Activation of WNT/β‐catenin signaling results in resistance to a dual PI3K/mTOR inhibitor in colorectal cancer cells harboring PIK3CA mutations

Abstract

PIK3CA is a frequently mutated gene in cancer, including about ~15 to 20% of colorectal cancers (CRC). PIK3CA mutations lead to activation of the PI3K/AKT/mTOR signaling pathway, which plays pivotal roles in tumorigenesis. Here, we investigated the mechanism of resistance of PIK3CA-mutant CRC cell lines to gedatolisib, a dual PI3K/mTOR inhibitor. Out of a panel of 29 CRC cell lines, we identified 7 harboring one or more PIK3CA mutations; of these, 5 and 2 were found to be sensitive and resistant to gedatolisib, respectively. Both of the gedatolisib-resistant cell lines expressed high levels of active glycogen synthase kinase 3-beta (GSK3β) and harbored the same frameshift mutation (c.465_466insC; H155fs*) in TCF7, which encodes a positive transcriptional regulator of the WNT/β-catenin signaling pathway. Inhibition of GSK3β activity in gedatolisib-resistant cells by siRNA-mediated knockdown or treatment with a GSK3β-specific inhibitor effectively reduced the activity of molecules downstream of mTOR and also decreased signaling through the WNT/β-catenin pathway. Notably, GSK3β inhibition rendered the resistant cell lines sensitive to gedatolisib cytotoxicity, both in vitro and in a mouse xenograft model. Taken together, these data demonstrate that aberrant regulation of WNT/β-catenin signaling and active GSK3β induced by the TCF7 frameshift mutation cause resistance to the dual PI3K/mTOR inhibitor gedatolisib. Cotreatment with GSK3β inhibitors may be a strategy to overcome the resistance of PIK3CA- and TCF7-mutant CRC to PI3K/mTOR-targeted therapies.

Highly‐expressed P2X7 receptor promotes growth and metastasis of human HOS/MNNG osteosarcoma cells via PI3K/Akt/GSK3β/β‐catenin and mTOR/HIF1α/VEGF signaling

“…The Wnt/β-catenin signaling pathway is necessary for the pathobiology and progression of osteosarcoma by inactivating GSK3β and increasing expression of nuclear factor Snail. 21 We observed increased GSK3β phosphorylation in osteosarcoma cells after P2X7 activation (Fig. 4a).…”

“…The phosphatidylinositol 3‐kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway is known to contribute to many human cancers, including osteosarcoma . Moreover, PI3K/Akt/mTOR signaling regulates tumor cell growth and angiogenesis by inducing expression of hypoxia inducible factor (HIF) 1α and VEGF .…”

“…EMT is characterized by loss of the epithelial marker E‐cadherin and increased expression of mesenchymal markers, such as Fibronectin and Vimentin . Although the biological roles of these pathways in the initiation and progression of osteosarcoma are well established, efficacy for drugs interfering with downstream signaling molecules has been less than expected . Therefore, identification of novel tumor‐specific upstream pharmacological targets that modulate the PI3K/Akt/mTOR axis and/or canonical Wnt/β‐catenin signaling may offer better treatment strategies for osteosarcoma.…”

“…The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway is known to contribute to many human cancers, including osteosarcoma. 21,22 Moreover, PI3K/Akt/mTOR signaling regulates tumor cell growth and angiogenesis by inducing expression of hypoxia inducible factor (HIF) 1α and VEGF. 23,24 S. Jeffrey's group recently reported that P2X7 receptor activation upregulated the canonical Wnt/β-catenin pathway via increased phosphorylation and inhibition of glycogen synthase kinase 3β (GSK3β) in osteoblast-like cells.…”

Targeting Wnt/β‐catenin and PI3K/Akt/mTOR pathways in T‐cell acute lymphoblastic leukemia

“…Evidence suggests that both PI3K/Akt/mTOR and Wnt/β-catenin pathways contribute to carcinogenesis and sustain neoplastic cell proliferation (Deming et al, 2014;Jefferies et al, 2017;Yang et al, 2015;Zhang, Zhao, Yan, & Huang, 2019). On the bases of these premises, inhibition of Wnt/β-catenin and PI3K/Akt/mTOR pathways is regarded as a possible innovative therapeutic strategy for cancer treatment (Arques et al, 2016;Park et al, 2019). Surprisingly; however, the efficacy of simultaneous targeting of PI3K/Akt/mTOR and Wnt/β-catenin pathways has never been explored in T-ALL preclinical models.…”