Rudimentary Structure-Activity-Relationship study of the MMV Pathogen Box compound MMV675968 (2,4-diaminoquinazoline) unveils novel inhibitors of Trypanosoma brucei brucei DHFR enzyme

New drugs are urgently needed for the treatment of human African trypanosomiasis (HAT). In line with our quest for dihydrofolate reductase (DHFR) inhibitors in trypanosomes, a small library of analogs of the antitrypanosomal hit (MMV675968) available at MMV as solid materials was screened for antitrypanosomal activity. In silico confirmation of two potent antitrypanosomal analogs as inhibitors of DHFR was achieved, together with elucidation of other antitrypanosomal modes of action. Overall, two analogs of the diaminoquinazoline derivative, MMV675968 reputed to inhibit the enzyme DHFR, displayed approximately 40-fold and 60-fold more potency and selectivity than the parent hit, respectively (MMV1578445 (10): IC50 = 0.045 {micro}M, SI=1737; MMV1578467 (7): IC50 = 0.06 {micro}M; SI=412). Analogs 7 and 10 were also strong binders of the DHFR enzyme, in all their accessible protonation states, and interacted with key DHFR ligand recognition residues Val32, Asp54, and Ile160. MMV1578445 (10) portrayed fast and irreversible trypanosomes growth arrest after 72 h and 4 h at IC99. Analogs 7 and 10 induced ferric iron reduction and DNA fragmentation or apoptosis induction, respectively. The two potent analogs endowed with suitable physicochemical properties are good candidates for further deciphering their potential as starting points for new drug development for HAT. Author summaryAfrican trypanosomiasis is a disease caused by parasites of the Trypanosoma brucei species which affect both humans and animals. We have adopted the fast-track drug repurposing approach to determine the antitrypanosomal activity of the open access MMV Pathogen Box compound library. The compound 2,4-diaminoquinazoline (MMV675998), known as a dihydrofolate reductase (DHFR) inhibitor was identified. Rudimentary structure-activity relationship investigation of this compound unveiled two highly active and selective derivatives MMV1578445 and MMV1578467 which were found to strongly inhibit the Trypanosoma brucei dihydrofolate reductase enzyme in silico. Besides, we demonstrated that analogues MMV1578445 and MMV1578467 could respectively reduce intrinsic ferric iron and induce apoptosis in trypanosomes. The two identified inhibitors of trypanosomes qualify as potential drug candidates that could be useful for future development as novel antitrypanosomal drugs.