Oncolytic viruses promise to significantly improve current cancer treatments through their tumour-selective replication and multimodal attack against cancer cells. However, one of the biggest setbacks for oncolytic virus therapies is the intravenous delivery of the virus, as it can be cleared by neutralizing antibodies (nAbs) from the bloodstream before it reaches the tumour cells. In our group, we have succeeded in developing aptamers to vesicular stomatitis virus (VSV), as well as to rabbit anti-VSV polyclonal neutralizing antibodies (nAbs). We tested these aptamers’ biological activity with a cell-based plaque forming assay and found that the aptamers prevented in vitro neutralization of VSV by nAbs and increased the virus infection rate of transformed cells up to 77%. In line with this approach, we enhanced the delivery of oncolytic viruses by selecting aptamers to the CT26 colon carcinoma cell line. The binding of aptamer pools has been tested on flow cytometry and the best pools were subjected to high throughput sequencing. Selected aptamers were linked to anti-VSV aptamers and applied for target delivery of the virus to cancer cells. Development of this aptamer-based technology aims to improve viral anti-cancer therapies, with a potential to be applied as treatment for patients affected with cancer. Finally, in collaboration with a group from Erlangen University, we performed an aptamer selection using capillary electrophoresis and cell-SELEX. The target, the extracellular domain of human CD83, is a maturation marker for dendritic cells and is involved in the regulation of the immune system. Selected aptamer sequences bound selectively to mature dendritic cells, in comparison to immature dendritic cells, and thus hold promise to be applied for further studies leading to a better understanding of CD83’s mechanism of action.

<p>We showed previously that histone deacetylase (HDAC) inhibition with MS-275 in the context of boosting oncolytic immunotherapy can drive heightened antitumor responses, leading to increased survival in mouse intracranial melanoma models. However, it is currently unclear how the co-administration of MS-275 directly impacts tumor growth. Here, we investigated the role of MS-275 in preventing the outgrowth of antigen-deficient tumor variants as a result of suboptimal treatment protocols. By adoptively transferring tumor antigen-specific memory T cells (Tm) that were expanded <em>in vivo</em> with recombinant Vesicular Stomatitis Virus (VSV-gp33), we observed complete regression of 5-day old, intradermal B16-gp33 tumors (B16-F10 overexpressing the LCMV GP33-41 epitope); however, the tumors relapsed within a month of treatment. Relapsing tumor explants were able to grow in mice that were prophylactically immunized with recombinant Adenovirus (Ad-gp33), indicating that the tumor could no longer be recognized. Strikingly however, there was zero tumor recurrence if MS-275 was co-administered with Tm and VSV-gp33, suggesting that MS-275 may prevent the emergence and/or escape of antigen loss variants. Such a benefit is lost if the administration of the drug is delayed as little as five days post VSV treatment, suggesting that its synergistic effects coincide with early immune responses and oncolytic activity. Furthermore, transplantation studies of relapsing tumor explants showed that combination treatment was unable to provide tumor protection, confirming that the mechanisms by which MS-275 prevents tumor recurrence are unlikely through direct up-regulation of antigen presentation in low- or non-antigen-expressing variants <em>in vivo</em>. Indeed, CD4 depletion in the absence of MS-275 resulted in sustained tumor regression, implying that immunoregulatory cells such as CD4+ Treg play a prominent role in sustaining tumor regression. Moreover, MS-275 modulates the phenotypic status of tumor-infiltrating MDSCs toward the differentiation of inflammatory macrophages. Taken together, the data suggests that combination therapy with HDACi with oncolytic immunotherapy mediates a synergized immune attack against the tumor through subversion of immunomodulatory mechanisms.</p> / Master of Science in Medical Sciences (MSMS)

Le cancer est une maladie qui touche des millions de personnes et ne discrimine pas. La forme de cancer la plus répandue chez les femmes au Canada est le cancer du sein et la deuxième cause de décès par le cancer chez cette population. Les traitements dépendent de plusieurs facteurs dont le stade du cancer, la ménopause, le statut des récepteurs hormonaux et du récepteur HER2 du cancer, etc. Les traitements qui existent sont la chirurgie suivie par la radio- et/ou chimiothérapie et l’hormonothérapie. Malgré les nombreuses études et les avancées dans les traitements pour différents cancers, plusieurs patients ont des cancers du sein qui sont réfractaires aux traitements disponibles. Une alternative naissante est l’utilisation de virus oncolytiques, c’est-à-dire des virus qui ciblent spécifiquement les cellules cancéreuses et laissent intact les cellules saines. Malheureusement, certains cancers demeurent réfractaires aux traitements avec virus oncolytiques. Ceci nous amène donc à regarder plus en détail des facteurs de l’environnement tumoral qui pourraient prédire la susceptibilité virale et engendrer des résultats positifs. C’est dans cette perspective que nous avons découvert que l'estrogène, précisément l’estradiol, rend les cellules cancéreuses qui en expriment le récepteur plus sensible au virus oncolytique VSV (virus de la stomatite vésiculaire). Cependant, nous ignorons toujours si d’autres hormones peuvent également moduler l’action de VOs. Nous émettons donc l’hypothèse que, comme l’estrogène, d’autres hormones vont affecter l’efficacité des VOs et qu’il serait possible de manipuler ces interactions pour améliorer la réponse au traitement. Notre étude nous permettra de concevoir des stratégies thérapeutiques améliorées pour les patients atteints du cancer du sein. L’importance de cette étude est que jusqu’à présent l’impact des hormones sur l’efficacité des virus oncolytiques reste un sujet inexploré. Nous allons déterminer l’effet de différents niveaux d’hormones sur la réplication et l’effet oncolytique de VSV. Ceci nous donnera ainsi la possibilité et les connaissances d’améliorer la sélection des patients pour le traitement et la conception d’une nouvelle génération de virus oncolytiques perfectionnés. / Cancer is a disease that affects millions of people across the world. The most common cancer in Canadian women is breast cancer and it also represents the second cause of death by cancer in this same group. The treatment depends on multiple factors including the stage of the cancer, menopause status, hormone receptor status, HER2 receptor status, etc. The available treatments for breast cancer are surgery followed by either radiation or chemotherapy as well as endocrine therapy. Despite numerous studies and advances in the treatment of different cancers, many patients’ cancer still remains refractory to these treatments. An exciting new alternative treatment is the use of oncolytic viruses. An oncolytic virus is a virus that can specifically target cancer cells all while leaving healthy normal cells intact. However, many cancers remain refractory to treatment with oncolytic viruses. There was thus a need to investigate different factors or the tumor microenvironment that may predict viral susceptibility and obtain positive outcomes. In this vein, it was found that estrogen (specifically estradiol), a hormone found in the body, can render cancer cells that express its receptor more sensitive to oncolytic virus infection by VSV (vesicular stomatitis virus). In spite of that, we are unaware if there are other hormones capable of modulating the actions of oncolytic viruses. Our hypothesis is that, like estrogen, other hormones will affect the efficacy of oncolytic viruses and that it will be possible to manipulate these interactions with the goal to improve treatment response. Our research will allow the conception of enhanced therapeutic strategies for patients with breast cancer. The importance of this study is that as of now the interplay between hormones and oncolytic viruses remains unexplored. We will determine the effects of hormone levels on viral replication and oncolytic ability of VSV. This knowledge will allow for a greater selection of patients for which oncolytic virus treatment will have a positive outcome. Additionally, it will allow for the development of a new generation of perfected oncolytic virus platforms.