Aza-peptide aldehydes and ketones: synthesis and evaluation as human 20S proteasome inhibitors

Aza-peptide aldehydes and ketones were developed as a new class of peptidyl analogues to inhibit the human constitutive (c)20S proteasome as alternative therapeutics to treat multiple myeloma (MM). Eleven new aza-peptide aldehydes and ketones were designed based on their preference to bind at the ß5 catalytic subunit of c20S proteasome with benzyloxycarbonyl(Cbz)-Leu-Leu-Leu (MG132-like) and morpholinyl(Mp)-Homophenylalanyl(HPh)-Leu-Phe-Leu (Carfilzomib-like) sequences, synthesized, structurally characterized and evaluated for their inhibitory potency in competitive kinetic assays in vitro. Additionally, cell viability assays and molecular modeling experiments were designed and performed in support. Aza-peptide aldehydes and ketones generated inhibitory activity with IC₅₀ values in the µM range when tested at the ß5 catalytic subunit of the human c20S proteasome. Compound 1 was the most potent compound with an IC₅₀ value of 2.3 ± 1.5 µM. When tested for concentration-dependent killing of three multiple myeloma, one leukemic and two normal natural killer (NK) cell lines, two compounds generated mid-µM EC₅₀ values only for the cancer cells after 48 h. Overall, aza-peptide aldehydes and ketones are a new class of selective human c20S proteasome inhibitors with the potential for further development as alternative therapeutics for multiple myeloma.