MUC12 is a transmembrane mucin that is highly expressed in >50% of primary and metastatic colorectal tumors. MUC12 is also expressed by normal epithelial cells of the colon and small intestine. Although MUC12 localization in normal epithelial cells is restricted to the apical membrane, expression in tumors is depolarized and shows broad membrane localization. The differential localization of MUC12 in tumor cells as compared with normal cells makes it a potential therapeutic target. Here, we evaluated targeting of MUC12 with a BiTE (bispecific T-cell engager) molecule. We generated a panel of proof-of-concept half-life extended (HLE) BiTE molecules that bind MUC12 on tumor cells and CD3 on T cells. We prioritized one molecule based on in vitro activity for further characterization in vivo . In vitro , the MUC12 HLE BiTE molecule mediated T-cell–redirected lysis of MUC12-expressing cells with half-maximal lysis of 4.4 ± 0.9 to 117 ± 78 pmol/L. In an exploratory cynomolgus monkey toxicology study, the MUC12 HLE BiTE molecule administered at 200 μg/kg with a step dose to 1,000 μg/kg was tolerated with minimal clinical observations. However, higher doses were not tolerated, and there was evidence of damage in the gastrointestinal tract, suggesting dose levels projected to be required for antitumor activity may be associated with on-target toxicity. Together, these data demonstrate that the apically restricted expression of MUC12 in normal tissues is accessible to BiTE molecule target engagement and highlight the difficult challenge of identifying tumor-selective antigens for solid tumor T-cell engagers.

中文翻译：

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MUC12 靶向 BiTE（双特异性 T 细胞接合剂）分子的临床前评估

MUC12 是一种跨膜粘蛋白，在 >50% 的原发性和转移性结直肠肿瘤中高度表达。MUC12 也由结肠和小肠的正常上皮细胞表达。虽然 MUC12 在正常上皮细胞中的定位仅限于顶膜，但在肿瘤中的表达是去极化的并显示出广泛的膜定位。与正常细胞相比，MUC12 在肿瘤细胞中的不同定位使其成为潜在的治疗靶点。在这里，我们评估了用 BiTE（双特异性 T 细胞接合剂）分子靶向 MUC12。我们生成了一组概念验证半衰期延长 (HLE) BiTE 分子，它们结合肿瘤细胞上的 MUC12 和 T 细胞上的 CD3。我们根据体外活性优先考虑一种分子，以便在体内进行进一步表征。体外 ，MUC12 HLE BiTE 分子介导 MUC12 表达细胞的 T 细胞重定向裂解，半数最大裂解为 4.4 ± 0.9 至 117 ± 78 pmol/L。在一项探索性食蟹猴毒理学研究中，MUC12 HLE BiTE 分子以 200 μg/kg 的剂量以 1,000 μg/kg 的阶梯剂量给药，临床观察很少。然而，不能耐受更高的剂量，并且有证据表明胃肠道受损，这表明预计抗肿瘤活性所需的剂量水平可能与靶向毒性有关。总之，这些数据表明，正常组织中 MUC12 的顶端限制性表达可用于 BiTE 分子靶标接合，并突出了为实体瘤 T 细胞接合器识别肿瘤选择性抗原的困难挑战。