CBIO 4 Tissue invasion & metastasis

Hallmark 6: tissue invasion & metastasis - metastases = 90% of cancer deaths Landmark discoveries - 1st description in 1758 but relevance recognised in the 19th century => Paget’s ‘Seed and Soil’ theory: metastatic patterns do not follow blood flow distribution => ‘seeds’ (tumour cells) + ‘congenial soil’ (receptive metastatic microenvironment) interaction => non-random: preference of metastasis at distinct sites (lung, liver, bone) - 1970: cancer cells travel through all organs BUT metastasis only develop in compatible organs - stage by stage process => primary tumour growth (invasion of adjacent tissue) => angiogenesis = vascularisation => detachment => intravasation (blood vessel penetration) => transport through circulatory and/or lymphatic system - cell arrest at a secondary site => extravasation (escaping blood vessels) => growth in a secondary organ (micrometastasis - macrometastasis) - metastasis in an organ is still the primary site cancer (ex: breast cancer in the lung) Monoclonal & polyclonal metastasis - genetic mutations => genomic instability => create cell subtypes: ‘clones’ => may be metastatic - metastasis with further genetic alterations of clone = phenotypically heterogenic monoclonal - metastasis containing many clones = polyclonal - metastasis containing 1 clone = monoclonal Clinical considerations - metastatic tumour often indicates a terminal disease: survival is not improving (only breast cancer) - cancer cells travelling in blood vessels = circulating tumour cells (CTCs) => blood also contains cell-free tumour DNA (ctDNA), RNA (ctRNA), proteins, vesicles (exosomes) - liquid biopsy = clinical test to detect circulating tumour cells or tumour-derived material in the blood & other fluids (urine, saliva, pleural effusions, cerebrospinal fluid CSF) => uses highly sensitive assays: CellSearch platform (selection cells expressing EpCAM => distinguish CTCs using cytokeratin monoclonal ab, DAPI stain, lack CD45 p) => non-invasive monitoring => BUT ctDNA is fragmented & very rare & CTCs are rare, w/ no universal surface marker => samples enriched for CTCs => negative enrichment: remove other blood cell => positive enrichment: select surface markers (ex: epithelial cell adhesion molecules EpCAM) BUT do not distinguish malignant or not => characterise CTCs molecularly Overview - angiogenesis = formation of new blood vessel from existing vasculature => driven through pro-angiogenic molecules released by cancer cells (ex: VEGF) => around the tumour mass to provide nutrients & O2 to fast-growing cancer cells => role in intravasation & extravasation: leaky structures of the new vessel around the tumour enter blood stream - during intravasation + extravasation: degradation & remodelling of basement membrane (BM) - BM produced by cells (epithelial, endothelial, stromal = mesenchymal) => separate epithelium/ endothelium from stroma & interstitial matrix - ECM = BM + interstitial matrix => BM (w/ basal lamina underlying epithelium) more compact, less porous, consists of collagen IV, laminin, fibronectin, nidogen, perlecan => I.M. consists of fibrillar collagen, proteoglycan (hyaluronan), fibronectin - proteases enzymes (secreted by tumours) degrade ECM proteins by hydrolysis of peptide bonds => cathepsins: cathepsin D (type of aspartic protease), cathepsin B, L, H (type of cysteine protease), cathepsin A (type of serine protease) => turnover & degradation of ECM => processing of GF, cytokines, chemokines => influence cell-cell adhesion m => urokinase (type of serine protease): urokinase-type plasminogen activator receptor (uPAR) => regulation of ECM degradation => regulation of cell adhesion, migration, proliferation, survival by interaction with integrins... => binds to vitronectin in ECM => changes in cell morpho, migration, signalling => induce EMT => matrix metalloproteinases (MMPs): collagenases, gelatinases, stromelysins, membrane-type... => degradation of collagen & other ECM p => regulation of cell behaviour Cell attachment and motility - important cell-cell junction: the adherens junction (composed of cadherins) => regulate other cell-cell junctions + cause cells to adhere to their neighbours - integrins: adhesion m that interact w/ ECM ligands & recruit focal adhesion kinase (FAK) => autophosphorylate, form complex w/ Src & activate both kinases => FAK/Src complex activate signalling molecules - epithelial to mesenchymal transition (EMT) by EMT-activating transcription factor => cancerous cells lose epithelial characteristics & gain mesenchymal (stromal) characteristics - loss/ reduction of cell-cell adhesion (cadherin) + dysmorphic shape (loss of polarity), integrins => invasive + migratory properties - at new site: reverse process => mesenchymal to epithelial transition (MET) - integrins couple with intracellular p of cytoskeleton (ex: actin) => filamentous (F)-actin important for forward cell protrusion => mesenchymal migration on BM => rapid production & retraction of actin protrusions w/ blebs (non-actin protrusions produced by hydrostatic pressure + cytoplasmic flow) => amoeboid migration on BM (round & ellipsoïde cell, doesn’t adhere strongly to ECM) - epithelial/ bulk migration: group of cells that move in clusters, sheets, strands, fluid-like masses Routes of metastasis - routes of metastasis: => haematogenous spread (blood vessels): common for sarcomas & carcinomas => lymphatic spread (lymphatic vessels): common for carcinomas => can then lead to haematogenous spread (see after): in breast cancers for ex => transcoelomic spread (surfaces of body cavities):