Dynamic Analyses of the Short-Term Effects of Different Bisphosphonates Using Intravital Two-Photon Microscopy

A Bivalent Activatable Fluorescent Probe for Screening and Intravital Imaging of Chemotherapy-Induced Cancer Cell Death

The detection and quantification of apoptotic cells is a key process in cancer research, particularly during the screening of anticancer therapeutics and in mechanistic studies using preclinical models. Intravital optical imaging enables high-resolution visualisation of cellular events in live organisms; however, there are few fluorescent probes that can reliably provide functional readouts in situ without interference from tissue autofluorescence. We report the design and optimisation of the fluorogenic probe Apotracker Red for real-time detection of cancer cell death. The strong fluorogenic behaviour, high selectivity, and excellent stability of Apotracker Red make it a reliable optical reporter for the characterisation of the effects of anticancer drugs in cells in vitro and for direct imaging of chemotherapy-induced apoptosis in vivo in mouse models of breast cancer.

A Bivalent Activatable Fluorescent Probe for Screening and Intravital Imaging of Chemotherapy-Induced Cancer Cell Death

The detection and quantification of apoptotic cells is a key process in cancer research, particularly during the screening of anticancer therapeutics and in mechanistic studies using preclinical models. Intravital optical imaging enables high-resolution visualisation of cellular events in live organisms; however, there are few fluorescent probes that can reliably provide functional readouts in situ without interference from tissue autofluorescence. We report the design and optimisation of the fluorogenic probe Apotracker Red for real-time detection of cancer cell death. The strong fluorogenic behaviour, high selectivity, and excellent stability of Apotracker Red make it a reliable optical reporter for the characterisation of the effects of anticancer drugs in cells in vitro and for direct imaging of chemotherapy-induced apoptosis in vivo in mouse models of breast cancer.

New Insights Into Osteoclast Biology

Osteoclasts are multinucleated cells that are characterized by their unique ability to resorb large quantities of bone. Therefore, they are frequently the target of therapeutic interventions to ameliorate bone loss. In an adult organism, osteoclasts derive from hematopoietic stem cells and differentiate into osteoclasts within a multistep process under the influence of macrophage colony‐stimulating factor (M‐CSF) and receptor activator of NF‐κB ligand (RANKL). Historically, the osteoclast life cycle has been defined as linear, whereby lineage‐committed mononuclear precursors fuse to generate multinucleated highly specialized and localized bone phagocytic cells, which then undergo apoptosis within weeks. Recent advances through lineage tracing, single cell RNA sequencing, parabiosis, and intravital imaging approaches have challenged this dogma, revealing they have greater longevity and the capacity to circulate and undergo cell recycling. Indeed, these new insights highlight that under homeostatic conditions very few incidences of osteoclast apoptosis occur. More importantly, as we revisit the formation and fate of the osteoclast, novel methods to target osteoclast biology in bone pathology and regeneration are emerging. This review briefly summarizes the historical life cycle of osteoclasts and highlights recent discoveries made through advanced methodologies, which have led to a paradigm shift in osteoclast biology. These findings are discussed in light of both existing and emerging bone targeted therapeutics, bone pathologies, and communication between osteoclasts and cells resident in bone or at distant sites. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

From latency to overt bone metastasis in breast cancer: potential for treatment and prevention

Bone metastasis is present in a high percentage of breast cancer (BCa) patients with distant disease, especially in those with the estrogen receptor‐positive (ER⁺) subtype. Most cells that escape primary tumors are unable to establish metastatic lesions, which suggests that target organ microenvironments are hostile for tumor cells. This implies that BCa cells must achieve a process of speciation to adapt to the new conditions imposed in the new organ. Bone has unique characteristics that can be exploited by cancer cells: it undergoes constant remodeling and comprises diverse environments (including osteogenic, perivascular, and hematopoietic stem cell niches). This allows colonizing cells to take advantage of numerous adhesion molecules, matrix proteins, and soluble factors that facilitate homing, survival, and, eventually, metastatic outgrowth. However, in most cases, metastatic lesions enter into a latency state that can last months, years, or even decades, before forming a clinically detectable macrometastasis. This dormant state challenges the effectiveness of adjuvant chemotherapy. Detecting which tumors are more prone to metastasize to bone and developing new specific therapies that target bone metastasis represent urgent clinical needs. Here, we review the biological mechanisms of BCa bone metastasis and provide the latest options of treatments and predictive markers that are currently in clinical use or are being tested in clinical assays. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

In Vivo Multicolor Imaging with Fluorescent Probes Revealed the Dynamics and Function of Osteoclast Proton Pumps

In vivo two-photon fluorescence imaging is a powerful modality to monitor cell dynamics in biomedical studies. To detect protein functions in living animals in real-time, fluorescent probes must show a quick response to the target function in specific tissues. Here, we developed a rhodamine-based small-molecule fluorescent probe called Red-pHocas (red pH-activatable fluorescent probe for osteoclast activity sensing) to reversibly detect the acidic environments for the spatiotemporal analysis of the function of osteoclast proton pumps. The introduction of electron-withdrawing N-alkyl substituents in the rhodamine spirolactam fluorophore remarkably increased the kinetics of the fluorescence response to acidic pHs, which allowed the rapid and reversible monitoring of acidic compartments and the analysis of the dynamics of osteoclast proton pumps during osteoclastic bone resorption. In vivo multicolor two-photon imaging using Red-pHocas in fluorescent reporter mice revealed that bone acidification occurred synchronously with the accumulation of proton pumps onto the bone surfaces. To our knowledge, this is the first study to demonstrate the direct involvement of osteoclast proton pumps in bone acidification under intravital conditions by means of an imaging probe.