Chemistry Weekly Seminar - Brady Vigliarolo, PhD Candidate

Title

Dual-mode prodrug-inspired substrates of cathepsin B: Fluorogenic substrates, immobilizing reporters groups, and their ¹⁸F-isotopologues

Abstract

The increased proteolytic activity of cathepsin B (CTB) within the tumor microenvironment is known to promote tumor metastasis, the leading cause of death among cancer patients. Positron emission tomography (PET) is a noninvasive molecular imaging technique which may enable the in vivo characterization of this aberrant activity, yet previously radiolabeled cathepsin inhibitors suffer from a lack of selectivity and sensitivity. In this capacity, substrate-based PET tracers which are catalytically hydrolyzed by extracellular CTB may offer the advantage of signal amplification compared to previously reported inhibitors which bind to the enzyme with 1:1 stoichiometry. However, trapping the radiolabeled hydrolysis product (reporter) within the target tissue is a significant challenge when using an extracellular substrate-based approach. Using a prodrug-inspired approach, we have designed several substrates and several latent lysosome-targeted reporters. The lead substrates are hydrolyzed by the target enzyme with remarkable efficiency and the quinoline-based reporters rapidly sequester within the lysosomes of live cancer cells. Most of the fluorine-bearing reporters are highly fluorescent and enable organelle-targeted live cell imaging, effectively tracking lysosomal pH changes induced by chloroquine and ammonium chloride (“LysoFluor” and “LysoGhost”). We communicate here the design, synthesis, fluorogenic properties, enzyme kinetics, live cell imaging, and ¹⁸F-radiolabeling of these prodrug-inspired probes. As an extension of the platform, we will also present a CTB-targeted drug conjugate bearing an elongated spacer and a cytotoxic payload.

Date:    Friday, March 26, 2021

Time:    1:30 p.m.

Zoom link available by request from chem.dept@usask.ca