Abstract CT110: A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in solid tumor cohorts
Authors: Yamamoto Noboru , Koyama Takafumi , Katsuya Yuki , Sato Jun , Shimizu Toshio , Tanoue Yasushi , Yamamoto Maki , Tozaki Hirokazu , Takahara Eiji , Shoji Shingo , Mizutani Akio , Morishita Daisuke , Oda Robert W. , Miyake Hiroshi , Yonemori Kan 
Published: April 2024

Background: Aberrant splicing contributes to the progression of cancer but lacks targeted drugs. CTX-712 is a potent oral CDC2-like kinase (CLK) inhibitor affecting RNA splicing, CTX-712 demonstrated potent inhibition of proliferation in human tumor cell lines and elicited robust anti-tumor activity in xenograft models. This study aimed to evaluate CTX-712’s maximum tolerated dose (MTD), dose-limiting toxicity (DLT), safety, pharmacokinetics (PK)/pharmacodynamics (PD) profiles, and preliminary efficacy in patients with advanced solid tumors.

Methods: This study consisted of a dose escalation cohort (A) and three dose expansion cohorts (C, D and E) for solid tumors. The dose escalation cohort (A) was initiated with accelerated titration and then switched to a 3+3 design (10, 20, 40, 70, 105, 140 and 175 mg twice a week [TW]). The dosing regimens for dose expansion cohorts were 105 mg TW (C), 70 mg TW (D), and 105 mg once a week (QW) (E).

Results: As of November 20, 2023, a total of 46 patients with solid tumors were enrolled in the dose escalation cohort (16 patients) and dose expansion cohorts (30 patients total). In the dose escalation cohort, CTX-712 was administered at a dose of 10/20/40/70 mg TW (n=1 each), 105/175 mg TW (n=3 each) and 140 mg TW (n=6). DLTs were observed in 2 patients (140 mg TW [platelet count decreased, hypokalemia], 175 mg TW [dehydration]) and MTD was determined to be 140 mg TW. Among the safety analysis population (n=46), median treatment duration was 77 days (Range 1-413+ days); 1 patient is ongoing, and 45 patients discontinued. The common any-grade related adverse events (AEs) (≥30%) were nausea (93.5%), vomiting (65.2%), diarrhea (54.3%), decreased appetite (45.7%) and blood creatinine increase (32.6%). The most common related Grade 3 or higher AE was platelet count decrease (6.5%). Among all the patients (n=46), partial responses were observed in 4 (8.7%) patients (40 (n=1)/70 (n=2)/105 (n=1) mg TW cohorts), who were all patients with ovarian cancer; the median treatment duration of ovarian cancer (n=14) was 84 days (Range 1-413+ days). In PK analysis, a dose-dependent increase in systemic exposure of CTX-712 was observed. PD response was assessed in RNA extracted from peripheral blood cells. Dose-dependent increases of exon skipping in two marker RNAs (S6K and THAP9-AS1) demonstrated mRNA splicing modification induced by CTX-712.

Conclusions: CTX-712 demonstrated an acceptable safety profile in patients with solid tumors. Additionally, CTX-712 demonstrated favorable clinical efficacy for patients with ovarian cancer and further investigation is warranted.

Clinical trial information: jRCT2080224127

Citation Format: Noboru Yamamoto, Takafumi Koyama, Yuki Katsuya, Jun Sato, Toshio Shimizu, Yasushi Tanoue, Maki Yamamoto, Hirokazu Tozaki, Eiji Takahara, Shingo Shoji, Akio Mizutani, Daisuke Morishita, Robert W. Oda, Hiroshi Miyake, Kan Yonemori. A first-in-human phase I study of CTX-712 in patients with advanced, relapsed or refractory malignant tumors (CTX-712-CL-01 study): Efficacy and safety in solid tumor cohorts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT110.