Abstract OT2-19-08: Phase IB/II trial of palbociclib and binimetinib in advanced triple-negative breast cancer with hyperactivation of ERK and/or CDK4/6
Authors: Manso Luis , Cortes Alfonso , Cejalvo Juan M , Morales Serafin , Saenz Jose A García , Colomer Ramon , Sanchez-Bayona Rodrigo , Silva Jorge , Guerra Juan A , Malon Diego , Mouron Silvana , Caleiras Eduardo , Quintela-Fandino Miguel 
Published: March 2022

Background: Novel effective and safe therapies are required for advanced TNBC after progression to standard-of-care first line treatment with anti-PD-1/L1 + chemotherapy. We have found that the most aggressive TNBC variants are driven by a heterogeneous set of genetic aberrations that converge in the increased activity of 6 kinases: KIT, PNKP, PRKCE, P70S6K, ERK and CDK6 (Nat Commun; 9:3501-18). Although the inhibition of each kinase in monotherapy yielded little efficacy in preclinical models, the combinations targeting pairs of the former kinases led to therapeutic synergy in most cases. The combined inhibition of CDK6 and ERK led to 5-fold increase in overall survival in preclinical TNBC models (PDXs and spontaneous murine cancer models). The greatest activity was observed in models with increased activity of either CDK6 or ERK. Thus, we aimed to test the safety and preliminary efficacy of combined ERK and CDK6 inhibition with binimetinib and palbociclib in women with advanced TNBC with hyperactivation of ERK and/or CDK6. The combination has been preliminary tested in lung cancer, where a phase I dose-escalation trial established the RP2D in binimetinib 45 mg/BID plus Palbociclib 125 mg daily 21/7. Trial design: Single-arm, prospective, multicentric, open-label, phase IB/II trial with intra-patient dose-escalation. Patients candidate for pre-screening will have determined the activity of ERK and CDK6 with an in-house developed assay and acquisition algorithm at the central lab. Those testing positive for either marker will undergo full screening. Patients will start treatment with continuous oral binimetinib at 45 mg/BID and palbociclib 100 mg/day from days 1 to 21, in 28-day cycles. Patients experiencing ≤ grade 1 tolerable side effects as the greatest toxicity will be allowed to escalate to palbociclib to 125 in cycle 2. Fresh biopsies will be harvested at baseline and disease progression, in order to establish patient-derived organoids (PDOs) and perform WES. PBMCs will be harvested at baseline, +24 hours, and at the beginning of cycle 2, to study changes in the immunophenotype. RECIST 1.1 and NCI CTC AE V 5.0 criteria will be used for assessing disease control (q8 weeks) and toxicity. Eligibility criteria: Pre-screening: Women &gt;18 year old diagnosed of advanced, non-curable TNBC; 2) who have received a minimum of 1 treatment line including immunotherapy; 3) no more than 2 treatment lines for advanced disease; 4) Adequate organ function and recovery from previous toxicity to &lt; tolerable G2. Full screening: 5) Demonstration of hyper-activation of CDK6 and/or ERK in the tumor sample; 6) PD to the previous treatment regimen within the last 28 days. Specific aims: Primary: 1) To determine the progression-free survival time of the combination of binimetinib and palbociclib in TNBC patients with hyperactivation of ERK and/or CDK6 in second/third line 2) To assess the safety and tolerability of the former combination Secondary: 1) 6-month PFS rate, response rate, and overall survival of the combination 2) To study biomarkers of sensitivity and primary and acquired resistance to the combination taking advantage of PDOs 3) To determine the immunodynamics of the combination. Statistical methods: The null hypothesis is that the median PFS time for second/third line TNBC with best physician’s choice is 1.7 months (NEJM; 384:1529-41, 2021). With alpha and beta errors of 0.05 and 0.2, the minimum number of patients to demonstrate a 30% improvement in PFS to 2.5 months is 25. Preliminary data suggest that approximately 40% of the patients show hyper-activation of CDK6 and/or ERK; thus, and assuming a methodological failure of 10%, the minimum number of patients to screen is 69. Present accrual/target accrual: 27 screened of 69 planed; 11 accrued of 25 planned

Citation Format: Luis Manso, Alfonso Cortes, Juan M Cejalvo, Serafin Morales, Jose A García Saenz, Ramon Colomer, Rodrigo Sanchez-Bayona, Jorge Silva, Juan A Guerra, Diego Malon, Silvana Mouron, Eduardo Caleiras, Miguel Quintela-Fandino. Phase IB/II trial of palbociclib and binimetinib in advanced triple-negative breast cancer with hyperactivation of ERK and/or CDK4/6 [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 OT2-19-08.