Oncolytic adenoviruses targeted to cancer stem cells

Cancer stem cells (CSC) represent a distinct subpopulation of cancer cells of integral importance. CSCs embody the refractory nature observed among many cancers: very competent initial tumor establishment and extremely aggressive metastatic nature. Recent discoveries indicate that CSCs embody chemo- and radioresistance and have been correlated with advanced disease and resistance to current therapies, and thus help explain the treatment resistance of many cancers. As CSCs are critical for tumor initiation, progression, persistence, and the development of metastasis, the success or failure of treatment approaches may be influenced greatly by the presence and treatment sensitivity of these cells. There also seems to be a direct link between epithelial-mesenchymal transition phenomena and CSCs. Cancer cure is predicated upon effectively targeting and eradicating the CSC population. Oncolytic viruses have undergone many developments and through multiple generations offer an effective way to specifically target and eradicate CSCs, while still maintaining the ability to affect the general tumor cell population. Conditionally replicative adenoviruses (CRAd) are one virotherapy that is especially promising. Multiple advanced targeting and infectivity enhancement schemes have been developed to allow the necessary specificity and transduction efficiency required for an effective therapy. Furthermore, these advanced generation CRAds can be armed with therapeutic transgenes to generate greater antitumor effects. Although ultimately, the rewards of targeting and eradicating CSCs will be evaluated in clinical trials, there are numerous methods for isolating primary CSCs based on surface marker expression and multiple established cell lines representative of CSCs for preliminary evaluation. [Mol Cancer Ther 2009;8(8):2096-102]