Selectively targeting apoptosis in PIK3CA mutant colorectal cancers

项目摘要 大约20%的结直肠癌(CRC)，即美国每年2.5万名患者，有 激活PIK3CA基因的驱动突变，该基因编码 磷脂酰肌醇-3-激酶(PI3K)。这些患者在接受治疗时预后特别差。 标准护理化疗，对PI3K途径的单一药物抑制剂也不起作用，a 这一问题突显了对PIK3CA突变的更有效治疗策略的迫切需要 CRC。最近，通过将人类结直肠癌患者的磷酸蛋白质组数据与联合药物相结合， 在对结直肠癌细胞株的筛选中，我们发现细胞外信号调节激酶(ERK)的抑制物 PIK3CA突变型CRC对酪氨酸激酶SRC抑制剂的选择性增敏作用 其他常见突变基因的突变状态，包括KRAS和BRAF。通过机械论 研究表明，这种结合对PIK3CA突变体CRCs的选择性归因于(1)SRC 仅在PIK3CA突变细胞中选择性激活，其药理抑制与ERK协同作用 通过诱导促凋亡蛋白BIM来抑制触发细胞凋亡的途径，以及(2)事实 PIK3CA突变体CRC对由结构性PI3K激活驱动的慢性BIM抑制上瘾， 因此，它们对BIM的诱导比它们的野生型PIK3CA要敏感得多。收购的 对SRC和ERK途径抑制剂组合的耐药性集中在抗-ERK途径抑制剂的激活上 凋亡蛋白BCL-XL，直接拮抗BIM。联合应用对bcl-xl的前期抑制作用 抑制SRC和ERK通路导致穿透性细胞杀伤，同时阻止获得性细胞的出现 抵抗。在这项建议中，我们通过一系列综合研究来研究(1) PIK3CA突变体SRC激活及其与ERK途径协同作用的分子机制 (2)联合应用SRC和ERK通路抑制在患者中的翻译潜力 衍生异种移植(PDX)模型及相关临床研究；(3) BCL-XL抑制逆转或阻断获得性耐药的能力，以及阐明其分子的研究 耐药状态下bclxl激活的调控机制。这项工作将定义一种基本的生存 PIK3CA突变体CRC中的信号网络，有望导致第一次选择性靶向治疗 针对这种侵袭性疾病亚型的策略。

Project Summary Approximately 20% of colorectal cancers (CRCs), representing 25,000 patients in the U.S. each year, harbor activating driver mutations in the PIK3CA gene, which encodes the catalytic alpha subunit of phosphatidylinositol-3-kinase (PI3K). These patients have particularly poor prognoses when treated with standard-of-care chemotherapies and also fail to respond to single agent inhibitors of the PI3K pathway, a problem that underscores the compelling need for more effective therapeutic strategies for PIK3CA mutant CRC. Recently, by combining phosphoproteomic data from human CRC patients with combinatorial drug screening in CRC cell lines, we discovered that inhibitors of the extracellular signal-regulated kinase (ERK) pathway selectively sensitize PIK3CA mutant CRCs to inhibitors of the tyrosine kinase SRC without regard to the mutational status of other commonly mutated genes, including KRAS and BRAF. Through mechanistic studies, it was revealed that the selectivity of this combination for PIK3CA mutant CRCs owes to (1) SRC's selective activation only in PIK3CA mutant cells, where its pharmacological inhibition cooperates with ERK pathway inhibition to trigger apoptosis through the induction of the pro-apoptotic protein BIM, and (2) the fact that PIK3CA mutant CRCs are “addicted” to chronic BIM suppression driven by constitutive PI3K activation, and are thus vastly more sensitive to BIM induction than their PIK3CA wild-type counterparts. Acquired resistance to combinations of SRC and ERK pathway inhibitors converges on the activation of the anti- apoptotic protein BCL-XL, which directly antagonizes BIM. Upfront inhibition of BCL-XL in combination with SRC and ERK pathway inhibition leads to penetrant cell killing while blocking the emergence of acquired resistance. In this proposal, we build on these findings through a series of integrated studies examining (1) the molecular mechanisms governing SRC activation and its cooperation with the ERK pathway in PIK3CA mutant CRC; (2) the translational potential of combined SRC plus ERK pathway inhibition using studies in patient- derived xenograft (PDX) models alongside correlative clinical studies in human patient tumors; and (3) the ability of BCL-XL inhibition to reverse or block acquired resistance, alongside studies to elucidate the molecular mechanisms governing BCL-XL activation in the resistant state. The work will define an essential survival signaling network in PIK3CA mutant CRC and is expected to lead to the first selective targeted therapeutic strategies for this aggressive disease subtype.