Stimuli-Responsive Conformational Transformation of Peptides for Tunable Cytotoxicity.

The stimuli-responsive conformational transformation of peptides possessing a constrained form triggered by specific biological microenvironment would provide an effective strategy for the development of highly specific peptide therapeutics. Here, we developed a peptide containing a cytotoxic helical KLA sequence with therapeutic specificity through the use of stimuli-responsive conformational transformation. The KLA peptide is modified to form a cyclic structure to allow for constrained helicity that confers low cytotoxicity. The modified KLA peptide is electrostatically complexed to hyaluronic acid to facilitate enhanced endocytosis into the cancer cells. After endocytosis, the peptide is released from the complex into the cellular cytoplasm by hyaluronidases on the surface of the cellular membrane. Specific intracellular stimuli then trigger the release of the strain that suppresses peptide helicity, and the inherent helical conformation of the KLA peptide is restored. Therefore, the stimuli-responsive conformational transformation of a peptide from low to high helicity selectively induces cell death by disruption of the plasma and mitochondrial membrane.

Quinacrine-Mediated Inhibition of Nrf2 Reverses Hypoxia-Induced 5-Fluorouracil Resistance in Colorectal Cancer.

5-Fluorouracil (5-FU) is an important chemotherapeutic agent for the systemic treatment of colorectal cancer (CRC), but its effectiveness against CRC is limited by increased 5-FU resistance caused by the hypoxic tumor microenvironment. The purpose of our study was to assess the feasibility of using quinacrine (QC) to increase the efficacy of 5-FU against CRC cells under hypoxic conditions. QC reversed the resistance to 5-FU induced by hypoxia in CRC cell lines, as determined using ATP-Glo cell viability assays and clonogenic survival assays. Treatment of cells with 5-FU under hypoxic conditions had no effect on the expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a regulator of cellular resistance to oxidative stress, whereas treatment with QC alone or in combination with 5-FU reduced Nrf2 expression in all CRC cell lines tested. Overexpression of Nrf2 effectively prevented the increase in the number of DNA double-strand breaks induced by QC alone or in combination with 5-FU. siRNA-mediated c-Jun N-terminal kinase-1 (JNK1) knockdown inhibited the QC-mediated Nrf2 degradation in CRC cells under hypoxic conditions. The treatment of CRC xenografts in mice with the combination of QC and 5-FU was more effective in suppressing tumor growth than QC or 5-FU alone. QC increases the susceptibility of CRC cells to 5-FU under hypoxic conditions by enhancing JNK1-dependent Nrf2 degradation.

Combination treatment with docetaxel and histone deacetylase inhibitors downregulates androgen receptor signaling in castration-resistant prostate cancer.

Backgrounds Since most patients with castration-resistant prostate cancer (CRPC) develop resistance to its standard therapy docetaxel, many studies have attempted to identify novel combination treatment to meet the large clinical unmet need. In this study, we examined whether histone deacetylase inhibitors (HDACIs) enhanced the effect of docetaxel on AR signaling in CRPC cells harboring AR and its splice variants. Methods HDACIs (vorinostat and CG200745) were tested for their ability to enhance the effects of docetaxel on cell viability and inhibition of AR signaling in CRPC 22Rv1 and VCaP cells by using CellTiter-Glo™ Luminescent cell viability assay, synergy index analysis and Western blotting. The nuclear localization of AR was examined via immunocytochemical staining in 22Rv1 cells and primary tumor cells from a patient with CRPC. Results Combination treatment with HDACIs (vorinostat or CG200745) and docetaxel synergistically inhibited the growth of 22Rv1 and VCaP cells. Consistently, the combination treatment decreased the levels of full-length AR (AR-FL), AR splice variants (AR-Vs), prostate-specific antigen (PSA), and anti-apoptotic Bcl-2 proteins more efficiently compared with docetaxel or vorinostat alone. Moreover, the combination treatment accelerated the acetylation and bundling of tubulin, which significantly inhibited the nuclear accumulation of AR in 22Rv1 cells. The cytoplasmic colocalization of AR-FL and AR-V7 with microtubule bundles increased after combination treatment in primary tumor cells from a patient with CRPC. Conclusions The results suggested that docetaxel, in combination with HDACIs, suppressed the expression and nuclear translocation of AR-FL and AR-Vs and showed synergistic anti-proliferative effect in CRPC cells. This combination therapy may be useful for the treatment of patients with CRPC.

Downregulation of androgen receptors by NaAsO2 via inhibition of AKT-NF-κB and HSP90 in castration resistant prostate cancer.

BACKGROUND: Androgen and androgen receptor (AR) play essential roles in the development and maintenance of prostate cancer. The recently identified AR splice variants (AR-Vs) have been considered as a plausible mechanism for the primary resistance against androgen deprivation therapy (ADT) in castration-resistant prostate cancer (CRPC). Sodium meta-arsenite (NaAsO2 ; KML001; Kominox), a trivalent arsenical, is an orally bioavailable and water soluble, which is currently in phase I/II clinical trials for the treatment of prostate cancer. It has a potent anti-cancer effect on prostate cancer cells and xenografts. The aim of this study was to examine the effect of NaAsO2 on AR signaling in LNCaP and 22Rv1 CRPC cells. METHODS: We used hormone-sensitive LNCaP cells, hormone-insensitive 22Rv1 cells, and CRPC patient-derived primary cells. We analyzed anti-cancer effect of NaAsO2 using real-time quantitative reverse transcription-PCR, Western blotting, immunofluorescence staining and CellTiter Glo® luminescent assay. Statistical evaluation of the results was performed by one-way ANOVA. RESULTS: NaAsO2 significantly reduced the translocation of AR and AR-Vs to the nucleus as well as their level in LNCaP and 22Rv1 cells. Besides, the level of the prostate-specific antigen (PSA), downstream target gene of AR, was also decreased. This compound was also an effective modulator of AKT-dependent NF-κB activation which regulates AR. NaAsO2 significantly inhibited phosphorylation of AKT and expression and nuclear translocation of NF-κB. We then investigated the effect of NaAsO2 on AR stabilization. NaAsO2 promoted HSP90 acetylation by down-regulating HDAC6, which reduces the stability of AR in prostate cancer cells. CONCLUSIONS: Here, we show that NaAsO2 disrupts AR signaling at multiple levels by affecting AR expression, stability, and degradation in primary tumor cell cultures from prostate cancer patients as well as CRPC cell lines. These results suggest that NaAsO2 could be a novel therapeutics for prostate cancer.

Mesoporous Silica Nanocarriers with Cyclic Peptide Gatekeeper: Specific Targeting of Aminopeptidase†N and Triggered Drug Release by Stimuli-Responsive Conformational Transformation.

Utilizing stimuli-responsive conformational transformation of a cyclic peptide as a gatekeeper for mesoporous nanocarriers has several advantages such as facile introduction of targeting capabilities, low enzymatic degradation during blood circulation and enhanced specific binding to selected cells. In this report, a Asn-Gly-Arg (NGR)-containing dual-functional cyclic peptide gatekeeper on the surface of mesoporous nanocarrier is prepared not only for active targeting of the aminopeptidase N (APN) expressed on cancer cells but also stimuli-responsive intracellular drug release triggered by a glutathione (GSH)-induced conformational transformation of the peptide gatekeeper. The peptide gatekeeper on the surface of nanocarriers exhibits on-off gatekeeping by conformational transformation triggered by intracellular glutathione of the cancer cells. H1299 cells (high APN expression) showed greater uptake of the nanocarrier by endocytosis and higher apoptosis than A549 cells (low APN expression).

NQO1 regulates cell cycle progression at the G2/M phase.

Rationale: Overexpression of NAD(P)H:quinone oxidoreductase 1 (NQO1) is associated with tumor cell proliferation and growth in several human cancer types. However, the molecular mechanisms underlying the activity of NQO1 in cell cycle progression are currently unclear. Here, we report a novel function of NQO1 in modulation of the cell cycle regulator, cyclin-dependent kinase subunit-1 (CKS1), at the G2/M phase through effects on the stability of c­Fos. Methods: The roles of the NQO1/c-Fos/CKS1 signaling pathway in cell cycle progression were analyzed in cancer cells using synchronization of the cell cycle and flow cytometry. The mechanisms underlying NQO1/c-Fos/CKS1-mediated regulation of cell cycle progression in cancer cells were studied using siRNA approaches, overexpression systems, reporter assays, co-immunoprecipitation, pull-down assays, microarray analysis, and CDK1 kinase assays. In addition, publicly available data sets and immunohistochemistry were used to investigate the correlation between NQO1 expression levels and clinicopathological features in cancer patients. Results: Our results suggest that NQO1 directly interacts with the unstructured DNA-binding domain of c-Fos, which has been implicated in cancer proliferation, differentiation, and development as well as patient survival, and inhibits its proteasome-mediated degradation, thereby inducing CKS1 expression and regulation of cell cycle progression at the G2/M phase. Notably, a NQO1 deficiency in human cancer cell lines led to suppression of c-Fos-mediated CKS1 expression and cell cycle progression. Consistent with this, high NQO1 expression was correlated with increased CKS1 and poor prognosis in cancer patients. Conclusions: Collectively, our results support a novel regulatory role of NQO1 in the mechanism of cell cycle progression at the G2/M phase in cancer through effects on c­Fos/CKS1 signaling.

Tuning of Peptide Cytotoxicity with Cell Penetrating Motif Activatable by Matrix Metalloproteinase-2.

Although diverse cell penetrating motifs not only from naturally occurring proteins but also from synthetic peptides have been discovered and developed, the selectivity of cargo delivery connected to these motifs into the desired target cells is generally low. Here, we demonstrate the selective cytotoxicity tuning of an anticancer KLA peptide with a cell penetrating motif activatable by matrix metalloproteinase-2 (MMP2). The anionic masking sequence introduced at the end of the KLA peptide through an MMP2-cleavable linker is selectively cleaved by MMP2 and the cationic cell penetrating motif is activated. Upon treatment of the peptide to H1299 cells (high MMP2 level), it is selectively internalized into the cells by MMP2, which consequently induces membrane disruption and cell death. In contrast, the peptide shows negligible cytotoxicity toward A549 cancer cells with low MMP2 levels. Furthermore, the selective therapeutic efficacy of the peptide induced by MMP2 is also corroborated using in vivo study.

Multi-Layer Nanofibrous PCL Scaffold-Based Colon Cancer Cell Cultures to Mimic Hypoxic Tumor Microenvironment for Bioassay.

Three-dimensional (3D) cancer cell culture systems have been developed to aid the study of molecular mechanisms in cancer development, identify therapeutic targets, and test drug candidates. In this study, we developed a strategy for mimicking the hypoxic tumor microenvironment in a 3D cancer cell culture system using multi-layer, nanofibrous poly(ε-caprolactone) (PCL) scaffold (pNFS)-based cancer cell cultures. We found that human colon cancer cells infiltrated pNFS within 3 days and could be cultured three-dimensionally within the NFS. When incubated in four stacks of 30 µm-thick pNFS for 3 days, colon cancer cells in layer three showed partially reduced entry into the S phase, whereas those in layer four, located farthest from the media, showed a marked reduction in S-phase entry. As a consequence, cells in layer four exhibited hypoxia-induced disorganization of F-actin on day 3, and those in layers three and four showed an increase in the expression of the hypoxia-induced transcription factor HIF-1α and its target genes, Glut1, CA9, VEGF, and LDHA. Consistent with these results, doxorubicin- and ionizing radiation-induced cell death was reduced in colon cancer cells cultured in layers three and four. These results suggest that pNFS-based multi-layer colon cancer cell cultures mimic the hypoxic tumor microenvironment and are useful for bioassays.

Quasi-Irreversible Inhibition of CYP2D6 by Berberine.

In our previous study, Hwang-Ryun-Hae-Dok-Tang, which contains berberine (BBR) as a main active ingredient, inhibited cytochrome P450 (CYP) 2D6 in a quasi-irreversible manner. However, no information is available on the detailed mechanism of BBR-induced CYP2D6 inhibition. Thus, the present study aimed to characterize the inhibition mode and kinetics of BBR and its analogues against CYP2D6 using pooled human liver microsomes (HLM). BBR exhibited selective quasi-irreversible inhibition of CYP2D6 with inactivation rate constant (kinact) of 0.025 min-1, inhibition constant (KI) of 4.29 µM, and kinact/KI of 5.83 mL/min/µmol. In pooled HLM, BBR was metabolized to thalifendine (TFD), demethyleneberberine (DMB), M1 (proposed as demethylene-TFD), and to a lesser extent berberrubine (BRB), showing moderate metabolic stability with a half-life of 35.4 min and a microsomal intrinsic clearance of 7.82 µL/min/mg protein. However, unlike BBR, those metabolites (i.e., TFD, DMB, and BRB) were neither selective nor potent inhibitors of CYP2D6, based on comparison of half-maximal inhibitory concentration (IC50). Notably, TFD, but not DMB, exhibited metabolism-dependent CYP2D6 inhibition as in the case of BBR, which suggests that methylenedioxybenzene moiety of BBR may play a critical role in the quasi-irreversible inhibition. Moreover, the metabolic clearance of nebivolol (ß-blocker; CYP2D6 substrate) was reduced in the presence of BBR. The present results warrant further evaluation of BBR-drug interactions in clinical situations.

Stimulus-Induced Conformational Transformation of a Cyclic Peptide for Selective Cell-Targeting On-Off Gatekeeper for Mesoporous Nanocarriers.

αv ß3 Integrin is upregulated on many cancer cells. We designed a dual functional cyclic peptide gatekeeper with a capability of stimuli-responsive conformational transformation which could serve as a selective cell-targeting on-off gatekeeper for mesoporous nanocarriers. The advantage of employing the motif of stimuli-induced conformational transformation of cyclic peptides is that they could be utilized not only as an on-off gatekeeper for the triggered release of cargo drugs but also as a targeting ligand of the carriers to desired cells with their respective binding receptors. The peptide gatekeepers on the surface of nanocarriers exhibited on-off gatekeeping via conformational transformation triggered by intracellular glutathione levels of the cancer cells. The cyclic RGD sequence of the peptide gatekeepers enhanced the intracellular uptake into tumor cells (A549) and the therapeutic efficacy of the nanocarrier.

Brusatol-Mediated Inhibition of c-Myc Increases HIF-1α Degradation and Causes Cell Death in Colorectal Cancer under Hypoxia.

HIF-1 (hypoxia-inducible factor-1) regulates the expression of ~100 genes involved in angiogenesis, metastasis, tumor growth, chemoresistance and radioresistance, underscoring the growing interest in targeting HIF-1 for cancer control. In the present study, we investigated the molecular mechanisms underlying brusatol-induced HIF-1α degradation and cell death in colorectal cancer under hypoxia (0.5% O2). Under hypoxia, pretreatment of cancer cells with brusatol increased HIF-1α degradation and cancer cell death in a dose-dependent manner. This effect was mediated by activation of prolyl hydroxylases (PHDs), as evidenced by the block of brusatol-induced HIF-1α degradation and cancer cell death by both pharmacological inhibition and siRNA-mediated knockdown of PHDs. In addition, a ferrous iron chelator (2,2'-bypyridyl) blocked brusatol-induced degradation of HIF-1α and cancer cell death in hypoxia by inhibiting PHD activation. We further found that brusatol inhibited c-Myc expression, and showed that overexpression of c-Myc prevented brusatol-induced degradation of HIF-1α and cancer cell death by increasing mitochondrial ROS production and subsequent ROS-mediated transition of ferrous iron to ferric iron. Consistent with these results, treatment of tumor-bearing mice with brusatol significantly suppressed tumor growth by promoting PHD-mediated HIF-1α degradation. Collectively, our results suggest that brusatol-mediated inhibition of c-Myc/ROS signaling pathway increases HIF-1α degradation by promoting PHD activity and induces cell death in colorectal cancer under hypoxia.

BIX-01294 induces autophagy-associated cell death via EHMT2/G9a dysfunction and intracellular reactive oxygen species production.

We screened a chemical library in MCF-7 cells stably expressing green fluorescent protein (GFP)-conjugated microtubule-associated protein 1 light chain 3 (LC3) (GFP-LC3-MCF-7) using cell-based assay, and identified BIX-01294 (BIX), a selective inhibitor of euchromatic histone-lysine N-methyltransferase 2 (EHMT2), as a strong autophagy inducer. BIX enhanced formation of GFP-LC3 puncta, LC3-II, and free GFP, signifying autophagic activation. Inhibition of these phenomena with chloroquine and increasement in punctate dKeima ratio (550/438) signal indicated that BIX activated autophagic flux. BIX-induced cell death was suppressed by the autophagy inhibitor, 3-methyladenine, or siRNA against BECN1 (VPS30/ATG6), ATG5, and ATG7, but not by caspase inhibitors. Moreover, EHMT2 siRNA augmented GFP-LC3 puncta, LC3-II, free GFP, and cell death, implying that inhibition of EHMT2 caused autophagy-mediated cell death. Treatment with EHMT2 siRNA and BIX accumulated intracellular reactive oxygen species (ROS). BIX augmented mitochondrial superoxide via NADPH oxidase activation. In addition, BIX increased hydrogen peroxide and glutathione redox potential in both cytosol and mitochondria. Treatment with N-acetyl-L-cysteine (NAC) or diphenyleneiodonium chloride (DPI) decreased BIX-induced LC3-II, GFP-LC3 puncta, and cell death, indicating that ROS instigated autophagy-dependent cell death triggered by BIX. We observed that BIX potentiated autophagy-dependent and caspase-independent cell death in estrogen receptor (ESR)-negative SKBr3 and ESR-positive MCF-7 breast cancer cells, HCT116 colon cancer cells, and importantly, in primary human breast and colon cancer cells. Together, the results suggest that BIX induces autophagy-dependent cell death via EHMT2 dysfunction and intracellular ROS accumulation in breast and colon cancer cells, therefore EHMT2 inhibition can be an effective therapeutic strategy for cancer treatment.