Does hyperthermia increase adenoviral transgene expression or dissemination in tumors?

Viral vectors used for cancer gene therapy are usually delivered by direct intratumoral administration. We studied the role of hyperthermia (HT) in vitro and in vivo in an attempt to achieve higher transfection rates (especially, larger volume of spread).

Replication-deficient adenoviruses containing either the human sodium-iodide symporter (Ad5-CMV-hNIS) or green fluorescent protein (Ad5-CMV-eGFP) as reporter genes were used. For in vitro studies, human lung cancer A549 cells were transfected with the virus and assayed for hNIS expression by radioactive pertechnetate uptake or green fluorescence activity using a gamma-counter or fluoroscopy respectively in the presence and absence of HT. For in vivo studies, A549 tumors were established intramuscularly in CD1 athymic mice. The adenoviral constructs (10(10) viral particles/tumor) were injected intratumorally when the tumors reached 10-11 mm in diameter. Different timing sequences of HT were examined and viral spread was assessed using technetium-autoradiography or GFP-fluorescence microscopy.

In the in vitro studies, A549 cells infected with the adenoviral construct did not show any difference in gene expression level in the presence or absence of HT. In vivo, the effect of HT on the volume of gene expression in A549 tumors was highly variable with some groups of mice showing better spread in the presence of HT and others showing reduced spread with HT.

Improvements in intratumoral adenoviral spread in response to hyperthermia were not consistently observed in a mouse tumor model using two quantitative endpoints of gene expression.