(M1130-05-33) Novel Caffeic Acid Phenethyl Ester (CAPE) Derivatives Inhibit Human Multiple Myeloma Cell Growth

Purpose: Multiple Myeloma (MM) is a disorder characterized by the accumulation of malignant plasma cells in the bone marrow microenvironment with elevated levels of abnormal monoclonal proteins (M-proteins) in the blood. These M-proteins offer no beneficial effects, but crowding out normally functioning antibodies and preventing them from fighting infection. It is estimated that there will be 35,730 new cases in the United States in 2023 with a 5-year survival rate of 53% [1]. Caffeic acid phenethyl ester (CAPE) is reported to have a plethora of bioactive properties including anti-cancer traits [2-3]. We previously reported that CAPE inhibits growth of MM cells through induction of apoptosis and oxidative stress [4]. The objective of this study is to evaluate the effects of novel CAPE derivatives on human MM cell growth.

Methods: CAPE derivatives were synthesized by coupling caffeic acid with derivatives of phenylalanine and tyrosine. Cultured MM cells (RPMI8226, U266, NCI-H929) were exposed to CAPE and its derivatives (0 – 40 μM) for 24, 48, or 72 hours, and effects on cell viability were measured using Presto Blue assays. Effects of CAPE derivatives at 50 μM on the viability of the normal cell counterpart (human peripheral blood mononuclear cells) were also measured. Two most potent derivatives were identified and further assessed for their effects on apoptosis induction in RPMI8226 MM cells through western blotting for proapoptotic proteins (cleaved caspase-3 and cleaved PARP-1). Physicochemical properties and ADMET profiles of these CAPE derivatives were predicted by importing their canonical SMILES codes into the ADMET Predictor® software (Simulations Plus) and SwissADME.

Results: Eleven new CAPE derivatives were synthesized and characterized. CAPE and most of the synthesized derivatives had the greatest cytotoxic effects in the RPMI8226 cells compared to U266 and NCI-H929 MM cells. Overall, the synthesized CAPE derivatives reduced the viability of RPMI8226 MM cells in dose- and time-dependent manners while exhibiting minimal toxicity in human peripheral blood mononuclear cells. CAPE-7 and CAPE-9 were identified to be the most potent derivatives across the three MM cell lines tested, exhibiting more anti-myeloma activity in RPMI8226 and U266 cells than the parent CAPE compound. Though CAPE-7 and CAPE-9 were generally more toxic than CAPE, they did not significantly induce apoptosis in the MM cells apart from CAPE-9 in U266 cells. ADMET predictions for these two compounds indicated slight risk of mutagenicity but lower overall ADMET risk compared to CAPE.

Conclusion: A number of new CAPE derivatives were successfully synthesized and exhibited cytotoxic effects in human MM cells. These results may shed a light on the structure activity relationship of CAPE. Further research is needed to specify nonapoptotic targeting mechanisms by the more potent CAPE derivatives.

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