Abstract CT196: First-in-human phase 1/2a trial of a macrocyclic ATR inhibitor (ATRN-119) in patients with advanced solid tumors
Authors: Simpkins Fiona , Mahipal Amit , LoRusso Patricia , Schneider Reva , Miller Crystal , Stenehjem David , Brown Eric J. , Carleton Mike , Gullbo Joachim , Mirza Nadeem Q. 
Published: April 2024

Abstract
Background: ATRN-119 is an orally bioavailable, potent, selective macrocyclic small molecule inhibitor of Ataxia Telangiectasia and Rad3- related (ATR) kinase. As the master regulator of DNA damage response (DDR), ATR orchestrates cellular response to DNA replication stress to preserve DNA replication fork integrity. Cancer cells with markedly increased oncogenic stress or dysfunctional DDR are more reliant on ATR for genome stabilization. Thus, inhibition of ATR can result in cancer cell-selective replication fork collapse and cancer cell death.
Methods: This ongoing, first-in-human, multi-site phase 1/2a trial (NCT04905914) is investigating ATRN-119 safety and pharmacokinetic properties (primary objectives), preliminary efficacy in various solid tumors (secondary objective), and biomarker profile (exploratory objective). This study uses an open-label, standard 3+3 dose escalation and dose expansion study design. Key inclusion criteria include: advanced solid tumor, measurable disease (RECIST v1.1), tumor with at least 1 DDR mutation by next-generation-sequencing, at least 1 failed standard-of-care therapy, ECOG PS 0 or 1, and adequate organ function. Key exclusion criteria are cancer therapy within 4 weeks or at least 5 half-lives, unresolved therapy-related AEs, investigational agent within 5 half-lives or 30 days of study drug, CNS metastases or unstable involvement, and concomitant treatment with strong CYP3A4 or CYP2D6 inhibitors or inducers.
Results: This trial is currently enrolling at Dose level 5 (550 mg). Among 12 patients in the first four dose levels, the median age is 62 years (range: 48 to 79), where 67% (n=8) are female, 75% (n=9) are White, and 25% (n=3) are Black. The median number of prior treatments is 3 (range: 1 to 6, and 92% have received platinum-based chemotherapy). The majority of tumors, 75% (n=9), had a TP53 mutation. There have been no reports of dose-limiting toxicities, treatment-related serious adverse events (AE), and treatment-related AEs Grade 3 or higher in these cohorts. The three most commonly reported all-cause AEs are fatigue (33%, n=4), nausea (25%, n=3), and diarrhea (25%, n=3). Increasing exposure and maximum serum concentrations (Cmax) were observed by dose level. The half-life of ATRN-119 is ~5 hours. Two of 12 patients achieved stable disease (SD): one patient from Dose level 1 (50 mg) who progressed on Day 112 and one patient from Dose level 3 (200 mg) who remains on treatment as of Day 118 (data cut off date: January 2, 2024).
Conclusion: In these early cohorts, once-daily oral ATRN-119 appears to be well tolerated with a manageable safety profile, exhibits near dose proportionality, and demonstrates disease stabilization warranting further investigation. Further studies to explore a twice-daily schedule are being considered.
Citation Format: Fiona Simpkins, Amit Mahipal, Patricia LoRusso, Reva Schneider, Crystal Miller, David Stenehjem, Eric J. Brown, Mike Carleton, Joachim Gullbo, Nadeem Q. Mirza. First-in-human phase 1/2a trial of a macrocyclic ATR inhibitor (ATRN-119) in patients with advanced solid tumors [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 CT196.