Apoptosis In Skin Cancer Cells Research Articles

The Protective Effects of Mcl-1 on Mitochondrial Damage and Oxidative Stress in Imiquimod-Induced Cancer Cell Death.

Mitochondria, vital organelles that generate ATP, determine cell fate. Dysfunctional and damaged mitochondria are fragmented and removed through mitophagy, a mitochondrial quality control mechanism. The FDA-approved drug IMQ, a synthetic agonist of Toll-like receptor 7, exhibits antitumor activity against various skin malignancies. We previously reported that IMQ promptly reduced the level of the antiapoptotic Mcl-1 protein and that Mcl-1 overexpression attenuated IMQ-triggered apoptosis in skin cancer cells. Furthermore, IMQ profoundly disrupted mitochondrial function, promoted mitochondrial fragmentation, induced mitophagy, and caused cell death by generating high levels of ROS. However, whether Mcl-1 protects mitochondria from IMQ treatment is still unknown. In this study, we demonstrated that Mcl-1 overexpression induced resistance to IMQ-induced apoptosis and reduced both IMQ-induced ROS generation and oxidative stress in cancer cells. Mcl-1 overexpression maintained mitochondrial function and integrity and prevented mitophagy in IMQ-treated cancer cells. Furthermore, IL-6 protected against IMQ-induced apoptosis by increasing Mcl-1 expression and attenuating IMQ-induced mitochondrial fragmentation. Mcl-1 overexpression ameliorates IMQ-induced ROS generation and mitochondrial fragmentation, thereby increasing mitochondrial stability and ultimately attenuating IMQ-induced cell death. Investigating the roles of Mcl-1 in mitochondria is a potential strategy for cancer therapy development.

Anethole suppresses the growth of human skin cancer cells by targeting microRNA498/STAT4 axis

Purpose: To investigate the effects of anethole on human skin cancer cells.
 Methods: Cell viability was determined using CCK-8 and colony formation assay, while AO/EB and Annexin V/PI assays were used to assess apoptosis. The mRNA expressions of genes were assayed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR).
 Results: The growth of skin cancer cells was significantly reduced by anethole (p < 0.05). On the other hand, normal human skin cells were marginally affected by anethole. Furthermore, anethole significantly suppressed the colony formation potential of CRL-6475 skin cancer cells in a concentration-dependent manner (p < 0.05). Results from AO/EB and annexin V/PI staining assays revealed that anethole induced apoptosis in skin cancer cells, while qRT-PCR results indicate that anethole significantly up-regulated microRNA-498 in skin cancer cells (p < 0.05). However, anethole had no effect on the expression levels of miR-7, miR-9, miR-145, miR-31, miR-27, miR-498 miR-1298, miR-1299, 1179, miR-375, miR-508 and miR-23. CCK-8 assay results confirmed that miR-498 up-regulation significantly mimicked the anti-proliferative effects of anethole. Bioinformatics analysis and luciferase reporter assay led to identification of STAT4 as the regulatory target of miR-498. Furthermore, silencing of STAT4 significantly mimicked the effects of anethole administration (p < 0.05).
 Conclusion: These results indicate that anethole inhibits skin cancer cell growth by targeting the miR-498/STAT4 axis, and therefore, has potentials for use in the management of skin cancer.

Plant derived coumestrol phytochemical targets human skin carcinoma cells by inducing mitochondrial-mediated apoptosis, cell cycle arrest, inhibition of cell migration and invasion and modulation of m-TOR/PI3K/AKT signalling pathway.

The current study was undertaken to investigate anticancer activity of coumestrol phytoestrogen against human skin cancer. MTT assay was performed for cell viability assessment and clonogenic assay for cell colony formation assessment. Apoptosis was analysed by Annexin V/FITC staining, AO/EB staining and western blotting assays. Effects on the m-TOR/PI3K/AKT signalling pathway were investigated by western blotting. Results indicated that coumestrol induced significant toxicity in human skin cancer cells in contrast to mouse skin cancer cells. The proliferation rate in normal skin cells remained almost intact. Annexin V-FITC and AO/EB staining assays indicated coumestrol induced cytotoxicity in skin cancer cells is mediated through apoptosis stimulation. The apoptosis in skin cancer cells was mediated through caspase-activation. Cell migration and invasion was inhibited by coumestrol in human skin cancer cells via inhibition of MMP-2 and MMP-9 expressions. Moreover, m-TOR/PI3K/AKT signalling pathway in SKEM-5 cells was blocked by coumestrol.

Downregulation of survivin by adenovirus-mediated shRNA promotes apoptosis in skin cancer cells.

BackgroundSurvivin, a member of the inhibitor of apoptosis protein family, is highly expressed in many cancers and has important roles in inhibiting apoptosis by blocking caspase activation. However, its antitumor effects remain largely unknown. Here we explore the function of survivin in skin cancer.MethodsWe used qPCR and Western blot to examine survivin expression in skin cancer patients and cell line. We generated several survivin shRNA constructs and tested the effects of survivin shRNA on cancer cell viability using MTT assay, flow cytometry, and TUNEL assay.ResultsWe found that survivin was upregulated in both skin cancer patients and skin cancer cell line A431. Knockdown survivin via shRNA inhibited cancer cell proliferation and promoted apoptosis in both A431 cell and in vivo xenograft tumor mouse model. The antitumor effect is comparable to resveratrol, a drug known to inhibit cancer progression. Moreover, we showed that inhibition of survivin was able to increase the expression of cleaved caspase 7/caspase 9 and activate the ataxia-telangiectasia mutated-NF-κB pathway in A431 cells.ConclusionSurvivin-shRNA possesses antitumor abilities in vitro and in vivo by inhibiting the proliferation and promoting apoptosis of A431 cells. It may serve as a potential anticancer target for skin cancer therapy in the future.

Ibrutinib presents antitumor activity in skin cancer and induces autophagy.

Skin cancer is one of the most common malignancies in dermatology. Patient compliance and prognosis of skin cancer are poor. Ibrutinib, a Bruton's Tyrosine Kinase (BTK) inhibitor, is a new anticancer drug used to treat many cancers. Therefore, we aimed to explore the role of ibrutinib in the treatment of skin cancer. Cell Counting Kit-8 (CCK8) and plate cloning assay were used to detect cell proliferation. Apoptosis was determined by flow cytometry. Western blotting analysis was used to analyze the expression of key proteins that regulated autophagy. Proliferation and apoptosis of skin cancer cells and induction of autophagy induced by ibrutinib were evaluated. CCK8 plate cloning assays showed that ibrutinib can gradually inhibit the skin cancer cell proliferation as the treatment time and dose increased. Results of flow cytometry showed that apoptosis in skin cancer cells were induced after ibrutinib treatment. Western blot showed that autophagy in skin cancer cells was found induced by ibrutinib and also related to the time and concentration of ibrutinib treatment. Combination treatment of ibrutinib and 3MA for skin cancer cells can significantly increase apoptosis. Ibrutinib has anti-tumor activity in skin cancer and can induce autophagy. Binding to autophagy inhibitors can promote ibrutinib's anti-skin cancer activity. Our experimental results provided new ideas for developing skin cancer drugs.

Demethoxycurcumin in combination with ultraviolet radiation B induces apoptosis through the mitochondrial pathway and caspase activation in A431 and HaCaT cells.

Photodynamic therapy is widely used in the clinical treatment of tumors, especially skin cancers. It has been reported that the photosensitizer curcumin, in combination with ultraviolet radiation B, induces HaCaT cell apoptosis, and this effect may be due to the activation of caspase pathways. In this study, we examined the photodynamic effects of demethoxycurcumin, a more stable analogue of curcumin, to determine whether it could induce apoptosis in skin cancer cells. We investigated the effects of a combination of ultraviolet radiation B and demethoxycurcumin on apoptotic cell death in A431 and HaCaT cells and determined the molecular mechanism of action. Our results showed increased apoptosis with a combination of ultraviolet radiation B with demethoxycurcumin, as compared to ultraviolet radiation B or demethoxycurcumin alone. The combination of ultraviolet radiation B irradiation with demethoxycurcumin synergistically induced apoptotic cell death in A431 and HaCaT cells through activation of p53 and caspase pathways, as well as through upregulation of Bax and p-p65 expression and downregulation of Bcl-2, Mcl-1, and nuclear factor-κB expression. In addition, we found that reactive oxygen species significantly increased with treatment, and mitochondrial membrane potential depolarization was remarkably enhanced. In conclusion, our data indicate that demethoxycurcumin may be a promising photosensitizer for use in photodynamic therapy to induce apoptosis in skin cancer cells.

2-O-Methylmagnolol upregulates the long non-coding RNA, GAS5, and enhances apoptosis in skin cancer cells

Magnolol, a hydroxylated biphenol compound isolated from the bark of Magnolia officinalis, has been shown to exhibit anti-proliferative effect in various cancer cells, including skin cancer cells. Methoxylation of magnolol appears to improve its anti-inflammatory activity, yet the effect of this modification on the agent’s antitumor activity remains unknown. In this work, we report that 2-O-methylmagnolol (MM1) displays improved antitumor activity against skin cancer cells compared to magnolol both in vitro and in vivo. The increased antitumor activity of MM1 appears to correlate with its increased ability to induce apoptosis. DNA microarray and network pathway analyses suggest that MM1 affects certain key factors involved in regulating apoptosis and programmed cell death. Interestingly, the level of the long non-coding (lnc) RNA of growth arrest-specific 5 (GAS5) was increased in MM1-treated cells, and inhibition of lncRNA GAS5 inhibited MM1-induced apoptosis. Conversely, overexpression of lncRNA GAS5 inhibited cell proliferation and promoted cell apoptosis in skin cancer cells. The expression of lncRNA GAS5 in the skin cancer tissues was found to be lower than that in the adjacent normal tissues in a majority of patients. Taken together, our findings suggest that MM1 has improved antitumor activity in skin cancer cells, and that this is due, at least in part, to the upregulation of lncRNA GAS5 and the enhancement of apoptosis.

Comparative Studies to Evaluate Relative in vitro Potency of Luteolin in Inducing Cell Cycle Arrest and Apoptosis in HaCaT and A375 Cells

Luteolin is a naturally occurring flavonoid present in many plants with diverse applications in pharmacology. Despite several studies elucidating its significant anti-cancer activity against various cancer cells, the mechanism of action in skin cancer is not well addressed. Hence, we investigated the effects of luteolin in HaCaT (human immortalized keratinocytes) and A375 (human melanoma) cells. The radical scavenging abilities of luteolin were determined spectrophotometrically, prior to a cytotoxic study (XTT assay). Inhibitory effects were assessed by colony formation assay. Further, the capability of luteolin to induce cell cycle arrest and apoptosis were demonstrated by flow cytometry and cellular DNA fragmentation ELISA, respectively. The results revealed that luteolin possesses considerable cytotoxicity against both HaCaT and A375 cells with IC50 values of 37.1 μM and 115.1 μM, respectively. Luteolin also inhibited colony formation and induced apoptosis in a dose and time-dependent manner by disturbing cellular integrity as evident from morphological evaluation by Wright- Giemsa staining. Accumulation of cells in G2/M (0.83-8.14%) phase for HaCaT cells and G0/G1 (60.4-72.6%) phase for A375 cells after 24 h treatment indicated cell cycle arresting potential of this flavonoid. These data suggest that luteolin inhibits cell proliferation and promotes cell cycle arrest and apoptosis in skin cancer cells with possible involvement of programmed cell death, providing a substantial basis for it to be developed into a potent chemopreventive template for skin cancer.

The Oncolytic Effect of Respiratory Syncytial Virus (RSV) in Human Skin Cancer Cell Line, A431

BackgroundOncolytic viruses have become of noticeable interest as a novel biological approach for selectively infecting cancer cells and triggering apoptosis in a number of malignant cells. Many researches are devoted to characterize more viruses with oncolytic properties.ObjectivesEvidences on the oncolytic feature of respiratory syncytial virus (RSV) are conflicting; therefore, this study was designed to elucidate the possible role of RSV on the modulation of cell growth and apoptosis in the skin cancer cells.Materials and MethodsPlaque assay was used to determine RSV titers. The cytotoxic effect of RSV in A431 (skin carcinoma cell line) was determined using MTT assay. The detection of apoptosis was performed via Annexin-V-FITC staining method and analyzed with flow cytometry.ResultsThe results indicated that A431 cell growth was inhibited following infection by RSV in a dose- and time-dependent manner. The most growth inhibitory effect of RSV was occurred at the MOI of 3, and 48 hour after infection. The inhibitory effect of RSV on the cell growth was accompanied by the induction of apoptosis in the skin cancer cells. The percentages of early and late apoptotic cells were increased following exposure to RSV in a concentration- and time-dependent manner.ConclusionsThis study delineated the beneficial role of RSV for growth regulation of skin cancer cells and highlighted the involvement of RSV in the induction of apoptosis in A431 cells. These findings might conduct evidence into the oncolytic properties of RSV in the skin cancer. Further studies are required to indicate intracellular targets for RSV-induced apoptosis in skin cancer cells.

Apoptosis Induction by Rafflesia kerrii Meijer Flower Extract via Caspase-Dependent and Down-Regulation of ERK Signaling Pathway in Epidermoid Carcinoma Cells

Plant extracts have been shown to be important sources of anti-cancer agents. Rafflesia kerrii Meijer (RM) is found in the rainforest of southern part of Thailand and its local name is Bua Phut. The single biggest flower has awful smell to attract flies for pollination. This study aims to investigate the activity of RM flower extract on apoptosis induction in skin cancer cells. The results showed that the RM flower extract showed the anti-proliferative activity in A431 skin cancer cells in a time- and dose-dependent manner. The morphological changes and nuclear staining with Hoechst 33342 showed evidence of apoptosis including nuclear condensation and fragmentation. RM flower extract also activated caspase-3 expression. Furthermore, phosphorylated-ERK was decreased but phosphorylated-JNK and phosphorylated-p38 were increased in A431 cells treated with RM flower extract. RM flower extract also decreased phosphorylated Akt. These results suggest that RM flower extract induced apoptosis in skin cancer cells through down-regulation of ERK and Akt signaling pathway. RM flower extract may represent an important source of novel potential antitumor agents due to its cytotoxic activity towards malignant cells. Keywords: Rafflesia kerrii Meijer, cytotoxicity, apoptosis, skin cancer, A431 cells. Read more →

Human Multipotent Stem Cell Proteins Induce Apoptosis in Skin Cancer Cells

Unique characteristics in fetal development include scar-less wound healing and the paucity of tumor formation. Recent studies have demonstrated that the embryonic microenvironment can reverse melanoma cells to a benign melanocyte phenotype. We bioengineered embryonic-like compositions and tested the anti-cancer activity of this material on a panel of skin cancer lines. To simulate the embryonic environment, neonatal fibroblasts were grown in hypoxic suspension cultures. The cells reverted back into multipotent stem cells as evidenced by the upregulation of SOX2, Oct4, NANOG, and KLF4 genes, and by the expression of stem cell-associated proteins including Nodal, Brachyury, Nestin, and Oct4. Cell Conditioned Media (CCM) and human Extracellular Matrix Proteins (hECM) produced by these cells were tested for their ability to reduce cell viability in skin cancer cell lines. In vitro studies with CCM and hECM show reduction in Squamous Cell Carcinoma (SCC), Basal Cell Carcinoma (BCC) and melanoma cell number through upregulation of caspases and induction of apoptosis. In the chick allantoic membrane assay, melanoma load was reduced by up to 80% with hECM treatment compared to vehicle treated controls (p 0.05). Similar inhibition was seen with SCC cells. In a xenograft mouse model of subcutaneous melanoma, tumor growth was inhibited by 70% - 90%. These data suggest that CCM and hECM have anti tumor potential and might offer a new treatment strategy in skin cancer.

P53 modulates the AMPK inhibitor compound C induced apoptosis in human skin cancer cells

Compound C, a well-known inhibitor of the intracellular energy sensor AMP-activated protein kinase (AMPK), has been reported to cause apoptotic cell death in myeloma, breast cancer cells and glioma cells. In this study, we have demonstrated that compound C not only induced autophagy in all tested skin cancer cell lines but also caused more apoptosis in p53 wildtype skin cancer cells than in p53-mutant skin cancer cells. Compound C can induce upregulation, phosphorylation and nuclear translocalization of the p53 protein and upregulate expression of p53 target genes in wildtype p53-expressing skin basal cell carcinoma (BCC) cells. The changes of p53 status were dependent on DNA damage which was caused by compound C induced reactive oxygen species (ROS) generation and associated with activated ataxia-telangiectasia mutated (ATM) protein. Using the wildtype p53-expressing BCC cells versus stable p53-knockdown BCC sublines, we present evidence that p53-knockdown cancer cells were much less sensitive to compound C treatment with significant G2/M cell cycle arrest and attenuated the compound C-induced apoptosis but not autophagy. The compound C induced G2/M arrest in p53-knockdown BCC cells was associated with the sustained inactive Tyr15 phosphor-Cdc2 expression. Overall, our results established that compound C-induced apoptosis in skin cancer cells was dependent on the cell's p53 status.

The glucose availability and the induction of HIF-1 alpha expression determine the imiquimod induced apoptosis in cancer cells

Tumor cells uptake more glucose and rely on glycolysis even on the presence of abundant oxygen and decrease mitochondrial respiration. Imiquimod can against skin cancers by activation of cellular-mediated immune response in vivo and also directly induces autophagic cell death and intrinsic apoptosis in skin cancer cells in vitro. Whether imiquimod modulate glucose metabolic pathways and these effects on its anti-tumor activity are still unknown. In this study, we observed that imiquimod promoted extracellular glucose depletion, enhanced lactate production and decreased oxygen consumption in several tumor cell lines.

Sulforaphane Induction of p21Cip1 Cyclin-dependent Kinase Inhibitor Expression Requires p53 and Sp1 Transcription Factors and Is p53-dependent

Sulforaphane (SFN) is an important cancer preventive agent derived from cruciferous vegetables. We show that SFN treatment suppresses normal human keratinocyte proliferation via a mechanism that involves increased expression of p21(Cip1). SFN treatment produces a concentration-dependent increase in p21(Cip1) promoter activity via a mechanism that involves stabilization of the p53 protein leading to increased p53 binding to the p21(Cip1) promoter p53 response elements. The proximal p21(Cip1) promoter GC-rich Sp1 factor binding elements are also required, as the SFN-dependent increase is lost when these sites are mutated. SFN treatment increases Sp1 binding to these elements, and the response is enhanced in the presence of exogenous Sp1 and reduced in the presence of ΔN-Sp3. CpG island methylation alters p21(Cip1) promoter activity some systems; however, expression in SFN-treated keratinocytes does not involve changes in proximal promoter methylation. The promoter is minimally methylated, and the methylation level is not altered by SFN treatment. This study indicates that SFN increases p21(Cip1) promoter transcription via a mechanism that involves SFN-dependent stabilization of p53 and increased p53 and Sp1 binding to their respective response elements in the p21(Cip1) promoter. These results are in marked contrast to the mechanisms observed in skin cancer cell lines and suggest that SFN may protect normal keratinocytes from damage while causing cancer cells to undergo apoptosis.

Dihydroartemisinin induces apoptosis in skin cancer cell line A-431 via ROS pathway

–Dihydroartemisinin (DHA) is a derivative of artemisinin that has been shown to inhibit cell growth and induce apoptosis in the several cancer cells via reactive oxygen species (ROS) formation. The present study was designed to understand the mechanism underlying Dihydroartemisinin-induced apoptosis in the A-431 human skin cancer cell line.MTT viability assay was used to study the cell proliferation effect of Dihydroartemisinin. Annexin V-FITC and reactive oxygen species (ROS) formation were assessed to detect apoptosis. Dihydroartemisinin significantly inhibited cell proliferation in a concentration-dependent manner in A-431 cell line. Dihydroartemisinin significantly induced apoptosis, which was determined by Annexin VFITC staining. Moreover, increase of ROS formation was observed in response to Dihydroartemisinin treatment. The results of this study suggest that Dihydroartemisinin inhibited cell proletarian and induced apoptosis in skin cancer cells via ROS pathways. These data might suggest that Dihydroartemisinin could be used as an agent for the treatment of skin cancer. Keywords––Skin cancer, Dihydroartemisinin, apoptosis, ROS.

Acitretin induces apoptosis through CD95 signalling pathway in human cutaneous squamous cell carcinoma cell line SCL‐1

Skin cancers are by far the most common human malignancies. Retinoids have shown promising preventive and therapeutic effects against a variety of human malignancies. The aim of this study was to investigate the apoptosis-inducing effect of acitretin on human skin squamous cell carcinoma (SCC) SCL-1 cells. We found that acitretin preferentially inhibited the growth of SCL-1 cells in a dose- and time-dependent manner, but not of non-malignant keratinocyte HaCaT cells. This inhibition appeared to be due to induction of apoptosis as revealed by enzyme-linked immunosorbent assay. AnnexinV/propidium iodide assay and morphological observation confirmed the pro-apoptotic effect of acitretin on SCL-1 cells. We further demonstrated that apoptosis was induced within 1–2 days and involved activation of caspases-8, -9, -3 and poly (ADP-ribose) polymerase (PARP). Caspase-8 inhibitor effectively suppressed acitretin-induced apoptosis whereas caspase-9 inhibitor did not. Acitretin increased the levels of CD95 (Fas), CD95-ligand and Fas-associated death domain. Neutralizing ZB4 anti-Fas antibody significantly inhibited the apoptosis in SCL-1 cells induced by acitretin. These results suggest that acitretin is able to induce apoptosis in skin cancer cells possibly via death receptor CD95 apoptosis pathway without affecting the viability of normal keratinocyte.

Photosensitizer effect of curcumin on UVB-irradiated HaCaT cells through activation of caspase pathways

Photodynamic therapy (PDT) using photosensitizer can induce diverse cellular responses, including apoptosis. Recently, it has been reported that PDT using methylaminolaevulinate may be effective in basal cell carcinoma. However, it is largely unknown whether PDT using a natural product such as curcumin can induce apoptosis in skin cancer. In this study, to confirm the photodynamic effect of curcumin, we investigated the synergistic effect of the combination of UVB with curcumin on apoptotic cell death in HaCaT cells and molecular mechanisms underlying apoptosis. Our data showed that HaCaT cells were markedly undergoing apoptosis, evidenced by DNA laddering, by combination of UVB with curcumin, compared to UVB or curcumin alone. Furthermore, combination of UVB irradiation with curcumin synergistically induces apoptotic cell death in HaCaT cells through activation of caspase-8, and -3 as well as caspase-9 activation followed by release of cytochrome c. Thus, our data indicate that curcumin may be a promising photosensitizer used in PDT to induce apoptosis in skin cancer cells.

Betulinic acid induces apoptosis in skin cancer cells and differentiation in normal human keratinocytes

Betulinic acid (BA), a pentacyclic triterpene of plant origin, induces cell death in melanoma cells and other malignant cells of neuroectodermal origin. Little is known about additional biological effects in normal target cells. We show, in this study, that BA induces differentiation as well as cell death in normal human keratinocytes (NHK). Cytotoxicity profiles of BA are compared among normal human keratinocytes, HaCaT cells, IGR1 melanoma cells and normal melanocytes. As expected, BA is toxic to all cell types, normal and malignant, but varies in its cytotoxic potency and in the extent of induction of apoptotic vs. necrotic cell death in the four different skin cell types. Apoptosis is proved by annexin V and Apo2.7 binding and by DNA fragmentation. Induction of differentiation-associated antigens in keratinocytes--filaggrin and involucrin--is demonstrated, together with specific morphological changes in treated cell cultures. BA, apart from its cytotoxic activities in cellular systems, is capable of inducing differentiation of NHK into corneocytes without immediately provoking apoptotic cell death.

Apoptosis induction by the natural product cancer chemopreventive agent deguelin is mediated through the inhibition of mitochondrial bioenergetics.

Deguelin exhibits chemopreventive properties in animal carcinogenesis models. The mechanism underpinning the chemopreventive effects of deguelin has not been fully elucidated. However, it has been suggested that this agent reduces ornithine decarboxylase activity, and perhaps the activity of other signaling intermediates associated with tumorigenesis, by inhibiting mitochondrial bioenergetics. We sought to determine if deguelin could trigger apoptosis by inhibiting mitochondrial bioenergetics. Therefore, we compared and contrasted the effects of deguelin on cells from two human cutaneous squamous cell carcinoma cell lines (parental cells) and their respiration-deficient clones lacking mitochondrial DNA (rho0). While deguelin promoted marked apoptosis in the parental cells in a dose- and time-dependent manner, it failed to do so in the rho0 clones. Furthermore, short-term exposure to deguelin diminished oxygen consumption by the parental cells and promoted mitochondrial permeability transition as evidenced by the dissipation of mitochondrial inner transmembrane potential, reactive oxygen species production, cardiolipin peroxidation, caspase activation, and mitochondrial swelling. Mitochondrial permeability transition was not observed in the rho0 clones exposed to deguelin. These results demonstrate that deguelin induces apoptosis in skin cancer cells by inhibiting mitochondrial bioenergetics and provide a novel mechanism for the putative anticancer activity of this agent.

Tumor-selective induction of apoptosis and the small-molecule immune response modifier imiquimod.

The incidence of nonmelanoma skin cancer, basal cell carcinomas (BCCs), and squamous cell carcinomas (SCCs) is increasing, representing a major medical and economic problem. Imiquimod, a topical small-molecule immune response modifier, has shown efficacy toward BCC and actinic keratoses in clinical trials. Imiquimod acts both indirectly, via cytokine-mediated stimulation of cellular immune responses, and directly, through unknown mechanisms against tumor cells. We examined the mechanism by which imiquimod induces apoptosis in cancer cells. Apoptosis was assessed by enzyme-linked immunosorbent assay, western blot analysis, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays in five SCC cell lines, HaCaT cells (a spontaneously immortalized human keratinocyte cell line), and normal keratinocytes treated with imiquimod, with its analog resiquimod, or with neither. Expression of death receptors, caspases, and cytochrome c in the apoptotic signaling cascade was analyzed using western blot and flow cytometric analyses. The functional relevance of imiquimod-induced cytochrome c release was assessed by transfection of HaCaT cells with Bcl-2. Apoptosis in BCCs in vivo was assessed by TUNEL assays of imiquimod-treated and untreated tumors from three patients. Differences between treated and untreated cells and tumors were determined using a two-tailed Student's t test. Imiquimod, but not resiquimod, induced apoptosis in all SCC cell lines and HaCaT cells. This induction involved activation of several caspases and Bcl-2-dependent cytosolic translocation of cytochrome c but was independent of the membrane-bound death receptors Fas, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-R1-R4 receptors, and tumor necrosis factor-R1 and -R2 receptors. Topical application of imiquimod to BCC tumors in vivo induced apoptosis. Imiquimod has the potential to induce apoptosis in skin cancer cells, possibly by circumventing mechanisms developed by malignant tumors to resist apoptotic signals.