Safety and Pharmacology Study of SNX-5422 in Subjects With Resistant Lung Adenocarcinoma

Inclusion Criteria: * Males or non-pregnant, non-breastfeeding females 18 years-of-age or older. * Received treatment with erlotinib/gefitinib throughout the one month prior to enrollment and at least six months at any time. * Must have undergone a biopsy after the development of acquired resistance. * Pathologic evidence of advanced lung adenocarcinoma (stage IIIB or stage IV) confirmed histologically/cytologically * Radiographic progression by RECIST during treatment with erlotinib/gefitinib. * Measurable (RECIST) indicator lesion not previously irradiated. * No more than 4 prior lines of cytotoxic chemotherapy, including erlotinib/gefitinib * Karnofsky performance score ≥70. * Adequate baseline laboratory assessments, including * Absolute neutrophil count (ANC) ≥1.5 x 109/L. * WBC \>3000/microliter * Platelet count of ≥100 x 109/L. * Total bilirubin level ≤1.5 times institutional upper limit of normal (ULN), alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤1.5 x ULN. * Hemoglobin ≥9 mg/dL. * Creatinine \<1.5 X upper limit of normal or estimated plasma creatinine clearance of ≥40 mL/min (using the Cockroft-Gault equation) * Signed informed consent form (ICF). * Subjects with reproductive capability must agree to practice adequate contraception methods. * Adequate venous access. Exclusion Criteria: * CNS metastases which are symptomatic and /or requiring escalating doses of steroids. * Prior treatment with any Hsp90 inhibitor. * Conventional chemotherapy, radiation or monoclonal antibodies within 4 weeks (erlotinib/gefitinib therapy within the past 4 weeks IS allowed). * Palliative radiation within 2 weeks. * The need for treatment with medications with clinically-relevant metabolism by the cytochrome P450 (CYP) 3A4 isoenzyme within 3 hours before or after administration of SNX-5422 * Screening ECG QTc interval ≥470 msec for females, ≥450 msec for males. * At increased risk for developing prolonged QT interval, including hypokalemia or hypomagnesemia, unless corrected to within normal limits prior to first dose of SNX-5422; congenital long QT syndrome or a history of torsade de pointes; currently receiving anti-arrhythmics or other medications that may be associated with QT prolongation. * Patients with chronic diarrhea or with grade 2 or greater diarrhea despite maximal medical management. * Gastrointestinal diseases or conditions that could affect drug absorption, including gastric bypass. * Gastrointestinal diseases that could alter the assessment of safety, including irritable bowel syndrome, ulcerative colitis, Crohn's disease, or hemorrhagic coloproctitis. * History of documented adrenal dysfunction not due to malignancy. * Known seropositive for human immunodeficiency virus (HIV) or hepatitis C virus (HCV). * History of chronic liver disease. * Active hepatitis A or B. * Current alcohol dependence or drug abuse. * Use of an investigational treatment from 30 days prior to the first dose of SNX-5422 and during the study. * Glaucoma, retinitis pigmentosa, macular degeneration, or any retinal changes detected by ophthalmological examination. * Other serious concurrent illness or medical condition. * Psychological, social, familial, or geographical reasons that would hinder or prevent compliance with the requirements of the protocol or compromise the informed consent process.