Structure of puromycin-sensitive aminopeptidase and polyglutamine binding

Regulation of volume-regulated anion channels alters sensitivity to platinum chemotherapy

Cisplatin-based chemotherapy is used across many common tumor types, but resistance reduces the likelihood of long-term survival. We previously found the puromycin-sensitive aminopeptidase, NPEPPS, as a druggable driver of cisplatin resistance in vitro and in vivo and in patient-derived organoids. Here, we present a general mechanism where NPEPPS interacts with the volume-regulated anion channels (VRACs) to control cisplatin import into cells and thus regulate cisplatin response across a range of cancer types. We also find the NPEPPS/VRAC gene expression ratio is a predictive measure of cisplatin response in multiple cancer cohorts, showing the broad applicability of this mechanism. Our work describes a specific mechanism of cisplatin resistance, which, given the characteristics of NPEPPS as a drug target, has the potential to improve cancer patient outcomes. In addition, we describe an intracellular mechanism regulating VRAC activity, which is critical for volume regulation in normal cells - a finding with functional implications beyond cancer.

Discovery of 8-hydroxy-2-quinoline carbaldehyde derivatives as inhibitors for M1 aminopeptidase of Leishmania donovani

M1 aminopeptidase is a metallopeptidase that plays a vital role in protein catabolism and has been identified as a validated drug target in various parasites; however, our understanding of this enzyme is restricted for leishmanial parasite. The present investigation involved the purification of Leishmania donovani M1 aminopeptidase (LdM1AP) to homogeneity by affinity chromatography. Purified LdM1AP was observed to be enzymatically active and displayed maximal activity in the presence of cobalt ions, whereas secondary structure analysis confirmed the dominance of α-helices. Intrinsic fluorescence and quenching studies of LdM1AP has revealed that tryptophan residues were predominantly concealed within the hydrophobic areas. The synthesized 8-hydroxy-2-quinoline carbaldehyde derivatives were screened, wherein HQ2 and HQ12 were found as potent inhibitors for LdM1AP that compete with the substrate and exhibit pharmacokinetic properties as well as no toxicity for macrophages. Moreover, structural insights of protein and ligand complexes demonstrated that lead compounds mostly interact via hydrophobic contacts into the substrate binding pocket of LdM1AP. Furthermore, lead compounds exhibited a greater affinity for LdM1AP compared to the substrate during in vitro and in silico studies. This report establishes the possibility of quinoline derivatives to target the LdM1AP activity and provide a platform to design the specific antileishmanial drugs.

Modulation of endogenous opioid signaling by inhibitors of puromycin-sensitive aminopeptidase

The endogenous opioid system regulates pain through local release of neuropeptides and modulation of their action on opioid receptors. However, the effect of opioid peptides, the enkephalins, is short-lived due to their rapid hydrolysis by enkephalin-degrading enzymes. In turn, an innovative approach to the management of pain would be to increase the local concentration and prolong the stability of enkephalins by preventing their inactivation by neural enkephalinases such as puromycin-sensitive aminopeptidase (PSA). Our previous structure-activity relationship studies offered the S-diphenylmethyl cysteinyl derivative of puromycin (20) as a nanomolar inhibitor of PSA. This chemical class, however, suffered from undesirable metabolism to nephrotoxic puromycin aminonucleoside (PAN). To prevent such toxicity, we designed and synthesized 5'-chloro substituted derivatives. The compounds retained the PSA inhibitory potency of the corresponding 5'-hydroxy analogs and had improved selectivity toward PSA. In vivo treatment with the lead compound 19 caused significantly reduced pain response in antinociception assays, alone and in combination with Met-enkephalin. The analgesic effect was reversed by the opioid antagonist naloxone, suggesting the involvement of opioid receptors. Further, PSA inhibition by compound 19 in brain slices caused local increase in endogenous enkephalin levels, corroborating our rationale. Pharmacokinetic assessment of compound 19 showed desirable plasma stability and identified the cysteinyl sulfur as the principal site of metabolic liability. We gained additional insight into inhibitor-PSA interactions by molecular modeling, which underscored the importance of bulky aromatic amino acid in puromycin scaffold. The results of this study strongly support our rationale for the development of PSA inhibitors for effective pain management.

Modulation of endogenous opioid signaling by inhibitors of puromycin sensitive aminopeptidase

The endogenous opioid system regulates pain through local release of neuropeptides and modulation of their action on opioid receptors. However, the effect of opioid peptides, the enkephalins, is short-lived due to their rapid hydrolysis by enkephalin-degrading enzymes. In turn, an innovative approach to the management of pain would be to increase the local concentration and prolong the stability of enkephalins by preventing their inactivation by neural enkephalinases such as puromycin sensitive aminopeptidase (PSA). Our previous structure-activity relationship studies offered the S-diphenylmethyl cysteinyl derivative of puromycin (20) as a nanomolar inhibitor of PSA. This chemical class, however, suffered from undesirable metabolism to nephrotoxic puromycin aminonucleoside (PAN). To prevent such toxicity, we designed and synthesized 5'-chloro substituted derivatives. The compounds retained the PSA inhibitory potency of the corresponding 5'-hydroxy analogs and had improved selectivity toward PSA. In vivo treatment with the lead compound 19 caused significantly reduced pain response in antinociception assays, alone and in combination with Met-enkephalin. The analgesic effect was reversed by the opioid antagonist naloxone, suggesting the involvement of opioid receptors. Further, PSA inhibition by compound 19 in brain slices caused local increase in endogenous enkephalin levels, corroborating our rationale. Pharmacokinetic assessment of compound 19 showed desirable plasma stability and identified the cysteinyl sulfur as the principal site of metabolic liability. We gained additional insight into inhibitor-PSA interactions by molecular modeling, which underscored the importance of bulky aromatic amino acid in puromycin scaffold. The results of this study strongly support our rationale for the development of PSA inhibitors for effective pain management.