• Ali R Jazirehi and Benjamin Bonavida.
• Department of Surgery, Jonsson Comprehensive Cancer Center, David Geffen School of Medicine, University of California, Los Angeles, CA, USA. AJazirehi@mednet.ucla.edu
• Methods Mol. Biol. 2011 Jan 1; 731: 407-19.

AbstractTherapeutic strategies for cancer include chemotherapy, immunotherapy, and radiation. Such therapies result in significant short-term clinical responses; however, relapses and recurrences occur with no treatments. Targeted therapies using monoclonal antibodies have improved responses with minimal toxicities. For instance, Rituximab (chimeric anti-CD20 monoclonal antibody) was the first FDA-approved monoclonal antibody for the treatment of patients with non-Hodgkin's lymphoma (NHL). The clinical response was significantly improved when used in combination with chemotherapy. However, a subset of patients does not respond or becomes resistant to further treatment. Rituximab-resistant (RR) clones were used as a model to address the potential mechanisms of resistance. In this chapter, we discuss the underlying molecular mechanisms by which rituximab signals the cells and modifies several intracellular survival/antiapoptotic pathways, leading to its chemo/immunosensitizing activities. RR clones were developed to mimic in vivo resistance observed in patients. In comparison with the sensitive parental cells, the RR clones are refractory to rituximab-mediated cell signaling and chemosensitization. Noteworthy, interference with the hyperactivated survival/antiapoptotic pathways in the RR clones with various pharmacological inhibitors mimicked rituximab effects in the parental cells. The development of RR clones provides a paradigm for studying resistance by other anticancer monoclonal antibodies in various tumor models.

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