PI3Kinase Isoforms in Pancreatic cancer

Pancreatic ductal adenocarcinoma is one of the most lethal cancers, with a 5 year-survival rate below 5%. Lack of curative treatment and failure of targeted therapies urge the need to identify novel efficient therapeutic strategy. Achievement of this goal will be obtained through the identification of diagnosis and prognosis biomarkers, identification of novel therapeutic targets and the knowledge of resistance mechanisms induced by these targeted therapies. PI3K/Akt/mTOR signalling, one of the most altered in cancers, is overactivated in pancreatic cancer and correlated with poor prognosis. In the Vertebrates, the family of class I phosphoinoitide-3-kinase (PI3K) includes four isoforms: p110α, p110β, p110δ and p110γ. Although they all perform the same biochemical reaction (phosphorylation of PIP2 in PIP3, a membrane lipid messenger), each isoform were demonstrated to have specific physiological roles. Global PI3K inhibitors are currently being tested in phase I/II clinical trials in advanced solid cancers, but show at maximal doses tolerated a limited therapeutic benefit. Isoform-selective PI3K inhibitors are currently the most promising agents because, at low doses, they are more efficient to inhibit one PI3K isoform, and thus, less toxic than pan-PI3K inhibitors. The objectives of this thesis are to determine isoform-specific PI3K roles and the therapeutic interest to target one or more isoforms in pancreatitis and PDAC, by the identification of isoform-specific pathways and the study of adaptive responses induced by targeting of one or all isoforms of PI3K. In a first part, my work has highlighted, validated and completed results obtained in the team, to demonstrate the significance of PI3K/Akt signalling in two physiological processes: chronic pancreatitis and initiation of pancreatic carcinogenesis. Precisely, the overactivation of PI3K/Akt pathway measured on human and murine chronic pancreatitis samples is correlated with a specific p110α activation gene expression signature. Moreover, genetic and pharmacologic inactivation of p110α during pancreatic chronic inflammation or cancerogenesis (by oncogenic Kras) prevents the formation of acino-ductal metaplasia, structures at the origin of pancreatic carcinogenesis initiation. Development of in vitro acino-ductal transdifferentiation protocol allowed me to demonstrate that only p110α is necessary at this initial step of pancreatic carcinogenesis by the regulation of Rho small GTPases, further regulating actin remodelling. In the second part, by a phosphoproteomic-based approach, I quantified PI3K downstream phosphorylation-regulated targets in a pancreatic cancer cell line treated or not by a pan- or selective PI3K inhibitor at different times. I demonstrated for the first time existence of targets, signalling pathways and adaptive responses regulated by each PI3K isoform. To conclude, all these results demonstrate the rational of combinatorial use of isoform-specific PI3K inhibitors in patients with pancreatic cancer for better clinical response

胰腺导管腺癌（Pancreatic ductal adenocarcinoma, PDAC）是致死性最高的恶性肿瘤之一，5年生存率低于5%。由于缺乏根治性治疗手段且靶向治疗屡屡失败，亟需探索新型高效的治疗策略。这一目标的实现，有赖于诊断与预后生物标志物的挖掘、新型治疗靶点的筛选，以及对靶向治疗诱导耐药机制的阐明。

PI3K/Akt/mTOR信号通路是癌症中最常发生异常的通路之一，在胰腺癌中呈过度激活状态，且与不良预后密切相关。在脊椎动物中，I类磷酸肌醇3-激酶（class I phosphoinositide-3-kinase, PI3K）家族包含四种亚型：p110α、p110β、p110δ与p110γ。尽管四类亚型均催化相同的生化反应——将膜脂质信使PIP2磷酸化生成PIP3，但研究证实各亚型具有独特的生理功能。

目前，泛PI3K抑制剂正在晚期实体瘤患者中开展I/II期临床试验，但在最大耐受剂量下仅能带来有限的治疗获益。亚型选择性PI3K抑制剂则是当前最具前景的治疗候选药物：低剂量下即可精准抑制单一PI3K亚型，相比泛PI3K抑制剂毒性更低。

本论文的研究目标为，通过筛选亚型特异性信号通路、探究靶向单个或全部PI3K亚型所诱导的适应性应答，明确PI3K亚型在胰腺炎与胰腺导管腺癌中的特异性功能，以及靶向单个或多个PI3K亚型的治疗价值。

在第一部分研究中，本团队对前期已获得的实验结果进行了验证、补充与完善，证实了PI3K/Akt信号通路在慢性胰腺炎与胰腺癌起始这两个生理病理过程中的关键作用。具体而言，在人类及小鼠慢性胰腺炎样本中检测到的PI3K/Akt通路过度激活，与p110α特异性激活的基因表达特征显著相关。此外，在胰腺慢性炎症或致癌性Kras驱动的肿瘤发生过程中，对p110α进行遗传学或药理学灭活，可阻止腺泡-导管化生（acino-ductal metaplasia, ADM）的形成——而腺泡-导管化生正是胰腺癌起始的前驱病变结构。通过建立体外腺泡-导管转分化模型，本研究进一步证实，在胰腺癌起始的初始阶段，仅p110α亚型可通过调控Rho家族小GTP酶，进而影响肌动蛋白重塑，发挥关键调控作用。

在第二部分研究中，本研究采用基于磷酸化蛋白质组学的分析方法，对经泛PI3K抑制剂或选择性PI3K抑制剂处理不同时长的胰腺癌细胞系中，PI3K下游磷酸化调控靶点的表达水平进行了定量分析。本研究首次证实，不同PI3K亚型可分别调控特定的靶点与信号通路，并诱导不同的适应性应答。

综上，本研究全部结果均支持联合使用亚型特异性PI3K抑制剂可改善胰腺癌患者的临床治疗应答，具备合理的临床转化价值。