Trastuzumab is a therapeutic monoclonal antibody to HER2 that has significantly improved the survival of HER2-positive breast and gastric cancer. The drug reduces proliferation and angiogenesis in treated tumors, and can induce antibody-dependent cell-mediated cytotoxicity (ADCC) by immune cells. Unfortunately, systemic administration is expensive and carries the risk of cardiomyopathy. Thus, local production and antibody activity at the tumor site would be optimal. However, antibodies are normally produced by B-cells and it is unknown if tumor cells are able to produce functional antibody. Here, we constructed an oncolytic adenovirus coding for human trastuzumab antibody heavy and light-chain genes, linked with an IRES. This virus has dual anticancer activity: First, Ad5/3-D24-tras is a chimeric serotype 5 oncolytic adenovirus exhibiting selective replication and oncolysis in cancer cells. Second, effective viral protein expression can lead to high and sustained local concentrations of trastuzumab. We aimed to study the trastuzumab production, mechanism of action and efficacy of Ad5/3-D24-tras in gastric cancer in vitro and in vivo.

Trastuzumab heavy and light chain expression by the virus construct was confirmed by Western blot in vitro. Cancer cells were able to produce full-length assembled antibody, which was released from infected cells to supernatant and could be detected by ELISA. Ad5/3-D24-tras showed cytotoxicity in gastric and esophageal cancer cell lines similar to the oncolytic parent virus. In addition in HER2-positive gastric cancer, Ad5/3-D24-tras treatment induced potent ADCC mediated by peripheral blood mononuclear immune cells. We assessed the efficacy of Ad5/3-D24-tras in a HER2-positive gastric cancer xenograft mouse model; Ad5/3-D24-tras treatment significantly enhanced tumor-growth inhibition over oncolytic parent virus Ad5/3-D24 or commercial trastuzumab (P<0.05, both). Importantly, higher local concentrations of trastuzumab were detected in Ad5/3-D24-tras treated tumors compared to controls. Flow cytometry analysis of the harvested immune cells suggested dendritic cell and natural killer cell induction in local lymph nodes of the Ad5/3-D24-tras treated mice.

In conclusion, Ad5/3-D24-tras is an attractive anticancer approach combining local production of trastuzumab with oncolytic potency of a replicating adenovirus, resulting in improved in vivo efficacy in HER2-positive gastric cancer. Moreover, antibody-mediated immune cell activation via ADCC could also potentiate effects of immunotherapeutic agents such as oncolytic viruses.

Citation Format: Ilkka Liikanen, Paula Savola, Akseli Hemminki. Tumor-specific oncolytic adenovirus coding for trastuzumab results in local production of functional monoclonal antibody from tumor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3643. doi:10.1158/1538-7445.AM2014-3643

©2014 American Association for Cancer Research.
2014