Strategies to Improve Adenovirus and Reovirus Vectors for Oncolytic Virotherapy

Abstract

The research described in this thesis focused on generating more effective adenovirus and reovirus vectors and to obtain more reliable parameters of anticancer efficacy. Four different approaches were studied 1) Modification of capsid proteins to alter the tropism of the wild-type virus; 2) Forward-genetic strategies were used to obtain more potent viruses; 3) The modified viruses, obtained with the help of forward genetics, have been analyzed and compared with wild-type viruses on primary cultures and stem-like cultures; 4) Mesenchymal stromal cells (MSC) were evaluated as carrier cells for reovirus delivery to cancer cells.
Adenovirus does not have a natural preference for transformed cells. Modifications endowing the oncolytic preference are widely study. In chapter 4 the effect of the removal of adenovirus capsid protein IX was studied. Next to a virus vector with an altered cell tropism fundamental knowledge about protein IX was gained. In chapter 5 it was shown that truncation of the i-leader open-reading-frame enhanced the cytolytic activity on glioma cells in comparison to wild-type adenovirus. In contrast to adenovirus has reovirus an intrinsic preference for transformed cells. However, modification of the genome is challenging due to its segmented dsRNA genome. In chapter 6 and 7, two strategies to modify reovirus are described; a rational and a random approach. In addition with the mutants obtained with the random approach further studies were conducted. In chapter 8 the reovirus susceptibility of glioblastoma stem-like cells (GSC) was evaluated. In this study wild-type reovirus was compared to mutant. Here it was shown that there is a heterogeneous reovirus susceptibility in GSC cultures. In addition results on 2D cultures did not always correspond to results on 3D cultures. In chapter 9 the feasibility of using mesenchymal stem cells (MSC) as carrier cells was investigated. Here it was shown that MCS are potential cell-carriers for reovirus. Altogether, from these studies it can be concluded that - Modification of capsid proteins can change the cell tropisms and these modifications may provide more insight into the function of the capsid proteins; - Random and rational modification strategies both obtain modified vectors with increased oncolytic efficiency; - The structure of a culture, monolayer (2D) or spheroids (3D), may result in differences determination of the oncolytic efficacy of the viral vector - GSC cultures show a heterogeneous susceptibility to reovirus which may reflect the clinical variation.