The purpose of this study is to assess the safety and effectiveness of APR-1051 through the performance of a Phase 1, open-label, safety, PK, and preliminary efficacy study of oral APR-1051 in patients with advanced solid tumors.

Inclusion Criteria:

• Age ≥ 18 years
• Diagnosis of advanced/metastatic solid tumor
• Measurable or evaluable disease per RECIST version 1.1 (radiographic disease progression per PCWG3 criteria for patients with mCRPC)
• Eastern Cooperative Oncology Group (ECOG) performance status ≤ 1 or Karnofsky Performance Status (KPS) ≥ 70%
• Patients must have recovered to Grade 1 or baseline levels from toxicity or adverse events related to prior treatment for their cancer, excluding Grade ≤ 2 neuropathy, alopecia, or skin pigmentation
• Adequate bone marrow and organ function
• Women of child-bearing potential (WOCBP) or men of child-fathering potential must agree to use adequate contraception prior to study entry

Exclusion Criteria:

• Patient has had prior systemic anti-cancer therapy (cytotoxic chemotherapy, immunotherapy, targeted therapy) within 3 weeks (6 weeks in cases of mitomycin C, nitrosourea, lomustine) or at least 5 half-lives (whichever is shorter, but no less than 2 weeks) prior to Day 1
• Prior radiation therapy at the target lesion unless there is evidence of disease progression. If patient has had prior radiation therapy for disease progression, see Exclusion Criterion 1 for allowed interval between radiotherapy and Day 1 and recovery of AEs
• Treatment with any investigational agent administered within 30 days or 5 half-lives, whichever is shorter, before the first dose of APR-1051
• Major surgery within 21 days prior to Day 1
• Concomitant treatment with other anti-cancer therapy, including chemotherapy, immunotherapy, biological therapy, radiation therapy (except palliative local radiation therapy), or other novel anti-cancer agents. Note: endocrine therapy for breast and prostate cancer is allowed along with agents to treat or prevent skeletal related events (zoledronic acid, pamidronate, denosumab)
• Subjects with active (uncontrolled, metastatic) second malignancies or requiring therapy