The role of proteolytic enzymes in metastatic bone disease

Importance of Metalloproteinase Enzyme Group in Selected Skeletal System Diseases

Bone tissue is a dynamic structure that is involved in maintaining the homeostasis of the body due to its multidirectional functions, such as its protective, endocrine, or immunological role. Specialized cells and the extracellular matrix (ECM) are responsible for the remodeling of specific bone structures, which alters the biomechanical properties of the tissue. Imbalances in bone-forming elements lead to the formation and progression of bone diseases. The most important family of enzymes responsible for bone ECM remodeling are matrix metalloproteinases (MMPs)-enzymes physiologically present in the body's tissues and cells. The activity of MMPs is maintained in a state of balance; disruption of their activity is associated with the progression of many groups of diseases, including those of the skeletal system. This review summarizes the current understanding of the role of MMPs in bone physiology and the pathophysiology of bone tissue and describes their role in specific skeletal disorders. Additionally, this work collects data on the potential of MMPs as bio-markers for specific skeletal diseases.

Bone recurrence in early breast cancer patients: The paradox of aromatase inhibitors induced bone resorption

BACKGROUND

Despite the increase in chances of cure for early breast cancer (EBC) patients, approximately 20-45% of them will experience a disease recurrence, particularly bone metastases in 60-80% of cases, which occur more frequently in luminal subtypes. Endocrine therapy (ET) has always been the milestone of adjuvant treatment for hormone receptor-positive EBC patients, leading to indubitable reduction of disease recurrence risk. However, adjuvant aromatase inhibitors (AIs) therapy may promote a progressive decrease in bone mineral density (BMD), which can lead to osteoporosis. The increased bone resorption associated with osteoporosis may provide fertile soil for cancer growth and accelerate the development of bone metastases.

PATIENTS AND METHODS

In this single-institution cohort study, we performed a retrospective analysis of "luminal-like" EBC patients who experienced bone recurrence after a subsequent disease free interval. The aim of the study was to evaluate the median time to skeletal recurrence (TSkR).

RESULTS

143 patients experienced bone recurrence. Median TSkR was 54 months (95%CI: 45-65). Among patients who received adjuvant AIs median TSkR was 35 months (95%CI: 25-54), while among patients who did not was 61 months (95%CI: 50-80) (HR = 1.45 [95%CI: 0.97-2.17], p = 0.0644). After adjusting for TNM stage (AJCC 8th edition), adjuvant AIs treatment was significantly related to a shorter TSkR (HR = 1.60 [95%CI: 1.06-2.42], p = 0.0244). Adjuvant Tamoxifen, adjuvant AIs/Tamoxifen and no-treatment did not revealed to be associated to TSkR.

CONCLUSIONS

In this cohort of EBC patients with bone recurrence, AIs treatment seems to be related to a shorter TSkR. AIs-induced bone resorption might represent the underlying mechanism.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Toward more accurate prediction of caspase cleavage sites: a comprehensive review of current methods, tools and features

As one of the few irreversible protein posttranslational modifications, proteolytic cleavage is involved in nearly all aspects of cellular activities, ranging from gene regulation to cell life-cycle regulation. Among the various protease-specific types of proteolytic cleavage, cleavages by casapses/granzyme B are considered as essential in the initiation and execution of programmed cell death and inflammation processes. Although a number of substrates for both types of proteolytic cleavage have been experimentally identified, the complete repertoire of caspases and granzyme B substrates remains to be fully characterized. To tackle this issue and complement experimental efforts for substrate identification, systematic bioinformatics studies of known cleavage sites provide important insights into caspase/granzyme B substrate specificity, and facilitate the discovery of novel substrates. In this article, we review and benchmark 12 state-of-the-art sequence-based bioinformatics approaches and tools for caspases/granzyme B cleavage prediction. We evaluate and compare these methods in terms of their input/output, algorithms used, prediction performance, validation methods and software availability and utility. In addition, we construct independent data sets consisting of caspases/granzyme B substrates from different species and accordingly assess the predictive power of these different predictors for the identification of cleavage sites. We find that the prediction results are highly variable among different predictors. Furthermore, we experimentally validate the predictions of a case study by performing caspase cleavage assay. We anticipate that this comprehensive review and survey analysis will provide an insightful resource for biologists and bioinformaticians who are interested in using and/or developing tools for caspase/granzyme B cleavage prediction.

Aromatase inhibitor-induced bone loss increases the progression of estrogen receptor-negative breast cancer in bone and exacerbates muscle weakness in vivo

Aromatase inhibitors (AIs) cause muscle weakness, bone loss, and joint pain in up to half of cancer patients. Preclinical studies have demonstrated that increased osteoclastic bone resorption can impair muscle contractility and prime the bone microenvironment to accelerate metastatic growth. We hypothesized that AI-induced bone loss could increase breast cancer progression in bone and exacerbate muscle weakness associated with bone metastases. Female athymic nude mice underwent ovariectomy (OVX) or sham surgery and were treated with vehicle or AI (letrozole; Let). An OVX-Let group was then further treated with bisphosphonate (zoledronic acid; Zol). At week three, trabecular bone volume was measured and mice were inoculated with MDA-MB-231 cells into the cardiac ventricle and followed for progression of bone metastases. Five weeks after tumor cell inoculation, tumor-induced osteolytic lesion area was increased in OVX-Let mice and reduced in OVX-Let-Zol mice compared to sham-vehicle. Tumor burden in bone was increased in OVX-Let mice relative to sham-vehicle and OVX-Let-Zol mice. At the termination of the study, muscle-specific force of the extensor digitorum longus muscle was reduced in OVX-Let mice compared to sham-vehicle mice, however, the addition of Zol improved muscle function. In summary, AI treatment induced bone loss and skeletal muscle weakness, recapitulating effects observed in cancer patients. Prevention of AI-induced osteoclastic bone resorption using a bisphosphonate attenuated the development of breast cancer bone metastases and improved muscle function in mice. These findings highlight the bone microenvironment as a modulator of tumor growth locally and muscle function systemically.

The microenvironment matters: estrogen deficiency fuels cancer bone metastases

Factors released during osteoclastic bone resorption enhance disseminated breast cancer cell progression by stimulating invasiveness, growth, and a bone-resorptive phenotype in cancer cells. Postmenopausal bone loss may accelerate progression of breast cancer growth in bone, explaining the anticancer benefit of the bone-specific antiresorptive agent zoledronic acid in the postmenopausal setting. Clin Cancer Res; 20(11); 2817-9. ©2014 AACR.

Discovery of Pyridyl Bis(oxy)dibenzimidamide Derivatives as Selective Matriptase Inhibitors

Matriptase belongs to trypsin-like serine proteases involved in matrix remodeling/degradation, growth regulation, survival, motility, and cell morphogenesis. Herein, we report a structure-based approach, which led to the discovery of sulfonamide and amide derivatives of pyridyl bis(oxy)benzamidine as potent and selective matriptase inhibitors. Co-crystal structures of selected compounds in complex with matriptase supported compound designing. Additionally, WaterMap analyses indicated the possibility of occupying a distinct pocket within the catalytic domain, exploration of which resulted in >100-fold improvement in potency. Co-crystal structure of 10 with matriptase revealed critical interactions leading to potent target inhibition and selectivity against other serine proteases.