"Introduction: Pancreatic ductal adenocarcinoma (PDAC) is one of the most fibrotic tumors, which can possess up to 90% tumor stroma of the total tumor mass (1). The tumor stroma is comprised of cancer-associated fibroblasts (CAFs), extracellular matrix (ECM) and many immune cells. The physical and biochemical characteristics of the tumor stroma control cancer cell proliferation, invasion, and metastasis. Also, the tumor stroma enhances intratumoral solid stress leading to the compression and collapse of blood vessels and also becomes a physical barrier which in turn prevents delivery of chemotherapy. Currently, there is lack of relevant in vitro models that are able to replicate these mechanical characteristics of PDAC (2).
Methodology: A multi-layered vascularized 3D PDAC model was developed consisting of primary human pancreatic stellate cells (PSC) in a collagen/fibrinogen (Col/Fib) matrix. A central endothelialized channel was introduced to study the cell-mediated contraction of vasculature in PDAC. The activation of PSCs due to mechanical and biological stimulation was studied using contraction assay and gene analysis. The clinical relevance of the model was studied for PDAC specific gene markers and compared with publicly available patient data. The effects on the blood flow inside the channel was determined using computational fluid dynamics (CFD) simulations. The effect of AV3 peptide (3), an integrin inhibitor developed by us, was tested for its effect on stroma and vasculature in this model and the effects were correlated with in vivo data in mice.
Results: PDAC samples from patients and mouse tumor models showed an abundant stroma and collapsed blood vessels. Our 3D model showed mimicking of the vasculature in the tumor tissue and adjunct healthy tissue. PSCs differentiated into myofibroblastic CAFs leading to high contraction of the matrix and upregulation of gene markers (ACTA2, Col-1a1, PDGFbR, HAS2 and CDC42). Interestingly, these genes were also positively correlated in PDAC clinical samples. The CFD simulation analysis revealed a clear pressure drop within the compressed vessels with high intravascular pressure before the compression. Furthermore, the flow velocity drastically increased in the compressed vessels. Interestingly, treatment with AV3 suppressed the compression of vessels which according to CFD simulation should result into enhanced drug delivery. The latter was proven in stroma-rich PANC-1+PSC and MiaPaCa+PSC tumor models in mice. We found that treatment with AV3 reduced desmoplasia, decompressed vasculature and enhanced delivery of chemotherapy in vivo.
Conclusion: Altogether, our 3D PDAC model provides a better understanding of mechanical characteristics of PDAC in view of stroma-induced vasculature compression as well as allows for evaluating novel anti-stromal therapeutics for the treatment of fibrotic tumors.
1) Heinrich MA,….Prakash J. Translating complexity and heterogeneity of pancreatic tumor: 3D in vitro to in vivo models. Advanced Drug Delivery Reviews 2021 Jul;174:265-293.
2) Rodrigues J, Heinrich MA, Teixeira LM, Prakash J. 3D In Vitro Model (R)evolution: Unveiling Tumor-Stroma Interactions. Trends in Cancer. 2021 Mar;7(3):249-264.
3) Kuninty PR, …Prakash J. ITGA5 inhibition in pancreatic stellate cells attenuates desmoplasia and potentiates efficacy of chemotherapy in pancreatic cancer. Science Advances. 2019 Sep 4;5(9):eaax2770."