A Study of Orally Administered JBI-802, an LSD1/HDAC6 Inhibitor, in Patients With Advanced Solid Tumors

Inclusion Criteria: * Males or females aged ≥18 years at Screening * Absolute neutrophil count (ANC) ≥1500 cells/mm3. * Platelet count ≥100,000 cells/mm3. * Total bilirubin ≤1.5×ULN. Patients with Gilbert's syndrome may be enrolled with up to 3.0xULN. * AST and ALT ≤2.5×ULN (unless liver metastases are present then up to 5×ULN is allowed). * Calculated creatinine clearance (CrCL) ≥60 mL/min (Cockcroft-Gault formula). * Prothrombin time (PT) or activated partial thromboplastin time (aPTT) ≤1.5×ULN if participant is not anticoagulated (Note: If participant is on anticoagulants, the participant must be on a stable dose for at least 2 weeks prior to study entry. * Must have at least one measurable lesion on CT scan or MRI per RECIST 1.1 * Eastern Cooperative Oncology Group (ECOG) performance status of ≤2 * Other criteria may apply Part 1: * Participants with a histologically confirmed diagnosis of locally advanced or metastatic solid tumors (except microsatellite stable colorectal cancer and hepatocellular carcinoma) who have no available effective therapeutic options. Part 2: * Small cell lung cancer: Participants must have a histologic diagnosis of advanced SCLC not amenable to curative therapy and have received ≤2 prior regimens, which must have included a checkpoint inhibitor and a platinum-based chemotherapy. * De novo or treatment-emergent NEPC * Basket of neuroendocrine-derived tumors, excluding SCLC and treatment-induced NEPC. Participants must have unresectable locally advanced or metastatic disease and have no available effective therapeutic options. Exclusion Criteria: * Known malignant central nervous system (CNS) disease other than neurologically stable, treated brain metastases - defined as metastasis having no evidence of progression or hemorrhage for at least 4 weeks after treatment (including brain radiotherapy). Must be off any systemic corticosteroids for the treatment of symptomatic brain metastases for at least 14 days prior to enrollment. * Severe or unstable medical condition, such as congestive heart failure (New York Heart Association \[NYHA\] Class III or Class IV), ischemic heart disease, uncontrolled hypertension, uncontrolled diabetes mellitus, psychiatric condition, as well as an uncontrolled cardiac arrhythmia requiring medication (≥Grade 2, according to NCI CTCAE Version 5), myocardial infarction within 6 months prior to starting study treatment, or any other significant or unstable concurrent cardiac illness. Note: Stable chronic atrial fibrillation is allowed. * Use of strong inhibitors of CYP3A within 14 days or 5 half-lives (whichever is longer) or grapefruit juice or grapefruit containing products within 7 days prior to Cycle 1 Day 1. * Use of strong inducers of CYP3A within 14 days or 5 half-lives (whichever is longer) prior to Cycle 1 Day 1. * Use of strong inhibitors of cytochrome CYP2D6 within 14 days or 5 half-lives (whichever is longer) prior to Cycle 1 Day 1. * Use of strong inducers of CYP2D6 within 14 days or 5 half-lives (whichever is longer) prior to Cycle 1 Day 1. * History of other previous or concurrent cancer that would interfere with the determination of safety or efficacy assessment * Surgery (eg, stomach bypass) or medical condition that might significantly affect absorption of medicines * Other criteria may apply