Abstract PD10-04: PD10-04 Combination of the next generation oral SERD camizestrant (AZD9833) with CDK4/6 and mTOR/AKT inhibitors delivers robust efficacy in a broad range of ER+ breast tumors

Abstract

Abstract Next-generation oral selective estrogen receptor degraders (ngSERDs) are aiming to become the backbone endocrine therapy (ET) for patients with estrogen receptor positive (ER+) breast cancer (BC) by achieving greater ER signaling blockade than current therapies and tackling key mechanisms of resistance. Camizestrant (AZD9833) is an ngSERD for the treatment of ER+ BC which has demonstrated selective ERα degradation, pure ER antagonism and significant anti-tumor activity in ESR1 wild-type (ESR1wt) and mutant (ESR1m) tumors, as well as encouraging clinical activity in early phase trials. ER+ BC is responsive to therapies targeting ER and CDK4/6 signaling in the adjuvant and metastatic settings. To explore camizestrant combination potential as a backbone ET, camizestrant was partnered with either palbociclib or abemaciclib in CDK4/6 inhibitor (CDK4/6i) naïve and resistant in vitro and in vivo models. Combination benefit was observed in vitro in 3 parental ER+ BC cell lines, moreover camizestrant plus abemaciclib showed activity in palbociclib-resistant cell lines including lines harboring CCNE1amp and RB1 loss. In vivo, combination of camizestrant and either CDK4/6i was well tolerated with the combinations promoting improved efficacy in ESR1wt and ESR1m PDX tumor models compared to monotherapy arms. ER+ BC has a high prevalence of alterations in the PI3K/AKT/PTEN pathway which provides opportunities for treatment with PI3K/AKT pathway inhibitors. Camizestrant delivered enhanced efficacy when combined with mTORC1 inhibitor everolimus and AKT inhibitor capivasertib in CTC-174, an ESR1m and PI3KCAm tumor model. Additionally, combination with capivasertib was more efficacious than single treatments, at clinically relevant dose and schedules, in both PI3Kwt and mutated pathway in PDX models. These data demonstrate the interplay between PI3K/AKT/PTEN pathway inhibition and camizestrant mechanism of action. Finally, we explored a potential triple combination of camizestrant, capivasertib and palbociclib in Palbociclib-resistant models representative of PI3KCA/AKT/PTEN wt and altered tumors. This strategy delivered robust efficacy across these models comparing to single treatments and double combinations. The triplet led to durable regressions at clinically achievable doses of all compounds, irrespective of genetic background and aligned to biomarker modulation of the three signaling axis. These preclinical data demonstrate the potential of camizestrant to become the backbone ET, with high combinability in vivo with inhibitors of CDK4/6, mTOR and AKT. These combinations demonstrate the opportunity to impact care of patients with early and metastatic ER+BC, delivering benefit to broad patient populations including those with ESR1wt or ESR1m tumors, independent of PI3K/AKT/PTEN pathway mutation status, and in patients with both CDK4/6i sensitive and resistant tumors. Citation Format: Larissa Carnevalli, Susana Ros, Jelena Urosevic, Natalie Cureton, Sophie Darcy, Mandy Lawson, Stuart Williamson, Pablo Morentin Gutierrez, Azadeh Bashi, Jennifer Moss, Christopher Morrow, Barry Simon, Teresa Klinowska. PD10-04 Combination of the next generation oral SERD camizestrant (AZD9833) with CDK4/6 and mTOR/AKT inhibitors delivers robust efficacy in a broad range of ER+ breast tumors. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD10-04.