Gene therapy of brain and endocrine tumors

Abstract Gene therapy of cancer has become a major interest of medical research since more than 60% of the ongoing gene therapy protocols today involve cancer patients. To increase the therapeutic index of cancer gene therapy, targeting strategies have been developed to ensure that the expression of therapeutic genes is restricted exclusively to the tissue of interest. An attractive approach lies in the possibility to control the expression of therapeutic genes at the transcriptional level by the introduction of tissue-specific or tumor-specific enhancers/promoters offers. We have developed transcriptionally targeted vectors for gene therapy of solid tumors, including malignant gliomas and epithelial thyroid tumors. The choice of these tumor types relies on their clinical impact, ie, morbidity and mortality, the lack of effective conventional therapeutic strategies, and the ability of these tumors to express tissue/tumor-specific genes, whose transcriptional control elements (enhancer/promoter) may be used for achieving selective transgene expression. Here we report our clinical and preclinical experience in gene therapy of brain and thyroid tumors, and review the literature published on this topic

Transcriptionally targeted retroviral vector for combined suicide and immunomodulating gene therapy of thyroid cancer

Gene therapy may be an effective approach to thyroid carcinoma refractory to conventional treatment. A transcriptionally targeted retroviral vector for gene therapy of thyroid carcinomas was generated replacing the viral enhancer with the enhancer sequence of the human thyroglobulin (TG) gene, yielding a chimeric long-terminal repeat. The TG enhancer was used to drive the expression of either a reporter gene (beta-galactosidase) or two therapeutic genes, i.e. the prodrug-activating enzyme thymidine kinase of herpes simplex virus (HSV-TK) and human IL-2, separated by an internal ribosome entry site. The corresponding vector having an unmodified long-terminal repeat was used as control. The targeted vector allowed selective transgene expression and cell killing in differentiated thyroid tumor cells but not in anaplastic thyroid carcinoma cells and nonthyroid cells, as demonstrated by quantitative RT-PCR and cytotoxicity assays. Nude mice injected with tumor cells underwent near complete or complete regression of tumors transduced with the control vector after ganciclovir treatment. On the other hand, infection with the thyroid-specific vector led to regression only of TG-expressing tumors. In addition, tumors expressing human IL-2 showed significant growth retardation, compared with nontransduced tumors while exhibiting signs of necrosis and presence of an inflammatory infiltrate. However, HSV-TK/IL-2 plus ganciclovir was significantly more efficient than HSV-TK/IL-2 alone in eradicating tumor masses. Our results indicate that replacement of viral enhancer with TG enhancer confers selectivity of transgene expression in thyroid cells. Thus, the combined thyroid-specific expression of two therapeutic genes (cytokine and suicide genes), although a safe tumor-targeted treatment, would allow an increased anticancer effect

Modulation of retrovirally driven therapeutic genes by mutant TP53 in anaplastic thyroid carcinoma.

We previously demonstrated that restoration of TP53 activity in anaplastic thyroid carcinoma inhibits cell growth and induces expression of thyroid differentiation markers. Here, we investigated whether TP53 status may condition the expression of therapeutic genes driven by retroviral LTR or tissue-specific enhancer elements. The TP53-defective ARO anaplastic thyroid carcinoma cells were transfected with TP53(Val135), which exhibits wild-type activity at 32 degrees C, and transduced with retroviral vectors, in which therapeutic genes were driven either by wild-type LTR or by a reshuffled LTR containing thyroglobulin (TG) enhancer. Both at 37 and 32 degrees C, expression of transgenes driven by TG enhancer was 10-fold lower than that obtained with wild-type LTR retroviral vector. TP53(Val135) transfer into ARO cells repressed transcription from wild-type LTR but increased expression of TG-driven therapeutic genes. This effect was markedly enhanced by cell culture at 32 degrees C and by TSH treatment. Cytotoxic effects shown after ganciclovir treatment paralleled therapeutic gene expression levels. In conclusion, TP53 status in the tumor cell can influence expression of therapeutic genes. When using retroviral-vector-based gene therapy, wild-type LTR vectors should be employed to target TP53-defective tumors, whereas thyroid-specific promoters should be used for transcriptional targeting of thyroid carcinomas carrying wild-type TP53