Targeting the Immunosuppressive Tumor Microenvironment for Colorectal Cancer Treatment

项目总结/摘要 尽管结肠直肠癌（CRC）治疗有显著改善，但 转移性CRC（mCRC）仍然较差，中位总生存期约为30个月。 免疫治疗如免疫检查点阻断（ICB）代表了一种新的治疗方法， 多种癌症，包括具有微卫星不稳定性高的mCRC（MSI-H）。然而，ICB治疗显示很少 或在约95%的微卫星稳定（MSS）mCRC患者中无临床活性。我们和其他人 已经表明，给予生酮饮食（KD）或酮体β-羟基丁酸酯（βHB）， 增强ICB在小鼠肿瘤模型中对CRC的抗癌作用。然而，KD/βHB是否能改善 对于患有MSS的CRC的ICB治疗尚不清楚。此外，改变生酮作用对 免疫抑制性肿瘤微环境（TME）仍有待确定，代表了我们研究的一个主要空白。 了解肿瘤免疫抵抗。 癌相关成纤维细胞（CAF）是肿瘤基质细胞的主要成分，在肿瘤的发生发展中起关键作用。 肿瘤抑制性TME。我们已经表明，酮生成下调是CRC TME的标志。激活 致癌信号传导（例如，WNT和KRAS）减少CRC中的生酮。酮生成恢复 抑制CAF的有氧糖酵解活性，并抑制组蛋白脱乙酰酶1（HDAC 1）/KLF 5依赖性CAF 增殖和细胞因子表达和分泌。重要的是，我们发现KD改善了 免疫抑制性TME，表现为CD 8 + T细胞和NK细胞浸润增加以及M2 巨噬细胞群体，并增强ICB的功效。我们的发现证明了一个以前未知的 在TME中下调的从头生酮、代谢改变和CAF功能之间的关联， 将癌症酮生成确定为潜在的免疫靶点。基于这些新发现，我们 假设下调的生酮作用有助于细胞增殖和免疫抑制作用， CAF，从而重新编程CRC TME，导致ICB耐药性和CRC进展。我们的长期 目的是鉴定癌症和/或间质区室中的异常代谢， 改善mCRC患者的治疗。为了检验我们的中心假设，我们已经收集了一个高度 协作团队，在CRC进展和治疗、肿瘤代谢、肿瘤 免疫和肿瘤生酮，以及计划的实验，将确定改变的影响， 结直肠癌中免疫抑制性TME的生酮作用，描述CAF代谢的生酮控制， 增殖和TME中的功能效力，并定义靶向生酮代谢对TME的影响。 ICB治疗CRC的疗效。最终，我们的发现将：i）彻底改变我们的CRC TME概念， 免疫抗性; ii）关于KD/βHB影响的显著先进范例; iii）可能提供一种 通过靶向生酮代谢失调的新CRC治疗策略。

Project Summary/Abstract Despite notable improvements in colorectal cancer (CRC) treatment, the prognosis of patients with metastatic CRC (mCRC) remains poor, with a median overall survival of approximately 30 months. Immunotherapy such as immune checkpoint blockade (ICB) represents a novel therapeutic approach for a variety of cancers including mCRC with microsatellite instability-high (MSI-H). However, ICB therapy shows little or no clinical activity in approximately 95% of patients with microsatellite-stable (MSS) mCRC. We and others have shown that administration of either a ketogenic diet (KD) or the ketone body β-hydroxybutyrate (βHB), enhances the anticancer effects of ICB for CRC in mouse tumor models. However, whether KD/βHB can improve ICB therapy for CRCs with MSS is not known. Moreover, the impact of altered ketogenesis on the immunosuppressive tumor microenvironment (TME) remains to be defined and represents a major gap in our understanding of tumor immunoresistance. Cancer associated fibroblasts (CAFs), the major component of tumor stromal cells, play a critical role in the tumor suppressive TME. We have shown that downregulated ketogenesis is a hallmark in CRC TME. Activation of oncogenic signaling (e.g., WNT and KRAS) decreases ketogenesis in CRCs. Restoration of ketogenesis inhibits aerobic glycolytic activity in CAFs and inhibits histone deacetylase 1 (HDAC1)/KLF5 dependent CAF proliferation and cytokine expression and secretion. Importantly, we showed that KD improves the immunosuppressive TME, as noted by increased CD8+ T cell and NK cell infiltration and decreased M2 macrophage populations, and enhances the efficacy of ICB. Our findings demonstrate a previously unknown association of downregulated de novo ketogenesis, metabolic alteration and CAF functions in the TME and have identified cancer ketogenesis as a potential immunotherapeutic target. Based on these novel findings, we hypothesize that downregulated ketogenesis contributes to the proliferation and immunosuppressive effects of CAFs and thus, reprograms the CRC TME, which leads to ICB resistance and CRC progression. Our long-term goal is to identify aberrant metabolism within the cancer and/or stromal compartments that can be used to improve the treatment of patients with mCRC. To examine our central hypothesis, we have assembled a highly collaborative team with significant expertise in CRC progression and treatment, tumor metabolism, tumor immunity and neoplastic ketogenesis, and planned experiments which will determine the impact of alterations of ketogenesis on the immunosuppressive TME in CRC, delineate ketogenic control of CAF metabolism, proliferation, and functional potency in the TME, and define the impact of targeting ketogenic metabolism on the efficacy of ICB for CRC. Ultimately, our findings will: i) revolutionize our concept of CRC TME and immunoresistance; ii) significantly advance paradigms regarding the effects of KD/βHB; and iii) may provide a novel CRC treatment strategy by targeting dysregulated ketogenic metabolism.