Exploiting synthetic-lethal interactions to target triple-negative breast cancers

描述（由申请人提供）：目前尚无针对三阴性（TN）乳腺癌的靶向治疗策略，TN是最难治疗的乳腺癌形式，不过度表达人表皮生长因子受体2 (HER2)，缺乏雌激素和孕激素受体的表达。因此，迫切需要加深我们对这种侵袭性乳腺癌亚型的理解，并确定临床相关的治疗干预靶点。我们最近发现，一种致癌转录因子MYC以及MYC依赖的信号通路在原发性人类三阴性乳腺肿瘤中显著上调。此外，我们发现MYC激活与患者预后不良相关，这表明MYC通路可能在驱动这些侵袭性肿瘤的形成中发挥了重要作用。我们如何杀死myc驱动的TN肿瘤？由于MYC是一种转录因子，合理设计可直接抑制其活性的小分子抑制剂无法用于临床。选择性杀死MYC驱动的肿瘤的另一种方法是利用存在的“合成致死”相互作用。我们的研究小组之前采用了细胞周期偏向的方法，发现抑制有丝分裂激酶周期蛋白依赖性激酶（CDK） 1导致MYC过表达的细胞凋亡。这种细胞死亡的机制与BCL-2家族成员BIM的促凋亡上调有关。我们随后使用这种方法治疗MYC表达升高的TN细胞系和异种移植物肿瘤。这些观察结果表明，myc依赖性合成致死性相互作用是存在的，而且重要的是，可以靶向选择性地杀死myc驱动的肿瘤。本研究的目的1将进一步研究小分子CDK抑制myc驱动的TN癌的临床潜力，特别是与抗凋亡BCL-2成员的临床抑制剂联合使用。这是基于我们的新假设，因为CDK抑制上调BIM并激活线粒体内在途径，CDK抑制剂和抗凋亡BCL-2家族成员的联合使用可能会显著提高细胞死亡率。Aim 2将描述MYC激活和Pim1抑制之间新发现的合成致死相互作用，Pim1是一种非必需的激酶，以前被证明与MYC基因相互作用。Aim 3将进行高通量小分子筛选，以确定能够在乳腺细胞中诱导myc依赖性合成致死的潜在导联分子。我们将使用人类乳腺上皮细胞模型、基因定义的癌细胞系和一组新型人鼠原位肿瘤移植模型的组合来进行这些实验。如果成功，这项研究不仅将扩大我们对MYC生物学的认识，还将为TN肿瘤患者提供新的治疗概念。

DESCRIPTION (provided by applicant): No targeted therapeutic strategies are currently available against triple-negative (TN) breast cancer, the most difficult-to-treat form of breast cancer, which does not overexpress human epidermal growth factor receptor 2 (HER2) and lacks the expression of the estrogen and progesterone receptors. Thus, there is an urgent need in deepening our understanding of this aggressive breast cancer subtype and identifying clinically relevant targets for therapeutic intervention. We have recently discovered that an oncogenic transcription factor MYC as well as the MYC-dependent signaling pathways are significantly up-regulated in primary human triple-negative breast tumors. In addition, we found that MYC activation is associated with patients¿ poor prognosis suggesting that the MYC pathways may play a fundamental role in driving the formation of these aggressive tumors. How can we kill MYC-driven TN tumors? Because MYC is a transcription factor, rationally designed small molecule inhibitors that can directly inhibit its activity are not available for clinical use An alternative approach in selectively killing MYC-driven tumors is to exploit the existence of "synthetic-lethal" interactions. Our group previously took a cell cycle-biased approach and discovered that inhibition of the mitotic kinase cyclin-dependent kinase (CDK) 1 resulted in apoptosis in cells engineered to overexpress MYC. The mechanism of such cell death involved an up-regulation of a pro-apoptotic BCL-2 family member BIM. We subsequently used this approach to treat TN cell lines and xenograft tumors with elevated MYC expression. These observations suggest that MYC-dependent synthetic-lethal interactions exist, and importantly, can be targeted to selectively kill MYC-driven tumors. Aim 1 of this proposed research will further study the clinical potential of small molecule CDK inhibition against MYC-driven TN cancers particularly in combination with clinical inhibitors of anti-apoptotic BCL-2 members. This is based on our novel hypothesis that, because CDK inhibition up-regulates BIM and activates mitochondrial intrinsic pathway, the combined use of the inhibitors for CDK and anti-apoptotic BCL-2 family members may significantly enhance the rate of cell death. Aim 2 will characterize a newly discovered synthetic-lethal interaction between MYC activation and inhibition of Pim1, a non-essential, kinase previously shown to genetically interact with MYC. Aim 3 will conduct a high-throughput small molecule screen to identify potential lead molecules capable of inducing MYC-dependent synthetic lethality in mammary cells. We will carry out these experiments using a combination of model human mammary epithelial cells, genetically defined cancer cell lines, and a panel of novel human-in-mouse orthotopic tumor grafts models. If successful, the proposed research will not only expand our knowledge on MYC biology but will also provide novel therapeutic concepts to be tested again patients with TN tumors.