A promising new strategy for cancer therapy is the use of engineered oncolytic viruses, adapted from their natural properties of seeking out and destroying cells to effectively find and specifically eliminate cancer cells. The overarching goal of the work presented here is to engineer powerful new adenoviruses that can preferentially infect tumor cells via disparate receptors, and replicate exclusively in cells that have lost tumor suppressor pathways.
Since the creation of adenoviruses with novel tropism is limited by the ability to build and test new genetic designs, we desired targetable oncolytic adenoviruses with a modular platform that would enable rapid identification of new and controllable targeting moieties. We employed the property of rapamycin-induced FRB/FKBP heterodimerization to construct adenoviruses with chemically-controlled tropism by inserting FRB into the adenovirus and genetically encoding a functionalized FKBP fusion protein. We validated the targeting of this new class of viruses in culture using a panel of NCI breast cancer cell lines, targeting the frequently-upregulated cancer marker EGFR. We demonstrate that our targeting components are compatible with other virus modifications and that new adenoviruses with these mutations are able to infect and destroy a model of intractable triple negative breast cancer. Based on our findings, rapid discovery of effective targeting moieties for oncolytic adenoviruses should be possible, and we should avoid limiting the potency of future vectors by disrupting the highly evolved adenovirus capsid structure.
While oncolytic adenoviruses have already shown to be safe in clinical trials, we have improved the replication specificity of an oncolytic virus based on the function of adenovirus genes that overlap with frequent tumor mutations. It has been shown that mutation in adenovirus E1A can prevent its inactivation of cell cycle-regulator retinoblastoma protein (Rb), and this mutation is the basis of selectivity for an oncolytic adenovirus in clinical trials. However, adenovirus also encodes E4orf6/7, which acts downstream of Rb by activating the cellular transcription factor E2F1 that also drives the cell cycle. We have combined mutations in E1A and E4orf6/7 and discovered highly selective oncolytic adenoviruses that have the promise to be the basis for safe and potent oncolytic cancer therapies.