ABSTRACT
Cancer treatments o´en fail at the individual cellular and tumor levels. At the cellular level, cancer cells frequently do not respond to pharmaceutical treatments because of acquired multiple drug resistance by active pump mechanisms (Szakcas et al. 2006), inhibitors of apoptosis (Dean et al. 2005, Putt et al. 2006), and inhibition of signaling molecules (Sebolt-Lepold and English 2006). Molecular mechanisms inhibiting apoptosis pathways may also hinder physical therapies, such as localized ionizing radiation as well as systemic pharmaceutical interventions (Galluzzi et al. 2006, Reed 2006a,b). At the multicellular tissue level, there are additional barriers within solid tumors to drug therapies, which may arise from the inability of drugs to fully penetrate abnormal, heterogeneous, and irregularly vascularized tumor tissue and thereby fail to reach all of the cancer cells at their therapeutic levels (Jain 1996, 2001, Padera et al. 2004, Minchinton and Tannock 2006).
