An accelerated Rauhut-Currier dimerization enabled the synthesis of (±)-incarvilleatone and anticancer studies.

The total synthesis of racemic incarvilleatone has been achieved by utilizing unexplored accelerated Rauhut-Currier (RC) dimerization. The other key steps of the synthesis are oxa-Michael and aldol reactions in a tandem sequence. Racemic incarvilleatone was separated by chiral HPLC and the configuration of each enantiomer was determined by single-crystal X-ray analysis. In addition, a one-pot synthesis of (±)-incarviditone has been achieved from rac-rengyolone by using KHMDS as a base. We have also assessed the anticancer activity of all the synthesized compounds in breast cancer cells nonetheless, they exhibited very limited growth suppression activity.

Ccn2a-FGFR1-SHH signaling is necessary for intervertebral disc homeostasis and regeneration in adult zebrafish.

Intervertebral disc (IVD) degeneration is the primary cause of back pain in humans. However, the cellular and molecular pathogenesis of IVD degeneration is poorly understood. This study shows that zebrafish IVDs possess distinct and non-overlapping zones of cell proliferation and cell death. We find that, in zebrafish, cellular communication network factor 2a (ccn2a) is expressed in notochord and IVDs. Although IVD development appears normal in ccn2a mutants, the adult mutant IVDs exhibit decreased cell proliferation and increased cell death leading to IVD degeneration. Moreover, Ccn2a overexpression promotes regeneration through accelerating cell proliferation and suppressing cell death in wild-type aged IVDs. Mechanistically, Ccn2a maintains IVD homeostasis and promotes IVD regeneration by enhancing outer annulus fibrosus cell proliferation and suppressing nucleus pulposus cell death through augmenting FGFR1-SHH signaling. These findings reveal that Ccn2a plays a central role in IVD homeostasis and regeneration, which could be exploited for therapeutic intervention in degenerated human discs.

Microtubule-targeting agents impair kinesin-2-dependent nuclear transport of ß-catenin: Evidence of inhibition of Wnt/ß-catenin signaling as an important antitumor mechanism of microtubule-targeting agents.

An aberrant accumulation of nuclear ß-catenin is closely associated with the augmentation of cancer malignancy. In this work, we report that several microtubule-targeting agents (MTAs) such as vinblastine, taxol, and C12 (combretastatin-2-aminoimidazole analog) inhibit Wnt/ß-catenin signaling in oral squamous cell carcinoma (OSCC). We showed that the inhibition of microtubule dynamics by MTAs decreased the level of ß-catenin by increasing Axin and adenomatous polyposis coli levels and reducing the level of dishevelled. Furthermore, MTAs strongly reduced the localization of ß-catenin in the nucleus. The reduction in the level of nuclear ß-catenin was neither due to the degradation of ß-catenin in the nucleus nor due to an increase in the export of nuclear ß-catenin from the nucleus. A motor protein kinesin-2 was found to assist the nuclear transportation of ß-catenin. Interestingly, Wnt/ß-catenin signaling antagonist treatment synergized with MTAs and the activators of Wnt/ß-catenin signaling antagonized with the MTAs. C12 potently suppressed the growth of 4-Nitroquinoline 1-oxide-induced OSCC in the tongue of C57 black 6 mice and also abrogated Wnt/ß-catenin signaling pathway in the tumor. Our results provide evidence that the decrease in Wnt/ß-catenin signaling is an important antitumor effect of MTAs and the combined use of MTAs with Wnt/ß-catenin signaling antagonists could be a promising strategy for cancer chemotherapy.

Proteomics and functional study reveal marginal zone B and B1 cell specific protein as a candidate marker of multiple myeloma.

Multiple myeloma (MM) is a plasma cell­associated cancer and accounts for 13% of all hematological malignancies, worldwide. MM still remains an incurable plasma cell malignancy with a poor prognosis due to a lack of suitable markers. Therefore, discovering novel markers and targets for diagnosis and therapeutics of MM is essential. The present study aims to identify markers associated with MM malignancy using patient­derived MM mononuclear cells (MNCs). Label­free quantitative proteomics analysis revealed a total of 192 differentially regulated proteins, in which 79 proteins were upregulated and 113 proteins were found to be downregulated in MM MNCs as compared to non­hematological malignant samples. The identified differentially expressed candidate proteins were analyzed using various bioinformatics tools, including Ingenuity Pathway Analysis (IPA), Protein Analysis THrough Evolutionary Relationships (PANTHER), Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and Database for Annotation, Visualization and Integrated Discovery (DAVID) to determine their biological context. Among the 192 candidate proteins, marginal zone B and B1 cell specific protein (MZB1) was investigated in detail using the RPMI-8226 cell line model of MM. The functional studies revealed that higher expression of MZB1 is associated with promoting the progression of MM pathogenesis and could be established as a potential target for MM in the future.

Synthesis of artemisinic acid derived glycoconjugates and their anticancer studies.

Glycoconjugates, due to their diverse functions, are widely regarded as biologically important molecules. Artemisinic acid 1 occurs naturally in the plant Artemisia annua and is considered to be the biogenetic precursor of the antimalarial drug, artemisinin 2. We report herein the design and synthesis of diverse artemisinic acid derived glycoconjugates. We have synthesized 12-O-artemisinic acid-glycoconjugates (7a-k) and 12-N-artemisinic acid-glycoconjugates (8a-k) by utilizing Cu(i)-catalyzed azide-alkyne cycloaddition reactions (Click chemistry) with various synthesized sugar azides (6a-k) in good to excellent yields along with two fluorescently labeled compounds, 12-O-artemisinic acid-glycoconjugate 11 and 12-N-artemisinic acid-glycoconjugate 12, to investigate the mode of action of these compounds in biological systems. All the synthesized artemisinic acid glycoconjugates were assayed for their efficacy against the MCF7 cell line. Our anticancer studies indicated that all the synthesized compounds inhibited the growth of MCF7 cells in a dose dependent manner, barring compounds 4 and 7d. However, these compounds exhibit moderate cytotoxicity, as is evident from their IC50 values.

Proteomic Alterations in Multiple Myeloma: A Comprehensive Study Using Bone Marrow Interstitial Fluid and Serum Samples.

Multiple myeloma (MM) is a plasma cell-associated cancer and exists as the second most common hematological malignancy worldwide. Although researchers have been working on MM, a comprehensive quantitative Bone Marrow Interstitial Fluid (BMIF) and serum proteomic analysis from the same patients' samples is not yet reported. The present study involves the investigation of alterations in the BMIF and serum proteome of MM patients compared to controls using multipronged quantitative proteomic approaches viz., 2D-DIGE, iTRAQ, and SWATH-MS. A total of 279 non-redundant statistically significant differentially abundant proteins were identified by the combination of three proteomic approaches in MM BMIF, while in the case of serum 116 such differentially abundant proteins were identified. The biological context of these dysregulated proteins was deciphered using various bioinformatic tools. Verification experiments were performed in a fresh independent cohort of samples using immunoblotting and mass spectrometry based SRM assays. Thorough data evaluation led to the identification of a panel of five proteins viz., haptoglobin, kininogen 1, transferrin, and apolipoprotein A1 along with albumin that was validated using ELISA in a larger cohort of serum samples. This panel of proteins could serve as a useful tool in the diagnosis and understanding of the pathophysiology of MM in the future.

Synthesis and cytotoxic evaluation of apioarabinofuranosyl pyrimidines.

In view of the potent anticancer activity of the d-arabino-configured cytosine nucleoside (ara-C), apioarabinofuranosyl pyrimidine nucleosides were designed and synthesized from d-ribose as starting material. The synthetic strategy signifies that tosylation followed by in situ cyclization, one-pot controlled oxidative cleavage and acetylation by Pb(OAc)4 , stereoselective nucleobase condensation, inversion of hydroxyl group and uracil group converted to cytosine as the key steps. Synthesized apioarabinofuranosyl pyrimidine nucleosides were tested using breast, colon, and ovarian cancer cell lines. However, only compound 19a, 19b, and 22b have a moderate growth-suppressive effect against the luminal A breast cancer cell line MCF7.

C12, a combretastatin-A4 analog, exerts anticancer activity by targeting microtubules.

Combretastatin A4 and its analogs are undergoing various clinical trials for the treatment of different cancers. This study illustrated the molecular mechanism and antitumor activity of C12, (5-Quinolin-3-yl and 4-(3,4,5-trimethoxyphenyl) substituted imidazol-2-amine), a synthetic analog of CA-4. C12 reduced the tumor volume of MCF-7 xenograft in NOD-SCID mice without affecting the bodyweight of the mice. Further, C12 inhibited the proliferation of several types of cancer cells more efficiently than their noncancerous counterparts. Using GFP-EB1 imaging, the effects of C12 on the interphase microtubule dynamics were determined in live HeLa cells. C12 (10 nM, half-maximal proliferation inhibitory concentration) reduced the growth rate of microtubules by 52% and increased the pause time of microtubules by 68%. In addition, fluorescence recovery after photobleaching analysis demonstrated that 10 nM C12 strongly suppressed spindle microtubule dynamics in HeLa cells. C12 treatment reduced the interpolar distance between the two spindle poles, increased the chromosome congression index, inhibited chromosome movement, and increased the level of mitotic checkpoint complex proteins BubR1 and Mad2. The evidence presented here indicated that C12 could induce different modes of cell death, depending on the extent of microtubule depolymerization. Since C12 targets both the mitotic and non-mitotic cells and showed a stronger activity against cancerous cells than non-cancerous cells, it may have an advantage in cancer chemotherapy. The results significantly enhance our understanding of the antitumor mechanism of the microtubule-depolymerizing agents.

XPO1 is a critical player for bortezomib resistance in multiple myeloma: A quantitative proteomic approach.

Among the blood cancers, 13% mortality is caused by Multiple myeloma (MM) type of hematological malignancy. In spite of therapeutic advances in chemotherapy treatment, still MM remains an incurable disease is mainly due to emergence of chemoresistance. At present time, FDA approved bortezomib is the first line drug for MM treatment. However, like other chemotherapy, MM patients are acquiring resistance against bortezomib. The present study aims to identify and validate bortezomib resistant protein targets in MM using iTRAQ and label free quantitative proteomic approaches. 112 differentially expressed proteins were commonly found in both approaches with similar differential expression pattern. Exportin-1 (XPO1) protein was selected for further validation as its significant high expression was observed in both iTRAQ and label free analysis. Bioinformatic analysis of these common differentially expressed proteins showed a clear cluster of proteins such as SMC1A, RCC2, CSE1, NUP88, NUP50, TPR, HSPA14, DYNLL1, RAD21 and RANBP2 being associated with XPO1. Functional studies like cell count assay, flow cytometry assay and soft agar assay proved that XPO1 knock down in RPMI 8226R cell line results in re-sensitization to bortezomib drug. The mass spectrometry data are available via ProteomeXchange with identifier PXD013859. BIOLOGICAL SIGNIFICANCE: Multiple myeloma (MM) is a type of hematological malignancy which constitutes about 13% of all blood cell related malignancies. Chemoresistance is one of the major obstacles for the successful treatment for MM. Bortezomib is a first proteasome inhibitor drug, widely used in MM treatment. The present study aims to identify and validate bortezomib resistant protein targets in MM. Here, we identified 112 candidate proteins to be associated with bortezomib resistance using global quantitative proteomic analysis. Among these candidate proteins, we show that XPO1 plays crucial role in emerging bortezomib resistance using functional studies like cell count assay, flow cytometry assay and soft agar assay. XPO1 could be a potential therapeutic target for MM and development of inhibitors of XPO1 might help to cure MM.

Current Understanding of the Potential of Proteomics and Metabolomics Approaches in Cancer Chemoresistance: A Focus on Multiple Myeloma.

Chemoresistance is one of the major hurdles in cancer treatment leading to recurrence of cancer and affects the overall survival of patients. Cancer chemoresistance can be associated with various phenomena including modulation of vital cellular pathways. Unrevealing these alterations could provide a better understanding of chemoresistance and assist in the identification of new targets to overcome it. Recent advances in the field of proteomics and metabolomics have substantially helped in the identification of potential targets for chemoresistance in various cancers. This review highlights the potential of proteomics and metabolomics research to explore the putative targets associated with cancer chemoresistance with a special focus on Multiple Myeloma (MM). MM is a type of hematological malignancy which constitutes about 13% of all blood cell cancers. The therapeutic advancements for MM have increased the median overall survival rate to over 3-fold in the last one and half decade. Although in recent times, significant improvements in the overall survival rate of MM are achieved, MM remains an incurable disease with unpredictable refractory mechanisms. In spite of therapeutic advances, chemoresistance thrives to be a major hurdle in the treatment of multiple myeloma which demands a better understanding of chemoresistance. In this review, we have attempted to highlight the potential applications of proteomics and metabolomics research in the understanding of chemoresistance in MM.

Synthesis and Anticancer Properties of Novel Truncated Carbocyclic Nucleoside Analogues.

BACKGROUND: Modified nucleosides established a prime role as therapeutic drugs. OBJECTIVE: Design and synthesis of novel truncated carbocyclic nucleoside with modified nucleobases and evaluation of their anticancer properties. METHODS: Novel truncated carbocyclic nucleoside analogues were synthesized from a versatile starting material D-ribose. The synthetic route includes stereoselective Grignard reaction, Wittig olefination, ring closing metathesis, double bond hydrogenation and Mitsunobu nucleobase condensation as the key steps. Cytotoxicity was measured using MTT assay in breast cancer cell lines (MCF7 and MDA-MB-231), ovarian cancer cell lines (IGROV1 and OVCAR8). RESULT & CONCLUSION: The synthesized compounds were characterized using spectroscopy techniques. The synthesized compounds induced cytotoxicity in breast cancer cell lines (MCF7 and MDA-MB-231), ovarian cancer cell lines (IGROV1 and OVCAR8) while minimal effect on primary cell line. Among the eight analogues, 1b and 1d showed the highest cytotoxicity effect and induced autophagy mode of cell death. These compounds induced autophagy by inactivating AKT and mTOR pathway. In addition, PARP1 was found to be stabilized upon treatment with compound 1b and 1d and is one of the known markers associated with induction of autophagy through the AMPK/mTOR pathway after DNA damage. Taken together, these results suggest that compounds 1b and 1d inhibit cancer cell proliferation through mTOR inactivation-mediated induction of autophagy.

Metabolomic alterations in invasive ductal carcinoma of breast: A comprehensive metabolomic study using tissue and serum samples.

Invasive ductal carcinoma (IDC) is the most common type of breast cancer and the leading cause of breast cancer related mortality. In the present study, metabolomic profiles of 72 tissue samples and 146 serum samples were analysed using targeted liquid chromatography multiple reaction monitoring mass spectrometry (LC-MRM/MS) and untargeted gas chromatography mass spectrometry (GC-MS) approaches. Combination of univariate and multivariate statistical treatment identified significant alterations of 42 and 32 metabolites in tissue and serum samples of IDC, respectively when compared to control. Some of the metabolite changes from tissue were also reflected in serum, indicating a bi-directional interaction of metabolites in IDC. Additionally, 8 tissue metabolites and 9 serum metabolites showed progressive change from control to benign to IDC suggesting their possible role in malignant transformation. We have identified a panel of three metabolites viz. tryptophan, tyrosine, and creatine in tissue and serum, which could be useful in screening of IDC subjects from both control and benign. The metabolomic alterations in IDC showed perturbations in purine and pyrimidine metabolism, amino sugar metabolism, amino acid metabolism, fatty acid biosynthesis etc. Comprehensively, this study provides valuable insights into metabolic adaptations of IDC, which can help to identify diagnostic markers as well as potential therapeutic targets.

Synthesis and anticancer studies of Michael adducts and Heck arylation products of sesquiterpene lactones, zaluzanin D and zaluzanin C from Vernonia arborea.

Sesquiterpene lactones containing α-methylene-γ-lactones, zaluzanin D 1 and zaluzanin C 2 were isolated from the leaves of Vernonia arborea. Several diverse Michael adducts (3-22) and Heck arylation analogs (23-34) of 1 have been synthesized by reacting with various amines and aryl iodides, respectively and were assayed for their in vitro anticancer activities against human breast cancer cell lines MCF7 and MDA-MB-231. Among all the synthesized analogs, Michael adducts 9 and 10 showed better anticancer activities as compared to 1. However, among these compounds, only 10 has minimal cytotoxic effect on normal breast epithelial MCF10A cells. Our detailed mechanistic studies reveal that compounds 9 and 10 execute their antiproliferative activity through induction of apoptosis and thereby inhibit the cancer cells proliferation and compound 10 could be a lead compound for designing potential anti-cancer compound.

Multipronged quantitative proteomics reveals serum proteome alterations in breast cancer intrinsic subtypes.

Being molecularly heterogeneous, breast cancer tends to be a complicated oncological disease with high incidence rates throughout the world. The primary aim of this study was to identify the set of serum proteins with discriminatory capabilities towards the four major subtypes of breast cancer. We employed multipronged quantitative proteomic approaches like 2D-DIGE, iTRAQ and SWATH-MS and identified 307 differentially regulated proteins. Luminal A subtype consisted of 24, Luminal B subtype 38, HER2 Enriched subtype 17 and Triple negative breast cancer subtype 10 differentially regulated subtype specific proteins. These specific proteins were further subjected to bioinformatic tools which revealed the involvement in platelet degranulation, fibrinolysis, lipid metabolism, immune response, complement activation, blood coagulation, glycolysis and cancer signaling pathways in the subtypes of the breast cancer. The significant discrimination efficiency of the models generated through multivariate statistical analysis was decent to distinguish each of the four subtypes from controls. Further, some of the statistically significant differentially regulated proteins were verified and validated by immunoblotting and mass spectrometry based selected reaction monitoring (SRM) approach. Our Multipronged proteomics approaches revealed panel of serum proteins specifically altered for individual subtypes of breast cancer. The mass spectrometry data are available via ProteomeXchange with identifier PXD006441. BIOLOGICAL SIGNIFICANCE: Worldwide, breast cancer continues to be one of the leading causes of cancer related deaths in women and it encompasses four major molecular subtypes. As breast cancer treatment majorly depends on identification of specific subtype, it is important to diagnosis the disease at subtype level. Our results using multipronged quantitative proteomics identified 307 differentially regulated proteins in which 24 were specific for Luminal A, 38 for Luminal B, 17 for HER2 enriched and 10 proteins were specific for TN subtype. Bioinformatic analysis of these proteins revealed certain biological processes and pathways altered at subtype level and validation experiments of some of these proteins using immunoblotting and SRM assays are consistent with discovery data. This is the first comprehensive proteomic study on serum proteome alterations at subtype level which will not only help to distinguish subtype of breast cancer but also contribute to a better understanding of the molecular characteristic of breast cancer at individual subtype level.

Urinary proteome alterations in HER2 enriched breast cancer revealed by multipronged quantitative proteomics.

Globally, breast cancer is the second most common cancer among women. Although biomarker discoveries through various proteomic approaches of tissue and serum samples have been studied in breast cancer, urinary proteome alterations in breast cancer are least studied. Urine being a noninvasive biofluid and a significant source of proteins, it has the potential in early diagnosis of breast cancer. This study used complementary quantitative gel-based and gel-free proteomic approaches to find a panel of urinary protein markers that could discriminate HER2 enriched (HE) subtype breast cancer from the healthy controls. A total of 183 differentially expressed proteins were identified using three complementary approaches, namely 2D-DIGE, iTRAQ, and sequential window acquisition of all theoretical mass spectra. The differentially expressed proteins were subjected to various bioinformatics analyses for deciphering the biological context of these proteins using protein analysis through evolutionary relationships, database for annotation, visualization and integrated discovery, and STRING. Multivariate statistical analysis was undertaken to identify the set of most significant proteins, which could discriminate HE breast cancer from healthy controls. Immunoblotting and MRM-based validation in a separate cohort testified a panel of 21 proteins such as zinc-alpha2-glycoprotein, A2GL, retinol-binding protein 4, annexin A1, SAP3, SRC8, gelsolin, kininogen 1, CO9, clusterin, ceruloplasmin, and α1-antitrypsin could be a panel of candidate markers that could discriminate HE breast cancer from healthy controls.

Quantitative tissue proteomic investigation of invasive ductal carcinoma of breast with luminal B HER2 positive and HER2 enriched subtypes towards potential diagnostic and therapeutic biomarkers.

Worldwide, breast cancer is one of the frequently diagnosed cancers in women with high mortality if not diagnosed at early stage. Although biomarker discoveries through various proteomic approaches have been studied in breast cancer, a limited number of studies have explored the invasive ductal carcinoma with Luminal B HER2 positive (LB) and HER2 enriched (HE) subtypes. The present study employed the complementary quantitative proteomic approaches to find a panel of markers that could discriminate LB and HE subtypes as well as early (ES) and late stages (LS) of these subtypes. A total of 67 and 68 differentially expressed proteins were identified by DIGE for the subtype and stage wise categories, respectively. Multivariate statistical analysis was employed to identify the set of most significant proteins, which could discriminate between these two subtypes and also early and late stages under study. Immunoblotting and MRM based validation in a separate cohort of samples confirmed that panel of biosignatures for LB are APOA1, GELS, HS90B, EF1A1, NHRF1 and PRDX3 and for HE are PRDX1, CATD, CALR, ATPB and CH60. For the diagnosis of early and late stages the potential markers are TPM4, CATD, PRDX3, ANXA3, HSPB1 and CALR, TRFE, GELS, CH60, CAPG, NHRF1, 1433G, GRP78 respectively.

Novel hybrid nocodazole analogues as tubulin polymerization inhibitors and their antiproliferative activity.

We describe the design, synthesis and SAR profiling of a series of novel combretastatin-nocodazole conjugates as potential anticancer agents. The thiophene ring in the nocodazole moiety was replaced by a substituted phenyl ring from the combretastatin moiety to design novel hybrid analogues. The hydroxyl group at the ortho position in compounds 2, 3 and 4 was used as the conformationally locking tool by anticipated six-membered hydrogen bonding. The bioactivity profiles of all compounds as tubulin polymerization inhibitors and as antiproliferative agents against the A-549 human lung cancer cell line were investigated Compounds 1 and 4 showed µM IC50 values in both assays.

Correlation of hydrogen-bonding propensity and anticancer profile of tetrazole-tethered combretastatin analogues.

A series of 1,5-disubstituted tetrazole-tethered combretastatin analogues with extended hydrogen-bond donors at the ortho-positions of the aryl A and B rings were developed and evaluated for their antitubulin and antiproliferative activity. We wanted to test whether intramolecular hydrogen-bonding used as a conformational locking element in these analogues would improve their activity. The correlation of crystal structures with the antitubulin and antiproliferative profiles of the modified analogues suggested that hydrogen-bond-mediated conformational control of the A ring is deleterious to the bioactivity. In contrast, although there was no clear evidence that intramolecular hydrogen bonding to the B ring enhanced activity, we found that increased substitution on the B ring had a positive effect on antitubulin and antiproliferative activity. Among the various analogues synthesized, compounds 5d and 5e, having hydrogen-bonding donor groups at the ortho and meta-positions on the 4-methoxy phenyl B ring, are strong inhibitors of tubulin polymerization and antiproliferative agents having IC50 value in micromolar concentrations.

Mass spectrometry-based proteomics in molecular diagnostics: discovery of cancer biomarkers using tissue culture.

Accurate diagnosis and proper monitoring of cancer patients remain a key obstacle for successful cancer treatment and prevention. Therein comes the need for biomarker discovery, which is crucial to the current oncological and other clinical practices having the potential to impact the diagnosis and prognosis. In fact, most of the biomarkers have been discovered utilizing the proteomics-based approaches. Although high-throughput mass spectrometry-based proteomic approaches like SILAC, 2D-DIGE, and iTRAQ are filling up the pitfalls of the conventional techniques, still serum proteomics importunately poses hurdle in overcoming a wide range of protein concentrations, and also the availability of patient tissue samples is a limitation for the biomarker discovery. Thus, researchers have looked for alternatives, and profiling of candidate biomarkers through tissue culture of tumor cell lines comes up as a promising option. It is a rich source of tumor cell-derived proteins, thereby, representing a wide array of potential biomarkers. Interestingly, most of the clinical biomarkers in use today (CA 125, CA 15.3, CA 19.9, and PSA) were discovered through tissue culture-based system and tissue extracts. This paper tries to emphasize the tissue culture-based discovery of candidate biomarkers through various mass spectrometry-based proteomic approaches.

Epigenetic silencing of the RASSF1A tumor suppressor gene through HOXB3-mediated induction of DNMT3B expression.

The RASSF1A tumor suppressor gene is epigenetically silenced in a variety of cancers. Here, we perform a genome-wide human shRNA screen and find that epigenetic silencing of RASSF1A requires the homeobox protein HOXB3. We show that HOXB3 binds to the DNA methyltransferase DNMT3B gene and increases its expression. DNMT3B, in turn, is recruited to the RASSF1A promoter, resulting in hypermethylation and silencing of RASSF1A expression. DNMT3B recruitment is facilitated through interactions with Polycomb repressor complex 2 and MYC, which is bound to the RASSF1A promoter. Mouse xenograft experiments indicate that the oncogenic activity of HOXB3 is due, at least in part, to epigenetic silencing of RASSF1A. Expression analysis in human lung adenocarcinoma samples reveals that RASSF1A silencing strongly correlates with overexpression of HOXB3 and DNMT3B. Analysis of human cancer cell lines indicates that the RASSF1A epigenetic silencing mechanism described here may be common in diverse cancer types.