA mutant breast cancer cell lines, to a greater extent than other non-degrading inhibitors such as alpelisib. Combination studies of GDC-0077 with the CDK4/6 inhibitor palbociclib demonstrate a stronger effect in estrogen-depleted HR+ PIK3CA mutant breast cell lines, compared to cells grown in the presence of estrogen. Daily dosing of GDC-0077 in PIK3CA mutant breast cancer patient derived xenograft (PDX) models (n=4) resulted in tumor regressions, induction of apoptosis and a reduction of pAkt, pPRAS40, and pS6RP in a dose-dependent fashion. In vivo combination efficacy studies of GDC-0077 with fulvestrant and palbociclib also indicate the triple combination results in the greatest efficacy. Collectively, our preclinical data support evaluation of GDC-0077 in a triple combination with endocrine therapy and CDK4/6 inhibition in the clinic, in patients with locally advanced or metastatic hormone receptor positive breast cancer whose tumors harbor mutant PIK3CA. Citation Format: Kyle Edgar, Rebecca Hong, Kyung Song, Steven Schmidt, Marc Hafner, Alfonso Arrazate, Erin Williams, Cecile De La Cruz, Jason Oeh, Deepak Sampath, Steve Staben, Lori Friedman. GDC-0077 is a selective PI3K alpha inhibitor with robust efficacy in PIK3CA mutant hormone-positive breast cancer models [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-11-23.

Alpelisib: First Global Approval.

Alpelisib (Piqray™)-an orally available phosphatidylinositol 3-kinase (PI3K) inhibitor with specific activity against PI3K alpha (PI3Kα)-is being developed by Novartis for the treatment of breast cancer. Alpelisib has demonstrated efficacy in combination with fulvestrant as treatment for hormone receptor (HR)-positive, human epidermal growth factor receptor-2 (HER2)-negative breast cancer in patients with a PIK3CA mutation and was recently approved for this indication in the USA. This article summarizes the milestones in the development of alpelisib leading to this first approval.

Abstract 156: Preclinical characterization of GDC-0077, a specific PI3K alpha inhibitor in early clinical development

Abstract The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/ mammalian target of rapamycin (mTOR) signaling pathway is a major regulator of tumor cell growth, proliferation and survival. Dysregulation of the PI3K/Akt/mTOR signaling pathway through multiple mechanisms has been described in solid tumor malignancies, including activating and transforming “hotspot” mutations as well as amplification of PIK3CA that encodes the p110 alpha subunit of PI3K. Hotspot mutations of PIK3CA mutation are frequently observed in breast cancer with a prevalence of approximately 30%. GDC-0077 is a potent inhibitor of PI3K alpha (IC50 = 0.038 + 0.003 nM) and exerts its activity by binding to the ATP binding site of PI3K, thereby inhibiting the phosphorylation of PIP2 to PIP3. Biochemically, GDC-0077 is more than 300-fold selective over other Class I PI3K isoforms such as beta, delta, and gamma and more than 2000 fold more selective over PI3K class II and III family members. Importantly, GDC-0077 is more selective for mutant versus wild-type PI3K alpha in cell based assays. Compared to the PI3K inhibitor, taselisib, the improved biochemical selectivity of GDC-0077 against PI3K delta is demonstrated in human CD69+ B-cells, which are primarily dependent on PI3K delta for proliferation and survival and were more sensitive to taselisib than GDC-0077. Mechanism of action studies indicate that GDC-0077 induces depletion of mutant PI3K alpha protein resulting in reduction of PI3K pathway biomarkers such as pAkt and pPRAS40, inhibition of cell proliferation and increased apoptosis in human PIK3CA mutant breast cancer cell lines to a greater extent when compared to PIK3CA wild-type cells. In vivo, daily oral treatment with GDC-0077 in cell-culture-derived and patient derived PIK3CA mutant breast cancer xenograft models, resulted in tumor regressions, induction of apoptosis and a reduction of pAkt, pPRAS40, and pS6RP in a dose-dependent fashion. In vivo efficacy in a PIK3CA-mutant human breast cancer xenograft model was also improved when GDC-0077 was combined with standard-of-care therapies for hormone-receptor positive (HR+) breast cancer such as anti-estrogens (fulvestrant) or CDK4/6 inhibitor (palbociclib). Collectively, the preclinical data provide rationale for evaluating GDC-0077, a PI3K alpha mutant selective inhibitor, as a single agent and in combination with standard-of-care endocrine and targeted therapies that may provide additional benefit to patients that harbor PIK3CA mutations. Citation Format: Kyle Edgar, Emily Hanan, Steven Staben, Stephen Schmidt, Rebecca Hong, Kyung Song, Amy Young, Patricia Hamilton, Alfonso Arrazate, Cecile de la Cruz, Marcia Belvin, Michelle Nannini, Lori S. Friedman, Deepak Sampath. Preclinical characterization of GDC-0077, a specific PI3K alpha inhibitor in early clinical development [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 156. doi:10.1158/1538-7445.AM2017-156

Abstract P6-11-08: Safety and efficacy results from phase I study of BYL 719 plus nab-paclitaxel in HER 2 negative metastatic breast cancer

Abstract Introduction Mutations/deregulations in the phosphatidylinositol-3-kinase (PI3K) pathway are common in breast cancer, Inhibition of the PI3K pathway is recognized as a promising target for the treatment of breast cancer. Although taxanes are effective early on in advanced stage breast cancer, resistance often develops. It has been demonstrated that activation of the PI3K/AKT pathway confers resistance to paclitaxel, and in preclinical models, concomitant inhibition of the PI3K pathway enhances the efficacy of taxanes. BYL719 is a potent oral, class I PI3K inhibitor which strongly inhibits the PI3K alpha isoforms and is significantly less active against the other class I isoforms. Targeting the alpha isoform of PI3K is expected to improve the therapeutic window over inhibitors with less isoform specificity. Nab-Paclitaxel is a solvent-free, nanoparticle, albumin-based paclitaxel which takes advantage of the antitumor activity of paclitaxel while decreasing the toxicities typically associated with the solvent (Cremophor) used to administer the most common formulation of paclitaxel. Methods A 3+3 dose-escalation design evaluated three dose levels of BYL719 (250mg, 300mg, and 350mg) administered PO once daily (D1-28) with nab-Paclitaxel (100 mg/m2 intravenously D 1, 8, 15) every 28 days in patients with metastatic HER 2 negative breast cancer. The aims of the study were to 1) determine the recommended phase II dose (RPTD) of BYL719 + nab-Paclitaxel, 2) assess pharmacokinetics of BYL and nab-paclitaxel, and 3) assess preliminary efficacy. Results 10 patients were enrolled at 3 dose levels of BYL719 and 3 patients were enrolled in expansion cohort at the RPTD of BYL719 of 350 mg PO daily plus nab-paclitaxel 100mg/m2 (D 1, 8, 15). Median age was 61years; 54% (7/13) of patients were hormone receptor positive and 46% (6/13) triple negative. 85% (11/13) had visceral disease, 69% (9/13) had received prior chemotherapy for metastatic disease and 85% (11/13) had received prior taxane in adjuvant/metastatic setting. There were no DLTs in the three cohorts and the MTD of BYL was not reached. Hyperglycemia (G3:31%, G4:0%) and neutropenia (G3:15%, G4:8%), were the most common grade 3/4 adverse events. There were no Grade 3/4 diarrhea or rash. Best overall response for 12 patients was 58% (7/12) (complete response=1, partial response=6), and an additional 33% (4/12) demonstrated stable disease. Objective responses were noted in both hormone positive and triple negative disease. Median duration of response is 6.5 months (range 2-14 months). No pharmacokinetic interactions were detected when BYL and nab-paclitaxel were co-administered. Discussion: This phase I study demonstrates that combination of BYL719 and nab-paclitaxel was well tolerated and shows encouraging efficacy in metastatic HER2 negative breast cancer. Enrollment in the phase II portion of the trial at the RPTD (BYL719 350mg PO daily plus nab-paclitaxel 100mg/m2 D1,8,15 every 28 days) continues. Ongoing analysis of PI3K pathway alterations in tumor and cfDNA will be correlated with clinical response. Citation Format: Sharma P, Abramson VG, O'Dea A, Lewis S, Scott JN, Ward J, De Jong JA, Lehn C, Brown AR, Williamson SK, Perez RP, Komiya T, Godwin AK, Reed GA, Khan QJ. Safety and efficacy results from phase I study of BYL 719 plus nab-paclitaxel in HER 2 negative metastatic breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-11-08.

Increasing metabolic stability via the deuterium kinetic isotope effect: An example from a proline-amide-urea aminothiazole series of phosphatidylinositol-3 kinase alpha inhibitors

In vitro metabolic identification studies with a PI3K-α inhibitor lead molecule 1 identified a single predominant site of oxidative metabolism to be occurring within a tert.butyl moiety. Modification of the tert.butyl group within the lead molecule 1, to the corresponding d9-tert.butyl analogue 2, led to an increase in both the in vitro and in vivo metabolic stability. This increase in metabolic stability resulted in a 2-fold increase in the oral bioavailability measured in the rat, and a 3-fold increase in potency in a chronic in vivo study in the mouse, for 2 when compared to 1.

Abstract P6-13-11: Phase I study of alpelisib and T-DM1 in trastuzumab-refractory HER2-positive metastatic breast cancer

Abstract BACKGROUND: Constitutive activation of the phosphatidylinositol-3-kinase (PI3K) signaling pathway is a mechanism of trastuzumab resistance in HER2-positive metastatic breast cancer (MBC). Alpelisib (BYL-719) is the first oral PI3K inhibitor that selectively inhibits the PI3K alpha isoform. We aimed to determine the maximum tolerated dose (MTD), safety, and activity of alpelisib in combination with ado-trastuzumab emtansine (T-DM1) in HER2-positive MBC that has progressed on or after trastuzumab and/or taxane-based regimens. METHODS: This phase I study enrolled patients with HER2-positive MBC who received alpelisib daily (cohort 1: 300 mg, cohort (-)1: 250 mg) and T-DM1 3.6 mg/m2 on Day 1 of a 3 week cycle using a 3+3 design with dose expansion at the MTD. Treatment was continued until progression, unacceptable toxicity, or patient preference. Blood was collected for pharmacokinetic (PK) and pharmacodynamic (PD) markers. Dose-limiting toxicity (DLT) was defined as CTCAE Grade 3 or 4 adverse events (AE) during the first cycle. Imaging and echocardiogram were obtained every 3 cycles. RESULTS: Dose escalation is completed and included in this analysis (N=8). Median age was 53 (range 46-79) with median ECOG Performance Status of 1. Median prior lines of therapy in the metastatic setting was 6 (range 0-12) including 5 patients who progressed on prior T-DM1 (after median 6 cycles). Two patients had de novo MBC and 3 with ER and/or PR positive disease. Median number of metastatic sites was 2 (range 1-5) including brain (inactive), liver, and lung. Median number of cycles of alpelisib and T-DM1 per patient was 5.5 (range 1-12). Five patients were enrolled in cohort 1 with 2 DLTs (both grade 3 rash), leading to cohort (-)1, in which there were no DLTs. The most common treatment-related AEs were fatigue (n=7, 86%), nausea (n=6, 75%), aspartate aminotransferase increase (n=4, 50%), and thrombocytopenia (n=4, 50%). Grade 3 AEs were rash (n = 3), hyperglycemia (n=1), hypertension (n=1) and thrombocytopenia (n=1), which occurred in only cohort 1. Grade 3 rash typically occurred during cycle 1, which resolved with temporary interruption and subsequent dose reduction of alpelisib and the use of topical steroids for median 9.3 days (range 6-12). Grade 3 hyperglycemia was reversible with oral anti-diabetic treatment. A total of 4 dose reductions occurred in cohort 1. No Grade 3/4 AEs or dose reductions occurred in cohort -1. In total, only 0.07% of all AEs were Grade 3 and none Grade 4. The MTD for alpelisib was established as 250 mg daily. In 7 evaluable patients, there were 6 objective responses after 3 cycles, a response rate of 86% (1 confirmed complete response, 2 confirmed partial response [PR], and 3 unconfirmed PR). Five (67%) of these patients continue to have durable responses (median 6.5 cycles) at doses 200-250 mg daily. One patient had progression of disease. PK/PD results and PIK3CA mutation testing are pending. CONCLUSION: The combination of alpelisib and T-DM1 appears to be safe, well tolerated, with clinical activity in HER2-positive MBC patients including those who progressed on prior T-DM1 therapy. The study is currently in dose expansion with goal of enrolling 10 additional patients with T-DM1 and alpelisib 250 mg daily. Citation Format: Jain S, Nye L, Santa-Maria C, Bontemps L, Williams A, Garrett H, Dammrich E, Giles F, Gradishar W. Phase I study of alpelisib and T-DM1 in trastuzumab-refractory HER2-positive metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-13-11.

Chronic Dietary Administration of the Glycolytic Inhibitor 2-Deoxy-D-Glucose (2-DG) Inhibits the Growth of Implanted Ehrlich’s Ascites Tumor in Mice

BackgroundDietary energy restriction (DER) has been well established as a potent anticancer strategy. Non-adoption of restricted diet for an extended period has limited its practical implementation in humans with a compelling need to develop agents that mimic effects similar to DER, without reduction in actual dietary intake. Glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), has recently been shown to possess potential as an energy restriction mimetic agent (ERMA). In the present study we evaluated the effect of dietary 2-DG administration on a mouse tumor model, with a focus on several potential mechanisms that may account for the inhibition of tumorigenesis.Methodology/Principal FindingsSwiss albino strain ‘A’ mice were administered with 0.2% and 0.4% w/v 2-DG in drinking water for 3 months prior to tumor implantation (Ehrlich’s ascites carcinoma; EAC) and continued till the termination of the study with no adverse effects on general physiology and animal growth. Dietary 2-DG significantly reduced the tumor incidence, delayed the onset, and compromised the tumor growth along with enhanced survival. We observed reduced blood glucose and serum insulin levels along with decreased proliferating cell nuclear antigen (PCNA) and bromodeoxyuridine positive (BrdU+) tumor cells in 2-DG fed mice. Also, reduced levels of certain key players of metabolic pathways such as phosphatidylinositol 3-kinase (PI3K), phosphorylated-Akt and hypoxia inducible factor-1 alpha (HIF-1α) were also noted in tumors of 2-DG fed mice. Further, decrease in CD4+/CD8+ ratio and T-regulatory cells observed in 2-DG fed mice suggested enhanced antitumor immunity and T cell effector function.Conclusion/SignificanceThese results strongly suggest that dietary 2-DG administration in mice, at doses easily achievable in humans, suitably modulates several pleotrophic factors mimicking DER and inhibits tumorigenesis, emphasizing the use of ERMAs as a promising cancer preventive strategy.

Identification and optimisation of a 4',5-bisthiazole series of selective phosphatidylinositol-3 kinase alpha inhibitors.

Exploring the affinity-pocket binding moiety of a 2-aminothiazole (S)-proline-amide-urea series of selective PI3Kα inhibitors using a parallel-synthesis approach led to the identification of a novel 4',5-bisthiazole sub-series. The synthesis and optimisation of both the affinity pocket and (S)-proline amide moieties within this 4',5-bisthiazole sub-series are described. From this work a number of analogues, including 14 (A66) and 24, were identified as potent and selective PI3Kα inhibitor in vitro tool compounds.

Identification and optimisation of 4,5-dihydrobenzo[1,2-d:3,4-d]bisthiazole and 4,5-dihydrothiazolo[4,5-h]quinazoline series of selective phosphatidylinositol-3 kinase alpha inhibitors.

A cyclisation within a 4',5-bisthiazole (S)-proline-amide-urea series of selective PI3Kα inhibitors led to a novel 4,5-dihydrobenzo[1,2-d:3,4-d]bisthiazole tricyclic sub-series. The synthesis and optimisation of this 4,5-dihydrobenzo[1,2-d:3,4-d]bisthiazole sub-series and the expansion to a related tricyclic 4,5-dihydrothiazolo[4,5-h]quinazoline sub-series are described. From this work analogues including 11, 12, 19 and 23 were identified as potent and selective PI3Kα inhibitor in vivo tool compounds.

Investigating the Structure and Dynamics of the PIK3CA Wild-Type and H1047R Oncogenic Mutant

The PIK3CA gene is one of the most frequently mutated oncogenes in human cancers. It encodes p110α, the catalytic subunit of phosphatidylinositol 3-kinase alpha (PI3Kα), which activates signaling cascades leading to cell proliferation, survival, and cell growth. The most frequent mutation in PIK3CA is H1047R, which results in enzymatic overactivation. Understanding how the H1047R mutation causes the enhanced activity of the protein in atomic detail is central to developing mutant-specific therapeutics for cancer. To this end, Surface Plasmon Resonance (SPR) experiments and Molecular Dynamics (MD) simulations were carried out for both wild-type (WT) and H1047R mutant proteins. An expanded positive charge distribution on the membrane binding regions of the mutant with respect to the WT protein is observed through MD simulations, which justifies the increased ability of the mutated protein variant to bind to membranes rich in anionic lipids in our SPR experiments. Our results further support an auto-inhibitory role of the C-terminal tail in the WT protein, which is abolished in the mutant protein due to loss of crucial intermolecular interactions. Moreover, Functional Mode Analysis reveals that the H1047R mutation alters the twisting motion of the N-lobe of the kinase domain with respect to the C-lobe and shifts the position of the conserved P-loop residues in the vicinity of the active site. These findings demonstrate the dynamical and structural differences of the two proteins in atomic detail and propose a mechanism of overactivation for the mutant protein. The results may be further utilized for the design of mutant-specific PI3Kα inhibitors that exploit the altered mutant conformation.

Discovery of NVP-BYL719 a potent and selective phosphatidylinositol-3 kinase alpha inhibitor selected for clinical evaluation

Phosphatidylinositol-3-kinase α (PI3Kα) is a therapeutic target of high interest in anticancer drug research. On the basis of a binding model rationalizing the high selectivity and potency of a particular series of 2-aminothiazole compounds in inhibiting PI3Kα, a medicinal chemistry program has led to the discovery of the clinical candidate NVP-BYL719.