Docetaxel-resistant prostate cancer cells become sensitive to gemcitabine due to the upregulation of ABCB1.

BACKGROUND: Docetaxel is the preferred chemotherapeutic agent for hormone-refractory prostate cancer (PC) patients. However, patients eventually develop docetaxel resistance, and no effective treatment options are available for them. OBJECTIVE: We aimed to establish docetaxel resistance in castration-resistant prostate cancer (CRPC) cell lines (DU145/TXR, PC-3/TXR, and CWR22/TXR) and characterized transcriptional changes upon acquiring resistance to the docetaxel. METHODS: Human PC cells (DU145, PC-3, CWR22) and all docetaxel-resistant cells were maintained in Roswell Park Memorial Institute Medium (RPMI) 1640 media supplemented with 10% fetal bovine serum and 1% penicillin/streptomycin. ABCB1 was detected by using both parental and docetaxel-resistant CRPCs prepared for flow cytometry. For the evaluation of tumor-suppressive effects under each chemotherapeutic agent, subcutaneous xenografts of DU145 or DU145/TXR were implanted at the mouse flank. RESULTS: The P-glycoprotein-encoding gene ABCB1 was distinctively upregulated in the resistant cells, and its overexpression played an essential role in docetaxel resistance in CRPC. When tested for the cytotoxicity of gemcitabine, another option for chemotherapy, the docetaxel-resistant cells were shown to become sensitive to the drug, implying additional phenotypic transformation in the docetaxel-resistant cells. Studies using xenograft animal models demonstrated that the growth of tumors composed of both docetaxel-sensitive and docetaxel-resistant cells was deterred most profoundly when docetaxel and gemcitabine were administered together. CONCLUSION: This study suggests that when a drug develops therapeutic resistance, sensitivity tests could be another option, ultimately providing insight into a novel alternative clinical strategy.

One-pot sequential synthesis of tetrasubstituted thiophenes via sulfur ylide-like intermediates.

Herein, we describe a novel approach for the practical synthesis of tetrasubstituted thiophenes 8. The developed method was particularly used for the facile preparation of thienyl heterocycles 8. The mechanism for this reaction is based on the formation of a sulfur ylide-like intermediate. It was clearly suggested by (i) the intramolecular cyclization of ketene N,S-acetals 7 to the corresponding thiophenes 8, (ii) 1H NMR studies of Meldrum's acid-substituted aminothioacetals 9, and (iii) substitution studies of the methoxy group on Meldrum's acid containing N,S-acetals 9b. Notably, in terms of structural effects on the reactivity and stability of sulfur ylide-like intermediates, 2-pyridyl substituted compound 7a exhibited superior properties over those of others.

Polypyrrole-based nanotheranostics for activatable fluorescence imaging and chemo/photothermal dual therapy of triple-negative breast cancer.

Here, we fabricated polypyrrole nanoparticles (PPys) (termed HA10-PPy, HA20-PPy, and HA40-PPy) doped with different average molecular weight hyaluronic acids (HAs) (10, 20, and 40 kDa, respectively), and evaluated the effect of molecular weight of doped HA on photothermal induction, fluorescence quenching, and drug loading efficiencies. Doxorubicin-loaded HA-doped PPys (DOX@HA-PPys) could be used for imaging and therapy of triple-negative breast cancer (TNBC). Fluorescence turn-on, stimuli-responsive drug release, and photo-induced heating of DOX@HA-PPys enabled not only activatable fluorescence imaging but also subsequent chemo/photothermal dual therapy for TNBC. In particular, we illustrated the potential usefulness of the photothermal effect of the nanoparticles for overcoming chemoresistance in TNBC.

Intravesical instillation of c-MYC inhibitor KSI-3716 suppresses orthotopic bladder tumor growth.

PURPOSE: c-MYC is a promising target for cancer therapy but its use is restricted by unwanted, devastating side effects. We explored whether intravesical instillation of the c-MYC inhibitor KSI-3716 could suppress tumor growth in murine orthotopic bladder xenografts. MATERIALS AND METHODS: The small molecule KSI-3716, which blocks c-MYC/MAX binding to target gene promoters, was used as an intravesical chemotherapy agent. KSI-3716 action was assessed by electrophoretic mobility shift assay, chromatin immunoprecipitation, transcription reporter assay and quantitative reverse transcriptase-polymerase chain reaction. Inhibition of cell proliferation and its mechanism was monitored by cell cytotoxicity assay, EdU incorporation assay and flow cytometry. The in vivo efficacy of KSI-3716 was examined by noninvasive luminescence imaging and histological analysis after intravesical instillation of KSI-3716 in murine orthotopic bladder xenografts. RESULTS: KSI-3716 blocked c-MYC/MAX from forming a complex with target gene promoters. c-MYC mediated transcriptional activity was inhibited by KSI-3716 at concentrations as low as 1 µM. The expression of c-MYC target genes, such as cyclin D2, CDK4 and hTERT, was markedly decreased. KSI-3716 exerted cytotoxic effects on bladder cancer cells by inducing cell cycle arrest and apoptosis. Intravesical instillation of KSI-3716 at a dose of 5 mg/kg significantly suppressed tumor growth with minimal systemic toxicity. CONCLUSIONS: The c-MYC inhibitor KSI-3716 could be developed as an effective intravesical chemotherapy agent for bladder cancer.

Helical repeat structure of apoptosis inhibitor 5 reveals protein-protein interaction modules.

Apoptosis inhibitor 5 (API5) is an anti-apoptotic protein that is up-regulated in various cancer cells. Here, we present the crystal structure of human API5. API5 exhibits an elongated all α-helical structure. The N-terminal half of API5 is similar to the HEAT repeat and the C-terminal half is similar to the ARM (Armadillo-like) repeat. HEAT and ARM repeats have been implicated in protein-protein interactions, suggesting that the cellular roles of API5 may be to mediate protein-protein interactions. Various components of multiprotein complexes have been identified as API5-interacting protein partners, suggesting that API5 may act as a scaffold for multiprotein complexes. API5 exists as a monomer, and the functionally important heptad leucine repeat does not exhibit the predicted a dimeric leucine zipper. Additionally, Lys-251, which can be acetylated in cells, plays important roles in the inhibition of apoptosis under serum deprivation conditions. The acetylation of this lysine also affects the stability of API5 in cells.

MYC amplification-conferred primary resistance to capmatinib in a MET-amplified NSCLC patient: a case report.

Background: Capmatinib, a potent and selective mesenchymalepithelial transition factor (MET) inhibitor, is an effective treatment option for non-small cell lung cancer (NSCLC) patients with MET exon 14 skipping mutations or gene amplification. However, the mechanisms that confer resistance to capmatinib remain elusive. Here, we present a case of primary resistance to capmatinib in a MET-amplified NSCLC patient which was conferred by concurrent MYC amplification. Case Description: Capmatinib was administered as first-line treatment in an 82-year-old MET-amplified [gene copy number (GCN) 13.5] and MET overexpressed (immunohistochemical staining 3+/3, >50%) NSCLC patient. However, the tumor rapidly progressed and showed primary resistance to capmatinib. Next-generation target sequencing using rebiopsy tumor samples revealed MYC amplification. We also performed functional drug susceptibility testing using patient-derived cells (PDCs), which showed overexpression of MYC mRNA and resistance to capmatinib. Meanwhile, ICX-101, an investigational MYC inhibitor, successfully inhibited the growth of PDCs at a relatively low IC50 value. Also, a synergistic effect was shown when capmatinib treatment was followed by ICX-101. Conclusions: Concurrent MYC amplification could potentially confer primary resistance to capmatinib in highly MET amplified NSCLC patients. Further clinical studies are warranted to corroborate these findings, and treatment with MYC inhibitors could be suggested as an alternative therapeutic strategy for this subset of patients.

Targeted Inhibition of O-Linked ß-N-Acetylglucosamine Transferase as a Promising Therapeutic Strategy to Restore Chemosensitivity and Attenuate Aggressive Tumor Traits in Chemoresistant Urothelial Carcinoma of the Bladder.

Acquisition of acquired chemoresistance during treatment cycles in urothelial carcinoma of the bladder (UCB) is the major cause of death through enhancing the risk of cancer progression and metastasis. Elevated glucose flux through the abnormal upregulation of O-linked ß-N-acetylglucosamine (O-GlcNAc) transferase (OGT) controls key signaling and metabolic pathways regulating diverse cancer cell phenotypes. This study showed that OGT expression levels in two human UCB cell models with acquired resistance to gemcitabine and paclitaxel were significantly upregulated compared with those in parental cells. Reducing hyper-O-GlcNAcylation by OGT knockdown (KD) markedly facilitated chemosensitivity to the corresponding chemotherapeutics in both cells, and combination treatment with OGT-KD showed more severe growth defects in chemoresistant sublines. We subsequently verified the suppressive effects of OGT-KD monotherapy on cell migration/invasion in vitro and xenograft tumor growth in vivo in chemoresistant UCB cells. Transcriptome analysis of these cells revealed 97 upregulated genes, which were enriched in multiple oncogenic pathways. Our final choice of suspected OGT glycosylation substrate was VCAN, S1PR3, PDGFRB, and PRKCG, the knockdown of which induced cell growth defects. These findings demonstrate the vital role of dysregulated OGT activity and hyper-O-GlcNAcylation in modulating treatment failure and tumor aggression in chemoresistant UCB.

Involvement of Cox-2 in the metastatic potential of chemotherapy-resistant breast cancer cells.

BACKGROUND: A major problem with the use of current chemotherapy regimens for several cancers, including breast cancer, is development of intrinsic or acquired drug resistance, which results in disease recurrence and metastasis. However, the mechanisms underlying this drug resistance are unknown. To study the molecular mechanisms underlying the invasive and metastatic activities of drug-resistant cancer cells, we generated a doxorubicin-resistant MCF-7 breast cancer cell line (MCF-7/DOX). METHODS: We used MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays, flow cytometry assays, DNA fragmentation assays, Western blot analysis, cell invasion assays, small interfering RNA (siRNA) transfection, reverse transcription-polymerase chain reaction, experimental lung metastasis models, and gelatin and fibrinogen/plasminogen zymography to study the molecular mechanism of metastatic activities in MCF-7/DOX cells. RESULTS: We found that MCF-7/DOX acquired invasive activities. In addition, Western blot analysis showed increased expression of epidermal growth factor receptor (EGFR) and Cox-2 in MCF-7/DOX cells. Inhibition of Cox-2, phosphoinositide 3-kinase (PI3K)/Akt, or mitogen-activated protein kinase (MAPK) pathways effectively inhibited the invasive activities of MCF-7/DOX cells. Gelatin and fibrinogen/plasminogen zymography analysis showed that the enzymatic activities of matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-type plasminogen activator were markedly higher in MCF-7/DOX cells than in the MCF-7 cells. In vitro invasion assays and mouse models of lung metastasis demonstrated that MCF-7/DOX cells acquired invasive abilities. Using siRNAs and agonists specific for prostaglandin E (EP) receptors, we found that EP1 and EP3 played important roles in the invasiveness of MCF-7/DOX cells. CONCLUSIONS: We found that the invasive activity of MCF-7/DOX cells is mediated by Cox-2, which is induced by the EGFR-activated PI3K/Akt and MAPK pathways. In addition, EP1 and EP3 are important in the Cox-2-induced invasion of MCF-7/DOX cells. Therefore, not only Cox-2 but also EP1 and EP3 could be important targets for chemosensitization and inhibition of metastasis in breast cancers that are resistant to chemotherapy.

Prognostic significance of nephrectomy in metastatic renal cell carcinoma treated with systemic cytokine or targeted therapy: A 16-year retrospective analysis.

We compared progression-free survival (PFS) and overall survival (OS) among 292 metastatic renal cell carcinoma (mRCC) patients either undergoing nephrectomy (Nx, 61.6%) or not (non-Nx, 38.4%), stratified according to the MSKCC and Heng risk models, treated with either immunotherapy (IT, 45.2%) or targeted therapy (TT, 54.8%) between 2000 and 2015. During the follow-up duration of 16.6 months, PFS/OS of the Nx (6.0/30 months) and non-Nx (3.0/6.0 months) groups were significantly different despite differences among baseline parameters (p < 0.05). The intermediate- and poor-risk patients defined using either model showed significantly longer PFS and OS in the Nx group than in the non-Nx group (p < 0.05). After stratifying groups by systemic therapy and risk models, both the Nx and non-Nx groups showed no significant differences in intermediate and poor-risk models (p > 0.05). In both synchronous and metachronous mRCC patients, both PFS and OS showed similar survivals; the Nx group had significantly longer PFS and OS than the non-Nx group, even after considering each systemic therapy and prognostic model. Nx showed a significant positive benefit in PFS and OS compared to no Nx upon patient stratification according to the MSKCC and Heng risk models. The metastatic type did not significantly affect survival between the two groups.

Electrostatic interaction of tumor-targeting adenoviruses with aminoclay acquires enhanced infectivity to tumor cells inside the bladder and has better cytotoxic activity.

In a previous report, 3-aminopropyl functionalized magnesium phyllosilicate (aminoclay) improved adenovirus transduction efficiency by shielding the negative surface charges of adenovirus particles. The present study analyzed the physicochemical characterization of the electrostatic complex of adenoviruses with aminoclay and explored whether it could be utilized for enhancing tumor suppressive activity in the bladder. As a result of aminoclay-adenovirus nanobiohybridization, its transduction was enhanced in a dose-dependent manner, increasing transgene expression in bladder cancer cells and in in vivo animal models. Physicochemical studies demonstrated that positively charged aminoclay led to the neutralization of negative surface charges of adenoviruses, protection of adenoviruses from neutralizing antibodies and lowered transepithelial electrical resistance (TEER). As expected from the physicochemical properties, the aminoclay enabled tumor-targeting adenoviruses to be more potent in killing bladder cancer cells and suppressing tumor growth in orthotopic bladder tumors, suggesting that aminoclay would be an efficient, versatile and biocompatible delivery carrier for intravesical instillation of adenoviruses.

The establishment of a growth-controllable orthotopic bladder cancer model through the down-regulation of c-myc expression.

To properly evaluate the biological effects of immunotherapy, it is critical to utilize a model of cancer in immune-competent mice. Currently, MBT-2 is the most common murine bladder cancer cell line used in orthotopic bladder cancer models, even though this cell type often has an inappropriate genetic mutation landscape. In these models, after tumors are detected with in vivo imaging, the mouse usually dies within two to three weeks due to post-renal azotemia caused by the rapidly growing mass. This event prohibits the evaluation of tumor behavior upon intravesical drug treatment. We explored whether an shRNA-induced decrease in the expression of the c-myc oncogene in MBT-2 cells could slow down their in vitro proliferation and in vivo tumor growth. We transduced MBT-2 cells with shRNA lentiviruses that bound c-myc, established MBT2.cMYCshRNA and confirmed the retardation of the growth of tumors implanted in C3H/He mice. Accordingly, this study suggests that this novel orthotopic bladder cancer model in immune-competent mice may be more appropriate for the analysis of the effects of the intravesical instillation of immunotherapeutic agents.

Recommended oral sodium bicarbonate administration for urine alkalinization did not affect the concentration of mitomycin-C in non-muscle invasive bladder cancer patients.

OBJECTIVE: Sodium bicarbonate has been reported to maximize the efficacy of intravesical instillation of mitomycin-C (IVI-MMC) therapy by urine alkalinization in non-muscle-invasive bladder cancer (NMIBC). This study aimed to analyze the changes in MMC concentration according to urinary pH and evaluate the efficacy of sodium bicarbonate to maintain the concentration of active form of MMC during IVI-MMC. METHODS: We prospectively enrolled 26 patients with NMIBC after transurethral resection of bladder tumor. Patients with very high-risk and low-risk NMIBC were excluded. Urinary creatinine, volume, pH, and concentrations of MMC and its degraded form were measured immediately before and after IVI-MMC. The patients were administered 1.5 g of oral sodium bicarbonate during the preceding evening, in the morning, and immediately before the fourth cycle of the six-cycle IVI-MMC. The correlation between MMC concentration and urinary pH changes was explored with or without oral bicarbonate therapy. RESULTS: Recurrence without progression to muscle-invasive disease was noted in 4 of 26 patients in a 23.7-month follow-up. The mean urinary pH before and after the therapy increased from 6.03 to 6.50, and 6.46 to 7.24, without or with oral SB therapy, respectively. Despite this increase, the concentration of active form of MMC did not change significantly. No correlation was found between urinary pH and MMC concentration. Urine alkalinization by SB administration did not maintain the high concentration of urinary MMC. CONCLUSIONS: Urine alkalinization by sodium bicarbonate administration for IVI-MMC did not maintain the high concentration of active urinary MMC in NMIBC.

Regulation of cancer cell death by a novel compound, C604, in a c-Myc-overexpressing cellular environment.

The proto-oncogene c-Myc has been implicated in a variety of cellular processes, such as proliferation, differentiation and apoptosis. Several c-Myc targets have been studied; however, selective regulation of c-Myc is not easy in cancer cells. Herein, we attempt to identify chemical compounds that induce cell death in c-Myc-overexpressing cells (STF-cMyc and STF-Control) by conducting MTS assays on approximately 4000 chemical compounds. One compound, C604, induced cell death in STF-cMyc cells but not STF-Control cells. Apoptotic proteins, including caspase-3 and poly(ADP-ribose) polymerase (PARP), were cleaved in C604-treated STF-cMyc cells. In addition, SW620, HCT116 and NCI-H23 cells, which exhibit higher basal levels of c-Myc, underwent apoptotic cell death in response to C604, suggesting a role for C604 as an inducer of apoptosis in cancer cells with c-Myc amplification. C604 induced cell cycle arrest at the G2/M phase in cells, which was not affected by apoptotic inhibitors. Interestingly, C604 induced accumulation of c-Myc and Cdc25A proteins. In summary, a chemical compound was identified that may induce cell death in cancer cells with c-Myc amplification specifically through an apoptotic pathway.

A pathway-based approach for identifying biomarkers of tumor progression to trastuzumab-resistant breast cancer.

Although trastuzumab is a successful targeted therapy for breast cancer patients with tumors expressing HER2 (ERBB2), many patients eventually progress to drug resistance. Here, we identified subpathways differentially expressed between trastuzumab-resistant vs. -sensitive breast cancer cells, in conjunction with additional transcriptomic preclinical and clinical gene datasets, to rigorously identify overexpressed, resistance-associated genes. From this approach, we identified 32 genes reproducibly upregulated in trastuzumab resistance. 25 genes were upregulated in drug-resistant JIMT-1 cells, which also downregulated HER2 protein by >80% in the presence of trastuzumab. 24 genes were downregulated in trastuzumab-sensitive SKBR3 cells. Trastuzumab sensitivity was restored by siRNA knockdown of these genes in the resistant cells, and overexpression of 5 of the 25 genes was found in at least one of five refractory HER2 + breast cancer. In summary, our rigorous computational approach, followed by experimental validation, significantly implicate ATF4, CHEK2, ENAH, ICOSLG, and RAD51 as potential biomarkers of trastuzumab resistance. These results provide further proof-of-concept of our methodology for successfully identifying potential biomarkers and druggable signal pathways involved in tumor progression to drug resistance.

Development of replication-competent adenovirus for bladder cancer by controlling adenovirus E1a and E4 gene expression with the survivin promoter.

Survivin is a member of the inhibitors of apoptosis protein family. Here, we examined survivin expression and confirmed abundant survivin expression in bladder cancer cells. This expression pattern indicated that the transcriptional regulatory elements that control survivin expression could be utilized to discriminate cancer from normal cells. We therefore generated a novel adenovirus termed Ad5/35E1apsurvivinE4 with the following characteristics: 1) E1A and E4 protein expression was dependent on survivin promoter activity; 2) the green fluorescence protein gene was inserted into the genome under the control of the CMV promoter; 3) most of the E3 sequences were deleted, but the construct was still capable of expressing the adenovirus death protein with potent cytotoxic effects; and 4) the fiber knob was from serotype 35 adenovirus. As expected from the abundant survivin expression observed in bladder cancer cells, Ad5/35E1apsurvivinE4 replicated better in cancer cells than in normal cells by a factor of 106 to 102. Likewise, Ad5/35E1apsurvivinE4 exerted greater cytotoxic effects on all bladder cancer cell lines tested. Importantly, Ad5/35E1apsurvivinE4 inhibited the growth of Ku7-Luc orthotopic xenografts in nude mice. Taken together, Ad5/35E1apsurvivinE4 indicates that the survivin promoter may be utilized for the development of a replication-competent adenovirus to target bladder cancers.

Antitumor activity of the c-Myc inhibitor KSI-3716 in gemcitabine-resistant bladder cancer.

Intravesical instillation of chemotherapeutic agents is a well-established treatment strategy to decrease recurrence following transurethral resection in non-muscle invasive bladder cancer. Gemcitabine is a recently developed treatment option. However, the curative effects of gemcitabine are far from satisfactory due to de novo or acquired drug resistance. In a previous study, we reported that intravesical administration of the c-Myc inhibitor KSI-3716 suppresses tumor growth in an orthotopic bladder cancer model. Here, we explored whether KSI-3716 inhibits gemcitabine-resistant bladder cancer cell proliferation. As expected from the in vitro cytotoxicity of gemcitabine in several bladder cancer cell lines, gemcitabine effectively suppressed the growth of KU19-19 xenografts in nude mice, although all mice relapsed later. Long-term in vitro exposure to gemcitabine induced gemcitabine-specific resistance. Gemcitabine-resistant cells, termed KU19-19/GEM, formed xenograft tumors even in the presence of 2 mg/kg gemcitabine. Interestingly, KU19-19/GEM cells up-regulated c-Myc expression in the presence of the gemcitabine and resisted to the gemcitabine, however was suppressed by the KSI-3716. The sequential addition of gemcitabine and KSI-3716 inhibited gemcitabine-resistant cell proliferation to a great extent than each drug alone. These results suggest that sequential treatment with gemcitabine and KSI-3716 may be beneficial to bladder cancer patients.

Crystal structure of Pyrococcus furiosus PF2050, a member of the DUF2666 protein family.

Pyrococcus furiosus PF2050 is an uncharacterized putative protein that contains two DUF2666 domains. Functional and structural studies of PF2050 have not previously been performed. In this study, we determined the crystal structure of PF2050. The structure of PF2050 showed that the two DUF2666 domains interact tightly, forming a globular structure. Each DUF2666 domain comprises an antiparallel ß-sheet and an α-helical bundle. One side of the PF2050 structure has a positively charged basic cleft, which may have a DNA-binding function. Furthermore, we confirmed that PF2050 interacts with circular and linear dsDNA.

Development of a high-content screening method for chemicals modulating DNA damage response.

The cellular response to DNA damage is emerging as a promising target for cancer therapy. In the present study, the authors exploited the relationship between the level of the phosphorylated form of histone H2AX (γH2AX) and the extent of DNA damage and developed a quantitative, cell-based, high-content screening system for measuring the DNA damage response (DDR). In this system, the authors quantified the level of γH2AX by measuring DNA damage-induced γH2AX nuclear foci using an automated cell imager. They found that the total area of γH2AX foci per cell exhibited a good correlation with the concentration of DNA damage-inducing agents, including etoposide. The effects of 2 well-known inhibitors of DNA damage could be quantified using this system, suggesting the suitability of the γH2AX-foci quantification method for large-scale screening applications. This was confirmed by using this method to screen a chemical library; the resulting "hits" included compounds that inhibited early signaling events in DDR, as well those that inhibited subsequent DNA damage repair processes. Overall, this γH2AX foci-measuring system may be an effective screening method for identifying DNA damage response inhibitors that could eventually be used to develop novel anticancer drugs.

Small-molecule inhibitors of c-Myc transcriptional factor suppress proliferation and induce apoptosis of promyelocytic leukemia cell via cell cycle arrest.

c-Myc plays a decisive role in the proliferation of HL-60 promyelocytic leukemia cells. In the present study, we demonstrated that an inhibitor of c-Myc/Max/DNA complex formation has a high potentiality as a suppressor of c-Myc-involved cell signaling. We prepared recombinant c-Myc and Max proteins encompassing the human-origin DNA binding and dimerization domains, and tested a chemical library of 6480 small molecules for their inhibitory effect on the in vitro formation of the c-Myc/Max/DNA complex as well as their influence on DMSO-differentiated HL-60 cells. We found several hit compounds through in vitro and cell-based screening tests, and also confirmed these compounds significantly inhibited the formation of the recombinant c-Myc/Max/DNA complex in the low micromolar range. Indeed, these inhibitors effectively blocked c-Myc-associated gene expression in cancer cell line, suppressed the proliferation and induced the apoptosis of HL-60 promyelocytic leukemia cells via cell cycle arrest without altering the expression level of c-Myc in the DMSO-differentiated HL-60 cells. These successive results suggest that our c-Myc/Max/DNA complex inhibitors potently contribute to the suppression of the Myc-dependent proliferation of leukemia cells and to the induction of apoptosis. Accordingly, we would expect that these compounds could serve as lead compounds in the development of novel anticancer drugs.