A Study of SGT-53 in Children With Refractory or Recurrent Solid Tumors

Inclusion Criteria: * All patients and/or their parents or legally authorized representatives must sign a written informed consent. * Patients must be \> than 12 months and ≤ 21 years of age at the time of study enrollment. * Body surface Area (For Dose Level -1): Patients must be ≥ 0.38 m² at the time of study enrollment. * Patients with relapsed or refractory solid tumors (excluding primary central nervous system tumors) are eligible. Patients must have had histologic verification of malignancy at original diagnosis or relapse. * Patients must have either measurable or evaluable disease. * Patient's current disease state must be one for which there is no known curative therapy or therapy proven to prolong survival with an acceptable quality of life. * Karnofsky ≥ 50% for patients \> 16 years of age and Lansky ≥ 50 for patients ≤ 16 years of age. * Patients must have fully recovered from the acute toxic effects of all prior anti-cancer chemotherapy: * At least 21 days after the last dose of myelosuppressive chemotherapy (42 days if prior nitrosourea). * At least 14 days after the last dose of a long-acting growth factor (e.g. Neulasta) or 7 days for short-acting growth factor. * At least 7 days after the last dose of a biologic agent. * At least 42 days after the completion of any type of immunotherapy, e.g. tumor vaccines. * At least 3 half-lives of the antibody after the last dose of a monoclonal antibody. * At least 14 days after local palliative XRT (small port); At least 150 days must have elapsed if prior TBI, craniospinal XRT or if ≥ 50% radiation of pelvis; At least 42 days must have elapsed if other substantial bone marrow radiation. * No evidence of active graft vs. host disease and at least 84 days must have elapsed after transplant or stem cell infusion. * Patient must not have had prior exposure to gene vector delivery products within 3 months. * Patients may not have had prior SGT-53. Patient who have received prior topotecan, cyclophosphamide, or both are eligible. * Adequate Bone Marrow Function: * Peripheral absolute neutrophil count (ANC) ≥ 1000/mm³. * Platelet count ≥ 100,000/mm³. * Adequate Renal Function: * Creatinine clearance or radioisotope GFR ≥ 70ml/min/1.73 m² OR age/gender appropriate serum creatinine. * Adequate Liver Function: * Bilirubin (sum of conjugated + unconjugated) ≤ 1.5 x upper limit of normal (ULN) for age. * SGPT (ALT) ≤ 110 U/L. * Serum albumin ≥ 2 g/dL. Exclusion Criteria: * Are pregnant or breast-feeding women. * Concomitant medications: * Patients receiving corticosteroids who have not been on a stable or decreasing dose of corticosteroid for at least 7 days prior to enrollment are not eligible. * Patients who are currently receiving another investigational drug are not eligible. * Patients who are currently receiving other anti-cancer agents are not eligible. * Patients who are receiving cyclosporine, tacrolimus or other agents to prevent graft-versus-host disease post bone marrow transplant are not eligible for this trial. * Patients who have an uncontrolled infection are not eligible. * Patients who have received a solid organ transplantation are not eligible. * Patients who in the opinion of the investigator may not be able to comply with the safety monitoring requirements of the study are not eligible.