Investigating Rational Combination Therapies for Triple-Negative Breast Cancer

项目摘要/摘要 三阴性乳腺癌(TNBC)是指缺乏表达的异质性乳腺肿瘤的集合 可立即下药的分子，如雌激素和孕激素受体和人类表皮 生长因子受体2。目前还没有针对绝大多数TNBC患者批准的靶向治疗。TNBC 接受目前标准护理的患者，包括化疗、放射治疗和手术， 通常会经历早期肿瘤复发和明显更差的死亡率。因此，关键是要确定 并验证临床上可行的、挽救生命的针对TNBC患者的靶向治疗。我们之前报道过， 与非TNBC患者相比，~50%的TNBC患者的致癌MYC通路被激活， 在TNBC患者中，MYC水平与不良预后相关。不幸的是，临床研究进展 直接针对MYC活性的抑制剂仍然具有挑战性。为了克服这一挑战，我们以前 采用了一种称为合成致死筛选法的替代方法来识别容易下药的 MYC驱动的肿瘤存活所需的靶点，但在非肿瘤细胞中不是必需的。我们的屏幕识别出 PIM激酶家族，由密切相关的非必需激酶亚型PIM1、-2和 -3(以下简称PIM)，作为MYC驱动的TNBC中有希望的靶点。我们发现PIM的表达在 临床样本中的三阴性(TN)肿瘤，与患者预后不良有关。临床相关性 PAN-PIM抑制剂在不同的TNBC实验模型中显示出活性。然而，我们的单剂疗效 使用临床前PIM抑制剂的研究表明，尽管PIM抑制显著减缓了TN的生长 肿瘤，它在体内仅诱导肿瘤细胞轻度死亡和消退，提示需要联合应用 治疗。我们采取了强有力的药物筛选方法，并出人意料地发现该药物 以PIM激酶和蛋白酶体为靶点的组合可以急性地诱导有毒水平的蛋白毒性应激 在MYC过表达的TNBC细胞中选择性表达。从机制上讲，我们的初步观察表明，PIM 抑制，它提高了活性氧的水平，当与蛋白酶体抑制相结合时， 使TNBC细胞持续降解受损蛋白质的能力不堪重负，导致蛋白质毒性危机。 因此，我们的观察提出了这样一种可能性--我们的研究将检验这一假设--PIM抑制 代表了一个独特的和临床可行的工具，以提高TNBC肿瘤对蛋白酶体抑制的敏感性。成功者 这项研究的实施将允许识别和询问临床上可利用的漏洞 在MYC驱动的实体癌类型中，如TNBC。这项研究的结果也可能鼓励FDA- 已批准的蛋白酶体抑制剂(例如，carfilzomib)，尚未成功用于液体肿瘤外 类型，结合PAN-PIM激酶抑制剂在早期MYC驱动的固体- 肿瘤试验。

PROJECT SUMMARY/ABSTRACT Triple-negative breast cancer (TNBC) refers to a collection of heterogeneous breast tumors that lack expression of immediately druggable molecules, such as the estrogen and progesterone receptors and human epidermal growth factor receptor 2. No targeted therapy is currently approved for the vast majority of TNBC patients. TNBC patients who have received the current standard of care, consisting of chemotherapy, radiation, and surgery, often experience early tumor recurrence and a significantly worse mortality rate. Therefore, it is critical to identify and validate clinically viable, life-saving targeted therapies for patients with TNBC. We previously reported that the oncogenic MYC pathways were activated in ~50% of TNBC cases compared with non-TNBC cases and that MYC levels were associated with poor outcomes among TNBC patients. Unfortunately, clinical development of inhibitors that directly target MYC activity has remained challenging. To overcome this challenge, we previously took an alternative approach known as the synthetic lethal screening approach to identify readily druggable targets required for MYC-driven tumor viability but that are not essential in non-tumor cells. Our screen identified the PIM family of kinases, which is composed of the closely related nonessential kinase isoforms PIM1, -2, and -3 (PIM hereafter), as a promising target in MYC-driven TNBC. We found that PIM expression was elevated in triple-negative (TN) tumors in clinical samples and was associated with poor patient outcomes. Clinically relevant pan-PIM inhibitors showed activity in various experimental models of TNBC. However, our single-agent efficacy studies using preclinical PIM inhibitors showed that although PIM inhibition significantly slowed the growth of TN tumors, it induced only modest in vivo tumor cell death and regression, suggesting the need for combination therapies. We have taken robust drug screening approaches and have unexpectedly found that the drug combination that targets PIM kinases and the proteasome can acutely induce toxic levels of proteotoxic stress selectively in MYC-overexpressing TNBC cells. Mechanistically, our preliminary observations indicate that PIM inhibition, which elevates the levels of reactive oxygen species, when combined with proteasome inhibition, overwhelms the capacity of TNBC cells to continuously degrade damaged proteins, resulting in proteotoxic crisis. Thus, our observations raise the possibility—and our study will test the hypothesis—that PIM inhibition represents a unique and clinically viable tool to sensitize TNBC tumors to proteasome inhibition. The successful execution of this research will allow for the identification and interrogation of clinically exploitable vulnerabilities in MYC-driven solid-cancer types such as TNBC. The outcomes of this research could also encourage the FDA- approved proteasome inhibitors (e.g., carfilzomib), which have not been successfully used outside of liquid tumor types, to be rapidly evaluated in combination with pan-PIM kinase inhibitors in early-stage MYC-driven solid- tumor trials.