Simvastatin protects Sertoli cells against cisplatin cytotoxicity through enhanced gap junction intercellular communication

Simvastatin Enhances the Cytotoxic Effects of Doxorubicin in a Mammary Adenocarcinoma Cell Model by Involving Connexin 43

Gap Junctions channels formed by Connexins (Cx) provide intercellular communication enabling the coordination of cell growth, differentiation, and metabolism, and their reduction has been shown in many tumor types. Expression levels of Cx43, the most extensively studied Gap Junctions forming protein, are reduced or completely absent in breast cancer cells, while their overexpression correlates with increased cellular permeability to anticancer agents and, consequently, reduced resistance to drug treatments. So, drug associations targeting Cx43 are being considered to overcome chemoresistance. Previous studies demonstrated that Simvastatin (Sim) interferes with Cx43 expression and localization, and chemo-sensitizing effects of Sim in several tumor cell lines treated with antineoplastic chemotherapeutics have been shown. This study aimed to evaluate whether Sim cotreatment enhances Doxorubicin-induced cytotoxicity by affecting Cx43 expression and/or phosphorylation, so MCF-7 cells were treated with Sim (10 µM) for 4 h and then coexposed to Sim and Doxorubicin (1 µM) for 20 h. In Sim cotreated cells, increased membrane levels of Cx43 have been shown; moreover, decreased levels of Cx43 phosphorylated on Ser368 and Ser262 residues, involved in channel closure and disruption of cell-cell communication, have been demonstrated in these cells. In Sim cotreated cells increased Doxorubicin uptake and enhanced Doxorubicin-induced cytotoxic effects have been demonstrated together with reduced migratory capacity. Our data support the notion that Sim cotreatment could be a possible strategy to overcome chemoresistance, since the observed increase in Cx43 membrane levels, and the concomitant reduction of Cx43 phosphorylation, could be responsible for increased sensitization of cells to Doxorubicin treatment.

SLFN12 Expression Significantly Effects the Response to Chemotherapy Drugs in Triple-Negative Breast Cancer

BACKGROUND/OBJECTIVES

Schlafen12 (SLFN12) is an intermediate human Schlafen protein shown to correlate with survivability in triple-negative breast cancer (TNBC). SLFN12 causes differential expressions of significant cancer genes, but how they change in response to chemotherapy remains unknown. Our aim is to identify the effect of chemotherapy on genes that improve TNBC outcomes and other SLFN family members following SLFN12 knockout or overexpression.

METHODS

We overexpressed SLFN12 using a lentiviral vector and knocked out SLFN12 (AdvShSLFN12) using a hairpin adenovirus in MDA-MB-231 TNBC cells. Cells were treated with camptothecin, paclitaxel, zoledronic acid, or carboplatin to evaluate the SLFN12 signature cancer genes associated with improved TNBC outcomes using qPCR. Additionally, cells were treated alone and in combination with AdvShSLFN12, IFN-α2 (known SLFN12 stimulator), carboplatin, and paclitaxel. After treatment, the viable cell numbers were analyzed utilizing a colorimetric crystal violet assay for cell viability.

RESULTS

The SLFN family and SLFN12 cancer signature gene mRNA expressions were analyzed by RT-qPCR. Treating SLFN12-overexpressing TNBC cells with chemotherapy agents resulted in the differential expressions of eight cancer-related genes. Notably, GJB3 was downregulated following treatment with each chemotherapeutic drug. Inducing SLFN12 with IFN-α2 resulted in decreased cell viability and increased SLFN12 mRNA levels following treatment with paclitaxel or carboplatin.

CONCLUSIONS

These results suggest that SLFN12 overexpression significantly affects the expressions of genes driving phenotypic changes in response to chemotherapy and influences additional SLFN family members following IFN-α2 treatment. This may contribute to improving the survival of patients with SLFN12 overexpression. Additionally, patient SLFN12 levels can be used as a factor when pursuing personalized chemotherapy treatments.

Beneficial effect of simvastatin on human umbilical vein endothelial cells gap junctions induced by TNF-α

Although simvastatin has been shown to inhibit vascular permeability, which might be amplified via gap junction intercellular communication (GJIC), the underlying mechanism of action remains unclear. In the present study, we investigated the effects and mechanisms of simvastatin on endothelial cells GJIC. Specifically, human umbilical vein endothelial cells (HUVECs) were stimulated with TNF-α (10 ng/mL) alone or in combination with simvastatin (5 µM), and their effects on vascular endothelial cell GJIC tested via the scrape loading/dye transfer (SL/DT) assay. Next, we performed immunofluorescence, real-time PCR and western blot assays to analyze expression of Cx37, Cx40 and Cx43 in HUVECs. Results showed that GJIC activity in HUVECs was markedly elevated in HUVECs treated with TNF-α in combination with simvastatin. In addition, simvastatin treatment significantly upregulated expression of Cx37 and Cx40 but downregulated Cx43 mRNAs and proteins. Taken together, these marked changes indicated that simvastatin exerts its regulatory effects on gap junction function by upregulating Cx37 and Cx40 and downregulating Cx43 expression.

Connexins-Therapeutic Targets in Cancers

Connexins (Cx) are members of a protein family that forms intercellular channels localised in gap junction (GJ) plaques and single transmembrane channels called hemichannels. They participate in intercellular communication or communication between the intracellular and extracellular environments. Connexins affect cell homeostasis, growth and differentiation by enabling the exchange of metabolites or by interfering with various signalling pathways. Alterations in the functionality and the expression of connexins have been linked to the occurrence of many diseases. Connexins have been already linked to cancers, cardiac and brain disorders, chronic lung and kidney conditions and wound healing processes. Connexins have been shown either to suppress cancer tumour growth or to increase tumorigenicity by promoting cancer cell growth, migration and invasiveness. A better understanding of the complexity of cancer biology related to connexins and intercellular communication could result in the design of novel therapeutic strategies. The modulation of connexin expression may be an effective therapeutic approach in some types of cancers. Therefore, one important challenge is the search for mechanisms and new drugs, selectively modulating the expression of various connexin isoforms. We performed a systematic literature search up to February 2020 in the electronic databases PubMed and EMBASE. Our search terms were as follows: connexins, hemichannels, cancer and cancer treatment. This review aims to provide information about the role of connexins and gap junctions in cancer, as well as to discuss possible therapeutic options that are currently being studied.

Connexins in cancer: bridging the gap to the clinic

Gap junctions comprise arrays of intercellular channels formed by connexin proteins and provide for the direct communication between adjacent cells. This type of intercellular communication permits the coordination of cellular activities and plays key roles in the control of cell growth and differentiation and in the maintenance of tissue homoeostasis. After more than 50 years, deciphering the links among connexins, gap junctions and cancer, researchers are now beginning to translate this knowledge to the clinic. The emergence of new strategies for connexin targeting, combined with an improved understanding of the molecular bases underlying the dysregulation of connexins during cancer development, offers novel opportunities for clinical applications. However, different connexin isoforms have diverse channel-dependent and -independent functions that are tissue and stage specific. This can elicit both pro- and anti-tumorigenic effects that engender significant challenges in the path towards personalised medicine. Here, we review the current understanding of the role of connexins and gap junctions in cancer, with particular focus on the recent progress made in determining their prognostic and therapeutic potential.

A novel role of Cx43-composed GJIC in PDT phototoxicity: an implication of Cx43 for the enhancement of PDT efficacy

In spite of initially promising responses, 5-year recurrence after photodynamic therapy (PDT) sustains high level and an increase in PDT effectiveness is needed. It has been demonstrated that gap junctional intercellular communication (GJIC) formed by Connexin (Cx)43 could improve the transfer of "death signal" between cells, thereby causing the enhancement of cytotoxicity of chemotherapeutics and suicide gene therapy. Nevertheless, whether Cx43-composed GJIC has an effect on PDT phototoxicity remains unknown. This study showed that Cx43-formed GJIC could improve PDT phototoxicity to tumor cells in vitro and in vivo. Specifically, Cx43-formed GJIC under the condition of high cellular density could improve PDT phototoxicity in Cx43-transfected HeLa cells and Cx43-expressing U87 glioma cells. This effect was remarkably inhibited when Cx43 was not expressed or Cx43-formed GJ channels were prohibited. Additionally, the presence of Cx43-mediated GJIC could decrease the mean RTV and tumor weights of xenografts after Photofrin-PDT. The improved PDT efficacy by Cx43-composed GJIC was correlated with stress signaling pathways mediated by ROS, calcium and lipid peroxide. The present study demonstrates the presence of Cx43-composed GJIC improves PDT phototoxicity and suggests that therapeutic strategies designed to upregulate the expression of Cx43 or enhance Cx43-mediated GJIC function may increase the sensitivity of malignant cell to PDT, leading to the increment of PDT efficacy. Oppositely, factors that retard Cx43 expression or prohibit the function of Cx43-mediated GJIC may cause insensitivity of malignant cells to PDT, leading to PDT resistance.

Connexins and Pannexins: Important Players in Tumorigenesis, Metastasis and Potential Therapeutics

Since their characterization more than five decades ago, gap junctions and their structural proteins-the connexins-have been associated with cancer cell growth. During that period, the accumulation of data and molecular knowledge about this association revealed an apparent contradictory relationship between them and cancer. It appeared that if gap junctions or connexins can down regulate cancer cell growth they can be also implied in the migration, invasion and metastatic dissemination of cancer cells. Interestingly, in all these situations, connexins seem to be involved through various mechanisms in which they can act either as gap-junctional intercellular communication mediators, modulators of signalling pathways through their interactome, or as hemichannels, which mediate autocrine/paracrine communication. This complex involvement of connexins in cancer progression is even more complicated by the fact that their hemichannel function may overlap with other gap junction-related proteins, the pannexins. Despite this complexity, the possible involvements of connexins and pannexins in cancer progression and the elucidation of the mechanisms they control may lead to use them as new targets to control cancer progression. In this review, the involvements of connexins and pannexins in these different topics (cancer cell growth, invasion/metastasis process, possible cancer therapeutic targets) are discussed.

Evaluation of cebranopadol, a dually acting nociceptin/orphanin FQ and opioid receptor agonist in mouse models of acute, tonic, and chemotherapy-induced neuropathic pain

BACKGROUND

Cebranopadol (a.k.a. GRT-6005) is a dually acting nociceptin/orphanin FQ and opioid receptor agonist that has been recently developed in Phase 2 clinical trials for painful diabetic neuropathy or cancer pain. It also showed analgesic properties in various rat models of pain and had a better safety profile as compared to equi-analgesic doses of morphine. Since antinociceptive properties of cebranopadol have been studied mainly in rat models, in the present study, we assessed analgesic activity of subcutaneous cebranopadol (10 mg/kg) in various mouse pain models.

METHODS

We used models of acute, tonic, and chronic pain induced by thermal and chemical stimuli, with a particular emphasis on pharmacoresistant chronic neuropathic pain evoked by oxaliplatin in which cebranopadol was used alone or in combination with simvastatin.

KEY RESULTS

As shown in the hot plate test, the analgesic activity of cebranopadol developed more slowly as compared to morphine (90-120 min vs. 60 min). Cebranopadol displayed a significant antinociceptive activity in acute pain models, i.e., the hot plate, writhing, and capsaicin tests. It attenuated nocifensive responses in both phases of the formalin test and reduced cold allodynia in oxaliplatin-induced neuropathic pain model. Its efficacy was similar to that of morphine. Used in combination and administered simultaneously, 4 or 6 h after simvastatin, cebranopadol did not potentiate antiallodynic activity of this cholesterol-lowering drug. Cebranopadol did not induce any motor deficits in the rotarod test.

CONCLUSION

Cebranopadol may have significant potential for the treatment of various pain types, including inflammatory and chemotherapy-induced neuropathic pain.

Regulation of gap junction channels and hemichannels by phosphorylation and redox changes: a revision

Post-translational modifications of connexins play an important role in the regulation of gap junction and hemichannel permeability. The prerequisite for the formation of functional gap junction channels is the assembly of connexin proteins into hemichannels and their insertion into the membrane. Hemichannels can affect cellular processes by enabling the passage of signaling molecules between the intracellular and extracellular space. For the intercellular communication hemichannels from one cell have to dock to its counterparts on the opposing membrane of an adjacent cell to allow the transmission of signals via gap junctions from one cell to the other. The controlled opening of hemichannels and gating properties of complete gap junctions can be regulated via post-translational modifications of connexins. Not only channel gating, but also connexin trafficking and assembly into hemichannels can be affected by post-translational changes. Recent investigations have shown that connexins can be modified by phosphorylation/dephosphorylation, redox-related changes including effects of nitric oxide (NO), hydrogen sulfide (H2S) or carbon monoxide (CO), acetylation, methylation or ubiquitination. Most of the connexin isoforms are known to be phosphorylated, e.g. Cx43, one of the most studied connexin at all, has 21 reported phosphorylation sites. In this review, we provide an overview about the current knowledge and relevant research of responsible kinases, connexin phosphorylation sites and reported effects on gap junction and hemichannel regulation. Regarding the effects of oxidants we discuss the role of NO in different cell types and tissues and recent studies about modifications of connexins by CO and H2S.