Towards novel paradigms for cancer therapy

Cancer is a complex progressive multistep disorder that results from the accumulation of genetic and epigenetic abnormalities, which lead to the transformation of normal cells into malignant derivatives. Despite enormous progress in the understanding of cancer biology including the decryption of multiple regulatory networks governing cell growth and death, and despite the possibility of analyzing (epi)genetic deregulation at the genome-wide scale, cancer-targeted therapy is still the exception. In fact, to date there are still far too few examples of therapies leading to cure; treatment-derived toxicity is a major issue, and cancer remains to be one of the largest causes of death worldwide. The purpose of this review is to discuss the state of the art of cancer therapy with respect to the key issue of any treatment, namely its target selectivity. Therefore, we recapitulate and discuss current concepts and therapies targeting tumor-specific features, including oncofusion proteins, aberrant kinase activities and epigenetic tumor makeup. We analyze strategies designed to induce tumor-selective death such as the use of oncolytic virus, tumoricidal proteins (NS1, Eorf4, apoptin, HAMLET (human α-lactalbumin made lethal to tumor cells)) and activation of signaling pathways involved in tumor surveillance. We emphasize the potential of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway, an essential component of the evolutionary developed defense systems that eradicate malignant cells. Finally, we discuss the necessity of targeting tumor-initiating cells (TICs) to avoid relapse and increase the chances of complete remission, and describe emerging concepts that might provide novel avenues for cancer therapy.