Immune Checkpoint Inhibitors for Cancer Therapy: Status and Future Directions

Among various treatment modalities available for the treatment of cancer, immunotherapy is one of the important strategies used for the management of different malignancies. Immune checkpoint inhibitors are used for the treatment of cancers based on immunotherapy. Immune checkpoints are implicated when the proteins on the immune cells identify and bind to the ligand on the surface of other cells. These proteins are referred as immune checkpoint proteins. As soon as the checkpoint protein and ligand combine, they convey an “off” signal to the immune cells and prevent the immune system from killing the cancerous cells. Thus, immunotherapy drugs such as immune checkpoint inhibitors act by inhibiting the checkpoint protein molecules. This act stops the “off” signal, permitting the immune cells to destroy the cancerous cells. Programmed Death Ligand-1 (PD-L1) and Programmed Death-1 (PD-1) inhibitors have achieved clinical success with good overall survival rates in solid tumors. Considering remarkable outcomes in clinical investigations, various PD-L1 and PD-1 inhibitors have gained significant attention as onco-immunotherapeutic agents to treat various malignancies effectively. The present review aimed to explain the fundamentals of cancer immunotherapy, basics of checkpoints, inhibitors implicated in immune checkpoints, chemistry, clinical status, adverse events, resistance to checkpoint inhibitors and future scope.