Current approaches for treating
cancer are limited, in part, by the inability of drugs to affect the poorly vascularized regions of tumors. We have found that spores of
anaerobic bacteria in combination with agents which interact with microtubules can cause the destruction of both the vascular and avascular compartments of tumors. Two classes of
microtubule inhibitors were found to exert markedly different effects. Some agents that inhibited
microtubule synthesis, such as
vinorelbine, caused rapid, massive hemorrhagic
necrosis when used in combination with spores. In contrast, agents that stabilized microtubules, such as the
taxane docetaxel, resulted in slow tumor regressions that killed most neoplastic cells. Remaining cells in the poorly perfused regions of tumors could be eradicated by sponzlated
bacteria. Mechanistic studies showed that the
microtubule destabilizers, but not the microtubule stabilizers, radically reduced
blood flow to tumors, thereby enlarging the hypoxic niche in which spores could germinate. A single intravenous injection of spores plus selected microtubule-interacting agents was able to cause regressions of several tumors in the absence of excessive
toxicity.