In vivo tibial compression decreases osteolysis and tumor formation in a human metastatic breast cancer model

Abstract

Bone metastasis, the leading cause of breast cancer-related deaths, is characterized by bone degradation due to increased osteoclastic activity. In contrast, mechanical stimulation in healthy individuals upregulates osteoblastic activity, leading to new bone formation. However, the effect of mechanical loading on the development and progression of metastatic breast cancer in bone remains unclear. Here, we developed a new in vivo model to investigate the role of skeletal mechanical stimuli on the development and osteolytic capability of secondary breast tumors. Specifically, we applied compressive loading to the tibia following intratibial injection of metastatic breast cancer cells (MDA-MB231) into the proximal compartment of female immunocompromised (SCID) mice. In the absence of loading, tibiae developed histologically-detectable tumors with associated osteolysis and excessive degradation of the proximal bone tissue. In contrast, mechanical loading dramatically reduced osteolysis and tumor formation and increased tibial cancellous mass due to trabecular thickening. These loading effects were similar to the baseline response we observed in non-injected SCID mice. In vitro mechanical loading of MDA-MB231 in a pathologically relevant 3D culture model suggested that the observed effects were not due to loading-induced tumor cell death, but rather mediated via decreased expression of genes interfering with bone homeostasis. Collectively, our results suggest that mechanical loading inhibits the growth and osteolytic capability of secondary breast tumors after their homing to the bone, which may inform future treatment of breast cancer patients with advanced disease.

Biomechanical forces in the skeleton and their relevance to bone metastasis: Biology and engineering considerations

“…Tibial compression increased cortical and cancellous bone mass and improved structural indices in a variety of mouse models, such as hormone-deficient male mice [141] and mice with age-related bone loss [14]. When combined with intratibial injection of breast cancer cells, a common model of metastasis-related secondary tumor growth [142], tibial compression prevented osteolysis and secondary tumor formation in tumor-bearing tibiae [143], suggesting that anabolic loading can be used to inhibit osteolytic remodeling during breast cancer bone metastasis (Figure 5). Nevertheless, it remains to be defined whether these differences were due to interference with tumor cell homing and/or growth.…”

“…Yet human breast cancer cells subjected to 50% static compression, corresponding to ~0.1 kPa in agarose gels, increase expression of genes related to ECM proteolysis, adhesion, and migration [221]. In contrast, human breast cancer cells subjected to 10% cyclic compression of a 3-D model of the bone microenvironment decreased expression of genes interfering with bone homeostasis [143] (Figure 7C). Applying compression and perfusion simultaneously may best mimic the in vivo bone mechanical microenvironment, and indeed this approach increases osteoblast differentiation relative to perfusion alone [196].…”

“…The box indicates region of interest for analysis in the proximal compartment. B) Representative microCT images of sham-injected (Control) and tumor-injected (Tumor) tibiae revealed that nonloaded tumor-bearing tibiae exhibited osteolytic degradation, whereas loading inhibited these adverse changes [143]. Reproduced with permission from John Wiley and Sons.…”

“…(Right) Additionally, this percentage increased with increasing flow rate [53]. C) Cyclic compression applied to human breast cancer cells cultured in mineral-containing poly(lactide-co-glycolide) (PLG) scaffolds reduced their expression of Runx2, a gene associated with initiating osteolysis [143]. D) Production of osteocalcin was greatest when both compression and perfusion was applied to bone marrow-derived mesenchymal stem cells cultured in spongiosa disks [222].…”

Mechanics of intact bone marrow

“…Many studies have looked at properties of homogenized marrow, by extracting marrow from the medullary cavity and performing bulk rheology, but these approaches are destructive and create a critical gap in our knowledge of intact marrow mechanics (Bryant, 1988; Bryant et al, 1988; Saito et al, 2002; Sobotkova et al, 1988; Zhong and Akkus, 2011). Additionally, researchers have used techniques to measure intramedullary pressure (IMP) to better understand how lifestyle choices, such as loading, disuse, steroid use, and diseases such as osteoporosis and cancer change marrow content, blood flow, and bone remodeling (Bloomfield, 2010; Gurkan and Akkus, 2008; Lynch et al, 2013; Miyanishi et al, 2002; Zhang et al, 2007). It is clear that many external factors impact IMP changes, but no work has gone into characterizing the mechanics of the intact matrix, which we suggest plays a stiffness-dependent role in disease progression.…”