This is a Phase 1, first-in-human, open-label study of JAB-8263 to determine the maximum tolerated dose (MTD), recommended Phase 2 dose (RP2D) and assess the DLT. 30 subjects with advanced solid tumor will be enrolled.

JAB-8263 is a small-molecule inhibitor of the highly conserved bromodomain pockets of the bromodomain and extraterminal (BET) proteins.

The objectives of this study are:

To determine the maximum-tolerated dose (MTD) and assess the dose-limiting toxicity (DLT) of JAB-8263 as a single agent to adult subjects with advanced solid tumors To assess the safety and tolerability of JAB-8263 To characterize the pharmacokinetic (PK) parameters and pharmacodynamics (PDc) To evaluate preliminary antitumor activity of JAB-8263

Inclusion Criteria:

Subjects must meet all the following criteria in order to be included in the research study:

1. Subject must be ≥18 years-of-age at the time of signature of the informed consent form (ICF).
2. Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
3. Subjects with histologically or cytologically confirmed advanced solid tumors which have progressed despite standard therapy(ies), or are intolerant to standard therapy(ies), or have a tumor for which no standard therapy(ies) exists.
4. Subjects with life expectancy ≥3 months.
5. Patients must have at least one measurable lesion as defined by RECIST v1.1.
6. Patients who have sufficient baseline organ function.

Exclusion Criteria:

1. History (≤3 years) of cancer that is histologically distinct from the cancer under study.
2. Known serious allergy to investigational drug or excipients
3. Active brain or spinal metastases
4. History of pericarditis or Grade ≥2 pericardial effusion
5. History of interstitial lung disease.
6. History of Grade ≥2 active infections within 2 weeks
7. Known human immunodeficiency virus (HIV) infection
8. Seropositive for hepatitis B virus (HBV)
9. Seropositive for hepatitis C virus (HCV), or HCV-RNA viral levels are not detectable.
10. Any severe and/or uncontrolled medical conditions
11. History of myocardial infarction, unstable angina pectoris, coronary artery bypass graft, or cerebrovascular accident
12. Impaired cardiac function or clinically significant cardiac diseases
13. QTcF >470 msec at screening
14. History of medically significant thromboembolic events or bleeding diathesis
15. Unresolved Grade >1 toxicity
16. History of malignant biliary obstruction
17. Pregnant or breast-feeding