The purpose of this study is to determine if nilotinib is safe, if it can be tolerated by patients with Parkinson's disease (PD) and to learn if nilotinib has the possibility of effectively treating PD symptoms. Nilotinib has been approved by the Food and Drug Administration (FDA) to treat certain types of cancer (leukemia) but is considered investigational in this study because it has not been approved for treating PD. Twenty-five sites will enroll participants into 2 cohorts,approximately 75 in Cohort 1 and 60 in Cohort 2. Participants with moderate to advanced PD symptoms will be enrolled in Cohort 1, randomly assigned to take nilotinib (150 mg or 300mg) or placebo, and will complete 13 in-person study visits over 8.5 months.