Guided genes for tumor warfare

Combining Oncolytic Virotherapy with p53 Tumor Suppressor Gene Therapy

Oncolytic virus (OV) therapy utilizes replication-competent viruses to kill cancer cells, leaving non-malignant cells unharmed. With the first U.S. Food and Drug Administration-approved OV, dozens of clinical trials ongoing, and an abundance of translational research in the field, OV therapy is poised to be one of the leading treatments for cancer. A number of recombinant OVs expressing a transgene for p53 (TP53) or another p53 family member (TP63 or TP73) were engineered with the goal of generating more potent OVs that function synergistically with host immunity and/or other therapies to reduce or eliminate tumor burden. Such transgenes have proven effective at improving OV therapies, and basic research has shown mechanisms of p53-mediated enhancement of OV therapy, provided optimized p53 transgenes, explored drug-OV combinational treatments, and challenged canonical roles for p53 in virus-host interactions and tumor suppression. This review summarizes studies combining p53 gene therapy with replication-competent OV therapy, reviews preclinical and clinical studies with replication-deficient gene therapy vectors expressing p53 transgene, examines how wild-type p53 and p53 modifications affect OV replication and anti-tumor effects of OV therapy, and explores future directions for rational design of OV therapy combined with p53 gene therapy.

Perspectives of Cellular and Molecular Neurosurgery

Therapeutic efforts for human glial tumors have over the past years been redirected towards a compartmental treatment concept. The diffusely infiltrative nature of the disease calls for therapeutic agents to reach single cells far beyond the focus of attention which present therapies like surgery and radiation are able to treat. Specific drug discovery approaches which seek to define targets which are specific for gliomas have generated therapeutic options which allow for a highly selective development of new reagents. Combined with new modalities for compartmental drug delivery, systemic complications might be reduced and advantage taken of a compartmental specificity of a target which otherwise in the context of systemic application would not be as specific or burdened with side effects. From the present status of therapeutic developments in neuro-oncology it can be expected that a sufficient number of drug targets emerge which can be exploited by means of interstitial or intracavitary delivery, which are not neurotoxic and which may even be imaged in their action with the new metabolic imaging modalities. Convection enhanced delivery, conditionally replicating oncolytic viruses and motile, genetically engineered neural stem cells all seem to fulfill the distribution requirements which an effective therapeutic for gliomas will need to overcome the very limited efficacy which surgery, conventional chemotherapy and radiation have to offer. Whereas the genomics based discovery approaches are not specific for neuro-oncology, the development of delivery strategies is highly specific for the central nervous system, thus creating a unique set of organ and disease specific therapies.

Intravascular delivery of neural stem cell lines to target intracranial and extracranial tumors of neural and non-neural origin

The remarkable migratory and tumor-tropic capacities of neural stem cells (NSCs and/or neuroprogenitor cells) represent a potentially powerful approach to the treatment of invasive brain tumors, such as malignant gliomas. We have previously shown that whether implanted directly into or at distant sites from an experimental intracranial glioma, NSCs distributed efficiently throughout the main tumor mass and also tracked advancing tumor cells, while stably expressing a reporter transgene. As therapeutic proof-of-concept, NSCs genetically modified to produce the prodrug activating enzyme cytosine deaminase (CD), effected an 80% reduction in the resultant tumor mass, when tumor animals were treated with the systemic prodrug, 5-fluorocytosine. We now extend our findings of the tumor-tropic properties of NSCs (using a well-characterized, clonal NSC line C17.2), by investigating their capacity to target both intracranial and extracranial tumors, when administered into the peripheral vasculature. We furthermore demonstrate their capacity to target extracranial non-neural tumors such as prostate cancer and malignant melanoma. Well-characterized NSC lines (lacZ and/or CD-positive) were injected into the tail vein of adult nude mice with established experimental intracranial and/or subcutaneous flank tumors of neural and non-neural origin. The time course and distribution of NSCs within the tumor and internal organs was assessed in various models. Resulting data suggest that NSCs can localize to various tumor sites when injected via the peripheral vasculature, with little accumulation in normal tissues. Our findings suggest the novel use of intravascularly administered NSCs as an effective delivery vehicle to target and disseminate therapeutic agents to invasive tumors of neural and nonneural origin, both within and outside of the brain.