Engineering Macrophages to Synthesize Recombinant Adenoviruses in Hypoxic Areas of Human Prostate Tumours

Like many other forms of human malignancy, prostate carcinomas contain multiple areas of transient and chronic hypoxia. New therapies targeting the hypoxic areas of tumors need to be designed as these sites are highly resistant to conventional cancer therapies. We have recently shown that inflammatory cells called macrophages accumulate in these hypoxic areas of prostate tumors, thereby opening up the possibility of using these cells as cellular vehicles to deliver gene therapy to these otherwise inaccessible sites. We have designed a novel system in which macrophages are used to deliver hypoxia-regulated therapeutic adenovirus. In this approach, macrophages are co-transfected with a hypoxically activated E1A/B plasmid and an E1A/B deficient adenovirus containing a therapeutic gene under the control of a prostate-specific promoter (eg. PSA). When such co-transfected cells reach an area of extreme hypoxia, the E1A/B proteins are expressed, thereby activating replication of the adenovirus. The virus is released by the host macrophage and infects neighboring tumor cells. The PSA promoter-driven therapeutic gene is then expressed. We have shown that this takes place both in co-transfected human macrophages exposed to hypoxia (but not normoxia) in vitro, and when such cells are allowed to migrate into the central, hypoxic areas of human prostate (PC3) tumor spheroids. This novel approach employs three distinct levels of tumor-specific targeting, the homing of the macrophages to tumors, the synthesis and release of therapeutic adenovirus only in hypoxia tumor areas, and the restriction of therapeutic gene expression to prostate tumor cells.