CBT-502 (anti-PD-L1) is an investigational immunotherapy being developed Chia Tai TianQing (CTTQ) of China. The rights to CBT-502 is held by the U.S.-based CBT Pharmaceuticals for the rest of the world.

How CBT-502 works

CBT-502 is a type of immunotherapy. Immunotherapies do not directly attack cancer but aim to help the body’s own immune system recognize and kill the cancer cells.

The immune system has the innate ability to identify abnormal or infected cells, such as cancer cells, by directing specialized immune cells, called T-cells, against them. However, to prevent the accidental damage to healthy body tissues, there are several checkpoint systems in place to inhibit the immune response and signal to the T-cells not to attack.

One pathway is the PD-1, or programmed cell death 1, pathway. T-cells produce a receptor called PD-1 on their surface. When PD-1 is stimulated by its ligand, a smaller protein that can bind and interact with the receptor, called PD-L1, this triggers an inhibitory response in the T-cells, preventing them from producing an immune response.

Normally PD-L1 is only produced by healthy body cells; however, some cancer cells take advantage of this system and also produce PD-L1. This allows them to evade detection by the immune system and continue to grow unchecked.

CBT-502 is an antibody, a protein designed to interact with a specific target, that binds to PD-L1. This way it prevents PD-L1 from binding to PD-1, preventing the inactivating signal from being sent to the T-cells. This should result in the T-cells being able to identify and attack the cancer cells, slowing tumor growth and potentially reducing tumor size.

CBT-502 in pre-clinical studies

Currently, CBT-502 has only been tested in preclinical studies and has not been investigated in patients.

Results of work testing CBT-502 in mouse models of colon cancer and melanoma were presented at the 2017 AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics in Philadelphia. CBT announced that the safety profile and anti-tumor activity of CBT-502 were comparable to that of the approved anti-PD-L1 drug, Tecentriq (atezolizumab).

CBT plans to begin studies to support an investigational new drug (IND) application to the U.S. Food and Drug Administration (FDA) in 2018 — a necessary step for clinical studies in patients — and hopes to initiate a Phase 1/2 clinical trial in Australia later that year.


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