The purpose of this study is to assess NEO6860, a modality selective TRPV1 antagonist, in patients with pain associated with osteoarthritis of the knee.

The study will be randomized, double blind, placebo and active control, a 3-way, 3-period crossover design, where each of the estimated 50 enrolled patients will receive alternately (i) NEO6860 (500 mg bid), (ii) placebo and (iii) Naproxen (500 mg bid). To ensure blinding, double dummy techniques will be used, so that at each period, patient will receive an oral liquid suspension (NEO6860 or its placebo) and one capsule (naproxen or its placebo).

Following a screening period, a maximum of 28 days before dosing, subjects will be randomized to one of the scheduled sequences. At each dosing period, subjects will be requested to participate in 2 clinic visits:

• One residential visit, the morning of investigational product dosing. Subjects will stay in the Clinical Research Unit approximately 13 hours
• One end of period visit, 24 h after first dosing A total of 2 washout periods of 1 to 3 weeks will separate the dosing periods. Once the 3 dosing periods will be completed, the subjects will come back to the clinic for a follow up visit (7 to 10 days post last dose).

Note: for a subpopulation, at one site, an assessment of heat pain threshold and tolerance will be conducted requiring a residential period of approximately 24 hours.

Inclusion Criteria:

• Body mass index (BMI) between 18.0 and 35.0 kg/m2 inclusive;
• Patients diagnosed with osteoarthritis of the knee, according to American College of Rheumatology (ACR) guidelines, by meeting at least 3 of the following: age > 50, morning stiffness < 30 minutes, crepitus on active motion, bone tenderness, bone enlargement, no palpable warmth of synovium;
• Grade I, II or III using Kellgren-Lawrence classification on an X-Ray of the knee
• WOMAC pain subscale ≥ 8
• R square of the Focused Analgesia Selection Task (FAST) outcome value greater than 0.70

Exclusion Criteria:

• Patients with, or with a history of, any clinically significant disorders (including fibromyalgia and other painful disorders) which may interfere with the primary objectives of the study
• Patients treated in the previous 3 months with topical capsaicin or intra-articular corticosteroids;
• Patients with a contra-indication for the use of Naproxen or acetaminophen;