Synthesis, Characterization, and Optimization for in Vivo Delivery of a Nonselective Isopeptidase Inhibitor as New Antineoplastic Agent

Bis-arylidenecycloalkanones structurally
related to the nonselective
isopeptidase inhibitor G5 were synthesized and tested
for cytotoxic activity against glioblastoma cells. Cytotoxicities
correlate well with Hammett σ constants for substituted arylidene
groups, confirming the proposed inhibition mechanism. A new inhibitor
(2c) based on the 4-hydroxycyclohexanone scaffold, which
favors apoptosis over necrosis, was selected for further development. 2c inhibited representative deubiquitinases with micromolar
IC50, and its proapoptotic activity was studied on several
cancer cell lines. Inhibitor 2c was conjugated to PEG
via dicarbamate and diester linkers. While the dicarbamate was inactive,
the diester (2cPE) behaves like a prodrug and is converted into the
active species 2c by secreted esterase activities. Finally,
2cPE was also tested in vivo on A549 lung
carcinoma xenografts generated in mice. Intravenous treatment with
2cPE led to a significant reduction in primary tumor growth, without
appreciable toxicity to mice.