Each cohort will be conducted sequentially. Advancement to higher dose cohorts is dependent upon satisfactory safety and tolerability profiles of the preceding cohort as determined by Sponsor review (conducted in consultation with the Lead Investigator[s]). Progression to Cohort 4 (5 mg dose strength) will not require a safety review of Cohort 3 (80 mg dose strength); screening and randomization for Cohort 4 may begin immediately after fully enrolling Cohort 3. Alternatively, if a dose-response relationship is apparent in review of the blinded activity data from the first three cohorts, the final 5 mg cohort may be omitted.