This will be a crossover study with 2 cohorts and an interleaving design with placebo substitution. The study will be conducted over 4 treatment periods in Cohort 1 (n=9) and over 3 treatment periods in Cohort 2 (n=9). Six subjects will be allocated to receive PF-04991532 and three subjects will be allocated to receive placebo treatment during each dosing period, except for the 4th period of Cohort 1. The 4th period of Cohort 1 will be dedicated to assess the effect of food on PF-04991532 PK parameters at one of the doses previously tested in Cohort 1; hence all 9 subjects will be dosed with PF-04991532 in an open-label fashion. A washout period of at least 7 days will occur between each dose.

This will be a crossover study with 2 cohorts and an interleaving design with placebo substitution. The study will be conducted over 4 treatment periods in Cohort 1 (n=9) and over 3 treatment periods in Cohort 2 (n=9). Six subjects will be allocated to receive PF-04991532 and three subjects will be allocated to receive placebo treatment during each dosing period, except for the 4th period of Cohort 1. The 4th period of Cohort 1 will be dedicated to assess the effect of food on PF-04991532 PK parameters at one of the doses previously tested in Cohort 1; hence all 9 subjects will be dosed with PF-04991532 in an open-label fashion. A washout period of at least 7 days will occur between each dose.

The tentative dosing schedule is 30, 100, 300, 600, 1200, and 2000 mg. Doses shown may be adjusted upwards or downwards and may be adjusted to include intermediate doses. All doses will be administered as extemporaneously-prepared powder in capsule (PIC) formulation.