This is an open-label, Phase 1b/2a study to evaluate the safety and tolerability of IDX-1197 and determine the MTD and RP2D 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.