Synthesis and Anticancer Activity of Novel Indole Derivatives as Dual EGFR/SRC Kinase Inhibitors

Recent studies showed that the cooperation between c-SRC and EGFR is responsible for the more aggressive phenotype in diverse tumors, including glioblastomas and carcinomas of the colon, breast, and lung. Studies show that a combination of SRC and EGFR inhibitors can induce apoptosis and delay the acquired resistance to chemotherapy. Therefore, such a combination may lead to a new therapeutic strategy for the treatment of EGFR-mutant lung cancer.  Osimertinib was developed as a third-generation EGFR-TKI to combat the toxicity of EGFR mutant inhibitors. Due to the resistance and adverse reaction of osimertinib and other kinase inhibitors, 12 novel compounds structurally similar to osimetinib were designed and synthesized. 

Methods: Compounds were synthesized by developing novel original synthesis methods and receptor interactions were evaluated through a molecular docking study. To evaluate their inhibitory activities against EGFR and SRC kinase, in vitro enzyme assays were used. Anticancer potencies were determined using lung, breast, and prostate (A549, MCF6, PC3) cancer cell lines. Compounds were also tested against normal (HEK293) cell line to evaluate their cytotoxic effects.

Results: Although, none of the compounds showed stronger inhibition compared to osimertinib in the EGFR enzyme inhibition studies, compound 16 showed the highest efficacy with an IC₅₀ of 1.026 μM. It also presented potent activity against SRC kinase with an IC₅₀ of 0.002 μM. Among the tested compounds, the urea-containing derivatives 6-11 exhibited a strong inhibition profile (80.12-89.68%) against SRC kinase in comparison to the reference compound dasatinib (93.26%). Most of the compounds caused more than 50% of cell death in breast, lung, and prostate cancer cell lines and weak toxicity for normal cells in comparison to reference compounds osimertinib, dasatinib, and cisplatin. Compound 16 showed strong cytotoxicity on lung and prostate cancer cells. Treatment of prostate cancer cell lines with the most active compound, 16, significantly increased the caspase-3 (8-fold), caspase-8 (6-fold), and Bax (5.7-fold) levels and decreased the Bcl-2 level (2.3-fold) compared to the control group. These findings revealed that compound 16 strongly induces apoptosis in the prostate cancer cell lines.

Conclusion: Overall kinase inhibition, cytotoxicity, and apoptosis assays presented that compound 16 has dual inhibitory activity against SRC and EGFR kinases while maintaining low toxicity against normal cells. Other compounds also showed considerable activity profiles in kinase and cell culture assays.