Unique metabolic features of pancreatic cancer stroma: relevance to the tumor compartment, prognosis, and invasive potential.

Erik S Knudsen,Elizaveta Freinkman,Uthra Balaji,Agnieszka K Witkiewicz,Peter Mccue

doi:10.18632/oncotarget.11893

Abstract

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis. The aggressiveness and therapeutic recalcitrance of this malignancy has been attributed to multiple factors including the influence of an active desmoplastic stroma. How the stromal microenvironment of PDAC contributes to the fatal nature of this disease is not well defined. In the analysis of clinical specimens, we observed diverse expression of the hypoxic marker carbonic anhydrase IX and the lactate transporter MCT4 in the stromal compartment. These stromal features were associated with the epithelial to mesenchymal phenotype in PDAC tumor cells, and with shorter patient survival. Cultured cancer-associated fibroblasts (CAFs) derived from primary PDAC exhibited a high basal level of hypoxia inducible factor 1a (HIF1α) that was both required and sufficient to modulate the expression of MCT4. This event was associated with increased transcription and protein synthesis of HIF1α in CAFs relative to PDAC cell lines, while surprisingly the protein turnover rate was equivalent. CAFs utilized glucose predominantly for glycolytic intermediates, whereas glutamine was the preferred metabolite for the TCA cycle. Unlike PDAC cell lines, CAFs were resistant to glucose withdrawal but sensitive to glutamine depletion. Consistent with the lack of reliance on glucose, CAFs could survive the acute depletion of MCT4. In co-culture and xenograft studies CAFs stimulated the invasive potential and metastatic spread of PDAC cell lines through a mechanism dependent on HIF1α and MCT4. Together, these data indicate that stromal metabolic features influence PDAC tumor cells to promote invasiveness and metastatic potential and associate with poor outcome in patients with PDAC.

Highlights

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis with a 5 year survival rate of less than 6%[1,2,3]
We found that the marker of hypoxia carbonic anhydrase IX (CAIX) was expressed in the stromal environment of PDAC (Figure 1A), and interestingly was not significantly associated with expression in the tumor cells (p = 0.085, Supplemental Table 2)
CAIX expression in the stromal compartment was associated with poor prognosis, while the expression in the tumor cells only trended toward poor outcome (Figure 1B)

Summary

Introduction

Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis with a 5 year survival rate of less than 6%[1,2,3]. It is established that growth of tumor cells is supported by oncogenic signaling and altered metabolism [7,8,9]. Understanding the metabolic features of PDAC, key mediators, and related www.impactjournals.com/oncotarget dependencies could yield important insights into the pathogenesis of disease and new targets for tumor therapy. It has been demonstrated that KRAS and TP53 mutations are key determinants of the PDAC metabolic state [10,11,12,13]. In this context, studies have shown that PDAC exhibits increased glycolysis and concomitant use of glucose intermediates into the hexosamine and pentose phosphate pathways. A recent study indicated that there are specific metabolic subtypes of PDAC, and that metabolic state impacts on vulnerabilities to metabolic challenges and therapy [17]

Methods

Results

Conclusion