Abstract 6065: Preclinical evaluation of LM-168: A next-generation anti-CTLA4 antibody with promising efficacy and reduced toxicity

Abstract Background: Anti-CTLA-4 antibodies have demonstrated encouraging clinical outcomes across various tumor types, but systemic immune activation leads to severe immune-related adverse events. Thus, there is a medical need for novel CTLA-4 targeting therapies with improved benefit-risk profile. ANP (ATP/ADP/AMP) levels are highly elevated to micromolar levels in the tumor microenvironment (TME), whereas physiological ANP levels in healthy tissues remain in the nanomolar range. LM-168 is engineered to selectively bind CTLA-4 at high ANP level in TME, with weakly binding in healthy tissues, thereby reducing “on target off tumor” toxicity. Methods: The target binding activity, specificity, and cross-species reactivity of LM-168 were evaluated by flow cytometry. The blocking efficacy of LM-168 against human CTLA-4 was determined by ELISA. In vivo efficacy was evaluated using three syngeneic models: monotherapy in MC38 and CT26 models, and combination therapy with anti-PD-1 in MCA205 model. The toxicity of LM-168 was evaluated in 4-week repeated-dose toxicity studies in SD rats and rhesus monkeys. Results: LM-168 exhibited potent ANP-dependent binding affinity to huCTLA4-CHOK1 cells, with an EC50 of 1.56 nM in presence of high levels of ANP. In ANP-dependent binding assays, LM-168 exhibited a favorable specificity margin, achieving a 9.5-fold binding selectivity window. In addition, LM-168 demonstrated strong affinity for CTLA-4 in non-human primate and rodent models. In MC38 syngeneic model with hCTLA4 knock-in mice, LM-168 at 10 mg/kg significantly inhibited tumor growth with a tumor growth inhibition (TGI) of 102.6%. Tumor infiltrating lymphocytes were analyzed after treatment with either LM-168 or ipilimumab. Intratumoral Treg cells were significantly reduced, while CD8+ T cells were increased. Peripheral Treg cell proliferation was lower in LM-168 treated mice compared to those treated with ipilimumab. In CT26 syngeneic model, LM-168 showed comparable anti-tumor efficacy to ipilimumab, achieving a TGI of 67.2% at a dose of 3 mg/kg. The combination of LM-168 with an anti-mPD-1 antibody provided a synergistic anti-tumor effect, achieving 98.4% TGI in the MC205 syngeneic model. 4-week repeated-dose toxicity studies indicated that LM-168 was well tolerated in both SD rats and rhesus monkeys, and 248 mg/kg was considered the highest non-severely toxic dose. Conclusion: By targeting CTLA-4 conditionally, LM-168 is designed to address the potency and tolerability challenges associated with current anti-CTLA-4 antibodies, and thus has the potential to be a next generation CTLA-4 target therapy with promising clinical efficacy and reduced toxicity. LM-168 is also expected act synergistically with anti-PD-1/PD-L1 therapy. The preclinical data support clinical development of LM-168. It is currently in the FDA IND stage with a first-in-human trial expected in Q1 2025. Citation Format: Lei Shi, Yun Zhang, Tianen Yao, Xia Qin, Da Fei, Yuan Li, Runsheng Li. Preclinical evaluation of LM-168: A next-generation anti-CTLA4 antibody with promising efficacy and reduced toxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6065.