Study to Assess the Safety, Tolerability, and Efficacy of IDX-1197 in Combination With XELOX or Irinotecan in Patients With Advanced Gastric Cancer

Inclusion Criteria: * Group 1, patients with treatment-naïve recurrent or advanced metastatic gastric cancer including gastroesophageal junction or upper part of the stomach. * Group 2, patients with recurrent or advanced metastatic gastric cancer including gastroesophageal junction or upper part of the stomach, who were treated ≥2 times with palliative chemotherapy before screening. * At least 1 evaluable lesion for the dose escalation part and at least 1 measurable lesion according to RECIST v1.1 for the dose expansion part. * Eastern Cooperative Oncology Group (ECOG) performance status ≤1. * Group 2 Part C, patients should have UGT1A1 genotype tested during or prior to screening. Exclusion Criteria: * Symptomatic central nervous system or uncontrolled brain metastasis * Carcinomatous meningitis or its history. * For Group 1, patients who are HER 2 positive. * Any other concurrent uncontrolled illness including, but not limited to, active or ongoing symptomatic infection requiring IV antibiotic treatment, uncontrolled diabetes, hepatic, renal, or respiratory illness. * Severe or unstable angina, myocardial infarction or ischemia, symptomatic congestive heart failure, arterial or venous thromboembolism requiring coronary artery bypass graft or stent within the past 6 months or clinically significant cardiac dysrhythmia or New York Heart Association class II \~ IV heart disease within 6 months of randomization. * Uncontrolled hypertension * Immunocompromised patients, such as patients known to be serologically positive for HIV. * Patients with known active Hepatitis B or C infection. * Patients with known active or symptomatic pneumonitis, or history of non-infectious pneumonitis requiring steroids. * Diagnosis of a myelodysplastic syndrome/acute myeloid leukemia or its suspicious characteristics. * Any unresolved clinically significant Common Terminology Criteria for Adverse Events (CTCAE) Grade ≥2 toxicity * Resting ECG with measurable QTcF \> 470 msec on 2 or more time points within a 24-hour period or family history of long QT syndrome. * Current use of a cytochrome P3A4 inhibitor or inducer and strong uridine diphosphate (UDP)-glucuronosyltransferase 1A1 (UGT1A1) inhibitors.