• Using parts of the knee joint and the surrounding fluid that is taken out at the time of knee replacement, measure 1) the activity of aggrecansase (an enzyme that breaks down cartilage) and 2) the amount of study drug using lab tests. [ Time Frame: 4 weeks ] [ Designated as safety issue: No ]
  

This is a multicenter study of 2 dosing regimens of AGG-523, an investigational aggrecanase inhibitor that is taken orally. Potential study subjects are those with severe Osteoarthritis (OA) of the knee who are scheduled to undergo total joint replacement surgery.

Study subjects will be randomly assigned to 1 of 2 dosing regimens (once-daily or twice-daily dosing) of either 1800 mg AGG-523 or placebo, which will be taken during the 4-week period before having the total knee replacement. The treatments will be assigned using a 4:1 ratio of active to placebo treatment, which means that more subjects will receive the active treatment than the placebo (see below).

• AGG-523 1800 mg once a day (32 subjects)
• AGG-523 900 mg twice a day (32 subjects)
• Placebo once a day (8 subjects)
• Placebo twice a day (8 subjects)

Study subjects will have weekly evaluations as outpatients during the 4-week dosing period. The purpose of these evaluations is to monitor for potential complications, ensure compliance with taking the study drug, ask about the use of other medications, and, when necessary, replenish the supply of study drug. These assessments may be conducted by telephone, as a home visit, or by having the subject travel to the clinic for an outpatient office visit. A final (in person) visit will happen 2 weeks after having total knee replacement surgery.