GRP78-targeting subtilase cytotoxin sensitizes cancer cells to photodynamic therapy

Abstract

Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER)-resident chaperone and a major regulator of the unfolded protein response (UPR). Accumulating evidence indicate that GRP78 is overexpressed in many cancer cell lines, and contributes to the invasion and metastasis in many human tumors. Besides, GRP78 upregulation is detected in response to different ER stress-inducing anticancer therapies, including photodynamic therapy (PDT). This study demonstrates that GRP78 mRNA and protein levels are elevated in response to PDT in various cancer cell lines. Stable overexpression of GRP78 confers resistance to PDT substantiating its cytoprotective role. Moreover, GRP78-targeting subtilase cytotoxin catalytic subunit fused with epidermal growth factor (EGF-SubA) sensitizes various cancer cells to Photofrin-mediated PDT. The combination treatment is cytotoxic to apoptosis-competent SW-900 lung cancer cells, as well as to Bax-deficient and apoptosis-resistant DU-145 prostate cancer cells. In these cells, PDT and EGF-SubA cytotoxin induce protein kinase R-like ER kinase and inositol-requiring enzyme 1 branches of UPR and also increase the level of C/EBP (CCAAT/enhancer-binding protein) homologous protein, an ER stress-associated apoptosis-promoting transcription factor. Although some apoptotic events such as disruption of mitochondrial membrane and caspase activation are detected after PDT, there is no phosphatidylserine plasma membrane externalization or DNA fragmentation, suggesting that in DU-145 cells the late apoptotic events are missing. Moreover, in SW-900 cells, EGF-SubA cytotoxin potentiates PDT-mediated cell death but attenuates PDT-induced apoptosis. In addition, the cell death cannot be reversed by caspase inhibitor z-VAD, confirming that apoptosis is not a major cell death mode triggered by the combination therapy. Moreover, no typical features of necrotic or autophagic cell death are recognized. Instead, an extensive cellular vacuolation of ER origin is observed. Altogether, these findings indicate that PDT and GRP78-targeting cytotoxin treatment can efficiently kill cancer cells independent on their apoptotic competence and triggers an atypical, non-apoptotic cell death.

Improvement of chemotherapeutic drug efficacy by endoplasmic reticulum stress

“…Indeed, treatment of A549 lung and HepG2 liver cancer-bearing mice with TUN strongly inhibited tumor growth and prolonged the survival of the experimental mice in association with DOX, which confirms and extends earlier results revealing the chemosensitizing activity of ER-stress induction (Farmaki et al 2011, Firczuk et al 2013, Ahmad et al 2014, Liu et al 2014.…”

“…ER stress is involved in various pathologic conditions, while its modulation increasingly appears to have therapeutic value for several conditions including cancer (Farmaki et al 2011, Firczuk et al 2013, Ahmad et al 2014, Liu et al 2014). An important aspect of ER stress and subsequent UPR is the regulation of the balance between the prosurvival (adaptive) and pro-apoptotic mode of action.…”

The interplay between GRP78 expression and Akt activation in human colon cancer cells under celecoxib treatment

“…There is increasing evidence showing that GRP78 expression correlates with poor survival in many types of cancers and confers resistance to many chemotherapeutic drugs [23][24][25]. To prevent cells from apoptosis induced by celecoxib, during short-term treatment, we believed that it was rational that GRP78 could enhance Akt activation.…”

GRP78 regulates sensitivity of human colorectal cancer cells to DNA targeting agents

“…Elevation of GRP78 has been shown to mediate resistance of the MCF-7 breast cancer cell line to radiation (Li et al 2013) and oesophageal adenocarcinomas to neoadjuvant chemotherapy (Slotta- Huspenina et al 2013). In addition, overexpression of GRP78 in several cancer cell lines promoted resistance to photodynamic therapy (Firczuk et al 2013) and resulted in chemoresistance against etoposide and camptothecin by inhibiting apoptosis (Reddy et al 2003). Moreover, downregulation of GRP78 has been shown to induce apoptosis in colorectal carcinoma (Xing et al 2011), abrogate chemoresistance of hypopharyngeal carcinoma cells to cisplatin (Pi et al 2014), and reverse cisplatin resistance in human ovarian cancer (Fan et al 2013).…”