Mcl-1 antisense therapy chemosensitizes human melanoma in a SCID mouse xenotransplantation model

Understanding MCL1: from cellular function and regulation to pharmacological inhibition

Myeloid cell leukemia-1 (MCL1), an antiapoptotic member of the BCL2 family characterized by a short half-life, functions as a rapid sensor that regulates cell death and other relevant processes that include cell cycle progression and mitochondrial homeostasis. In cancer, MCL1 overexpression contributes to cell survival and resistance to diverse chemotherapeutic agents; for this reason, several MCL1 inhibitors are currently under preclinical and clinical development for cancer treatment. However, the nonapoptotic functions of MCL1 may influence their therapeutic potential. Overall, the complexity of MCL1 regulation and function represent challenges to the clinical application of MCL1 inhibitors. We now summarize the current knowledge regarding MCL1 structure, regulation, and function that could impact the clinical success of MCL1 inhibitors.

Myeloid cell leukemia-1: a formidable barrier to anticancer therapeutics and the quest of targeting it

The antiapoptotic B cell lymphoma-2 (Bcl-2) family members are apical regulators of the intrinsic pathway of apoptosis that orchestrate mitochondrial outer membrane permeabilization (MOMP) through interactions with their proapoptotic counterparts. Overexpression of antiapoptotic Bcl-2 family proteins has been linked to therapy resistance and poor prognosis in diverse cancers. Among the antiapoptotic Bcl-2 family members, predominant overexpression of the prosurvival myeloid cell leukemia-1 (Mcl-1) has been reported in a myriad of hematological malignancies and solid tumors, contributing to therapy resistance and poor outcomes, thus making it a potential druggable target. The unique structure of Mcl-1 and its complex regulatory mechanism makes it an adaptive prosurvival switch that ensures tumor cell survival despite therapeutic intervention. This review focusses on diverse mechanisms adopted by tumor cells to maintain sustained elevated levels of Mcl-1 and how high Mcl-1 levels contribute to resistance in conventional as well as targeted therapies. Moreover, recent developments in the Mcl-1-targeted therapeutics and the underlying challenges and considerations in designing novel Mcl-1 inhibitors are also discussed.

New insights into the roles of antiapoptotic members of the Bcl-2 family in melanoma progression and therapy

Prosurvival and antiapoptotic B cell lymphoma-2 (Bcl-2) family proteins are often overexpressed in cutaneous melanoma, one of the most aggressive types of human cancer. They are also implicated in resistance to therapy and participate in melanoma progression by regulating various processes, including cell proliferation, migration, invasion, and crosstalk with the tumor microenvironment. In this review, we summarize recent findings related to prosurvival members of the Bcl-2 family beyond their canonical functions in the apoptotic pathway, mainly focusing on their potential roles as diagnostic and prognostic biomarkers in cutaneous melanoma. We also provide an overview of different approaches used to inhibit Bcl-2 proteins in preclinical and clinical studies, which are mainly based on the inhibition of protein expression or the disruption of their antiapoptotic functions.

Gene Therapy with MiRNA-Mediated Targeting of Mcl-1 Promotes the Sensitivity of Non-Small Cell Lung Cancer Cells to Treatment with ABT-737

BACKGROUND

Despite the dramatic efficacy of ABT-737, a large percentage of cancer cells ultimately become resistance to this drug. Evidences show that over-expression of Mcl-1 is linked to ABT-737 resistance in NSCLC cells. The aim of this study was to investigate the effect of miRNA-101 on Mcl-1 expression and sensitivity of the A549 NSCLC cells to ABT-737.

METHODS

After miRNA-101 transfection, the Mcl-1 mRNA expression levels were quantified by RT-qPCR. Trypan blue staining was used to explore the effect of miRNA-101 on cell growth. The cytotoxic effects of miRNA-101 and ABT-737, alone and in combination, were measured using MTT assay. The effect of drugs combination was determined using the method of Chou-Talalay. Cell death was assessed using cell death detection ELISA assay kit.

RESULTS

Results showed that miRNA-101 markedly suppressed the expression of Mcl-1 mRNA in a time dependent manner, which led to A549 cell proliferation inhibition and enhancement of apoptosis (p < 0.05, relative to blank control). Pretreatment with miRNA-101 synergistically decreased the cell survival rate and lowered the IC50 value of ABT-737. Furthermore, miRNA-101 dramatically enhanced the apoptotic effect of ABT-737. Negative control miRNA had no remarkable effect on cellular parameters.

CONCLUSIONS

Our findings propose that suppression of Mcl-1 by miRNA-101 can effectively inhibit the cell growth and sensitize A549 cells to ABT-737. Therefore, miRNA-101 can be considered as a potential therapeutic target in patients with non-small cell lung cancer.
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Inhibition of BCL2 Family Members Increases the Efficacy of Copper Chelation in BRAFV600E-Driven Melanoma

The principal unmet need in BRAF^V600E-positive melanoma is lack of an adequate therapeutic strategy capable of overcoming resistance to clinically approved targeted therapies against oncogenic BRAF and/or the downstream MEK1/2 kinases. We previously discovered that copper (Cu) is required for MEK1 and MEK2 activity through a direct Cu-MEK1/2 interaction. Repurposing the clinical Cu chelator tetrathiomolybdate (TTM) is supported by efficacy in BRAF^V600E-driven melanoma models, due in part to inhibition of MEK1/2 kinase activity. However, the antineoplastic activity of Cu chelators is cytostatic. Here, we performed high-throughput small-molecule screens to identify bioactive compounds that synergize with TTM in BRAF^V600E-driven melanoma cells. Genetic perturbation or pharmacologic inhibition of specific members of the BCL2 family of antiapoptotic proteins (BCL-W, BCL-XL, and MCL1) selectively reduced cell viability when combined with a Cu chelator and induced CASPASE-dependent cell death. Further, in BRAF^V600E-positive melanoma cells evolved to be resistant to BRAF and/or MEK1/2 inhibitors, combined treatment with TTM and the clinically evaluated BCL2 inhibitor, ABT-263, restored tumor growth suppression and induced apoptosis. These findings further support Cu chelation as a therapeutic strategy to target oncogene-dependent tumor cell growth and survival by enhancing Cu chelator efficacy with chemical inducers of apoptosis, especially in the context of refractory or relapsed BRAF^V600E-driven melanoma. SIGNIFICANCE: This study unveils a novel collateral drug sensitivity elicited by combining copper chelators and BH3 mimetics for treatment of BRAF^V600E mutation-positive melanoma.

MIM1 induces COLO829 melanoma cell death through mitochondrial membrane breakdown, GSH depletion, and DNA damage

Malignant melanoma is a high aggressive malignancy in humans and causes 60-80% of deaths from skin cancer. Defect in an intrinsic pathway of apoptosis via overexpression of Mcl-1 is responsible for malignant melanoma development and progression, and also for resistance to chemotherapeutic agents. MIM1 is a specific low molecular Mcl-1 protein inhibitor that is able to induce Mcl-1-dependent cancer cells death. Here, we examined the effect of MIM1 as well as MIM1 and dacarbazine (DTIC) mixture on cell viability, apoptosis, and cell cycle progression in COLO829 melanoma cells. Cell viability was performed by the WST-1 assay. Analysis of apoptosis as well as cell cycle progression was determined by fluorescence image cytometer NucleoCounter NC-3000. The obtained results demonstrated that the MIM1 exhibited high cytotoxicity against melanotic melanoma cells and induced mitochondrial membrane breakdown, GSH depletion, and DNA fragmentation. Additionally, MIM1 enhanced the proapoptotic effect of DTIC toward melanoma cells; furthermore, a mixture of these drugs caused cell cycle arrest at G2/M phase in COLO829 cells. Taken together, these data provide, for the first time, evidence that a low molecular weight Mcl-1 inhibitor-MIM1 may be a promising agent with antitumor and proapoptotic properties toward melanoma cells.

Mcl-1 Inhibitor Induces Cells Death in BRAF-Mutant Amelanotic Melanoma Trough GSH Depletion, DNA Damage and Cell Cycle Changes

Mcl-1 is a potent antiapoptotic protein and amplifies frequently in many human cancer. Currently, it is considered that the extensively expressed of Mcl-1 protein in melanoma cells is associated with rapid tumor progression, poor prognosis and low chemosensitivity. Therefore, the antiapoptotic protein Mcl-1 could be considered as a potential target for malignant melanoma treatment. The aim of this study was to assess the effect of MIM1 a specific low molecular Mcl-1 protein inhibitor and mixture of MIM1 and dacarbazine on the viability, cell cycle progression and apoptosis induction in amelanotic C32 melanoma cells. The cytotoxic activity of MIM1 towards C32 melanoma cells was examined by the WST-1 test. The Mcl-1 protein level as a drug target in amelanotic melanoma cells was defined by Western blot analysis. Cell cycle progression, DNA fragmentation as well as GSH depletion were determined by fluorescence image cytometer NucleoCounter NC-3000. The obtained results demonstrate that the specific Mcl-1 protein inhibitor - MIM1 decreases cell viability and induce apoptosis (S-phase arrest, DNA fragmentation and redox imbalance) in amelanotic melanoma cells and intensify the proapoptotic properties of DTIC, as a result of interactions with Mcl-1 protein. Taken together, the presented data suggest that Mcl-1 protein is a an important target in malignant melanoma treatment and provide for the first time convincing evidence that MIM1, which inhibits Mcl-1 antiapoptotic protein is able to induce apoptosis and sensitize melanoma cells to alkylating agent.

Mcl-1 targeting could be an intriguing perspective to cure cancer

The Bcl-2 family, which plays important roles in controlling cancer development, is divided into antiapoptotic and proapoptotic members. The change in the balance between these members governs the life and death of the cells. Mcl-1 is an antiapoptotic member of this family and its distribution in normal and cancerous tissues strongly differs from that of Bcl-2. In human cancers, where upregulation of antiapoptotic proteins is common, Mcl-1 expression is regulated independent of Bcl-2 and its inhibition promotes senescence, a major barrier to tumorigenesis. Cancer chemotherapy determines various kinds of responses, such as senescence and autophagy; however, the ideal response to chemotherapy is apoptosis. Mcl-1 is a potent oncogene that is regulated at the transcriptional, posttranscriptional, and posttranslational levels. Mcl-1 is a short-lived protein that, in the NH2 terminal region, contains sites for posttranslational regulation that can lead to proteasomal degradation. The USP9X Mcl-1 deubiquitinase regulates Mcl-1 and the levels of these two proteins are strongly correlated. Mcl-1 has three splicing variants (the antiapoptotic protein Mcl-1L and the proapoptotic proteins Mcl-1S and Mcl-1ES), each contributing toward apoptosis regulation. In cancers responsible for the most deaths in the world, the presence of Mcl-1 is associated with malignant cell growth and evasion of apoptosis. Mcl-1 is also one of the key regulators of cancer stem cells' self-renewal that contributes to tumor survival. A great number of indirect and selective Mcl-1 inhibitors have been produced and some of these have shown efficacy in several clinical trials. Thus, therapeutic manipulation of Mcl-1 can be a useful strategy to combat cancer.

Apoptosis induced by 9,11‑dehydroergosterol peroxide from Ganoderma Lucidum mycelium in human malignant melanoma cells is Mcl‑1 dependent

9,11-Dehydroergosterol peroxide [9(11)-DHEP] is an important steroid from medicinal mushroom, which has been reported to exert antitumor activity in several tumor types. However, the role of 9(11)-DHEP toward the malignant melanoma cells has not been investigated. In the present study, the steroid from Ganoderma lucidum was purified on a submerged culture, and its antitumor mechanisms on A375 human malignant melanoma cells was investigated by MTT, flow cytometry and western blotting. The studies demonstrated that apoptotic mechanisms of the steroid were caspase-dependent and mediated via the mitochondrial pathway. The steroid did not cause significant changes in the expression levels of B-cell lymphoma 2 (Bcl-2) family proteins, Bcl-2-like protein 11, p53 upregulated modulator of apoptosis, Bcl-2-associated X protein, BH3 interacting-domain death agonist, Bcl-2-associated death promoter and Bcl-2, but it significantly downregulated induced myeloid leukemia cell differentiation protein Mcl-1 (Mcl-1) in melanoma cells, suggesting the key role of Mcl-1 in regulating apoptosis of melanoma cells induced by the steroid. These properties of 9(11)-DHEP advocate its usage as supplements in human malignant melanoma chemoprevention. The present study also suggests that mycelium of G. lucidum has a potential for producing bioactive substances and extracts with applications in medicine.

Small-molecule Mcl-1 inhibitors: Emerging anti-tumor agents

The anti-apoptotic members of B-cell lymphoma-2 (Bcl-2) proteins family, such as Bcl-2 and myeloid cell leukemia-1 (Mcl-1), are the key regulators of the intrinsic pathway of apoptosis and overexpressed in many tumor cells, which have been confirmed as potential drug targets for cancers. A number of Bcl-2 proteins inhibitors have been developed and conducted clinical trials, but no Mcl-1 inhibitors are presented in the clinics. In addition, Mcl-1 is an important reason for the resistance to radio- and chemotherapies, including inhibitors that target other Bcl-2 family members. For example, the recently launched Bcl-2-selective inhibitor ABT-199 displays highly potency in the treatment of chronic lymphocytic leukemia (CLL), but it cannot induce the apoptosis controlled by Mcl-1 in some tumor cell lines. Therefore, developing potent Mcl-1 inhibitors become urgently needed in clinical therapy. This review briefly introduces the structure of Mcl-1 protein, the role in cancers and focuses on the progress of small-molecule Mcl-1 inhibitors from 2012 to 2017.

A structural perspective on the interactions of TRAF6 and Basigin during the onset of melanoma: A molecular dynamics simulation study

Metastatic melanoma is the most fatal type of skin cancer. The roles of matrix metalloproteinases (MMPs) have well been established in the onset of melanoma. Basigin (BSG) belongs to the immunoglobulin superfamily and is critical for induction of extracellular MMPs during the onset of various cancers including melanoma. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an E3-ligase that interacts with BSG and mediates its membrane localization, which leads to MMP expression in melanoma cells. This makes TRAF6 a potential therapeutic target in melanoma. We here conducted protein-protein interaction studies on TRAF6 and BSG to get molecular level insights of the reactions. The structure of human BSG was constructed by protein threading. Molecular-docking method was applied to develop the TRAF6-BSG complex. The refined docked complex was further optimized by molecular dynamics simulations. Results from binding free energy, surface properties, and electrostatic interaction analysis indicate that Lys340 and Glu417 of TRAF6 play as the anchor residues in the protein interaction interface. The current study will be helpful in designing specific modulators of TRAF6 to control melanoma metastasis.

Immune surveillance in melanoma: From immune attack to melanoma escape and even counterattack

Pharmacologic inhibition of the cytotoxic T lymphocyte antigen 4 (CTLA4) and the programmed death receptor-1 (PD1) has resulted in unprecedented durable responses in metastatic melanoma. However, resistance to immunotherapy remains a major challenge. Effective immune surveillance against melanoma requires 4 essential steps: activation of the T lymphocytes, homing of the activated T lymphocytes to the melanoma microenvironment, identification and episode of melanoma cells by activated T lymphocytes, and the sensitivity of melanoma cells to apoptosis. At each of these steps, there are multiple factors that may interfere with the immune surveillance machinery, thus allowing melanoma cells to escape immune attack and develop resistance to immunotherapy. We provide a comprehensive review of the complex immune surveillance mechanisms at play in melanoma, and a detailed discussion of how these mechanisms may allow for the development of intrinsic or acquired resistance to immunotherapeutic modalities, and potential avenues for overcoming this resistance.

Mcl-1 inhibitors: a patent review

INTRODUCTION

The myeloid cell leukemia-1 (MCL-1) protein is one of the key anti-apoptotic members of the B-cell lymphoma-2 (BCL-2) protein family. Over-expression of MCL-1 has been closely related to tumor progression as well as to resistance, not only to traditional chemotherapies but also to targeted therapeutics including BCL-2 inhibitors such as ABT-263. Therefore, there has been extensive research and development in the last decade in both academic and industrial settings to address this unmet medical need. Areas covered: This review covers the research and patent literature of the past 10 years in the field of discovery and development of small-molecule inhibitors of the MCL-1 anti-apoptotic protein. Expert opinion: Small-molecule strategies to disrupt the protein-protein interactions between MCL-1 and its pro-apoptotic counterparts, such as BAK and BIM, have recently emerged. Several small-molecules based on different scaffolds describe promising in vitro data as MCL-1 selective inhibitors. While many lead compounds remain at the in vitro preclinical development stage, the two most recent patent applications describe promising in vivo data, and one small molecule inhibitor has recently entered into clinical development. It is such an exciting moment that the long awaited clinical studies will generate some insight into the therapeutic potential of this anti-cancer approach, and possibly facilitate the further development of other early stage inhibitors.

Resveratrol and clofarabine induces a preferential apoptosis-activating effect on malignant mesothelioma cells by Mcl-1 down-regulation and caspase-3 activation

We previously demonstrated that resveratrol and clofarabine elicited a marked cytotoxicity on malignant mesothelioma (MM) MSTO-211H cells but not on the corresponding normal mesothelial MeT-5A cells. Little is known of the possible molecules that could be used to predict preferential chemosensitivity on MSTO-211H cells. Resveratrol and clofarabine induced down-regulation of Mcl-1 protein level in MSTO-211H cells. Treatment of cells with cycloheximide in the presence of proteasome inhibitor MG132 suggested that Mcl-1 protein levels were regulated at the post-translational step. The siRNA-based knockdown of Mcl-1 in MSTO-211H cells triggered more growth-inhibiting and apoptosis-inducing effects with the resultant cleavages of procaspase-3 and its substrate PARP, increased caspase-3/7 activity, and increased percentage of apoptotic propensities. However, the majority of the observed changes were not shown in MeT-5A cells. Collectively, these studies indicate that the preferential activation of caspase cascade in malignant cells might have important applications as a therapeutic target for MM. [BMB Reports 2015; 48(3): 166-171]

Mcl-1 Is a Novel Target of miR-26b That Is Associated with the Apoptosis Induced by TRAIL in HCC Cells

Aim. To investigate the role of miR-26b and Mcl-1 in TRAIL-inducing cell death in hepatocellular carcinoma. Methods. The expression of miR-26b and Mcl-1 in HCC was detected by RT-qPCR and western blot. The regulation of Mcl-1 by miR-26b was determined by luciferase reporter assay. MTT and flow cytometry were employed to detect the cell viability and apoptosis. Results. miR-26b is commonly downregulated in HCC cell lines compared with the LO2 cell line. In contrast, the Mcl-1 expression is upregulated in HCC cell lines. Bioinformatic analysis identified a putative target site in the Mcl-1 mRNA for miR-26b and luciferase reporter assay showed that miR-26b directly targeted the 3′-UTR (3′-Untranslated Regions) of Mcl-1 mRNA. Transfection of miR-26b mimics suppressed Mcl-1 expression in HCC cells and sensitized the cancer cells to TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) cytotoxicity. In addition, transfection of HCC cells with Mcl-1 expression plasmid abolished the sensitization effect of miR-26b to TRAIL-inducing apoptosis. Conclusions. Our study showed that miR-26b was a negative regulator of Mcl-1 gene and sensitized TRAIL-inducing apoptosis in HCC cells, suggesting that the miR-26b-Mcl-1 pathway might be a novel target for the treatment of HCC.

Mcl-1 antagonism is a potential therapeutic strategy in a subset of solid cancers

Cancer cell survival is frequently dependent on the elevated levels of members of the Bcl-2 family of prosurvival proteins that bind to and inactivate BH3-domain pro-apoptotic cellular proteins. Small molecules that inhibit the protein-protein interactions between prosurvival and proapoptotic Bcl-2 family members (so-called "BH3 mimetics") have a potential therapeutic value, as indicated by clinical findings obtained with ABT-263 (navitoclax), a Bcl-2/Bcl-xL antagonist, and more recently with GDC-0199/ABT-199, a more selective antagonist of Bcl-2. Here, we report study results of the functional role of the prosurvival protein Mcl-1 against a panel of solid cancer cell lines representative of different tumor types. We observed silencing of Mcl-1 expression by small interfering RNAs (siRNAs) significantly reduced viability and induced apoptosis in almost 30% of cell lines tested, including lung and breast adenocarcinoma, as well as glioblastoma derived lines. Most importantly, we provide a mechanistic basis for this sensitivity by showing antagonism of Mcl-1 function with specific BH3 peptides against isolated mitochondria induces Bak oligomerization and cytochrome c release, therefore demonstrating that mitochondria from Mcl-1-sensitive cells depend on Mcl-1 for their integrity and that antagonizing Mcl-1 function is sufficient to induce apoptosis. Thus, our results lend further support for considering Mcl-1 as a therapeutic target in a number of solid cancers and support the rationale for development of small molecule BH3-mimetics antagonists of this protein.

Small molecule Mcl-1 inhibitors for the treatment of cancer

The Bcl-2 family of proteins serves as primary regulators of apoptosis. Myeloid cell leukemia 1 (Mcl-1), a pro-survival member of the Bcl-2 family of proteins, is overexpressed and the Mcl-1 gene is amplified in many tumor types. Moreover, the overexpression of Mcl-1 is the cause of resistance to several chemotherapeutic agents. Thus, Mcl-1 is a promising cancer target. This review highlights the current progress on the discovery of small molecule Mcl-1 inhibitors.

3-Substituted-N-(4-hydroxynaphthalen-1-yl)arylsulfonamides as a novel class of selective Mcl-1 inhibitors: structure-based design, synthesis, SAR, and biological evaluation

Mcl-1, an antiapoptotic member of the Bcl-2 family of proteins, is a validated and attractive target for cancer therapy. Overexpression of Mcl-1 in many cancers results in disease progression and resistance to current chemotherapeutics. Utilizing high-throughput screening, compound 1 was identified as a selective Mcl-1 inhibitor and its binding to the BH3 binding groove of Mcl-1 was confirmed by several different, but complementary, biochemical and biophysical assays. Guided by structure-based drug design and supported by NMR experiments, comprehensive SAR studies were undertaken and a potent and selective inhibitor, compound 21, was designed which binds to Mcl-1 with a Ki of 180 nM. Biological characterization of 21 showed that it disrupts the interaction of endogenous Mcl-1 and biotinylated Noxa-BH3 peptide, causes cell death through a Bak/Bax-dependent mechanism, and selectively sensitizes Eμ-myc lymphomas overexpressing Mcl-1, but not Eμ-myc lymphoma cells overexpressing Bcl-2. Treatment of human leukemic cell lines with compound 21 resulted in cell death through activation of caspase-3 and induction of apoptosis.

HCMV reprogramming of infected monocyte survival and differentiation: a Goldilocks phenomenon

The wide range of disease pathologies seen in multiple organ sites associated with human cytomegalovirus (HCMV) infection results from the systemic hematogenous dissemination of the virus, which is mediated predominately by infected monocytes. In addition to their role in viral spread, infected monocytes are also known to play a key role in viral latency and life-long persistence. However, in order to utilize infected monocytes for viral spread and persistence, HCMV must overcome a number of monocyte biological hurdles, including their naturally short lifespan and their inability to support viral gene expression and replication. Our laboratory has shown that HCMV is able to manipulate the biology of infected monocytes in order to overcome these biological hurdles by inducing the survival and differentiation of infected monocytes into long-lived macrophages capable of supporting viral gene expression and replication. In this current review, we describe the unique aspects of how HCMV promotes monocyte survival and differentiation by inducing a “finely-tuned” macrophage cell type following infection. Specifically, we describe the induction of a uniquely polarized macrophage subset from infected monocytes, which we argue is the ideal cellular environment for the initiation of viral gene expression and replication and, ultimately, viral spread and persistence within the infected host.

Therapeutic Effects of Myeloid Cell Leukemia-1 siRNA on Human Acute Myeloid Leukemia Cells

PURPOSE

Up-regulation of Mcl-1, a known anti-apoptotic protein, is associated with the survival and progression of various malignancies including leukemia. The aim of this study was to explore the effect of Mcl-1 small interference RNA (siRNA) on the proliferation and apoptosis of HL-60 acute myeloid leukemia (AML) cells.

METHODS

siRNA transfection was performed using Lipofectamine™2000 reagent. Relative mRNA and protein expressions were quantified by quantitative real-time PCR and Western blotting, respectively. Trypan blue assay was performed to assess tumor cell proliferation after siRNA transfection. The cytotoxic effect of Mcl-1 siRNA on leukemic cells was measured using MTT assay. Apoptosis was detected using ELISA cell death assay.

RESULTS

Mcl-1 siRNA clearly lowered both Mcl-1 mRNA and protein levels in a time-dependent manner, leading to marked inhibition of cell survival and proliferation. Furthermore, Mcl-1 down-regulation significantly enhanced the extent of HL-60 apoptotic cells.

CONCLUSION

Our results suggest that the down-regulation of Mcl-1 by siRNA can effectively trigger apoptosis and inhibit the proliferation of leukemic cells. Therefore, Mcl-1 siRNA may be a potent adjuvant in AML therapy.

Proteasomal degradation of Mcl-1 by maritoclax induces apoptosis and enhances the efficacy of ABT-737 in melanoma cells

Background and purpose

Metastatic melanoma remains one of the most invasive and highly drug resistant cancers. The over expression of anti-apoptotic protein Mcl-1 has been associated with inferior survival, poor prognosis and chemoresistance of malignant melanoma. A BH3 mimetic, ABT-737, has demonstrated efficacy in several forms of cancers. However, the efficacy of ABT-737 depends on Mcl-1. Because the over expression of Mcl-1 is frequently observed in melanoma, specifically targeting of Mcl-1 may overcome the resistance of ABT-737. In this study, we investigated the effects of Maritoclax, a novel Mcl-1-selective inhibitor, alone and in combination with ABT-737, on the survival of human melanoma cells.

Experimental approach

For cell viability assessment we performed MTT assay. Apoptosis was determined using western blot and flow cytometric analysis.

Key results

The treatment of Maritoclax reduced the cell viability of melanoma cells with an IC₅₀ of between 2.2–5.0 µM. Further, treatment of melanoma cells with Maritoclax showed significant decrease in Mcl-1 expression. We found that Maritoclax was able to induce apoptosis in melanoma cells in a caspase-dependent manner. Moreover, Maritoclax induced Mcl-1 degradation via the proteasome system, which was associated with its pro-apoptotic activity. We also found that Maritoclax treatment increased mitochondrial translocation of Bim and Bmf. Importantly, Maritoclax markedly enhanced the efficacy of ABT-737 against melanoma cells in both two- and three-dimensional spheroids.

Conclusions and implications

Taken together, these results suggest that targeting of Mcl-1 by Maritoclax may represent a new therapeutic strategy for melanoma treatment that warrants further investigation as a single therapy or in combination with other agents such as Bcl-2 inhibitors.

Phytochemicals as chemosensitizers: from molecular mechanism to clinical significance

This review provides an overview of the clinical relevance of chemosensitization, giving special reference to the phenolic phytochemicals, curcumin, genistein, epigallocatechin gallate, quercetin, emodin, and resveratrol, which are potential candidates due to their ability to regulate multiple survival pathways without inducing toxicity. We also give a brief summary of all the clinical trials related to the important phytochemicals that emerge as chemosensitizers. The mode of action of these phytochemicals in regulating the key players of the death receptor pathway and multidrug resistance proteins is also abridged. Rigorous efforts in identifying novel chemosensitizers and unraveling their molecular mechanism have resulted in some of the promising candidates such as curcumin, genistein, and polyphenon E, which have gone into clinical trials. Even though considerable research has been conducted in identifying the salient molecular players either contributing to drug efflux or inhibiting DNA repair and apoptosis, both of which ultimately lead to the development of chemoresistance, the interdependence of the molecular pathways leading to chemoresistance is still the impeding factor in the success of chemotherapy. Even though clinical trials are going on to evaluate the chemosensitizing efficacy of phytochemicals such as curcumin, genistein, and polyphenon E, recent results indicate that more intense study is required to confirm their clinical efficacy. Current reports also warrant intense investigation about the use of more phytochemicals such as quercetin, emodin, and resveratrol as chemosensitizers, as all of them have been shown to modulate one or more of the key regulators of chemoresistance.

Fangchinoline induces G0/G1 arrest by modulating the expression of CDKN1A and CCND2 in K562 human chronic myelogenous leukemia cells

Chronic myeloid leukemia (CML) is a hematopoietic stem cell disease caused by the oncoprotein BCR-ABL, which exhibits a constitutive tyrosine kinase activity. Imatinib mesylate (IM), an inhibitor of the tyrosine kinase activity of BCR-ABL, has been used as a first-line therapy for CML. However, IM is less effective in the accelerated phase and blastic phases of CML and certain patients develop IM resistance due to the mutation and amplification of the BCR-ABL gene. Fangchinoline, an important chemical constituent from the dried roots of Stephaniae tetrandrae S. Moore, exhibits significant antitumor activity in various types of cancers, including breast, prostate and hepatocellular carcinoma. However, the effects and the underlying mechanisms of fangchinoline in CML remain unclear. In the present study, we identified that fangchinoline inhibits cell proliferation in a dose- and time-dependent manner in K562 cells derived from the blast crisis of CML. Additional experiments revealed that fangchinoline induces cell cycle arrest at the G0/G1 phase and has no effect on apoptosis, which is mediated through the upregulation of cyclin-dependent kinase (CDK)-N1A and MCL-1 mRNA levels, as well as the downregulation of cyclin D2 (CCND2) mRNA levels. These findings suggest the potential of fangchinoline as an effective antitumor agent in CML.

Inhibition of Wee1, AKT, and CDK4 underlies the efficacy of the HSP90 inhibitor XL888 in an in vivo model of NRAS-mutant melanoma

The HSP90 inhibitor XL888 is effective at reversing BRAF inhibitor resistance in melanoma, including that mediated through acquired NRAS mutations. The present study has investigated the mechanism of action of XL888 in NRAS-mutant melanoma. Treatment of NRAS-mutant melanoma cell lines with XL888 led to an inhibition of growth, G2-M phase cell-cycle arrest, and the inhibition of cell survival in three-dimensional spheroid and colony formation assays. In vitro, HSP90 inhibition led to the degradation of ARAF, CRAF, Wee1, Chk1, and cdc2 and was associated with decreased mitogen-activated protein kinase (MAPK), AKT, mTOR, and c-jun NH2 kinase (JNK) signaling. Apoptosis induction was associated with increased BIM expression and a decrease in the expression of the prosurvival protein Mcl-1. The critical role of increased BIM and decreased Mcl-1 expression in the survival of NRAS-mutant melanoma cell lines was shown through siRNA knockdown and overexpression studies. In an animal xenograft model of NRAS-mutant melanoma, XL888 treatment led to reduced tumor growth and apoptosis induction. Important differences in the pattern of client degradation were noted between the in vivo and in vitro studies. In vivo, XL888 treatment led to degradation of CDK4 and Wee1 and the inhibition of AKT/S6 signaling with little or no effect observed upon ARAF, CRAF, or MAPK. Blockade of Wee1, using either siRNA knockdown or the inhibitor MK1775, was associated with significant levels of growth inhibition and apoptosis induction. Together, these studies have identified Wee1 as a key target of XL888, suggesting novel therapeutic strategies for NRAS-mutant melanoma.

Anti-apoptotic proteins on guard of melanoma cell survival

Apoptosis plays a pivotal role in sustaining proper tissue development and homeostasis. Evading apoptosis by cancer cells is a part of their adaption to microenvironment and therapies. Cellular integrity is predominantly maintained by pro-survival members of Bcl-2 family and IAPs. Melanoma cells are characterized by a labile and stage-dependent phenotype. Pro-survival molecules can protect melanoma cells from apoptosis and mediate other processes, thus enhancing aggressive phenotype. The essential role of Bcl-2, Mcl-1, Bcl-X(L), livin, survivin and XIAP was implicated for melanoma, often in a tumor stage-dependent fashion. In this review, the current knowledge of pro-survival machinery in melanoma is discussed.

Molecular mechanism implicated in Pemetrexed-induced apoptosis in human melanoma cells

Background

Metastatic melanoma is a lethal skin cancer and its incidence is rising every year. It represents a challenge for oncologist, as the current treatment options are non-curative in the majority of cases; therefore, the effort to find and/or develop novel compounds is mandatory. Pemetrexed (Alimta®, MTA) is a multitarget antifolate that inhibits folate-dependent enzymes: thymidylate synthase, dihydrofolate reductase and glycinamide ribonucleotide formyltransferase, required for de novo synthesis of nucleotides for DNA replication. It is currently used in the treatment of mesothelioma and non-small cell lung cancer (NSCLC), and has shown clinical activity in other tumors such as breast, colorectal, bladder, cervical, gastric and pancreatic cancer. However, its effect in human melanoma has not been studied yet.

Results

In the current work we studied the effect of MTA on four human melanoma cell lines A375, Hs294T, HT144 and MeWo and in two NSCLC cell lines H1299 and Calu-3. We have found that MTA induces DNA damage, S-phase cell cycle arrest, and caspase- dependent and –independent apoptosis. We show that an increment of the intracellular reactive oxygen species (ROS) and p53 is required for MTA-induced cytotoxicity by utilizing N-Acetyl-L-Cysteine (NAC) to blockage of ROS and p53-defective H1299 NSCLC cell line. Pretreatment of melanoma cells with NAC significantly decreased the DNA damage, p53 up-regulation and cytotoxic effect of MTA. MTA was able to induce p53 expression leading to up-regulation of p53-dependent genes Mcl-1 and PIDD, followed by a postranscriptional regulation of Mcl-1 improving apoptosis.

Conclusions

We found that MTA induced DNA damage and mitochondrial-mediated apoptosis in human melanoma cells in vitro and that the associated apoptosis was both caspase-dependent and –independent and p53-mediated. Our data suggest that MTA may be of therapeutic relevance for the future treatment of human malignant melanoma.

Melanoma: new insights and new therapies

Metastatic melanoma has historically been considered as one of the most therapeutically challenging malignancies. However, for the first time after decades of basic research and clinical investigation, new drugs have produced major clinical responses. The discovery of BRAF mutations in melanoma created the first opportunity to develop oncogene-directed therapy in this disease and led to the development of compounds that inhibit aberrant BRAF activity. A decade later, vemurafenib, an orally available and well-tolerated selective BRAF inhibitor, ushered in a new era of molecular treatments for advanced disease. Additional targets have been identified, and novel agents that impact on various signaling pathways or modulate the immune system hold the promise of a whole new therapeutic landscape for patients with metastatic melanoma. One of the major thrusts in melanoma therapy is now focused on understanding and targeting the network of signal transduction pathways and on attacking elements that underlie the tumor's propensity for growth and chemoresistance. In this article, we review the novel targeted anticancer approaches that are under consideration in melanoma treatment.

Targeting Mcl-1 for the therapy of cancer

INTRODUCTION

Human cancers are genetically and epigenetically heterogeneous and have the capacity to commandeer a variety of cellular processes to aid in their survival, growth and resistance to therapy. One strategy is to overexpress proteins that suppress apoptosis, such as the Bcl-2 family protein Mcl-1. The Mcl-1 protein plays a pivotal role in protecting cells from apoptosis and is overexpressed in a variety of human cancers.

AREAS COVERED

Targeting Mcl-1 for extinction in these cancers, using genetic and pharmacological approaches, represents a potentially effectual means of developing new efficacious cancer therapeutics. Here we review the multiple strategies that have been employed in targeting this fundamental protein, as well as the significant potential these targeting agents provide in not only suppressing cancer growth, but also in reversing resistance to conventional cancer treatments.

EXPERT OPINION

We discuss the potential issues that arise in targeting Mcl-1 and other Bcl-2 anti-apoptotic proteins, as well problems with acquired resistance. The application of combinatorial approaches that involve inhibiting Mcl-1 and manipulation of additional signaling pathways to enhance therapeutic outcomes is also highlighted. The ability to specifically inhibit key genetic/epigenetic elements and biochemical pathways that maintain the tumor state represent a viable approach for developing rationally based, effective cancer therapies.

Gastric cancer growth control by BEZ235 in vivo does not correlate with PI3K/mTOR target inhibition but with [18F]FLT uptake

PURPOSE

In this study, we tested the antitumor activity of the dual phosphoinositide 3-kinase (PI3K)/mTOR inhibitor BEZ235 against gastric cancer in vitro and in vivo.

EXPERIMENTAL DESIGN

Gastric cancer cell lines (N87, MKN45, and MKN28) were incubated with BEZ235 and assessed for cell viability, cell cycle, and PI3K/mTOR target inhibition. In vivo, athymic nude mice were inoculated with N87, MKN28, or MKN45 cells and treated daily with BEZ235. 3'-Deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) uptake was measured via small animal positron emission tomography (PET).

RESULTS

In vitro, BEZ235 dose dependently decreased the cell viability of gastric cancer cell lines. The antiproliferative activity of BEZ235 was linked to a G(1) cell-cycle arrest. In vivo, BEZ235 treatment resulted in PI3K/mTOR target inhibition as shown by dephosphorylation of AKT and S6 protein in all xenograft models. However, BEZ235 treatment only inhibited tumor growth of N87 xenografts, whereas no antitumor effect was observed in the MKN28 and MKN45 xenograft models. Sensitivity to BEZ235 in vivo correlated with downregulation of the proliferation marker thymidine kinase 1. Accordingly, [(18)F]FLT uptake was only significantly reduced in the BEZ235-sensitive N87 xenograft model as measured by PET.

CONCLUSION

In conclusion, in vivo sensitivity of gastric cancer xenografts to BEZ235 did not correlate with in vitro antiproliferative activity or in vivo PI3K/mTOR target inhibition by BEZ235. In contrast, [(18)F]FLT uptake was linked to BEZ235 in vivo sensitivity. Noninvasive [(18)F]FLT PET imaging might qualify as a novel marker for optimizing future clinical testing of dual PI3K/mTOR inhibitors.

Born to be alive: a role for the BCL-2 family in melanoma tumor cell survival, apoptosis, and treatment

The global incidence of melanoma has dramatically increased during the recent decades, yet the advancement of primary and adjuvant therapies has not kept a similar pace. The development of melanoma is often centered on cellular signaling that hyper-activates survival pathways, while inducing a concomitant blockade to cell death. Aberrations in cell death signaling not only promote tumor survival and enhanced metastatic potential, but also create resistance to anti-tumor strategies. Chemotherapeutic agents target melanoma tumor cells by inducing a form of cell death called apoptosis, which is governed by the BCL-2 family of proteins. The BCL-2 family is comprised of anti-apoptotic proteins (e.g., BCL-2, BCL-xL, and MCL-1) and pro-apoptotic proteins (e.g., BAK, BAX, and BIM), and their coordinated regulation and function are essential for optimal responses to chemotherapeutics. Here we will discuss what is currently known about the mechanisms of BCL-2 family function with a focus on the signaling pathways that maintain melanoma tumor cell survival. Importantly, we will critically evaluate the literature regarding how chemotherapeutic strategies directly impact on BCL-2 family function and offer several suggestions for future regimens to target melanoma and enhance patient survival.

Akt3-mediated resistance to apoptosis in B-RAF-targeted melanoma cells

Melanoma cells are highly resistant to anoikis, a form of apoptosis induced in nonadherent/inappropriate adhesion conditions. Depleting B-RAF or the prosurvival Bcl-2 family protein Mcl-1 renders mutant B-RAF melanoma cells susceptible to anoikis. In this study, we examined the effect of targeting B-RAF on the survival of primary stage melanoma cells cultured in three-dimensional type I collagen gels, which partially mimics the dermal microenvironment. Depletion/inhibition of B-RAF with small interfering RNA or the mutant B-RAF inhibitor, PLX4720, induced apoptosis of mutant B-RAF melanoma cells in three-dimensional collagen. Apoptosis was dependent on two upregulated BH3-only proteins, Bim-EL and Bmf, and was inhibited by ectopic Mcl-1 expression. Akt3 activation has been associated with the survival of melanoma cells. Mutant B-RAF melanoma cells ectopically expressing a constitutively activated form of Akt3 or endogenously expressing mutant Akt3 were protected from apoptosis induced by B-RAF knockdown or PLX4720 treatment. Furthermore, intrinsically resistant metastatic melanoma cells displayed elevated Akt phosphorylation in three-dimensional collagen and were rendered susceptible to PLX4720 by Akt3 knockdown. Importantly, myristylated Akt3 prevented B-RAF targeting-induced upregulation of Bim-EL and Bmf in three-dimensional collagen and partially protected Mcl-1-depleted cells from apoptosis. These findings delineate how mutant B-RAF protects melanoma cells from apoptosis and provide insight into possible resistance mechanisms to B-RAF inhibitors.

Mcl-1 is required for melanoma cell resistance to anoikis

Melanoma is a particularly aggressive tumor type that exhibits a high level of resistance to apoptosis. The serine/threonine kinase B-RAF is mutated in 50% to 70% of melanomas and protects melanoma cells from anoikis, a form of apoptosis induced by lack of adhesion or adhesion to an inappropriate matrix. Mutant B-RAF down-regulates two BH3-only proapoptotic proteins, Bim(EL) and Bad. BH3-only proteins act, at least in part, by sequestering prosurvival Bcl-2 family proteins and preventing them from inhibiting the mitochondrial apoptotic pathway. Several Bcl-2 proteins are up-regulated in melanoma; however, the mechanisms of up-regulation and their role in melanoma resistance to anoikis remain unclear. Using RNA interference, we show that depletion of Mcl-1 renders mutant B-RAF melanoma cells sensitive to anoikis. By contrast, minor effects were observed following depletion of either Bcl-2 or Bcl-(XL). Mcl-1 expression is enhanced in melanoma cell lines compared with melanocytes and up-regulated by the B-RAF-MEK-extracellular signal-regulated kinase 1/2 pathway through control of Mcl-1 protein turnover. Similar to B-RAF knockdown cells, adhesion to fibronectin protected Mcl-1 knockdown cells from apoptosis. Finally, expression of Bad, which does not sequester Mcl-1, further augmented apoptosis in nonadherent Mcl-1 knockdown cells. Together, these data support the notion that BH3 mimetic compounds that target Mcl-1 may be effective for the treatment of melanoma in combinatorial strategies with agents that disrupt fibronectin-integrin signaling.

IFN-alpha and bortezomib overcome Bcl-2 and Mcl-1 overexpression in melanoma cells by stimulating the extrinsic pathway of apoptosis

We hypothesized that IFN-alpha would enhance the apoptotic activity of bortezomib on melanoma cells. Combined treatment with bortezomib and IFN-alpha induced synergistic apoptosis in melanoma and other solid tumor cell lines. Apoptosis was associated with processing of procaspase-3, procaspase-7, procaspase-8, and procaspase-9 and with cleavage of Bid and poly(ADP-ribose) polymerase. Bortezomib plus IFN-alpha was effective at inducing apoptosis in melanoma cells that overexpressed Bcl-2 or Mcl-1, suggesting that this treatment combination can overcome mitochondrial pathways of cell survival and resistance to apoptosis. The proapoptotic effects of this treatment combination were abrogated by a caspase-8 inhibitor, led to increased association of Fas and FADD before the onset of cell death, and were significantly reduced in cells transfected with a dominant-negative FADD construct or small interfering RNA targeting Fas. These data suggest that bortezomib and IFN-alpha act through the extrinsic pathway of apoptosis via FADD-induced caspase-8 activation to initiate cell death. Finally, bortezomib and IFN-alpha displayed statistically significant antitumor activity compared with either agent alone in both the B16 murine model of melanoma and in athymic mice bearing human A375 xenografts. These data support the future clinical development of bortezomib and IFN-alpha for malignant melanoma.

Melanoma genetics and therapeutic approaches in the 21st century: moving from the benchside to the bedside

Metastatic melanoma is notoriously one of the most difficult cancers to treat. Although many therapeutic regimens have been tested, very few achieve response rates greater than 25%. Given the rising incidence of melanoma and the paucity of effective treatments, there is much hope and excitement in leveraging recent genetic and molecular insights for therapeutic advantage. Over the past 30 years, elegant studies by many groups have helped decipher the complex genetic networks involved in melanoma proliferation, progression and survival, as well as several genes involved in melanocyte development and survival. Many of these oncogenic loci and pathways have become crucial targets for pharmacological development. In this article we review: (1) our current understanding of melanoma genetics within the context of signaling networks; (2) targeted therapies, including an extensive discussion of promising agents that act in the Bcl-2 signaling network; (3) future areas of research.

Expression and function of bcl-2 proteins in melanoma

Bcl-2 proteins are critical regulators of mitochondrial membrane permeability and the proapoptotic mitochondrial pathway. The family encloses pro- and antiapoptotic factors encoded by over 15 genes, which frequently give rise to alternative splice products. Antiapoptotic, proapoptotic multidomain, and proapoptotic BH3-only proteins are characterized by the presence of at least one of four Bcl-2 homology domains (BH 1-4). Their expression and activities are controlled by survival pathways as MAP kinases and protein kinase B/Akt, which are in touch with a number of transcription factors. In melanoma, the mitochondrial apoptosis pathways and Bcl-2 proteins appear of particular importance for apoptosis resistance, which has been addressed in clinical trials applying antisense-Bcl-2. Overexpression or induction of proapoptotic Bcl-2 proteins as well as the use of small molecule mimetics for the proapoptotic BH3 domain are further promising strategies.

Malignant melanoma in the 21st century: the emerging molecular landscape

Malignant melanoma presents a substantial clinical challenge. Current diagnostic methods are limited in their ability to diagnose early disease and accurately predict individual risk of disease progression and outcome. The lack of adequate approaches to properly define disease subgroups precludes rational treatment design and selection. Better tools are urgently needed to provide more accurate and personalized melanoma patient management. Recent progress in the understanding of the molecular aberrations that underlie melanoma oncogenesis will likely advance the diagnosis, prognosis, and treatment of melanoma. The emerging pattern of molecular complexity in melanoma tumors mirrors the clinical diversity of the disease and highlights the notion that melanoma, like other cancers, is not a single disease but a heterogeneous group of disorders that arise from complex molecular changes. Understanding of molecular aberrations involving important cellular processes, such as cellular signaling networks, cell cycle regulation, and cell death, will be essential for better diagnosis, accurate assessment of prognosis, and rational design of effective therapeutics. Defining an individual patient's unique tumor characteristics may lead to personalized prediction of outcomes and selection of therapy. We review the emerging molecular landscape of melanoma and its implications for better management of patients with melanoma.

Bcl-2 family members as molecular targets in cancer therapy

Escape from apoptosis is often a hallmark of cancer cells, and is associated to chemotherapy resistance or tumor relapse. Proteins from the Bcl-2 family are the key regulators of the intrinsic pathway of apoptosis, controlling the point-of no-return and setting the threshold to engage the death machinery in response to a chemical damage. Therefore, Bcl-2 proteins have emerged as an attractive target to develop novel anticancer drugs. Current pharmacological approaches are focused on the use of peptides, small inhibitory molecules or antisense oligonucleotides to neutralize antiapoptotic Bcl-2 proteins, lowering the threshold and facilitating apoptosis of cancer cells. We discuss here recent advances in the development of Bcl-2 targeted anticancer therapies.

Down-regulation of mcl-1 by small interfering RNA sensitizes resistant melanoma cells to fas-mediated apoptosis

Resistance of malignant melanoma cells to Fas-mediated apoptosis is among the mechanisms by which they escape immune surveillance. However, the mechanisms contributing to their resistance are not completely understood, and it is still unclear whether antiapoptotic Bcl-2-related family proteins play a role in this resistance. In this study, we report that treatment of Fas-resistant melanoma cell lines with cycloheximide, a general inhibitor of de novo protein synthesis, sensitizes them to anti-Fas monoclonal antibody (mAb)-induced apoptosis. The cycloheximide-induced sensitization to Fas-induced apoptosis is associated with a rapid down-regulation of Mcl-1 protein levels, but not that of Bcl-2 or Bcl-xL. Targeting Mcl-1 in these melanoma cell lines with specific small interfering RNA was sufficient to sensitize them to both anti-Fas mAb-induced apoptosis and activation of caspase-9. Furthermore, ectopic expression of Mcl-1 in a Fas-sensitive melanoma cell line rescues the cells from Fas-mediated apoptosis. Our results further show that the expression of Mcl-1 in melanoma cells is regulated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and not by phosphatidylinositol 3-kinase/AKT signaling pathway. Inhibition of ERK signaling with the mitogen-activated protein/ERK kinase-1 inhibitor or by expressing a dominant negative form of mitogen-activated protein/ERK kinase-1 also sensitizes resistant melanoma cells to anti-Fas mAb-induced apoptosis. Thus, our study identifies mitogen-activated protein kinase/ERK/Mcl-1 as an important survival signaling pathway in the resistance of melanoma cells to Fas-mediated apoptosis and suggests that its targeting may contribute to the elimination of melanoma tumors by the immune system.

Topical CpG enhances the response of murine malignant melanoma to dacarbazine

Malignant melanoma is a potentially fatal skin cancer that is increasing in incidence. Standard chemoimmunotherapy consisting of dacarbazine (DTIC) given with IFN-alpha has had disappointing results. We describe a chemoimmunotherapy protocol for cutaneous melanoma that combines the administration of DTIC with the topical application of CpG oligodinucleotide (ODN). Subcutaneous B16 melanoma tumors in C57BL/6 mice were treated with intraperitoneal injections of DTIC followed by the topical application of CpG-ODN over the tumors. This therapeutic approach abrogated the growth of established tumors and significantly enhanced survival. Topical CpG application was more effective than intratumoral CpG. Cell depletion studies indicated that the antitumor effect was dependent on both CD4(+) and CD8(+) cells but not on natural killer (NK) cells. Tumor-specific cytotoxic T-lymphocyte activity was generated in treated animals and was highest in topically treated animals. Immunohistochemical analysis revealed that DTIC, but not CpG, enhanced tumor cell apoptosis. Further, topical CpG induced an expansion of a B220(+)CD8(+) subset of dendritic cells and a subset of NK1.1(+) CD11c(+) cells within the tumors. By enhancing both tumor cell death and local immune activation, DTIC/topical CpG chemoimmunotherapy induced an effective T-cell-dependent host-immune response against melanoma.