Small-Molecule Drugs in Immunotherapy

Immunotherapy has been increasingly used in the treatment of cancer. Compared with chemotherapy, immunotherapy relies on the autoimmune system with fewer side effects. Small molecule immune-oncological medicines usually have good bioavailability, higher tissue and tumor permeability, and a reasonable half-life. In this work, we summarize the current advances in the field of small molecule approaches in tumor immunology, including small molecules in clinical trials and preclinical studies, containing PD1/PD-L1 small molecule inhibitors, IDO inhibitor, STING activators, RORγt agonists, TGF-β inhibitors, etc. PD-1/DP-L1 is the most attractive target at present. Some small molecule drugs are being in clinical trial studies. Among them, CA-170 has attracted much attention as an oral small molecule drug. IDO is another popular target after PD-1/PDL1. The dual IDO and PD-1 inhibitor can improve the low response of PD-1 and has a good synergistic effect. STING is a protein that occurs naturally in the human body and can enhance the body's immunity. RORγt is mainly expressed in cells of the immune system. It promotes the differentiation of Th17 cells and produces the key factor IL-17, which plays a key role in the development of autoimmune diseases. TGFβ signaling exhibits potent immunosuppressive activity on the coordinate innate and adaptive immunity, impairing the antitumor potential of innate immune cells in the tumor microenvironment. It is worth mentioning that immunotherapy drugs can often achieve better effects when used in combination, which will help defeat cancer.