Targeting the unfolded protein response in head and neck and oral cavity cancers

Phytochemical-mediated modulation of autophagy and endoplasmic reticulum stress as a cancer therapeutic approach

Autophagy and endoplasmic reticulum (ER) stress are conserved processes that generally promote survival, but can induce cell death when physiological thresholds are crossed. The pro-survival aspects of these processes are exploited by cancer cells for tumor development and progression. Therefore, anticancer drugs targeting autophagy or ER stress to induce cell death and/or block the pro-survival aspects are being investigated extensively. Consistently, several phytochemicals have been reported to exert their anticancer effects by modulating autophagy and/or ER stress. Various phytochemicals (e.g., celastrol, curcumin, emodin, resveratrol, among others) activate the unfolded protein response to induce ER stress-mediated apoptosis through different pathways. Similarly, various phytochemicals induce autophagy through different mechanisms (namely mechanistic target of Rapamycin [mTOR] inhibition). However, phytochemical-induced autophagy can function either as a cytoprotective mechanism or as programmed cell death type II. Interestingly, at times, the same phytochemical (e.g., 6-gingerol, emodin, shikonin, among others) can induce cytoprotective autophagy or programmed cell death type II depending on cellular contexts, such as cancer type. Although there is well-documented mechanistic interplay between autophagy and ER stress, only a one-way modulation was noted with some phytochemicals (carnosol, capsaicin, cryptotanshinone, guangsangon E, kaempferol, and δ-tocotrienol): ER stress-dependent autophagy. Plant extracts are sources of potent phytochemicals and while numerous phytochemicals have been investigated in preclinical and clinical studies, the search for novel phytochemicals with anticancer effects is ongoing from plant extracts used in traditional medicine (e.g., Origanum majorana). Nonetheless, the clinical translation of phytochemicals, a promising avenue for cancer therapeutics, is hindered by several limitations that need to be addressed in future studies.

NRF3 suppresses squamous carcinogenesis, involving the unfolded protein response regulator HSPA5

Epithelial skin cancers are extremely common, but the mechanisms underlying their malignant progression are still poorly defined. Here, we identify the NRF3 transcription factor as a tumor suppressor in the skin. NRF3 protein expression is strongly downregulated or even absent in invasively growing cancer cells of patients with basal and squamous cell carcinomas (BCC and SCC). NRF3 deficiency promoted malignant conversion of chemically induced skin tumors in immunocompetent mice, clonogenic growth and migration of human SCC cells, their invasiveness in 3D cultures, and xenograft tumor formation. Mechanistically, the tumor-suppressive effect of NRF3 involves HSPA5, a key regulator of the unfolded protein response, which we identified as a potential NRF3 interactor. HSPA5 levels increased in the absence of NRF3, thereby promoting cancer cell survival and migration. Pharmacological inhibition or knock-down of HSPA5 rescued the malignant features of NRF3-deficient SCC cells in vitro and in preclinical mouse models. Together with the strong expression of HSPA5 in NRF3-deficient cancer cells of SCC patients, these results suggest HSPA5 inhibition as a treatment strategy for these malignancies in stratified cancer patients.

Advantages of the Combinatorial Molecular Targeted Therapy of Head and Neck Cancer-A Step before Anakoinosis-Based Personalized Treatment

The molecular initiators of Head and Heck Squamous Cell Carcinoma (HNSCC) are complex. Human Papillomavirus (HPV) infection is linked to an increasing number of HNSCC cases, but HPV-positive tumors generally have a good prognosis. External factors that promote the development of HPV-negative HNSCC include tobacco use, excessive alcohol consumption, and proinflammatory poor oral hygiene. On a molecular level, several events, including the well-known overexpression of epidermal growth factor receptors (EGFR) and related downstream signaling pathways, contribute to the development of HNSCC. Conventional chemotherapy is insufficient for many patients. Thus, molecular-based therapy for HNSCC offers patients a better chance at a cure. The first molecular target for therapy of HNSCC was EGFR, inhibited by monoclonal antibody cetuximab, but its use in monotherapy is insufficient and induces resistance. This article describes attempts at combinatorial molecular targeted therapy of HNSCC based on several molecular targets and exemplary drugs/drug candidates. The new concept of anakoinosis-based therapy, which means treatment that targets the intercellular and intracellular communication of cancer cells, is thought to be the way to improve the clinical outcome for HNSCC patients. The identification of a link between molecular targeted therapy and anakoinosis raises the potential for further progress in HPV-negative HNSCC therapy.

The Chaperone Protein GRP78 Promotes Survival and Migration of Head and Neck Cancer After Direct Radiation Exposure and Extracellular Vesicle-Transfer

Background and Purpose

Increased levels of the chaperone protein GRP78 have been implicated in poorer outcomes of cancer therapy. We have therefore explored the functional connection between the expression of GRP78 and the development of radioresistance and metastatic behavior in HNSCC.

Material and Methods

The association between gene expression of GRP78 and survival in HNSCC patients was examined using the TCGA database. The influence of ionizing radiation on the GRP78 levels in HNSCC cell lines, their secreted extracellular vesicles (EV) and non-irradiated EV-recipient cells was investigated by Western Blot and FACS. The consequences of chemical inhibition or experimental overexpression of GRP78 on radioresistance and migration of HNSCC cells were analyzed by clonogenic survival and gap closure assays.

Results

Elevated levels of GRP78 RNA in HNSCC correlated with poorer overall survival. Radiation increased GRP78 protein expression on the surface of HNSCC cell lines. Experimental overexpression of GRP78 increased both radioresistance and migratory potential. Chemical inhibition of GRP78 impaired cell migration. EVs were identified as a potential source of increased GRP78 content as elevated levels of surface GRP78 were found in EVs released by irradiated cells. These vesicles transferred GRP78 to non-irradiated recipient cells during co-cultivation.

Conclusions

We have identified the chaperone protein GRP78 as a potential driver of increased radioresistance and motility in HNSCC. The uptake of GRP78-rich EVs originating from irradiated cells may contribute to a poorer prognosis through bystander effects mediated by the transfer of GRP78 to non-irradiated cells. Therefore, we consider the chaperone protein GRP78 to be an attractive target for improving radiotherapy strategies.

HTS Identification of Activators and Inhibitors of Endoplasmic Reticulum (ER) Stress and the Unfolded Protein Response (UPR)

The identification of small molecules and natural product extracts that enhance or interfere with the productivity of protein folding in the endoplasmic reticulum (ER) has the potential to improve a wide variety of human pathologies. Every protein that is destined for a lysosome, integral to the cell membrane, or secreted, is folded, post-translationally modified, and exported to the cytoplasm from the ER-Golgi complex. The following protocols have successfully employed several high-fidelity cell-based luciferase high-throughput screens (HTS) to identify activators and inhibitors of ER stress and the unfolded protein response (UPR).

Mitochondrial dysfunction, UPRmt signaling, and targeted therapy in metastasis tumor

In modern research, mitochondria are considered a more crucial energy plant in cells. Mitochondrial dysfunction, including mitochondrial DNA (mtDNA) mutation and denatured protein accumulation, is a common feature of tumors. The dysfunctional mitochondria reprogram molecular metabolism and allow tumor cells to proliferate in the hostile microenvironment. One of the crucial signaling pathways of the mitochondrial dysfunction activation in the tumor cells is the retrograde signaling of mitochondria-nucleus interaction, mitochondrial unfolded protein response (UPR^mt), which is initiated by accumulation of denatured protein and excess ROS production. In the process of UPR^mt, various components are activitated to enhance the mitochondria-nucleus retrograde signaling to promote carcinoma progression, including hypoxia-inducible factor (HIF), activating transcription factor ATF-4, ATF-5, CHOP, AKT, AMPK. The retrograde signaling molecules of overexpression ATF-5, SIRT3, CREB, SOD1, SOD2, early growth response protein 1 (EGR1), ATF2, CCAAT/enhancer-binding protein-d, and CHOP also involved in the process. Targeted blockage of the UPR^mt pathway could obviously inhibit tumor proliferation and metastasis. This review indicates the UPR^mt pathways and its crucial role in targeted therapy of metastasis tumors.

Anti-growth and pro-apoptotic effects of dasatinib on human oral cancer cells through multi-targeted mechanisms

Dasatinib is an inhibitor of Src that has anti-tumour effects on many haematological and solid cancers. However, the anti-tumour effects of dasatinib on human oral cancers remain unclear. In this study, we investigated the effects of dasatinib on different types of human oral cancer cells: the non-tumorigenic YD-8 and YD-38 and the tumorigenic YD-10B and HSC-3 cells. Strikingly, dasatinib at 10 µM strongly suppressed the growth and induced apoptosis of YD-38 cells and inhibited the phosphorylation of Src, EGFR, STAT-3, STAT-5, PKB and ERK-1/2. In contrast, knockdown of Src blocked the phosphorylation of EGFR, STAT-5, PKB and ERK-1/2, but not STAT-3, in YD-38 cells. Dasatinib induced activation of the intrinsic caspase pathway, which was inhibited by z-VAD-fmk, a pan-caspase inhibitor. Dasatinib also decreased Mcl-1 expression and S6 phosphorylation while increased GRP78 expression and eIF-2α phosphorylation in YD-38 cells. In addition, to its direct effects on YD-38 cells, dasatinib also exhibited anti-angiogenic properties. Dasatinib-treated YD-38 or HUVEC showed reduced HIF-1α expression and stability. Dasatinib alone or conditioned media from dasatinib-treated YD-38 cells inhibited HUVEC tube formation on Matrigel without affecting HUVEC viability. Importantly, dasatinib's anti-growth, anti-angiogenic and pro-apoptotic effects were additionally seen in tumorigenic HSC-3 cells. Together, these results demonstrate that dasatinib has strong anti-growth, anti-angiogenic and pro-apoptotic effects on human oral cancer cells, which are mediated through the regulation of multiple targets, including Src, EGFR, STAT-3, STAT-5, PKB, ERK-1/2, S6, eIF-2α, GRP78, caspase-9/3, Mcl-1 and HIF-1α.

Growth hormone releasing hormone in the unfolded protein response context

The effects of Growth Hormone Releasing Hormone in human pathophysiology are not limited to those mediated by the Growth Hormone Releasing Hormone-Growth Hormone-Insulin-like Growth Factor-I axis. Receptors specific for this neuropeptide are expressed in a diverse variety of human tissues, to initiate multifarious signaling cascades, regulators of cellular homeostasis and survival. The Unfolded Protein Response is in charge of adaptive responses towards a plethora of challenges, able to trigger cellular repair or death. The possible involvement of Growth Hormone Releasing Hormone and its agonistic and antagonistic analogs in those events, may deliver exciting possibilities in the treatment of human disease, including the Acute Respiratory Distress Syndrome.

Impact and Relevance of the Unfolded Protein Response in HNSCC

Head and neck squamous cell carcinomas (HNSCC) encompass a heterogeneous group of solid tumors that arise from the upper aerodigestive tract. The tumor cells face multiple challenges including an acute demand of protein synthesis often driven by oncogene activation, limited nutrient and oxygen supply and exposure to chemo/radiotherapy, which forces them to develop adaptive mechanisms such as the Unfolded Protein Response (UPR). It is now well documented that the UPR, a homeostatic mechanism, is induced at different stages of cancer progression in response to intrinsic (oncogenic activation) or extrinsic (microenvironment) perturbations. This review will discuss the role of the UPR in HNSCC as well as in the key processes that characterize the physiology of HNSCC. The role of the UPR in the clinical context of HNSCC will also be addressed.