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PRO 140 is a humanized monoclonal antibody targeted against the CCR5 receptor found on T lymphocytes of the human immune system. It is being investigated as a potential therapy in the treatment of HIV infection. The United States Food and Drug Administration has designated PRO 140 for fast-track approval. In February 2008, the drug entered Phase 2 clinical trials.
PRO 140 is being developed by Cytodyn Inc. In May 2007, results from the phase I clinical trial of the drug demonstrated "potent, rapid, prolonged, dose-dependent, highly significant antiviral activity" for PRO 140. Participants in the highest-dosing group received 5 mg per kilogram (2.3 mg/lb) and showed an average viral load decrease of -1.83 log10. On average, reductions of greater than -1 log10 copies/ml were maintained for between two and three weeks, from only a single dose of the drug. The largest individual HIV RNA reductions ranged up to -2.5 log10 among patients receiving both the 2 and 5 mg/kg doses.
Mechanism of action
PRO 140 is a lab-made antibody that functions as an entry inhibitor. PRO 140 binds to the CCR5 receptor on the CD4 cells, and interferes with HIV's ability to enter the cell. PRO 140, a humanized form of a PA14 antibody, is a chemokine-receptor CCR5 monoclonal antibody and can inhibit CCR5 tropic HIV-1 at concentrations that do not antagonize the natural activity of CCR5 in vitro. HIV-1 entry is mediated by the HIV-1 envelope glycoproteins gp120 and gp41. The gp120 will bind CD4 and the CCR5co receptor molecule, and this triggers gp41-mediated fusion of the viral and cellular membranes. CCR5 is hence needed for the entry of the virus and this infection of healthy cells. PRO 140, the anti-CCR5 monoclonal antibody, can stop HIV from entering the cell and stop viral replication. It prevents the virus-cell binding at a distinct site in the CCR5 co-receptor without interfering with its natural activity. Unlike other entry inhibitors, PRO 140 is a monoclonal antibody. The mechanism of inhibition is competitive rather than allosteric. As such, it must be injected to be effective. However, once inside the body, PRO 140 binds to CCR5 for >60 days, which may allow for dosing as infrequently as every other week. Compared to highly-active antiretroviral therapy which has been shown to have treatment-related toxicities for HIV-infected patients, PRO140 has no multi-drug resistance or toxicities.
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