Osteoclasts control reactivation of dormant myeloma cells by remodelling the endosteal niche

Abstract

Multiple myeloma is largely incurable, despite development of therapies that target myeloma cell-intrinsic pathways. Disease relapse is thought to originate from dormant myeloma cells, localized in specialized niches, which resist therapy and repopulate the tumour. However, little is known about the niche, and how it exerts cell-extrinsic control over myeloma cell dormancy and reactivation. In this study, we track individual myeloma cells by intravital imaging as they colonize the endosteal niche, enter a dormant state and subsequently become activated to form colonies. We demonstrate that dormancy is a reversible state that is switched ‘on' by engagement with bone-lining cells or osteoblasts, and switched ‘off' by osteoclasts remodelling the endosteal niche. Dormant myeloma cells are resistant to chemotherapy that targets dividing cells. The demonstration that the endosteal niche is pivotal in controlling myeloma cell dormancy highlights the potential for targeting cell-extrinsic mechanisms to overcome cell-intrinsic drug resistance and prevent disease relapse.

Confocal/two-photon microscopy in studying colonisation of cancer cells in bone using xenograft mouse models

“…Lo Celso and Sipkins et al [30][31][32] have successfully established protocols to tracking of individual haematopoietic stem cells in mouse calvarium bone marrow. Lawson et al 23 also described such a method using two-photon microscopy to imaging tumour cell engraftment in real time within intact tibia of live mice. Other limitations associated with using this procedure are: (1) Using fluorescent lipophilic dyes could induce microenvironment contamination which possibly occurs via trogocytosis or diffusible microparticles.…”

“…The configuration settings and beam paths for different channels are shown in Figure 4a Note: As two-photon microscopy has the ability to excite multiple fluorescent markers with a single excitation wavelength, two-photon excitation can be set at 820 nm and multiple fluorescence can be detected using the following: BP 435-485 to detect blue (SHG), BP 500-550 to detect green (GFP), and BP 650-710 to detect far-red (DiD). 23 However, this will increase the energy level of photon and hence higher risk of photobleaching.…”

“…As bone structures heavily scatter lights and the high collagen content generates second-harmonic signals (SHG), these advantages won two-photon microscopy increasing popularity in research of cellular activities and interactions within bone and marrow, particularly in identifying the haematopoietic stem cell niche and detecting bone metastasis-initiating cancer cells in bone. [17][18][19][20][21][22][23] In this article, using the detection of breast cancer cell bone colonisation by confocal and two-photon microscopy as a representative example, we will describe a step-by-step methodology, from sample preparation to data analyses, used to investigate cellular events in frozen and fixed/decalcified mouse bone samples ex vivo (see schematic outline, Figure 2). Advantages and limitations of this technology is also discussed to guide the reader as to which is the most appropriate for their research question.…”

Inhibiting the osteocyte-specific protein sclerostin increases bone mass and fracture resistance in multiple myeloma

“…Immunohistochemistry was used to identify tumor cells with CD138 and osteocytes with sclerostin protein as described in supplemental Information. 47 Osteomeasure (Osteometrics) quantified osteoblasts and osteoclast parameters on endosteal surfaces and dynamic osteoblast activity on trabecular surfaces by using standard methods. 20,23,48,49 Compression testing of L4 vertebra L4 vertebrae were biomechanically tested by compression testing on an Instron 5944 load frame (Instron, Norwood, MA), and data were collected by using BlueHill 3 software (Instron).…”

The myeloma stem cell concept, revisited: from phenomenology to operational terms

“…The idea that resistant MMSCs are the source of post-therapeutic recurrence is not a new one; it was first described in studies of the stem-cell hierarchy and the self-renewal gene expression signature in leukemia with poor clinical outcome, which was also suggested to be associated with drug resistance. [91][92][93][94] In myeloma, it has recently been documented that the level of drug resistance is a function related to the cellular hierarchy 95 and its active or dormant stage 96 that we need to identify and target to overcome it. These findings highlight the potential to develop predictive, drug-specific sensitivity assays.…”