Potent antitumor agent proteasome inhibitors: a novel trigger for Bcl2 phosphorylation to induce apoptosis

A versatile nanoplatform for synergistic combination therapy to treat human esophageal cancer

One of the major goals of precision oncology is to promote combination therapy to improve efficacy and reduce side effects of anti-cancer drugs based on their molecular mechanisms. In this study, we aimed to develop and validate new nanoformulations of docetaxel (DTX) and bortezomib (BTZ) for targeted combination therapy to treat human esophageal cancer. By leveraging our versatile disulfide cross-linked micelles (DCMs) platform, we developed nanoformulations of DTX and BTZ (named DTX-DCMs and BTZ-DCMs). Their physical properties were characterized; their anti-cancer efficacies and mechanisms of action were investigated in a human esophageal cancer cell line in vitro. Furthermore, the in vitro anti-tumor activities of combination therapies (concurrent drug treatment, sequential drug treatment, and treatment using different ratios of the drugs) were examined in comparison with the single drug treatment and free drug strategies. These drug-loaded nanoparticles were spherical in shape and relatively small in size of approximately 20-22 nm. The entrapment efficiencies of DTX and BTZ into nanoparticles were 82.4% and 84.1%, respectively. The drug release rates of DTX-DCMs and BTZ-DCMs were sustained, and greatly increased in the presence of GSH. These nanodrugs were effectively internalized by KYSE30 esophageal cancer cells, and dose-dependently induced cell apoptosis. We further revealed a strong synergistic effect between DTX-DCMs and BTZ-DCMs against KYSE30 esophageal cancer cells. Sequential combination therapy with DTX-DCMs followed by BTZ-DCMs exhibited the best anti-tumor efficacy in vitro. This study demonstrates that DTX and BTZ could be successfully nanoformulated into disulfide cross-linked micelles. The nanoformulations of DTX and BTZ demonstrate an immense potential for synergistic combination therapy to treat human esophageal cancer.

Inhibition of constitutively activated nuclear factor-κB radiosensitizes human melanoma cells

Melanoma tumors and cultured cell lines are relatively resistant to the cytotoxic effects of ionizing radiation, thereby limiting the use of radiotherapy for the clinical treatment of melanoma. New strategies for sensitizing melanoma cells therefore deserve examination. In an attempt to identify and target signaling pathways that contribute to radioresistance, we investigated the role of nuclear factor-κB (NF-κB), a transcription factor known to inhibit apoptosis induced by a variety of stimuli and promote radioresistance. Two human metastatic melanoma cell lines, A375 and MeWo, were used to examine the radiosensitizing effects of inhibitors of the NF-κB pathway. Nuclear extracts from these cell lines were tested for active NF-κB using the electrophoretic mobility shift assay. Both melanoma cell lines had constitutively activated NF-κB as observed by electrophoretic mobility shift assay. In an attempt to reverse NF-κB activity, cells were treated either with vehicle alone (DMSO) or with a proteasome inhibitor Z-Leu-Leu-Leu-H (MG132; 10 μmol/L for 2 hours prior to irradiation) that inhibited both constitutive and radiation-induced NF-κB activity. The clonogenic cell survival assay showed that pretreatment with MG132 enhanced tumor cell radiosensitivity with the survival factor at 2 Gy being reduced from 48 ± 0.8% and 48 ± 1.6% in vehicle-treated cells to 27.7 ± 0.32% and 34.3 ± 0.7% in MG132-treated MeWo and A375 cells, respectively. To test the role of NF-κB in radioresistance more directly, MeWo cells were stably transfected with a dominant-negative mutant IκBα construct, which led to the inhibition of both constitutive and radiation-induced NF-κB activity. A modest restoration of radiosensitivity was also observed in the stably transfected MeWo cells with survival factor at 2 Gy values being reduced from 47 ± 0.8% in parental MeWo cells to 32.9 ± 0.7% in stable transfectants. Because constitutively activated mitogen-activated protein kinase kinase (MEK) pathway has been shown to lead to activated NF-κB, we wanted to determine the relative contribution of activated MEK in the human melanoma cells. To test this, MeWo and A375 melanoma cells were exposed to the MEK inhibitor PD184352. Treatment with PD184352 partially reversed NF-κB activity but did not impart radiation sensitivity to these cells. Our results indicate that activated NF-κB may be one of the pathways responsible for the radioresistance of melanoma cells and that strategies for inhibiting its influence may be useful in restoring the radioresponse of melanomas.

Proteasome inhibitors stimulate interleukin-8 expression via Ras and apoptosis signal-regulating kinase-dependent extracellular signal-related kinase and c-Jun N-terminal kinase activation

In this study, we investigated the effects of proteasome inhibibors (MG132 and lactacystin) on interleukin (IL)-8 induction. In human epithelial A549 cells, MG132 and lactacystin induced IL-8 release within the range of 0.1-30 microM. The effect of MG132 resulted from IL-8 gene transcription and was blocked by PD 98059, but was unaffected by GF109203X, Ro 31-8220, or SB 203580. Mutational analysis of the 5' flanking region of the IL-8 gene revealed that activator protein (AP)-1-binding element, but not that element responsive to nuclear factor (NF)-IL-6 or NF-kappaB, was necessary for MG132 stimulation. Consistent with this, MG132 and lactacystin increased the DNA-binding and reporter activities of AP-1, but reduced cytokine-elicited kappaB activation. Moreover, AP-1 stimulation was associated with increased extracellular signal-related kinase (ERK), mitogen-activated protein/ERK kinase (MEK), and c-Jun N-terminal kinase (JNK) phosphorylation, whereas IL-8 activity was sensitive to the dominant-negative mutants of JNK1, JNK2, SEK, ASK, ERK2, and Ras, but not those of MEKK1, TAK, and p38 mitogen-activated protein kinase. In addition, activations of the IL-8 gene and AP-1 by MG132 and lactacystin were inhibited by GSH and NAC. Herein we present a novel action of proteasome inhibitors, possibly through ROS production, of targeting the upstream signaling molecules, ERK and JNK, which leads to AP-1 activation and IL-8 gene expression.