Intrahepatic Cholangiocarcinoma: Continuing Challenges and Translational Advances

Abstract

Intrahepatic cholangiocarcinoma (iCCA) has over the last 10-20 years become the focus of increasing concern, largely due to its rising incidence and high mortality rates worldwide. The significant increase in mortality rates from this primary hepatobiliary cancer, particularly over the past decade, has coincided with a rapidly growing interest among clinicians, investigators, and patient advocates to seek greater mechanistic insights and more effective biomarker-driven targeted approaches for managing and/or preventing this challenging liver cancer. In addition to discussing challenges posed by this aggressive cancer, this review will emphasize recent epidemiological, basic, and translational research findings for iCCA. In particular, we will highlight emerging demographic changes and evolving risk factors, the critical role of the tumor microenvironment, extracellular vesicle biomarkers and therapeutics, intertumoral and intratumoral heterogeneity, and current and emerging targeted therapies regarding iCCA. Specifically, recent evidence linking non-bile duct medical conditions, such as nonalcoholic fatty liver disease and nonspecific cirrhosis, to intrahepatic cholangiocarcinogenesis together with geographic and ethnic variation will be assessed. Recent developments concerning the roles played by transforming growth factor-β and platelet-derived growth factor D in driving the recruitment and expansion of cancer-associated myofibroblasts within cholangiocarcinoma (CCA) stroma as well as their therapeutic implications will also be discussed. In addition, the potential significance of extracellular vesicles as bile and serum biomarkers and therapeutic delivery systems for iCCA will be described. An integrated systems approach to classifying heterogeneous iCCA subtypes will be further highlighted, and recent clinical trials and emerging targeted therapies will be reviewed, along with recommendations for future translational research opportunities. Established international CCA networks are now facilitating collaborations aimed at advancing iCCA translational and clinical research.

Figure 1.

Graphic representation of the number of intrahepatic cholangiocarcinoma (iCCA) articles published yearly in PubMed from 1950 to 2017. Between 1950 and 1970, only 14 publications on iCCA were indexed compared with 10,852 being indexed from the years 2000 to 2017. From Alexandru Dan Corlan. Medline trend: automated yearly statistics of PubMed results for any query. Web resource at URL:http://dancorlan.net/medline-trend.html.

Figure 2.

Schematic representation illustrating PDGF-D and TGF-β as key drivers of the desmoplastic reaction in iCCA. Resident liver fibroblasts that include portal fibroblasts, hepatic stellate cells, and periductular fibroblasts, as well as possibly fibroblastic cells derived from bone marrow progenitor cells have been suggested as potential sources of CAFs in iCCA stroma. By interacting with its cognate receptor PDGFRβ expressed by fibroblastic cells, PDGF-D secreted by cholangiocarcinoma cells has been shown to stimulate fibroblast migration mediated by Rho GTPases, notably Rac1, Cdc42 and JNK, thereby providing a novel mechanism for CAF recruitment in cholangiocarcinoma. Selective inhibition of PDGFRβ with imatinib mesylate, a tyrosine kinase inhibitor currently in clinical use for other cancer inhibitory indications, significantly blocked fibroblast migration by cholangiocarcinoma cells in vitro. In addition, PDGF-D was demonstrated to prime CAFs for apoptosis via Puma-mediated Bak activation, which could then be converted to full-blown apoptosis by BH3 mimetics. TGF-β, which is overexpressed in iCCA, being produced by both cholangiocarcinoma cells and by stromal cells, has further been shown to be an essential mediator of the desmoplastic cholangiocarcinoma phenotype in a 3-dimensional cholangiocarcinoma cell-α-SMA+CAF co-culture model, by provoking significant increases in proliferative α-SMA+CAFs together with the formation of a dense fibrocollagenous extracellular matrix characteristic of the in situ tumor. Galunisertib (LY2157299), a clinically relevant TGF-β signaling pathway inhibitor was further determined to produce a prominent dose-dependent attenuation of the dense fibrocollagenous matrix, which was accompanied by a significant decrease in α-SMA+CAFs accumulated within the supporting matrix. These findings collectively support PDGF-D and TGF-β as being important regulators of the desmoplastic reaction in iCCA and suggest novel strategies for abrogating CAF recruitment and accumulation within iCCA that may be of potential therapeutic benefit.

Figure 3.

Extracellular vesicles (EVs) as bile and serum biomarkers for cholangiocarcinoma diagnosis and as carriers of tumor growth suppressing miRNA for cholangiocarcinoma therapy. As illustrated in the upper panel of the figure, human bile was shown to contain abundant EVs with a distinctive 5-miRNA signature panel for cholangiocarcinoma diagnosis that demonstrated a sensitivity of 67% and a specificity of 96%, and which was further reported to be better than CA19–9 in identifying patients with early cancers. As also illustrated here, human serum EVs were determined to contain a distinctive proteomic signature for cholangiocarcinoma that had differentiated diagnostic capacity in distinguishing cholangiocarcinoma patients from those with primary sclerosing cholangitis (PSC). Interestingly, some EV containing protein biomarkers, such as fibrinogen gamma chain, alpha-1-acid glycoprotein 1, and S100A8 showed higher diagnostic values in early stage cholangiocarcinoma versus PSC patients than CA19–9. The lower panel depicts the results of a preclinical study demonstrating that LX2 hepatic stellate cell-derived EVs loaded with miRNA-195 administered by intravenous (I.V) injection in a rat model of aggressive orthotopic cholangiocarcinoma significantly suppressed intrahepatic tumor growth and improved the survival of the treated animals over the control group. iCCA, intrahepatic cholangiocarcinoma. eCCA, extrahepatic cholangiocarcinoma. See text for additional details.

Figure 4.

Schematic depiction of an integrated systems biology-based approach to sub-classifying iCCAs into distinct subgroups having important clinical implications for their diagnosis, prognosis, and targeted treatment designs. Adapted from Wang XW and Thorgeirsson SS (29). iCCA, intrahepatic cholangiocarcinoma; SNP, Single nucleotide polymorphism.