The extracellular matrix (ECM) has remained an enigmatic component of the tumor microenvironment. It drives metastasis via its interaction with the integrin signaling pathway, contributes to tumor progression and confers therapy resistance by providing a physical barrier around the tumor. The complexity of the ECM lies in its heterogeneous composition and complex glycosylation that can provide a support matrix as well as trigger oncogenic signaling pathways by interacting with the tumor cells. In this review, we attempt to dissect the role of the ECM in enriching for the treatment refractory cancer stem cell population and how it may be involved in regulating their metabolic needs. Additionally, we discuss how the ECM is instrumental in remodeling the tumor immune microenvironment and the potential ways to target this component in order to develop a viable therapy.

In pancreatic cancer, the robust fibroinflammatory stroma contributes to immune suppression and renders tumors hypoxic, altering intra-tumoral metabolic pathways and leading to poor survival. One metabolic enzyme activated during hypoxia is lactate dehydrogenase A (LDHA). As a result of its promiscuous activity under hypoxia, LDHA produces L-2 hydroxyglutarate, an epigenetic modifier, that regulates the tumor transcriptome. However, the role of L-2HG in remodeling the pancreatic tumor microenvironment is not known. Here we used mass spectrometry to detect L-2HG in serum samples from pancreatic cancer patients, comprising tumor cells as well as stromal cells. Both hypoxic pancreatic tumors as well as serum from pancreatic cancer patients accumulated L-2HG as a result of promiscuous activity of LDHA. This abnormally accumulated L-2HG led to H3 hypermethylation and altered gene expression, which regulated a critical balance between stemness and differentiation in pancreatic tumors. Secreted L-2HG inhibited T cell proliferation and migration, suppressing anti-tumor immunity. In a syngeneic orthotopic model of pancreatic cancer, inhibition of LDHA with GSK2837808A decreased L-2HG, induced tumor regression, and sensitized tumors to anti-PD1 therapy. In conclusion, hypoxia-mediated promiscuous activity of LDHA produces L-2HG in pancreatic tumor cells, regulating the stemness-differentiation balance and contributing to immune evasion.Targeting LDHA can be developed as a potential therapy to sensitize pancreatic tumors to checkpoint inhibitor therapy.

Obesity causes chronic inflammation and changes in gut microbiome. However, how this contributes to poor survival and therapy resistance in patients with pancreatic cancer remain undetermined. Our current study shows that high fat diet-fed obese pancreatic tumor bearing mice do not respond to standard of care therapy with gemcitabine and paclitaxel when compared to corresponding control diet-fed mice. C57BL6 mice were put on control and high fat diet for 1 month following with pancreatic tumors were implanted in both groups. Microbiome of lean (control) and obese (high fat diet fed) mice was analyzed. Fecal matter transplant from control mice to obese mice sensitized tumors to chemotherapy and demonstrated extensive cell death. Analysis of gut microbiome showed an enrichment of queuosine (Q) producing bacteria in obese mice and an enrichment of S-adenosyl methionine (SAM) producing bacteria in control diet-fed mice. Further, supplementation of obese animals with SAM sensitized pancreatic tumors to chemotherapy. Treatment of pancreatic cancer cells with Q increased PRDX1 involved in oxidative stress protection. In parallel, tumors in obese mice showed increase in CD133 + treatment refractory tumor populations compared to control animals. These observations indicated that microbial metabolite Q accumulation in high fat diet-fed mice protected tumors from chemotherapy induced oxidative stress by upregulating PRDX1. This protection could be reversed by treatment with SAM. We conclude that relative concentration of SAM and queuosine in fecal samples of pancreatic cancer patients can be developed as a potential biomarker and therapeutic target in chemotherapy refractory pancreatic cancer.

Pancreatic cancer is among the leading causes of cancer death in the United States with limited effective treatment options. A major contributor to the formation and persistence of pancreatic cancer is the dysregulation of the hepatocyte growth factor (HGF)/Met (HGF receptor) and the macrophage stimulating protein (MSP)/Ron (MSP receptor) systems. These systems normally mediate a variety of cellular behaviors including proliferation, survival, and migration, but are often over-activated in pancreatic cancer and contribute to cancer progression. Previous studies have shown that HGF must dimerize in order to activate Met. Small molecule antagonists with homology to a “hinge” region within the putative dimerization domain of HGF have been developed that bind to HGF and block dimerization, therefore inhibiting Met signaling. Due to the structural and sequence homology between MSP and HGF, we hypothesized that the inhibition of HGF by the hinge analogs may extend to MSP. The primary purpose of this “proof-of-concept” study was to determine if hinge analogs could inhibit cellular responses to both HGF and MSP in pancreatic cancer cells. Our results demonstrated that these compounds inhibited HGF and MSP activity. Hinge analog treatment resulted in decreased Met and Ron activation, and suppressed malignant cell behaviors including proliferation, migration, and invasion in pancreatic cancer cells in vitro. These results suggest that the hinge analogs represent a novel group of molecules that may offer a therapeutic approach for the treatment of pancreatic cancer and warrant further development and optimization.

Pancreatic cancer is a leading cause of cancer deaths in the USA and is characterized by an exceptionally poor long-term survival rate compared with other major cancers. The hepatocyte growth factor (HGF) and macrophage stimulating protein (MSP) growth factor systems are frequently over-activated in pancreatic cancer and significantly contribute to cancer progression, metastasis, and chemotherapeutic resistance. Small molecules homologous to the 'hinge' region of HGF, which participates in its dimerization and activation, had been developed and shown to bind HGF with high affinity, antagonize HGF's actions, and possess anticancer activity. Encouraged by sequence homology between HGF's hinge region and a similar sequence in MSP, our laboratory previously investigated and determined that these same antagonists could also block MSP-dependent cellular responses. Thus, the purpose of this study was to establish that the dual HGF/MSP antagonist Norleual could inhibit the prosurvival activity imparted by both HGF and MSP to pancreatic cancer cells in vitro, and to determine whether this effect translated into an improved chemotherapeutic impact for gemcitabine when delivered in combination in a human pancreatic cancer xenograft model. Our results demonstrate that Norleual does indeed suppress HGF's and MSP's prosurvival effects as well as sensitizing pancreatic cancer cells to gemcitabine in vitro. Most importantly, treatment with Norleual in combination with gemcitabine markedly inhibited in-vivo tumor growth beyond the suppression observed with gemcitabine alone. These results suggest that dual functional HGF/MSP antagonists like Norleual warrant further development and may offer an improved therapeutic outcome for pancreatic cancer patients.