This is a 2-arm, noncomparative phase 2 trial designed to evaluate treatment outcomes with or without the addition of ciprofloxacin, metronidazole, and aspirin to first-line chemotherapy for patients with stage IV colorectal cancer (CRC).

This is a pilot study to evaluate the efficacy and safety of chemotherapy with or without MBMT in patients with metastatic CRC. The primary objective is to evaluate the efficacy, as determined by the ORR, of fluorouracil (5FU) based treatment regimen with and without MBMT in patients with CRC.

Inclusion Criteria:

• Diagnosis of stage IV colorectal cancer
• Measurable disease by Response evaluation criteria in solid tumors (RECIST) 1.1 criteria
• Planned first-line treatment with a 5FU-based doublet chemotherapy regimen for colon cancer, specifics of the regimen at the discretion of the treating physician Note: Patients who have received adjuvant therapy >6 months prior are eligible
• Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0-2
• Absolute neutrophil count (ANC) ≥1,500 cells/μL
• Platelet count ≥100,000 cells/μL
• Hemoglobin ≥8 g/dL Note: The use of transfusion or other intervention to achieve hemoglobin ≥8 g/dL is acceptable.
• Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤2.5 × upper limit of normal (ULN) Note: Patients with documented liver metastases: AST and ALT ≤5 × ULN
• Serum creatinine ≤1.5 x ULN or calculated creatinine clearance ≥40 mL/min using the Cockcroft-Gault equation: (140 - age) × body weight/plasma creatinine × 72 (× 0.85 if female)
• Radiographically measurable disease by RECIST 1.1
• Nonpregnant and not actively breastfeeding
• Sexually active patients of childbearing potential and their partners must agree to use medically acceptable form of contraception, per treating investigator, throughout the study Patients should continue to use medically acceptable methods of contraception after study treatment ends, following the guidance for their specific chemotherapy regimen.

Childbearing potential excludes:

Age > 50 years and naturally amenorrhoeic for > 1 year OR previous hysterectomy or bilateral salpingo-oophorectomy

• Patients on a pre-existing daily aspirin regimen may participate in the study without interrupting this regimen.
• Patients with a contraindication to aspirin may participate in the study. These patients will not be required to take aspirin as part of the study treatment.

Exclusion Criteria:

• Total colectomy
• Diagnosed with Cockayne Syndrome
• Using disulfiram, tizanidine, or theophylline and unable to stop taking these medications for the length of the microbiome modulation therapy
• On methotrexate doses of 15 mg/week or more
• History of allergic reaction to ciprofloxacin, metronidazole, or aspirin
• Fuss course of antibiotics in the 30 days before chemotherapy start Note: Full course is defined as ≥5 doses with an intent to treat a defined infection. Use of antibiotics intended for prophylaxis at the time of surgery is allowed
• Corrected QT interval (QTc) >480 on baseline ECG
• Diagnosed with a malabsorptive syndrome
• Inability to swallow tablets