Abstract C081: Discovery and characterization of AKT1-E17K mutant-selective inhibitors for the treatment of AKT1-E17K mutant cancers

Abstract The AKT1-E17K hotspot mutation is an oncogenic driver present in approximately 4% of breast and 1-4% of gynecologic cancers. Although AKT1-E17K is a clinically validated therapeutic target, the efficacy of the approved pan-AKT inhibitor capivasertib is limited by its inhibition of wild-type (WT) AKT paralogs leading to dose-limiting toxicities such as hyperglycemia and rash. To address this limitation and improve the therapeutic index, we developed AKT1-E17K-selective inhibitors designed for high-specificity toward the mutant isoform, while sparing all WT AKT paralogs. Through structure-based drug design and structure-activity relationship (SAR) studies utilizing AKT1/2-KO DLD1 cells ectopically expressing individual AKT variants, we identified VVD-4009 as a potent (IC50 = 54 nM) and highly selective (52-fold vs WT AKT1, >185-fold vs AKT2, >185-fold vs AKT3) inhibitor of AKT1-E17K. These inhibitors form a covalent, reversible bond with E17K, enabling sustained cellular activity as demonstrated post wash-out. Oral administration of VVD-4009 (120 mg/kg BID) led to complete and durable tumor regression in an AKT1-E17K TNBC PDX model, with sustained effects even after treatment discontinuation. In contrast, capivasertib (100 mg/kg BID, 4D/3D) showed only partial regression followed by tumor rebound. In an AKT1-E17K-expressing ER+ BC CDX model (CRISPR MCF7-AKT1-E17K), VVD-4009 (30 mg/kg QD) combined with fulvestrant achieved tumor regression without inducing hyperglycemia, a dose-limiting toxicity observed with the capivasertib/fulvestrant combination. Consistent with its robust in vivo efficacy, VVD-4009 suppressed pAKT levels by >80% for 16 hours. Importantly, pAKT levels were preserved in skin (pAKT1 and pAKT2) and liver (pAKT2), unequivocally confirming absolute mutant selectivity in vivo. Because PI3K/AKT inhibitor–associated skin toxicity is not recapitulated in mice, we employed a human in vitro skin model. In contrast to alpelisib, MK-2206, and capivasertib, VVD-4009 preserved skin barrier integrity. VVD-4406, a follow-up compound, retained mutant potency/selectivity while offering improved PK and lower efficacious doses (10–30 mg/kg QD). In a fulvestrant-resistant ER+ BC (luminal B) PDX model, VVD-4406 achieved deeper tumor growth inhibition than capivasertib. At its maximal tolerated dose, VVD-4406 also outperformed VVD-4009 in this model, further highlighting the benefits of high mutant selectivity and an improved therapeutic index. In summary, we have developed potent and highly selective AKT1-E17K inhibitors that demonstrate superior in vivo efficacy in AKT1-E17K-driven models compared to capivasertib. These findings underscore the value of high mutant selectivity combined with optimized PK for effectively treating aggressive, refractory AKT1-E17K mutant cancers. Citation Format: Tine Wyseure, Noah Ibrahim, Zoe Rush, Sarah Jacinto, Joseph McLaughlin, John Sigler, Alanna Sedgwick, Rediet Zewdu, Albert Parker, Sarah Ur, Marie Pariollaud, Dylan Nelson, Tomas Vilimas, Debarati Mukherjee, Betty Lam, Fabian Goericke, Blake Houser, Jonathan Pollock, Benjamin Horning, Nil Roy, Shota Kikuchi, Brian Cook, Gabe Simon, David Weinstein, Todd Kinsella, Matt Patricelli. Discovery and characterization of AKT1-E17K mutant-selective inhibitors for the treatment of AKT1-E17K mutant cancers [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr C081.