Antibody-Based Targeting of Cell Surface GRP94 Specifically Inhibits Cetuximab-Resistant Colorectal Cancer Growth

Water-soluble Yb3+, Er3+ codoped NaYF4 nanoparticles induced SGC-7901 cell apoptosis through mitochondrial dysfunction and ROS-mediated ER stress

BACKGROUND

Nanoparticles are potential luminescent probes; among them, upconversion nanoparticles (UCNP) are currently being developed as fluorescent probes for biomedical applications. However, the molecular mechanisms of UCNP in human gastric cell lines remain poorly understood. Here, we aimed to examine UCNP cytotoxicity to SGC-7901 cells and explore its underlying mechanisms.

METHODS

The effects of 50-400 μg/mL UCNP on human gastric adenocarcinoma (SGC-7901) cells were investigated. Flow cytometry was used to evaluate reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), intracellular Ca²⁺ levels, and apoptosis. Activated caspase-3 and nine activities were measured; meanwhile, cytochrome C (Cyt C) in the cytosol and B-cell lymphoma 2 (Bcl-2), Bcl-2 associated X protein (Bax), protein kinase B (Akt), phosphorylated-Akt (p-Akt), 78 kDa glucose-regulated protein (GRP78), 94 kDa glucose-regulated protein (GRP94), calpain-1, and calpain-2 protein levels were also detected.

RESULTS

UCNP inhibited the viability of SGC-7901 cells in a concentration- and time-dependent manner and increased the proportion of cell apoptosis. Exposure to UCNP enhanced the ratio of Bax/Bcl-2, elevated the level of ROS, decreased ΔΨm, increased intracellular Ca²⁺ and Cyt C protein levels, decreased the levels of phosphorylated Akt, increased the activity of caspase-3 and caspase-9, and upregulated the protein expression of GRP-78, GRP-94, calpain-1 and calpain-2 in SGC-7901 cells.

CONCLUSION

UCNP induced SGC-7901 cell apoptosis by promoting mitochondrial dysfunction and ROS-mediated endoplasmic reticulum (ER) stress, initiating the caspase-9/caspase-3 cascade.

The biology and inhibition of glucose-regulated protein 94/gp96

The 94 kDa molecular chaperone, glucose-regulated protein 94 (Grp94), has garnered interest during the last decade due to its direct association with endoplasmic reticulum (ER) stress and disease. Grp94 belongs to the Hsp90 family of molecular chaperones and is a master regulator of ER homeostasis due to its ability to fold and stabilize proteins/receptors, and to chaperone misfolded proteins for degradation. Multiple studies have demonstrated that Grp94 knockdown or inhibition leads to the degradation of client protein substrates, which leads to disruption of disease-dependent signaling pathways. As a result, small molecule inhibitors of Grp94 have become a promising therapeutic approach to target a variety of disease states. Specifically, Grp94 has proven to be a promising target for cancer, glaucoma, immune-mediated inflammation, and viral infection. Moreover, Grp94-peptide complexes have been utilized effectively as adjuvants for vaccines against a variety of disease states. This work highlights the significance of Grp94 biology and the development of therapeutics that target this molecular chaperone in multiple disease states.

An internalizing antibody targeting of cell surface GRP94 effectively suppresses tumor angiogenesis of colorectal cancer

Colorectal cancer (CRC) is one of the life-threatening malignancies worldwide. Thus, novel potential therapeutic targets and therapeutics for the treatment of CRC need to be identified to improve the clinical outcomes of patients with CRC. In this study, we found that glucose-regulated protein 94 (GRP94) is overexpressed in CRC tissues, and its high expression is correlated with increased microvessel density. Next, through phage display technology and consecutive in vitro functional isolations, we generated a novel human monoclonal antibody that specifically targets cell surface GRP94 and shows superior internalizing activity comparable to trastuzumab. We found that this antibody specifically inhibits endothelial cell tube formation and simultaneously promotes the downregulation of GRP94 expression on the endothelial cell surface. Finally, we demonstrated that this antibody effectively suppresses tumor growth and angiogenesis of HCT116 human CRC cells without causing severe toxicity in vivo. Collectively, these findings suggest that cell surface GRP94 is a novel potential anti-angiogenic target in CRC and that antibody targeting of GRP94 on the endothelial cell surface is an effective strategy to suppress CRC tumor angiogenesis.

Clinicopathologic and Prognostic Association of GRP94 Expression in Colorectal Cancer with Synchronous and Metachronous Metastases

Patients with advanced colorectal cancer (CRC) with distant metastases have a poor prognosis. We evaluated the clinicopathological relevance of GRP94 expression in these cases. The immunohistochemical expression of GRP94 was studied in 189 CRC patients with synchronous (SM; n = 123) and metachronous metastases (MM; n = 66), using tissue microarray; the association between GRP94 expression, outcome, and tumor-infiltrating lymphocytes (TILs) was also evaluated. GRP94 was expressed in 64.6% (122/189) patients with CRC; GRP94 positivity was found in 67.5% and 59.1% patients with SM and MM, respectively. In the SM group, high GRP94 expression was more common in patients with a higher density of CD4+ TILs (p = 0.002), unlike in the MM group. Survival analysis showed that patients with GRP94 positivity had significantly favorable survival (p = 0.030); after multivariate analysis, GRP94 only served as an independent prognostic factor (p = 0.034; hazard ratio, 0.581; 95% confidence interval, 0.351-0.961) in the SM group. GRP94 expression was detected in 49.4% of metastatic sites and showed significant heterogeneity between primary and metastatic lesions (p = 0.012). GRP94 is widely expressed in CRC with distant metastases; its expression was associated with favorable prognosis in the SM group, unlike in the MM group.

Molecular Chaperone GRP94/GP96 in Cancers: Oncogenesis and Therapeutic Target

During tumor development and progression, intrinsic and extrinsic factors trigger endoplasmic reticulum (ER) stress and the unfolded protein response, resulting in the increased expression of molecular chaperones to cope with the stress and maintain tumor cell survival. Heat shock protein (HSP) GRP94, also known as GP96, is an ER paralog of HSP90 and has been shown to promote survival signaling during tumor-induced stress and modulate the immune response through its multiple clients, including TLRs, integrins, LRP6, GARP, IGF, and HER2. Clinically, elevated expression of GRP94 correlates with an aggressive phenotype and poor clinical outcome in a variety of cancers. Thus, GRP94 is a potential molecular marker and therapeutic target in malignancies. In this review, we will undergo deep molecular profiling of GRP94 in tumor development and summarize the individual roles of GRP94 in common cancers, including breast cancer, colon cancer, lung cancer, liver cancer, multiple myeloma, and others. Finally, we will briefly review the therapeutic potential of selectively targeting GRP94 for the treatment of cancers.

Cell Surface GRP94 as a Novel Emerging Therapeutic Target for Monoclonal Antibody Cancer Therapy

Glucose-regulated protein 94 (GRP94) is an endoplasmic reticulum (ER)-resident member of the heat shock protein 90 (HSP90) family. In physiological conditions, it plays a vital role in regulating biological functions, including chaperoning cellular proteins in the ER lumen, maintaining calcium homeostasis, and modulating immune system function. Recently, several reports have shown the functional role and clinical relevance of GRP94 overexpression in the progression and metastasis of several cancers. Therefore, the current review highlights GRP94’s physiological and pathophysiological roles in normal and cancer cells. Additionally, the unmet medical needs of small chemical inhibitors and the current development status of monoclonal antibodies specifically targeting GRP94 will be discussed to emphasize the importance of cell surface GRP94 as an emerging therapeutic target in monoclonal antibody therapy for cancer.