Study update of the oral CDK9 inhibitor KB-0742 in relapsed or refractory transcriptionally addicted advanced solid tumors.
Authors: Miguel Angel Villalona-Calero, Glenn J. Hanna, Mark Agulnik, Monica M. Mita, Alain C. Mita, David R. Spigel, Jia Luo, Gregory Michael Cote, Jyoti Malhotra, Mohamad Adham Salkeni, Natraj Reddy Ammakkanavar, Amol Rao, Kamalesh Sankhala, Richard E. Cutler, Tressa Hood, Luis A. Carvajal, Charles Lin, Jorge F. DiMartino, Elizabeth Olek, Brian Andrew Van Tine
Journal: Journal of Clinical Oncology (2024)

3102 Background: KB-0742 is a potent, and selective, oral inhibitor of CDK9 being evaluated in a phase I/II study in patients with transcriptionally addicted advanced solid tumors (NCT04718675). Interim data from the first 4 dose levels were presented previously noting manageable safety (MTD not reached), a 24-hour plasma half-life, linear PK, CDK9 target engagement in peripheral blood mononuclear cells (PBMCs), and anti-tumor activity in patients with transcription factor fusion (TFF) driven sarcomas. Here we present updated KB-0742 safety, pharmacokinetics (PK), pharmacodynamic data (PD) and anti-tumor activity for patients from the ongoing dose escalation through 5 dose levels and 60 mg expansion. Methods: Study objectives include evaluation of safety, tolerability, PK, PD, and identification of KB-0742 MTD and RP2D. KB-0742 is administered orally once daily for 3 consecutive days followed by 4 days off, weekly in 28-day cycles, until unacceptable toxicity or disease progression. Eligible patients were enrolled in 5 escalation cohorts (10, 20, 40, 60 and 80 mg) or 60 mg dose expansion. Eligibility criteria include age &gt;18 years, relapsed or refractory solid tumors, and ECOG PS &lt; 2. PD is assessed in (PBMCs) and tumor tissue from pre- and on-treatment biopsy samples. Results: As of January 4, 2024, 112 patients were enrolled, 42 in dose escalation and 70 in expansion. Patients received a median of 3 lines of prior therapy. The most common tumor types enrolled were soft tissue sarcoma (STS) (n=36; 18 TFF positive) and adenoid cystic carcinoma (ACC) (n=18). Treatment-emergent adverse events occurring in &gt;15% of patients include nausea, vomiting, anemia, fatigue, diarrhea, and constipation; none assessed as grade 4 or 5. The most common reason for treatment discontinuation was disease progression (54.5%). Across 5 dose levels, PK remains linear with a terminal half-life of 24 hours. At 60 mg, evidence of target engagement was observed in post-treatment paired tumor tissue biopsies. Within STS, TFF positive patients displayed a trend towards improved outcomes vs. those without a TFF with a disease control rate (DCR) of 42.8% vs. 29.4%, and one partial response was observed in a patient with TFF positive myxoid liposarcoma at 60mg. The best observed response was durable stable disease (SD) yielding a DCR of 53.8% in ACC (n=18), and 83% in NSCLC (n=6). Two patients (MYCL1+ ovarian, NSCLC) with prolonged SD (&gt;140 days) continue treatment on 60mg. Conclusions: KB-0742 treatment at 60 and 80 mg was well tolerated, with manageable toxicity. Achievement of long-term SD and some preliminary anti-tumor efficacy in highly pretreated patients motivates continued enrollment of patients with transcriptionally addicted tumors. Dose escalation and expansion in transcriptionally addicted ( MYC amplification/overexpression) or TFF driven tumors continues. Clinical trial information: NCT04718675 .