Abstract 4024: Overcoming ALK Resistance with Covalent Cysteine-Reactive Inhibitors in Lung Cancer

The EML4-ALK fusion gene is the main oncogenic driver in 5% of non-small cell lung cancer and has been effectively targeted using ALK-specific tyrosine kinase inhibitors. While survival rates have improved steadily with each new generation of ALK TKI, resistance generally develops, including second site ALK kinase mutations as well as by-pass track activation. Since almost all anti-ALK approaches have focused on kinase domain inhibition, we sought to develop novel inhibitors with alternative mechanisms of action against ALK to overcome current drug resistance. Cysteine-reactive small molecule drugs may enable new mechanisms of target inhibition, and clinically successful examples of recent FDA-approved drugs in NSCLC include afatinib, osimertinib, sotorasib, and adagrasib.We aimed to explore and uncover novel cysteine-reactive covalent inhibitors of EML4-ALK. Using cysteine druggability mapping (CDM), a proteome-wide mass spectrometry target engagement assay, we first determined the landscape of reactive cysteines in ALK-positive cell lines and identified various targetable cysteines within the MAPK pathway and within the EML4-ALK fusion protein itself. To identify small molecules that modulate ALK activation, degradation, and downstream signaling, we conducted a high-content phosphorylated protein screen by testing 4,400 reactive cysteine compounds and found 20 potential hits that impacted ALK phosphorylation or expression. Using proteomic analysis, we have determined the comparative specificity of these compounds, and have ranked them based on p-ALK reduction efficiency and on their off-target binding patterns. We have initiated hit-to-lead development on a compound that binds to the EML4 portion of the fusion and we are performing a detailed analysis of its mechanism of action. To further optimize the potency of the compound, we designed, synthesized, and are testing several hundred analog compounds. By applying the hit compounds from the screen in ALK TKI-resistant models, we will be able to evaluate the ability of these compounds to overcome ALK resistance. To our knowledge, we have identified the first EML4-ALK covalent binder targeting the EML4 domain. Using the unique mechanism of action of the current ALK kinase inhibitor, we have uncovered a potential compound to overcome ALK resistance. Citation Format: Diane Yang, Stefan Harry, Edwin Zhang, Zavontae Oppong-Holmes, Alexander Daniel Carlin, Wenxin Yang, Abigail Smith, Maristela Onozato, Liron Bar-Peled, Anthony J. Iafrate. Overcoming ALK resistance with covalent cysteine-reactive inhibitors in lung cancer. [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 4024.