RESUMO
Cancer, a group of diseases characterized by uncontrollable cell proliferation and metastasis, remains a global health challenge. This study investigates quercetin, a natural compound found in many fruits and vegetables, for its potential to inhibit the phosphomonoesterase activity of protein tyrosine phosphatase nonreceptor type 22 (PTPN22), a key immune response regulator implicated in cancer and autoimmune diseases. We started by screening seven (7) natural compounds against the activities of PTPN22 in vitro. The initial screening identified quercetin with the highest percentage inhibition (81%) among the screened compounds when compared with ursolic acid that has 84%. After the identification of quercetin, we proceeded by investigating the effect of increasing concentrations of the compound on the activity of PTPN22. In vitro studies showed that quercetin inhibited PTPN22 with an IC50 of 29.59 µM, outperforming the reference standard ursolic acid, which had an IC50 of 37.19 µM. Kinetic studies indicated a non-competitive inhibition by quercetin with a Ki of 550 µM. In silico analysis supported these findings, showing quercetin's better binding affinity (ΔGbind -24.56 kcal/mol) compared to ursolic acid, attributed to its higher reactivity and electron interaction capabilities at PTPN22's binding pocket. Both quercetin and ursolic acid improved the structural stability of PTPN22 during simulations. These results suggest quercetin's potential as an anticancer agent, meriting further research. However, in vivo studies and clinical trials are necessary to fully assess its efficacy and safety, and to better understand its mechanisms of action.
RESUMO
Malaria is a devastating disease, and its management is only achieved through chemotherapy. However, resistance to available medication is still a challenge; therefore, there is an urgent need for the discovery and development of therapeutics with a novel mechanism of action to counter the resistance scourge consistent with the currently available antimalarials. Recently, plasmepsin V was validated as a therapeutic target for the treatment of malaria. The pepsin-like aspartic protease anchored in the endoplasmic reticulum is responsible for the trafficking of parasite-derived proteins to the erythrocytic surface of the host cells. In this study, a small library of compounds was preliminarily screened in vitro to identify novel modulators of Plasmodium falciparum plasmepsin V (PfPMV). The results obtained revealed kaempferol, quercetin, and shikonin as possible PfPMV inhibitors, and these compounds were subsequently probed for their inhibitory potentials using in vitro and in silico methods. Kaempferol and shikonin noncompetitively and competitively inhibited the specific activity of PfPMV in vitro with IC50 values of 22.4 and 43.34 µM, respectively, relative to 62.6 µM obtained for pepstatin, a known aspartic protease inhibitor. Further insight into the structure-activity relationship of the compounds through a 100 ns molecular dynamic (MD) simulation showed that all the test compounds had a significant affinity for PfPMV, with quercetin (-36.56 kcal/mol) being the most prominent metabolite displaying comparable activity to pepstatin (-35.72 kcal/mol). This observation was further supported by the compactness and flexibility of the resulting complexes where the compounds do not compromise the structural integrity of PfPMV but rather stabilized and interacted with the active site amino acid residues critical to PfPMV modulation. Considering the findings in this study, quercetin, kaempferol, and shikonin could be proposed as novel aspartic protease inhibitors worthy of further investigation in the treatment of malaria.