SPARC dependent collagen deposition and gemcitabine delivery in a genetically engineered mouse model of pancreas cancer.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is characterised by extensive matrix deposition that has been implicated in impaired drug delivery and therapeutic resistance. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that regulates collagen deposition and is highly upregulated in the activated stroma subtype with poor prognosis in PDAC patients. METHODS: KrasG12D;p48-Cre;SPARC-/- (KC-SPARC-/-) and KrasG12D;p48-Cre;SPARCWT (KC-SPARCWT) were generated and analysed at different stages of carcinogenesis by histological grading, immunohistochemistry for epithelial and stromal markers, survival and preclinical analysis. Pharmacokinetic and pharmacodynamic studies were conducted by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunohistochemistry following gemcitabine treatment (100 mg/kg) in vivo. FINDINGS: Global genetic ablation of SPARC in a KrasG12D driven mouse model resulted in significantly reduced overall and mature collagen deposition around early and advanced pancreatic intraepithelial neoplasia (PanIN) lesions and in invasive PDAC (p < .001). However, detailed pathological scoring and molecular analysis showed no effects on PanIN to PDAC progression, vessel density (CD31), tumour incidence, grading or metastatic frequency. Despite comparable tumour kinetics, ablation of SPARC resulted in a significantly shortened survival in KC-SPARC-/- mice (280 days versus 485 days, p < .03, log-rank-test). Using LC-MS/MS, we show that SPARC dependent collagen deposition does not affect intratumoural gemcitabine accumulation or immediate therapeutic response in tumour bearing KC-SPARCWT and KC-SPARC-/-mice. INTERPRETATION: Global SPARC ablation reduces the collagen-rich microenvironment in murine PDAC. Moreover, global SPARC depletion did not affect tumour growth kinetics, grading or metastatic frequency. Notably, the dense-collagen matrix did not restrict access of gemcitabine to the tumour. These findings may have direct translational implications in clinical trial design

Stromal Features of the Primary Tumor Are Not Prognostic in Genetically Engineered Mice of Pancreatic Cancer

The KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) mouse model is frequently employed for preclinical therapeutic testing, in particular in regard to antistromal therapies. Here, we investigate the prognostic implications of histopathological features that may guide preclinical trial design. Pancreatic tumor tissue from n = 46 KPC mice was quantitatively analyzed using immunohistochemistry and co-immunofluorescence for proliferation (Ki67), mitotic rate (phospho-Histone 3, PHH3), apoptosis (cleaved caspase-3, CC3), collagen content, secreted protein acidic and rich in cysteine (SPARC), hyaluronic acid (HA), and &alpha;-smooth muscle actin (&alpha;-SMA). Furthermore, mean vessel density (MVD), mean lumen area (MLA), grading, activated stroma index (ASI), and fibroblast-proliferation rate (&alpha;-SMA/Ki67) were assessed. Univariate analysis using the Kaplan&ndash;Meier estimator and Cox regression model for continuous variables did not show association between survival and any of the analyzed parameters. Spearman correlation demonstrated that desmoplasia was inversely correlated with differentiated tumor grade (&rho; = &minus;0.84). Ki67 and PHH3 synergized as proliferation markers (&rho; = 0.54), while SPARC expression was positively correlated with HA content (&rho; = 0.37). MVD and MLA were correlated with each other (&rho; = 0.31), while MLA positively correlated with CC3 (&rho; = 0.45). Additionally, increased MVD was correlated with increased fibroblast proliferation rate (&alpha;-SMA + Ki67; &rho; = 0.36). Our pilot study provides evidence that individual histopathological parameters of the primary tumor of KPC mice are not associated with survival, and may hint at the importance of systemic tumor-related effects such as cachexia