SPP1 facilitates sorafenib resistance in hepatocellular carcinoma by upregulating aerobic glycolysis in endothelial cells

Abstract

The occurrence of resistance to sorafenib, a first-line treatment for hepatocellular carcinoma (HCC), significantly limits its clinical efficacy. Therefore, investigating the potential mechanism of sorafenib resistance in HCC is highly important for developing HCC treatment strategies. In the present study, we identify that SPP1 (encoding osteopontin; OPN) is significantly elevated in sorafenib-resistant HCC. Furthermore, the upregulation of SPP1 is related to vascular invasion, advanced disease stage and poor prognosis in HCC patients. As the IC50 value of sorafenib increases in HepG2 cells, the SPP1 protein secreted by the cells is significantly upregulated, which subsequently facilitates the proliferation of human umbilical vein endothelial cells (HUVECs) and resistance to sorafenib. Further studies reveal that SPP1 induces resistance to sorafenib in HepG2 cells by upregulating glycolysis in HUVECs and further producing lactate. Mechanistically, SPP1 increases the expressions of the glucose transporter GLUT1 and the key glycolytic enzymes PFK1 and PKM2 in HUVECs, resulting in lactate accumulation, which in turn promotes the phosphorylation levels of BRAF and ERK as well as HIF-1α expression in HepG2 cells, leading to sorafenib resistance in HCC. Notably, SPP1 silencing can inhibit the proliferation and invasion of sorafenib-resistant HepG2 cells both in vitro and in vivo. Importantly, lactate derived from HUVECs plays a more dominant role in sorafenib resistance than does SPP1 in HepG2 cells. In summary, SPP1 enhances sorafenib resistance in HepG2 cells through promoting aerobic glycolysis in HUVECs, suggesting that the SPP1-aerobic glycolysis axis might be a prognostic biomarker as well as a potential therapeutic target for sorafenib-resistant HCC.

1. Introduction

Hepatocellular carcinoma (HCC) is the most prevalent form of primary liver cancer, with etiological factors including chronic alcohol consumption, persistent viral hepatitis infection, and nonalcoholic fatty liver disease [1–4]. In clinical practice, HCC treatment is determined by factors such as the stage of the cancer, tumor size and location, and overall condition of the patient [5,6]. At present, conventional options for treating HCC include surgery, chemotherapy, targeted therapy (such as sorafenib) and immunotherapy [7–9]. However, the treatment of HCC remains challenging, as most cases are diagnosed at intermediate to advanced stages and frequently exhibit resistance to multiple therapeutic agents, especially sorafenib [10,11]. Sorafenib plays an important role in first-line standard targeted therapy for HCC, but only approximately 30% of patients benefit from sorafenib treatment, and resistance often emerges within six months, significantly limiting its therapeutic efficacy [12]. Considering that HCC has developed resistance to sorafenib treatment, there is an urgent need to conduct in-depth research on the causes and mechanisms of its resistance in an attempt to overcome resistance and strengthen HCC treatment.

Angiogenesis plays a critical role in HCC progression, metastasis and resistance to sorafenib in highly vascularized tumors. Angiogenesis in HCC is a complex, multi-step process regulated by various factors, including angiogenic factors, chemokines and the extracellular matrix [13,14]. Vascular endothelial growth factor (VEGF) emerges as a pivotal regulator of angiogenesis, which promotes endothelial cell proliferation and angiogenesis in HCC by binding to corresponding receptors [15]. Additionally, fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF) also contribute to angiogenesis, which mainly modulates the function of neovascularization by affecting endothelial cells and smooth muscle cells [16,17]. Notably, the tumor microenvironment is also crucial for angiogenesis, especially under hypoxic conditions, where elevated levels of HIF-1α ultimately promote the expression of VEGF and other angiogenic factors [18,19]. Furthermore, matrix metalloproteinases (MMPs) are able to degrade the extracellular matrix, providing the necessary physical space for neovascularization and releasing matrix-bound angiogenic factors [20,21]. Similarly, inflammatory cytokines, including TNF-α and ILs, can influence the expression of VEGF as well as other angiogenic factors to promote angiogenesis [22,23]. Notably, the regulation of key genes also plays an important role in angiogenesis. SPP1 (encoding osteopontin; OPN), a secreted protein, was found to contribute to the promotion of tumor angiogenesis [24,25]. In tumors, a high level of SPP1 expression leads to increased angiogenesis, thereby promoting tumor invasion and metastasis [26,27]. SPP1 can also modulate the expression and activity of multiple angiogenesis factors, including VEGF and MMPs, thus regulating the process of angiogenesis [28,29]. Moreover, SPP1 can influence angiogenesis by modulating cell-cell interactions and altering the extracellular matrix within the tumor microenvironment [30,31]. Thus, investigating the role of SPP1 in tumor angiogenesis is crucial for gaining deeper insights into cancer progression and drug resistance mechanisms, as well as for developing novel therapeutic strategies. However, the critical mechanisms of SPP1 in HCC angiogenesis and sorafenib resistance remain unclear.