Abstract A17: Targeting PI3K/Akt-mediated MADD phosphorylation improves TRAIL sensitivity in anaplastic thyroid cancer

Abstract

Abstract Anaplastic thyroid cancer is an extremely hard-to-treat malignancy due to its aggressiveness, metastasis and inherent therapeutic resistance. Despite using all available armamentaria, the median survival of ATC patients remains dismal. In this regard, TNF-related apoptosis-inducing ligand (TRAIL) is known to induce cancer-specific apoptosis without affecting nontumor cells. However, development of resistance to TRAIL hampers its clinical use. One of the mechanisms of TRAIL resistance is mediated through phosphorylation of Map kinase Activating Death Domain-containing protein (MADD) by Akt. In light of this, preventing MADD phosphorylation might be a rational approach to overcome TRAIL resistance. To test this, we examined MADD expression and TRAIL sensitivity by Western blotting and active caspase-3 staining in several ATC cell lines harboring mutations in cancer driver genes including BRAF, Akt, and PTEN. MADD phosphorylation was inhibited by introducing site-directed mutations in Akt phosphorylation sites of MADD and exogenously expressing the mutant constructs to determine the effect on TRAIL-induced apoptosis. Our results showed that MADD was differentially overexpressed in all ATC cells compared to the normal thyroid tissues irrespective of their mutational landscape. Further, exogenous expression of non-phosphorylatable MADD resulted in a significantly increased TRAIL-induced apoptosis accompanied by the activation of both intrinsic and extrinsic apoptotic pathways. Thus, this study establishes a concept of prevention of MADD phosphorylation to improve TRAIL susceptibility of ATC cells as it can yield similar results as that of blocking PI3k/Akt pathway without any off-target effects. Further studies are warranted to explore specific inhibitors to target MADD phosphorylation. Note: This abstract was not presented at the conference. Citation Format: Shikha Saini, Aditi Mathur, Fei Yue, Ajay Maker, Bellur S. Prabhakar. Targeting PI3K/Akt-mediated MADD phosphorylation improves TRAIL sensitivity in anaplastic thyroid cancer [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr A17.