Connexin 43 confers chemoresistance through activating PI3K

Selective regulation of chemosensitivity in glioblastoma by phosphatidylinositol 3-kinase beta

Resistance to chemotherapies such as temozolomide is a major hurdle to effectively treat therapy-resistant glioblastoma. This challenge arises from the activation of phosphatidylinositol 3-kinase (PI3K), which makes it an appealing therapeutic target. However, non-selectively blocking PI3K kinases PI3Kα/β/δ/γ has yielded undesired clinical outcomes. It is, therefore, imperative to investigate individual kinases in glioblastoma's chemosensitivity. Here, we report that PI3K kinases were unequally expressed in glioblastoma, with levels of PI3Kβ being the highest. Patients deficient of O6-methylguanine-DNA-methyltransferase (MGMT) and expressing elevated levels of PI3Kβ, defined as MGMT-deficient/PI3Kβ-high, were less responsive to temozolomide and experienced poor prognosis. Consistently, MGMT-deficient/PI3Kβ-high glioblastoma cells were resistant to temozolomide. Perturbation of PI3Kβ, but not other kinases, sensitized MGMT-deficient/PI3Kβ-high glioblastoma cells or tumors to temozolomide. Moreover, PI3Kβ-selective inhibitors and temozolomide synergistically mitigated the growth of glioblastoma stem cells. Our results have demonstrated an essential role of PI3Kβ in chemoresistance, making PI3Kβ-selective blockade an effective chemosensitizer for glioblastoma.

Increased interaction between connexin43 and microtubules is critical for glioblastoma stem-like cell maintenance and tumorigenicity

Glioblastoma (GBM) is the most common primary tumor of the central nervous system. One major challenge in GBM treatment is the resistance to chemotherapy and radiotherapy observed in subpopulations of cancer cells, including GBM stem-like cells (GSCs). These cells hold the ability to self-renew or differentiate following treatment, participating in tumor recurrence. The gap junction protein connexin43 (Cx43) has complex roles in oncogenesis and we have previously demonstrated an association between Cx43 and GBM chemotherapy resistance. Here, we report, for the first time, increased direct interaction between non-junctional Cx43 with microtubules in the cytoplasm of GSCs. We hypothesize that non-junctional Cx43/microtubule complexing is critical for GSC maintenance and survival and sought to specifically disrupt this interaction while maintaining other Cx43 functions, such as gap junction formation. Using a Cx43 mimetic peptide of the carboxyl terminal tubulin-binding domain of Cx43 (JM2), we successfully ablated Cx43 interaction with microtubules in GSCs. Importantly, administration of JM2 significantly decreased GSC survival in vitro , and limited GSC-derived tumor growth in vivo . Together, these results identify JM2 as a novel peptide drug to ablate GSCs in GBM treatment.

Mapping the Anti-Cancer Activity of α-Connexin Carboxyl-Terminal (aCT1) Peptide in Resistant HER2+ Breast Cancer

Connexin 43 (Cx43) is a protein encoded by the GJA1 gene and is a component of cell membrane structures called gap junctions, which facilitate intercellular communication. Prior evidence indicates that elevated GJA1 expression in the HER2-positive (HER2+) subtype of breast cancer is associated with poor prognosis. Prior evidence also suggests that HER2+ breast cancers that have become refractory to HER2-targeted agents have a loss of Cx43 gap junction intercellular communication (GJIC). In this study, a Cx43-targeted agent called alpha-connexin carboxyl-terminal peptide (aCT1) is examined to determine whether GJIC can be rescued in refractory HER2+ breast cancer cells. A proposed mechanism of action for aCT1 is binding to the tight junction protein Zonal Occludens-1 (ZO-1). However, the true scope of activity for aCT1 has not been explored. In this study, mass spectrometry proteomic analysis is used to determine the breadth of aCT1-interacting proteins. The NanoString nCounter Breast Cancer 360 panel is also used to examine the effect of aCT1 on cancer signaling in HER2+ breast cancer cells. Findings from this study show a dynamic range of binding partners for aCT1, many of which regulate gene expression and RNA biology. nCounter analysis shows that a number of pathways are significantly impacted by aCT1, including upregulation of apoptotic factors, leading to the prediction and demonstration that aCT1 can boost the cell death effects of cisplatin and lapatinib in HER2+ breast cancer cells that have become resistant to HER2-targeted agents.

Systematic Review of Photodynamic Therapy in Gliomas

Over the last 20 years, gliomas have made up over 89% of malignant CNS tumor cases in the American population (NIH SEER). Within this, glioblastoma is the most common subtype, comprising 57% of all glioma cases. Being highly aggressive, this deadly disease is known for its high genetic and phenotypic heterogeneity, rendering a complicated disease course. The current standard of care consists of maximally safe tumor resection concurrent with chemoradiotherapy. However, despite advances in technology and therapeutic modalities, rates of disease recurrence are still high and survivability remains low. Given the delicate nature of the tumor location, remaining margins following resection often initiate disease recurrence. Photodynamic therapy (PDT) is a therapeutic modality that, following the administration of a non-toxic photosensitizer, induces tumor-specific anti-cancer effects after localized, wavelength-specific illumination. Its effect against malignant glioma has been studied extensively over the last 30 years, in pre-clinical and clinical trials. Here, we provide a comprehensive review of the three generations of photosensitizers alongside their mechanisms of action, limitations, and future directions.

Integrins in cancer: Emerging mechanisms and therapeutic opportunities

Integrins are vital surface adhesion receptors that mediate the interactions between the extracellular matrix (ECM) and cells and are essential for cell migration and the maintenance of tissue homeostasis. Aberrant integrin activation promotes initial tumor formation, growth, and metastasis. Recently, many lines of evidence have indicated that integrins are highly expressed in numerous cancer types and have documented many functions of integrins in tumorigenesis. Thus, integrins have emerged as attractive targets for the development of cancer therapeutics. In this review, we discuss the underlying molecular mechanisms by which integrins contribute to most of the hallmarks of cancer. We focus on recent progress on integrin regulators, binding proteins, and downstream effectors. We highlight the role of integrins in the regulation of tumor metastasis, immune evasion, metabolic reprogramming, and other hallmarks of cancer. In addition, integrin-targeted immunotherapy and other integrin inhibitors that have been used in preclinical and clinical studies are summarized.

Connexin 45 is a novel suppressor of melanoma metastasis

The expression spectra of connexin (Cx) isoforms were investigated in three mouse melanoma cell lines: B16-F1 (F1), B16-F10 (F10), and B16-BL6 (BL6). Metastatic potential intensity was higher in the order of F1, F10, and BL6. A remarkable behavior of Cx45 was found among 20 isoforms. The expression level of Cx45 was highest in F1 and lowest in BL6. It was inductively predicted that Cx45 might be a novel suppressor of metastasis. A Cx45-overexpressing BL6 cell line (Cx45 +BL6) was developed and its properties were compared with those of a wild-type cell line of BL6 (W-BL6). Compared to W-BL6, Cx45 +BL6 showed reduced wound healing, Transwell® permeability, and matrix metalloproteinase 9 expression, suggesting the suppression of cellular migration and invasion. The expression of E-cadherin and integrin β1 in Cx45 +BL6 was also lower than in W-BL6, suggesting reduced cell adhesion. The decrease in cell adhesion was supported by the cell washing-out assay. In contrast, no difference between W-BL6 and Cx45 +BL6 was observed in cell proliferation, suggesting no effect on cell-cycle regulating factors. Finally, an in vivo assay revealed a significant decrease in the number of metastatic colonies of Cx45 +BL6 (176 ± 25/lung) in comparison with those of W-BL6 (252 ± 23/lung) in a mouse model. In conclusion, Cx45 is a novel suppressor of melanoma metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00563-x.

αCT1 peptide sensitizes glioma cells to temozolomide in a glioblastoma organoid platform

Glioblastoma (GBM) is the most common form of brain cancer. Even with aggressive treatment, tumor recurrence is almost universal and patient prognosis is poor because many GBM cell subpopulations, especially the mesenchymal and glioma stem cell populations, are resistant to temozolomide (TMZ), the most commonly used chemotherapeutic in GBM. For this reason, there is an urgent need for the development of new therapies that can more effectively treat GBM. Several recent studies have indicated that high expression of connexin 43 (Cx43) in GBM is associated with poor patient outcomes. It has been hypothesized that inhibition of the Cx43 hemichannels could prevent TMZ efflux and sensitize otherwise resistance cells to the treatment. In this study, we use a three-dimensional organoid model of GBM to demonstrate that combinatorial treatment with TMZ and αCT1, a Cx43 mimetic peptide, significantly improves treatment efficacy in certain populations of GBM. Confocal imaging was used to visualize changes in Cx43 expression in response to combinatorial treatment. These results indicate that Cx43 inhibition should be pursued further as an improved treatment for GBM.

Progress in targeting PTEN/PI3K/Akt axis in glioblastoma therapy: Revisiting molecular interactions

Glioblastoma (GBM) is one of the most malignant cancers of central nervous system and due to its sensitive location, surgical resection has high risk and therefore, chemotherapy and radiotherapy are utilized for its treatment. However, chemoresistance and radio-resistance are other problems in GBM treatment. Hence, new therapies based on genes are recommended for treatment of GBM. PTEN is a tumor-suppressor operator in cancer that inhibits PI3K/Akt/mTOR axis in diminishing growth, metastasis and drug resistance. In the current review, the function of PTEN/PI3K/Akt axis in GBM progression is evaluated. Mutation or depletion of PTEN leads to increase in GBM progression. Low expression level of PTEN mediates poor prognosis in GBM and by increasing proliferation and invasion, promotes malignancy of tumor cells. Moreover, loss of PTEN signaling can result in therapy resistance in GBM. Activation of PTEN signaling impairs GBM metabolism via glycolysis inhibition. In contrast to PTEN, PI3K/Akt signaling has oncogenic function and during tumor progression, expression level of PI3K/Akt enhances. PI3K/Akt signaling shows positive association with oncogenic pathways and its expression similar to PTEN signaling, is regulated by non-coding RNAs. PTEN upregulation and PI3K/Akt signaling inhibition by anti-cancer agents can be beneficial in interfering GBM progression. This review emphasizes on the signaling networks related to PTEN/PI3K/Akt and provides new insights for targeting this axis in effective GBM treatment.

MicroRNA-206 in human cancer: Mechanistic and clinical perspectives

MicroRNAs (miRNAs), small non-coding RNAs approximately 20-25 nt in length, play important roles via directly binding to the corresponding 3' UTR of target mRNAs. Recent research has shown that miRNAs cover a wide range of diseases, including several types of cancer. It is interesting to note that miR-206 operates as a tumor suppressor and is downregulated in abundant cancer types, such as breast cancer, lung cancer, colorectal cancer, and so forth. Interestingly, a growing number of studies have also reported that miR-206 could function as an oncogene and promote tumor cell proliferation. Thereby, miR-206 may act as either oncogenes or tumor suppressors under certain conditions. In addition, it was widely acknowledged that restoring tumor-suppressor miR-206 has emerged as an unconventional cancer therapy strategy. Therefore, miR-206 might be a newfangled procedure for achieving a more significant treatment outcome for cancer patients. This review summarizes the role of miR-206 in several cancer types and the contributions made between miR-206 and the diagnosis, treatment, and drug resistance of solid tumors.

CRISPR-Induced Loss of Connexin 43 Expression Sensitizes KRAS Mutant Cells to Cisplatin

Gap Junction intercellular communication (GJIC) is often dysregulated in cancers, and this dysregulation has been shown to have pro-tumorigenic effects. Connexins (Cxs) are transmembrane proteins that make up gap junctions. Previous studies have indicated that RNA interference (RNAi)-based suppression of Cx43 increases cellular resistance to the chemotherapeutic agent cisplatin. Interestingly, we found that the loss of Cx43 expression induced by the CRISPR-Cas9 technology sensitizes cells to cisplatin in a KRAS mutant-dependent manner.

Connexins and Glucose Metabolism in Cancer

Connexins are a family of transmembrane proteins that regulate diverse cellular functions. Originally characterized for their ability to mediate direct intercellular communication through the formation of highly regulated membrane channels, their functions have been extended to the exchange of molecules with the extracellular environment, and the ability to modulate numerous channel-independent effects on processes such as motility and survival. Notably, connexins have been implicated in cancer biology for their context-dependent roles that can both promote or suppress cancer cell function. Moreover, connexins are able to mediate many aspects of cellular metabolism including the intercellular coupling of nutrients and signaling molecules. During cancer progression, changes to substrate utilization occur to support energy production and biomass accumulation. This results in metabolic plasticity that promotes cell survival and proliferation, and can impact therapeutic resistance. Significant progress has been made in our understanding of connexin and cancer biology, however, delineating the roles these multi-faceted proteins play in metabolic adaptation of cancer cells is just beginning. Glucose represents a major carbon substrate for energy production, nucleotide synthesis, carbohydrate modifications and generation of biosynthetic intermediates. While cancer cells often exhibit a dependence on glycolytic metabolism for survival, cellular reprogramming of metabolic pathways is common when blood perfusion is limited in growing tumors. These metabolic changes drive aggressive phenotypes through the acquisition of functional traits. Connections between glucose metabolism and connexin function in cancer cells and the surrounding stroma are now apparent, however much remains to be discovered regarding these relationships. This review discusses the existing evidence in this area and highlights directions for continued investigation.

Regulation of temozolomide resistance via lncRNAs: Clinical and biological properties of lncRNAs in gliomas (Review)

Gliomas are a primary types of intracranial malignancies and are characterized by a poor prognosis due to aggressive recurrence profiles. Temozolomide (TMZ) is an auxiliary alkylating agent that is extensively used in conjunction with surgical resection and forms the mainstay of clinical treatment strategies for gliomas. However, the frequent occurrence of TMZ resistance in clinical practice limits its therapeutic efficacy. Accumulating evidence has demonstrated that long non‑coding RNAs (lncRNAs) can play key and varied roles in glioma progression. lncRNAs have been reported to inhibit glioma progression by targeting various signaling pathways. In addition, the differential expression of lncRNAs has also been found to mediate the resistance of glioma to several chemotherapeutic agents, particularly to TMZ. The present review article therefore summarizes the findings of previous studies in an aim to report the significance and function of lncRNAs in regulating the chemoresistance of gliomas. The present review may provide further insight into the clinical treatment of gliomas.