The prodrugs are phosphorylated and converted into cytotoxic drugs that lead to termination of DNA synthesis during cell division and tumor growth, or during DNA repair, after radiation or chemotherapy damage (see Fig. 3 below).  This kills the targeted cells, sorrounding tumor cells and fast growing tumor blood vessels (anti-angiogenesis).

AdV-tk protein is a powerful antigen that in combination with surgery or radiation effectively stimulates a potent anti-tumor immune response: GMCI™.  GMCI™ stimulates all three of the essential elements for a potent immune response (see Fig. 4 below), rather than only a subset of the required steps as used by previous only moderately effective immunotherapy attempts. GMCI™ includes the following:

      a. It exposes tumor-associated antigens (TAAs),

      b. It promotes effective antigen presentation to the immune cells, and

Figure 1  Mechanism of cell killing in tumor cells that take up the tk gene and are treated with an anti-herpetic drug such as gancyclovir (GCV)

The local cell death reduces primary tumor burden.  This is good, but such an effect can also be achieved by cancer therapies currently in use, such as radiation and surgery.  Although AdV-tk, as a radio-sensitizer, improves local efficacy without increased toxicity, the key aspect of GMCI™ is the complete induction of a systemic anti-tumor immune response, unlike many previous immunotherapy technologies, which address only a subset of the required immune-response components (Figure 2).

Figure 2. Mechanism for induction of systemic anti tumor immune response from local intratumoral administration of Advantagene’s agents.  GMCI™ induces (1) tumor cell killing and release of tumor associated antigens (TAA, what makes the tumor different from normal cells) (2) the attraction of professional antigen presenting cells (APCs, cells specialized to process, package and present the TAAs to effector immune), and (3) the expansion of T-cells for systemic effect. 

Scores of publications from our laboratory and others have described the anti-tumor effects of AdV-tk after direct injection into tumor tissue in mouse models. The important systemic effect when this is used with radiation is illustrated in Figure 3.

Figure 3. Mouse prostate tumor model with a primary subcutaneous tumor and a lung metastatic load. Left: increased survival of mice with ProstAtak™ plus radiation (XRT) in the subcutaneous tumor, compared to radiation or AdV-tk alone or to no treatment controls. Right: reduction in metastatic load occurs most significantly in mice treated locally with ProstAtak™ and radiation.  Radiation alone has no effect on metastasis.

The complete immunologic effect of GMCI™ using AdV-tk was discovered by Advantagene’s scientists and helps explain the potent cell-mediated antitumor response observed in animal and clinical trials.  GMCI™ technology is the first to proactively combine all the components necessary to generate a potent immune response.  Previous immunotherapy approaches with a subset of these components have shown little clinical significance due to short duration or limited potency.  Independent presentation of tumor antigens generates immunity to the antigens but this has not translated to clinical improvement.  Recruitment of APCs by GM-CSF recruitment or physical isolation have reported some clinical successes but can be very complicated and of limited in duration. Finally, T-cell expansion by cytokine stimulation, such as IL-2, or by physical expansion in the laboratory have also had enticing but limited success.  Advantagenes GMCI™ technology combines all three of the components for a very potent response and can be easily and repeatedly administered.