Phosphoproteomics Identifies PI3K Inhibitor-selective Adaptive Responses in Pancreatic Cancer Cell Therapy and Resistance.

The PI3K pathway is highly active in human cancers. The four class I isoforms of PI3K are activated by distinct mechanisms leading to a common downstream signaling. Their downstream redundancy is thought to be responsible for treatment failures of PI3K inhibitors. We challenged this concept, by mapping the differential phosphoproteome evolution in response to PI3K inhibitors with different isoform-selectivity patterns in pancreatic cancer, a disease currently without effective therapy. In this cancer, the PI3K signal was shown to control cell proliferation. We compared the effects of LY294002 that inhibit with equal potency all class I isoenzymes and downstream mTOR with the action of inhibitors with higher isoform selectivity toward PI3Kα, PI3Kß, or PI3Kγ (namely, A66, TGX-221 and AS-252424). A bioinformatics global pathway analysis of phosphoproteomics data allowed us to identify common and specific signals activated by PI3K inhibitors supported by the biological data. AS-252424 was the most effective treatment and induced apoptotic pathway activation as well as the highest changes in global phosphorylation-regulated cell signal. However, AS-252424 treatment induced reactivation of Akt, therefore decreasing the treatment outcome on cell survival. Reversely, AS-252424 and A66 combination treatment prevented p-Akt reactivation and led to synergistic action in cell lines and patient organoids. The combination of clinically approved α-selective BYL-719 with γ-selective IPI-549 was more efficient than single-molecule treatment on xenograft growth. Mapping unique adaptive signaling responses to isoform-selective PI3K inhibition will help to design better combinative treatments that prevent the induction of selective compensatory signals.

Pancreatic cancer intrinsic PI3Kα activity accelerates metastasis and rewires macrophage component.

Pancreatic ductal adenocarcinoma (PDAC) patients frequently suffer from undetected micro-metastatic disease. This clinical situation would greatly benefit from additional investigation. Therefore, we set out to identify key signalling events that drive metastatic evolution from the pancreas. We searched for a gene signature that discriminate localised PDAC from confirmed metastatic PDAC and devised a preclinical protocol using circulating cell-free DNA (cfDNA) as an early biomarker of micro-metastatic disease to validate the identification of key signalling events. An unbiased approach identified, amongst actionable markers of disease progression, the PI3K pathway and a distinctive PI3Kα activation signature as predictive of PDAC aggressiveness and prognosis. Pharmacological or tumour-restricted genetic PI3Kα-selective inhibition prevented macro-metastatic evolution by hindering tumoural cell migratory behaviour independently of genetic alterations. We found that PI3Kα inhibition altered the quantity and the species composition of the produced lipid second messenger PIP3 , with a selective decrease of C36:2 PI-3,4,5-P3 . Tumoural PI3Kα inactivation prevented the accumulation of pro-tumoural CD206-positive macrophages in the tumour-adjacent tissue. Tumour cell-intrinsic PI3Kα promotes pro-metastatic features that could be pharmacologically targeted to delay macro-metastatic evolution.

Organismal roles for the PI3Kα and ß isoforms: their specificity, redundancy or cooperation is context-dependent.

PI3Ks are important lipid kinases that produce phosphoinositides phosphorylated in position 3 of the inositol ring. There are three classes of PI3Ks: class I PI3Ks produce PIP3 at plasma membrane level. Although D. melanogaster and C. elegans have only one form of class I PI3K, vertebrates have four class I PI3Ks called isoforms despite being encoded by four different genes. Hence, duplication of these genes coincides with the acquisition of coordinated multi-organ development. Of the class I PI3Ks, PI3Kα and PI3Kß, encoded by PIK3CA and PIK3CB, are ubiquitously expressed. They present similar putative protein domains and share PI(4,5)P2 lipid substrate specificity. Fifteen years after publication of their first isoform-selective pharmacological inhibitors and genetically engineered mouse models (GEMMs) that mimic their complete and specific pharmacological inhibition, we review the knowledge gathered in relation to the redundant and selective roles of PI3Kα and PI3Kß. Recent data suggest that, further to their redundancy, they cooperate for the integration of organ-specific and context-specific signal cues, to orchestrate organ development, physiology, and disease. This knowledge reinforces the importance of isoform-selective inhibitors in clinical settings.

The type of KRAS mutation drives PI3Kα/γ signalling dependency: Implication for the choice of targeted therapy in pancreatic adenocarcinoma patients.

Pancreatic ductal adenocarcinoma PDAC is a complex disease with an important diversity of genetic alterations found between patients. KRAS mutation is considered as a major oncogenic driver in this cancer (around 90% of the patients), but there exists different KRAS mutation types. The type of KRAS mutation was recently shown to be of importance to detect signalling vulnerabilities in a subset of PDAC patients. We comment on these innovative results and discuss their importance when designing clinical trials with PI3K targeted therapies in this cancer.