Cancer immunotherapy with a gene modified serotype 3 oncolytic adenovirus

In 2012 WHO announced cancer as the leading cause of death. Every day 20 000 people die due to cancer, and the rate is estimated to double before year 2030. While treatments have progressed, there are still few good treatment options for advanced cancer. Thus, there is an urgent need for new treatments. Immunotherapy with gene modified oncolytic adenoviruses provides novel promising means of treating cancer. These treatments incorporate two basic concepts. Firstly, adenoviruses are modified so that they replicate only in cancer cells, which makes the treatments safer. Secondly, the virus induced cancer cell oncolysis elicits a danger signal that awakens the immune system to fight the cancer. Viruses can be further armed with different genes that can stimulate the immune system even more. Most of these oncolytic viruses are based on adenovirus serotype 5, as indicated in thousands of publications. However, the primary receptor for serotype 5 is down-regulated in advanced cancer. On the contrary, adenovirus serotype 3 receptor is known to be abundant in advanced cancer making it an interesting subject of research. While a different serotype per see offers an alternative immune response, serotype 3 incorporates also other interesting features that might further potentiate its utility. Our first goal was to create serotype 3 based oncolytic adenoviruses for the treatment of human cancer. The goal was achieved, making this virus, to our knowledge, the first non- adenovirus 5 based oncolytic adenovirus in the world used in humans. The publications, study I and II, are now part of this thesis. The virus was designed to have a human telomerase reverse transcriptase (hTERT) promoter diverting the replication of the virus into cancer cells. This virus, Ad3-hTERT-E1A, was successfully cloned, rescued and produced in large scale, which was followed by rigorous preclinical testing of the virus. Rigorous preclinical testing of the virus followed. Several in vitro and in vivo experiments were performed, including sequencing, qPCR, electron microscopy and neutralizing antibody assays, while the most convincing data was gained from the cell cultures and the animal models. We found the serotype 3 effective in all major cancer types in vitro. In vivo, the serotype 3 virus was found at least as potent as serotype 5 based control viruses in several murine models of human cancer. Before clinical treatments, biodistribution and toxicity experiments were performed. In toxicity studies, adenovirus 3 was found less toxic than the serotype 5 based control viruses in an immune competent murine model. The histology of all major organs and basic blood values were analyzed. The preclinical data suggested strong efficacy with good safety. In study II, we publish the data of the first 25 patients treated with the Ad3-hTERT-E1A virus. All patients had advanced solid tumors refractory to standard therapies. Th e safety of the treatment was good with up to 4x10 12 virus particles given intravenously and/or intratumorally. Overall, all patients experienced mild (grade 1-2) self-limiting flu-like adverse events. No severe adverse events were noted attributable to the treatments. After treatment, many patients showed signs of efficacy. Of the 15 patients with elevated tumor markers before the treatment, 73% responded with a decrease or no change in the markers. Even a few complete responses were reported, while some patients also showed a clear decrease in the tumor mass according to imaging. Also the clinical data suggested strong efficacy with good safety, proposing a need for a randomized study. Our next goal was to evaluate better ways in finding treatment responders, as size based computed tomography (CT) is known to be suboptimal in evaluating immunotherapeutics where initial swelling of the tumor due to the immune response is common. In study III, we examined the ability of magnetic resonance imaging (MRI) and spectroscopy (MRS) in immunocompetent Syrian hamsters. T2 weighed MRI seemed encouraging in finding responding hamsters as soon as two days after treatment. Similar findings were noted with a patient responding to oncolytic treatments. MRS of taurine, choline and unsaturated fatty acids were found to be promising metabolites when evaluating responders after oncolytic immunotherapy. These results propose MRI and MRS as potential methods in evaluating responding patients. T2 weighed MRI is already widely used in the clinics, thus a clinical trial should be easy to implement. In study IV, we evaluated the first 16 patients treated with a quadruple modified oncolytic serotype 5 adenovirus. Th e fiber knob of this virus is from serotype 3, while the virus also produces an immunostimulatory GM-CSF molecule. Th e two other modifications restrict the replication to cancer cells. The safety profile of the virus resembled that of the oncolytic serotype 3 virus, and also numerous signs of effi cacy were noted. Immunological studies indicated activation of the immune system in responding patients. Rationale for a randomized study exists also for this virus.