title: Functions of paracrine PDGF signaling in the proangiogenic tumor stroma revealed by pharmacological targeting.
abstract: BACKGROUND
  Important support functions, including promotion of tumor growth, angiogenesis, and invasion, have been attributed to the different cell types populating the tumor stroma, i.e., endothelial cells, cancer-associated fibroblasts, pericytes, and infiltrating inflammatory cells. Fibroblasts have long been recognized inside carcinomas and are increasingly implicated as functional participants. The stroma is prominent in cervical carcinoma, and distinguishable from nonmalignant tissue, suggestive of altered (tumor-promoting) functions. We postulated that pharmacological targeting of putative stromal support functions, in particular those of cancer-associated fibroblasts, could have therapeutic utility, and sought to assess the possibility in a pre-clinical setting.
  
  
  RESULTS
  We used a genetically engineered mouse model of cervical carcinogenesis to investigate platelet-derived growth factor (PDGF) receptor signaling in cancer-associated fibroblasts and pericytes. Pharmacological blockade of PDGF receptor signaling with the clinically approved kinase inhibitor imatinib slowed progression of premalignant cervical lesions in this model, and impaired the growth of preexisting invasive carcinomas. Inhibition of stromal PDGF receptors reduced proliferation and angiogenesis in cervical lesions through a mechanism involving suppression of expression of the angiogenic factor fibroblast growth factor 2 (FGF-2) and the epithelial cell growth factor FGF-7 by cancer-associated fibroblasts. Treatment with neutralizing antibodies to the PDGF receptors recapitulated these effects. A ligand trap for the FGFs impaired the angiogenic phenotype similarly to imatinib. Thus PDGF ligands expressed by cancerous epithelia evidently stimulate PDGFR-expressing stroma to up-regulate FGFs, promoting angiogenesis and epithelial proliferation, elements of a multicellular signaling network that elicits functional capabilities in the tumor microenvironment.
  
  
  CONCLUSIONS
  This study illustrates the therapeutic benefits in a mouse model of human cervical cancer of mechanism-based targeting of the stroma, in particular cancer-associated fibroblasts. Drugs aimed at stromal fibroblast signals and effector functions may prove complementary to conventional treatments targeting the overt cancer cells for a range of solid tumors, possibly including cervical carcinoma, the second most common lethal malignancy in women worldwide, for which management remains poor.
authors.affiliation: Department of Biochemistry and Biophysics, Diabetes Center and Comprehensive Cancer Center, University of California San Francisco, San Francisco, California, United States ofAmerica. kristian.pietras@licr.ki.se
authors.forename: Kristian
authors.initials: K
authors.lastname: Pietras
authors.forename: Jessica
authors.initials: J
authors.lastname: Pahler
authors.forename: Gabriele
authors.initials: G
authors.lastname: Bergers
authors.forename: Douglas
authors.initials: D
authors.lastname: Hanahan
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001549:Benzamides; D002277:Carcinoma / Q000098:blood supply* / Q000188:drug therapy / Q000503:physiopathology / Q000821:virology; D004847:Epithelial Cells / Q000378:metabolism; D004958:Estradiol / Q000008:administration & dosage / Q000633:toxicity; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D051523:Fibroblast Growth Factor 7 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D052162:Human papillomavirus 16; D006801:Humans; D000068877:Imatinib Mesylate; D051379:Mice; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009389:Neovascularization, Pathologic / Q000188:drug therapy* / Q000503:physiopathology; D019899:Paracrine Communication / Q000187:drug effects / Q000502:physiology*; D020286:Pericytes / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use*; D010982:Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D019009:Proto-Oncogene Proteins c-kit / Q000096:biosynthesis / Q000235:genetics; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D017479:Receptors, Platelet-Derived Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D017154:Stromal Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D002583:Uterine Cervical Neoplasms / Q000098:blood supply* / Q000188:drug therapy / Q000503:physiopathology / Q000821:virology
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; C496454:Fgf7 protein, mouse; D009363:Neoplasm Proteins; D010879:Piperazines; D010982:Platelet-Derived Growth Factor; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D016222:Fibroblast Growth Factor 2; D051523:Fibroblast Growth Factor 7; D004958:Estradiol; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D017479:Receptors, Platelet-Derived Growth Factor