Pro-Soft Val-boroPro: A Strategy for Enhancing in Vivo Performance of Boronic Acid Inhibitors of Serine Proteases

Abstract

Val-boroPro, 1, is a potent, but relatively nonspecific inhibitor of the prolyl peptidases. It has antihyperglycemic activity from inhibition of DPPIV but also striking anticancer activity and a toxicity for which the mechanisms are unknown. 1 cyclizes at physiological pH, which attenuates its inhibitory potency >100-fold, which is a "soft drug" effect. Here we show that this phenomenon can be exploited to create prodrugs with unique properties and potential for selective in vivo targeting. Enzyme-mediated release delivers 1 to the target in the active form at physiological pH; cyclization attenuates systemic pharmacological effects from subsequent diffusion. This "pro-soft" design is demonstrated with a construct activated by and targeted to DPPIV, including in vivo results showing improved antihyperglycemic activity and reduced toxicity relative to 1. Pro-soft derivatives of 1 can help to illuminate the mechanisms underlying the three biological activities, or to help localize 1 at a tumor and thereby lead to improved anticancer agents with reduced toxicity. The design concept can also be applied to a variety of other boronic acid inhibitors.

Fibroblast Activation Protein-α

“…The prosoft compound cyclohexyl(glycine)-Pro-Val-boroPro (Chg-Pro-Val-boroPro) was used to show proof of principle (Poplawski et al, 2011). This approach can preserve the inhibitory activity of the compound, so that it is only activated and reactive with the target protease.…”

Fibroblast Activation Protein-Alpha, a Serine Protease that Facilitates Metastasis by Modification of Diverse Microenvironments

“…show proof of principle (Poplawski et al, 2011). Chg-Pro-Val-boroPro is specifically cleaved and activated by DPPIV, after which it exhibits long-lasting DPPIV inhibition with reduced toxicity in rats, as compared to Val-boroPro (Poplawski et al, 2011).…”

“…show proof of principle (Poplawski et al, 2011). Chg-Pro-Val-boroPro is specifically cleaved and activated by DPPIV, after which it exhibits long-lasting DPPIV inhibition with reduced toxicity in rats, as compared to Val-boroPro (Poplawski et al, 2011). This strategy could be exploited to design a target portion of pro-soft Val-boroPro, Gly-boroPro or other dipeptide boronic acid derivative that makes it specific to FAP.…”

“…They took advantage of the well known NH 2 -Xaa-Pro motif to synthesize boronic acid based inhibitors, such as Pro-boroPro, Ala-boroPro, and Val-boroPro Flentke et al, 1991;Kubota et al, 1992;Poplawski et al, 2011). These inhibitors are effective against most post-prolyl peptidases and, as such, have broad specificity.…”

Solid‐phase synthesis of peptide β‐aminoboronic acids

“…On the basis of the known coordination of neighboring amides and amines to boronic acid moieties, we were interested in seeing if similar interactions in peptide boronic acids were at work . Upon analysis of our generated compounds, we found that there was no interaction between the adjacent carbonyl amide oxygen and the tethered boronic acid moiety at various pHs.…”