This phase I/II, multi-centered, non-randomized trial is designed to determine a safe dose of PT-523 for subjects, and to make preliminary evaluations on the activity of PT-523 as therapy in subjects with NSCLC.

Inclusion Criteria:

• Age ≥ 18 years
• Histologically or cytologically confirmed NSCLC which is stage III or stage IV, or recurrent disease, and failed therapy with a standard first line (Phase I/II) as well as second line chemotherapy regimen (Phase I), or be intolerant of standard chemotherapy. Receipt of one additional prior chemotherapy regimen for neoadjuvant, adjuvant, or neoadjuvant plus adjuvant is allowable. A prior epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TK) antagonist is allowable (Phase II).
• Asymptomatic or treated brain metastases (including steroids) if last therapy was received > 4 weeks from study entry and is deemed by the investigator to have a low likelihood of rapid deterioration.
• ECOG performance status 0 - 2.
• Adequate organ function and bone marrow reserve.
• Use of appropriate contraceptive method.
• Signed patient informed consent.

Exclusion Criteria:

• Investigational agents within 30 days prior to Day 1 of study.
• Known symptomatic or uncontrolled brain metastases.
• Uncontrolled intercurrent illness.
• Known human immunodeficiency virus (HIV), hepatitis A, B, C, D and E.
• Patient has uncontrolled pleural effusions.
• Patient has received nitrosoureas or mitomycin-C within 6 weeks or other chemotherapy or radiation therapy within 3 weeks before study entry.