The purpose of this study is to evaluate the safety and preliminary efficacy of four doses of SGX201 in subjects with rectal cancer treated with concurrent radiation and chemotherapy.

Inclusion Criteria:

• Primary rectal cancer
• Planned course of conventional neoadjuvant radiation therapy before surgery
• Scheduled to receive chemotherapy
• >/= 18 years of age
• Negative pregnancy test

Exclusion Criteria:

• History of acute or chronic regional enteritis or inflammatory bowel disease
• Stool incontinence
• Uncontrollable diarrhea
• Abdominal-perineal resection or other surgery leaving patient without a functioning rectum
• Patients using colostomy or ileostomy
• Liver function tests > 3x upper limit of normal, or bilirubin test result > 1.5 the upper limit of normal
• Calculated creatinine clearance <60 mL/minute
• Planned hyperfractionated or split course radiation
• Planned brachytherapy prior to completion of all external beam radiation therapy
• Prior pelvic RT
• An on-going infection
• ECOG score >/= 3
• Leukopenia <2,000 WBC/mm3 or Hg <10.5 g/dL
• Participation in an investigational drug trial within the previous 30 days
• Patients with a medical condition that would interfere with study compliance
• Known hypersensitivity to 5-FU or capecitabine
• Anticipated inability to tolerate oral administration of SGX201
• Pregnant or breastfeeding