Oncolytic vaccinia virus for the treatment of liver cancer

Aims: Current treatment of colorectal cancer (CRC) liver metastases has a success rate of 50% 5-year survival, and recurrence rates of 50%. There is therefore still a
need for a novel treatment modality. We aimed to examine the ability of JX-594 to preferentially replicate in and kill CRLM in vitro and ex vivo, and induce immunemediated
tumour cytotoxicity by activation of natural killer (NK) cells.

Methods: The Wyeth strain of vaccinia virus has been genetically manipulated to encode for granulocyte macrophage colony stimulating factor (JX-594-GM-CSFfLuc)
and green fluorescent protein (JX-594-GM-CSF-GFP) in the disrupted thymidine kinase locus. Viability assays and Enzyme Linked Immunoabsorbent Assay (ELISA) was used to confirm tumour cell killing and production of inflammatory cytokines when CRC cell lines were infected with JX-594. Viral replication in vitro was investigated by plaque assay and using an ex vivo ‘tissue core’ method. Induction of the innate immune response was measured by upregulation of activatory markers on virus-treated-NK cells and monocytes by flow cytometry and anti-tumour cytotoxicity by chromium release.

Results: JX-594 can directly lyse CRC cell lines, with greater lysis and replication (up to 250-fold) in cells with upregulated surface EGFR. JX-594 treatment resulted
in substantial expression of GM-CSF and induction of inflammatory cytokines within the tumour microenvironment, and inhibition of anti-inflammatory and proangiogenic
cytokines. Ex vivo infection of CRLM with JX-594-GFP-GM-CSF
resulted in tumour-specific GFP and GM-CSF expression. Treatment of NK cells with JX-594-GM-CSF led to activation, degranulation and increased cytotoxicity against CRC cell targets. This was dependent on the presence of CD14+ve
monocytes, which acquired an antigen-presenting phenotype
(CD86+veCD11c+veClassIIDR+ve).

Conclusions: JX-594 holds promise as a novel treatment modality for disseminated CRC. Direct tumour-specific lysis and transgene expression and the induction of tumour-specific innate immunity means that it may provide a twopronged attack against tumour cells whilst sparing normal tissue.