Pentoxifylline triggers autophagy via ER stress response that interferes with Pentoxifylline induced apoptosis in human melanoma cells

Pentoxifylline and Norcantharidin Modify p62 Expression in 2D and 3D Cultures of B16F1 Cells

Three-dimensional cell cultures have improved the evaluation of drugs for cancer therapy, due to their high similarity to solid tumors. In melanoma, autophagy appears to show a dual role depending on the progression of the disease. p62 protein has been proposed for the evaluation of autophagic flux since its expression is an indicator of the state of autophagy. Pentoxifylline (PTX) and Norcantharidin (NCTD) are drugs that have been shown to possess anticancer effects. In this work, we used B16F1 mouse melanoma cells in two-dimensional (2D) monolayer cultures and three-dimensional (3D) spheroids to test the effect of PTX and NCTD over the p62 expression. We analyzed the effect on p62 expression through Western blot and immunofluorescence assays. Our results indicate that PTX decreases p62 expression in both cell culture models, while Norcantharidin increases its expression in 3D cultures at 24 h. Therefore, these drugs could have a potential therapeutic use for the regulation of autophagy in melanoma, depending on the state of evolution of the disease.

Tumor-Infiltrating iNKT Cells Activated through c-Kit/Sca-1 Are Induced by Pentoxifylline, Norcantharidin, and Their Mixtures for Killing Murine Melanoma Cells

The involvement of NK and other cytotoxic cells is considered the first defense line against cancer. However, a significant lack of information prevails on the possible roles played by factors considered characteristic of primitive cells, such as c-kit and Sca-1, in activating these cells, particularly in melanoma models subjected to treatments with substances under investigation, such as the case of norcantharidin. In this study, B16F1 murine melanoma cells were used to induce tumors in DBA/2 mice, estimating the proportions of NK and iNKT cells; the presence of activation (CD107a+) and primitive/activation (c-kit+/Lya6A+) markers and some tumor parameters, such as the presence of mitotic bodies, nuclear factor area, NK and iNKT cell infiltration in the tumor, infiltrated tumor area, and infiltrating lymphocyte count at 10x and 40x in specimens treated with pentoxifylline, norcantharidin, and the combination of both drugs. Possible correlations were estimated with Pearson's correlation analysis. It should be noted that, despite having demonstrated multiple correlations, immaturity/activation markers were related to these cells' activation. At the tumor site, iNKT cells are the ones that exert the cytotoxic potential on tumor cells, but they are confined to specific sites in the tumor. Due to the higher number of interactions of natural killer cells with tumor cells, it is concluded that the most effective treatment was PTX at 60 mg/kg + NCTD at 0.75 mg/kg.

A Naturally Derived Watercress Flower-Based Phenethyl Isothiocyanate-Enriched Extract Induces the Activation of Intrinsic Apoptosis via Subcellular Ultrastructural and Ca2+ Efflux Alterations in an In Vitro Model of Human Malignant Melanoma

The aim of the current study was to (i) extract isolated fractions of watercress flowers enriched in polyphenols, phenethyl isothiocyanate and glucosinolates and (ii) characterize the anticancer mode of action of non-lethal, sub-lethal and lethal concentrations of the most potent extract fraction in primary (A375) and metastatic (COLO-679) melanoma cells as well as non-tumorigenic immortalized keratinocyte (HaCaT) cells. Cytotoxicity was assessed via the Alamar Blue assay, whereas ultrastructural alterations in mitochondria and the endoplasmic reticulum were determined via transmission electron microscopy. Mitochondrial membrane depolarization was determined using Mito-MP dye, whereas apoptosis was evaluated through the activation of caspases-3, -8 and -9. Among all extract fractions, the phenethyl isothiocyanate-enriched one (PhEF) possessed significant cytotoxicity against A375 and COLO-679 cells, while HaCaT cells remained relatively resistant at sub-lethal and lethal concentrations. Additionally, ultrastructural subcellular alterations associated with apoptosis were observed by means of increased mitochondrial area and perimeter, decreased cristae density and a shorter distance of the endoplasmic reticulum to the mitochondria, all taking place during "early" time points (2-4 h) of exposure. Moreover, PhEF induced mitochondrial membrane depolarization associated with "late" time points (24 h) of exposure, thereby leading to the activation of intrinsic apoptosis. Finally, the inhibition of cytosolic Ca2+ efflux reduced levels of caspases-9 and -3 activity, suggesting the involvement of Ca2+ efflux in modulating the activation of intrinsic apoptosis. To conclude, our data demonstrate an association of "early" ultrastructural alterations in mitochondria and the endoplasmic reticulum with the "late" induction of intrinsic apoptosis via the modulation of Ca2+ efflux.

Perspectives of PDE inhibitor on treating idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease (ILD) without an identifiable cause. If not treated after diagnosis, the average life expectancy is 3-5 years. Currently approved drugs for the treatment of IPF are Pirfenidone and Nintedanib, as antifibrotic drugs, which can reduce the decline rate of forced vital capacity (FVC) and reduce the risk of acute exacerbation of IPF. However these drugs can not relieve the symptoms associated with IPF, nor improve the overall survival rate of IPF patients. We need to develop new, safe and effective drugs to treat pulmonary fibrosis. Previous studies have shown that cyclic nucleotides participate in the pathway and play an essential role in the process of pulmonary fibrosis. Phosphodiesterase (PDEs) is involved in cyclic nucleotide metabolism, so PDE inhibitors are candidates for pulmonary fibrosis. This paper reviews the research progress of PDE inhibitors related to pulmonary fibrosis, so as to provide ideas for the development of anti-pulmonary fibrosis drugs.

DNA-Unresponsive Platinum(II) Complex Induces ERS-Mediated Mitophagy in Cancer Cells

Mitophagy is a selective autophagic process that degrades dysfunctional mitochondria. Monofunctional platinum(II) complexes are candidates for anticancer drugs with the potential to circumvent the drug resistance and side effects of cisplatin and its analogues, but their mechanism of action is elusive. Complex Mono-Pt kills cancer cells through a mitophagic pathway. The mechanism involves the stimulation of endoplasmic reticulum stress (ERS) and activation of the unfolded protein response. Mono-Pt severely impairs the structure and function of mitochondria, including disruption of morphological integrity, dissipation of membrane potential, elevation of reactive oxygen species, inhibition of mtDNA transcription, and reduction of adenosine triphosphate (ATP), which ultimately leads to mitophagy. Mono-Pt does not react with nuclear DNA but exhibits potent antiproliferative activity against cancer cells, thus breaking the DNA-binding paradigm and classical structure-activity rules for platinum drugs. The ERS-mediated mitophagy provides an alternative mechanism for platinum complexes, which broadens the way for developing new platinum anticancer drugs.

The Road of Solid Tumor Survival: From Drug-Induced Endoplasmic Reticulum Stress to Drug Resistance

Endoplasmic reticulum stress (ERS), which refers to a series of adaptive responses to the disruption of endoplasmic reticulum (ER) homeostasis, occurs when cells are treated by drugs or undergo microenvironmental changes that cause the accumulation of unfolded/misfolded proteins. ERS is one of the key responses during the drug treatment of solid tumors. Drugs induce ERS by reactive oxygen species (ROS) accumulation and Ca²⁺ overload. The unfolded protein response (UPR) is one of ERS. Studies have indicated that the mechanism of ERS-mediated drug resistance is primarily associated with UPR, which has three main sensors (PERK, IRE1α, and ATF6). ERS-mediated drug resistance in solid tumor cells is both intrinsic and extrinsic. Intrinsic ERS in the solid tumor cells, the signal pathway of UPR-mediated drug resistance, includes apoptosis inhibition signal pathway, protective autophagy signal pathway, ABC transporter signal pathway, Wnt/β-Catenin signal pathway, and noncoding RNA. Among them, apoptosis inhibition is one of the major causes of drug resistance. Drugs activate ERS and its downstream antiapoptotic proteins, which leads to drug resistance. Protective autophagy promotes the survival of solid tumor cells by devouring the damaged organelles and other materials and providing new energy for the cells. ERS induces protective autophagy by promoting the expression of autophagy-related genes, such as Beclin-1 and ATG5–ATG12. ABC transporters pump drugs out of the cell, which reduces the drug-induced apoptosis effect and leads to drug resistance. In addition, the Wnt/β-catenin signal pathway is also involved in the drug resistance of solid tumor cells. Furthermore, noncoding RNA regulates the ERS-mediated survival and death of solid tumor cells. Extrinsic ERS in the solid tumor cells, such as ERS in immune cells of the tumor microenvironment (TME), also plays a crucial role in drug resistance by triggering immunosuppression. In immune system cells, ERS in dendritic cells (DCs) and myeloid-derived suppressor cells (MDSCs) influences the antitumor function of normal T cells, which results in immunosuppression. Meanwhile, ERS in T cells can also cause impaired functioning and apoptosis, leading to immunosuppression. In this review, we highlight the core molecular mechanism of drug-induced ERS involved in drug resistance, thereby providing a new strategy for solid tumor treatment.

Pentoxifylline Can Reduce the Inflammation Caused by LPS after Inhibiting Autophagy in RAW264.7 Macrophage Cells

Pentoxifylline (PTX), as a methylxanthine derivative and nonspecific phosphodiesterase inhibitor, has the characteristics of anti-inflammatory and partial inflammatory process inhibition. However, the regulatory effect of PTX on inflammatory cytokines is unclear. Autophagy can regulate the activation of inflammasomes and then inhibit inflammation as previously described. Our study attempts to explore the relationship between autophagy and PTX-mediated regulation of inflammasome suppression. Macrophage-like RAW264.7 cells were studied as the in vitro macrophage model. We investigated the anti-inflammatory effect caused by PTX with time and dose response against the LPS-induced inflammatory factors (TNF-α, IL-1β). Western blot detected the levels of autophagy-related proteins Beclin-1 and LC3, as well as the signal pathways of AMPK and p-AMPK. Fluorescence microscope and transmission electron microscope were used to observe the autophagy bodies in cells influenced by PTX. The autophagy in cells inhibited by PTX exhibited dose- and time-dependent effects, and PTX alleviated LPS-induced inflammation caused by retarded autophagy. Furthermore, in RAW264.7 macrophage cells, our data indicated that AMPK signaling perhaps functioned importantly in repressed autophagy. In addition, in RAW264.7 macrophages, our data suggested that AMPK signaling might play an important role in inhibiting autophagy during the process of PTX ameliorating LPS-mediated inflammation.

Cumingianoside A, a Phyto-Triterpenoid Saponin Inhibits Acquired BRAF Inhibitor Resistant Melanoma Growth via Programmed Cell Death

Mutated proto-oncogene BRAF is a bona fide therapeutic target for melanomas. Regrettably, melanoma acquires resistance to BRAF inhibitors, e.g., vemurafenib (PLX4032) casting doubt on this promising melanoma targeted therapy. In this study, we explored the bioactivity of triterpenoid saponin cumingianoside A (CUMA), isolated from leaves and twigs of Dysoxylum cumingianum against PLX4032-resistant BRAF^{V 600E} mutant melanoma A375-R in vitro and in vivo. Our data show that CUMA treatment inhibited A375-R melanoma cell proliferation in a time- and dose-dependent manner. CUMA also suppressed the activity of CDK1/cyclin B1 complex and led to G₂/M-phase arrest of A375-R cells. Furthermore, CUMA treatment resulted in induction of apoptosis as shown by the increased activation of caspase 3 and caspase 7, and the proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). We also observed that CUMA induced autophagy-like activity in A375-R cells, as shown by the increased expression of autophagy-related genes and increased formation of autophagosomes. Moreover, we found that CUMA treatment induced ER stress response and co-treatment with an ER stress inhibitor (4-PBA) could attenuate apoptosis induced by CUMA. Importantly, orally administered CUMA as a single agent or in combination with PLX4032 exhibited strong tumor growth inhibition in a PLX4032-resistant A375-R xenograft mouse model, and with little toxicity. This is the first report to explore the anti-tumor activity of CUMA in vitro and in vivo mechanistically, and our results imply that this triterpenoid saponin may be suitable for development into an anti-melanoma agent.

Effect of the cross-talk between autophagy and endoplasmic reticulum stress on Mn-induced alpha-synuclein oligomerization

Overexposure to manganese (Mn) has been known to induce alpha-synuclein (α-Syn) oligomerization, which is degraded mainly depending on endoplasmic reticulum stress (ER stress) and autophagy pathways. However, little data reported the cross-talk between ER stress and autophagy on Mn-induced α-Syn oligomerization. To explore the relationship between ER stress and autophagy, we used 4-phenylbutyric acid (4-PBA, the ER stress inhibitor), rapamycin (Rap, autophagy activator) and 3-methyladenine (3-MA, autophagy inhibitor) in mice model of manganism. After 4 weeks of treatment with Mn, both ER stress and autophagy were activated. Exposed to Mn also resulted in α-Syn oligomerization and neuronal cell damage in the brain tissue of mice, which could be relieved by 4-PBA pretreatment. Moreover, when the ER stress was inhibited, the activation of autophagy was also inhibited. Rap pretreatment significantly activated autophagy and decreased α-Syn oligomers. However, 3-MA pretreatment inhibited autophagy resulting in increase of α-Syn oligomers, and compensatorily activated PERK signaling pathway. Our results also demonstrated that the inhibition of autophagy by 3-MA aggravated neuronal cell damage. The findings clearly demonstrated that the cross-talking between autophagy and ER stress might play an important role in the α-Syn oligomerization and neurotoxicity by Mn.

Synergistic promoting effects of pentoxifylline and simvastatin on the apoptosis of triple-negative MDA-MB-231 breast cancer cells

Pentoxifylline (PTX), a xanthine family molecule and simvastatin (SIM), an anti-hypercholesterolemic agent, have recently been considered as sensitizers to chemotherapy and radiotherapy. The present in vitro study evaluated their antitumor synergistic effects on MDA‑MB‑231 breast cancer cells characterized by the triple‑negative phenotype (TNP). The anti-proliferative effects of these two agents were evaluated by MTT and clonogenic assays. Cell cycle progression was examined using propidium iodide staining. Apoptosis was investigated by Annexin V labeling, and by examining caspase 3 activity and DNA fragmentation. Autophagic vesicles and reactive oxygen species (ROS) levels were monitored by flow cytometry. Western blot analysis was performed to evaluate molecular targets. Our results revealed that when used alone, PTX and SIM exerted antitumor effects. Nevertheless, used in combination, the inhibition of cell proliferation was synergistically superior (80% vs 42%) than that observed following treatment with each agent alone after 48 h. PTX alone (0.5 mM) induced both apoptosis (25%) and autophagy (25%); however, when used in combination with SIM (0.5 µM), the balance between these processes was disrupted and the cells underwent apoptosis (>65%) as opposed to autophagy (<13%). This imbalance was associated with an increase in ERK1/2 and AKT activation, but not with an increase in mTOR phosphorylation, and with the suppression of the NF-κB pathway. In addition, in the cells treated with both agents, almost 78% of the cells were arrested at the G0/G1 phase and lost their colony-forming ability (38±5%) compared to the cells treated with PTX alone (115±5%). On the whole, these results suggest that the induction of autophagy may be a protective mechanism preventing MDA‑MB‑231 cancer cell death. The combined use of PTX and SIM may drive dormant autophagic cancer cells to undergo apoptosis and thus this may be a novel treatment strategy for breast cancer characterized by the TNP.

Autophagy: In the cROSshairs of cancer

Two prominent features of tumors that contribute to oncogenic survival signaling are redox disruption, or oxidative stress phenotype, and high autophagy signaling, making both phenomena ideal therapeutic targets. However, the relationship between redox disruption and autophagy signaling is not well characterized and the clinical impact of reactive oxygen species (ROS)-generating chemotherapeutics on autophagy merits immediate attention as autophagy largely contributes to chemotherapeutic resistance. In this commentary we focus on melanoma, using it as an example to provide clarity to current literature regarding the roles of autophagy and redox signaling which can be applicable to initiation and maintenance of most tumor types. Further, we address the crosstalk between ROS and autophagy signaling during pharmacological intervention and cell fate decisions. We attempt to elucidate the role of autophagy in regulating cell fate following treatment with ROS-generating agents in preclinical and clinical settings and discuss the emerging role of autophagy in cell fate decisions and as a cell death mechanism. We also address technical aspects of redox and autophagy evaluation in experimental design and data interpretation. Lastly, we present a provocative view of the clinical relevance, emerging challenges in dual targeting of redox and autophagy pathways for therapy, and the future directions to be addressed in order to advance both basic and translational aspects of this field.

Functional inhibition of Hsp70 by Pifithrin-μ switches Gambogic acid induced caspase dependent cell death to caspase independent cell death in human bladder cancer cells

Heat shock protein-70kDa (Hsp70) is a member of molecular chaperone family, involved in the proper folding of various proteins. Hsp70 is important for tumor cell survival and is also reported to be involved in enhancing the drug resistance of various cancer types. Hsp70 controls apoptosis both upstream and downstream of the mitochondria by regulating the mitochondrial membrane permeabilization (MMP) and apoptosome formation respectively. In the present study, we have elucidated the role of Hsp70 in Gambogic acid (GA) induced apoptosis in bladder cancer cells. We observed that functional inhibition of Hsp70 by Pifithrin-μ switches GA induced caspase dependent (apoptotic) cell death to caspase independent cell death. However, this cell death was not essentially necrotic in nature, as shown by the observations like intact plasma membranes, cytochrome-c release and no significant effect on nuclear condensation/fragmentation. Inhibition of Hsp70 by Pifithrin-μ shows differential effect on MMP. GA induced MMP and cytochrome-c release was inhibited by Pifithrin-μ at 12h but enhanced at 24h. Pifithrin-μ also reverted back GA inhibited autophagy which resulted in the degradation of accumulated ubiquitinated proteins. Our results demonstrate that Hsp70 plays an important role in GA induced apoptosis by regulating caspase activation. Therefore, inhibition of Hsp70 may hamper with the caspase dependent apoptotic pathways induced by most anti-cancer drugs and reduce their efficacy. However, the combination therapy with Pifithrin-μ may be particularly useful in targeting apoptotic resistant cancer cells as Pifithrin-μ may initiate alternative cell death program in these resistant cells.

Pentoxifylline Inhibits WNT Signalling in β-Cateninhigh Patient-Derived Melanoma Cell Populations

Background

The heterogeneity of melanoma needs to be addressed and combination therapies seem to be necessary to overcome intrinsic and acquired resistance to newly developed immunotherapies and targeted therapies. Although the role of WNT/β-catenin pathway in melanoma was early demonstrated, its contribution to the lack of the melanoma patient response to treatment was only recently recognized. Using patient-derived melanoma cell populations, we investigated the influence of pentoxifylline on melanoma cells with either high or low expression of β-catenin.

Findings

Our results indicate that pentoxifylline inhibits the activity of the canonical WNT pathway in melanoma cell populations with high basal activity of this signalling. This is supported by lowered overall activity of transcription factors TCF/LEF and reduced nuclear localisation of active β-catenin. Moreover, treatment of β-catenin^high melanoma cell populations with pentoxifylline induces downregulation of genes that are targets of the WNT/β-catenin pathway including connective tissue growth factor (CTGF) and microphthalmia-associated transcription factor (MITF-M), a melanocyte- and melanoma cell-specific regulator.

Conclusions

These results suggest that pentoxifylline, a drug approved by the FDA in the treatment of peripheral arterial disease, might be tested in a subset of melanoma patients with elevated activity of β-catenin. This pharmaceutical might be tested as an adjuvant drug in combination therapies when the response to immunotherapy is prevented by high activity of the WNT/β-catenin pathway.