Chemical Synthesis of Novel DDR1 Inhibitors and Their Activity Against Gefitinib-Resistant Non-Small Cell Lung Cancer

Objective: The discoidin domain receptor-1 (DDR1) has been demonstrated as a potential target in gefitinib-resistant non-small cell lung cancer (NSCLC). However, drug development in this area remains limited. Therefore, this study aims to chemically synthesize novel DDR1 inhibitors and explore their activity against gefitinib-resistant NSCLC. Methods: The structures of the synthesized compounds were confirmed by electrospray ionization mass spectrometry (ESI-MS), ¹H, ¹³C NMR, and elemental analysis, followed by kinase screening experiments. The inhibitory impact of these compounds on the proliferation of PC-9 cells and gefitinib-resistant cell lines (PC-9GR and HCC827GR) was evaluated using the cell counting kit-8 (CCK-8) assay. Furthermore, the invasion capability of the cells was assessed using the Transwell assay. Additionally, Western blot analysis was employed to explore the targeting effects of these compounds on DDR1. Results and Discussion: Twenty-four 4,6-disubstituted pyrimidine derivatives were synthesized in series A, B, and C. Some compounds in series A and C exhibited promising inhibitory effects against DDR1 and DDR2, with compounds (A04), (A05), and (C04) demonstrating more pronounced activities. Moreover, compounds (A02), (A03), (A07), and (C04) significantly impeded the viability of PC-9 and PC-9GR cells, with (A07) exhibiting the strongest inhibition, with half-maximal inhibitory concentration (IC₅₀) values of 1.12 ± 0.07, 1.03 ± 0.18, and 1.56 ± 0.19 µM against PC-9, PC-9GR, and HCC827GR cells, respectively. Furthermore, 1 µM of (A03) and (A07) significantly inhibited the protein expression of p-DDR1 and DDR1, with compound (A07) being the most significant inhibitor (p < 0.001). Additionally, the Transwell assay demonstrated that 1 µM of (A07) substantially inhibited the invasion of PC-9 (p = 0.0003) and PC-9GR cells (p = 0.0019). Conclusions: The newly synthesized DDR1 inhibitor (A07) effectively inhibits the proliferation and invasion of gefitinib-resistant NSCLC cells, offering a potential new therapeutic option for treating NSCLC.