Targeting RANKL for the treatment of muscle and bone defects in cachexia

PROJECT SUMMARY
Cachexia is defined by abnormal loss of body weight and muscle mass that occurs secondary to chronic
diseases, such as cancer. It is estimated that musculoskeletal complications affect up to 80% of patients
diagnosed with cancer, dramatically impacting patient survival. Thus, there is an urgent need to develop novel
treatments for cachexia-related musculoskeletal symptoms. Our recently published observations showing that
cancer cachexia can present with bone loss, even in the absence of direct metastases to bone, suggest that
tumor-derived soluble factors may play a critical role in the onset of such skeletal phenotype. In this regard, our
preliminary findings suggest that receptor activator of NFkB ligand (RANKL), a factor involved in osteoclast-
induced bone resorption, plays a causative role in cancer-associated musculoskeletal complications.
In our published and preliminary studies we found that patients affected with ovarian cancer present cachexia,
as well as elevated RANKL and CTX-I, a marker of bone resorption. Similarly, mice bearing ES-2 ovarian tumors
present with muscle and bone loss, along with high RANKL and bone resorption, also consistent with high
positivity for the osteoclast marker, TRAP, as well as dramatic osteocyte death. Contrarily, mice carrying C26
tumors, characterized by low RANKL expression, substantially maintain their bone mass, despite evidence of
muscle wasting. Interestingly, myotubes exposed to recombinant RANKL undergo atrophy, similar to mice
infected with AAV-RANKL or bearing C26 cells overexpressing RANKL, whereas the use of anti-RANKL
neutralizing antibodies preserves myotube size in C2C12 myotubes co-cultured with ES-2 cells and counteracts
bone and muscle loss in ES-2 tumor hosts.
The objective of this proposal is to define the mechanisms by which RANKL-expressing tumors participate in
bone and muscle loss in cachexia. Our central hypothesis is that tumor-derived RANKL participates in the
activation of bone resorption, and triggers mechanisms adversely affecting muscle mass. In Aim 1, we will
determine the effects of tumor-derived RANKL on bone loss in the absence of bone metastases. We hypothesize
that tumor-derived RANKL directly activates bone resorption. In Aim 2, we will elucidate the mechanism(s)
responsible for RANKL-induced muscle wasting. We hypothesize that activation of the RANKL/RANK-dependent
pathway in skeletal muscle is sufficient to induce atrophy and exacerbate cachexia. In Aim 3, we will validate
antiresorptive therapies to preserve muscle size and function in mice bearing RANKL-expressing tumors. We
hypothesize that tumor-derived RANKL, along with IL-6 consequential to bone resorption, negatively impact
muscle.
The findings from the proposed studies will define the mechanistic effects of RANKL in cachexia and identify
RANKL as a new therapeutic target for the treatment of musculoskeletal complication associated with non-
metastatic RANKL-expressing cancers. These results will also open new avenues for cachexia research.

Grant Number: 5R01AR079379-06
NIH Institute/Center: NIH
Principal Investigator: Andrea Bonetto