Tumor And Microenvironment


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Tumor And Microenvironment

  2. 2. REFERENCES ● Abellof's Clinical Oncology ● Seminars in Radiation Oncology October 2009.
  3. 3. Abberant Cell Clonal Proliferation Immune Response MetastasisMetastasis Angiogenesis
  5. 5. ● Cancer involves complex multiple heterotypic interactions. ● Tumor microenvironment or STROMA influences 1) Growth 2) Ability to progress 3) Metastasise
  6. 6. IMMUNE RESPONSE CHRONIC INFLAMMATION ● Hepatitis B & C lead to hepatic cancer; H Pylori leading to Gastric Cancer. ● Rudolf Virchow in 1863 linked association of leukocytes in tumor tissues. ● Experimentally, pro-inflammatory substances favor tumor growth, angiogenesis and metastasis.
  7. 7. Colony Stimulating Factors Chemokines And Interleukins Angiogeneic Factors (VEGF) Tumor Stroma Growth Factors (Fibroblast, Hepatocyte)
  8. 8. ROLE OF TGF β ● Associated with T Cell suppression and inhibition of proliferation of lymphocytes. ● Reduces immune cell activation, blocks anti tumor activity. ● Promotes angiogenesis and over expression causes abberant extracellular matrix. ● Production tightly regulated in normal cells.
  9. 9. COX 2 and Prostaglandin Synthesis Chemoprevention strategy
  10. 10. CHRONIC INFLAMMATION ● Upregulation of non specific proinflammatory cytokines. ● Increased conversion of normal cells to pre- neoplastic foci. ● Gain of function in somatic mutations transforms cells for tumor initiation.
  11. 11. TUMOR ANGIOGENESIS ● Switching on of “angiogenic switch”: balance between 1) Tumor genes 2) Signals from tumor stroma and recruited inflammatory cells. 3) Hypoxia ● Endothelial cells are influenced majorly by Vascular Endothelial Growth Factor (VEGF).
  12. 12. VEGF VEGFR1 VEGF A 1) Hematopoeisis 2) Induction of metal metaloproteinases 3) Generation of chemotactic signal- further growth of cancer.
  13. 13. Within the tumor stroma HIF 1α generation. Normally ubiquitinated by Von Hippel Lindau (VHL) gene product. VEGF mRNA is found in 1) Renal Cell Carcinomas 2) Promotes the stem cell multipotency and self renewal. 3) Promotes lymphangiogenesis
  14. 14. Extensive cross talk between the inflammatory cascade and tumor angiogenesis
  15. 15. METASTASISMETASTASIS ““Change of state”Change of state”
  16. 16. Fidler called the metastatic cells as “dectathlon champions” because few cells escape the primary tumor....
  17. 17. Barriers to MetastasisBarriers to Metastasis
  18. 18. Changes in Cell Adhesion
  19. 19. Switch from E Cadherin to N-cadherin expression (a Mesenchymal cell marker)
  20. 20. Constant interaction between malignantConstant interaction between malignant Cell and Extracelular MatrixCell and Extracelular Matrix Constant interaction between malignantConstant interaction between malignant Cell and Extracelular MatrixCell and Extracelular Matrix
  21. 21. Movement is similar to an inchworm Focal Adhesion along with Activation of GTPases and Actin and Myosin Contraction Recruitment of Matrix Metalloproteases to focal adhesion sites; Degradation of Extracellular Matrix and Cell glides forward.
  22. 22. Disruption of the basement membrane; alteration of balance Between proteases and their inhibitory proteins. Collagenases degrade Collagen Type IV; Releases activated chemokines and other Bioactive compunds Increased in cells with metastatic Potential.
  23. 23. INTRAVASATION ● The entry of tumor cells into circulation is intravasation. ● The exit of tumor cells from circulation is extravasation. ● Escape easy through abnormal vasculature. ● Chemokines as “attractants” guide cells in circulation.
  24. 24. Chemokines act as “honey pots” to attract metastatic cells
  25. 25. SURVIVAL IN CIRCULATORY SYSTEM Heterotypic Foci; Tumor aggregation with Coagulation factors. Homotypic Foci: Tumor aggregation with Platelets. Tipping of balance between anti and pro apoptotic pathways; survival of anoikis
  26. 26. EXTRAVASATION 1) Increased expression of Cell Adhesion Molecules 2) VEGF increases vascular permeability 3) Some tumor cells may follow White Blood Cell motility patterns
  27. 27. PROLIFERATION ● Final step; host tissue influences growth by auto/para/endocrine pathways. ● e.g. Liver synthesises IGF-1 (Insulin Like Growth Factor) which stimulates cells from breast, colon and bladder. ● These cells over express receptors for these ligands.
  28. 28. ANGIOGENESIS ● VEGF is well characterised. ● Stimulates endothelial cells; pericytes and increasing vascular permeability. ● Key molecule for homing of VEGF-R positive bone marrow derived progenitor cells.
  29. 29. Paget's Seed and Soil Hypothesis Tumors Cells= Seed Permissive role of environment=Soil. The hypothesis where cancer cells are able to survive and proliferate is still the conceptual model in modern cancer research.
  30. 30. Role of Cancer Stem Cells or Cancer Initiating Cells. (CSC/CIC)
  31. 31. PERMISSIVE ROLE OF VEGF-1 BONE MARROW DERIVED CELLS ● They migrate to colonise target areas. ● Express hematopoietic markers- CD34, CD116, c-kit, integrins and chemokine receptors. ● Promote homing and attachment to the target tissue.
  32. 32. RECREATE SUPPORTIVE MICROENVIRONMENT ● Secretion of chemokines + Release of angiogenic factors (VEGF-A). ● Chemoattractant proteins S100A8 and S100A9 were initially detected. ● Metastatic niches and process has major clinical implications.
  33. 33. THERAPY INDUCED MODIFICATION OF STROMA IMPACTS TUMOR PROGRESSION Radiotherapy: 1) Affects tumor stroma 2) Bidirectional cell signalling 3) Stroma exerts tumor promoting effects ● Tumor recurrences in irradiated field have a poor prognosis.
  34. 34. CULPRIT? ● Impaired angiogenic response ● Hypoxia upregulates matricellular protein CYR61 and integrin άVβ5 mediating survival in hypoxic conditions. ● Selects hypoxia resistant, invasive and metastatic phenotype.
  35. 35. FURTHER INSULT ● Antiapoptotic factors like IGF and pro inflammatory cytokines (GM-CSF) are generated. ● Generation of tumor promoting factors like EGF.
  36. 36. INCREASED SURVIVAL OF CSC/CIC ● Identified by Cluster of Differentiation (CD Number). ● Breast cancer experimental model CD44+/CD24- shows few or absent double strand breaks. ● CD133+ glioma cell lines is more resistant as compared to CD133- lines. ● Radio Resistance= efficient repair.
  38. 38. 1) PERMISSIVE ROLE OF TGF-β Prime role identified in : ● Suppression of host immune responses ● Augments angiogenesis. Inactivating mutations of TGFβ2 are infrequent. TGFβ antisense compound AP12009 targets mRNA; reduces cell proliferation in all glioma cell lines. Hau P et al. Oligonucleotides 17;201-212, 2007
  39. 39. ● Phase I/II clinical data. ● Reported proonged survival compared with literature data. ● Observed time course are consistent with proposed reversal of tumor induced immunosupression.
  40. 40. THERAPEUTIC INHIBITION OF VASCULOGENESIS ● Bevacizumab: Humanised monoclonal antibody inhibits VEGF. ● Phase II trials with bevacizumab and irinotecan resulted in radiologic response of 47% to 67% and 6- month survival of 62% to 77%. ● Phase II study for combination of TMZ & Bevacizumab showed radiological responses in 13/14 assessable patients. ● 1 year PFS and OS were 59.3% and 86.7% respectively. Narayana A et al. J Neurosurg 110:173-180, 2009 and IJORBP 72:383-389, 2008. Chen et al. JCO 25:4714-4721, 2007.
  41. 41. ● Although impressive results; 70% patients recur locally; 30% recurred as extensive gliomatosis. ● Biopsy correlation showed invasive mesenchymal phenotype. ● Blocking VEGF results in angiogenic independent GBM stem cell growth with upregulation of proinvasive genes. Sakariassen et al. Proc Natl Acad Sci USA 101:16466-16471,2006
  42. 42. ● Interesting aspect of Lithium used for bipolar disorders. ● Inhibits migration of glioblastoma cells; inhibits GSK 3 protein regulating metabolism, cell division and death. ● Phase II multi institutional trial of Lithium, TMZ and Bevacizumab is proposed.
  43. 43. HYPOXIA ● HIF 1α upregulates invasive genotype: CXCR4, SDF- 1(ligand of CXCR4), VEGF and MMP. ● SDF-1 exerts proliferative, anti apoptotic, and chemotactic effects on glioma cell lines in vitro. ● Promotes glioma cell line invasion by recruitment of MMP. ● Attractive targets for future therapy to prevent invasion.
  45. 45. RADIATION INDUCED TGF-β ● Reactive Oxygen Species promotes generation of TGF-β by LAP (latency Associated Peptide) complex by conformational change. ● Inhibits DNA Repair genes; blunts ATM identified radiation damaged DNA strand breaks. ● Inhibitor to TGF causes reduced invasiveness and potentially increase effectiveness of external radiation.
  46. 46. SEED AND SOIL REVISITED ● Glioblastoma is like pulled out weed; but soil still remains hospitable to scattered seeds. ● Therapy by itself affects the microenvironment. ● Potentially blocking the deleterious effect of cytokine cascade would limit toxicity and protect normal brain function.