Introduction
Currently, esophageal cancer is the seventh most common worldwide
malignant tumors. More than 456,000 new cases of esophageal cancer and
300,000 deaths were recorded globally in 2018, accounting for 3.2% and
5.3% of all cancers, respectively (Brayet al. , 2018). According to histopathological classification,
esophageal cancer is composed of two main histologic subtypes,
oesophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma
(EA).
East Asia is a region with a high incidence of esophageal cancer, and
China accounts for approximately half of the world’s esophageal cancer
cases (Ferlay et al. , 2010).
Notably, more than 90% patients are diagnosed with ESCC in China
(Zhao et al. , 2012;
Liang et al. , 2017). The major
treatment for ESCC patients is surgical resection, and the prognosis is
favorable in the early stages.
But
the early symptoms of ESCC are more hidden, and invasive and aggressive,
cause most diagnosed ESCC patients are in moderate and advanced stages
(Mariette et al. , 2007).
Therefore, for these patients, chemotherapy helps to reduce the primary
tumor bulk, to increase the possibility of radical resection and to
treat micro-metastatic disease and prolong the survival period of
patients (Lordick et al. ,
2016).These chemotherapeutic drugs include combinations of
platinum-based drugs, 5-fluorouracil, paclitaxel and doxorubicin.
However, conventional chemotherapeutics is often seriously hindered by a
number of limitations, including high-systemic toxicity, chemoresistance
and short in vivo circulation half-life.
Currently, targeted therapy was recognized as promising strategy for
cancer treatment due to its high specificity and minimal side effects.
The ubiquitin-proteasome system (UPS) plays a critical role in
regulating 80-90% protein degradation and turnover as well as
regulation of multiple cellular events, including the cell cycle, signal
transduction, response to oxidative stress, cell proliferation and
apoptosis (Ciechanover, 1994;
Hochstrasser, 1995;
Jana, 2012). As the critical endpoint for
the UPS, the 26S proteasome is the
chief proteolytic effector responsible for recognized and degraded the
ubiquitylated protein, which consists of a core particle 20S proteasome,
and two 19S regulatory particles (Bardet al. , 2018). In the past decade, proteasome as a target for
cancer treatment, has gained increasing attention. Among them, the
proteasome inhibitor (e.g., bortezomib, carfilzomib) has been confirmed
to show excellent therapeutic effects in the treatment of multiple
myeloma and other tumors (Johnson, 2015;
Manasanch et al. , 2017).
Ixazomib, an oral 20S subunit-selective inhibitor being developed used
for treatment of a broad range of human malignant tumor. Compared with
bortezomib, ixazomib has a shorter proteasome dissociation half-life
which is a critical role in improving the distribution of drug in solid
tumor tissues (Kupperman et al. ,
2010). Currently, ixazomib was approved for treatment of multiple
myeloma patient combination with lenalidomide and dexamethasone by the
US FDA (Shirley, 2016). Besides
haematological neoplasms, a series of studies have suggested that
ixazomib also have therapeutic anticancer functions in solid tumor,
including colorectal cancer, bladder cancer, osteosarcoma and breast
cancer (Kupperman et al. , 2010;
Sato et al. , 2017;
Yue et al. , 2019;
Harris et al. , 2020). However, the
detailed mechanisms underlying ixazomib induced cancer cell death remain
unclear.
In recent years, endoplasmic reticulum stress (ERS) pathway is
discovered regulated cellular processes, including protein folding,
sorting, secretion, and play a crucial role in the process of apoptosis
(Oakes et al. , 2015;
Minchenko et al. , 2016). Early ERS
is a response promoting survival, while the unfolded protein response
reduces the accumulation of unfolded protein and restores the function
to the endoplasmic reticulum (Oakeset al. , 2015). However, when the unfolded protein response is
not sufficient to protect cell survival, the endoplasmic reticulum will
act as the trigger point of apoptosis signals to induce apoptosis and
promote the expression of apoptosis-inducing factors, such as the Bcl-2
homology 3 (BH3)-only pro-apoptotic protein NOXA, a key mediator for
ERS-induced apoptosis (Kelly et
al. , 2012; Cano-Gonzalez et al. ,
2018). Proteasome inhibitor MG-132 was found induces apoptosis via
activation of NOXA signaling pathways in hepatic stellate and chronic
lymphocytic leukemia cell lines (Baouet al. , 2010; Sosa Seda et
al. , 2010). Furthermore, Many studies have found evidence of sustained
and high-level activation of ERS in esophagus cancer cells
(Rosekrans et al. , 2015;
Hu et al. , 2019). These studies
suggest that ixazomib could potentially be used for induce ESCC cell
apoptosis via ER stress-mediated NOXA induction.
In the present study, we evaluate the preclinical efficacy of ixazomib
in ESCC cell lines and animal xenograft models by a series of in vitro
and in vivo experiments. Our results demonstrate that that ixazomib is
strongly apoptotic and blocks ESCC cell growth and survival. We further
show that ixazomib exerts its pro-apoptotic action via a mechanism
involving the activation of the NOXA-c-Myc pathway. These results
indicate that the ixazomib may be an additional useful strategy to
improve the treatment outcome for ESCC patient.