Citations

206 Background: XTX101 is an investigational tumor-activated, Fc-enhanced, high affinity binding aCTLA-4 designed to block CTLA-4 and deplete regulatory T cells upon activation in the tumor by proteases. XTX101 also contains mutations designed to enhance Fcγ receptor binding. Fc enhancement augments FcγR co-engagement on antigen presenting cells and has been linked with efficacy of aCTLA-4 combinations in patients (pts) with “cold tumors”, including microsatellite stable (MSS) colorectal cancer (CRC). Parts 1A/1B of the study evaluated XTX101 monotherapy in pts with advanced solid tumors. XTX101 was generally well tolerated with limited peripheral XTX101 activation (~13%) compared to evidence of XTX101 activation in the tumor microenvironment (73-96%, in n=2 on-treatment tumor biopsies). A durable partial response (PR) and resolution of hepatic metastases was observed in a pt with PD-L1 negative NSCLC at the monotherapy recommended phase 2 dose (RP2D) of 150 mg once every six weeks (Q6W) [1]. Methods: Part 1C evaluated the safety and feasibility of XTX101 in combination with atezolizumab in pts with advanced solid tumors using 3+3 dose escalation to establish the RP2D. Phase 2 is enrolling pts with MSS CRC with at least 1 prior regimen for metastatic CRC. Initial safety and anti-tumor activity data from Phase 2 in ~20 pts will be presented. Results: As of July 15, 2024, 15 pts were enrolled in Part 1C: MSS CRC (n=12), esophageal cancer, NSCLC, and ampullary carcinoma (n=1 each). Median age 69 and 3 prior lines of therapy (1-12). Across all XTX101 dose levels (75 mg to 150 mg), treatment-related adverse events (TRAEs) of any grade with >10% incidence included infusion reactions (n=4), fatigue and diarrhea (n=2 each), no G4 or G5 TRAEs were reported. In Part 1C, 2 pts experienced a dose limiting toxicity: 1 pt had G3 colitis, and 1 pt had G3 liver enzyme elevation (both were at the XTX101 150 mg dose level and resolved with immunosuppression). Two unconfirmed PRs were reported: in a pt with MSS CRC, including resolution of a liver target lesion, and in a pt with ampullary carcinoma (accompanied by a Ca 19-9 decrease from 700 to 41). In addition, a decrease in intra-tumoral Tregs was observed in paired tumor biopsies from a pt. The combination RP2D was established as XTX101 100 mg Q6W and atezolizumab 1200 mg once every three weeks (Q3W), and enrollment in the Phase 2 part of the study for pts with MSS CRC is ongoing at the RP2D. Conclusions: In Part 1C dose escalation, the combination of XTX101, a tumor-activated, Fc-enhanced aCTLA-4, and atezolizumab was generally well tolerated in pts with advanced solid tumors and demonstrated initial evidence of anti-tumor activity in cold tumors. These data support the initiation of an ongoing Phase 2 study evaluating the combination in pts with MSS CRC with and without liver metastases. 1. Davar ESMO IO 2023. Clinical trial information: NCT04896697 .

e19049 Background: Acala and zanu are 2nd generation Bruton tyrosine kinase inhibitors (BTKis) that have demonstrated improved safety profiles vs 1st generation BTKi ibrutinib in clinical trials. While head-to-head comparison of zanu vs acala is lacking, a recent meta-analysis of clinical trials provided a comprehensive, indirect comparison of the AE profiles in B-cell malignancies (Hwang, Hemasphere. 2023;7(S3):1134). This study aims to evaluate costs and impacts on quality of life (QoL) for zanu vs acala using their AE profiles. Methods: A health economic model was developed to determine cost and QoL associated with AE management for zanu and acala. The incidence rates ( IRs) of all grade and grade ≥3 AEs of interest (n=21, including bleeding events, hypertension, atrial fibrillation, cytopenias, infections, headache, arthralgia, diarrhea) were taken from the meta-analysis. Additional model inputs, such as disutility, average duration of AE, and unit cost of each AE were sourced from published literature and publicly available cost databases in consultation with clinical experts. The model was developed from the US perspective, considering Medicare costs, inflated to 2023 USD. Model outcomes were AE management cost (= IR * unit cost) and quality-adjusted life years (QALYs) lost due to AE (= IR * Disutility * Duration/365.25). Results: In the base-case scenario (considering all AEs), treating a hypothetical cohort of 1000 patients (pts) with zanu instead of acala yielded cost savings of $124K and 3.7 QALY gains (i.e., 3.7 years extra in full health). Subgroup analysis for severe (grade ≥3) and non-severe AEs (grade 1-2) demonstrated similar trends. A sensitivity analysis limited to AEs significantly different between zanu and acala (n=13) yielded consistent results. Additionally, a probabilistic sensitivity analysis, conducted with 1000 iterations to account for uncertainty in model parameters, confirmed robustness of the model, indicating stable conclusions across a wide range of parameter uncertainties. Conclusions: This analysis suggested that zanu is cost-saving and associated with added health benefits compared to acala in terms of AE management in pts with B-cell malignancies. Should these results derived from meta-analysis of clinical trial data be applicable to real-world pt populations across different indications, the potential cost savings could be considerable. These results could be further improved if the differences in efficacy of zanu vs acala are also incorporated. [Table: see text]