Anti-epidermal growth factor receptor monotherapy in the treatment of metastatic colorectal cancer: where are we today?

Epidermal growth factor receptor in relation to tumor development: EGFR-targeted anticancer therapy

The discovery that signaling by the epidermal growth factor receptor (EGFR) plays a key role in tumorigenesis prompted efforts to target this receptor in anticancer therapy. Two different types of EGFR-targeted therapeutic agents were subsequently developed: mAbs, such as cetuximab and panitumumab, which target the extracellular domain of the receptor, thereby inhibiting ligand-dependent EGFR signal transduction; and small-molecule tyrosine kinase inhibitors, such as gefitinib and erlotinib, which target the intracellular tyrosine kinase domain of the EGFR. Furthermore, recent clinical and laboratory studies have identified molecular markers that have the potential to improve the clinical effectiveness of EGFR-targeted therapies. This minireview summarizes the emerging role of molecular profiling in guiding the clinical use of anti-EGFR therapeutic agents.

Engineered therapeutic antibodies with improved effector functions

In the past decade, more than 20 therapeutic antibodies have been approved for clinical use and many others are now at the clinical and preclinical stage of development. Fragment crystallizable (Fc)-dependent antibody functions, such as antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and a long half-life, have been suggested as important clinical mechanisms of therapeutic antibodies. These functions are primarily triggered through direct interaction of the Fc domain with its corresponding receptors: FcgammaRIIIa for ADCC, C1q for CDC, and neonatal Fc receptor for prolongation of the clearance rate. However, current antibody therapy still faces the critical issues of insufficient efficacy and the high cost of the therapeutic agents. A possible solution to these issues could be to engineer antibody molecules to enhance their antitumor activity, leading to improved therapeutic outcomes and reduced doses. Here, we review advanced Fc engineering approaches for the enhancement of effector functions, some of which are now ready for evaluation of their effectiveness in clinical trials.

Understanding the causes of multidrug resistance in cancer: a comparison of doxorubicin and sunitinib

Multiple molecular, cellular, micro-environmental and systemic causes of anticancer drug resistance have been identified during the last 25 years. At the same time, genome-wide analysis of human tumor tissues has made it possible in principle to assess the expression of critical genes or mutations that determine the response of an individual patient's tumor to drug treatment. Why then do we, with a few exceptions, such as mutation analysis of the EGFR to guide the use of EGFR inhibitors, have no predictive tests to assess a patient's drug sensitivity profile. The problem urges the more with the expanding choice of drugs, which may be beneficial for a fraction of patients only. In this review we discuss recent studies and insights on mechanisms of anticancer drug resistance and try to answer the question: do we understand why a patient responds or fails to respond to therapy? We focus on doxorubicin as example of a classical cytotoxic, DNA damaging agent and on sunitinib, as example of the new generation of (receptor) tyrosine kinase-targeted agents. For both drugs, classical tumor cell autonomous resistance mechanisms, such as drug efflux transporters and mutations in the tumor cell's survival signaling pathways, as well as micro-environment-related resistance mechanisms, such as changes in tumor stromal cell composition, matrix proteins, vascularity, oxygenation and energy metabolism may play a role. Novel agents that target specific mutations in the tumor cell's damage repair (e.g. PARP inhibitors) or that target tumor survival pathways, such as Akt inhibitors, glycolysis inhibitors or mTOR inhibitors, are of high interest. In order to increase the therapeutic index of treatments, fine-tuned synergistic combinations of new and/or classical cytotoxic agents will be designed. More quantitative assessment of potential resistance mechanisms in real tumors and in real time, such as by kinase profiling methodology, will be developed to allow more precise prediction of the optimal drug combination to treat each patient.