Abstract
Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal digestive tract malignancies. Hypoxia-inducible factor (HIF-1) is over-expressed in pancreatic cancer and associated with poor prognosis. During the past several years, we focused on identifying the function of HIF-1 and the antitumor effect of HIF-1 inhibitors on PDAC, especially in regards to immunogenic cell death.
Despite advances in diagnostic and therapeutic approaches, the prognosis of pancreatic ductal adenocarcinoma (PDAC) remains dismal, with a 5-year survival rate lower than 5%. The aggressive course of PDAC is mostly due to the development of resistance to chemotherapies and radiotherapies. PDAC is characterized by a desmoplastic reaction, and constructs a dense fibro-inflammatory microenvironment. Thus, this disease can promote a hypoxic milieu and limit the effects of immune cells in PDAC patients.
HIF-1 plays crucial roles in the pathogenesis and progression of PDAC, especially in metastasis. Our data has confirmed that HIF-1 can directly bind to the promoter of fascin actin-bundling protein 1 (FSCN1)Citation1 as well as that of Lim and SH3 protein 1 (LASP1).Citation2 HIF-1 activated transcription of FSCN1 and LASP1, promoting the metastasis of pancreatic cancer cells.
Patients with PDAC frequently experience neuropathic pain. Tumor neurotropism is an established cause of PDAC recurrence after curative resection. Our prior study explored the influence of the chemokine (C-X3-C) ligand 1 (CX3CL1) and it's receptor (CX3CR1) in the process of neurotropism in PDAC. The results showed that HIF-1 bound to the CX3CR1 promoter under normoxia. Importantly, HIF-1 regulated pancreatic cancer cell migration and the process of neurotropism via CX3CR1.Citation3
While exploring the axis of CX3CL1/CX3CR1, we found that the CX3CL1/CX3CR1 pair can activate the MAPK and PI3K/Akt signaling pathways. HIF-1 expression was upregulated concurrently with the activation of the MAPK and PI3K/Akt signaling pathways and glucose metabolism was reprogrammed by HIF-1 through the CX3CL1/CX3CR1 pathway.Citation4
In addition, we demonstrated that HIF-1 can influence the proliferation of PDAC by directly binding to the promoter of peptidylprolyl isomerase A (cyclophilin A) CYPACitation5 and KIT ligand (KITLG) encoding stem cell factor (SCF). Leptin is a tumor-suppressive cytokine in pancreatic cancer cell lines.Citation6 Our recent data showed that HIF-1 can regulate leptin receptor (LEPR, also known as Ob-R) expression in PDAC cell lines by binding its promoter.Citation7 Finally, HIF-1 can influence leptin's suppressive function by regulating Ob-R.
Single nucleotide polymorphism (SNPs) may affect the activity and stability of HIF-1. We have verified that C1772T and G1790A SNP increase an individuals susceptibility to develop pancreatic cancer. In addition, G1790A SNP is associated with HIF-1expression in tumors and in the progression of pancreatic cancer.Citation8
The current gold-standard treatment for advanced pancreatic cancer is gemcitabine (Gem). However, Gem's clinical effect is persistently modest because of both an inherent and acquired chemo-resistance. Therefore, there is an urgent need to design new treatment strategies to improve the efficacy of Gem. Considering the hypoxic and immunosuppressive milieu, we seek to use the HIF-1 inhibitor (PX-478) to improve the unfavorable microenvironment. PX-478 (S-2-amino-3-[4V-N,N,-bis(2-chloroethyl) amino]-phenyl propionic acid N-oxide dihydrochloride) is a specific agent that can suppress HIF-1 expression in cancer cells at transcript, translation, and post-translation levels.Citation9
To provide effective treatment, chemotherapies should improve anticancer immunity and reduce intra-tumoral immunosuppression. Immunogenic cell death (ICD) has been considered the best way to develop an adaptive immune response and to improve the efficacy of anticancer therapy. ICD is a type of cell death induced by an immune response against tumor cells. The distinguishing features of ICD include (a) the exposure of damage-associated molecular patterns (DAMPs) of dying cells, including calreticulin (CRT) and/or heat shock proteins (HSPs), in early apoptotic stages; (b) the pre-apoptotic secretion of ATP; and (c) the later apoptotic passive release of chromatin protein high mobility group box 1 (HMGB1) and possibly HSP70 and HSP90. The exposure of DAMPs produces specific recognition by antigen-presenting cells (APCs), macrophages, and dendritic cells (DCs). Maturation of these immune cells leads to priming of tumor-specific T and natural killer (NK) cells reactive against tumor cell antigens.Citation10
Our data showed that the combination of Gem with PX-478 significantly enhanced the antitumor effects and increased the proportion of tumor-infiltrating T lymphocytes in Panc02-bearing immunocompetent mice in vivo. The combination treatment did not produce the same effects in immunodeficient mice. Vaccination with cells treated with the single agent or the combination showed significant antitumor effects. After mice were immunized with Gem combined with PX-478, tumor growth reached complete inhibition and survival was significantly prolonged. Gem/PX-478-treatment induced an increase in eIF2α phosphorylation, which was correlated with downregulation of HIF-1α and elicited CRT exposure and the release of HMGB1 and ATP. Only co-treated cells induced DC maturation/phagocytosis and interferon γ (IFNγ) secretion by cytotoxic T lymphocytes. Therefore, the combination of Gem with PX-478 may be a valuable strategy to improve the efficacy of Gem therapy in patients with pancreatic cancer.
In conclusion, the combination of Gem with PX-478 obviously inhibited tumor growth. HIF-1α inhibition prompted a Gem-induced immune response and killed PDAC cells by inducing ICD. Importantly, we found that vaccinations of Gem/PX-478-treated cells have great potential to treat pancreatic cancer. We believe HIF-1 plays a crucial role in the progression of pancreatic cancer. Targeting HIF-1 may be a valuable therapeutic strategy for the efficacious treatment of this recalcitrant malignant disease.
Disclosure of Potential Conflicts of Interest
No potential conflicts of interest were disclosed.
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