Viral vectors have been used to deliver a wide range of therapeutic genes to tumors. In this study, a novel tumor therapy was achieved by the delivery of a mammalian brain sodium channel, ASIC2a, carrying a mutation that renders it constitutively open. This channel was delivered to tumor cells using a herpes simplex virus-1/Epstein-Barr virus (HSV/ EBV) hybrid amplicon vector in which gene expression was controlled by a tetracycline regulatory system (tet-on) with silencer elements. Upon infection and doxycycline induction of mutant channel expression in tumor cells, the open channel led to amiloride-sensitive sodium influx as assessed by patch clamp recording and sodium imaging in culture. Within hours, tumor cells swelled and died. In addition to cells expressing the mutant channel, adjacent, noninfected cells connected by gap junctions also died. Intratumoral injection of HSV/EBV amplicon vector encoding the mutant sodium channel and systemic administration of doxycycline led to regression of subcutaneous tumors in nude mice as assessed by in vivo bioluminescence imaging. The advantage of this direct mode of tumor therapy is that all types of tumor cells become susceptible and death is rapid with no time for the tumor cells to become resistant.
Bibliographical noteFunding Information:
We thank Dr Bujard for providing tetracycline regulatory elements used in the amplicon vector and Dr Fraefel for providing the HSV-TK amplicon plasmid; Dr Rachamimov (Pathologist at MGH) for analyzing the hematoxylin and eosin stained sections. Nicole Lewandrowski, Juliet Fernandez, Ozlem Senol, and Johanna M. Niers for technical help; Dr Yellen for access to the sodium imaging microscope; Suzanne McDavitt for skilled editorial assistance; and Igor Bagayev for assistance with confocal microscopy. This work was supported by grants from the National Cancer Institute (CA69246 and CA86355 to XOB and RW, and 1K99CA126839 to BAT), from NINDS (NS44363 to JG-A) and from the Brain Tumor Society (to B.A.T. and X.O.B.). D.P.C. is an Investigator of the Howard Hughes Medical Institute.