Intramuscular CMT-167 Tumors Produce a Mild Cachexia Phenotype in C57BL/6J Mice

Cancer cachexia is a debilitating syndrome characterized by irreversible losses in skeletal muscle mass, with or without losses in adipose tissue. Cancer cachexia is an underrecognized syndrome that impacts ~50% of all cancer patients and accounts for up to ~20% of all cancer deaths [1, 2]. Lung cancer remains one of the deadliest cancers in the United States with an estimated 137,000 deaths in the year 2021 alone [3]. Lung cancer is highly comorbid with cancer cachexia [4]. Pre-clinical models are heavily relied upon to study both lung cancer and cancer cachexia, however there is a need to develop novel models to study the relationship between the two diseases. We therefore characterized the cachexia phenotype in the CMT-167 syngeneic lung cancer model.

Male C57BL6/J mice, aged 8-10 weeks, were administered an intramuscular (IM) injection of either 0.5x10⁶ CMT-167 cells or vehicle. Clinically relevant features of cancer cachexia were assessed 23 days after CMT-167 cell administration in tumor bearing mice by assessment of terminal skeletal muscle and adipose tissue mass, gastrocnemius myofiber cross sectional area (CSA), circulating biomarkers of cachexia, and skeletal muscle E3 ubiquitin ligase mRNA. A single intravenous dose pharmacokinetic study of pembrolizumab was completed to assess tumor status influence upon antibody pharmacokinetics.

Compared to tumor free (TF) mice, we observed lower terminal tumor-adjusted bodyweight, adipose tissue mass, gastrocnemius mass, quadriceps mass, and gastrocnemius myofiber CSA. CMT-167 tumor bearing (TB) mice did not lose bodyweight relative to starting weight, but instead failed to gain as much weight as TF controls. CMT-167 TB mice exhibited increased concentrations of circulating markers of cachexia and muscle wasting, such as IL-6 and TNF-α, although there was no difference in transcription of E3 ubiquitin ligases Trim63 (MuRF-1) and Fbxo32 (atrogin-1) in skeletal muscle compared to TF mice. CMT-167 TB mice exhibited increased catabolic clearance (CL) of the human IgG4 anti-PD-1, pembrolizumab, agreeing with published literature showing increased CL of immune checkpoint inhibitors in cachectic populations [5, 6]. Comparing the IM CMT-167 model to historical data with the well-established IM Lewis Lung Carcinoma model, CMT-167 TB mice displayed a less severe cachectic phenotype in terms of bodyweight and skeletal muscle effects.

The IM CMT-167 model is a syngeneic lung cancer model of mild cachexia. CMT-167 TB mouse is a novel model in which to study cancer cachexia induction, skeletal muscle atrophy, and immune checkpoint inhibitor clearance mechanisms in the context of lung cancer.