Inhibitors against the proteasome a

Inhibitors against the proteasome, a component of the ubiquitin-proteasome pathway that degrades cellular proteins, provide a new strategy for targeting the 26S proteasome [25]. Proteasome inhibitors can exhibit potent anti-cancer effects against different tumor trifluoperazine hydrochloride and were shown to induce apoptosis in pancreatic, renal, prostate and squamous cell carcinomas in vivo and in vitro [26]. Bortezomib (BTZ) is a proteasome inhibitor that can regulate canonical as well as non-canonical NF-κB signaling [27]. Another anti-tumor mechanism of BTZ may be associated with the upregulation of NOXA [28]. In addition to BTZ regulation of NF-κB and NOXA, BTZ has a variety of targets in malignant cells, such as caspase-8 and caspase-9 [29]. cFLIP can block the activation of caspase-8 to inhibit apoptosis [30]. However, BTZ is associated with various systemic toxicities in patients, including vomiting, nausea, diarrhea and constipation, as well as peripheral neuropathy and other effects [31]. Previous studies have shown that a combination of proteasome inhibitor and histone deacetylase exhibits synergistic effects against malignant tumors, including multiple myeloma, chronic lymphocytic leukemia and mantle cell lymphoma [[32], [33], [34]]. Other studies showed anti-cancer effects with the combination of GSIs with other agents [35]. Several reports have shown a synergetic anti-cancer effect from BTZ in combination with other chemotherapeutic agents, suggesting a promising role for BTZ in combined therapy regimens [36]. However, no studies have examined the potential therapeutic effects of the combination of BTZ and GSIs in ALK+ ALCL. Because of the limitations using γ-secretase or proteasome inhibitors as single agents in treating ALK+ ALCL, we hypothesized that combining both inhibitors may be a superior and safer strategy to treat ALK+ ALCL than each agent alone. In this study, we examined the effects of the combination of BTZ with GSI-I in ALK+ ALCL in vivo and in vitro and explored the therapeutic mechanism.
Materials and methods
Results
Discussion Our study reveals the effect of the combination treatment of GSI-I with BTZ on ALK+ ALCL both in vivo and in vitro. We examined the effects of the combination of low dose BTZ and GSI-I based on isobologram studies ensuring drug availability and fewer side effects in ALK+ ALCL cells in vivo and in vitro. Our results indicated that the combination treatment of BTZ and GSI-I inhibited cell proliferation and promoted apoptosis in ALK+ ALCL cell lines more potently than the single treatments alone. Our understanding of the biological function of apoptosis has evolved from its role as mechanism for “programmed cell death” to acting as a barrier against malignancy [38]. Studies have demonstrated that the apoptosis programmed cell death pathway serves as mechanism to block cancer development [39], and the mechanisms of apoptosis and the strategies used by cancer cells to evade apoptosis have been intensively explored over the last decade. Apoptosis is induced through the activation of a cascade of normal latent proteases, including effector caspases (caspase-8 and caspase-9). Currently, the intrinsic apoptotic process is considered to be the main defense for the pathogenesis of cancer [38]. Consistent with the induction of apoptosis by the combination treatment, we observed increased production of cleaved PARP, cleaved caspase-3, and cleaved caspase-8 production, which is consistent with the results of Chen et al. [40]. We also observed that BTZ and GSI-I reduced levels of Bcl-2, Bcl-xL and cFLIP. The anti-cancer activities of BTZ and GSI-I were further confirmed in the mouse model. Mice treated with the combination of BTZ and GSI-I demonstrated significant tumor regression compared with mono-therapy or untreated controls. Our findings indicated that multiple molecular mechanisms may be contributing to the synergistic effect between BTZ and GSI-I in ALK+ ALCL cells. Cytoprotective pathways, including ERK, Notch and AKT/mTOR, confer a survival advantage on ALK+ ALCL, not only rendering these tumors resistant to conventional cytotoxic drugs, but also protecting cells from apoptosis [5]. The Notch signaling pathway is a key pathway that regulates cell differentiation, proliferation and survival and plays a critical role in several developmental processes, such as neurogenesis, angiogenesis and hematopoiesis [41]. The multiple abilities of the Notch signaling pathway to inhibit or induce differentiation, to drive or arrest proliferation and to promote survival or induce apoptosis in a cell-specific way enables the Notch signaling pathway to promote or prevent tumor formation in a variety of cells [42]. Notch receptors are divided into four types, and abnormal Notch1 activation is associated with ALCL [43]. Moreover, the Notch1 pathway interacts with a number of oncogenic signaling pathways. Notch1 activates the PI3K/AKT signaling pathway [44,45], while AKT upregulates Notch1 via vascular endothelial growth factor [46]. The AKT signaling pathway and its interaction with Notch1 interaction maintain the survival of T lymphoproliferative tumors [47]. Notch1 also phosphorylates ERK1/2 and promotes tumor cell proliferation, and the ERK signaling pathway also promotes the Notch1 signaling pathway [48,49]. GSI-I modulates Notch1-mediated induction of target genes through blocking proteolytic activation of Notch1 [50].