Inhibitor-induced counter-(up)regulation processes in gastric carcinoma: from secondary resistance mchanisms towards newly acquired tumor vulnerability

胃癌是最常见的肿瘤实体之一，也是癌症相关死亡的主要原因。在其通常晚期和不可手术的阶段，常规的细胞抑制剂仅显示有限的功效。虽然在其他肿瘤实体中，靶向抑制剂除了经典化疗外还提供了新的选择，但迄今为止，它们在胃癌中的应用仍然很大程度上不成功。例如，癌基因如MET或HER受体通常过表达、功能相关并且是负面预后因素。然而，尽管有前景的临床前数据，针对这些靶点的特异性抑制剂的使用在临床上仍然令人失望。因此，个性化治疗的改进需要鉴定导致原发性或继发性耐药的因素。在这种情况下，其他致癌（非靶）受体酪氨酸激酶（RTK）的补偿性上调可能非常重要。事实上，我们自己的初步数据表明，在用特异性抑制剂治疗开始时，其他HER受体或配体的快速上调。有趣的是，这种补偿性上调以及替代致癌RTK的伴随（过度）激活可能不仅是继发性耐药的主要原因。相反，它还可以提供新的治疗选择。在此基础上，该项目旨在（i）深入表征致癌RTK表达中抑制剂或RNAi/敲减诱导的改变，通过蛋白质组学鉴定其他候选物，并分析这些反（上）调节过程的细胞和分子效应（ii）定义有希望的特异性抑制剂/敲减组合，（iii）探索序贯治疗方案，其基础是作为“获得性脆弱性”的继发性抗性诱导概念。与单一治疗相比，这种已建立的抑制剂的"第二次击中概念”还可以包括剂量减少（iv）使用来自新鲜患者肿瘤的离体组织切片培养模型，对原发性肿瘤的最有希望的组合和序贯治疗方案进行验证。这也包括遗传特征和NGS诊断。除细胞培养外，还将在体外和离体（组织切片培养）的各种2D和3D模型中进行研究，并将继续进行临床前体内情况（肿瘤异种移植物、患者来源的异种移植物（PDX/AVATAR模型））和患者肿瘤的离体验证。此外，还将在此处建立的原位异种移植物/ PDX模型中进行治疗研究。因此，替代致癌RTK的代偿性上调和（过度）激活不仅将被分析为继发性耐药的可能原因，还将通过联合治疗来避免。相反，它将在序贯治疗方案中明确探索，作为增强治疗效果的新的有前途的途径。

Gastric cancer is one of the most frequent tumor entities and a leading cause of cancer-related deaths. In its often advanced and inoperable stage, conventional cytostatics show only limited efficacy. While in other tumor entities targeted inhibitors offer novel options in addition to classical chemotherapy, their use in gastric cancer has remained largely unsuccessful so far. For example, oncogenes like MET or HER receptors are often overexpressed, functionally relevant and a negative prognostic factor. Despite promising preclinical data, however, the use of specific inhibitors against these targets has remained disappointing in the clinics. Thus, the improvement of personalized therapies requires the identification of factors responsible for primary or secondary resistance. In this context, the compensatory upregulation of other oncogenic (non-target) receptor tyrosine kinases (RTKs) may well be of major importance. Indeed, own preliminary data demonstrated, upon treatment start with a specific inhibitor, the rapid upregulation of other HER receptors or ligands. Interestingly, this compensatory upregulation with concomitant (over-)activation of alternative oncogenic RTKs may not only be a major reason for secondary resistance. Rather, it could also offer novel therapeutic options. On this basis, this project aims at (i) the in-depth characterization of inhibitor- or RNAi/knockdown-induced alterations in the expression of oncogenic RTKs, the identification of other candidates by proteomics and the analysis of cellular and molecular effects of these counter-(up-)regulation processes (ii) the definition of promising combinations of specific inhibitors / knockdowns, for testing with regard to additive/synergistic effects (iii) the exploration of sequential therapy regimes, based on the concept of secondary resistance induction as “acquired vulnerability”. This „second hit concept“ with established inhibitors may also include dose reductions compared to single treatment (iv) the validation of most promising combinations and sequential therapy regimes on primary tumors, using ex vivo tissue slice culture models from fresh patient tumors. This also includes genetic characteristics and NGS diagnostics. Besides cell culture, studies will be conducted in various 2D- and 3D models in vitro and ex vivo (tissue slice-cultures) and will proceed towards the preclinical in vivo situation (tumor xenografts, patient-derived xenografts (PDX/AVATAR models)) and the ex vivo validation in patients’ tumors. Perspectively, therapy studies will also be performed in orthotopic xenograft-/ PDX models to be established here. Thus, the compensatory upregulation and (over-)activation of alternative oncogenic RTKs will not only be analyzed as possible reason for secondary resistance, to be avoided by combination therapies. Rather, it will be explicitly explored in sequential therapy regimens as novel promising avenue for enhancing therapeutic efficacies.