Abstract 4125: Exploring the efficacy of alpelisib and combined PI3Kα-S6K inhibition in LIN28B-mediated colorectal cancer metastasis
Authors: Shin Alice E. , Sugiura Kensuke , Kariuki Secunda W. , Cohen David A. , Lengner Christopher J. , Sims Peter A. , Gabre Joel T. , Rustgi Anil K. 
Published: March 2024

Abstract
Introduction: Colorectal cancer (CRC) is the third most diagnosed cancer worldwide. LIN28B, an RNA-binding protein that regulates mRNA translation, has garnered significant interest in recent cancer research. Our lab has established that LIN28B is an oncogene and promotes CRC metastasis. However, the exact mechanisms through which LIN28B exerts these effects remain elusive.
The phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway is altered in 50-70% of CRCs and is characterized by PIK3CA gene mutations in 20-30% of CRC cases. PIK3CA encodes the catalytic subunit p110α of the PI3Kα enzyme, which is critical for PI3K/AKT signaling. Activation of this pathway is associated with worse CRC prognosis. Among the components of this signaling cascade, the ribosomal protein S6 kinase (S6K) is a crucial downstream effector, playing a pivotal role in protein synthesis and cell growth. Despite the frequent occurrence of PIK3CA mutations in CRC, targeted therapies for PIK3CA-mutant CRC are lacking. Alpelisib, a PI3Kα-specific inhibitor approved by the FDA for a subset of PIK3CA-mutant breast cancers, remains largely unassessed in CRC. We hypothesize that LIN28B-mediated CRC metastasis is facilitated by the activation of the PI3K/AKT pathway, representing a potential target for Alpelisib or other related inhibitors.
Results: Our data indicate that LIN28B expression in CRC cells promotes liver metastasis in mouse models of metastatic CRC (mCRC). Furthermore, LIN28B expression activates the PI3K/AKT pathway, as measured by an AKT phosphorylation array. Treatment of CRC cells with SC79, a pan-AKT activator, enhanced cell migration and invasiveness. Similarly, VillinCre;R26Pik3ca transgenic mice, expressing a constantly active mutant form of PI3Kα in the intestinal epithelium, demonstrated crypt hyperplasia and an amplified propensity for tumorigenesis, mirroring the effects of LIN28B expression in CRC. Importantly, Alpelisib effectively hinders LIN28B-driven CRC progression in cell lines, transgenic mice-derived organoids, and mCRC mouse models, as well as the growth rate of CRC patient-derived organoids (PDOs). The effects observed with Alpelisib treatment were replicated with inhibition of S6K using either LY25284702 or PF4708671. Moreover, a combination of low-dose Alpelisib with low-dose LY25284702 or PF4708671 synergistically restricted the growth of PDOs.
Conclusion: Our data provide compelling evidence that the PI3K/AKT pathway regulates LIN28B-mediated CRC metastasis, and its inhibition by Alpelisib is feasible. This underscores the potential for precision medicine in CRC, offering targeted therapies to PIK3CA-mutant CRC patients who lack specific treatment options. Furthermore, our study highlights the clinical advantages of combined inhibition strategies for improved anti-metastatic outcomes, a field in dire need of interventions in mCRC.
Citation Format: Alice E. Shin, Kensuke Sugiura, Secunda W. Kariuki, David A. Cohen, Christopher J. Lengner, Peter A. Sims, Joel T. Gabre, Anil K. Rustgi. Exploring the efficacy of alpelisib and combined PI3Kα-S6K inhibition in LIN28B-mediated colorectal cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4125.