Designing selective Cys-ligands to unpair the binding of the Human Transcription Enhancer Associated Domain 4 (hTEAD-4) with its modulators to halt cancer cell growth

The Hippo Signalling cascade is an emerging target in tumour suppression regulation, neoplastic hypertrophy, and regenerative medicine. The pathway is activated by circulating anti-proliferative signals which leads to the phosphorylation of Yes Associated Protein (hYAP1) on Ser127/381, thus 14-3-3σ mediated cytosolic retention. Genetic alterations or exogenous factor may cause YAP nuclear migration and association to TEAD1-4 (Transcription Enhancer Associated Domain), triggering up-regulation of anti-apoptotic genes [1]. hTEAD is an enhancer that activates the nuclear transcription of genes as EMT’s, EGFR and cyclins, and promotes the synthesis of survivin, tyrosine kinase HER3, and mitochondrial Bcl-xL involved in cell proliferation. TEAD binds a palmitic (palm) or myristic (myr) acids, tethered at Cys367 pocket, however its biological role is still not well known. hTEAD isoform-4 is the most represented of its family in solid tumours and its overexpression or mutation leads to cancer development and metastasis. Recent studies have considered hTEAD a promising target for anticancer drugs. Its inhibition strategy includes the disruption/prevention of YAP1:TEAD4 complex formation [2]. With the aim to develop a specific cysteine-directed inhibition strategy, we studied Cys on the protein surface and investigated their reactivity. Hence, our studies focus on characterizing the recombinant hTEAD4-ybd (aa217-434) surface though the analysis of the reactivity of its four Cys thiols (Cys310, Cys335, Cys367, Cys410), all close to YAP binding area. First, myr-Cys-367 was investigated to confirm the auto-myristoilation of the E. coli recombinant hTEAD4 through RP-chromatography on UHPLC-Orbitrap Q-Ex (ThermoFisher™) by multicharged TIC deconvolution, and the total myr-TEAD was assessed around 25%. Myristate position was confirmed by FASP protein tryptic hydrolysis and tandem-MS peptide analysis. We studied hTEAD binding of a small disulphides and thiols library with different chemical properties through the exposed cysteines residues in presence of different concentration of reducing agent [3]. Top8 DDA (HCD)-MS/MS scan on the tryptic peptides suggested the ligands’ high selectivity towards Cys335. Cys367 was never found conjugated, even in the non-Myr fraction, hinting the low accessibility to the lipid pocket. The number of surface reactive Cys was confirmed by a reverse-titration of the protein against increasing amount of thiophenol; excess of unreacted thiophenol was measured by HPLC-UV-ELSD (Agilent™ 1260), suggesting a 1:1 stoichiometry. We confirmed hTEAD-ybd ligand ratio by fluoresceine labelling with absorption and fluorescence differential spectroscopy. The ongoing work engages the screening of a larger compound library to study YAP:TEAD interaction with a ligand displacement assay of labelled TEAD to a rhodamine-tagged peptidomimetic probe to achieve structural information of the heterodimer interface and to start a hit-optimization programme. REFERENCES [1] Santucci M, Vignudelli T, et al. The Hippo Pathway and YAP/TAZ-TEAD Protein-Protein Interaction as Targets for Regenerative Medicine and Cancer Treatment. J Med Chem. 2015 Jun 25;58(12):4857-73. [2] Elisi G.M, Santucci M, et al. Repurposing of Drugs Targeting YAP-TEAD Functions. Cancers 2018, 10, 329. [3] Malpezzi G MSc Degree Thesis, Solvent exposure, and reactivity of the cysteines of Transcription Enhancer Associate Domain (TEAD), a potential anticancer target, 2021. University of Pavia – University of Modena and Reggio Emilia.