Recent advances in targeting cancer stem cells using oncolytic viruses.

Oncolytic virotherapy is a promising antitumor strategy which utilizes the lytic nature of viral replication to kill cancer cells. Oncolytic viruses (OVs) can induce cancer cell death and trigger immune responses to metastatic cancer in vivo. Reverse genetic systems have aided the insertion of anticancer genes into various OVs to augment their oncolytic capacity. Furthermore, OVs target and destroy the population of tumor-initiating cancer stem cells. These cancer stem cells are associated with metastasis and development of resistance to conventional anticancer approaches. Targeting cancer stem cells is essential since killing only differentiated tumor cells may lead to enrichment of cancer stem cells and thus indicate a poor prognosis. In this review, we summarize the oncolytic activity of various classes of OVs towards different types of cancer stem cells and also discuss the synergistic activity achieved by the combination of OVs with traditional therapies on chemo- and radiotherapy-resistant cancer stem cells.