Abstract 1248: ERGi-USU-6 salt derivatives, a selective inhibitor for ERG positive prostate cancer cells

Background: Approximately half of prostate cancer patients harbor the oncogenic TMPRSS2-ERG gene fusion expressing the ERG oncoprotein. Our lead compound, ERGi-USU, is a potent small molecule inhibitor that binds the atypical kinase RIOK2 leading to the inhibition of the growth of ERG positive cancer cells reducing ERG levels. We have developed a new and more effective derivative, ERGi-USU-6. We have reported the new salts formula EB3P0-16 of ERGi-USU-6 inhibiting the growth of ERG positive prostate cancer cells at IC50=89nM achieving the range of FDA approved drugs. Encouraged by this success we have designed and tested a broad array of new salt formulations to further improve the biological activity of ERGi-USU-6. Methods: From fifty potential salt formulations, we prioritized candidate salts based on the structure, solubility, ionic hydrophobic/hydrophilic characteristics. Series of salts were synthesized by chemical reactions with ERGI-USU-6. Selected formulas include, bisulfate, butyrate, carbonate, salicylate, tartrate salts. The different stages of salt formulation included the testing of a) preformulation, b) pre-formulation processing, c) physicochemical properties, d) solubility, e) pKa, f) partition coefficient, g) pH- solubility profiling, h) prodrug formulation, and i) polymorphism. The IC50 values for ERG protein inhibition was compared to the parental compound and were calculated in a 12-step dilution range and were repeated thrice. The protein levels were quantified by measuring protein levels in a wide range using iBright instrument. Results: A total of 21 salt formulas were prioritized and synthesized. The result confirmed the lead characteristics of EB3P0-16. However, among the new formulas four other salt derivatives showed improved ERG protein inhibition compared to the parental compound. Also, we gained new insights in designing the next generation of formula by the exclusion of chemical structures that did not lead to improvement. Conclusion: This study confirmed EB3P0-16 as the lead formula of ERGi-USU-6. We found four new salt formulas with improved activity achieving ERG protein inhibition within the effective concentration range. The significance of our findings opens the possibility of new deigns towards the pre-clinical testing of ERG inhibitors. Disclaimer: The opinions or assertions contained herein are the private ones of the author/speaker and are not to be construed as official or reflecting the views of the Department of Defense, the Uniformed Services University of the Health Sciences or any other agency of the U.S. Government. The identification of specific products, scientific instrumentation, or organization is considered an integral part of the scientific endeavor and does not constitute endorsement or implied endorsement on the part of the author, DoD, or any component agency. Citation Format: Binil Eldhose, Charles P. Xavier, Mallesh Pandrala, Albert Dobi, Sanjay V. Malhotra. ERGi-USU-6 salt derivatives, a selective inhibitor for ERG positive prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1248.