Inclusion Criteria:

• Able to understand and willing to sign a written informed consent document
• Patients who have recurrent or metastatic NSCLC, who have failed initial therapy with a platinum-containing regimen and have not received any second-line therapy (adjuvant therapy is acceptable if it was completed greater than or equal to 12 months before the cancer recurrence)
• Measurable disease
• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1
• Laboratory Values within the normal or reasonable reference range as specified by the protocol

Exclusion Criteria:

• Prior exposure to SNS-595
• Pregnant or breastfeeding
• Women of childbearing potential or male partners of women of childbearing potential unwilling to use an approved, effective means of contraception according to the institution's standards
• Other active malignancies or other malignancies within the past 12 months except non-melanoma skin cancer, cervical intraepithelial neoplasia or prostatic intraepithelial neoplasia
• Brain metastases, if present, without radiologic evidence of progressive disease for at least 3 months after completion of therapy
• Myocardial infarction, cerebrovascular accident/transient ischemic attack (TIA) or thromboembolic event (deep vein thrombosis or pulmonary embolus) within 6 months before the first SNS-595 dose
• Requires kidney dialysis (hemodialysis or peritoneal)
• Prior chemotherapy, investigational agents, or radiation therapy within 28 days before Cycle 1 Day 0; however, nitrosoureas and mitomycin are not permitted for at least 42 days before Cycle 1 Day 0
• In patients with toxicities caused by prior cancer therapy, those toxicities must have returned to less than or equal to Grade 1, with the exception of alopecia
• Prior pelvic radiation therapy or radiation to greater than or equal to 25% of bone marrow reserve (prior palliative radiation is permitted as long as it does not exceed 25% of bone marrow reserve)
• Any other medical, psychological, or social condition that, in the opinion of the Principal Investigator, would contraindicate the patient's participation in the clinical trial due to safety concerns or compliance with study procedures