Vectors based on autonomous parvoviruses: novel tools to treat cancer?

Autonomous parvoviruses are small nuclear-replicating DNA viruses. The rodent parvoviruses usually are non- or weakly pathogenic in adult animals, bind to surface receptors which are expressed on most cells, and do not appear to integrate into host chromosomes during either lytic or persistent infections. Interestingly, malignant transformation of the target cells was often found to correlate with an increase in their capacity for amplifying and/or expressing the incoming parvoviral DNA, and is associated with oncolysis, i.e., the selective killing of the infected tumor cells. Moreover, the closely related parvoviruses MVM, H-1 and LuIII efficiently infect human cell lines. This finding makes these parvoviruses promising candidate vectors for therapies that require transient expression of a transduced gene. In particular, parvoviruses may be suitable to target and kill tumor cells and simultaneously deliver appropriate transgenes, e.g., genes coding for immuno-stimulatory factors. Pilot experiments performed in animals to assess whether parvovirus-based vectors carrying the interleukin 2 (IL-2) cytokine gene have reinforced anti-cancer capacity showed that these recombinant viruses suppressed tumor formation more efficiently than viruses devoid of a transgene. Strong anti-cancer effects of recombinant parvoviruses expressing interferon gamma-inducible protein 10 (IP-10) and monocyte chemotactic protein 3 (MCP-3) were also observed against established hemangiosarcomas and melanomas in immuno-competent mice, respectively. Altogether, these data illustrate the enormous potential of recombinant autonomous parvoviruses as anti-tumor agents and give hope of using them against human cancer.