Microtubule-Actin Crosslinking Factor 1 and Plakins as Therapeutic Drug Targets

Plakins are a family of seven cytoskeletal cross-linker proteins (microtubule-actin crosslinking factor 1 (MACF), bullous pemphigoid antigen (BPAG1) desmoplakin, envoplakin, periplakin, plectin, epiplakin) that network the three major filaments that comprise the cytoskeleton. Plakins have been found to be involved in disorders and diseases of the skin, heart, nervous system, and cancer that are attributed to autoimmune responses and genetic alterations of these macromolecules. Despite their role and involvement across a spectrum of several diseases, there are no current drugs or pharmacological agents that specifically target the members of this protein family. On the contrary, microtubules have traditionally been targeted by microtubule inhibiting agents, used for the treatment of diseases such as cancer, in spite of the deleterious toxicities associated with their clinical utility. The Research Collaboratory for Structural Bioinformatics (RCSB) was used here to identify therapeutic drugs targeting the plakin proteins, particularly the spectraplakins MACF1 and BPAG1, which contain microtubule-binding domains. RCSB analysis revealed that plakin proteins had 329 ligands, of which more than 50% were MACF1 and BPAG1 ligands and 10 were documented, clinically or experimentally, to have several therapeutic applications as anticancer, anti-inflammatory, and antibiotic agents

Inhibition of the Spectraplakin Protein Microtubule Actin Crosslinking Factor 1 Sensitizes Glioblastomas to Radiation

Background Microtubule actin crosslinking factor 1 (MACF1) is a spectraplakin cytoskeletal crosslinking protein whose function and role in cancer biology has lacked investigation. Recent studies have identified MACF1 as a novel target in glioblastomas expressed in tissue from tumor patient explants but not normal brain tissue and when silenced has an antitumorigenic impact on these tumors. Radiation as a single agent therapy to treat glioblastomas has been used for decades and has done little to improve survival of individuals diagnosed with this disease. However, contemporary clinical radiotherapy protocols have provided evidence that combinatorial radiotherapy approaches confer a therapeutic benefit in glioblastoma patients. In this study MACF1 was investigated as a radiosensitization target in glioblastomas. Methods To provide context of MACF1 in glioblastomas, The Cancer Genome Atlas expression analyses were performed in conjunction with genes associated with glioblastoma evolution, while a genetic inhibitory approach, cell migratory assays, and immunofluorescence procedures were used to evaluate responses to MACF1 suppression with radiation. Additionally, expression analyses were conducted to assess co-expression of mTOR signaling pathway regulators and MACF1 in glioblastoma patient samples. Results Our amalgamation approach demonstrated that negative regulation of MACF1, which was positively correlated with epidermal growth factor receptor and p70s6k expression, enhanced the sensitivity of glioblastoma cells to radiation as a consequence of reducing glioblastoma cell viability and migration. Mechanistically, the antitumorigenic effects on glioblastoma cell behaviors after radiation and impairing MACF1 function were associated with decreased expression of ribosomal protein S6, a downstream effector of p70s6k. Conclusion MACF1 represents a diagnostic marker with target specificity in glioblastomas that can enhance the efficacy of radiation while minimizing normal tissue toxicity. This approach could potentially expand combinatorial radiation strategies for glioblastoma treatments via impairment of translational regulatory processes that contribute to poor patient survival

Microtubule actin cross-linking factor 1, a novel target in glioblastoma

Genetic heterogeneity is recognized as a major contributing factor of glioblastoma resistance to clinical treatment modalities and consequently low overall survival rates. This genetic diversity results in variations in protein expression, both intratumorally and between individual glioblastoma patients. In this regard, the spectraplakin protein, microtubule actin cross-linking factor 1 (MACF1), was examined in glioblastoma. An expression analysis of MACF1 in various types of brain tumor tissue revealed that MACF1 was predominately present in grade III-IV astroctyomas and grade IV glioblastoma, but not in normal brain tissue, normal human astrocytes and lower grade brain tumors. Subsequent genetic inhibition experiments showed that suppression of MACF1 selectively inhibited glioblastoma cell proliferation and migration in cell lines established from patient derived xenograft mouse models and immortalized glioblastoma cell lines that were associated with downregulation of the Wnt-signaling mediators, Axin1 and β-catenin. Additionally, concomitant MACF1 silencing with the chemotherapeutic agent temozolomide (TMZ) used for the clinical treatment of glioblastomas cooperatively reduced the proliferative capacity of glioblastoma cells. In conclusion, the present study represents the first investigation on the functional role of MACF1 in tumor cell biology, as well as demonstrates its potential as a unique biomarker that can be targeted synergistically with TMZ as part of a combinatorial therapeutic approach for the treatment of genetically multifarious glioblastomas

Caspase-dependent signaling underlies glioblastoma cell death in response to the fungal metabolite, fusarochromanone

Fungal metabolites continue to show promise as a viable class of anticancer agents. In the present study, we investigated the efficacy of the fungal metabolite, fusarochromanone (FC101), for its antitumor activities in glioblastomas, which have a median survival of less than two years and a poor clinical response to surgical resection, radiation therapy and chemotherapy. Using clinically applicable doses, we demonstrated that FC101 induced glioblastoma apoptotic cell death via caspase dependent signaling, as indicated by the cleavage of poly(ADP-ribose) polymerase, glioblastoma (PARP). FC101 also induced differential reactive oxygen species (ROS) levels in glioblastoma cells, contrasting a defined role of oxidative stress in apoptotic cell death observed with other fungal metabolites. Furthermore, the antitumorigenic effects of FC101 on tumor cell migration were assessed. Cell migration assays revealed that FC101 significantly reduced the migratory capacity of glioblastomas, which are incredibly invasive tumors. Taken together, the present study establishes FC101 as a candidate anticancer agent for the cooperative treatment of glioblastomas

Biological activities of fusarochromanone: a potent anti-cancer agent

Background Fusarochromanone (FC101) is a small molecule fungal metabolite with a host of interesting biological functions, including very potent anti-angiogenic and direct anti-cancer activity. Results Herein, we report that FC101 exhibits very potent in-vitro growth inhibitory effects (IC50 ranging from 10nM-2.5 μM) against HaCat (pre-malignant skin), P9-WT (malignant skin), MCF-7 (low malignant breast), MDA-231 (malignant breast), SV-HUC (premalignant bladder), UM-UC14 (malignant bladder), and PC3 (malignant prostate) in a time-course and dose-dependent manner, with the UM-UC14 cells being the most sensitive. FC101 induces apoptosis and an increase in proportion of cells in the sub-G1 phase in both HaCat and P9-WT cell lines as evidenced by cell cycle profile analysis. In a mouse xenograft SCC tumor model, FC101 was well tolerated, non-toxic, and achieved a 30% reduction in tumor size at a dose of 8 mg/kg/day. FC101 is also a potent anti-angiogenenic agent. At nanomolar doses, FC101 inhibits the vascular endothelial growth factor-A (VEGF-A)-mediated proliferation of endothelial cells. Conclusions Our data presented here indicates that FC101 is an excellent lead candidate for a small molecule anti-cancer agent that simultaneously affects angiogenesis signaling, cancer signal transduction, and apoptosis. Further understanding of the underlying FC101’s molecular mechanism may lead to the design of novel targeted and selective therapeutics, both of which are pursued targets in cancer drug discovery

Microtubule-Actin Crosslinking Factor 1 and Plakins as Therapeutic Drug Targets

Plakins are a family of seven cytoskeletal cross-linker proteins (microtubule-actin crosslinking factor 1 (MACF), bullous pemphigoid antigen (BPAG1) desmoplakin, envoplakin, periplakin, plectin, epiplakin) that network the three major filaments that comprise the cytoskeleton. Plakins have been found to be involved in disorders and diseases of the skin, heart, nervous system, and cancer that are attributed to autoimmune responses and genetic alterations of these macromolecules. Despite their role and involvement across a spectrum of several diseases, there are no current drugs or pharmacological agents that specifically target the members of this protein family. On the contrary, microtubules have traditionally been targeted by microtubule inhibiting agents, used for the treatment of diseases such as cancer, in spite of the deleterious toxicities associated with their clinical utility. The Research Collaboratory for Structural Bioinformatics (RCSB) was used here to identify therapeutic drugs targeting the plakin proteins, particularly the spectraplakins MACF1 and BPAG1, which contain microtubule-binding domains. RCSB analysis revealed that plakin proteins had 329 ligands, of which more than 50% were MACF1 and BPAG1 ligands and 10 were documented, clinically or experimentally, to have several therapeutic applications as anticancer, anti-inflammatory, and antibiotic agents

Violacein induces p44/42 mitogen-activated protein kinase‑mediated solid tumor cell death and inhibits tumor cell migration

Microbial secondary metabolites have emerged as alternative novel drugs for the treatment of human cancers. Violacein, a purple pigment produced by Chromobacterium violaceum, was investigated in the present study for its anti‑tumor properties in tumor cell lines. Clinically applicable concentrations of violacein were demonstrated to inhibit the proliferative capacity of tumor cell lines according to a crystal violet proliferation assay. The underlying mechanism was the promotion of apoptotic cell death, as indicated by poly(ADP ribose) polymerase cleavage and p44/42 mitogen‑activated protein kinase signaling determined by western blot analysis. Collectively, this provided mechanistic evidence that violacein elicits extracellular-signal regulated kinase‑induced apoptosis via the intrinsic pathway. The anti‑malignant properties of violacein in the present study were further demonstrated by its inhibitory effects on brain tumor cell migration, specifically glioblastomas, one of the most invasive and therapeutically resistant neoplasms in the clinic. Additionally, solid tumors examined in the present study displayed differential cellular responses and sensitivities to violacein as observed by morphologically induced cellular changes that contributed to its anti‑migratory properties. In conclusion, violacein is a novel natural product with the potential to kill several types of human tumor cell lines, as well as prevent disease recurrence by antagonizing cellular processes that contribute to metastatic invasion