Provided herein are methods for enhancing infection, growth, spread, or titer of an oncolytic RNA virus in a cancer or tumor cell; enhancing the oncolytic activity, cytokine-induced cell death activity, and/or cytotoxic activity of an oncolytic RNA virus in a cancer or tumor cell; upregulating cytokine response to, and/or enhancing the immunotherapeutic activity of an oncolytic RNA virus in a cancer or tumor cell; and/or treating a tumor or cancer in a subject in need thereof. Such methods employ a vanadium-containing compound, administered to the cancer or tumor cells before, after, or concurrently with infection of the cancer or tumor cells with the oncolytic RNA virus. Related compositions, uses, and kits therefor are also provided. Methods for producing RNA viruses, RNA virus-based cancer vaccines, and RNA virus-based cancer gene therapy vectors are also provided.