Effects of Tyrphostin A9 and Structurally Related Tyrphostins on Colorectal Carcinoma Cells

Background/Objectives: Colorectal carcinoma (CRC) is among the most commonly diagnosed cancers in both men and women. Although CRC mortality is generally decreasing, new therapeutic options are needed for unresponsive subgroups of CRC patients. Methods: A series of known and new tyrphostin derivatives was tested for their efficacy against three CRC cell lines with varying KRAS, p53, and/or BRAF statuses. Growth inhibition, apoptosis induction, and inhibition of EGFR and VEGFR-2 were investigated. Results: Tyrphostin A9, the known RG13022-related tyrphostin 1a and its dichlorido(p-cymene)ruthenium(II) complex 1b, and the new SF5-substituted compounds 2a and 2b showed selective antiproliferative activity against KRAS-mutant HCT-116 CRC cells expressing wildtype p53, while p53-knockout HCT-116 and KRAS-wildtype BRAF/p53-mutant HT-29 CRC cells were distinctly less sensitive. In HCT-116 cells, only tyrphostin A9 increased mRNA expression of caspases 3 and 8, as well as the kinases MEK1 and MEK2, whereas 2a reduced caspase 8 mRNA levels. Tyrphostin A9 increased caspase 3 activity and induced apoptosis in HCT-116 p53-wildtype cells while simultaneously inhibiting the receptor tyrosine kinases EGFR and VEGFR-2 at low nanomolar concentrations. Conclusions: Tyrphostin A9 could be a promising therapeutic option for the treatment of KRAS-mutant CRC that expresses wildtype p53.