A series of 3-hydroxypropanamidines originally developed as potent antiplasmodial agents were assessed for antibacterial potential. Three derivatives—compound 4 (BLK278), compound 5 (BLK280), and compound 6 (TKK088)—were tested against clinically relevant Gram-positive and Gram-negative bacteria. The study evaluated antibacterial potency, cytotoxicity in human cell lines, in vitro pharmacokinetic properties, and bacterial proteomic responses to treatment. Key findings include notable activity of TKK088 against multidrug-resistant Staphylococcus aureus strains and a broader Gram-negative activity profile for BLK280. The preprint emphasizes high plasma protein binding and good human microsomal and plasma stability for the compounds, and proteomic data suggest a major effect on the bacterial cell envelope. The work is reported as a preprint and has not been peer reviewed.
The compounds investigated are structurally related 3-hydroxypropanamidines that had been optimized for antimalarial activity. In this study the investigators focused on three specific molecules identified by internal codes: 4 (BLK278), 5 (BLK280), and 6 (TKK088). A previously reported related compound, 7 (TKK129), is referenced in the cytotoxicity comparisons. These identifiers are used throughout the evaluation of antibacterial effectiveness, cytotoxicity, and pharmacokinetic profiling.
Activity was reported against clinically relevant bacteria. For Gram-positive organisms, the panel included Staphylococcus aureus; among these strains, multidrug-resistant MRSA and VISA isolates were tested. Compound 6 (TKK088) displayed the highest activity against MRSA and VISA. Compound 5 (BLK280) showed the broadest spectrum of antibacterial activity, extending efficacy to several Gram-negative pathogens: Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae, Klebsiella aerogenes, and Shigella sonnei. The abstract does not provide numeric minimum inhibitory concentrations (MICs) or full susceptibility tables; those specific values were not reported in the source abstract.
Cytotoxicity was evaluated using two human cell types: HUVEC (human umbilical vein endothelial cells) and HAOSMC (human aortic smooth muscle cells). Among the tested 3-hydroxypropanamidines, compound 4 (BLK278) and the previously described compound 7 (TKK129) exhibited the most favorable overall cytotoxicity profiles. Despite antibacterial activity, the calculated selectivity indices for S. aureus were reported as below 2.5 for all compounds, indicating a relatively narrow therapeutic window in these assays. The authors also note cell-type-dependent differences in cytotoxicity for all compounds, including mefloquine, underscoring that improving antibacterial selectivity will be an important goal for future optimization. Exact CC50 values or numerical selectivity index calculations were not provided in the abstract.
The three investigated 3-hydroxypropanamidines displayed consistent in vitro pharmacokinetic characteristics: notably high plasma protein binding and good stability in human microsomal and plasma assays. These properties suggest metabolic stability and significant protein association in plasma, but the abstract does not report precise percentages, clearance rates, or half-life estimates. Further in vivo pharmacokinetic and ADME profiling would be required to translate these in vitro observations into predictive exposure or dosing considerations.
Gel-based proteomic analyses of bacteria treated with the compounds revealed a pronounced impact on the bacterial cell envelope. The observed acute proteomic responses were described as pleiotropic, affecting multiple systems. The pattern of responses is consistent with earlier literature implicating F0F1-ATPase as a potential molecular target of mefloquine in Streptococcus pneumoniae, suggesting shared or overlapping effects on bacterial energy metabolism or membrane-associated processes. The abstract does not list individual proteins or provide detailed proteomic datasets; those specifics were not reported in the source abstract.
This study identifies 3-hydroxypropanamidines—originally antiplasmodial leads—as a promising scaffold for antibacterial drug discovery. TKK088 (compound 6) showed particularly strong activity against multidrug-resistant S. aureus, while BLK280 (compound 5) demonstrated broader activity that includes several Gram-negative clinical pathogens. In vitro pharmacokinetic data indicate substantial plasma protein binding and favorable microsomal and plasma stability. However, cytotoxicity findings and low selectivity indices (below 2.5 for S. aureus) highlight a need for medicinal chemistry optimization to improve antibacterial selectivity and safety margins. Proteomic responses point to a major effect on the bacterial cell envelope and mirror prior mechanistic suggestions involving F0F1-ATPase. As this work is presented as a preprint, the findings have not been peer reviewed. The abstract does not include detailed numerical potency, cytotoxicity, or proteomic data; readers should consult the full preprint and supplementary materials for experimental details and datasets if available.