Dynamic Contrast-enhanced MRI Detects Responses To Stroma-Directed Therapy In Mouse Models Of Pancreatic Ductal Adenocarcinoma

Background:Pancreatic ductal adenocarcinoma(PDA)is a highly lethal cancer and the 7th leading cancer-related death all around the world and 4th in United States.Unlike the other kind of cancers,there is less significant progress during the past two decades,and the 5-year survival rate is below 10%.PDA is characterized by a dense,desmoplastic stroma,composed by different kind of cellular and non-cellular compartment include stellate cells(PSCs),endothelial cells,immune cells,glycosaminoglycan(GAG),extracellular matrix(ECM)proteins,fibroblasts and so on.All these components work independently or interact with each other to enhance the aggressive nature of this disease.In PDA,PSCs transform from quiescent to an activated state to proliferate and produce different kind of ECM proteins such as ?-smooth muscle actin(aSMA),fibronectin and collagen,thus contribute to the resistance to chemotherapy and radiation therapy.The hyaluronic acid(HA),a kind of protein-free GAG,maintains significant interaction with water molecules,dramatically increase the interstitial fluid pressure(IFP)in the diseased tissue,which compress the capillaries and featuring a profound lack of functional perfusion in the tumor microenvironment.All these characteristics contribute significantly to the pathogenesis of tumors and ultimately to chemoresistance.Nowadays,therapeutic target the tumor stroma has been widely investigated.The vitamin D receptor(VDR)ligand Calcipotriol reprise the PSCs to quiescent state,resulting in reduced inflammation and fibrosis,increased drug delivery and prolong the survival in PDA animal model.And PEGPH20(pegvorhyaluronidase alfa),a PEGylated recombinant human hyaluronidase enzyme,which specificity deplete the HA in the stroma,re-open the unfunctional blood vessel in the stroma,significantly decrease the IFP and increase the drug delivery.One barrier to the development and clinical implementation of these drugs is the lack of a robust noninvasive marker that can be used to evaluate the pharmacodynamic effect of the drug,identify responsive patients,and guide combination strategies.DCE-MRI is a non-invasive imaging method which inject the contrast agent during a series repeated quick images.By measuring the CA concentration change,it can reflect the blood flow and permeability in different tissue.This technique has been firmly established in cancer diagnostic,treatment effect monitoring and drug development.But now there is no thorough research about its application in stroma targeted therapy in PD AC.In this study,we hypothesized that a DCE-MRI-derived quantitative marker of microvascular function,Ktrans,can detect the early response of the PDA to stroma-specific treatment,and utilize different animal models to examine the effects of a single PEGPH20 injection and in combination with gemcitabine Taken together the imaging and assessments of tumor HA level and quantitative measurement of drug delivery,we conclude that a quantitative DCE-MRI marker can sensitively detect early responses of PDA to stroma-directed drug and monitor the sustained effect of combination treatment.Materials and methods:SubQ xenografts of human,orthotopic model and genetically engineered mouse models are used in this study.SubQ and orthotopic models were scanned at baseline and 24 h post one intravenous(iv)injection of PEGPH20 or vehicle(VEH).KPC mice received an injection of PEGPH20 or VEH were treated weekly for three weeks and followed by iv injection of Gemcitabine on the consecutive day.MRI was performed in KPC mice before the treatment was started and then one day after it was completed.The DCE-MRI protocol includes T1 m apping and DCE series using an ECG-gated multi-slice saturation-recovery gradient-echo sequence with Cartesian k-space sampling.Shutter-Speed model using least squares methods to yield maps of Ktrans,Kep and ?i.Immunostaining for HA was performed on tumor sections and the fraction of HA-positive pixels was estimated(Leica).Results:Paired imaging studies clearly show 24 hours after a single dose of PEGPH20,Ktran significantly increase 56%and 50%in SubQ and orthotopi model compare to the baseline,while the VEH treated mice decrease 4%and 6%.In the combine treatment group,mice treated with PEGPH20 plus gemcitabine shows a 54%Ktrans increase,while the VEH plus gemcitabine animals shows a 4%decrease of Ktrans.The IHC result shows HA content dramatically decrease after a single injection of PEGPH20 in all three models and drug delivery increase 2.6-fold.Conclusion:The DCE-MRI is a powerful tool in monitoring the changes of tumor microenvironment induced by stroma-directed drugs in murine PDA models.The Ktrans derived from DCE-MRI is a quantitative imaging marker to detect early responses to stroma-directed drug for pancreatic ductal adenocarcinoma with a high level of hyaluronan(HA).This imaging tool has the potential to noninvasively evaluate the stromal hyaluronan level of the entire tumor mass.