Abstract 2484: The role of the PI3K/Akt signaling pathway on LIN28B-mediated colorectal cancer metastasis

Abstract Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the second most common cause of cancer death worldwide. The 5-year survival rate is 90% in patients with localized tumors, but the survival rate drastically decreases to 14% in patients with distant metastasis. Therefore, it is imperative to elucidate the molecular mechanisms underlying CRC metastasis. The RNA-binding protein LIN28B is overexpressed in over 30% of patients with CRC and is associated with poor prognosis. Indeed, our previous work revealed that LIN28B promotes colorectal polyps and tumors in a genetic mouse model (PMID: 24142874) and metastasis in a subcutaneous xenograft model of CRC (PMID: 21512136). In the present study, we investigated the mechanism by which LIN28B promotes colorectal tumor progression and metastasis. To assess LIN28B-mediated biological changes, we established CRC cells (DLD-1 and LoVo) with overexpression of LIN28B. LIN28B overexpression increased the activation of the phosphoinositide 3-kinase (PI3K)/Akt pathway in CRC cells. Knockdown of claudin-1 (CLDN1) or NOTCH3 expression in LIN28B-overexpresed CRC cells, or treatment of the cells with the pan-Notch inhibitor DAPT (γ-secretase inhibitor), revealed that the PI3K/Akt pathway works downstream of the tight junction protein CLDN1 and the transmembrane receptor NOTCH3. Furthermore, cell-cell contact of CRC cells was required for the activation of the NOTCH3 and PI3K/Akt signaling pathways, suggesting for an important role of CLDN1 as a tight junction protein upstream of NOTCH3 and PI3K. Inhibition of PI3K by either the pan-PI3K inhibitor LY294002 or PI3K-α-specific inhibitor Alpelisib (BYL719) suppressed LIN28B-mediated CRC cell migration and wound healing rate. Using a mouse model of metastatic CRC, we show that Alpelisib treatment significantly reduced LIN28B-induced liver metastases formation. Interestingly, the inhibitory effect of Alpelisib was even more pronounced when Alpelisib was given in combination with the pan-Notch inhibitor DAPT, resulting in complete inhibition of visible liver metastases formation. Immunohistochemical staining revealed that Alpelisib did not affect proliferation, apoptosis, or angiogenesis of the liver metastases, whereas DAPT may inhibit angiogenesis. Taken together, our results indicate that LIN28B promotes cell migration and liver metastasis formation through CLDN1 and NOTCH3-mediated activation of PI3K signaling. Development of new therapies that target the PI3K/Akt pathway may provide an effective strategy for preventing metastases in CRC patients. This work is supported by NIH 9R01CA277795-22, NIH 5P30CA0113696 and the American Cancer Society. The authors declare no conflicts of interest. Citation Format: Alice E. Shin, Kensuke Sugiura, Kensuke Suzuki, Yasunori Masuike, Christopher J. Lengner, Anil K. Rustgi. The role of the PI3K/Akt signaling pathway on LIN28B-mediated colorectal cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2484.