Noxa/Mcl-1 balance influences the effect of the proteasome inhibitor MG-132 in combination with anticancer agents in pancreatic cancer cell lines

MUS81 cleaves TOP1-derived lesions and other DNA-protein cross-links

BACKGROUND

DNA-protein cross-links (DPCs) are one of the most deleterious DNA lesions, originating from various sources, including enzymatic activity. For instance, topoisomerases, which play a fundamental role in DNA metabolic processes such as replication and transcription, can be trapped and remain covalently bound to DNA in the presence of poisons or nearby DNA damage. Given the complexity of individual DPCs, numerous repair pathways have been described. The protein tyrosyl-DNA phosphodiesterase 1 (Tdp1) has been demonstrated to be responsible for removing topoisomerase 1 (Top1). Nevertheless, studies in budding yeast have indicated that alternative pathways involving Mus81, a structure-specific DNA endonuclease, could also remove Top1 and other DPCs.

RESULTS

This study shows that MUS81 can efficiently cleave various DNA substrates modified by fluorescein, streptavidin or proteolytically processed topoisomerase. Furthermore, the inability of MUS81 to cleave substrates bearing native TOP1 suggests that TOP1 must be either dislodged or partially degraded prior to MUS81 cleavage. We demonstrated that MUS81 could cleave a model DPC in nuclear extracts and that depletion of TDP1 in MUS81-KO cells induces sensitivity to the TOP1 poison camptothecin (CPT) and affects cell proliferation. This sensitivity is only partially suppressed by TOP1 depletion, indicating that other DPCs might require the MUS81 activity for cell proliferation.

CONCLUSIONS

Our data indicate that MUS81 and TDP1 play independent roles in the repair of CPT-induced lesions, thus representing new therapeutic targets for cancer cell sensitisation in combination with TOP1 inhibitors.

Carfilzomib and Paclitaxel Co-Loaded Protein Nanoparticles an Effective Therapy Against Pancreatic Adenocarcinomas

Purpose

Therapeutic efficacy of pancreatic adenocarcinomas (PACs) with combined therapy of carfilzomib (CFZ) and paclitaxel (PTX) co-loaded in human serum albumin (HSA) nanoparticles (NPs) was examined.

Methods

CFZ and PTX were encapsulated individually or combined into HSA NPs by a simple reverse self-assembly method developed to achieve an optimal combination ratio for synergistic therapy. CFZ or/and PTX loaded HSA nanoparticles were physically characterized and the evaluation of combination index, drug release, pharmacokinetic, anti-tumor, and biodistribution studies were conducted.

Results

All resultant drug-loaded HSA NPs were spherical with a particle size of <150 nm and a zeta potential of −21.1~−23.0 mV. Drug loading rates and entrapment efficiencies were 9.1%~10.1% and 90.7%~97.1%, respectively. CFZ and PTX demonstrated synergistic effects in an MIA PaCa-2 cytotoxicity at a 1:2 ratio (CI₅₀ were 0.01~0.25). In vitro dissolution revealed that the CFZ/PTX ratio released from the co-loaded HSA NPs (CFZ/PTX/HSA NPs) was about 1.77~2.08, which conformed to the designated loaded ratio. In vivo evaluation showed that the combined therapy of CFZ and PTX at a 1:2 ratio co-loaded in HSA NPs (CFZ/PTX/HSA NPs) demonstrated optimal synergistic improvement of the growth inhibition of MIA PaCa-2 cells with less systematic toxicity, even though the pharmacokinetic profiles observed did not show obvious beneficial and their biodistributions in tumors were found to be smaller.

Conclusion

The one-pot reverse assembly method developed was environmentally friendly and capable of co-loading an optimal combination ratio of two chemodrugs into HSA NPs for synergistic therapy.

Inhibition of Autophagy Enhances the Antitumor Effect of Thioridazine in Acute Lymphoblastic Leukemia Cells

Acute lymphoblastic leukemia (ALL) is an aggressive malignant disorder of lymphoid progenitor cells that affects children and adults. Despite the high cure rates, drug resistance still remains a significant clinical problem, which stimulates the development of new therapeutic strategies and drugs to improve the disease outcome. Antipsychotic phenothiazines have emerged as potential candidates to be repositioned as antitumor drugs. It was previously shown that the anti-histaminic phenothiazine derivative promethazine induced autophagy-associated cell death in chronic myeloid leukemia cells, although autophagy can act as a "double-edged sword" contributing to cell survival or cell death. Here we evaluated the role of autophagy in thioridazine (TR)-induced cell death in the human ALL model. TR induced apoptosis in ALL Jurkat cells and it was not cytotoxic to normal peripheral mononuclear blood cells. TR promoted the activation of caspase-8 and -3, which was associated with increased NOXA/MCL-1 ratio and autophagy triggering. AMPK/PI3K/AKT/mTOR and MAPK/ERK pathways are involved in TR-induced cell death. The inhibition of the autophagic process enhanced the cytotoxicity of TR in Jurkat cells, highlighting autophagy as a targetable process for drug development purposes in ALL.

Proteostasis Dysregulation in Pancreatic Cancer

The most common form of pancreatic cancer, pancreatic ductal adenocarcinoma (PDAC), has a dismal 5-year survival rate of less than 5%. Radical surgical resection, in combination with adjuvant chemotherapy, provides the best option for long-term patient survival. However, only approximately 20% of patients are resectable at the time of diagnosis, due to locally advanced or metastatic disease. There is an urgent need for the identification of new, specific, and more sensitive biomarkers for diagnosis, prognosis, and prediction to improve the treatment options for pancreatic cancer patients. Dysregulation of proteostasis is linked to many pathophysiological conditions, including various types of cancer. In this review, we report on findings relating to the main cellular protein degradation systems, the ubiquitin-proteasome system (UPS) and autophagy, in pancreatic cancer. The expression of several components of the proteolytic network, including E3 ubiquitin-ligases and deubiquitinating enzymes, are dysregulated in PDAC, which accounts for approximately 90% of all pancreatic malignancies. In the future, a deeper understanding of the emerging role of proteostasis in pancreatic cancer has the potential to provide clinically relevant biomarkers and new strategies for combinatorial therapeutic options to better help treat the patients.

MG-132 treatment promotes TRAIL-mediated apoptosis in SEB-1 sebocytes

AIMS

This study aimed to identify the mechanism of how MG-132 stimulates cell death in SEB-1 sebocytes.

MATERIALS AND METHODS

TUNEL staining and annexin-FITC/PI flow cytometry were utilized to examine the apoptotic cell number of SEB-1 sebocytes and HaCaT keratinocytes upon MG-132 and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) treatment. MTT assay and CCK-8 assay monitored the proliferative rate and viability of both cell lines with different treatment. Western blotting (WB) and qPCR were performed to detect the expression of TRAIL and members of Bcl-2 family at protein and gene level. Additionally, RNA interfering was used to knockdown the mRNA transcription of TRAIL and BIK gene.

KEY FINDINGS

MG-132 treatment enhanced cell death in SEB-1 sebocytes but not in HaCaT keratinocytes. Meanwhile, TRAIL concentrations in SEB-1 sebocytes treated with MG-132 were markedly elevated. Furthermore, treatment with TRAIL or the TRAIL receptor-specific monoclonal antibody AY4 at various doses stimulated cell death in SEB-1 sebocytes in a time- and dose-dependent manner. Silencing of TRAIL restored the cell viability of SEB-1 cells to a normal level after MG-132 treatment. Combined treatment of SEB-1 sebocytes with TRAIL and MG-132 synergistically triggered cell death, suppressed cell proliferation and survival, and promoted BIK expression. Furthermore, BCL2 Interacting Killer (BIK) knockdown via RNA interference participated in the recovery of cell survival reduced by treatment with TRAIL and MG-132.

SIGNIFICANCE

These findings suggest that treatment with the selective proteasome suppressor MG-132 and TRAIL induces cell death in sebocytes through upregulation of BIK, a member of the Bcl-2 family.

Positioning of proteasome inhibitors in therapy of solid malignancies

Targeting of the protein degradation pathway, in particular, the ubiquitin-proteasome system, has emerged as an attractive novel cancer chemotherapeutic modality. Although proteasome inhibitors have been most successfully applied in the treatment of hematological malignancies, they also received continuing interest for the treatment of solid tumors. In this review, we summarize the current positioning of proteasome inhibitors in the treatment of common solid malignancies (e.g., lung, colon, pancreas, breast, and head and neck cancer), addressing topics of their mechanism(s) of action, predictive factors and molecular mechanisms of resistance.

The cyclin-dependent kinase inhibitor SNS-032 induces apoptosis in breast cancer cells via depletion of Mcl-1 and X-linked inhibitor of apoptosis protein and displays antitumor activity in vivo

Inhibitors of cyclin-dependent kinases (Cdks) have been reported to have activities in many types of cancer cells by inhibiting Cdk7 and Cdk9, which control transcription. SNS-032 is a potent and selective inhibitor of Cdk2, Cdk7 and Cdk9 and has emerged in clinical trials. Here, we examined the viability of MCF-7 and MDA-MB-435 breast cancer cells in the presence of SNS-032 and observed a dose-dependent inhibition of cellular proliferation in both cell lines. SNS-032 had a direct apoptosis-inducing effect through both the extrinsic and intrinsic apoptotic pathways in breast cancer cells as shown by a dose-dependent increase in Annexin V-positive cells and terminal deoxynucleotidyl transferase-mediated dUTP nick?end labeling (TUNEL)-positive cells, as well as activation of caspase-8, -9 and poly(ADP-ribose) polymerase (PARP). At the molecular level, SNS-032 induced a marked dephosphorylation of serine 2 and 5 of RNA polymerase (RNA Pol) II and blocked RNA synthesis. Consistent with the inherently rapid turnover rates of their transcripts and proteins, the anti-apoptotic proteins Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP) were rapidly reduced on exposure to SNS-032. Our results also indicated that SNS-032 suppressed the growth of breast cancer xenografts in mice. These data demonstrate that the use of SNS-032 may be a rational and novel therapeutic strategy for human breast cancer and warrants further clinical investigation.