Ref: Submission ID 0e636778-60d8-4db7-8504-1b5c099437d9 Preliminary In Vitro Evaluation of Dodecyl Trimethylammonium Bromide (DDTAB) as a Selective Inhibitor of Theileria annulata-Infected Lymphocyte Proliferation.

PURPOSE: Tropical theileriosis, caused by the protozoan parasite Theileria annulata, is an economically significant constraint to cattle production, with disease control increasingly compromised by emerging resistance to the primary chemotherapeutic agent, buparvaquone. This study aimed to screen candidate compounds for in vitro anti-theilerial activity and host cell safety.

METHODS

Four compounds - hesperidin methyl chalcone (HMC), p-coumaric acid, dodecyl trimethylammonium bromide (DDTAB), and diclofop-methyl - were evaluated for anti-theilerial activity using a resazurin-based viability assay on a T. annulata-infected bovine lymphocyte cell line. Host cell safety was assessed via cytotoxicity assays on bovine peripheral blood mononuclear cells and haemolytic assays on bovine erythrocytes.

RESULTS

DDTAB, a cationic surfactant, showed the strongest concentration-dependent inhibition among the four (IC₅₀ = 1125.4 μM), while the remaining compounds were substantially weaker (IC₅₀ 3048.2 - 5771.7 μM). All compounds, including DDTAB, showed low host cell toxicity (<19 % cytotoxicity and <6 % haemolysis at 1000 μM), yielding selectivity indices of 13.45 (cytotoxicity) and 4.92 (haemolysis) for DDTAB. These IC₅₀ values are in the micromolar range, and are in a higher range than buparvaquone (low nanomolar) and also higher than DDTAB's previously reported activity against Theileria equi (469.51 nM) from our laboratory.

CONCLUSION

DDTAB is not therapeutically potent in absolute terms but represents a preliminary hit compound necessitating mechanistic investigation. The findings alsohighlight the utility of the T. annulata-infected lymphocyte assay for future in vitro drug screening.