Tumor suppressor genes and oncogenes are both commonly altered during carcinogenesis. For oncogenes and other genes that drive growth, targeting mutated or activated forms (such as the EGFR-Her2/Nneu pathway) has been shown to be an effective anti-cancer approach. Pharmacologically targeting tumor suppressor genes has not been as fruitful, as many tumor suppressor genes are irreversibly silenced through somatic mutation or entirely deleted during carcinogenesis, thereby making it difficult to restore gene function. BRM, a key SWI/SNF complex subunit and a putative tumor suppressor gene, is inactivated in 15–20% of many solid tumor types. Unlike other tumor suppressor genes, the loss of BRM has been shown to be a reversible epigenetic change, rather than an irreversible genetic alteration. Using a high throughput drug screen, we identified a number of compounds that could effectively restore BRM expression and function. Two of these compounds, RH (RH02032) and GK (GK0037), were found to be such reactivating agents. Both compounds led to robust re-expression of BRM, induced downstream expression of BRM-dependent genes and inhibited BRM-dependent growth across a wide range of BRM-deficient cancer cell lines of different origins. We therefore show, for the first time, that pharmacologic reversal of epigenetic changes of the SWI/SNF chromatic remodeling complex subunit, BRM, is a potentially viable and novel therapeutic approach.

The SWI/SNF complex is a key catalyst for gene expression and regulates a variety of pathways, many of which have anticancer roles. Its central roles in cellular growth control, DNA repair, differentiation, cell adhesion and development are often targeted, and inactivated, during cancer development and progression. In this review, we will discuss what is known about how SWI/SNF is inactivated, and describe the potential impact of abrogating this complex. BRG1 and BRM are the catalytic subunits which are essential for SWI/SNF function, and thus, it is not surprising that they are lost in a variety of cancer types. As neither gene is mutated when lost, the mechanism of suppression, as well as the impact of potential gene activity restoration, are reviewed.

A wide variety of diunsaturated phosphonium salts have been synthesized in order to determine whether or not such structures undergo cyclopolymerization. As intermediates for these monomers, a number of previously unreported unsaturated phosphines have been prepared and characterized. Polymerization studies using a wide variety of free radical initiating conditions led to polymers in those cases which were predicted to undergo cyclopolymerization leading to five-, six-, or seven-membered rings with one exception. The properties of the polymers are consistent with the cyclopolymerization mechanism. The conversion of poly(diallyldipheny1phosphonium bromide) to polfidiallyldiphenylphosphine oxide) offers additional evidence for cyclopolymerization. Di-3-butenyldiphenylphosphonium bromide, a monomer functionally capable of forming a polymer containing an eightmembered ring, did not polymerize. Divinylphenylphosphine was found to undergo copolymerization with acrylonitrile in accordance with the cyclocopolymerization mechanism.

BACKGROUND: BRM, a catalytic subunit of the SWI/SNF chromatin remodeling complex, regulates expression/function of key signal transduction pathways with anticancer functions. In 15-25% of lung cancers, BRM protein expression is lacking. When BRM null mice (who display distinct cell cycle abnormalities) are exposed to carcinogens, they develop 10-fold more tumors then control mice. BRM silencing does not appear to be driven by mutational changes. We hypothesized that BRM silencing may be related to sequence variants in the BRM promoter region. METHODS: We compared novel BRM promoter polymorphisms to BRM protein expression in cancer cell lines and tumors of lung cancer patients. We then performed a case-control analysis of these polymorphisms with lung cancer risk. RESULTS: Sequencing of human cancer cell lines identified a 7-bp (rs34480940; located −741 from transcription start site) and 6-bp (rs3832613; located −1321) BRM insertion polymorphisms. In Caucasians, minor allele frequencies (MAF) of 45% were found for both polymorphisms. Cancer cell lines were evaluated for BRM protein expression (Western blot). Twelve BRM staining (BRM-positive) and twelve non-staining (BRM-negative) cancer cell lines were genotyped. In the BRM-negative cell lines, 11/12 cell lines were homozygous variant for at least one of the two BRM promoter polymorphisms (5/12 were double homozygous; 6/12 were homozygous for one polymorphism). In contrast, the BRM-positive cell lines yielded a good mix of genotypes for both polymorphisms. In lung cancer tissues, all ten BRM-negative samples carried at least one homozygous variant (eight were double homozygous variant, while two were homozygous for one polymorphism). In contrast, genotyping of normal adjacent tissue of twelve BRM-positive samples yielded population-normal MAFs of 42% for BRM −741 and 46% for BRM −1321. Tumour-normal tissue genotyping concordance rate was 86%. In the case-control analysis, 484 ever-smoker lung cancer cases were compared to 715 age and gender frequency-matched ever-smoker controls. Compared with a wildtype reference, carrying one homozygous variant was associated with an adjusted odds ratio (aOR) of 1.40 (95%CI:0.95-2.05; p=0.09); carrying two homozygous variants was associated with aOR=2.19 (1.40-3.43; p=0.0006), after adjusting for age, gender, and smoking variables. CONCLUSIONS: Homozygous variants of two novel BRM promoter polymorphisms are tightly associated with loss of BRM expression in lung cancer tissues and cancer cell lines. These homozygous variants are also associated with lung cancer risk in ever-smokers. Since epigenetic silencing of BRM can be reversed by various compounds (e.g. HDAC inhibitors, novel compounds from screening libraries), reversing BRM silencing could be developed as part of a chemoprevention strategy in smokers who carry the homozygous variants of these two BRM promoter polymorphisms. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 198.

BRM is a catalytic subunit of the SWI/SNF chromatin remodeling complex, which regulates the expression and function of key cellular proteins and signal transduction pathways, many of which have anticancer functions. BRM is lost in 15-25% of many solid tumor types. BRM is specifically tied to Rb function in that Rb-mediated growth arrest is thwarted by the loss of BRM, but restored when BRM expression is restored. Despite this observation, BRM null mice did not develop tumors, indicating that BRM is not a classic tumor suppressor protein. However, cells from these animals display distinct cell cycle abnormalities, and when these mice are exposed to carcinogens, they develop larger and 10-fold more tumors. Unlike many other anticancer proteins, however, BRM is reversibly silenced, and when it is re-expressed in BRM-deficient cell lines, growth is substantially inhibited. To understand how BRM is silenced, we sequenced the BRM promoter and found two 6-7bp inserts, so called insertion/deletion polymorphisms (IDPs). We sequenced DNA from 160 Caucasian individuals, and found that the frequency of the two polymorphism sites were approximately 20%, 50%, and 30% for the homozygous, heterozygous and wild type states respectively. In comparison, a set of 10 BRM-deficient cell lines were found to be homozygous for one or both of these polymorphic sites, while a set of 12 BRM-positive cell lines showed the opposite frequency of these IDPs_that is, almost all were wild type for both sites. From these observations, it appears that these polymorphic sites correlate with the loss of BRM. We next analyzed the presence or absence of these polymorphic sites in both BRM-positive and BRM-negative tumors. We found that the BRM-negative tumors were essentially uniformly homozygous for both polymorphic sites while the BRM-positive tumors demonstrated a distribution similar to those seen in the normal population. Because BRM appears to be a tumor susceptible gene, we hypothesize that BRM polymorphism causes the loss of BRM which then indicates a predisposition to cancer. To test this hypothesis, we are conducting a case control study and found that the ratio for lung cancer risk was 1.6 and 2.2 for the presence of one and both polymorphic sites respectively. Since BRM is silenced in cancer cells, we next determined the impact of pharmacologically restoring BRM. We next applied two BRM inducing compounds to two BRM-deficient cell lines. The application of these compounds resulted in the induction of several BRM-dependent genes indicting that the induced BRM is functional and has caused the cells to undergo growth arrest. Both of these observations were BRM-dependent because these effects could be blocked with either antiBRM shRNAi or dominant negative BRM. These findings have broad and novel implications for cancer treatment, as they show that it may it be possible to restore BRM and target treatment to the preferred patient population by simply genotyping patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1590.