Objective: The present study aimed to explore the cytotoxic effect of ortho- and para-positional isomers
of thiophene acetyl salicylic acid esters against cancer and normal cell lines.
Method: Two new thiophene-2-acetic acid esters (2-((2-(thiophen-2-yl)acetyl)thio)benzoic acid and 4-((2-(thiophen-2-
yl)acetyl)thio)benzoic acid) were synthesized and characterized by Elemental analysis, Fourier transform infrared
spectroscopy, 1H-nuclear magnetic resonance (NMR), 13C-NMR and High-resolution mass spectroscopy. The
compounds were tested for their in vitro cytotoxic activity against A549 and Caco2 tumor cell lines and CCD-
19Lu and CCD 841 CoN normal cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,4,diphenyltetrazolium bromide
assay. 2-((2-(thiophene-2-yl)acetyl)thio)benzoic acid showed a higher activity with (IC50 = 239.88µM/mL)
compared with a reference drug nearly as active as cyclophosphamide (IC50 = 257.11 µM/mL) on Caco2 cell line.
Apoptosis was observed by flow cytometric analysis on Caco2 cells.
Result: Thus, positional isomerism is critical for the pharmacological properties of thiophene acetyl salicylic acid
esters against colon cancer cell line compared with nonsmall cell lung cancer cell line. The ortho-isomer induced
cell death and was much more potent than the para-isomer.