PI3Kα-selective Inhibitor Research Articles

Preclinical Assessment of the PI3Kα Selective Inhibitor Inavolisib and Prediction of Its Pharmacokinetics and Efficacious Dose in Human

1. Small molecule inhibitors of the PI3K pathway have been extensively investigated as potential anticancer agents. Among the effectors in this pathway, PI3Kα is the kinase most frequently associated with the development of tumors, through mutations and amplifications of the PIK3CA gene encoding the p110α catalytic subunit. 2. Inavolisib (GDC-0077) is a potent and PI3Kα-selective inhibitor that also specifically triggers the degradation of the mutant p110α protein. 3. We characterized inavolisib ADME properties in preclinical in vitro and in vivo studies, assessed its efficacy in the PIK3CA mutant KPL-4 breast cancer xenograft model, and predicted its pharmacokinetics and efficacious dose in humans. 4. Inavolisib had a moderate permeability (1.9•10−6 cm/s) in MDCK cells and was a P-gp and Bcrp1 substrate. It appeared metabolically stable in hepatocytes incubations from human and preclinical species. The systemic clearance was low in mouse, monkey and dog and high in rat. Oral bioavailability ranged from 57.5% to 100%. Inavolisib was efficacious in the KPL-4 sub-cutaneous xenograft model. 5. The PK/PD model parameters estimated from the efficacy study, combined with PBPK model-predicted human PK profiles, projected that a dose of 3 mg could lead to clinical response. Inavolisib is currently being tested in phase 3 trials.

Rational Design of a Novel 6H-Benzo[c]chromen Series as Selective PI3Kα Inhibitors.

The phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway is a frequently dysregulated pathway in human cancer, and PI3Kα is one of the most frequently mutated kinases in human cancer. A selective PI3Kα inhibitor may provide the opportunity to spare patients the side effects associated with broader inhibition of the class I PI3K family. Here, we describe our efforts to discover a novel series of selective PI3Kα inhibitors using structure-based drug design and molecular docking to inform the design of 6H-benzo[c]chromen inhibitors. XJTU-L453 (21) was identified with PI3Kα inhibitory potency and unique selectivity over other PI3K isoforms and all other kinases tested. Further evaluation of pharmacokinetic properties and in vivo efficacy led to the identification of the preclinical potential of XJTU-L453 (21).

Design, synthesis and bioevaluation of dual EGFR-PI3Kα inhibitors for potential treatment of NSCLC

Aberrant activation or mutation of the EGFR-PI3K-Akt-mTOR signaling pathway has been implicated in a wide range of human cancers, especially non-small-cell lung cancer (NSCLC). Thus, dual inhibition of EGFR and PI3K has been investigated as a promising strategy to address acquired drug resistance resulting from the use of tyrosine kinase inhibitors. A series of dual EGFR/PI3Kα inhibitors was synthesized using pharmacophore hybridization of the third-generation EGFR inhibitor olmutinib and the PI3Kα selective inhibitor TAK-117. The optimal compound 30k showed potent kinase inhibitory activities with IC50 values of 3.6 and 30.0 nM against EGFRL858R/T790M and PI3Kα, respectively. Compound 30k exhibited a significant antiproliferative effect in NCI-H1975 cells with a higher selectivity profile than olmutinib. The potential antitumor mechanism, molecular binding modes, and in vitro metabolic stability of compound 30k were also clarified.

Delineation of the phenotypes and genotypes of PIK3CA-related overgrowth spectrum in East asians.

PIK3CA-related overgrowth spectrum (PROS) is an umbrella term to describe a diverse range of developmental disorders. Research to date has predominantly emerged from Europe and North America, resulting in a notable scarcity of studies focusing on East Asian populations. Currently, the prevalence and distribution of PIK3CA variants across various genetic loci and their correlation with distinct phenotypes in East Asian populations remain unclear. This study aims to elucidate the phenotype-genotype correlations of PROS in East Asian populations. We presented the phenotypes and genotypes of 82 Chinese patients. Among our cohort, 67 individuals carried PIK3CA variants, including missense, frameshift, and splice variants. Six patients presented with both PIK3CA and an additional variant. Seven PIK3CA-negative patients exhibited overlapping PROS manifestations with variants in GNAQ, AKT1, PTEN, MAP3K3, GNA11, or KRAS. An integrative review of the literature pertaining to East Asian populations revealed that specific variants are uniquely associated with certain PROS phenotypes. Some rare variants were exclusively identified in cases of megalencephaly and diffuse capillary malformation with overgrowth. Non-hotspot variants with undefined oncogenicity were more common in CNS phenotypes. Diseases with vascular malformation were more likely to have variants in the helical domain, whereas phenotypes involving adipose/muscle overgrowth without vascular abnormalities predominantly presented variants in the C2 domain. Our findings underscore the unique phenotype-genotype patterns within the East Asian PROS population, highlighting the necessity for an expanded cohort to further elucidate these correlations. Such endeavors would significantly facilitate the development of PI3Kα selective inhibitors tailored for the East Asian population in the future.

First-in-human study of RLY-2608, a pan-mutant and isoform selective PI3Kα inhibitor, as a single agent in patients (pts) with advanced solid tumors and in combination with fulvestrant in pts with advanced breast cancer.

TPS1128 Background: Oncogenic mutations in PIK3CA occur in ~35% of HR+, HER2– breast cancer (BC) and are frequent in multiple solid tumors. The approval of alpelisib, a non-mutant selective PI3Kα inhibitor, validates PI3Kα as a therapeutic target. However, inhibition of wild-type PI3Kα leads to significant toxicity, including hyperglycemia and rash. RLY-2608, a novel, oral allosteric PI3Kα inhibitor, is designed to overcome these limitations via mutant- and isoform-selective PI3Kα inhibition for greater target coverage, improved tolerability, and anti-tumor activity. ReDiscover (NCT05216432) is the ongoing, first-in-human study to investigate the maximum tolerated dose (MTD), recommended phase 2 doses (RP2Ds), safety, pharmacokinetics (PK), pharmacodynamics (PD) and anti-tumor activity of RLY-2608 monotherapy in pts with PIK3CA-mutant advanced solid tumors; and of RLY-2608 plus fulvestrant with or without ribociclib in pts with PIK3CA-mutant, HR+, HER2– BC. To date RLY-2608 plus fulvestrant has completed dose escalation; 400 and 600 mg BID is being investigated in the combination regimens, based on safety, PK, PD, and anti-tumor activity. Methods: This global, multi-center, dose escalation/expansion study of RLY-2608 monotherapy includes adult pts with advanced solid tumors who are refractory or intolerant to, or have declined, standard therapy. RLY-2608 is also being investigated in combination with fulvestrant and in combination with fulvestrant and ribociclib, each in previously treated pts with HR+, HER2– advanced/metastatic BC. Eligibility criteria include presence of a PIK3CA mutation (blood or tumor) per local assessment, ECOG performance status 0–1, evaluable disease per RECIST 1.1, and no prior treatment with a PI3K pathway inhibitor. RLY-2608 is administered daily in 4-week cycles. Adverse events (AEs) per CTCAE v5, PK, biomarkers (pAKT, mutant ctDNA and insulin pathway markers) and anti-tumor activity are assessed serially. Dose escalation employs a Bayesian Optimal Interval design to identify the MTD. Following dose escalation, expansion cohorts are enrolling patients with select PIK3CA-mutated solid tumors for treatment with RLY-2608 monotherapy and patients with HR+, HER2– metastatic BC for treatment with RLY-2608 plus fulvestrant with or without ribociclib. Primary endpoints are MTD/RP2D and AE profile; key secondary endpoints are PIK3CA genotype in blood and tumor, PK, biomarkers, and overall response rate. All dose expansion cohorts in ReDiscover are now enrolling in the United States and Europe. Clinical trial information: NCT05216432 .

INAVO121: Phase III study of inavolisib (INAVO) + fulvestrant (FUL) vs. alpelisib (ALP) + FUL in patients (pts) with hormone receptor-positive, HER2-negative (HR+, HER2–), PIK3CA-mutated (mut) locally advanced or metastatic breast cancer (LA/mBC).

TPS1136 Background: Standard-of-care (SoC) endocrine therapy (ET) for pts with HR+, HER2–, PIK3CAmut LA/mBC was transformed by combinations with cyclin-dependent kinase 4/6 inhibitors (CDK4/6is); a CDK4/6i-based combination is approved in high-risk, early BC. However, in most pts, mechanisms of resistance that emerge during or after treatment with a CDK4/6i and ET combination lead to relapse/disease progression. Dysregulating mutations in PIK3CA, occurring in ~40% of HR+, HER2– BCs, represent a common mechanism of resistance to CDK4/6is and ET combinations. ALP, a selective PI3Kα inhibitor (PI3Kαi) + FUL is approved for pts with HR+, HER2–, PIK3CAmut LA/mBC, but its widespread implementation in clinical practice has been challenging. As such, there is a significant need to develop PI3Kαis with a better therapeutic index. INAVO is a highly potent and selective PI3Kαi that also facilitates the degradation of mutated PI3Kα isoform. INAVO has demonstrated manageable safety/tolerability, alone and in combination with SoC treatments in HR+, HER2–, PIK3CAmut LA/mBC. Moreover, an ongoing Phase I trial showed that INAVO + FUL elicited encouraging preliminary antitumor activity in heavily pretreated pts, including in pts pretreated with a CDK4/6i-based regimen. Methods: INAVO121 is a Phase III, randomized, open-label study. Pts are randomized 1:1 to receive INAVO (9 mg oral daily [PO QD]) + FUL (500 mg intramuscularly on Days [D] 1 and 15 of Cycle 1, then D1 of subsequent cycles) or ALP (300 mg PO QD) + FUL. Randomization is stratified by visceral disease (yes vs. no) and prior CDK4/6i therapy (adjuvant vs. metastatic setting). Pts will receive treatment until disease progression or unacceptable toxicity. Pts have HR+, HER2–, PIK3CAmut LA/mBC (confirmed by circulating tumor DNA or tumor tissue), adequate hematologic and organ function, and disease progression after or during treatment with a CDK4/6i-based regimen. Up to two prior lines of systemic therapy in LA/mBC, including one line of chemotherapy, are allowed. The primary endpoint is progression-free survival (PFS) by blinded independent central review (BICR). Secondary endpoints include overall survival, BICR-objective response rate, BICR-best overall response, BICR-duration of response, BICR-clinical benefit rate, safety, tolerability, pt-reported outcomes, and pharmacokinetics. A stratified log-rank test at an overall 0.05 significance level (two-sided) will be used for the primary endpoint analysis. Median PFS will be estimated using Kaplan–Meier methodology. An independent data monitoring committee will be in place for safety and efficacy. The study is open for enrollment and has randomized 159 pts; the study is targeting 400 pts at ~200 sites globally. Clinical trial information: NCT05646862 .

Abstract PO3-20-03: First-in-human global study of RLY-2608, a pan-mutant and isoform selective PI3Kα inhibitor, as a single agent in patients with advanced solid tumors and in combination with fulvestrant in patients with advanced breast cancer

Abstract Background: Oncogenic mutations in PI3Kα are common driver events in ER+ breast cancer and other solid tumors. Alpelisib, a non-mutant selective PI3Kα inhibitor, is effective in ER+ breast cancer thus validating PI3Kα as a therapeutic target. Inhibition of wild-type PI3Kα results in toxicity including hyperglycemia which limits tolerability and drug exposure. RLY-2608, a novel, oral allosteric PI3Kα inhibitor, is uniquely designed to overcome these limitations via mutant- and isoform-selective PI3Kα inhibition for greater target coverage, improved tolerability, and antitumor activity. Initiated in December 2021, ReDiscover is the ongoing, first-in-human study to define the maximum tolerated dose (MTD), safety, pharmacokinetics (PK), pharmacodynamics (PD) and anti-tumor activity of RLY-2608 monotherapy in PIK3CA-mutant advanced solid tumor patients (pts) and of RLY-2608 plus fulvestrant in pts with PIK3CA-mutant, HR+HER2-BC. At AACR 2023, dose escalation data for RLY-2608 was reported and demonstrated encouraging target inhibition and anti-tumor activity (including partial response), across PIK3CA genotypes with minimal impact on glucose homeostasis. To date, pts have received RLY-2608 at doses of 100–2000 mg/day, with no reported dose-limiting toxicities; the MTD has not been reached. These proof-of-mechanism data indicate that RLY-2608 is the first allosteric, pan-mutant selective PI3Kα inhibitor and that RLY-2608 has broad therapeutic potential in PIK3CA-driven cancers. Methods: Enrollment is ongoing in this global, multi-center, dose escalation/expansion study of RLY-2608 as a single agent in adults who have advanced solid tumors and are refractory, intolerant, or have declined standard therapy; and RLY-2608 in combination with fulvestrant in previously treated pts with HR+/HER2– MBC. Eligibility criteria include presence of PIK3CA mutation (blood or tumor) per local assessment, ECOG performance status 0–1, evaluable disease per RECIST 1.1 and no prior PI3K inhibitor (except in expansion combination group 2). RLY-2608 is administered on a continuous schedule with 4-week cycles. Adverse events (AEs) per CTCAE v5, PK, biomarkers (pAKT, mutant ctDNAs and insulin pathway markers) and anti-tumor activity are assessed serially. Dose escalation employs a Bayesian Optimal Interval design to identify the MTD and/or the recommended Phase 2 dose (RP2D). Following dose escalation, expansion cohorts will enroll patients with select PIK3CA-mutated solid tumors for treatment with RLY-2608 monotherapy and patients with HR+/HER2– MBC for treatment with RLY-2608 and fulvestrant. The primary endpoints are MTD/RP2D and AE profile for single agent and combination; key secondary endpoints are PIK3CA genotype in blood and tumor, PK, biomarkers, and overall response rate. ReDiscover (NCT05216432) is enrolling worldwide. For further information, contact clinicaltrials@relaytx.com. Funding source: This study is funded by Relay Therapeutics, Cambridge, MA, United States. Citation Format: Andreas Varkaris, Komal Jhaveri, Elena Garralda Cabanas, Lucia Sanz, Janice Kim, Cesar A. Perez, Erika Hamilton, Alexander I. Spira, Kari Wisinski, Angel Guerrero, Jason Henry, Jordi Rodon Ahnert, Gege Tan, Xiaoyan Li, Diana Hummel, Tamieka Hunter, Alison Timm, Ramin Samadani, Erika Puente-Poushnejad, Eunice Kwak, Brenton G. Mar, Alison M. Schram. First-in-human global study of RLY-2608, a pan-mutant and isoform selective PI3Kα inhibitor, as a single agent in patients with advanced solid tumors and in combination with fulvestrant in patients with advanced breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-20-03.

Abstract PO2-19-08: INAVO121: Phase III study of inavolisib + fulvestrant vs alpelisib + fulvestrant in patients with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer

Abstract BACKGROUND Standard-of-care (SoC) endocrine therapy (ET) for patients (pts) with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer (HR+, HER2–, PIK3CA-mut LA/mBC) was transformed by combinations with cyclin-dependent kinase 4/6 inhibitors (CDK4/6is); a CDK4/6i-based combination is approved in high-risk early BC. However, in most pts, mechanisms of resistance that emerge during or after treatment with a CDK4/6i and ET combination lead to relapse/disease progression. Dysregulating mutations in PIK3CA, occurring in ~40% of HR+, HER2– BCs, represent a common mechanism of resistance to CDK4/6is and ET combinations. Alpelisib (ALP; a selective PI3Kα inhibitor; PI3Kαi) + fulvestrant (FUL) is approved for pts with HR+, HER2–, PIK3CA-mut LA/mBC, but its widespread implementation in clinical practice has been challenging. As such, there is a significant need to develop PI3Kαis with a better therapeutic index. Inavolisib (INAVO) is a highly potent and selective PI3Kαi that also facilitates the degradation of mutated PI3Kα isoform. INAVO has demonstrated manageable safety/tolerability, alone and in combination with SoC treatments in HR+, HER2–, PIK3CA-mut LA/mBC. Moreover, an ongoing Phase I trial showed that INAVO + FUL elicited encouraging preliminary antitumor activity in heavily pretreated pts, including a CDK4/6i-based regimen. TRIAL DESIGN INAVO121 is a Phase III, randomized, open-label study. Pts are randomized 1:1 to receive INAVO (9 mg oral daily; PO QD) + FUL (500 mg intramuscularly on Days [D] 1 and 15 of Cycle 1, then D1 of subsequent cycles), or ALP (300 mg PO QD) + FUL. Randomization is stratified by visceral disease (yes vs no) and prior CDK4/6i therapy (adjuvant vs metastatic setting). Pts will receive treatment until disease progression or unacceptable toxicity. ELIGIBILITY CRITERIA Pts have HR+, HER2–, PIK3CA-mut LA/mBC (confirmed by circulating-tumor DNA or tumor tissue), adequate hematologic and organ function, and disease progression after or during treatment with a CDK4/6i-based regimen. Up to two prior lines of systemic therapy in LA/mBC, including one line of chemotherapy, are allowed. AIMS The primary endpoint is progression-free survival (PFS) by blinded independent central review (BICR). Secondary endpoints include overall survival, BICR-objective response rate, BICR-best overall response, BICR-duration of response, BICR-clinical benefit rate, safety, tolerability, pt-reported outcomes, and pharmacokinetics. STATISTICAL METHODS A stratified log-rank test at an overall 0.05 significance level (two-sided) will be used for the primary endpoint analysis. Median PFS will be estimated using Kaplan–Meier methodology. An independent data monitoring committee will be in place for safety and efficacy. ACCRUAL The study is open for enrollment and has randomized four pts; the study is targeting 400 pts at ~200 sites globally. CONTACT INFORMATION For more information or to refer a patient, email global.rochegenentechtrials@roche.com or call 1-888-662-6728 (USA only). Clinicaltrials.gov number NCT05646862. This abstract was originally presented at ASCO 2023 (TPS1123). Citation Format: Dejan Juric, Kevin Kalinsky, Seock-Ah Im, Eva Ciruelos, Giampaolo Bianchini, Carlos Barrios, William Jacot, Peter Schmid, Sherene Loi, Hope Rugo, Veronica Craine, Katherine Hutchinson, Aulde Flechais, Eirini Thanopoulou, Nadia Harbeck. INAVO121: Phase III study of inavolisib + fulvestrant vs alpelisib + fulvestrant in patients with hormone receptor-positive, HER2-negative, PIK3CA-mutated locally advanced or metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-19-08.

Abstract PO3-20-04: A first-in-human study of the highly selective PI3Kα inhibitor RLY-5836 in patients with advanced breast cancer and other solid tumors

Abstract Background: Oncogenic activation of PI3Kα is a common driver event in solid tumors. Although PI3Kα is a validated therapeutic target, there is no approved highly selective inhibitor that targets mutant PI3Kα. Alpelisib, a non-selective orthosteric PI3Kα inhibitor, is approved in combination with fulvestrant for patients with PIK3CA-mutant, ER+, HER2– advanced breast cancer. Inhibition of wild-type PI3Kα causes hyperglycemia, limiting the tolerability, dosing, and efficacy of alpelisib. RLY-5836 is the second allosteric, selective pan-mutant PI3Kα inhibitor under clinical investigation. It is molecularly distinct with differentiated pharmaceutical properties compared to RLY-2608. This first-in-human study aims to further explore the tolerability and efficacy of highly selective PIK3CA-mutant inhibition as monotherapy and in combination treatment. Methods: This multicenter, open-label study is designed to evaluate the safety, maximum tolerated dose (MTD), recommended Phase 2 dose (RP2D), pharmacokinetics (PK) and preliminary anti-tumor efficacy of RLY-5836 as a single agent and in various combinations. A Bayesian Optimal Interval design is used for dose escalation, followed by a dose expansion part. As monotherapy, RLY-5836 will be investigated in pts with advanced solid tumors harboring a PIK3CA mutation (Arm 1) per local assessment (blood and/or tumor). In pts with PIK3CA-mutant, HR+, HER2– advanced or metastatic breast cancer, RLY-5836 combination arms will include anti-estrogen therapy with or without CDK4/6 inhibition: fulvestrant (Arm 2), and fulvestrant + CDK4/6 inhibitor(s) (Arms 3–5). RLY-5836 is administered orally, continuously in 28-day cycles until disease progression or study discontinuation. Enrollment criteria include age ≥18 years, ECOG PS 0–1, and measurable disease (Arm 1) or evaluable disease (Arms 2–5) per RECIST version 1.1. Participants in the combination arms are required to have received prior treatment with ≥1 CDK4/6 inhibitor and ≥1 anti-estrogen therapy. Prior treatment with a PI3Kα inhibitor is an exclusion criterion for the dose expansion parts of all arms. Planned overall sample size is ~220 pts (~145 pts for the dose escalation, and ~15 pts in each dose expansion arm). Primary endpoints are the MTD, RP2D and overall safety profile of RLY-5836, either as a single agent or in combination. The MTD will be determined as the dose with a dose-limiting toxicity rate closest to the target toxicity rate (30%) in Cycle 1. Secondary endpoints include PK and efficacy parameters. Statistical analyses will be descriptive. This study (NCT05759949) is enrolling in the United States. For further information, please contact clinicaltrials@relaytx.com. Funding source: This study is funded by Relay Therapeutics, Cambridge, MA, United States. Citation Format: Andreas Varkaris, Steven Isakoff, Cesar A. Perez, Bert O'Neil, Erika Hamilton, Erin Conlin, Gege Tan, Xiaoyan Li, Alison Timm, Ramin Samadani, Erika Puente-Poushnejad, Eunice Kwak, Brenton G. Mar, Alison M. Schram. A first-in-human study of the highly selective PI3Kα inhibitor RLY-5836 in patients with advanced breast cancer and other solid tumors [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-20-04.

Abstract PO2-18-04: STX-478 is a potentially best-in-class mutant-selective PI3Kα inhibitor that demonstrates robust efficacy in ER+ breast cancer models as monotherapy and in combination with standard of care agents

Abstract Activating mutations in PI3Kα are among the most prevalent genetic aberrations in breast cancer. Constitutive signaling of PI3Kα is an established oncogenic driver in these cancers, as these mutations are predictors of response to alpelisib, an approved PI3Kα inhibitor, which inhibits both wild type and mutant PI3Kα. While inhibiting PI3Kα has proven to be efficacious, the concomitant inhibition of wild type enzyme in normal tissue results in metabolic dysfunction and ultimately dose-limiting toxicities. Selectively targeting the mutant PI3Kα enzyme is expected to inhibit tumor growth while sparing normal tissues, thus increasing the therapeutic index compared to non-mutant selective PI3Kα inhibitors. Therefore, we have developed STX-478, an allosteric, CNS penetrant, mutant-selective PI3Kα inhibitor. In a high-throughput viability screen, STX-478 selectively inhibited growth of cell lines with kinase domain and helical domain mutations in PI3Kα. In a panel of PI3Kα mutant CDX and PDX models, STX-478 provided efficacy that was similar or superior to higher than clinically achievable doses of alpelisib. Robust suppression of pharmacodynamic (PD) markers, pAKT, was observed in tumors, but not in skeletal muscle. Importantly, the efficacy achieved with STX-478 occurred at doses that did not cause metabolic dysfunction, in contrast to alpelisib which caused insulin release and suppressed glucose uptake in skeletal muscle in a 13C glucose tolerance test. Collectively, these data indicate that STX-478 has an expanded therapeutic window to selectively target mutant PI3Kα in vivo. In efficacy studies using human tumor xenograft models, STX-478 caused tumor regressions as a single agent. In multiple advanced ER+ breast cancer PDX models including models that are insensitive to the approved CDK4/6 inhibitor palbociclib, STX-478 combined with standards of care was highly efficacious and well tolerated. In a representative PDX model, STX-478 combined with the ER degrader fulvestrant and palbociclib was well tolerated for > 90 days of dosing in mice and resulted in durable tumor regressions that were superior to STX-478 alone. In conclusion, these data demonstrate STX-478 is a highly efficacious, well tolerated, mutant-specific PI3Kα inhibitor that can be combined safely with standards of care in breast cancer and provide the therapeutic benefits of PI3Kα inhibition without the side effects associated with inhibiting WT PI3Kα. These properties combined with the potential for CNS penetration and excellent pharmacokinetic profile in higher species make STX-478 a potentially best-in-class mutant-selective PI3Kα inhibitor. STX-478 is currently being evaluated in a Phase I clinical trial (NCT05768139). Citation Format: Trang Tieu, Leonard Buckbinder, David St. Jean, Samantha Manimala, Gregory Dowdell, Michael Huff, Jacob Alltucker, Erica Jackson, Angel Guzman-Perez, Darrin Stuart. STX-478 is a potentially best-in-class mutant-selective PI3Kα inhibitor that demonstrates robust efficacy in ER+ breast cancer models as monotherapy and in combination with standard of care agents [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-18-04.

Abstract PO3-25-09: OKI-219, a PI3KαH1047R-mutant-selective inhibitor demonstrates efficacy as a single agent and drives combination responses with standard of care therapies in pre-clinical PI3KαH1047R mutant breast cancer models

Abstract Mutations in PI3Kα lead to constitutive activation of the PI3K/AKT/mTOR pathway and are highly prevalent in cancer. PI3KαH1047R is the most common amino acid substitution mutation and represents approximately one-third of all PI3Ka mutations, with 15% of breast cancers having a PI3KαH1047R mutation. In breast cancer, PI3KαH1047R mutations are associated with resistance to targeted therapies, including HER2- and estrogen receptor (ER)- targeted agents. Although targeting PI3Kα in cancer is a therapeutically proven strategy, with the currently approved drug alpelisib showing clinical efficacy alone or in combination with other therapies, treatment with non-mutant selective PI3Kα inhibitors such as alpelisib is associated with significant toxicities such as hyperglycemia, due to on-target inhibition of the wild-type enzyme. This often leads to dose modification or discontinuation. Therefore, there is a significant need to develop new PI3Kα-targeted therapies that can avoid or minimize on-target toxicity and improve the safety and clinical benefit for patients. OKI-219 is an orally bioavailable, PI3KαH1047R mutant-selective inhibitor, with ~100-fold cellular selectivity for the H1047R mutation over wild-type. OKI-219 demonstrates selectivity across a panel of 412 kinases, with no other kinases showing >30% inhibition at 1 µM. In vitro, OKI-219 drives decreased phosphorylated AKT (pAKT) and decreased proliferation specifically in PI3KαH1047R mutant cell lines across several tumor types, including breast cancer. In vivo, as a monotherapy, OKI-219 demonstrates dose dependent antitumor activity in multiple human tumor xenograft models, including the H1047R mutant breast cancer CDX models T47D and HCC1954 and several PDX models, with regression rates up to 100% at doses that show no sign of the metabolic dysfunction (increased glucose or insulin) associated with wild-type protein inhibition. The in vivo antitumor activity correlates with pathway inhibition, measured by decreased pAKT in tumors. Moreover, OKI-219 dosed in combination with the selective estrogen receptor degraders (SERDs) fulvestrant, elacestrant or camizestrant showed significant combination benefit leading to tumor regressions of up to 100% in the ER+ H1047R mutant breast cancer model xxT47D, at doses where no regressions were observed with single agent treatment. Dosing OKI-219 in combination with HER2-inhibitors, such as tucatinib, led to tumor regressions in the ER-HER2+ and H1047R mutant breast cancer CDX model HCC1954, also at doses where no regressions were observed with single agent treatment. These data indicate that OKI-219 offers improved efficacy and a wider therapeutic window compared to non-mutant selective PI3Kα inhibitors. OKI-219 is advancing into clinical trials. Citation Format: Molly A. Taylor, Qian Zhao, David Mareska, Maria Hoh, Yevgeniy Izrayelit, Kevin Litwiler, Mark L Boys, Rich Woessner, Duncan Walker, James D Winkler, Jennifer Diamond. OKI-219, a PI3KαH1047R-mutant-selective inhibitor demonstrates efficacy as a single agent and drives combination responses with standard of care therapies in pre-clinical PI3KαH1047R mutant breast cancer models [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-25-09.

Abstract PS17-07: Interim analysis of giredestrant + inavolisib in MORPHEUS Breast Cancer: a Phase Ib/II study of giredestrant treatment combinations in estrogen receptor-positive, HER2-negative, locally advanced/metastatic breast cancer

Abstract BACKGROUND Patients with estrogen receptor-positive metastatic breast cancer (ER+ mBC) almost always progress on first-line endocrine therapy (ET), which is usually combined with a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i). Finding effective ET combinations after progression following CDK4/6is remains a challenge. Giredestrant (GIR) is a highly potent, nonsteroidal, oral, selective ER antagonist and degrader. Inavolisib (INAVO) is a highly potent PI3Kα-selective inhibitor that promotes degradation of mutated p110α. After first-line treatment (tx) with a CDK4/6i, PIK3CA mutations (mut), which are common, persist and remain a sensitive oncogenic target in these patients. We present a 16-week interim analysis of GIR vs GIR + INAVO in MORPHEUS BC (NCT04802759). METHODS Patients whose tumors harbored a PIK3CAmut and who had disease progression on up to two lines of endocrine-based therapy (including at least one prior line of CDK4/6i) for locally advanced (LA)/mBC were randomized 1:6 to receive GIR (30 mg orally daily [PO QD]) or GIR + INAVO (9 mg PO QD) tx until disease progression or unacceptable toxicity. Given the small numbers, the GIR arm is presented for overall safety. Primary endpoints are safety and objective response rate (ORR). Other endpoints include progression-free survival (PFS), disease control rate (DCR), and pharmacokinetics. Genetic alterations were identified centrally in baseline circulating tumor DNA using the FoundationOne Liquid CDx assay. In cases where PIK3CAmut could not be determined centrally, local blood or tissue results are used. RESULTS As of April 18, 2023, seven and 15 patients were enrolled in the GIR and GIR + INAVO arms, respectively; 71% (n = 5) and 67% (n = 10) received one prior line of therapy in the LA/mBC setting; 14% (n = 1) and 33% (n = 5) received two prior lines; and one GIR-arm patient received four prior lines. Prior fulvestrant (FUL) was received by 53% of patients in the GIR + INAVO arm (n = 8). For GIR + INAVO, the ORR was 47% (n = 7); the complete response rate was 7% (n = 1); and the partial response (PR) rate was 40% (n = 6). The DCR at 12 weeks was 80% (12/15 patients). The median PFS was 10.3 months (95% confidence interval = 6.5, not evaluable) with 47% of patients (n = 7) having events. In the GIR + INAVO arm, 5/6 patients with an ESR1mut had a PR (83%) and one (17%) had stable disease. No clinically relevant drug–drug interaction was observed. Safety data are presented in the table. Two patients experienced grade 3 hyperglycemia, one of whom had baseline elevated HbA1c and has been on insulin therapy since the event. The other patient received a single day of insulin treatment. In the GIR + INAVO arm, the incidence of rash and stomatitis (all grade 1) was 13% each. CONCLUSIONS An encouraging efficacy signal was observed with GIR + INAVO when compared cross-trial with BYLieve arm A (PMID: 33794206). ORRs were 47% in MORPHEUS BC vs 21% in BYLieve for patients with measurable disease (although no prior FUL was allowed in BYLieve). Safety of GIR + INAVO was aligned to the individual safety profiles of each of the drugs, with no new safety signals identified and a favorable tolerability profile for a PI3Kα inhibitor-based combination. Table. Safety summary Data are % of patients. AE, adverse event; GIR, giredestrant; INAVO, inavolisib; TRAE, treatment-related adverse event; tx, treatment. Citation Format: Hope Rugo, Maria Gion, Cristina Hernando, Kyung Hae Jung, Mafalda Oliveira, Melinda Telli, Gregory Vidal, Sina Vatandoust, Jing Zhu, Richard Schwab, Huy Ngo, Erika Ferreira, Ann Collier, Vanessa Breton, Einav Gal-Yam. Interim analysis of giredestrant + inavolisib in MORPHEUS Breast Cancer: a Phase Ib/II study of giredestrant treatment combinations in estrogen receptor-positive, HER2-negative, locally advanced/metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS17-07.

Abstract LB449: Strategies to overcome resistance to PI3Kalpha-selective inhibitors mediated by acquired alterations in the PI3K/AKT pathway

Abstract PIK3CA is among the most frequently mutated kinases in multiple types of cancer, including in 40% of hormone receptor-positive, HER2-negative breast cancers. The PI3Kα-selective orthosteric inhibitor alpelisib is the only drug targeting PIK3CA currently approved in this patient population, in combination with fulvestrant. As commonly observed with other targeted therapies, resistance often develops during treatment with PI3Kα-selective inhibitors. In one of the largest patient cohorts to date, including serial liquid biopsies and rapid autopsies in 39 patients, our group has observed genomic alterations within the PI3K/AKT pathway as one of the major mechanisms of resistance to these agents. Among them, we have identified for the first-time secondary mutations in PIK3CA (W780R and Q859K) that decrease the affinity of the PI3Kα-selective inhibitors alpelisib and inavolisib, leading to acquired resistance. Multiple small molecule inhibitors designed to suppress signaling through the PI3K/AKT axis are currently in pre-clinical development. These include AKT inhibitors, isoform-selective as well as pan-PI3K inhibitors, and a novel subclass of allosteric PI3Kα-selective inhibitors designed to preferentially inhibit both kinase (H1047R) and helical (E545K) domain mutant PI3Kα activity. We have introduced all the emergent alterations observed in our patient cohort into breast cancer models and screen how they modify the effect of a structurally diverse array of PI3K/AKT inhibitors. While some acquired mutations compromise the effect of specific drugs, we have determined that the W780R mutation could drive universal resistance to ATP-competitive PI3K inhibitors that bind the catalytic pocket. Importantly, vertical pathway inhibition or allosteric inhibition with pan-mutant-selective PI3Kα inhibitors such as RLY-2608 or STX-478 could overcome resistance induced by all emerging secondary PIK3CA mutations.Dose-limiting toxicity in the form of hyperglycemia, rash or gastrointestinal issues are common in patients treated with orthosteric PI3Kα inhibitors. While mutant selective PI3Kα inhibitors induce less adverse effects in patients, they have a decreased potency targeting wildtype PIK3CA. We have identified wildtype PIK3CA-mediated feedback pathway reactivation as a potential mechanism of resistance to this type of inhibitors. Our work suggests that combining orthosteric and allosteric PI3Kα inhibitors as well as downstream pathway deactivation with AKT inhibitors could result in an increased therapeutic index and delay the emergence of resistance in patients. This work provides an insightful characterization of the current knowledge on clinical acquired resistance to PI3Kα inhibitors and proposes a detailed strategy to overcome resistance mediated by most PI3K/AKT alterations described to date. Citation Format: Ferran Fece de la Cruz, Andreas Varkaris, Elizabeth E. Martin, Bryanna L. Norden, Nicholas Chevalier, Allison M. Kehlmann, Ignaty Leshchiner, Haley Barnes, Sara Ehnstrom, Parasvi Patel, Janice S. Kim, Haley Ellis, Ioannis Sanidas, Kayao T. Lau, Aditya Bardia, Laura M. Spring, Steven J. Isakoff, Jochen K. Lennerz, Gad Getz, Ryan B. Corcoran, Dejan Juric. Strategies to overcome resistance to PI3Kalpha-selective inhibitors mediated by acquired alterations in the PI3K/AKT pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB449.

Abstract 1955: Novel long-acting covalent PI3Kα inhibitors boost potential action in cancer

Abstract Phosphoinositide 3-kinase (PI3K) is a key regulator of cell proliferation, survival, and metabolism. Hotspot mutations in the PIK3CA gene constitutively activate the catalytic subunit of the PI3Kα isoform and are found in 10-30% of solid tumors. The development of PI3K pathway inhibitors has been hampered by poor drug tolerance and release of negative feedback loops, leading to rapid reactivation of signaling in response to reversible inhibitors. To remedy these challenges, we developed highly selective covalent PI3Kα inhibitors that irreversibly bind to a non-conserved cysteine (C862) located 11 Å outside the ATP-binding site. Here we present the properties of an optimized drug-like covalent lead, dubbed compound 9, and describe the generation of a biotinylated probe developed to be used in conjunction with compound 9 to monitor PI3Kα target occupancy in relation to downstream PI3K signaling outputs. Biochemical investigations of compound 9 using TR-FRET assays showed high affinity binding (Ki), high reaction rates (kinact) for covalent bond formation with PI3Kα, and negligible off-target reactivity. Cellular NanoBRET assays revealed that compound 9 diffuses three times more rapidly into cells as compared to BYL719 (alpelisib), and leads to rapid and potent on-target engagement. Covalent bond formation to residue C862 of PI3Kα was further confirmed by X-ray crystallography. In PIK3CA mutant cancer cell lines, covalent binding of PI3Kα occurred at low nanomolar concentrations and led to persistent inhibition of Akt/PKB phosphorylation for more than 72 hours after drug removal. Notably, investigation of PI3Kα re-synthesis after labeling with compound 9 showed a negligible reappearance in cancer cell lines, which indicates that persistent suppression of PI3Kα signaling by compound 9 results in a much longer half-life for PI3Kα than previously reported. The irreversible inactivation of PI3Kα by compound 9 provides a marked gain in growth inhibition potency (10-600-fold) in PIK3CA mutant cancer cell lines in comparison to clinical reversible PI3Kα inhibitors and allows for intermittent dosing without compromising efficacy. These data collectively demonstrate that compound 9 enables precise and selective targeting of PI3Kα with high potency and long-lasting efficacy in cancer models. The new class of irreversible PI3Kα inhibitors have a unique pharmacology among PI3K inhibitors characterized by strong decoupling of drug exposure from efficacy which may provide opportunities to lower treatment burden in patients. Citation Format: Theodora A. Constantin, Lukas Bissegger, Erhan Keleş, Luka Raguž, Clara Orbegozo, Thorsten Schaefer, Isobel Barlow-Busch, John E. Burke, Chiara Borsari, Matthias P. Wymann. Novel long-acting covalent PI3Kα inhibitors boost potential action in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1955.

Abstract 1954: Development of highly potent, covalent, and selective inhibitors to target PI3Kα in cancer

Abstract Aberrant PI3K signaling is linked to various forms of cancer and proliferative disease. Approved clinical therapies targeting overactive PI3K are scarce and often accompanied by severe adverse effects due to lack of PI3K isoform selectivity. We recently reported a proprietary covalent proximity scanning (CoPS) approach to selectively target distant cysteines outside of the ATP-binding pocket in kinases. Using CoPS, we developed isoform specific, irreversible covalent PI3Kα inhibitors (cPI3Kαi) with outstanding target engagement profiles. Here, we report structure-guided scaffold and linker-optimizations resulting in cPI3Kαi with long-term and rapid inhibition of PI3Kα. Cellular activity was improved exploiting additional protein-inhibitor interactions inspired by X-ray crystallographic data, and introduction of structural elements to increase cell permeability. The cPI3Kαi series showed enhanced cellular potency and excellent on-target engagement. Kinetic parameters and covalent bond formation were determined using TR-FRET, nanoBRET tracer displacement assays, and LCMS/MS based proteomics. With our new cPI3Kαi, IC50s of PKB/Akt phosphorylation, pPKB/Akt recovery after drug washout, and growth inhibition experiments were performed in cancer cell lines harboring activating PIK3CA or inactivating PTEN mutations. Efficient and long-lasting inhibition of PKB/Akt phosphorylation was observed in PIK3CA mutant cell lines, while loss of PTEN was associated with partial responses, consistent with contributions of other class I PI3K isoforms to signal reactivation. A dynamic FOXO cytosolic/nuclear translocation assay was used to monitor distal PI3K signaling: cPI3Kαi blunted PI3K signaling rapidly with rates identical to the reversible BYL719/alpelisib. After drug washout, inhibition by BYL719/alpelisib was relieved within minutes, while a complete and prolonged shutdown of downstream signaling events was observed in PIK3CA mutant cell lines but not in cell lines where PTEN function was lost. This relapse in downstream signaling explains the lack of efficacy of PI3Kα selective inhibitors in models with PTEN loss and demonstrates that persistent inhibition across the PI3K pathway is required for efficacy. In summary, the new cPI3Kαi display outstanding specificity and cellular activity in PIK3CA-mutated cancer cells, and support the further development of cPI3Kαi as future clinical candidates and an alternative to established reversible inhibitors. Citation Format: Luka Raguž, Theodora A. Constantin, Lukas Bissegger, Erhan Keleş, Clara Orbegozo, Thorsten Schäfer, Rohitha Sriramaratnam, Chiara Borsari, Matthias P. Wymann. Development of highly potent, covalent, and selective inhibitors to target PI3Kα in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1954.

Discovery of Pyridopyrimidinones that Selectively Inhibit the H1047R PI3Kα Mutant Protein.

The H1047R mutation of PIK3CA is highly prevalent in breast cancers and other solid tumors. Selectively targeting PI3KαH1047R over PI3KαWT is crucial due to the role that PI3KαWT plays in normal cellular processes, including glucose homeostasis. Currently, only one PI3KαH1047R-selective inhibitor has progressed into clinical trials, while three pan mutant (H1047R, H1047L, H1047Y, E542K, and E545K) selective PI3Kα inhibitors have also reached the clinical stage. Herein, we report the design and discovery of a series of pyridopyrimidinones that inhibit PI3KαH1047R with high selectivity over PI3KαWT, resulting in the discovery of compound 17. When dosed in the HCC1954 tumor model in mice, 17 provided tumor regressions and a clear pharmacodynamic response. X-ray cocrystal structures from several PI3Kα inhibitors were obtained, revealing three distinct binding modes within PI3KαH1047R including a previously reported cryptic pocket in the C-terminus of the kinase domain wherein we observe a ligand-induced interaction with Arg1047.

Hybridization-based discovery of novel quinazoline-2-indolinone derivatives as potent and selective PI3Kα inhibitors

IntroductionPhosphatidylinositol 3-kinases (PI3Ks) overexpression can elicit cellular homeostatic dysregulation, which further contributes to tumorigenesis, with PI3Kα emerging as the most prevalent mutant isoform kinase among PI3Ks. Therefore, selective inhibitors targeting PI3Kα have attracted considerable interest in recent years. Molecular hybridization, with the advantage of simplified pharmacokinetics and drug-drug interactions, emerged as one of the important avenues for discovering potential drugs. ObjectivesThis study aimed to construct PI3Kα inhibitors by hybridization and investigate their antitumor activity and mechanism. Methods26 quinazoline-2-indolinone derivatives were obtained by molecular hybridization, and their structure–activity relationship was analyzed by MTT, in vitro kinase activity and molecular docking. The biological evaluation of compound 8 was performed by transwell, flow cytometry, laser scanning confocal microscopy, Western blot, CTESA and immunohistochemistry. ResultsHere, we employed molecular hybridization methods to construct a series of quinazoline-2-indolinone derivatives as PI3Kα selective inhibitors. Encouragingly, representative compound 8 exhibited a PI3Kα enzymatic IC50 value of 9.11 nM and 10.41/16.99/37.53-fold relative to the biochemical selectivity for PI3Kβ/γ/δ, respectively. Moreover, compound 8 effectively suppressed the viability of B16, HCT116, MCF-7, H22, PC-3, and A549 cells (IC50 values: 0.2 μM ∼ 0.98 μM), and dramatically inhibited the proliferation and migration of NSCLC cells, as well as induced mitochondrial apoptosis through the PI3K/Akt/mTOR pathway. Importantly, compound 8 demonstrated potent in vivo anti-tumor activity in non-small cell lung cancer mouse models without visible toxicity. ConclusionsThis study presented a new avenue for the development of PI3Kα inhibitors and provided a solid foundation for novel QHIDs as potential future therapies for the treatment of NSCLC.

Computational-guided approach for identification of PI3K alpha inhibitor in the treatment of hepatocellular carcinoma by virtual screening and water map analysis

Hepatocellular carcinoma (HCC) is one of the most deadly disorders, with a relative survival rate of 36% in the last 5 years. After an extensive literature survey and pathophysiology analysis, PI3Kα was found to be a promising biological target as PIK3CA gene upregulation was observed in HCC, resulting in the loss of apoptosis of cells, which leads to uncontrollable growth and proliferation. Due to superior selectivity and promising therapeutic activity, the PI3K-targeted molecule library was selected, and the ligand preparation was executed. The study mainly focused on e-pharmacophore development, virtual screening and receptor–ligand docking analysis. Then, MMGBSA and ADME prediction analysis was performed with the top 10 molecules; for further analysis of ligand–receptor binding affinity at the catalytic binding site, induced fit docking was performed with the top two molecules. The analysis of quantum chemical stability descriptors, i.e., frontier molecular orbital analysis, was performed followed by molecular dynamics simulation of 100 ns to better understand the ligand-receptor binding. In this study, water map analysis played a significant role in the hit optimization and analysis of the thermodynamic properties of the receptor–ligand complex. The two hit molecules K894-1435 and K894-1045 represented superior docking scores, enhanced stability, and inhibitory action targeting Valine 851 amino acid residue at the catalytic binding site. Hence, the study has significance for the quest for selective PI3Kα inhibitors through the process of hit-to-lead optimization. Communicated by Ramaswamy H. Sarma

Abstract B163: Discovery and characterization of OKI-219, an orally bioavailable H1047R-mutant-selective inhibitor of PI3Kα

Abstract Mutations in PI3Kα lead to constitutive activation of the PI3K/AKT/mTOR pathway and are found in approximately 13% of human cancers, with the PI3KαH1047R mutation being the most common. Targeting PI3Kα in cancer is a therapeutically proven strategy, with the currently approved drug alpelisib showing clinical efficacy alone or in combination with other therapies. However, treatment with non-mutant selective PI3Kα inhibitors, such as alpelisib, is associated with significant toxicities such as hyperglycemia due to on-target inhibition of the wild-type enzyme, which often leads to dose modification or discontinuation. Therefore, there is a significant need to develop new PI3Kα-targeted therapies that can avoid or minimize on-target toxicity and improve the safety and clinical benefit for patients. OKI-219 is a PI3KαH1047R mutant-selective inhibitor, with ~100-fold cellular selectivity for the H1047R mutation over wild-type and biochemical selectivity across a 412 kinase panel, with no other kinases showing >30% inhibition at 1 µM. In vitro, OKI-219 drives decreased phosphorylated AKT (pAKT) and decreased proliferation selectively in PI3KαH1047R mutant cell lines across several tumor types. In vivo, as a monotherapy, OKI-219 demonstrates dose-dependent antitumor activity in multiple human CDX and PDX tumor xenograft models, with regression rates up to 100% in PI3KαH1047R heterozygous (T47D) and homozygous (SUM185PE) CDX models, at doses that show no sign of the metabolic dysfunction (increased glucose or insulin) that is associated with wild-type protein inhibition. The in vivo antitumor activity correlates with pathway inhibition, measured by decreased pAKT in tumors. In addition to the monotherapy efficacy observed, OKI-219 in combination with the selective estrogen receptor degrader (SERD) fulvestrant showed significant combination benefit leading to tumor regressions in the H1047R-mutated ER+HER2- breast cancer model xxT47D, at doses where no regressions were observed with single agent treatment. These data support the hypothesis that OKI-219 will offer improved efficacy and a wider therapeutic window compared to non-mutant selective PI3Kα inhibitors. This hypothesis will be tested, as OKI-219 is moving into clinical investigation. Citation Format: Molly A Taylor, Qian Zhao, David Mareska, Maria Hoh, Yevgeniy Izrayelit, Kevin Litwiler, Mark L Boys, Rich Woessner, Duncan Walker, Jennifer Diamond, James D Winkler. Discovery and characterization of OKI-219, an orally bioavailable H1047R-mutant-selective inhibitor of PI3Kα [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B163.

Identification of natural product as selective PI3Kα inhibitor against NSCLC: multi-ligand pharmacophore modeling, molecular docking, ADME, DFT, and MD simulations.

Non-small cell lung cancer (NSCLC) is a widespread and often aggressive form of cancer affecting people worldwide. PIK3CA missense mutations play a significant role in the progression of growth factor signaling in cancer, making PI3Kα an important biological target for inhibition against NSCLC. Natural product molecules with PI3Kα inhibitory activity are promising therapeutic agents for the treatment of NSCLC, owing to their selectivity and potentially lower toxicity compared to synthetic compounds. To discover new natural product molecules, we integrated ligand-based virtual screening with structure-based virtual screening. We developed a multi-ligand pharmacophore hypothesis, validated it with 3D Field-based QSAR, and screened a Natural-Product-Based Library (ChemDiv) containing 3601 molecules. After initial screening, 137 hit molecules were generated and further screened using the extra precision (XP) Glide docking protocol. The best ten molecules were selected for free binding energy (ΔG) analysis using MMGBSA and ADME predictions. For further optimization, the top four hits were subjected to induced fit docking (IFD), quantum chemical descriptors analysis by Frontier Molecular Orbital (FMO) studies, and a 100ns molecular dynamics (MD) simulation. The compounds-S721-1955, CM4579-5085, S721-1963, and S721-1999-exhibited better results than the PI3Kα selective inhibitor alpelisib. In silico prediction analysis of S721-1955 and alpelisib revealed that the former exhibited superior selectivity theoretically, as evidenced by its higher affinity for the target protein. The selective natural product molecule identified in this study holds promise as a potential anti-cancer drug against NSCLC in the near future, but further in vitro and in vivo studies are necessary to confirm its efficacy.