Abstract: Disclosed inter alia is the use of quinazolinone derivatives, which are modulators of a mitotic kinesin such as KSP, in the treatment of cellular proliferative diseases. The quinazolinone derivatives are administered with another chemotherapeutic agent selected from alkylating agents, antimetabolites, platinating agents, topoisomerase inhibitors, tubulin agents and signalling inhibitors (e.g., kinase inhibitors). Pharmaceutical compositions comprising one or both types of active agents are also disclosed.