Apoptotic Effects of a Thioether Analog of Vitamin K3 in a Human Leukemia Cell Line

Research suggests that thioether analogs of vitamin K₃ (VK₃) can act to preserve the phosphorylation of epidermal growth factor receptors by blocking enzymes (phosphatases) responsible for their dephosphorylation. Additionally, these derivatives can induce apoptosis via mitogen-activated protein kinase and caspase-3 activation, inducing reactive oxygen species (ROS) production, and apoptosis. However, vitamin K₁ exhibits only weak inhibition of phosphatase activity, while the ability of VK₃ to cause oxidative DNA damage has raised concerns about carcinogenicity. Hence, in the current study, we designed, synthesized, and screened a number of VK₃ analogs for their ability to enhance phosphorylation activity, without inducing off-target effects, such as DNA damage. 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay revealed that each analog produced a different level of cytotoxicity in the Jurkat human leukemia cell line; however, none elicited a cytotoxic effect that differed significantly from that of the control. Of the VK₃ analogs, CPD5 exhibited the lowest EC₅₀, and flow cytometry results showed that apoptosis was induced at final concentrations of ≥10 μM; hence, only 0.1, 1, and 10 μM were evaluated in subsequent assays. Furthermore, CPD5 did not cause vitamin K-attributed ROS generation and was found to be associated with a significant increase in caspase 3 expression, indicating that, of the synthesized thioether VK₃ analogs, CPD5 was a more potent inducer of apoptosis than VK₃. Hence, further elucidation of the apoptosis-inducing effect of CPD5 may reveal its efficacy in other neoplastic cells and its potential as a medication.

[Research on Analysis of Final Diagnosis and Prognostic Factors, and Development of New Therapeutic Drugs for Malignant Tumors (Especially Malignant Pediatric Tumors)]

Outcomes of treatment for malignant pediatric tumors including leukemia are improving by conventional multimodal treatment with strong chemotherapy, surgical resection, radiotherapy, and bone marrow transplantation. However, patients with advanced neuroblastoma, metastatic Ewing's sarcoma family of tumor (ESFT), and metastatic osteosarcoma continue to have an extremely poor prognosis. Therefore novel therapeutic strategies are urgently needed to improve their survival. Apoptotic cell death is a key mechanism for normal cellular homeostasis. Intact apoptotic mechanisms are pivotal for embryonic development, tissue remodeling, immune regulation, and tumor regression. Genetic aberrations disrupting programmed cell death often underpin tumorigenesis and drug resistance. Moreover, it has been suggested that apoptosis or cell differentiation proceeds to spontaneous regression in early stage neuroblastoma. Therefore apoptosis or cell differentiation is a critical event in this cancer. We extracted many compounds from natural plants (Angelica keiskei, Alpinia officiarum, Lycaria puchury-major, Brassica rapa) or synthesized cyclophane pyridine, indirubin derivatives, vitamin K3 derivatives, burchellin derivatives, and GANT61, and examined their effects on apoptosis, cell differentiation, and cell cycle in neuroblastoma and ESFT cell lines compared with normal cells. Some compounds were very effective against these tumor cells. These results suggest that they may be applicable as an efficacious and safe drug for the treatment of malignant pediatric tumors.

Vitamin K3 derivative induces apoptotic cell death in neuroblastoma via downregulation of MYCN expression

Neuroblastoma is a pediatric malignant tumor arising from the sympathetic nervous system. The patients with high-risk neuroblastomas frequently exhibit amplification and high expression of the MYCN gene, resulting in worse clinical outcomes. Vitamin K3 (VK3) is a synthetic VK-like compound that has been known to have antitumor activity against various types of cancers. In the present study, we have asked whether VK3 and its derivative, VK3-OH, could have the antitumor activity against neuroblastoma-derived cells. Based on our results, VK3-OH strongly inhibited cell proliferation and induced apoptotic cell death compared to VK3. Treatment of MYCN-driven neuroblastoma cells with VK3-OH potentiated tumor suppressor p53 accompanied by downregulation of anti-apoptotic Bcl-2 and Mcl-1. Interestingly, VK3-OH also suppressed the MYCN at mRNA and protein levels. Furthermore, we found downregulation of LIN28B following VK3-OH treatment in MYCN-amplified and overexpressed neuroblastoma cells. Collectively, our current findings strongly suggest that VK3-OH provides a potential therapeutic strategy for patients with MYCN-driven neuroblastomas.

GAP-43 slows down cell cycle progression via sequences in its 3'UTR

Growth-associated protein 43 (GAP-43) is a neuronal phosphoprotein associated with initial axonal outgrowth and synaptic remodeling and recent work also suggests its involvement in cell cycle control. The complex expression of GAP-43 features transcriptional and posttranscriptional components. However, in some conditions, GAP-43 gene expression is controlled primarily by the interaction of stabilizing or destabilizing RNA-binding proteins (RBPs) with adenine and uridine (AU)-rich instability elements (AREs) in its 3'UTR. Like GAP-43, many proteins involved in cell proliferation are encoded by ARE-containing mRNAs, some of which codify cell-cycle-regulating proteins including cyclin D1. Considering that GAP-43 and cyclin D1 mRNA stabilization may depend on similar RBPs, this study evaluated the participation of GAP-43 in cell cycle control and its underlying mechanisms, particularly the possible role of its 3'UTR, using GAP-43-transfected NIH-3T3 fibroblasts. Our results show an arrest in cell cycle progression in the G0/G1 phase. This arrest may be mediated by the competition of GAP-43 3'UTR with cyclin D1 3'UTR for the binding of Hu proteins such as HuR, which may lead to a decrease in cyclin D1 expression. These results might lead to therapeutic applications involving the use of sequences in the B region of GAP-43 3'UTR to slow down cell cycle progression.

Tryptanthrin induces growth inhibition and neuronal differentiation in the human neuroblastoma LA-N-1 cells

Neuroblastoma is one of the most common extracranial solid cancers found in young children. The prognosis of neuroblastoma patients in advanced stages having N-myc amplification remains poor despite intensive multimodal therapy. Agents that trigger neuroblastoma cells to undergo cellular differentiation and thereby stop proliferation have attracted considerable interest as an alternative therapy. Tryptanthrin (12-dihydro-6,12-dioxoindolo-(2,1-b)-quinazoline) is a weakly basic alkaloid isolated from the dried roots of medicinal indigo plants known as Banlangen. It has been shown to possess various biological activities, such as anti-microbial, anti-inflammatory and anti-tumor activities. However, its effects and mechanism(s) of action on human neuroblastoma cells remain poorly understood. Therefore, the objective of this study is to investigate the effects of tryptanthrin on the growth and differentiation of human neuroblastoma LA-N-1 cells with N-myc amplification. Our results show that tryptanthrin inhibited the growth of the human neuroblastoma cells in a dose- and time-dependent manner. Mechanistic studies indicated that tryptanthrin induced cell cycle arrest of the human neuroblastoma LA-N-1 cells at the G0/G1 phase. Tryptanthrin also induced neuronal differentiation of LA-N-1 cells, as assessed by morphological criteria, enhancement of acetylcholine esterase activity and up-regulation of various differentiation markers. Moreover, tryptanthrin treatment led to the significant reduction of N-myc expression in LA-N-1 cells while siRNA directed against N-myc induced morphological differentiation of LA-N-1 cells. These results, when taken together, suggest that tryptanthrin suppressed the growth and induced neuronal differentiation in the human neuroblastoma LA-N-1 cells and might be exploited as a potential therapeutic candidate for the treatment of high-risk neuroblastomas with N-myc-amplification.

Cytotoxic effect of menadione and sodium orthovanadate in combination on human glioma cells

Gliomas are the most common primary brain tumor, and their treatment is still a challenge. Here, we evaluated the antiproliferative effect of a novel combination of two potent oxidative stress enhancers: menadione (M) and sodium orthovanadate (SO). We observed both short-term and prolonged growth inhibitory effects of M or SO alone as well as in combination (M:SO) on DBTRG.05MG human glioma cells. A stronger antiproliferative effect was observed in the short-term proliferation assay with the M:SO combination compared to either investigated agent alone. In the long-term proliferation assay, a 10-day exposure to M:SO at concentrations of 10 μM:17.5 μM or 17.5 μM:10 μM was enough to kill 100% of the cells; no cell regrowth was observed after re-incubation in drug-free media. When used in combination, the single concentration of M and SO could be decreased by 2.5- to 5-fold of those used for each experimental drug alone and still obtain a similar antiproliferative effect. The underlying molecular mechanism was investigated by co-incubating M:SO with dithiothreitol (DTT) and genistein. Both substances partially neutralized the effects of the M:SO combination, showing additive effects. This observation suggests a role of oxidative stress and tyrosine kinase stimulation in the M:SO cytotoxic effect. Our results indicate that M:SO combination is an attractive alternative for glioma treatment that encourages further study. The neutralizing effects of genistein and DTT reveal a possibility for their use in the minimization of potential M:SO systemic toxicity.