Role of stromal SPARC in PDAC tumorigenesis and drug delivery
by Iswarya Ramu
Date of Examination:2018-12-10
Date of issue:2019-11-13
Advisor:PD Dr. Dr. Albrecht Neesse
Referee:PD Dr. Dr. Albrecht Neesse
Referee:Prof. Dr. Steven Johnsen
Referee:Prof. Dr. Matthias Dobbelstein
Persistent Address:
http://dx.doi.org/10.53846/goediss-7723
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Abstract
English
Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive solid tumors in humans. Median survival is around 12 months and is due to late diagnosis, early metastatic spread, and a high resistance towards available chemotherapeutic regimens. The desmoplastic reaction is a key feature of PDAC which contributes to disease progression and has also been reported to confer to chemoresistance and impaired drug delivery. Secreted protein acidic and rich in cysteine (SPARC) is an important matricellular protein that regulates collagen deposition and ECM remodeling. In human PDAC, SPARC is expressed by peritumoral fibroblasts and high expression is associated with a poor prognosis. In several other cancer entities, SPARC has been shown to play either tumor promoting or tumor suppressing roles. However, the functional role of SPARC in PDAC is unclear. In my thesis, I investigated the expression of SPARC and its role during tumor progression from preneoplastic lesions to frank carcinomas in genetically engineered mouse models (GEMMs) of PDAC. In order to achieve this, I generated SPARCwt, SPARC-/-, KC-SPARCwt and KC-SPARC-/- mice with a global SPARC knock-out for in vivo studies. Furthermore, primary epithelial and fibroblast cell lines were derived from preneoplastic murine tissues and murine pancreas tumors for in vitro experiments. The in vivo results showed that the development of the murine pancreas was unaffected by germ- line SPARC knock-out. Immunohistochemical and western blot analysis revealed that SPARC is not expressed in the normal pancreas with a marked increase of SPARC in activated fibroblasts during preneoplastic stages and tumor progression. However, loss of SPARC in KC-SPARC-/- mice resulted in a significant reduction of intratumoral collagen deposition. Notably, SPARC and subsequent collagen depletion did not alter pancreatic intraepithelial neoplasia (PanIN) progression, tumor incidence or metastatic frequency to the liver. Both KC-SPARCwt and KC-SPARC-/- tumors exhibited similar tumor characteristic including proliferation, apoptosis and mean vessel density. Primary epithelial and fibroblast cell lines from both genotypes showed comparable morphology and proliferation rates. However, tumor bearing KC-SPARC-/- mice lived significantly shorter than of KC-SPARCwt mice, a finding that was most likely due to more severe clinical complications such as ascites, diarrhea and bile duct obstruction in KC-SPARC-/- mice. Interestingly, SPARC mediated collagen deposition did not impede the delivery and metabolism of gemcitabine in pre-neoplastic lesions and tumors as determined by LC-MS/MS. Strikingly, the amount of gemcitabine increased from normal pancreas tissues to pancreatic tumors questioning the drug delivery hypothesis for gemcitabine in PDAC.
Keywords: SPARC+Pancreatic ductal adenocarcinoma+stroma+ drug delivery
