Modulation of the host microbiome by black raspberries or their components and the therapeutic implications in cancer

Black raspberries (BRB) and their components have been demonstrated to prevent and inhibit the progression of cancers including oral, breast, esophageal, and colon in both preclinical studies and human clinical trials. The mechanism for their anticancer effect appears to vary by organ system, and include their anti-inflammatory, antiproliferative, antiangiogenic, and pro-apoptotic properties. Given findings that suggest that the host microbiome plays a distinct role in the development and progression of cancer, there has been a recent focus on discerning if BRB and their constituents modulate gut microbe levels. This review summarizes the reported effects BRB and their constituents have on the human microbiome and the implications that this has for their use in conjunction with traditional chemotherapies. BRB and their components have been shown to modulate the human gut flora in a positive manner, namely by promoting the population of the gut with "good" bacteria. These include BRB, their major polyphenol anthocyanins (AC), the major metabolite of AC protocatechuic acid (PCA), ellagic acid, and its major metabolite the urolithins. All of these components have been shown to modulate the gut flora, with variations between the individual components. This is in comparison to chemotherapeutic drugs including platinum-based entities and 5-flourouracil, which have been reported to negatively impact the human microbiome, leading to dysbiosis. Given these parallel findings, recent studies have attempted to discern if BRB or their components may reverse the negative effects traditional chemotherapies have on the gut microbiome, and if this results in an improvement in therapeutic outcomes.