MMP14 empowers tumor-initiating breast cancer cells under hypoxic nutrient-depleted conditions.

Tumor-initiating cells (TICs) existing in breast cancer are thought to be involved in initiation, progression, and relapse of tumors. In these processes, the epithelial-to-mesenchymal transition (EMT) and proteases are crucial factors that also dependent on the tumor milieu, including hypoxic nutrient-deprived, as well as normoxic nutrient-rich, environments. Therefore, we investigated EMT and proteases in TICs and their response to different environments by means of a newly generated immortalized TIC (iTIC) line. With the use of primary CD24+CD90+CD45- TICs from the mouse mammary tumor virus-polyoma middle T mouse breast cancer model, iTICs were generated by single cell-initiated sphere and subsequent 2-dimensional monolayer culture. Our data demonstrate the possibility to generate iTICs that are highly tumorigenic in culture and in mouse mammary fat pad. Contrasting environmental conditions provide these cells with a phenotypic and molecular plasticity that has a growth-promoting character in nutrient-rich normoxia and a motile character in nutrient-deprived hypoxia. Expression profiling revealed partial and dynamically changing EMT states, as well as a significantly up-regulated proteolytic signature, including many metalloproteinases, such as matrix metalloproteinase 14 ( Mmp14). Inhibitor treatment of metalloproteinases, as well as short hairpin RNA-mediated knockdown of Mmp14 strongly impacted TIC characteristics, including tumor initiation, cell growth, migration, and invasion, especially in starved environments. We conclude that metalloproteinases empower TICs to adapt to changing environments.-Hillebrand, L. E., Wickberg, S. M., Gomez-Auli, A., Follo, M., Maurer, J., Busch, H., Boerries, M., Reinheckel, T. MMP14 empowers tumor-initiating breast cancer cells under hypoxic nutrient-depleted conditions.

Final Results from RIBBIT: A Randomized Phase III Study to Evaluate Efficacy and Quality of Life in Patients with Metastatic Hormone Receptor-Positive, HER2-Negative Breast Cancer Receiving Ribociclib in Combination with Endocrine Therapy or Chemotherapy with or without Bevacizumab in the First-Line Setting.

Background: We investigated the efficacy and health-related quality of life (HRQoL) in patients receiving either ribociclib plus endocrine therapy (ET) or chemotherapy with/without bevacizumab as first-line treatment of metastatic hormone receptor (HR)-positive, HER2-negative breast cancer (BC). Patients and Methods: In this randomized, phase III study (RIBBIT), 38 patients diagnosed with metastatic HR-positive, HER2-negative BC with presence of visceral metastases recruited between May 2018 and December 2020 were randomly assigned in a 1:1 ratio to either arm A (ribociclib + ET) or arm B (chemotherapy with/without bevacizumab) at 12 sites in Germany. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall response rate (ORR), overall survival (OS), patient-reported HRQoL, and frequency and type of adverse events. During study conduction, the recruitment rate was persistently and considerably lower than originally expected. Therefore, the recruitment was ended prematurely. The study was initially designed to enroll and randomize 158 patients. Results: Median [95% CI] PFS was 27.3 months [19.1 - NA, parameter not estimable] in arm A and 15.8 months [8.2 - NA] in arm B. Complete responses were achieved only in arm A (n = 2, 10.5%). The ORR [95% CI] between arm A (57.9% [33.5-79.7]) and arm B (52.6% [28.9-75.6]) was comparable. Median OS [95% CI] was not reached in arm A, while in arm B median OS was 28.4 months [25.0 - NA]. Patients in arm A reported less burden by side-effects. No new safety signals emerged. Conclusion: Treatment of patients with visceral metastatic HR-positive, HER2-negative BC with ribociclib in combination with ET showed a tendency toward a more favorable clinical outcome. Despite small numbers of patients and sites, this head-to-head comparison with chemotherapy supports the use of ribociclib with ET in patients with visceral metastasis at risk of fast disease progression.

Impact of proteolysis on cancer stem cell functions.

Cancer cells within a tumor are heterogeneous and exist in a variety of functionally distinct cell states, which are thought to be hierarchically organized. The cell on top of this hierarchy, the cancer stem cell (CSC) or, alternatively, tumor initiating cell (TIC), is responsible for initiation, maintenance, progression, and relapse of tumors. For the execution of these functions, CSC are equipped with distinct molecular tools. Although proteolytic enzymes in cancers have been extensively studied in general, relatively few studies have addressed proteases in function and fate of CSC/TICs. Here we review protease involvement in cell biological hallmarks of CSC/TICs such as cellular self-renewal, extracellular matrix remodeling and cell motility, resistance to radio- and chemotherapies, as well as evasion of the immune system. In general, CSC/TICs are characterized by a comparatively high expression and activity of proteases. It appears that CSC/TICs install a high degree of pericellular proteolysis depending on metalloproteases such as ADAMs and MMPs but also on secreted serine- and cysteine proteases. Interestingly, it turned out that not all proteases promote the malignant behavior of CSC/TICs. In fact, some proteases, such as ADAM 23, cathepsin K, and granzyme B, have been shown to negatively regulate CSC/TIC functions, thereby exhibiting anti-tumor effects. Finally, we discuss how the enhanced proteolytic signature of CSC/TICs can be used for their therapeutic targeting in order to render this clinically decisive subpopulation of cancer cells harmless.

Inherited diseases caused by mutations in cathepsin protease genes.

Lysosomal cathepsins are proteolytic enzymes increasingly recognized as prognostic markers and potential therapeutic targets in a variety of diseases. In those conditions, the cathepsins are mostly overexpressed, thereby driving the respective pathogenic processes. Although less known, there are also diseases with a genetic deficiency of cathepsins. In fact, nowadays 6 of the 15 human proteases called 'cathepsins' have been linked to inherited syndromes. However, only three of these syndromes are typical lysosomal storage diseases, while the others are apparently caused by defective cleavage of specific protein substrates. Here, we will provide an introduction on lysosomal cathepsins, followed by a brief description of the clinical symptoms of the various genetic diseases. For each disease, we focus on the known mutations of which many have been only recently identified by modern genome sequencing approaches. We further discuss the effect of the respective mutation on protease structure and activity, the resulting pathogenesis, and possible therapeutic strategies.

Proteolysis-a characteristic of tumor-initiating cells in murine metastatic breast cancer.

Tumor initiating cells (TICs) have been identified and functionally characterized in hematological malignancies as well as in solid tumors such as breast cancer. In addition to their high tumor-initiating potential, TICs are founder cells for metastasis formation and are involved in chemotherapy resistance. In this study we explored molecular pathways which enable this tumor initiating potential for a cancer cell subset of the transgenic MMTV-PyMT mouse model for metastasizing breast cancer. The cell population, characterized by the marker profile CD24+CD90+CD45-, showed a high tumorigenicity compared to non-CD24+CD90+CD45- cancer cells in colony formation assays, as well as upon orthotopic transplantation into the mammary fat pad of mice. In addition, these orthotopically grown CD24+CD90+CD45- TICs metastasized to the lungs. The transcriptome of TICs freshly isolated from primary tumors by cell sorting was compared with that of sorted non-CD24+CD90+CD45- cancer cells by RNA-seq. In addition to more established TIC signatures, such as epithelial-to-mesenchymal transition or mitogen signaling, an upregulated gene set comprising several classes of proteolytic enzymes was uncovered in the TICs. Accordingly, TICs showed high intra- and extracellular proteolytic activity. Application of a broad range of protease inhibitors to TICs in a colony formation assay reduced anchorage independent growth and had an impact on colony morphology in 3D cell culture assays. We conclude that CD24+CD90+CD45- cells of the MMTV- PyMT mouse model possess an upregulated proteolytic signature which could very well represent a functional hallmark of metastatic TICs from mammary carcinomas.

Out-of-frame start codons prevent translation of truncated nucleo-cytosolic cathepsin L in vivo.

The lysosomal protease cathepsin L has been reported to cleave various functionally important cytosolic or nuclear proteins. To explain nucleo-cytosolic localization of cathepsin L, it has been hypothesized that skipping of the first start codon during translation initiation results in an N-terminally truncated protein lacking the endoplasmic reticulum-import signal. Here we demonstrate that out-of-frame AUGs prevent translation of truncated cathepsin L in cell culture as well as in a new knock-in mouse model. We further evaluate potential roles of nuclear cathepsin L during early embryonic development. Our analysis reveals normal epiblast development of cathepsin L-deficient embryos, but uncovers a pronounced lysosomal storage phenotype in the extra-embryonic tissue of the visceral endoderm. In conclusion, the phenotypes of cathepsin L deficiency can be fully assigned to lack of canonically targeted cathepsin L, while the biogenesis and functionality of nucleo-cytosolic cathepsin L remain elusive.