MK-4166 is an investigational immunotherapy being developed by Merck & Co. or MSD (for Merck Sharp & Dohme outside the U.S. and Canada) to treat various types of solid tumors.

How MK-4166 works

The body’s immune system is capable of identifying and killing abnormal cells, including cancer cells. MK-4166 is an immunotherapy, a drug that aims to boost the immune response to encourage the body to fight cancer.

Among other mechanisms, the immune system uses immune cells called effector T-cells that recognize tumor-specific antigens, or substances associated with a tumor, to kill cancerous cells. Another type of T-cells, called regulatory T-cells or Tregs, suppress the activation and proliferation of effector T-cells.

MK-4166 is an antibody, a protein that interacts with a specific target. Specifically, MK-4166 is designed to bind to and activate a protein called glucocorticoid-induced tumor necrosis factor receptor, or GITR.

GITR is found on the surface of several types of immune cells, including T-cells. It is thought to dampen the work of Tregs so as to stimulate the activation and proliferation of effector T-cells that can target and kill cancer cells.

By activating GITR, MK-4166 should boost the immune response against cancer, resulting in a reduction of tumor cells.

MK-4166 in clinical trials

Merck/MSD is currently investigating MK-4166 in an open-label Phase 1 dose-escalation study (NCT02132754), either alone or in combination with Keytruda (pembrolizumab). The study aims to enroll 92 patients with advanced solid tumors at sites in the U.S, Australia, and Israel. The trial is still recruiting participants — information is available by clicking on its identification number — and is estimated to close in October 2019.

This study aims to identify the maximum tolerated dose of MK-4166, and determine whether the drug is safe and well-tolerated by patients both alone and in combination with Keytruda. Patients will be monitored for adverse events for up to 25 months.

Other information

MK-4166 is administered through a roughly 30-minute injection into the bloodstream.


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