The Complement System and Cancer Cachexia

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Project Summary/Abstract Cachexia is characterized by progressive skeletal muscle and body weight loss and affects up to 80% of cancer patients. Since this loss of muscle mass contributes to weakness, reduced tolerance to conventional treatments, and increased mortality, understanding the mechanisms that drive muscle wasting is critical to the development of treatments to improve quality of life and enhance survival of cancer patients. However, in exploring the mechanisms that may drive cancer-induced atrophy of myofibers, it is important to do so in the context of the broader muscle pathologies that we and others have shown in the muscle of cachectic tumor bearing hosts, including tissue damage, non-resolute inflammation, impaired regeneration, and increased fat, collagen and calcium deposition. Unpublished proteomics data from our lab collected in the skeletal muscle of cachectic pancreatic cancer patients and, subsequently, cachectic mice bearing pancreatic tumors, releaved an enrichment of multiple pathways of the complement (Cp) system. Further immunohistochemical analyses revealed increased deposition of the central component of the Cp system, C3, and the terminal pathway/membrane attack complex (MAC) within muscle tissues of people and mice with pancreatic tumors, compared to controls. Based on these findings and the established roles of Cp proteins in causing inflammation and tissue damage, we injected mouse pancreatic cancer (KPC) cells into the pancreas of C3 knockout (C3-/-) mice and found significant protection against KPC-induced muscle wasting and weakness, that was further linked to reduced leukocyte infiltration into muscle and reduced fibrotic remodeling. These overall findings establish the requirement of Cp activation for the development of cachexia, with strong translational relevance. Aim 1 will build on these foundational findings and identify the specific Cp activation pathway and effector mechanism(s) required for the development of tumor-induced muscle pathologies and cachexia. This will reveal optimum points in the Cp pathway for pharmacological blockade. Aim 2 will utilize mouse Cp inhibitors that function at different points in the Cp pathway, targeted to sites of Cp deposition, to identify the most effective therapeutic strategy to prevent and reverse cachexia in tumor bearing mice using both the KPC model and C26 adenocarcinoma model. Aim 3 will determine the sufficiency and requirement of local myofiber-derived C3 in pancreatic cancer-induced immune cell infiltration into muscle, muscle damage, atrophy and weakness. This mechanistic aim is important because the role of local myofiber-derived Cp in muscle health and disease is almost completely unknown. Therefore, our findings here will provide mechanistic insights that will enable us to optimize and develop novel Cp inhibitory strategies for the treatment of a broad range of muscle conditions.