In an effort to discover therapies for treating diseases caused by EBV, a novel screening assay for identifying compounds that reactivate EBV latent infection and a family of small molecules based on a tetrahydrocarboline backbone were discovered. Specifically, the compounds have the structure of the formula (I), wherein R1-R11 are defined herein and activate/reactivate EBV in a variety of cell types in a patient and are, therefore, useful in preventing or treating EBV-positive cancer, optionally with an anti-viral agent. In screening these compounds, novel compositions, EBV-positive cell lines, and methods are provided. (Formula I)