Dipeptidyl peptidase IV (DPP-IV; E.C. 3.4.14.5), a serine protease that degrades the incretin hormones GLP-1 and GIP, is now a validated target for the treatment of type 2 diabetes. Dipeptide boronic acids, among the first, and still among the most potent DPP-IV inhibitors known, suffer from a concern over their safety. Here we evaluate the potency, in vivo efficacy, and safety of a selected set of these inhibitors. The adverse effects induced by boronic acid-based DPP-IV inhibitors are essentially limited to what has been observed previously for non-boronic acid inhibitors and attributed to cross-reactivity with DPP8/9. While consistent with the DPP8/9 hypothesis, they are also consistent with cross-reactivity with some other intracellular target. The results further show that the potency of simple dipeptide boronic acid-based inhibitors can be combined with selectivity against DPP8/9 in vivo to produce agents with a relatively wide therapeutic index (>500) in rodents.

Bortezomib, a dipeptidyl boronic acid and potent inhibitor of the 26S proteasome, is remarkably effective against multiple myeloma (MM) but not against solid tumors. Dose-limiting adverse effects from "on target" inhibition of the proteasome in normal cells and tissues appear to be a key obstacle. Achieving efficacy against solid tumors therefore is likely to require making the inhibitor more selective for tumor tissue over normal tissues. The simplest strategy that might provide such tissue specificity would be to employ a tumor specific protease to release an inhibitor from a larger, noninhibitory structure. However, such release would necessarily generate an inhibitor with a free N-terminal amino group, raising a key question: Can short peptide boronic acids with N-terminal amino groups have the requisite properties to serve as warheads in prodrugs? Here we show that dipeptides of boroLeu, the smallest plausible candidates for the task, can indeed be sufficiently potent, cell-penetrating, cytotoxic, and stable to degradation by cellular peptidases to serve in this capacity.

In a previously reported CD-1 mouse 2-year carcinogenicity study with the sodium glucose cotransporter-2 inhibitor empagliflozin, an increased incidence of renal tubular adenomas and carcinomas was identified only in the male high-dose group. Follow-up investigative studies have shown that the renal tumors in male high-dose mice were preceded by a number of renal degenerative/regenerative findings. Prior cross-species in vitro metabolism studies using microsomes identified an oxidative metabolite (M466/2) predominantly formed in the male mouse kidney and which spontaneously degrades to a metabolite (M380/1) and reactive 4-OH crotonaldehyde (CTA). In order to further evaluate potential modes of action for empagliflozin-associated male mouse renal tumors, we report here a series of in vitro investigative toxicology studies conducted to evaluate the cytotoxic and genotoxic potential of empagliflozin and M466/2. To assess the cytotoxic potential of empagliflozin and M466/2, a primary mouse renal tubular epithelial (mRTE) cell model was used. In mRTE cells, M466/2-derived in vitro 4-OH CTA exposure was cytotoxic, while empagliflozin was not cytotoxic or mitogenic. Empagliflozin and M466/2 were not genotoxic, supporting an indirect mode of action for empagliflozin-associated male mouse renal tumorigenesis. In conclusion, these in vitro data show that M466/2-derived 4-OH CTA exposure is associated with cytotoxicity in renal tubule cells and may be involved in promoting compound-related in vivo renal metabolic stress and chronic low-level renal injury, in turn supporting a nongenotoxic mode of tumor pathogenesis specific to the male mouse.

[structure: see text] Six new N-acyl-boroGly derivatives, along with their N-acyl-boroSar analogues, have been synthesized by modification of conventional procedures. Structural characterization of these alpha-amidoboronic acids was accomplished by extensive use of 11B and 1H NMR spectroscopy. These compounds were prepared to determine the extent of intramolecular B-O dative bond formation within the context of a five-membered (:O=C-N-C-B) ring motif. It is shown that the formation of such dative bonds depends on the nature of the substituents at both the acyl carbon and the nitrogen atoms. Computational evidence from second-order Møller-Plesset perturbation theory is provided in support of these findings.