The novel DNA alkylating agent BO-1090 suppresses the growth of human oral cavity cancer in xenografted and orthotopic mouse models

The comet assay in animal models: From bugs to whales - (Part 2 Vertebrates)

The comet assay has become one of the methods of choice for the evaluation and measurement of DNA damage. It is sensitive, quick to perform and relatively affordable for the evaluation of DNA damage and repair at the level of individual cells. The comet assay can be applied to virtually any cell type derived from different organs and tissues. Even though the comet assay is predominantly used on human cells, the application of the assay for the evaluation of DNA damage in yeast, plant and animal cells is also quite high, especially in terms of biomonitoring. The present extensive overview on the usage of the comet assay in animal models will cover both terrestrial and water environments. The first part of the review was focused on studies describing the comet assay applied in invertebrates. The second part of the review, (Part 2) will discuss the application of the comet assay in vertebrates covering cyclostomata, fishes, amphibians, reptiles, birds and mammals, in addition to chordates that are regarded as a transitional form towards vertebrates. Besides numerous vertebrate species, the assay is also performed on a range of cells, which includes blood, liver, kidney, brain, gill, bone marrow and sperm cells. These cells are readily used for the evaluation of a wide spectrum of genotoxic agents both in vitro and in vivo. Moreover, the use of vertebrate models and their role in environmental biomonitoring will also be discussed as well as the comparison of the use of the comet assay in vertebrate and human models in line with ethical principles. Although the comet assay in vertebrates is most commonly used in laboratory animals such as mice, rats and lately zebrafish, this paper will only briefly review its use regarding laboratory animal models and rather give special emphasis to the increasing usage of the assay in domestic and wildlife animals as well as in various ecotoxicological studies.

P-glycoprotein attenuates DNA repair activity in multidrug-resistant cells by acting through the Cbp-Csk-Src cascade

Recent studies have demonstrated that P-glycoprotein (P-gp) expression impairs DNA interstrand cross-linking agent-induced DNA repair efficiency in multidrug-resistant (MDR) cells. To date, the detailed molecular mechanisms underlying how P-gp interferes with Src activation and subsequent DNA repair activity remain unclear. In this study, we determined that the C-terminal Src kinase-binding protein (Cbp) signaling pathway involved in the negative control of Src activation is enhanced in MDR cells. We also demonstrated that cells that ectopically express P-gp exhibit reduced activation of DNA damage response regulators, such as ATM, Chk2, Braca1 and Nbs1 and hence attenuated DNA double-strand break repair capacity and become more susceptible than vector control cells to DNA interstrand cross-linking (ICL) agents. Moreover, we demonstrated that P-gp can not only interact with Cbp and Src but also enhance the formation of inhibitory C-terminal Src kinase (Csk)-Cbp complexes that reduce phosphorylation of the Src activation residue Y416 and increase phosphorylation of the Src negative regulatory residue Y527. Notably, suppression of Cbp expression in MDR cells restores cisplatin-induced Src activation, improves DNA repair capacity, and increases resistance to ICL agents. Ectopic expression of Cbp attenuates cisplatin-induced Src activation and increases the susceptibility of cells to ICL agents. Together, the current results indicate that P-gp inhibits DNA repair activity by modulating Src activation via Cbp-Csk-Src cascade. These results suggest that DNA ICL agents are likely to have therapeutic potential against MDR cells with P-gp-overexpression.

Tetrandrine induces programmed cell death in human oral cancer CAL 27 cells through the reactive oxygen species production and caspase-dependent pathways and associated with beclin-1-induced cell autophagy

Tetrandrine, a bisbenzylisoquinoline alkaloid, is extracted from the root of the Chinese herb Radix Stephania tetrandra S Moore. This compound has antitumor activity in different cancer cell types. In this study, the effects of tetrandrine on human oral cancer CAL 27 cells were examined. Results indicated that tetrandrine induced cytotoxic activity in CAL 27 cells. Effects were due to cell death by the induction of apoptosis and accompany with autophagy and these effects were concentration- and time-dependent manners. Tetrandrine induced apoptosis was accompanied by alterations in cell morphology, chromatin fragmentation, and caspase activation in CAL 27 cells. Tetrandrine treatment also induced intracellular accumulation of reactive oxygen species (ROS). The generation of ROS may play an important role in tetrandrine-induced apoptosis. Tetrandrine triggered LC3B expression and induced autophagy in CAL 27 cells. Tetrandrine induced apoptosis and autophagy were significantly attenuated by N-acetylcysteine pretreatment that supports the involvement of ROS production. Tetrandrine induced cell death may act through caspase-dependent apoptosis with Beclin-1-induced autophagy in human oral cancer cells. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 329-343, 2017.

Taiwanin C selectively inhibits arecoline and 4-NQO-induced oral cancer cell proliferation via ERK1/2 inactivation

Arecoline, the most abundant alkaloid in betel nut is known to promote abnormal proliferation of epithelial cells by enhancing epidermal growth factor receptor (EGFR) activation and cyclooxygenase-2 (COX2) expression. Taiwanin C, a naturally occurring lignan extracted from Taiwania cryptomerioides, has been found to be a potential inhibitor of COX2 expression. Based on the MTT assay results, taiwanin C was found to be effective in inhibiting the tumorous T28 cell than the non-tumorous N28 cells. The modulations in the expression of relevant proteins were determined to understand the mechanism induced by taiwanin C to inhibit T28 cell proliferation. The levels of activated EGFR and COX2 were found to be abnormally high in the T28 oral cancer cells. However, taiwanin C was found to inhibit the activation of EGFR and regulated other related downstream proteins and thereby inhibited the T28 cell proliferation. In conclusion the results indicate that taiwanin C suppresses COX2-EGFR and enhances P27 pathways to suppress arecoline induced oral cancer cell proliferation via ERK1/2 inactivation. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 62-69, 2017.

Effect of Ginsenoside Rh-2 via Activation of Caspase-3 and Bcl-2-Insensitive Pathway in Ovarian Cancer Cells

Ginsenoside has been reported to have therapeutic effects for some types of cancer, but its effect on ovarian cancer cells has not been evaluated. In this study, we monitored the effects of ginsenoside-Rh2 (Rh2) on the inhibition of cell proliferation and the apoptotic process in the ovarian cancer cell line SKOV3 using an MTT assay and TUNEL assay. We found that Rh2 inhibited cell proliferation and significantly induced apoptosis. We confirmed the apoptotic effects of Rh2 using western blot analysis of apoptosis-related proteins. Specifically, the levels of cleaved poly ADP ribose polymerase (PARP) and cleaved caspase-3 significantly increased in SKOV3 cells treated with Rh2. Therefore, Rh2 clearly suppressed the growth of SKOV3 cells in vitro, which was associated with induction of the apoptosis pathway. Moreover, the migration assay showed that Rh2 inhibited the invasive ability of SKOV3 cells. Taken together, our results suggest that Rh2 has anticancer effects in SKOV3 cells through inhibition of cell proliferation and induction of apoptosis. Considering the therapeutic potential of Rh2, more studies should be carried out to facilitate the future application of this natural product as a potential anti-cancer agent.

CCY-1a-E2 induces G2/M phase arrest and apoptotic cell death in HL-60 leukemia cells through cyclin-dependent kinase 1 signaling and the mitochondria-dependent caspase pathway

Our previous study demonstrated that 2-[(3-methoxybenzyl)oxy]benzaldehyde (CCY-1a-E2) is a potent compound that acts against multiple human leukemia cell lines. CCY-1a-E2 was also shown to have efficacious anti‑leukemic activity in vivo. However, the molecular mechanism of action of CCY‑1a‑E2 attributed to its anticancer effect remains poorly understood. In the present study, CCY‑1a‑E2 suppressed cell viability in multiple leukemia cell lines (HL‑60, K562, KG‑1 and KG‑1a) via inhibition of cell proliferation, cell cycle arrest and induction of apoptosis. CCY‑1a‑E2 exhibited a marked toxic effect on HL‑60 cells and displayed low cytotoxicity in normal human peripheral blood mononuclear cells (PBMCs). Results from flow cytometric analysis indicated that CCY‑1a‑E2 promoted G2/M phase arrest and promoted apoptosis in the HL‑60 cells. CCY‑1a‑E2 treatment upregulated cyclin B, cyclin‑dependent kinase 1 (CDK1), cell division cycle 25C (cdc25C) and p21 protein expression. CCY‑1a‑E2 caused apoptotic cell death and DNA fragmentation as determined by 4',6‑diamidino‑2‑phenylindole (DAPI) staining and DNA gel electrophoresis. Elevated activities of caspase‑8, ‑9 and ‑3 were observed during CCY‑1a‑E2‑induced cell apoptosis; their specific inhibitors were found to block CCY‑1a‑E2‑induced apoptosis, respectively. Moreover, CCY‑1a‑E2 time‑dependently disrupted the mitochondrial membrane potential (ΔΨm), and it enhanced the protein levels of Fas/CD95, cytochrome c, Bax, cleaved PARP, as well as attenuated Bcl‑2 expression in the HL‑60 cells. Our results provide direct evidence that supports the future potential therapeutic application of CCY-1a-E2 in leukemia.

A Potent Derivative of Indolizino[6,7-b]Indole for Treatment of Human Non-Small Cell Lung Cancer Cells

The therapeutic effect in non–small cell lung cancer (NSCLC) patients is limited because of intrinsic and acquired resistance. Thus, an unmet need exists for the development of new drugs to improve the therapeutic efficacy in NSCLC patients. In this study, the novel small molecule indolizino[6,7-b]indole derivative BO-1978 was selected to evaluate its therapeutic effects on NSCLC and its preclinical toxicity in animal models. An in vitro cytotoxicity assay revealed that BO-1978 significantly suppressed the growth of various NSCLC cell lines with or without mutations in epidermal growth factor receptor (EGFR). Mechanistically, we demonstrated that BO-1978 exhibited multiple modes of action, including inhibition of topoisomerase I/II and induction of DNA cross-linking. Treatment of NSCLC cells with BO-1978 caused DNA damage, disturbed cell cycle progression, and triggered apoptotic cell death. Furthermore, BO-1978 significantly suppressed the growth of EGFR wild-type and mutant NSCLC tumors in xenograft tumor and orthotopic lung tumor models with negligible body weight loss. The combination of BO-1978 with gefitinib further suppressed EGFR mutant NSCLC cell growth in xenograft tumor and orthotopic lung tumor models. Preclinical toxicity studies showed that BO-1978 administration did not cause apparent toxicity in mice. Based on its significant therapeutic efficacy and low drug toxicity, BO-1978 is a potential therapeutic agent for treatment of NSCLC.

PI3K Inhibition Augments the Therapeutic Efficacy of a 3a-aza-Cyclopenta[α]indene Derivative in Lung Cancer Cells

The synergistic targeting of DNA damage and DNA repair is a promising strategy for the development of new chemotherapeutic agents for human lung cancer. The DNA interstrand cross-linking agent BO-1509, a derivative of 3a-aza-cyclopenta[α]indene, was synthesized and combined with the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 to treat human lung cancer cells. Our results showed that the BO-1509 and LY294002 combination synergistically killed lung cancer cells in culture and also suppressed the growth of lung cancer xenografts in mice, including those derived from gefitinib-resistant cells. We also found that LY294002 suppressed the induction of several DNA repair proteins by BO-1509 and inhibited the nuclear translocation of Rad51. On the basis of the results of the γH2AX foci formation assays, LY294002 apparently inhibited the repair of DNA damage that was induced by BO-1509. According to the complete blood profile, biochemical enzyme analysis, and histopathologic analysis of major organs, no apparent toxicity was observed in mice treated with BO-1509 alone or in combination with LY294002. Our results suggest that the combination of a DNA cross-linking agent with a PI3K inhibitor is a feasible strategy for the treatment of patients with lung cancer.

Paxillin promotes tumor progression and predicts survival and relapse in oral cavity squamous cell carcinoma by microRNA-218 targeting

High-risk human papillomavirus (HPV) 16-infected oral cavity squamous cell carcinoma (OCSCC) differs significantly from non-HPV-infected OCSCC. However, the molecular pathogenesis of HPV-infected OCSCC remains unclear. Paxillin (PXN) has been reported to promote lung tumor progression by miR-218 targeting. In addition, expression of miR-218 has been shown to be reduced by HPV16 E6 in cervical cancer. We thus asked whether PXN can promote tumor progression by E6-reduced miR-218 in OCSCC, especially in HPV-infected OCSCC. Mechanistic studies demonstrated that PXN expression increased markedly upon E6-mediated reductions in miR-218, resulting in increased colony formation and invasion capabilities in HPV-infected OCSCC cells. Among tumor specimens, HPV16/18 infection was negatively associated with miR-218 expression and positively associated with PXN expression. Kaplan-Meier and Cox regression models demonstrated that patients with low-miR-218 tumors or high-PXN tumors exhibited shorter overall survival (OS) and relapse-free survival (RFS) than those with high-miR-218 tumors or low-PXN tumors. Interestingly, HPV-infected patients with low-miR-218, high-PXN tumors and both combinations exhibited the worst OS and RFS compared with patients in their counterparts. These observations in patients were consistent with the findings from the cell model. Therefore, we suggest that PXN might be targeted to suppress tumor progression and consequently to improve outcomes in OCSCC, especially in HPV-infected OCSCC.

Differential impact of IL-10 expression on survival and relapse between HPV16-positive and -negative oral squamous cell carcinomas

Human papillomavirus (HPV) is a risk factor in a subset of oropharyngeal cancer; however, the contribution of HPV in the malignancy of oral squamous cell carcinomas (OSCC) is not fully understood in Taiwanese. Herein, 61 patients with no risk factors and 117 patients with one or more risk factors were enrolled in this study. HPV16/18 infection rate in non-smokers, non-drinkers and non-betel quid chewers was higher than their counterparts. The development of HPV-infected cancer has been shown to be associated with interleukin-10 (IL-10) expression. To this end, IL-10 mRNA expression in OSCC tumors was evaluated by real-time RT-PCR. Data showed that HPV-positive patients had higher IL-10 mRNA levels than in HPV-negative patients. Kaplan-Meier and Cox-regression analysis indicated that the prognostic significance of IL-10 mRNA on overall survival and relapse free survival was only observed in HPV-positive OSCC, but not in HPV-negative OSCC. Mechanistically, the elevation of IL-10 by E6 was responsible for increased colony formation and migration capability in OSCC cells. Therefore, we suggest that IL-10 induced by E6 promotes cell growth and migration capability and consequent poor survival and relapse in HPV-positive OSCC.

Depleting IFIT2 mediates atypical PKC signaling to enhance the migration and metastatic activity of oral squamous cell carcinoma cells

Interferon-induced protein with tetratricopeptide repeats 2 (IFIT2) is one of the most highly responsive interferon-stimulated genes, but its biological functions are poorly understood. In this study, we aimed to explore the underlying mechanisms by which depleting IFIT2 induces the migration of oral squamous cell carcinoma (OSCC) cells. Stable IFIT2-depleted cells underwent epithelial-mesenchymal transition (EMT) and exhibited enhanced cell motility and invasiveness compared with control cells. Furthermore, our results indicated that atypical protein kinase C (aPKC) was activated in IFIT2-depleted cells. Inhibition of aPKC using a specific myristoylated PKCζ pseudosubstrate or aPKC-targeting small interfering RNA (siRNA) abolished IFIT2 depletion-induced EMT, migration and invasion, indicating that the activation of aPKC has an essential role in regulating the cellular responses induced by IFIT2 depletion. Following tail-vein injection, IFIT2-depleted OSCC cells colonized not only the lungs but also the heart, head and neck, retroperitoneal, and peritoneal cavities; whereas control cells predominantly localized in the lungs. IFIT2 mRNA and protein expression was positively associated with E-cadherin expression in OSCC patient specimens. The loss of E-cadherin and IFIT2 expression was observed at the invasive front of OSCC tumors, suggesting that the loss of IFIT2 may induce EMT and lead to the metastasis of OSCCs. OSCC patients possessing reduced IFIT2-expression levels (IFIT2 <50%) exhibited greater rates of distant metastasis and poor prognoses compared with OSCC patients who expressed greater levels of IFIT2 (IFIT2 ≥50%). These results demonstrate that IFIT2 depletion activates the aPKC pathway and consequently induces EMT, cell migration and invasion. Most importantly, depleting IFIT2 may participate in OSCC tumor progression, particularly during metastasis. Taken together, our study demonstrates that IFIT2, a protein responsible for interferon stimulation, may prevent OSCC metastasis and serve as a valuable prognostic marker.

AKT serine/threonine protein kinase modulates bufalin-triggered intrinsic pathway of apoptosis in CAL 27 human oral cancer cells

Bufalin has been reported to induce apoptosis in a variety of cancers but little is demonstrated in oral squamous cell carcinoma (OSCC) cells. The present study investigated the inhibition of proliferation, cell cycle arrest and apoptotic effects of bufalin in CAL 27 human oral cancer cells. Bufalin inhibited the growth of CAL 27 cells in a concentration-dependent manner and an IC50 value of bufalin was about 125 nM for 24 h treatment using the MTT assay. Moreover, the cell cycle distribution was arrested at the G0/G1 phase in CAL 27 cells after bufalin exposure. Upon bufalin stimulation, the expression of Bcl-2 was significantly decreased while that of cytochrome c, Apaf-1 and AIF was increased compared to the control group by western blot analysis. An increase in the expression of the active form of caspases was found in bufalin-treated cells, and the caspase activities were also elevated. Bufalin-triggered apoptosis was blocked by specific inhibitors of caspase-9 (z-LEHD-fmk) and caspase-3 (z-DEVD-fmk), respectively. In contrast, CAL 27 cells overexpressing constitutively active AKT (CAL 27/CA-AKT) were exposed to bufalin at different concentrations, and cell growth remained unchanged. Bufalin exhibited minimal apoptotic effects on CAL 27/CA-AKT cells. Taken together, bufalin induced G0/G1 phase arrest and provoked the intrinsic apoptotic pathway via AKT activation in CAL 27 cells. Our data suggest that bufalin could be potentially efficacious in the treatment of oral cancer in the future.

Triggering apoptotic death of human malignant melanoma a375.s2 cells by bufalin: involvement of caspase cascade-dependent and independent mitochondrial signaling pathways

Bufalin was obtained from the skin and parotid venom glands of toad and has been shown to induce cytotoxic effects in various types of cancer cell lines, but there is no report to show that whether bufalin affects human skin cancer cells. The aim of this investigation was to study the effects of bufalin on human malignant melanoma A375.S2 cells and to elucidate possible mechanisms involved in induction of apoptosis. A375.S2 cells were treated with different concentrations of bufalin for a specific time period and investigated for effects on apoptotic analyses. Our results indicated that cells after exposure to bufalin significantly decreased cell viability, and induced cell morphological changes and chromatin condensation in a concentration-dependent manner. Flow cytometric assays indicated that bufalin promoted ROS productions, loss of mitochondrial membrane potential (ΔΨ_m), intracellular Ca²⁺ release, and nitric oxide (NO) formations in A375.S2 cells. Additionally, the apoptotic induction of bufalin on A375.S2 cells resulted from mitochondrial dysfunction-related responses (disruption of the ΔΨ_m and releases of cytochrome c, AIF, and Endo G), and activations of caspase-3, caspase-8 and caspase-9 expressions. Based on those observations, we suggest that bufalin-triggered apoptosis in A375.S2 cells is correlated with extrinsic- and mitochondria-mediated multiple signal pathways.