Abstract P1-19-17: Dose escalation and expansion study of lerociclib (G1T38), an oral CDK4/6 inhibitor, dosed with no drug holiday in combination with fulvestrant in patients with HR+/HER2- advanced breast cancer
Authors: Bulat Iurie , Maglakelidze Marina , Murias Carmen , Krastev Boris , Baird Richard D , Wardley Andrew M , Roylance Rebecca , Crijanovschi Adrian , Gogiladze Maia , Pritchett Yili , McCullough Amy , Li Chao , Sorrentino Jessica A , Malik Rajesh , Beelen Andrew P 
Published: March 2020

Approved CDK4/6 inhibitors have demonstrated significant improvements in progression free survival when combined with fulvestrant in patients with HR+/HER2- advanced breast cancer, though limited by neutropenia and gastrointestinal side effects. Lerociclib is a potent selective CDK4/6 inhibitor with a differentiated PK/PD profile from currently approved CDK4/6 inhibitors that has demonstrated clinical proof-of-concept (Phase 1b data ASCO 2018). This Phase 1b/2a study assesses lerociclib dose escalation in combination with 500 mg fulvestrant using a 3+3 design followed by dose expansion in patients with metastatic or locally advanced HR+/HER2- breast cancer that had progressed following endocrine therapy. Up to two prior chemotherapies in Phase 1b and one prior in Phase 2a in the advanced setting are allowed. Prior fulvestrant was excluded for all patients; prior CDK4/6 inhibitors were excluded in Phase 2a only. Lerociclib is administered daily without a drug holiday. The objectives are to evaluate DLTs, safety, tolerability, PK, and tumor response and to determine the recommended dose and schedule (QD or BID) of lerociclib administered with fulvestrant for randomized trials. The BID dosing regimen demonstrated optimal safety, tolerability, and antitumor activity. To date, 35 patients (6 patients @ 100 mg BID, 9 patients @ 150 mg BID, 17 patients @ 200 mg BID, and 3 patients @ 250 mg BID) with mean age of 54 years, ECOG of 0 (86%) or 1 (14%), and a median of two prior anticancer therapies in the advanced setting have received lerociclib + fulvestrant for up to 804 days. A dose proportional increase in drug exposure has been observed. The most common lerociclib-related adverse events were neutropenia (63%), leukopenia (57%), nausea (37%), anemia (29%), diarrhea (20%), and thrombocytopenia (20%). The rates of lerociclib-related Grade 3 and Grade 4 neutropenia were 29% and 9%, respectively. Following an initial decline, ANC plateaued beginning at week 4. There were no reports of Grade 3 or greater nausea, vomiting, or diarrhea. One DLT of dose interruption due to Grade 2 fatigue and nausea was observed at 200 mg BID. There have been no reports of venous thromboembolism, QT prolongation or drug-induced liver injury. Twenty patients were evaluable for tumor response based on RECIST v1.1. Five patients (25%) had a confirmed PR; 8 patients (40 %) had stable disease; 6 patients (30 %) had PD. The CBR (CR + PR + SD ≥ 24 weeks) was 67% (12 of 18 patients either had SD at the week 24 tumor assessments or achieved an objective response). A population PK/PD/efficacy model was developed, and simulation data are concordant with existing clinical results. Additional patients are being enrolled at 150 mg BID and 200 mg BID, and updated data will be presented.

Lerociclib, dosed BID with no drug holiday, has a favorable safety profile with low rates of gastrointestinal AEs and Grade 3/4 neutropenia, as well as encouraging antitumor activity in patients with HR+/HER2- advanced breast cancer. Phase 2b is ongoing to confirm the BID dose (150 mg or 200 mg) for randomized clinical trials. Clinical trial information: NCT02983071.

Citation Format: Iurie Bulat, Marina Maglakelidze, Carmen Murias, Boris Krastev, Richard D Baird, Andrew M Wardley, Rebecca Roylance, Adrian Crijanovschi, Maia Gogiladze, Yili Pritchett, Amy McCullough, Chao Li, Jessica A Sorrentino, Rajesh Malik, Andrew P Beelen. Dose escalation and expansion study of lerociclib (G1T38), an oral CDK4/6 inhibitor, dosed with no drug holiday in combination with fulvestrant in patients with HR+/HER2- advanced breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-17.