Hepatocellular carcinoma (HCC) is counted among the top four causes of cancer-associated deaths globally and exhibits a grim 5-year survival rate less than 20 % (Lee et al., 2021, Wieckowski et al., 2009). Sorafenib, a multi-target tyrosine kinase inhibitor (TKI) approved by the Food and Drug Administration (FDA) as first-line therapy for advanced HCC, extends patient survival by approximately 6.5 months (Cheng et al., 2009). Nowadays, sorafenib serves as an important therapeutic approach in unresectable HCC, with its role supported by substantial evidence and clinical practice (Bruix et al., 2019). However, 30 % of patients who gain benefits from sorafenib may develop drug resistance within 6 months, markedly compromising its clinical benefit (Llovet et al., 2008). Thus, deciphering the underlying mechanism of sorafenib resistance is crucial for suppressing HCC progression and improving patients’ outcomes.

Hypoxia represents a classical feature within malignancies, contributing to its rapid growth (Wilson and Hay, 2011). HCC constitutes a hypervascular neoplasm characterized by extensive vascular abnormalities and heightened hypoxic susceptibility, especially in its core regions. This represents a primary factor contributing to tumor progression, unfavorable treatment response, and TKI resistance (Hong et al., 2024, Dal Bo et al., 2020, Zhao et al., 2024). Importantly, sorafenib demonstrates restricted cytotoxic effects on distal tumors, which can be attributed to its poor penetration and intra-tumoral hypoxia (Liang et al., 2013). This therapeutic shortcoming highlights the urgent need for interventions capable of mitigating hypoxia and potentiating drug activity. Over the past few years, hyperbaric oxygen (HBO) has been recognized as an alternative therapeutic approach by remodeling the hypoxic immunosuppressive microenvironment of HCC. HBO entails administering pure oxygen (i.e., 100 %) to patients under pressure surpassing one standard atmosphere. Furthermore, HBO plays a significant tumor-suppressing role by alleviating hypoxia-related metabolic adaptation (Moen and Stuhr, 2012), optimizing extracellular matrix (Wang et al., 2022, Liu et al., 2021), and improving drug penetration (Wu et al., 2018). As a FDA-authorized noninvasive approach, HBO has been broadly employed as a supplementary strategy to boost the effectiveness of chemotherapy (Al-Waili et al., 2005), photodynamic therapy (Matzi et al., 2004), radiotherapy (Philippou et al., 2020), photothermal therapy (Xiao et al., 2022), and immunotherapy (Graham and Unger, 2018). Liu and colleagues employed HBO to enhance intra-tumoral delivery of anti-PD-1 blockade, attaining positive immunotherapeutic results (Liu et al., 2021). Given the safety, accessibility, and effectiveness of HBO, combining it with oxygen-dependent tumor treatment strategies holds substantial promise for clinical use. However, the efficacy of HBO therapy and its potential hypoxia-targeting mechanisms in TKI-resistant HCC remain poorly understood.

Organelle metabolism mediated by endoplasmic reticulum (ER)-mitochondrial coupling promotes tumor progression by supplying essential biosynthetic precursors, maintaining redox homeostasis, and modulating cell death (Porporato et al., 2018). TKI-resistant tumor cells often exhibit enhanced mitochondrial biogenesis as an adaptive response. However, this metabolic adaptation can create a therapeutic vulnerability by rendering them dependent on mitochondrial function, thereby potentially increasing their susceptibility to mitochondria-targeted medications (Lissanu Deribe et al., 2018, Molina et al., 2018, Mukherjee et al., 2023). Mitochondria consume approximately 85–90 % of the oxygen humans breathe in and act as the primary location for ATP production. As a result, mitochondria may represent a primary intracellular target of HBO. Upon stress exposure, organelle interaction-driven responses can lead to maladaptive changes that promote tumor development (Galluzzi et al., 2018). Contemporary studies have revealed that functional impairments in ER and mitochondria could exert a vital influence on pathophysiological alterations induced by stress stimuli (Resende et al., 2020). Notably, clinical inquiries have identified potential correlations between ER stress, mitochondrial dysfunction, and innovative anti-tumor strategies (Wu et al., 2023). Recent studies emphasized the significance of mitochondria-associated ER membranes (MAMs), sitting between the ER and mitochondria. MAMs govern multiple critical physiological processes, such as calcium signaling and mitochondrial dynamics (Zheng et al., 2018, Wilson and Metzakopian, 2021). A tripartite complex composed of inositol 1,4,5-triphosphate receptor 1 (IP3R1), voltage-dependent anion channel 1 (VDAC1), and the MAMs tethering protein glucose-regulated protein 75 (GRP75) has become a key mediator of ER-mitochondrial Ca²⁺ signaling (Chami et al., 2008). Moreover, MAMs could transmit ER stress to mitochondria (Bronner et al., 2015). In addition, reactive oxygen species (ROS) and mitochondrial DNA (mtDNA) are critical factors that initiate assembly of NLRP3 inflammasome (Nakahira et al., 2011, Zhong et al., 2013). In this condition, it is critical to understand the change of calcium homeostasis regulated by ER-mitochondria contacts during the application of HBO treatment in TKI-treated HCC.

Here, the aim of this study is to explore the role of MAMs in ER-mitochondrial communication within TKI-resistant HCC and assess whether this organellar interplay-related mechanism contribute to HBO-induced mitochondrial dysfunction, thus aiding in the improvement of sorafenib’s therapeutic effectiveness. The findings of our study demonstrated that the establishment of a tripartite calcium signaling complex within MAMs enhanced the communication between the ER and mitochondria in the context of sorafenib-resistant HCC. This mechanism facilitated HBO-triggered mitochondrial dysfunction and augmented the TKI sensitivity of HCC.