Anna Maria Calcagno

Reversal of ABC drug transporter-mediated multidrug resistance in cancer cells: Evaluation of current strategies

Overexpression of ATP-binding cassette (ABC) drug transporters that actively efflux a variety of amphipathic compounds can cause multidrug resistance (MDR) in cancer cells, which is a major obstacle in the success of cancer chemotherapy. The development of synthetic small molecule compounds or the identification of natural products that block ABC transporter-mediated efflux has been the conventional approach used to combat MDR. The strategy of using chemosensitizers, however, has not been successful in clinical cancer chemotherapy. Therefore, alternative approaches to identify or to synthesize compounds that can induce selective toxicity in cancer cells overexpressing one or more ABC transporters have been undertaken. This review summarizes the recent advances in identifying strategies to restore sensitivity to chemotherapeutics in multidrug resistant cancer cells.

Single-step doxorubicin-selected cancer cells overexpress the ABCG2 drug transporter through epigenetic changes

Understanding the mechanisms of multidrug resistance (MDR) could improve clinical drug efficacy. Multidrug resistance is associated with ATP binding cassette (ABC) transporters, but the factors that regulate their expression at clinically relevant drug concentrations are poorly understood. We report that a single-step selection with low doses of anti-cancer agents, similar to concentrations reported in vivo, induces MDR that is mediated exclusively by ABCG2. We selected breast, ovarian and colon cancer cells (MCF-7, IGROV-1 and S-1) after exposure to 14 or 21u2009nM doxorubicin for only 10 days. We found that these cells overexpress ABCG2 at the mRNA and protein levels. RNA interference analysis confirmed that ABCG2 confers drug resistance. Furthermore, ABCG2 upregulation was facilitated by histone hyperacetylation due to weaker histone deacetylase 1-promoter association, indicating that these epigenetic changes elicit changes in ABCG2 gene expression. These studies indicate that the MDR phenotype arises following low-dose, single-step exposure to doxorubicin, and further suggest that ABCG2 may mediate early stages of MDR development. This is the first report to our knowledge of single-step, low-dose selection leading to overexpression of ABCG2 by epigenetic changes in multiple cancer cell lines.

Evidence for dual mode of action of a thiosemicarbazone, NSC73306: a potent substrate of the multidrug resistance–linked ABCG2 transporter

Multidrug resistance due to reduced drug accumulation is a phenomenon predominantly caused by the overexpression of members of the ATP-binding cassette (ABC) transporters, including ABCB1 (P-glycoprotein), ABCG2, and several ABCC family members [multidrug resistance–associated protein (MRP)]. We previously reported that a thiosemicarbazone derivative, NSC73306, is cytotoxic to carcinoma cells that overexpress functional P-glycoprotein, and it resensitizes these cells to chemotherapeutics. In this study, we investigated the effect of NSC73306 on cells overexpressing other ABC drug transporters, including ABCG2, MRP1, MRP4, and MRP5. Our findings showed that NSC73306 is not more toxic to cells that overexpress these transporters compared with their respective parental cells, and these transporters do not confer resistance to NSC73306 either. In spite of this, we observed that NSC73306 is a transport substrate for ABCG2 that can effectively inhibit ABCG2-mediated drug transport and reverse resistance to both mitoxantrone and topotecan in ABCG2-expressing cells. Interactions between NSC73306 and the ABCG2 drug-binding site(s) were confirmed by its stimulatory effect on ATPase activity (140–150 nmol/L concentration required for 50% stimulation) and by inhibition of [125I]iodoarylazidoprazosin photolabeling (50% inhibition at 250–400 nmol/L) of the substrate-binding site(s). Overall, NSC73306 seems to be a potent modulator of ABCG2 that does not interact with MRP1, MRP4, or MRP5. Collectively, these data suggest that NSC73306 can potentially be used, due to its dual mode of action, as an effective agent to overcome drug resistance by eliminating P-glycoprotein–overexpressing cells and by acting as a potent modulator that resensitizes ABCG2-expressing cancer cells to chemotherapeutics. [Mol Cancer Ther 2007;6(12):3287–96]

Enhancement of Drug Absorption through the Blood Brain Barrier and Inhibition of Intercellular Tight Junction Resealing by E-cadherin Peptides

E-cadherin-mediated cell-cell interactions in the zonula adherens play an important role in the formation of the intercellular tight junctions found in the blood-brain barrier. However, it is also responsible for the low permeation of drugs into the brain. In this study, HAV6 peptide derived from the EC1 domain of E-cadherin was found to enhance the permeation of ¹⁴C-mannitol and [³H(G)]-daunomycin through the blood-brain barrier of the in situ rat brain perfusion model. In addition, HAV6 peptide and verapamil have a synergistic effect in enhancing the BBB permeation of daunomycin. A new intercellular-junction resealing assay was also developed using Caco-2 monolayers to evaluate new peptides (BLG2, BLG3, and BLG4) derived from the bulge regions of the EC2, EC3, and EC4 domains of E-cadherin. BLG2 and BLG4 peptides but not BLG3 peptides were found to be effective in blocking the resealing of the intercellular junctions. The positive control peptides (ADT10, ADT6, and HAV10) block the resealing of the intercellular junctions in a concentration-dependent manner. All these findings suggest that E-cadherin-derived peptides can block E-cadherin-mediated cell-cell interactions. These findings demonstrate that cadherin peptides may offer a useful targeted permeation enhancement of therapeutic agents such as anticancer drugs into the brain.

N-cadherin involvement in the heterotypic adherence of malignant T-cells to epithelia.

N-cadherin, a cell adhesion molecule normally found in neural cell tissue, has been found recently to be expressed on the surface of malignant T-cells. The function of N-cadherin on these cells remains unclear. Heterotypic assays between Molt-3 T lymphoblastic leukemia cells and Caco-2 epithelial monolayers were examined under different conditions to assess the functional role of N-cadherin. The results indicate that adherence of Molt-3 cells to Caco-2 monolayers was reduced significantly following pretreatment of Molt-3 cells with 100 μM of an N-cadherin-derived antagonist decapeptide. In contrast, pretreatment of Molt-3 cells with an anti-N-cadherin antibody raised against the first 20 amino acids of N-cadherin sequence led to a surprisingly marked enhancement of Molt-3 cell adherence to Caco-2 monolayers. In addition, the presence of anti-N-cadherin antibody neutralized the inhibitory effect of anti-ICAM-1 on Molt-3 adhesion to Caco-2 monolayers. This novel finding demonstrates that external stimulus through the N-cadherin amino terminus can modulate adhesion of malignant T-cells to epithelia and may promote their ability to invade or metastasize to inflammatory sites.

Effects of An E-cadherin-Derived Peptide on the Gene Expression of Caco-2 Cells

AbstractPurpose. The goal of this study was to determine the effects of exposure to an HAV peptide (Ac-SHAVSS-NH2) on the protein and gene expression in Caco-2 cells, a model for the intestinal mucosa.nMethods. Caco-2 cells were incubated with either 100 or 500 μM of the hexapeptide then evaluated over a 48-h time period.nResults. Cell detachment from the monolayer was seen only after 48 h of exposure to the peptide, with the greatest effects occurring with a peptide concentration of 500 μM. Total protein expression of E-cadherin showed a decrease of nearly 20% at the 24-h time point for each concentration examined, whereas no significant changes were detected at the other time points studied. Short term exposure to a 500 μM solution of Ac-SHAVSS-NH2 caused few changes in gene expression as determined by Affymetrix GeneChip⌖ microarrays; however, longer exposure periods produced numerous changes in the treated cells. The variations in mRNA expression indicate that this HAV peptide has an effect in the E-cadherin signaling pathways. The greatest increases in mRNA expression were found in genes regulating excretion or degradation of the peptide.nConclusions. This work suggests that this HAV peptide produces effects that reach beyond modulation of adhesion.

Evolution of drug resistance in cancer: the emergence of unique mechanisms and novel techniques.

Dramatic decreases in the mortality rates due to both cardiovascular and cerebrovascular diseases have been reported over the last fifty years. Despite the age of molecular characterization of disease and the discovery of novel druggable targets leading to pharmaceutical breakthroughs, the mortality trends due to cancer in this time frame have not changed. The evolution of drug resistance to each of these new pharmaceutical entities has formed a nearly impassable barrier to successful drug treatment in cancer. The overexpression of ATP-binding cassette (ABC) drug transporters has been considered the predominant mechanism responsible for multidrug resistance (MDR). ABC transporters have been studied in vitro for decades; nevertheless, significant clinical advancement has been lacking possibly due to the multifactorial nature of resistance. This lack of clinical success has spurred investigators to uncover various other mechanisms of resistance and to generate new tools to illustrate the evolution of drug resistance at the molecular level and to better understand gene regulation in the presence of drug. Not so surprisingly, the use of evolutionary theory to investigate the dynamics of somatic evolution has emerged, giving rise to transdisciplinary programs to champion the application of evolutionary theory to understand the mechanisms involved in MDR. This issue will highlight the recent work of investigators, both within the cancer community and in the scientific community at large, as they apply evolutionary principles to MDR to illuminate alternate mechanisms of MDR and to establish tools to both elucidate the evolution of MDR and to circumvent it. One such work reviews therapeutics recently devised to alter the epigenetics of tumors by inhibiting histone deacetylase. Robey et al. discusses how mechanisms of resistance to histone deacetylase inhibitors have already surfaced and how they range from the overexpression of ABCB1 to NFKB activation. As in evolutionary biology, selection pressure plays a critical role in the development of MDR, and the Gillies laboratory describes the cellular adaptation that results from the extracellular acidosis within the tumor microenvironment. Advancements in technologies that probe the genome have provided unique opportunities for clinicians and researchers to study MDR. For instance, investigators have created molecular tumor clocks derived from passenger DNA methylation changes as well as a clinical gene signature utilizing TaqMan low density arrays and miRNA expression profiles for cells with increasing levels of MDR. Each of these tools is showcased in papers in this issue. Moreover, the use of evolutionary theory to bypass MDR is also considered. Getzenberg and Coffey look at the use of thermal

Abstract 954: Multidrug resistance transcriptome analysis highlights compounds that sensitize resistant hepatocellular carcinoma through increased histone acetylation.

No effective systemic therapy exists for patients with advanced hepatocellular carcinoma (HCC). Surgery is the mainstay treatment for patients with early stage HCC tumors. Either resection or transplantation is advocated if the HCC is within the Milan criteria. Nonsurgical treatments including percutaneous ethanol injection, radiofrequency ablation, and transcatheter arterial chemoembolization (TACE) are used as adjuvant therapy to surgery but also to treat unresectable HCC. Although a meta-analysis showed a beneficial survival effect for patients with intermediate HCC treated by TACE using doxorubicin and cisplatin, the survival benefit of systemic chemotherapy for the treatment of liver cancer is marginal at best. Although Sorafenib, a multi-tyrosine kinase inhibitor, is becoming established as the first line of therapy for advanced HCC, it was recently shown to be a substrate of ABCB1 and ABCG2, two major transporters involved in multidrug resistance (MDR) and expressed in hepatocytes. In this study, the MDR transcriptome was analyzed in a cohort of 38 patients using TaqMan-based qRT-PCR, with the aim of finding ways to sensitize this intrinsically MDR cancer. The study reveals a 45-gene signature, validated using an independent cohort of 53 patients, that predicts overall survival (OS). We used the Connectivity Map tool, designed to reveal connections among drugs, genes, and pathological states, to identify three compounds that converted the gene expression profile of HCC cell lines from one matching patients with poor OS to one with good OS. These compounds increased histone acetylation, resulting in the sensitization of tumor cells to conventional chemotherapy including cisplatin, sorafenib and 5-FU. This work provides new treatment strategies based on gene expression profiling and connectivity data for a disease for which no effective systemic treatments exist. More importantly, the current study reveals a new strategy to sensitize any type of refractory cancer to chemotherapy. Citation Format: Jean-Pierre Gillet, Jesper B. Andersen, James P. Madigan, Sudhir Varma, Chung-Pu Wu, Anna M. Calcagno, Suresh V. Ambudkar, Snorri S. Thorgeirsson, Michael M. Gottesman. Multidrug resistance transcriptome analysis highlights compounds that sensitize resistant hepatocellular carcinoma through increased histone acetylation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 954. doi:10.1158/1538-7445.AM2013-954

Abstract LB-51: Correlation of expression of MDR-associated genes with outcome in primary ovarian serous carcinoma

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DCnnWe have been developing tools to reproducibly correlate the expression of multidrug-resistance (MDR)-associated genes with response to chemotherapy in primary cancers. This study reports the results of a novel MDR gene expression analysis of primary serous carcinoma of the ovary utilizing a TaqMan Low Density Array (TLDA) chip which includes 380 previously characterized multidrug resistance (MDR)-associated genes that were initially identified in cultured cancer cells. Primary tumor samples from 133 patients from 4 sites were studied. All patients were subsequently treated with standard chemotherapy and had known clinical outcome. A 13 gene signature was identified whose expression added statistical power to the risk status of the patients based on standard clinical parameters (age, CA125, and success of surgical debulking) (log-rank statistic p=0.02). When subsets of patients with defined clinical risk were studied, we found that a subset of clinically high risk patients that had low expression of the 13 gene signature had a better outcome than would be predicted by purely clinical criteria. Similarly, clinically low risk patients with high expression of the 13 gene signature had a poorer prognosis. Since the mechanism of action of the 13 MDR genes involved in the signature are well-understood, it might be possible to devise therapeutic strategies to some of these targets with the goal of improving clinical outcome.nnCitation 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 LB-51.