Novel isatin-based hybrids as potential anti-rheumatoid arthritis drug candidates: Synthesis and biological evaluation

Rheumatoid arthritis (RA) is an autoimmune disease accompanied with serious symptoms, such as joint destruction and chronic synovitis. Though many anti-RA drugs could improve the outcome of RA patients to a certain extent, about 40% inefficient rate, severe side effects, and high costs have become urgent problems. Therefore, exploring new alternative drugs for RA therapy is still an urgent need so far. Isatin is an important structural motif found in numerous biologically active compounds and therapeutic agents. Herein, we aim to synthesize several novel isatin analogues for RA therapy and further explore the mechanism of the most potential anti-RA drug candidate in suppressing the pathological progress of RA in vitro and in vivo. We found that the most therapeutic potential compound, a novel small molecule isatin-honokiol hybrid named CT5-2 inhibited the viability of RA-fibroblast-like synoviocytes (FLSs), an effector cell of synovial hyperplasia in the RA synovial tissue with IC50 ranging from 8.54 to 10.66 μM. In addition, CT5-2 reduced the DNA replication and triggered cell cycle arrest and apoptosis of RA-FLSs. Moreover, differential analyses of RNA-sequencing and the mechanistic studies demonstrated that CDCA7 is a key gene correlated with RA progression, and CT5-2 could inhibit the c-Myc/CDCA7/p65 pathway to regulate CDK1, Bcl-2, and vimentin in RA-FLSs. Furthermore, CT5-2 relieved collagen-induced arthritis (CIA) and reduced the level of CDCA7, CDK1, Bcl-2, and vimentin of synovial tissue in CIA mice. Taken together, the novel small molecule isatin-honokiol hybrid CT5-2 exhibits a potential anti-RA drug candidate that inhibits proliferation and triggers cell cycle arrest and apoptosis of RA-FLSs by regulating the c-Myc/CDCA7/p65 pathway. Our study lays a good foundation for further clinical research and structuralmodification of CT5-2.