Abstract B109: Oral dual PI3K/mTOR inhibitor bimiralisib demonstrates tolerability and a signal of activity in head and neck squamous cell cancer with NOTCH1 loss-of-function mutation
Authors: Janku Filip , Johnson Faye M. , Opyrchal Mateusz , Dowlati Afshin , Hierro Cinta , Forester Martin , Blagden Sarah P. , Wicki Andreas , Schmitz Debora , Adjei Alex A. 
Published: March 2020

Background: Bimiralisib is a balanced dual panPI3K/mTOR inhibitor, which demonstrated anti-cancer activity in a number of preclinical models. Pharmacokinetic (PK) data suggested that intermittent targeting of the PI3K/mTOR pathway could be preferable to continuous daily dosing. Preclinical models in squamous cell head and neck cancer (SCCHN) demonstrated that NOTCH1 Loss of Function (LoF) mutations were associated with efficacy of bimiralisib and other PI3K inhibitors. Methods: We conducted a first-in-human dose-escalation study (3+3 design) to identify the maximum tolerated dose (MTD), recommended phase 2 dose (RP2D), dose-limiting toxicities (DLT) and overall safety (CTCAE v4) of bimiralisib administered either as a continuous (80 mg – 120 mg daily) or one of two intermittent schedules (schedule A: twice weekly 80 mg – 200 mg on Day 1 and 2, or schedule B: twice weekly 80mg – 200 mg on Day 1 and 4) until disease progression or unacceptable adverse events (AEs). Eligible patients had histologically confirmed solid cancers refractory to standard therapies, ECOG &lt;1, life expectancy &gt;12 weeks, adequate bone marrow, liver, and renal functions, HgbA1c &lt;7%, and fasting plasma glucose &lt; 7.0mmol/L. Tumor responses were evaluated according to RECIST v1.1 every 6 weeks. PK and blood biomarkers were analyzed. Results: 70 patients (female, 70%; white, 93%; median age 57 years [range, 49-65]) with heavily pretreated advanced solid cancers were enrolled (continuous schedule, 21; intermittent schedule A, 25; intermittent schedule B, 24). The MTD for the continuous schedule was established as 80 mg daily. For all treatment groups, DLTs included grade 2 and 3 fatigue. Clinically significant treatment-related AEs included fatigue in the continuous schedule, none in the intermittent schedule A and diarrhea, hyperglycemia in the intermittent schedule B. Intermittent schedules A and B did not reach the MTD, and after review of PK data, 140 mg administered in schedule A was selected as the RP2D for further exploration. Day 1 peak plasma concentration proportionally increased with increasing doses of bimiralisib only up to 140mg. Weekly AUC on intermittent dosing at all dose levels studied were considerably lower than continuous daily dosing at 80mg. There was one partial response (PR, -85% per RECIST) in a heavily pretreated patient with SCCHN and NOTCH1 LoF mutation, which was maintained for 8.2 months until death from pulmonary artery rupture in the setting of known fistula (assessed as unrelated to bimiralisib). In addition, 30 (42.9%) pts achieved stable disease (SD) including one with anal SCC carrying a NOTCH1 LoF mutation. SD &gt; 6 months was observed in five pts (23.8%) in continuous schedule, 12 (48%) in intermittent schedule A, and 13 (54.2%) in intermittent schedule B. Results on patients, who consented to the serial circulating tumor DNA collection will be presented. Conclusions: Bimiralisib was well tolerated and RP2D of 140 mg given orally twice weekly on Days 1 and 2 was selected for further studies. In agreement with our preclinical models, there was an encouraging activity in a SCCHN patient with NOTCH1 LoF mutation and this observation is now being validated in a proof-of-concept phase 2 study (NCT03740100).

Citation Format: Filip Janku, Faye M. Johnson, Mateusz Opyrchal, Afshin Dowlati, Cinta Hierro, Martin Forester, Sarah P. Blagden, Andreas Wicki, Debora Schmitz, Alex A. Adjei. Oral dual PI3K/mTOR inhibitor bimiralisib demonstrates tolerability and a signal of activity in head and neck squamous cell cancer with NOTCH1 loss-of-function mutation [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B109. doi:10.1158/1535-7163.TARG-19-B109