Multiscale characterization of the mineral phase at skeletal sites of breast cancer metastasis

Abstract

Skeletal metastases, the leading cause of death in advanced breast cancer patients, depend on tumor cell interactions with the mineralized bone extracellular matrix. Bone mineral is largely composed of hydroxyapatite (HA) nanocrystals with physicochemical properties that vary significantly by anatomical location, age, and pathology. However, it remains unclear whether bone regions typically targeted by metastatic breast cancer feature distinct HA materials properties. Here we combined high-resolution X-ray scattering analysis with large-area Raman imaging, backscattered electron microscopy, histopathology, and microcomputed tomography to characterize HA in mouse models of advanced breast cancer in relevant skeletal locations. The proximal tibial metaphysis served as a common metastatic site in our studies; we identified that in disease-free bones this skeletal region contained smaller and less-oriented HA nanocrystals relative to ones that constitute the diaphysis. We further observed that osteolytic bone metastasis led to a decrease in HA nanocrystal size and perfection in remnant metaphyseal trabecular bone. Interestingly, in a model of localized breast cancer, metaphyseal HA nanocrystals were also smaller and less perfect than in corresponding bone in disease-free controls. Collectively, these results suggest that skeletal sites prone to tumor cell dissemination contain less-mature HA (i.e., smaller, less-perfect, and less-oriented crystals) and that primary tumors can further increase HA immaturity even before secondary tumor formation, mimicking alterations present during tibial metastasis. Engineered tumor models recapitulating these spatiotemporal dynamics will permit assessing the functional relevance of the detected changes to the progression and treatment of breast cancer bone metastasis.

Bone Metastasis: Find Your Niche and Fit in

“…Furthermore, the bone tropic subline of MDA-MB-231 cells showed increased secretion of pro-osteoclastic interleukin-8 in an HA-rich environment, which may therefore contribute to the vicious cycle [147]. In a recent study, the skeletal sites with less mature HA were found to be more likely to develop bone metastasis in a mouse model of breast cancer [148].…”

Implantable pre-metastatic niches for the study of the microenvironmental regulation of disseminated human tumour cells

“…Often, CTCs that survive extravasation do not immediately proliferate, but instead lay dormant for months to decades until the surrounding milieu becomes favorable for regrowth 3 , 4 . Emerging evidence suggests that metastatic relapse may not be explained solely by intrinsic genetic instability of DTCs, instead bi-directional interaction with the surrounding microenvironment needs to be considered 5 – 7 . Understanding how the local milieu surrounding DTCs prevents or aids in regaining proliferative phenotypes is imperative to developing better therapeutic strategies to prevent or delay lethal metastasis.…”

Interior x-ray diffraction tomography with low-resolution exterior information

“…IR-TV is an optimization problem that minimizes the objective function in Eq. (8), which consists of a Poisson likelihood ( | ) of observing the measurement given the object , and a TV regularizer…”

“…Due to the high penetration depth and material-specific signatures, X-ray diffraction (XRD) is a powerful tool to probe the material properties at molecular level, such as solving the crystalline structure [1,2], identifying the chemical composition in compounds with high sensitivity [3][4][5], and more recently, diagnose structural defects in bones, prosthetic implants [6,7], or diseaserelated anomaly in soft tissues [8,9]. For heterogeneous object on the centimeter scale or larger, resolving the XRD profile of individual sample voxels requires a combination of XRD measurement and computed tomography (CT) [10], which captures the XRD signals under different projections and is termed X-ray diffraction tomography (XDT).…”