Cancer prevention and treatment using combination therapy with plant- and animal-derived compounds

Compounds naturally occurring in plants and animals play an essential role in the prevention and treatment of various cancers. There are more than 100 plant- and animal-based natural compounds currently in clinical use. Similar to synthetic compounds, these natural compounds are associated with dose-related toxicity that limits efficacy. Scientists have investigated combination therapy with compounds that have different toxicities in order to optimize efficacy. These combination therapies may work additively or synergistically, there may be no effect or they may promote tumor formation. Combination therapy with agents that have similar mechanisms of action may increase toxicity. In this article, combination therapies that have been investigated, their rationale, mechanism of action and findings are reviewed. When the data warrant it, combined (pharmacologic and natural; two or more natural) interventions that appear to increase efficacy (compared with monotherapy) while minimizing toxicity have been highlighted.