A comprehensive review of MR imaging changes following radiosurgery to 500 brain metastases.

BACKGROUND AND PURPOSE: Stereotactic radiosurgery is known to control 85%-95% of intracranial metastatic lesions during a median survival of 6-8 months. However, with the advent of newer systemic cancer therapies, survival is improving; this change mandates a longitudinal quantitative analysis of the radiographic response of brain metastases to radiosurgery. MATERIALS AND METHODS: MR imaging of 516 metastases in 120 patients treated with GK-SRS from June 2006 to December 2009 was retrospectively reviewed. Lesion volume at initial treatment and each follow-up was calculated by using the following formula: length × width × height / 2. Volume changes were correlated with patient demographics, histopathology, and radiation treatment variables. RESULTS: Thirty-two percent of lesions increased in volume following radiosurgery. Clinically, this translated into 54% of patients having ≥1 of their lesions increase in size. This increase begins at 6 weeks and can last beyond 15 months' post-SRS. Male sex (P = .002), mean voxel dose <37 Gy (P = .009), and initial treatment volume >500 mm(3) (P < .001) are associated with posttreatment increases in tumor size. Median survival following radiosurgery was 9.5 months for patients with all lesions exhibiting stable/decreased volumes, >18.4 months for patients with all lesions exhibiting increased volumes, and 16.4 months for patients with mixed lesional responses. CONCLUSIONS: Most metastatic lesions are stable or smaller in size during the first 36 months post-SRS. However, a transient increase in volume is seen in approximately one-third of lesions. Sex, treatment dose, initial lesion size, and histopathology all correlate with variations in lesion volume post-SRS. The longer the patient survives, the more likely an increase in lesion size will be seen on follow-up imaging.

HSV-tk gene therapy in head and neck squamous cell carcinoma. Enhancement by the local and distant bystander effect.

OBJECTIVES: To determine whether the bystander effect demonstrated in vitro for ganciclovir-mediated killing of a herpes simplex virus thymidine kinase (HSV-tk) gene-infected human squamous cell carcinoma is operative in vivo in a nude mouse model. DESIGN: Prospective study in a murine model. INTERVENTION: Human head and neck squamous cell carcinoma tumors were grown as xenografts on the flanks of 20 nude mice. The tumors in the left flank were then infected with the HSV-tk gene. Then, after 48 hours, the animals were treated with intraperitoneal ganciclovir twice daily. Assessment of the tumors on both flanks was performed over a 31-day period. MAIN OUTCOME MEASURES: Resolution of tumors infected with HSV-tk gene in animals treated with ganciclovir; resolution of tumors uninfected with HSV-tk gene on the contralateral flank in animals treated with ganciclovir. RESULTS: Following HSV-tk gene therapy in nude mice, complete resolution of HSV-tk-gene-infected human head and neck squamous cell carcinoma tumors was observed following ganciclovir treatment. Uninfected tumors were also noted to regress, but not completely resolve, in response to intraperitoneal ganciclovir (distant bystander effect). CONCLUSIONS: This study confirms that the local and distant bystander effects exist in this murine model, enhancing the possibility of its role for treatment of human squamous cell carcinoma of the head and neck.

Protein and messenger RNA expression of connexin43 in astrocytomas: implications in brain tumor gene therapy.

The expression of connexin43, the primary gap-junction constituent of glial cells, was evaluated at the messenger RNA and protein levels in different grades of astrocytoma to investigate the relevance of gap junctions in herpes simplex virus-thymidine kinase (HSV-tk)-mediated gene therapy of brain tumors. Transduction of the retroviral-mediated HSV-tk gene into tumor cells with subsequent administration of ganciclovir has recently been used as an experimental therapeutic strategy for treatment of brain tumors. One aspect of this approach is the bystander effect, which augments the efficacy of this therapeutic approach. Glioblastoma cells with minimum levels of connexin43 protein were transfected with a connexin43 complementary DNA. These cells manifested a marked increase in the in vitro bystander effect, supporting the contention that the in vitro bystander effect is a consequence of metabolic cooperation between cells mediated by gap junctions. To assess relative levels of gap-junction protein expression in the relevant tumor type, we examined primary astrocytomas, primary astrocytoma cell cultures, and glioblastoma cell lines. Although most astrocytoma tumor samples expressed connexin43, they differed in the level of expression, with the greatest variation exhibited in high-grade astrocytomas. Primary glioblastoma cell cultures and established glioblastoma cell lines also displayed some variability in connexin43 levels. In aggregate, our results anticipate that glioblastomas will have a varied bystander effect during HSV-tk gene therapy depending on the level of connexin43 expression.

In vitro evidence that metabolic cooperation is responsible for the bystander effect observed with HSV tk retroviral gene therapy.

Tumor cells transduced with a retroviral vector expressing a herpes virus thymidine kinase (HSV tk) gene are rendered sensitive to the antiherpetic drug, ganciclovir. The bystander effect refers to the observation that not all cells need be transduced to eradicate the cell population by treatment with ganciclovir. We demonstrate that metabolic cooperation can account for this bystander effect. When HT1080 human fibrosarcoma cells marked with a lacZ gene (LZ+5) were cocultured with HT1080 cells transduced with a retrovirus expressing HSVtk (HT1080tk11), at a density at which the majority of cells were in contact, both HT1080tk11 and LZ+5 cells were killed by ganciclovir. When cells were cocultured at a low density where the majority of cells are not in contact with one another, however, only the HT1080tk11 cells were killed. This result suggests that cell contact with HT1080tk11 cells is necessary to render the HSVtk- LZ+5 cells sensitive to ganciclovir. Because involvement of metabolic cooperation in the killing of the LZ+5 cells would require not only contact between HT1080tk11 and LZ+5 cells but also the capacity to transfer small cytotoxic molecules from the former cell to the latter, transfer of radioactive molecules between the two cell lines was assessed by autoradiography after treatment of a coculture with [3H]ganciclovir. Isolated HT1080tk11 cells incorporated the labeled ganciclovir into their nuclei, whereas isolated LZ+5 cells did not. LZ+5 cells incorporated [3H]ganciclovir, only when in contact with HT1080tk11 cells. These findings indicate that a ganciclovir metabolic product, presumably a phosphorylated form, can pass from HSV tk+ to HSV tk- cells and mediate cytotoxicity as a consequence of direct contact.

[Effect of endothelin on the release of angiotensin II from rat cardiovascular system].

The existence of angiotensin II immunoreactive substance in rat cardiovascular system was demonstrated by RIA and immunohistochemistry techniques. In atrium, aorta and cultured rat aorta smooth muscle cells, angiotensin II content is 7.2 + 2.7 pg/mg protein, 152.4 + 59.2 pg/mg protein and 3.5 + 0.8 pg/2 x 10(5) cells respectively. Endothelin, a potent vasoconstricting polypeptide, can enhance the release of angiotensin II from cultured rat aorta and aortic smooth muscle cells significantly. The results suggest that endothelin may be involved in the regulation of local blood flow and vascular tone, and it may also implicate the pathogenesis of some cardiovascular diseases such as cardiohypertrophy and vascular hypertrophy.