Treatment scheduling effects on the evolution of drug resistance in heterogeneous cancer cell populations

The effect of scheduling of targeted therapy combinations on drug resistance is underexplored in triple-negative breast cancer (TNBC). TNBC constitutes heterogeneous cancer cell populations the composition of which can change dynamically during treatment resulting in the selection of resistant clones with a fitness advantage. We evaluated crizotinib (ALK/MET inhibitor) and navitoclax (ABT-263; Bcl-2/Bcl-xL inhibitor) combinations in a large design consisting of 696 two-cycle sequential and concomitant treatment regimens with varying treatment dose, duration, and drug holiday length over a 26-day period in MDA-MB-231 TNBC cells and found that patterns of resistance depend on the schedule and sequence in which the drugs are given. Further, we tracked the clonal dynamics and mechanisms of resistance using DNA-integrated barcodes and single-cell RNA sequencing. Our study suggests that longer formats of treatment schedules in vitro screening assays are required to understand the effects of resistance and guide more realistically in vivo and clinical studies.

Whole-genome sequencing of phenotypically distinct inflammatory breast cancers reveals similar genomic alterations to non-inflammatory breast cancers

BACKGROUND

Inflammatory breast cancer (IBC) has a highly invasive and metastatic phenotype. However, little is known about its genetic drivers. To address this, we report the largest cohort of whole-genome sequencing (WGS) of IBC cases.

METHODS

We performed WGS of 20 IBC samples and paired normal blood DNA to identify genomic alterations. For comparison, we used 23 matched non-IBC samples from the Cancer Genome Atlas Program (TCGA). We also validated our findings using WGS data from the International Cancer Genome Consortium (ICGC) and the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium. We examined a wide selection of genomic features to search for differences between IBC and conventional breast cancer. These include (i) somatic and germline single-nucleotide variants (SNVs), in both coding and non-coding regions; (ii) the mutational signature and the clonal architecture derived from these SNVs; (iii) copy number and structural variants (CNVs and SVs); and (iv) non-human sequence in the tumors (i.e., exogenous sequences of bacterial origin).

RESULTS

Overall, IBC has similar genomic characteristics to non-IBC, including specific alterations, overall mutational load and signature, and tumor heterogeneity. In particular, we observed similar mutation frequencies between IBC and non-IBC, for each gene and most cancer-related pathways. Moreover, we found no exogenous sequences of infectious agents specific to IBC samples. Even though we could not find any strongly statistically distinguishing genomic features between the two groups, we did find some suggestive differences in IBC: (i) The MAST2 gene was more frequently mutated (20% IBC vs. 0% non-IBC). (ii) The TGF β pathway was more frequently disrupted by germline SNVs (50% vs. 13%). (iii) Different copy number profiles were observed in several genomic regions harboring cancer genes. (iv) Complex SVs were more frequent. (v) The clonal architecture was simpler, suggesting more homogenous tumor-evolutionary lineages.

CONCLUSIONS

Whole-genome sequencing of IBC manifests a similar genomic architecture to non-IBC. We found no unique genomic alterations shared in just IBCs; however, subtle genomic differences were observed including germline alterations in TGFβ pathway genes and somatic mutations in the MAST2 kinase that could represent potential therapeutic targets.

Multi-Omics Investigation of Innate Navitoclax Resistance in Triple-Negative Breast Cancer Cells

Cancer cells employ various defense mechanisms against drug-induced cell death. Investigating multi-omics landscapes of cancer cells before and after treatment can reveal resistance mechanisms and inform new therapeutic strategies. We assessed the effects of navitoclax, a BCL2 family inhibitor, on the transcriptome, methylome, chromatin structure, and copy number variations of MDA-MB-231 triple-negative breast cancer (TNBC) cells. Cells were sampled before treatment, at 72 h of exposure, and after 10-day drug-free recovery from treatment. We observed transient alterations in the expression of stress response genes that were accompanied by corresponding changes in chromatin accessibility. Most of these changes returned to baseline after the recovery period. We also detected lasting alterations in methylation states and genome structure that suggest permanent changes in cell population composition. Using single-cell analyses, we identified 2350 genes significantly upregulated in navitoclax-resistant cells and derived an 18-gene navitoclax resistance signature. We assessed the navitoclax-response-predictive function of this signature in four additional TNBC cell lines in vitro and in silico in 619 cell lines treated with 251 different drugs. We observed a drug-specific predictive value in both experiments, suggesting that this signature could help guiding clinical biomarker studies involving navitoclax.

Abstract 6333: Genomic, transcriptomic, and epigenetic profiling of triple-negative breast cancer cells after Navitoclax treatment

Cancer cells possess various anti-apoptotic defense mechanisms that can protect them from drug induced cell death. We investigated the effects of treatment with the bcl-2/bcl-XL inhibitor Navitoclax on transcriptome, methylome, and genome of MDA-MB-231 cells. Two biological replicates were treated simultaneously and profiled using 10x Genomics single-cell RNA sequencing (scRNAseq; gene expression), bulk RNA sequencing (bRNAseq; gene expression), ATAC sequencing (ATAC; chromatin accessibility), bisulphite targeted sequencing (DNAm; DNA methylation) and shallow whole-genome sequencing (WGS; copy number variants) at baseline before treatment, after 3 days of 10µM navitoclax treatment, and after 10 days of cell recovery from treatment. Variance between biological replicates on transcriptome level was minimal before the treatment (R>0.99), but we noticed divergence in gene expression after recovery from the treatment (both on bulk and single-cell level), mostly driven by cell cycle genes. On other platforms, biological replicates were similar in all 3 phases. After treatment, we observed more genes with decreased expression (n=151) in comparison to baseline, but after 10 days of recovery there were more up-regulated genes (n=655) in comparison to samples after treatment. Chromatin accessibility for most genomic regions increased after treatment in comparison to baseline, suggesting an acute response to the stress caused by drug treatment, and then returned to baseline level after recovery period. DNA methylation patterns showed more regions with decreased methylation after treatment (n=529) in comparison to baseline which remained detectable even after the recovery period. In WGS data, we found 752 genes with deletions and amplifications only in baseline samples representing genomic background of drug sensitive cells, mostly enriched in epithelial mesenchymal transition pathway. On single-cell level, we identified a subset of cells that were resistant to treatment and discovered 2,324 genes significantly up-regulated in these cells, that could be potential markers of resistance. In gene set analysis, these markers were enriched in MYC and E2F target gene sets, and were involved in angiogenesis and JAK-STAT pathway. We measured the expression of 16 top up-regulated markers of resistance in 4 different TNBC cell lines using qPCR and found that 5 were significantly enriched after treatment in 3 cell lines, 5 in 2 cell lines and 5 in a single cell line. Summarizing, we thoroughly described molecular effects of Navitoclax treatment and showed that most cells return to the basal transcriptional state after the drug recovery period, but bulk genome and methylome are permanently changed. Finally, we provided a list of new markers of resistance that may be useful in the studies of combinational therapies with other drugs. This work was funded by Breast Cancer Research Foundation.

Citation Format: Michal Marczyk, Vignesh Gunasekharan, Jun Zhao, Rihao Qu, Xiaotong Li, Gauri A. Patwardhan, Vikram B. Wali, Abhishek K. Gupta, Manoj M. Pillai, Yuval Kluger, Christos Hatzis, Lajos Pusztai. Genomic, transcriptomic, and epigenetic profiling of triple-negative breast cancer cells after Navitoclax treatment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6333.

Analysis of Pre- and Posttreatment Tissues from the SWOG S0800 Trial Reveals an Effect of Neoadjuvant Chemotherapy on the Breast Cancer Genome

PURPOSE

We performed whole-exome sequencing (WES) of pre- and posttreatment cancer tissues to assess the somatic mutation landscape of tumors before and after neoadjuvant taxane and anthracycline chemotherapy with or without bevacizumab.

EXPERIMENTAL DESIGN

Twenty-nine pretreatment biopsies from the SWOG S0800 trial were subjected to WES to identify mutational patterns associated with response to neoadjuvant chemotherapy. Nine matching samples with residual cancer after therapy were also analyzed to assess changes in mutational patterns in response to therapy.

RESULTS

In pretreatment samples, a higher proportion of mutation signature 3, a BRCA-mediated DNA repair deficiency mutational signature, was associated with higher rate of pathologic complete response (pCR; median signature weight 24%, range 0%-38% in pCR vs. median weight 0%, range 0%-19% in residual disease, Wilcoxon rank sum, Bonferroni P = 0.007). We found no biological pathway level mutations associated with pCR or enriched in posttreatment samples. We observed statistically significant enrichment of high functional impact mutations in the "E2F targets" and "G₂-M checkpoint" pathways in residual cancer samples implicating these pathways in resistance to therapy and a significant depletion of mutations in the "myogenesis pathway" suggesting the cells harboring these variants were effectively eradicated by therapy.

CONCLUSIONS

These results suggest that genomic disturbances in BRCA-related DNA repair mechanisms, reflected by a dominant mutational signature 3, confer increased chemotherapy sensitivity. Cancers that survive neoadjuvant chemotherapy frequently have alterations in cell-cycle-regulating genes but different genes of the same pathways are affected in different patients.

Abstract P2-06-06: Targeting loss of isoenzyme diversity as a novel therapeutic strategy in breast cancer

Background: Several metabolic steps are mediated by distinct proteins or isoenzymes that catalyze the same reaction, providing redundancy of metabolic functions. Metabolic states are frequently altered in cancer to support survival and proliferation in hypoxic and otherwise hostile microenvironments, and metabolic re-wiring often involve loss of isoenzyme diversity. We hypothesize that targeting enzymes that have lost isoenzyme diversity in cancer, but not in normal cells, provides an opportunity to selectively target cancers. In this study, we assessed mRNA expression of all known human isoenzyme families in breast cancer and normal breast tissue and identified isoenzymes with loss of diversity within each breast cancer subtype.

Methods: We obtained RNAseq data from cancer and patient-matched normal breast tissues from the TCGA (N=66 HR+, N=24 HER2+, and N=15 TNBC tumors). We retrieved annotated human isoenzyme families from the ENZYME nomenclature database. We compared expression in cancer and matched normal samples from the same patient to identify isoenzymes that had i) same or increased expression of the target isoenzyme in cancer vs normal and ii) reduced expression of the complementary isoenzymes in cancer. We developed five scores that capture various elements of these characteristics and prioritized candidates as targets based on clustering and their combined ranking based on the five scores. We validated overexpression of the candidate isoenzymes relative to other isoforms in breast cancer microarray data from ArrayExpress (E-GEOD-76250: 33 TNBC, and E-GEOD-70951: 30 TNBC, 108 HR+, 10 HER2+).

Results: We identified 321 enzymes in the TCGA discovery cohort that correspond to 829 unique isoenzymes. Overall, 636, 483 and 429 isoenzymes were differentially expressed in HR+, HER2+ and TNBC cancers, respectively, compared to corresponding normal samples. Of these, 308 isoenzymes were differentially expressed relative to normal in all 3 subtypes. In all, 112 and 92, and 84 were selected as candidate isoenzyme therapeutic targets in HR+, HER2+ and TNBC, respectively. 23 isoenzymes prioritized in clustering step were further validated. Finally, 6 isoenzymes were validated in HR+ (ALDOA, GUSB, GYG1, MIF, P3H1, PCK2), 10 in HER2+ (ALDH1L2, ALDOA, GLYATL2, GUSB, GYG1, GYS1, MIF, P3H1, PCK2, PTGS1) and 12 in TNBC (ADSS, ALAS1, ALDH1L2, ALDOA, ART3, GLYATL2, GUSB, GYS1, HS3ST1, MIF, PCK2, SOAT1), as potential targets for breast cancer treatment. Of these, 5 potential isoenzyme targets (ALDH1L2, GUSB, GLYATL2, MIF, PCK2), which were mostly hydrolases and transferases, were further selected for ongoing experimental validation in the laboratory. Decreased expression of the complementary isoforms of these 5 targets were primarily due to DNA methylation of the genes in cancer.

Conclusions: We found that loss of isoenzyme diversity is a broad phenomenon in breast cancers that may be explored therapeutically. We identified several instances of “isoenzyme addiction” in which cancers depend exclusively on a single isoenzyme while downregulating via methylation the complementary isoenzymes, providing cancer-specific targeting opportunities. We are currently validating several of these targets in cell line models.

Citation Format: Marczyk M, Gunasekharan V, Wali VB, Shi W, Patwardhan G, Qing T, Pusztai L, Hatzis C. Targeting loss of isoenzyme diversity as a novel therapeutic strategy in breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-06-06.

Increased epigenetic age in normal breast tissue from luminal breast cancer patients

Background

Age is one of the most important risk factors for developing breast cancer. However, age-related changes in normal breast tissue that potentially lead to breast cancer are incompletely understood. Quantifying tissue-level DNA methylation can contribute to understanding these processes. We hypothesized that occurrence of breast cancer should be associated with an acceleration of epigenetic aging in normal breast tissue.

Results

Ninety-six normal breast tissue samples were obtained from 88 subjects (breast cancer = 35 subjects/40 samples, unaffected = 53 subjects/53 samples). Normal tissue samples from breast cancer patients were obtained from distant non-tumor sites of primary mastectomy specimens, while samples from unaffected women were obtained from the Komen Tissue Bank (n = 25) and from non-cancer-related breast surgery specimens (n = 28). Patients were further stratified into four cohorts: age < 50 years with and without breast cancer and age ≥ 50 with and without breast cancer. The Illumina HumanMethylation450k BeadChip microarray was used to generate methylation profiles from extracted DNA samples. Data was analyzed using the “Epigenetic Clock,” a published biomarker of aging based on a defined set of 353 CpGs in the human genome. The resulting age estimate, DNA methylation age, was related to chronological age and to breast cancer status.

The DNAmAge of normal breast tissue was strongly correlated with chronological age (r = 0.712, p < 0.001). Compared to unaffected peers, breast cancer patients exhibited significant age acceleration in their normal breast tissue (p = 0.002). Multivariate analysis revealed that epigenetic age acceleration in the normal breast tissue of subjects with cancer remained significant after adjusting for clinical and demographic variables. Additionally, smoking was found to be positively correlated with epigenetic aging in normal breast tissue (p = 0.012).

Conclusions

Women with luminal breast cancer exhibit significant epigenetic age acceleration in normal adjacent breast tissue, which is consistent with an analogous finding in malignant breast tissue. Smoking is also associated with epigenetic age acceleration in normal breast tissue. Further studies are needed to determine whether epigenetic age acceleration in normal breast tissue is predictive of incident breast cancer and whether this mediates the risk of chronological age on breast cancer risk.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0534-8) contains supplementary material, which is available to authorized users.

Abstract P2-04-02: Comparison of DNA methylation patterns in normal breast tissue from women with and without breast cancer

BACKGROUND: Increasing evidence suggests that epigenetic mechanisms play critical roles in the development of breast cancer. However, precise DNA methylation signatures associated with breast cancer susceptibility remain unknown. We sought to compare DNA methylation changes in the normal breast tissue of women with and without breast cancer to identify patterns of aberrant DNA methylation in women with breast cancer.

METHODS:Samples of normal breast tissue were collected from four cohorts of women: age &lt; 50 years with and without breast cancer, and age ≥50 years with and without breast cancer. Normal breast tissue from healthy women was obtained from the Komen Tissue Bank at IU Simon Cancer Center and from women presenting for reduction mammoplasty at Yale New Haven Hospital. Normal breast tissue from women with breast cancer was obtained from patients undergoing adjuvant total mastectomy at Yale Breast Center. DNA was extracted using Qiagen AllPrep Universal kit. Raw data files in idat format were imported to Partek Genomics Suite 6.6 for normalization and differential methylation analysis. Raw intensities were normalized using With Array Normalization (SWAN) method. Principal component analysis (PCA) were performed as quality control. Differentially methylated loci (DML) between control and breast cancer groups were detected when False discovery rate (FDR) &lt; 0.05 and fold change &gt; 1.5. Functional enrichment analysis of genes with DML in the gene body were conducted using METACORE™. Pathways with FDR &lt; 0.05 were selected.

RESULTS: Ninety-three normal breast tissue samples from 89 subjects were analyzed (breast cancer=40, unaffected=53). Comparison of DNA methylation patterns between women with and without breast cancer revealed 200 DMLs. The majority of DMLs (186) were hyper-methylated in breast cancer patients, and 48 DMLs locate in enhancers of genes. 170 DMLs locate in 134 genes, enriched in two pathways: (1) Cell adhesion_Endothelial cell contacts by junctional mechanisms, and (2) Neurophysiological process_Constitutive and regulated NMDA receptor trafficking. Genes associated with cell adhesion and cell contacts included: ACTN2, GJA4, GJA7 and MAGI1. Two hyper-methylated loci were found in enhancers of ACTN2. In addition, one hyper-methylated locus in GJA4, one hyper-methylated and one hypo-methylated loci in GJA7, and two hyper-methylated loci in MAGI1 were detected in breast cancer patients. Genes associated with NMDA receptor trafficking include: TPK1, ADCY4 and LIN7C. One and two loci were found in TPK1 and ADCY4, respectively, that were hyper-methylated in normal breast tissue from cancer patients in the gene body, while a hypo-methylated locus in breast cancer patients was identified in LIN7C.

CONCLUSIONS: Comparison of DNA methylation patterns of normal breast tissue from women with and without breast cancer reveal specific mechanistic pathways and genes that are differentially methylated in women with breast cancer. DNA methylation of normal breast tissue deserves further study as a potential biomarker for breast cancer risk stratification and may lend new insight into mechanisms of breast cancer development.

Citation Format: Hofstatter EW, Zhu Y, Horvath S, Chagpar AB, Wali VB, Bossuyt V, Storniolo AM, Hatzis C, Patwardhan G, Von Wahlde M-K, Butler M, Epstein L, Stavris K, Sturrock T, Au A, Kwei S, Pusztai L. Comparison of DNA methylation patterns in normal breast tissue from women with and without breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-04-02.

Mitotic read-out genes confer poor outcome in luminal A breast cancer tumors

Luminal breast tumors have been classified into A and B subgroups, with the luminal A being associated with a more favorable clinical outcome. Unfortunately, luminal A tumors do not have a universally good prognosis. We used transcriptomic analyses using public datasets to evaluate the differential expression between normal breast tissue and breast cancer, focusing on upregulated genes included in cell cycle function. Association of selected genes with relapse free survival (RFS) and overall survival (OS) was performed using the KM Plotter Online Tool (http://www.kmplot.com). Seventy-seven genes were differentially expressed between normal and malignant breast tissue. Only five genes were associated with poor RFS and OS. The mitosis-related genes GTSE1, CDCA3, FAM83D and SMC4 were associated with poor outcome specifically in Luminal A tumors. The combination of FAM83D and CDCA3 for RFS and GTSE1 alone for OS showed the better prediction for clinical outcome. CDCA3 was amplified in 3.4% of the tumors, and FAM83D and SMC4 in 2.3% and 2.2%, respectively. In conclusion, we describe a set of genes that predict detrimental outcome in Luminal A tumors. These genes may have utility for stratification in trials of antimitotic agents or cytotoxic chemotherapy, or as candidates for direct target inhibition.

Abstract 2073: A systematic investigation of the effect of scheduling of targeted combination therapies on response and dynamics of relapse in triple negative breast cancer cells

Cancer treatment typically involves administration of combination of targeted therapies, but initial response is often followed by disease relapse. The efficacy of a treatment regimen depends on the complex interplay between cancer growth dynamics, drug specificity and kinetics, treatment dose and its scheduling. In standard high-throughput drug screening assays, cells are treated with a single drug cocktail bolus and cell viability is assessed after 2-3 days, thus not considering treatment interactions and long-term effects. Recently we have reported a promising synergistic combination of crizotinib (ALK/MET inhibitor) and ABT-263 (BCL2/BCL-XL inhibitor) against triple negative breast cancer cells. To understand the effect of the sequence and combination doses of crizotnib and ABT-263, we designed a comprehensive experimental plan that involved a total of 567 treatment regimens by varying treatment duration with the first drug (1, 2, or 3 days), followed by drug withdrawal and recovery period (2, 5 or 10 days) and then by a second cycle of treatment and recovery periods over a 26-day period. Cell viability was assessed by the CellTiter-Glo luminescence assay. Interestingly, ABT-263 alone induced higher cytotoxicity than an equivalent dose of crizotinib, but the remaining viable cells recovered much faster after ABT-263 withdrawal than cells after crizotinib withdrawal. Furthermore, cells exposed to higher doses of ABT-263 eventually become less sensitive to crizotinib. Among sequential regimens, crizotinib followed by ABT-263 was significantly more effective than ABT-263 followed by crizotinib, and combinations that included lower doses of ABT-263 were most effective. Taken together, our results show a significant interaction between the two targeted therapies, and suggest that it may be possible to select treatment scheduling that can delay drug resistance and tumor relapse in vivo.

Note: This abstract was not presented at the meeting.

Citation Format: Gauri A. Patwardhan, Vikram B. Wali, Lajos Pusztai, Christos Hatzis. A systematic investigation of the effect of scheduling of targeted combination therapies on response and dynamics of relapse in triple negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2073. doi:10.1158/1538-7445.AM2017-2073

Abstract 1141: Evaluation of GABRP as a novel therapeutic target in triple negative breast cancer

Triple Negative breast cancers (TNBC) represent nearly 20% of all breast cancers but do not have any targeted therapies available due to lack of amplification of HER2 and expression of estrogen and progesterone receptors. To identify potentially druggable targets for TNBC, we compared TNBC to non-TNBC tumors in large independent gene expression clinical datasets to identify highly expressed genes in TNBC that encode for proteins expressed on the cell surface. We found gamma-aminobutyric acid type A receptor pi (GABRP) to be the most overexpressed receptor protein gene in TNBC, while its expression in normal tissues was low and comparable to that of proteins targeted by drugs or therapeutic antibodies already in clinical testing. We compared GABRP mRNA and protein expression across panel of breast cancer cell lines and found it to be particularly elevated in HCC1143 and MDA-MB-468 TNBC cells. Knockdown of GABRP using siRNA suppressed TNBC cell growth and stable GABRP knock-down by shRNA suppressed growth of MDA-MB-468 xenografts in nude mice. Sub-cellular fractionation of TNBC cells and subsequent Western blot analysis confirmed that GABRP is located predominantly in the cell membrane. GABRP protein expression on cell surface was also detected by flowcytometry. Interestingly, treatment with 5-100μg/ml of anti-GABRP antibody that binds to the extracellular domain (ECD) itself inhibited growth of TNBC cell lines expressing higher GABRP, while the same doses of a control antibody had no effect in these cells in culture. Our goal is to generate an antibody drug conjugate (ADC) for TNBC by conjugating anti-GABRP antibody with a maytansinoid such as DM1, which has proven cytotoxicity in breast cancer cells. Together, our results suggest that GABRP is a potential therapeutic target for triple-negative breast cancers.

Citation Format: Vikram B. Wali, Gauri A. Patwardhan, Christos Hatzis, Lajos Pusztai. Evaluation of GABRP as a novel therapeutic target in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1141. doi:10.1158/1538-7445.AM2017-1141

Predictors of Chemosensitivity in Triple Negative Breast Cancer: An Integrated Genomic Analysis

BACKGROUND

Triple negative breast cancer (TNBC) is a highly heterogeneous and aggressive disease, and although no effective targeted therapies are available to date, about one-third of patients with TNBC achieve pathologic complete response (pCR) from standard-of-care anthracycline/taxane (ACT) chemotherapy. The heterogeneity of these tumors, however, has hindered the discovery of effective biomarkers to identify such patients.

METHODS AND FINDINGS

We performed whole exome sequencing on 29 TNBC cases from the MD Anderson Cancer Center (MDACC) selected because they had either pCR (n = 18) or extensive residual disease (n = 11) after neoadjuvant chemotherapy, with cases from The Cancer Genome Atlas (TCGA; n = 144) and METABRIC (n = 278) cohorts serving as validation cohorts. Our analysis revealed that mutations in the AR- and FOXA1-regulated networks, in which BRCA1 plays a key role, are associated with significantly higher sensitivity to ACT chemotherapy in the MDACC cohort (pCR rate of 94.1% compared to 16.6% in tumors without mutations in AR/FOXA1 pathway, adjusted p = 0.02) and significantly better survival outcome in the TCGA TNBC cohort (log-rank test, p = 0.05). Combined analysis of DNA sequencing, DNA methylation, and RNA sequencing identified tumors of a distinct BRCA-deficient (BRCA-D) TNBC subtype characterized by low levels of wild-type BRCA1/2 expression. Patients with functionally BRCA-D tumors had significantly better survival with standard-of-care chemotherapy than patients whose tumors were not BRCA-D (log-rank test, p = 0.021), and they had significantly higher mutation burden (p < 0.001) and presented clonal neoantigens that were associated with increased immune cell activity. A transcriptional signature of BRCA-D TNBC tumors was independently validated to be significantly associated with improved survival in the METABRIC dataset (log-rank test, p = 0.009). As a retrospective study, limitations include the small size and potential selection bias in the discovery cohort.

CONCLUSIONS

The comprehensive molecular analysis presented in this study directly links BRCA deficiency with increased clonal mutation burden and significantly enhanced chemosensitivity in TNBC and suggests that functional RNA-based BRCA deficiency needs to be further examined in TNBC.

Systematic Drug Screening Identifies Tractable Targeted Combination Therapies in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) remains an aggressive disease without effective targeted therapies. In this study, we addressed this challenge by testing 128 FDA-approved or investigational drugs as either single agents or in 768 pairwise drug combinations in TNBC cell lines to identify synergistic combinations tractable to clinical translation. Medium-throughput results were scrutinized and extensively analyzed for sensitivity patterns, synergy, anticancer activity, and were validated in low-throughput experiments. Principal component analysis revealed that a fraction of all upregulated or downregulated genes of a particular targeted pathway could partly explain cell sensitivity toward agents targeting that pathway. Combination therapies deemed immediately tractable to translation included ABT-263/crizotinib, ABT-263/paclitaxel, paclitaxel/JQ1, ABT-263/XL-184, and paclitaxel/nutlin-3, all of which exhibited synergistic antiproliferative and apoptotic activity in multiple TNBC backgrounds. Mechanistic investigations of the ABT-263/crizotinib combination offering a potentially rapid path to clinic demonstrated RTK blockade, inhibition of mitogenic signaling, and proapoptotic signal induction in basal and mesenchymal stem-like TNBC. Our findings provide preclinical proof of concept for several combination treatments of TNBC, which offer near-term prospects for clinical translation. Cancer Res; 77(2); 566-78. ©2016 AACR.

Abstract P6-13-06: Novel combination therapies for triple negative breast cancer identified by high-throughput screening

Background: Finding effective novel therapies for triple negative breast cancer (TNBC) remains an unmet challenge. Our objective was to assess the sensitivity of TNBC to single drugs and to combinations using a systematic screen of existing FDA approved drugs combined with other approved or experimental agents and to characterize the mechanism of action of the most promising combinations.

Methods: We conducted a comprehensive high-throughput drug combination screen in six TNBC cell lines with different genetic backgrounds. We tested a panel of 128 agents with known targets for their growth inhibitory potential individually and in pairwise combinations with six FDA approved anticancer drugs in MDA-MB-231, MDA-MB-436, MDA-MB-468, BT-20, BT-549, and HCC-38 TNBC cell lines. High-throughput assays were performed in 384-well plates and dose response curves were generated using 5 concentrations of the secondary drug, while keeping the first drug at fixed dose. Cell viability was measured 72h after treatment exposure using CellTiter-Glo®. Drug combinations were assessed for overall inhibitory effect and also for superadditivity, assessed as deviations from non-interaction using Bliss model of synergy. Selected synergistic and effective drug combinations identified from the high-throughput screen were subsequently validated in a 96-well low-throughput format in all TNBC cell lines.

Results: Cell cycle and apoptosis regulators were more inhibitory as single agents across TNBC cell lines relative to other drug classes. Bortezomib, carfilzomib, YM155, Flavopiridol, KP372-1, and dactinomycin were highly toxic to all TNBC lines as single agents. Combinations with either everolimus or erlotinib were particularly effective in BT-20 and MDA-MB-468, and combinations with crizotinib in MDA-MB-231 cells. Bay-11-7082/erlotinib and MK-1775/everolimus were few of the promising combinations that elicited potentiated response in all the cell lines. ABT-263/crizotinib was one of the top synergistic combination most effective in MDA-MB-231 cells that express highest relative mRNA and protein levels of respective drug targets, Bcl-xL, and AXL. The combination treatment with ABT-263 and crizotinib also resulted in apoptosis in MDA-MB-231 cells, indicated by marked PARP cleavage in these cells, while MDA-MB-436 cells with lowest expression of Bcl-xL were resistant to apoptosis or growth inhibition, indicating a potential efficacy of this combination in a subset of TNBCs.

Conclusions: This study reveals novel combinations of cell cycle or apoptosis regulators and crizotinib, everolimus, or erlotinib with enhanced anticancer activity. Combinations of Bay-11-7082 and erlotinib; and MK-1775 and everolimus had mild synergistic activity in all TNBC lines, while ABT-263 and Crizotinib showed large synergistic antiproliferative activity in a subset of TNBCs. These promising drug combinations have great potential to improve cure rates in TNBC patients. Since crizotinib, everolimus, and erlotinib are US FDA-approved while ABT-263 and MK-1775 are in advanced clinical trials, there is a rapid path for clinical translation for these drug-combinations after validation in animal studies.

Citation Format: Wali VB, Langdon CG, Held MA, Platt JT, Safonov A, Aktas B, Stern DF, Pusztai L, Hatzis C. Novel combination therapies for triple negative breast cancer identified by high-throughput screening. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-13-06.

Abstract P4-07-01: DNA repair deficiency enhances immune response and correlates with excellent clinical outcome in triple negative breast cancer

Background: Mutations or epigenetic silencing of BRCA1/2 genes result in DNA repair deficiency in a large proportion of TNBC cases. Yet it is unclear whether this deficiency is associated with increased chemosensitivity and improved benefit from standard-of-care chemotherapy. We systematically evaluated BRCA deficiency in TNBC using integrated DNA and RNA sequencing data and its association clinical outcome, exploring the potential role of tumor immune response.

Patients and Methods: Whole-exome, DNA methylation, copy number variation, and RNA sequencing data from 102 stage I-III TNBCs were retrieved from The Cancer Genome Atlas (TCGA). Almost all patients received adjuvant taxane-anthracycline-cyclophosphamide (T-AC) chemotherapy and had &gt;30 days of follow-up. The number of predicted neoantigens and an estimate of the level of immune cell activity for 77 of these tumors were previously published. Deleterious germline or somatic BRCA1/2 mutations were identified by majority voting on predictions of 5 variant scoring algorithms. Definition of BRCA1/2 deficiency (BRCA-D) included carrier of deleterious BRCA1/2 mutations or BRACA1/2 normal (BRCA-N) with wild type BRCA1/2 expression less than the maximum observed in mutation carriers. Normalized genomic mutation rate and mutant allele tumor heterogeneity (MATH) were computed as broad measures of genomic instability. Characteristics of BRCA-D vs N tumors were compared using the Wilcoxon rank test.

Results: Twenty tumors (19.6%) had mutations in BRCA1, 6 (5.8%) in BRCA2, and 2 (1.9%) in both. Based on the expanded definition, 39 cases (38%) were characterized as BRCA1 deficient, 5 (4.9%) as BRCA2 deficient and 4 (3.9%) as deficient in both. BRCA-D tumors (47%) were associated with a significantly higher mutation rate (P=8x10-4) but had similar clonal heterogeneity (P=0.55) as BRCA-N tumors. BRCA-D tumors had excellent 4-year overall survival (100%) compared to 79.5% (95%CI: 66.6- 94.9) for BRCA-N tumors (log-rank P=0.02). BRCA-D tumors also presented a significantly higher number of predicted neoantigents (P=0.003), which resulted in increased level of immune cell activity. In contrast, low immunogenic TNBC tumors were underrepresented in BRCA-D (p=0.05) and showed potential signs of immunoediting (observed/expected number of predicted neoantigens &lt; 1; p=0.07).

Conclusions: Deleterious mutations in BRCA1/2 genes occur in 25% of TNBC tumors, but parallel quantification of wild-type BRCA1/2 expression identifies 47% of TNBC samples with double strand break DNA repair deficiency. These BRCA-D TNBC tumors are characterized by a significantly higher mutation rate and present a significantly greater number of neoantigens that result in increased immune cell activity. Our analysis suggested that enhanced immune activation could explain to a large extent the excellent clinical outcome in patients with BRCA-D tumors treated with standard-of-care T-AC chemotherapy.

Citation Format: Jiang T, Safonov A, Bianchini G, Shi W, Wali VB, Pusztai L, Hatzis C. DNA repair deficiency enhances immune response and correlates with excellent clinical outcome in triple negative breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-07-01.

miR-34a Silences c-SRC to Attenuate Tumor Growth in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype with no clinically proven biologically targeted treatment options. The molecular heterogeneity of TNBC and lack of high frequency driver mutations other than TP53 have hindered the development of new and effective therapies that significantly improve patient outcomes. miRNAs, global regulators of survival and proliferation pathways important in tumor development and maintenance, are becoming promising therapeutic agents. We performed miRNA-profiling studies in different TNBC subtypes to identify miRNAs that significantly contribute to disease progression. We found that miR-34a was lost in TNBC, specifically within mesenchymal and mesenchymal stem cell-like subtypes, whereas expression of miR-34a targets was significantly enriched. Furthermore, restoration of miR-34a in cell lines representing these subtypes inhibited proliferation and invasion, activated senescence, and promoted sensitivity to dasatinib by targeting the proto-oncogene c-SRC. Notably, SRC depletion in TNBC cell lines phenocopied the effects of miR-34a reintroduction, whereas SRC overexpression rescued the antitumorigenic properties mediated by miR-34a. miR-34a levels also increased when cells were treated with c-SRC inhibitors, suggesting a negative feedback exists between miR-34a and c-SRC. Moreover, miR-34a administration significantly delayed tumor growth of subcutaneously and orthotopically implanted tumors in nude mice, and was accompanied by c-SRC downregulation. Finally, we found that miR-34a and SRC levels were inversely correlated in human tumor specimens. Together, our results demonstrate that miR-34a exerts potent antitumorigenic effects in vitro and in vivo and suggests that miR-34a replacement therapy, which is currently being tested in human clinical trials, represents a promising therapeutic strategy for TNBC.

Characterization of DNA variants in the human kinome in breast cancer

Kinases play a key role in cancer biology, and serve as potential clinically useful targets for designing cancer therapies. We examined nucleic acid variations in the human kinome and several known cancer-related genes in breast cancer. DNA was extracted from fine needle biopsies of 73 primary breast cancers and 19 metastatic lesions. Targeted sequencing of 518 kinases and 68 additional cancer related genes was performed using the SOLiD sequencing platform. We detected 1561 unique, non-synonymous variants in kinase genes in the 92 cases, and 74 unique variants in 43 kinases that were predicted to have major functional impact on the protein. Three kinase groups—CMGC, STE and TKL—showed greater mutational load in metastatic compared to primary cancer samples, however, after correction for multiple testing the difference was significant only for the TKL group (P = 0.04). We also observed that a higher proportion of histologic grade 1 and 2 cases had high functional impact variants in the SCYL2 gene compared with grade 3 cases. Our findings indicate that individual breast cancers harbor a substantial number of potentially functionally important nucleotide variations in kinase genes, most of which are present in unique combinations and include both somatic and germline functional variants.

Abstract PD3-4: Reliability of whole exome sequencing for assessing intratumor heterogeneity from breast tumor biopsies

BACKGROUND: False positive findings introduced by analytical noise in sequencing and bioinformatics pipelines constitute a challenge for accurate massively parallel sequencing (MPS). Reports of intratumor genomic heterogeneity based on MPS rarely estimate the impact of false positive mutation calls. The purpose of this study was to measure apparent genomic heterogeneity in different regions of the same tumor and to assess the technical noise in variant calling in replicate sequencing of the same DNA.

METHODS: Three anatomically distinct biopsies were obtained from 3 different regions of 11 breast cancers (33 samples) including 6 low/intermediate grade, estrogen receptor (ER)-positive and 5 high-grade, triple-negative (TNBC) cancers. DNA from 8 different biopsies was split and independently processed on different days to obtain technical replicates. The NimbleGen SeqCap EZ Exome Library preparation method was used for exome capture and paired-end sequencing of 75 base pair fragments was performed on Illumina HiSeq 2000. Read alignment and variant calling were performed with BWA and GATK haplotype caller. Concordance in variant calls and in minor allele frequencies (MAF) was assessed in the 3 biopsies of the same tumor and 8 technical replicates. We adjusted for uneven sequence coverage and analyzed known germline variants from dbSNP, known cancer related variants from COSMIC separately from novel variants (i.e. not previously reported in dbSNP or COSMIC). We estimated intratumor genomic heterogeneity of genes after removing alterations identified in areas where mapping is difficult and variant calls that had low analytical reliability in the technical replicates.

RESULTS: The mean coverage was over 150X and &gt; 90% of target regions had ≥ 20X coverage. We validated the specificity (98.2%) and sensitivity (86.7%) of the variant calling pipeline on the GIAB reference data. The concordance for germ line SNPs and variants in COSMIC in technical replicates was 94.9% and 92.7%, respectively. Novel variants had very low concordance, 55.9%, in technical replicates. The concordance between MAF estimates from the technical replicates was high (0.974, 0.957 and 0.969 for single nucleotide variations, insertions and deletions, respectively). The concordance for germline SNPs and COSMIC variants in pairwise comparisons of biopsies from the same tumor was 93.2% and 91.1%. For known variants, lower concordance was observed in TNBC (88.3%-98.5%) compared to ER-positive tumors (93.6%-98.8%, P&lt;0.05) indicating greater intratumor heterogeneity. We identified variants in a small number of genes (DNAH9, PPM1E, and MAP3K1) that were called inconsistently in most technical replicates, even after excluding low mappability regions. We assessed intratumor heterogeneity in the triplicate biopsies, after excluding the technically unreliable variants. On average, two different biopsies from the same tumor shared 14272 +/-1379 common variants and differed in 816 +/- 416 variants.

CONCLUSION: We observed heterogeneity to be slightly greater in high-grade, ER-negative compared to low-grade, ER-positive breast cancers. Differences in variants observed in multiple biopsies of the same tumor are only slightly greater than those expected by technical noise alone.

Citation Format: Weiwei Shi, Anees Chagpar, Tingting Jiang, Donald R Lannin, Brigid Killelea, Nina Horowitz, Raymond Lim, James Platt, Charlotte KY Ng, Vikram B Wali, Britta Weigelt, Jorge S Reis-Filho, Christos Hatzis, Lajos Pusztai. Reliability of whole exome sequencing for assessing intratumor heterogeneity from breast tumor biopsies [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr PD3-4.

Abstract PD3-2: Broad exonic DNA diversity is associated with resistance to taxane-FAC chemotherapy in triple negative breast cancer

Purpose: Previous efforts to develop transcriptional markers of chemotherapy sensitivity in TNBC had limited success due to the heterogeneity of this disease. The purpose of this study was to identify genomic differences between extremely chemotherapy sensitive and highly chemotherapy resistant TNBC through whole exome sequencing and to assess measures of genomic heterogeneity as predictive markers.

Methods: Twenty nine cases were selected from a prospectively collected cohort of fine needle aspiration specimens obtained before preoperative chemotherapy (MDACC) to represent two extreme response cohorts including pathologic complete response (pCR, N=17) or extensive residual cancer (eRD, N=12). DNA was extracted from specimens stored in RNAlater, exomes were captured using NimbleGen SeqCap EZ Exome Library preparation and paired-end sequencing of 75 base pair fragments was performed on Illumina HiSeq 2000. Alignment and variant calling were performed with BWA and GATK haplotype caller. Variants were filtered against the 1000 Genomes and TCGA normal breast samples to identify candidate somatic variants. Fisher-exact test was used to identify variant genes associated with sensitivity to chemotherapy. We calculated overall mutational load and normal-adjusted clonal entropy of driver mutations as measures of genome heterogeneity. The chi-squared test was used to compare differences in mutational spectra and genome heterogeneity between the two response groups.

Results: The mean coverage was over 150X and 93% of target regions had &gt; 20X coverage. The number of non-silent COSMIC mutations was similar in tumors from the two response groups (pCR: 63, range 49-82; eRD: 59, range 43-78) as well as the number of novel non-silent mutations (eRD: 223, range 113-388; pCR: 192, range 125-293). Gene level aggregation of variants identified 4 genes (MUC21, SLCO5A1, LRBA, STNE1) with response-associated mutational patterns. However, mutations were non recurrent and p-values were modest, ranging from 0.04 to 0.005. We observed greater overall mutational load and subclonal heterogeneity (clonal entropy of cancer related mutations) associated with eRD compared to pCR. Both measures suggest that higher genomic DNA diversity is associated with chemotherapy resistance. However, some genes (BRCA1 and MKI67) had higher mutational load (sum of minor allele frequencies per gene) associated with pCR compared to eRD. In general, a higher proportion of C&gt;T transition (P=0.011) and lower A&gt;G transition (P=0.028) was associated with eRD. The same mutational spectrum shift was previously described in the comparison of trunk and branch driver events suggesting that eRD tumors may undergo heterogeneous branched evolution.

Conclusion: We observed greater genomic diversity and distinctive mutational spectra in original pre-treatment samples of TNBC that were associated with extensive residual disease compared to pCR. Our analysis suggests that broad measures of genomic diversity may serve as markers of resistance to chemotherapy.

Citation Format: Tingting Jiang, Weiwei Shi, William F Symmans, Charles Li, James Platt, Rosanna Lau, Vikram B Wali, Richard Lifton, Lajos Pusztai, Christos Hatzis. Broad exonic DNA diversity is associated with resistance to taxane-FAC chemotherapy in triple negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr PD3-2.

Overexpression of ERBB4 JM-a CYT-1 and CYT-2 isoforms in transgenic mice reveals isoform-specific roles in mammary gland development and carcinogenesis

Introduction

Human Epidermal Growth Factor Receptor (ERBB4/HER4) belongs to the Epidermal Growth Factor receptor/ERBB family of receptor tyrosine kinases. While ERBB1, ERBB2 and ERBB3 are often overexpressed or activated in breast cancer, and are oncogenic, the role of ERBB4 in breast cancer is uncertain. Some studies suggest a tumor suppressor role of ERBB4, while other reports suggest an oncogenic potential. Alternative splicing of ERBB4 yields four major protein products, these spliced isoforms differ in the extracellular juxtamembrane domain (JM-a versus JM-b) and cytoplasmic domain (CYT-1 versus CYT-2). Two of these isoforms, JM-a CYT-1 and JM-a CYT-2, are expressed in the mammary gland. Failure to account for isoform-specific functions in previous studies may account for conflicting reports on the role of ERBB4 in breast cancer.

Methods

We have produced mouse mammary tumour virus (MMTV) -ERBB4 transgenic mice to evaluate potential developmental and carcinogenic changes associated with full length (FL) JM-a ERBB4 CYT-1 versus ERBB4 CYT-2. Mammary tissue was isolated from transgenic mice and sibling controls at various developmental stages for whole mount analysis, RNA extraction, and immunohistochemistry. To maintain maximal ERBB4 expression, transgenic mice were bred continuously for a year after which mammary glands were isolated and analyzed.

Results

Overexpressing FL CYT-1 isoform resulted in suppression of mammary ductal morphogenesis which was accompanied by decreased number of mammary terminal end buds (TEBs) and Ki-67 positive cells within TEBs, while FL CYT-2 isoform had no effect on ductal growth in pubescent mice. The suppressive ductal phenotype in CYT-1 mice disappeared after mid-pregnancy, and subsequent developmental stages showed no abnormality in mammary gland morphology or function in CYT-1 or CYT-2 transgenic mice. However, sustained expression of FL CYT-1 isoform resulted in formation of neoplastic mammary lesions, suggesting a potential oncogenic function for this isoform.

Conclusions

Together, we present isoform-specific roles of ERBB4 during puberty and early pregnancy, and reveal a novel oncogenic property of CYT-1 ERBB4. The results may be exploited to develop better therapeutic strategies in breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0501-z) contains supplementary material, which is available to authorized users.

Metabolic isoenzyme shifts in cancer as potential novel therapeutic targets

The functional redundancy of metabolic enzyme expression may present a new strategy for developing targeted therapies in cancer. To satisfy the increased metabolic demand required during neoplastic transformations and proliferation, cancer cells may rely on additional isoforms of a metabolic enzyme to satisfy the increased demand for metabolic precursors, which could subsequently render cancer cells more vulnerable to isoform-specific inhibitors. In this review, we provide a survey of common isoenzyme shifts that have been reported to be important in cancer metabolism and link those to metabolic pathways that currently have drugs in various stages of development. This phenomenon suggests a potentially new therapeutic strategy for the treatment of cancer by identifying shifts in the expression of metabolic isoenzymes between cancer and normal cells. We also delineate other putative metabolic isoenzymes that could be targets for novel targeted therapies for cancer. Changes in isoenzyme expression that occur during neoplastic transformations or in response to environmental pressure in cancer cells may result in isoenzyme diversity that may subsequently render cancer cells more vulnerable to isoform-specific inhibitors due to reliance on a single isoform to perform a vital enzymatic function.

Statistical measures of transcriptional diversity capture genomic heterogeneity of cancer

BACKGROUND

Molecular heterogeneity of tumors suggests the presence of multiple different subclones that may limit response to targeted therapies and contribute to acquisition of drug resistance, but its quantification has remained challenging.

RESULTS

We performed simulations to evaluate statistical measures that best capture the molecular diversity within a group of tumors for either continuous (gene expression) or discrete (mutations, copy number alterations) molecular data. Dispersion based metrics in the principal component space best captured the underlying heterogeneity. To demonstrate utility of these measures, we characterized the diversity in transcriptional and genomic profiles of different breast tumor subtypes, and showed that basal-like or triple-negative breast cancers (TNBC) are significantly more heterogeneous molecularly than other subtypes. Our analysis also suggests that transcriptional diversity is a global characteristic of the tumors observed across the majority of molecular pathways. Among basal-like tumors, those that were resistant to multi-agent chemotherapy showed greater transcriptional diversity compared to chemotherapy-sensitive tumors, suggesting that potentially multiple mechanisms may be contributing to chemotherapy resistance.

CONCLUSIONS

We proposed and validated measures of transcriptional and genomic diversity that can quantify the molecular diversity of tumors. We applied the new measures to genomic data from breast tumors and demonstrated that basal-like breast cancers are significantly more diverse than other breast cancers. The observation that chemo-resistant tumors are significantly more diverse molecularly than chemosensitive tumors implies that multiple resistance mechanisms may be active, thus limiting the sensitivity and accuracy of predictive markers of chemotherapy response.

Convergent and divergent cellular responses by ErbB4 isoforms in mammary epithelial cells

Associations of ErbB4 (ERBB4/HER4), the fourth member of the EGFR family, with cancer are variable, possibly as a result of structural diversity of this receptor. There are multiple structural isoforms of ERBB4 arising by alternative mRNA splicing, and a subset undergo proteolysis that releases membrane-anchored and soluble isoforms that associate with transcription factors and coregulators to modulate transcription. To compare the differential and common signaling activities of full-length (FL) and soluble intracellular isoforms of ERBB4, four JM-a isoforms (FL and soluble intracellular domain (ICD) CYT-1 and CYT-2) were expressed in isogenic MCF10A cells and their biologic activities were analyzed. Both FL and ICD CYT-2 promoted cell proliferation and invasion, and CYT-1 suppressed cell growth. Transcriptional profiling revealed several new and underexplored ERBB4-regulated transcripts, including: proteases/protease inhibitors (MMP3 and SERPINE2), the YAP/Hippo pathway (CTGF, CYR61, and SPARC), the mevalonate/cholesterol pathway (HMGCR, HMGCS1, LDLR, and DHCR7), and cytokines (IL8, CCL20, and CXCL1). Many of these transcripts were subsequently validated in a luminal breast cancer cell line that normally expresses ERBB4. Furthermore, ChIP-seq experiments identified ADAP1, APOE, SPARC, STMN1, and MXD1 as novel molecular targets of ERBB4. These findings clarify the diverse biologic activities of ERBB4 isoforms, and reveal new and divergent functions.

IMPLICATIONS

ErbB4 as a regulator of Hippo and mevalonate pathways provides new insight into milk production and anabolic processes in normal mammary epithelia and cancer.

Global gene expression changes induced by prolonged cold ischemic stress and preservation method of breast cancer tissue

BACKGROUND

Tissue handling can alter global gene expression potentially affecting the analytical performance of genomic signatures, but such effects have not been systematically evaluated.

METHODS

Tissue samples from 11 previously untreated breast tumors were minced and aliquots were either snap frozen or placed in RNAlater immediately or after 20, 40, 60, 120 or 180 min at room temperature. RNA was profiled on Affymetrix HG-U133A arrays. We used probe-set-wise hierarchical models to evaluate the effect of preservation method on transcript expression and linear mixed effects models to assess the effect of cold ischemic delay on the expression of individual probe sets. Gene set enrichment analysis identified pathways overrepresented in the affected transcripts. We combined the levels of 41 most sensitive transcripts to develop an index of ischemic stress.

RESULTS

Concordance in global gene expression between the baseline and 40 min delay was higher for samples preserved in RNAlater (average concordance correlation coefficient CCC = 0.92 compared to 0.88 for snap frozen). Overall, 481 transcripts (3%) were significantly affected by the preservation method, most of them involved in processes important in cancer. Prolonged cold ischemic delay of up to 3 h induced marginal global gene expression changes (average CCC = 0.90 between baseline and 3 h delay). However 41 transcripts were significantly affected by cold ischemic delay. Among the induced transcripts were stress response genes, apoptotic response genes; among the downregulated were genes involved in metabolism, protein processing and cell cycle regulation. An index combining the expression levels of these genes was proportional to the cold ischemic delay.

CONCLUSIONS

Prolonged cold ischemia induces significant transcriptional changes in a small subset of transcripts in the tissue. Furthermore, the expression level of about 3% of the transcripts is affected by the preservation method. These sensitive transcripts should not be included in genomic signatures for more reliable analytical performance.

Abstract 1401: Overexpression of HER4 isoforms in transgenic mice reveal isoform-specific role in mammary gland development and carcinogenesis

Human epidermal growth factor receptor 4 (HER4/ERBB4) belongs to the family of four receptor tyrosine kinases (HER1-4). While HER1, HER2 and HER3 are often overexpressed in breast cancer and predict poor prognosis, the role of HER4 in cancer is still unclear. Some studies suggest a tumor suppressor role of HER4, while contradictory reports suggest its oncogenic potential. HER4 gene produces multiple isoforms as a result of alternative splicing, in contrast to other members of this receptor family. We have used a gain-of-function MMTV-HER4 model isoforms, to evaluate potential developmental and carcinogenic roles of HER4-CYT1 and CYT2. Mammary gland ductal morphogenesis was significantly suppressed by expressing one of the transgene isoforms, strongly suggesting a role of HER4 in normal mammary ductal morphogenesis in addition to its role in lactation described previously. Interestingly, sustained expression of one HER4 transgene isoform resulted in formation of mammary tumor lesions, whereas no significant findings were observed in the control group. Formation of tumor lesions in these transgenic mice strongly suggests an oncogenic function of a HER4 isoform. These novel findings may help improve the rational design of targeted breast cancer therapy. Supported by NIH grant RO1 CA80065.

Citation Format: Vikram B. Wali, Maureen Gilmore-Hebert, Klaus Elenius, David F. Stern. Overexpression of HER4 isoforms in transgenic mice reveal isoform-specific role in mammary gland development and carcinogenesis. [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 1401. doi:10.1158/1538-7445.AM2013-1401

Tocotrienol combination therapy results in synergistic anticancer response

Vitamin E represents a family of compounds that is divided into two subgroups called tocopherols and tocotrienols, which act as important antioxidants that regulate peroxidation reactions and control free-radical production within the body. However, many of the biological effects of vitamin E are mediated independently of its antioxidant activity. Although tocopherols and tocotrienols have the same basic chemical structure characterized by a long phytyl chain attached to a chromane ring, only tocotrienols display potent anticancer activity, by modulating multiple intracellular signaling pathways associated with tumor cell proliferation and survival, and combination therapy with other chemotherapeutic agents result in a synergistic anticancer response. Combination therapy is most effective when tocotrienols are combined with agents that have complementary anticancer mechanisms of action. These findings strongly suggest that the synergistic antiproliferative and apoptotic effects demonstrated by combined low dose treatment of γ-tocotrienol with other chemotherapeutic agents may provide significant health benefits in the prevention and/or treatment of breast cancer in women, while at the same time avoiding tumor resistance and toxic side effects associated with high dose monotherapy.

Synthesis of Fluorescent Analogues of the Anticancer Natural Products 4-Hydroxyphenylmethylene Hydantoin and δ-Tocotrienol

4-Hydroxyphenylmethylene hydantoin (PMH, 1), isolated from the Red Sea sponge Hemimycale Arabica, and δ-tocotrienol (3), isolated from the tocotrienol-rich fraction of palm oil, are important antimetastatic and antiproliferative natural products that proved effective against metastatic prostate and breast cancers, respectively. New fluorescent derivatives of PMH (2) and δ-tocotrienol (4) were synthesized by Steglich esterification. Both 2 and 4 retained good anti-migratory and antiproliferative activities, respectively. Fluorescent analogues 2 and 4 can be used for the identification of molecular targets of 1 and 3 in tumor cell cultures.

Synthesis of fluorescent analogues of the anticancer natural products 4-hydroxyphenylmethylene hydantoin and delta-tocotrienol

4-Hydroxyphenylmethylene hydantoin (PMH, 1), isolated from the Red Sea sponge Hemimycale arabica, and delta-tocotrienol (3), isolated from the tocotrienol-rich fraction of palm oil, are important antimetastatic and antiproliferative natural products that proved effective against metastatic prostate and breast cancers, respectively. New fluorescent derivatives of PMH (2) and delta-tocotrienol (4) were synthesized by Steglich esterification. Both 2 and 4 retained good anti-migratory and antiproliferative activities, respectively. Fluorescent analogues 2 and 4 can be used for the identification of molecular targets of 1 and 3 in tumor cell cultures.

Abstract 4458: Antiproliferative effects of γ-tocotrienol are mediated by suppression in the activation of Met tyrosine kinase receptors in neoplastic +SA mammary epithelial cells

γ-Tocotrienol, a member of vitamin E family of compounds, displays potent anticancer activity against breast and other types of cancers. Previous studies have shown that the antiproliferative effects of γ-tocotrienol are associated with the suppression in the epidermal growth factor (EGF)-dependent phosphatidylinositol-3-kinase (PI3K)-dependent kinase-1 (PDK-1) and Akt phosphorylation in neoplastic +SA mammary epithelial cells. Also, studies showed that γ-tocotrienol treatment had no direct effect on Akt activity and did not alter the relative intracellular levels of PI3K, indicating that γ-tocotrienol might act upstream of the PI3K/PDK-1/Akt pathways at the level of membrane tyrosine kinase receptors in +SA mammary tumor cells. Since aberrant activation of the Met tyrosine kinase receptors is observed in various types of cancers and is associated with poor prognosis, studies were conducted to determine the effect of γ-tocotrienol on EGF and hepatocyte growth factor (HGF)-dependent activation of Met tyrosine kinase receptors in +SA mammary tumor cells. Treatment with serum-free media containing various doses of EGF (1-10 ng/ml) or HGF (1-10 ng/ml) significantly increased the growth of +SA mammary tumor cells as compared to serum-free control group over a 3-day culture period. Stimulation of +SA cells with EGF (10 ng/ml) or HGF (10 ng/ml) resulted in the activation of Met tyrosine kinase receptors. Treatment with Met tyrosine kinase inhibitor, SU11274 (5.5 μM) or γ-tocotrienol (4 μM) inhibited the EGF or HGF-dependent growth and activation of Met receptors in +SA mammary tumor cells after a 3-day culture period. Also, knockdown of Met receptors using Met specific siRNA decreased the expression of Met receptors and significantly inhibited the EGF or HGF-dependent growth of +SA cells. Additional studies showed that when +SA cells were simultaneously exposed to EGF (10 ng/ml) and HGF (10 ng/ml), the growth inhibitory effects of γ-tocotrienol (4 μM) and SU11274 (5.5 μM) were significantly reversed, associated with the activation of Met receptors. However, combined treatment with low doses of γ-tocotrienol (2 μM) and SU11274 (3 μM) inhibited the EGF and/or HGF-dependent growth of neoplastic +SA mammary epithelial cells. These results strongly suggest that γ-tocotrienol treatment may provide significant health benefit in the prevention and/or treatment of breast cancer in women with deregulated HGF/Met signaling. Supported by grants from NIH (CA86833) and First Tech International Ltd.

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 4458.

Abstract 5417: Suppression in mevalonate synthesis mediates the antiproliferative effects of combined statin and γ-tocotrienol treatment in mammary tumor cells

Statins directly inhibit 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) activity, while γ-tocotrienol, an isoform of vitamin E, enhances the degradation and reduces the cellular levels of HMGR in various tumor cell lines. Since treatment with statins or γ-tocotrienol alone induced a dose-responsive inhibition, whereas combined treatment with subeffective doses of these agents resulted in a synergistic inhibition in +SA mammary tumor cell growth, studies were conducted to investigate the role of the HMGR pathway in mediating the antiproliferative effects of combined low-dose statin and γ-tocotrienol treatment in +SA cells. Cells were maintained in serum-free defined media containing EGF (10 ng/mL) and insulin (10 µg/mL) as co-mitogens. Treatment with 8 μM simvastatin alone inhibited +SA cell growth and isoprenylation of Rap1A and Rab6, and supplementation with 2 µM mevalonate reversed these effects, indicating that simvastatin inhibits +SA cell growth by suppressing mevalonate synthesis. Also, treatment with 4 μM γ-tocotrienol alone inhibited +SA cell growth but had no effect on the isoprenylation of Rap1A and Rab6, and supplementation with 2 µM mevalonate had no effect on cell growth or isoprenylation, suggesting that γ-tocotrienol inhibits +SA cell growth through mechanisms independent of mevalonate suppression. The confocal immunofluorescence imaging revealed that treatment with subeffective doses of simvastatin (0.25 μM), lovastatin (0.25 μM), mevastatin (0.25 μM), pravastatin (10 μM), or γ-tocotrienol (2 μM) alone had no effect on the positive Ki-67 staining, while combined low-dose statin and γ-tocotrienol treatments markedly suppressed the positive Ki-67 staining in +SA cells as compared with control. Treatment with same subeffective doses of these statins or γ-tocotrienol alone had no effect on protein prenylation or mitogenic signaling, whereas combined treatment with these agents resulted in a significant inhibition in +SA cell growth, and a corresponding decrease in the relative levels of total HMGR, Rap1A and Rab6 prenylation, phosphorylated (active) MAPK, and cyclin D1, as compared with respective controls. However, these inhibitory effects on +SA cell growth, prenylation and mitogenic signaling were completely reversed by mevalonate supplementation. These findings demonstrate that the synergistic antiproliferative effects of combined low-dose statin and γ-tocotrienol treatment are directly related to an inhibition in HMGR activity and subsequent suppression in mevalonate synthesis. Since HMGR activity is characteristically elevated in cancer, these results strongly suggest that combination therapy with statins and γ-tocotrienol may be effective in suppressing the growth of breast cancer in women. Supported by grants from NIH (CA 86833) and First Tech International Ltd.

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 5417.

Enhanced antiproliferative and apoptotic response to combined treatment of gamma-tocotrienol with erlotinib or gefitinib in mammary tumor cells

Background

Aberrant ErbB receptor signaling is associated with various types of malignancies. γ-Tocotrienol is a member of the vitamin E family of compounds that displays potent anticancer activity that is associated with suppression in ErbB receptor phosphorylation and mitogenic signaling. Erlotinib and gefitinib are tyrosine kinase inhibitors that block ErbB1 receptor activation, whereas trastuzumab is a monoclonal antibody that has been designed to specifically inhibit ErbB2 receptor activation. However, the clinical effectiveness of these agents have been disappointing because of cooperation between different ErbB family members that can rescue cancer cells from agents directed against a single ErbB receptor subtype. It was hypothesized that targeting multiple ErbB receptor subtypes with combined treatment of γ-tocotrienol and ErbB receptor inhibitors would provide greater anticancer effects than monotherapy targeting only a single ErbB receptor subtype.

Methods

Highly malignant mouse +SA mammary epithelial cells were maintained in culture on serum-free defined media containing 10 ng/ml EGF as a mitogen. Cell viability wase determined by MTT assay, whereas Western blot and immunofluorescent staining was used to determine treatment effects on ErbB receptor subtype level and activation. Treatment-induced apoptosis was determined using annexin V staining and Western blot analysis of cleaved caspase-3 and PARP levels.

Results

Treatment with 3.5 μM γ-tocotrienol, 0.5 μM erlotinib or 1.0 μM gefitinib alone, significantly inhibited +SA tumor cell growth. Combined treatment with subeffective doses of erlotinib (0.25 μM) or gefitinib (0.5 μM) with subeffective doses of γ-tocotrienol (0.5-3.0 μM) significantly inhibited the growth and induced apoptosis in a dose-responsive manner. Trastuzumab treatment alone or in combination had no effect on +SA cell growth and viability. Combined treatment of γ-tocotrienol with erlotinib or gefitinib also cause a large decrease in ErbB3, ErbB4, and to a lesser extent ErbB2 receptor levels, and EGF-dependent ErbB2-4 tyrosine phosphorylation (activation), but had no effect on ErbB1 receptor levels or activation.

Conclusion

Combination treatment of γ-tocotrienol with specific ErbB receptor inhibitors is more effective in reducing mammary tumor cell growth and viability than high dose monotherapy, suggesting that targeting multiple ErbB receptors with combination therapy may significantly improve the therapeutic response in breast cancer patients.

Combined gamma-tocotrienol and erlotinib/gefitinib treatment suppresses Stat and Akt signaling in murine mammary tumor cells

BACKGROUND

Heterodimer cooperation between ErbB receptors has limited clinical usefulness of receptor tyrosine kinase inhibitors (TKIs), erlotinib and gefitinib in the treatment of cancer. However, combination treatment of TKIs with gamma-tocotrienol targets multiple ErbB receptors and significantly inhibit +SA murine mammary tumor cell growth.

MATERIALS AND METHODS

Cell proliferation was determined by tetrazolium (MTT) assay and immunofluorescent Ki-67 staining. Western blot analysis was used to determine treatment effects on epidermal growth factor (EGF)-dependent mitogenic signaling.

RESULTS

Combined treatment of 3 microM gamma-tocotrienol with 0.25 microM erlotinib or 0.5 microM gefitinib significantly inhibited +SA cell growth and reduced cyclin D1 and phosphorylated (active) Pdk-1, Akt, Stat3 and Stat5 levels.

CONCLUSION

Combined treatment of gamma-tocotrienol with erlotinib or gefitinib prevents ErbB receptor heterodimer cooperation and inhibits EGF-dependent mitogenic signaling in +SA murine mammary tumor cells. These findings strongly suggest that combination treatment may significantly improve therapeutic responsiveness in breast cancer patients.

Anti-proliferative effects of gamma-tocotrienol on mammary tumour cells are associated with suppression of cell cycle progression

OBJECTIVES

Previous studies have shown that gamma-tocotrienol induces potent anti-proliferative effects on +SA mammary tumour cells in culture; here, investigations have been conducted to determine its effects on intracellular signalling proteins involved in regulating cell cycle progression.

MATERIALS AND METHODS

+SA cells were maintained in mitogen-free defined media containing 0 or 4 micromgamma-tocotrienol, for 48 h to synchronize cell cycle in G(0) phase, and then they were exposed to 100 ng/ml EGF to initiate cell cycle progression. Whole cell lysates were collected at various time points from each treatment group and were prepared for Western blot analysis.

RESULTS AND CONCLUSIONS

Treatment with 4 micromgamma-tocotrienol significantly inhibited +SA cell proliferation over a 4-day culture period. Moreover, this treatment resulted in a relatively large reduction in cyclin D1, cyclin dependent kinase (CDK)4, CDK2 and CDK6 levels, between 4 and 24 h after EGF exposure. Tocotrienol treatment also resulted in a relatively large increase in CDK inhibitor (CKI) p27, prior to and after EGF exposure, but had little effect on levels of CKIs, p21 and p15. Tocotrienol treatment also induced a large relative reduction in retinoblastoma (Rb) protein phosphorylation at ser780 and ser807/811. These findings strongly suggest that anti-proliferative effects of gamma-tocotrienol are associated with reduction in cell cycle progression from G(1) to S, as evidenced by increased p27 levels, and a corresponding decrease in cyclin D1, CDK2, CDK4, CDK6 and phosphorylated Rb levels.

Suppression in mevalonate synthesis mediates antitumor effects of combined statin and gamma-tocotrienol treatment

Statins directly inhibit 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) activity, while gamma-tocotrienol, an isoform of vitamin E, enhances the degradation and reduces cellular levels of HMGR in various tumor cell lines. Since treatment with statins or gamma-tocotrienol alone induced a dose-responsive inhibition, whereas combined treatment with subeffective doses of these agents resulted in a synergistic inhibition in +SA mammary tumor cell growth, studies were conducted to investigate the role of the HMGR pathway in mediating the antiproliferative effects of combined low dose statin and gamma-tocotrienol. Treatment with 8 microM simvastatin inhibited cell growth and isoprenylation of Rap1A and Rab6, and supplementation with 2 microM mevalonate reversed these effects. However, the growth inhibitory effects of 4 microM gamma-tocotrienol were not dependent upon suppression in mevalonate synthesis. Treatment with subeffective doses of simvastatin (0.25 microM), lovastatin (0.25 microM), mevastatin (0.25 microM), pravastatin (10 microM), or gamma-tocotrienol (2 muM) alone had no effect on protein prenylation or mitogenic signaling, whereas combined treatment with these agents resulted in a significant inhibition in +SA cell growth, and a corresponding decrease in total HMGR, Rap1A and Rab6 prenylation, and MAPK signaling, and mevalonate supplementation reversed these effects. These findings demonstrate that the synergistic antiproliferative effects of combined low dose statin and gamma-tocotrienol treatment are directly related to an inhibition in HMGR activity and subsequent suppression in mevalonate synthesis.

Combined treatment of gamma-tocotrienol with statins induce mammary tumor cell cycle arrest in G1

Statins and gamma-tocotrienol (a rare isoform of vitamin E) both inhibit 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase activity and display anticancer activity. However, clinical application of statins has been limited by high dose toxicity. Previous studies showed that combined statin and gamma-tocotrienol treatment synergistically inhibits growth of highly malignant +SA mammary epithelial cells in culture. To investigate the mechanism mediating this growth inhibition, studies were conducted to determine the effect of combination low dose gamma-tocotrienol and statin treatment on +SA mammary tumor cell cycle progression. Treatment with 0.25 microM simvastatin, lovastatin, mevastatin, 10 microM pravastatin or 2.0 microM gamma-tocotrienol alone had no effect, while combined treatment of individual statins with gamma-tocotrienol significantly inhibited +SA cell proliferation during the 4-day culture period. Flow cytometric analysis demonstrated that combined treatment induced cell cycle arrest in G1. Additional studies showed that treatment with 0.25 microM simvastatin or 2 microM gamma-tocotrienol alone had no effect on the relative intracellular levels of cyclin D1, CDK2, CDK4 and CDK6, but combined treatment caused a large reduction in cyclin D1 and CDK2 levels. Combined treatments also caused a relatively large increase in p27, but had no effect on p21 and p15 levels, and resulted in a large reduction in retinoblastoma (Rb) protein phosphorylation at ser780 and ser807/811. Similar effects were observed following combined treatment of gamma-tocotrienol with low doses of lovastatin, mevastatin and pravastatin. These findings demonstrate that combination low dose statin and gamma-tocotrienol treatment induced mammary tumor cell cycle arrest at G1, resulting from an increase in p27 expression, and a corresponding decrease in cyclin D1, CDK2, and hypophosphorylation of Rb protein. These findings suggest that combined treatment of statins with gamma-tocotrienol may provide significant health benefits in the treatment of breast cancer in women, while avoiding myotoxicity associated with high dose statin monotherapy.

Sinulodurins A and B, antiproliferative and anti-invasive diterpenes from the soft coral Sinularia dura

Two new diterpenes, sinulodurin A (1) and sinulodurin B (2), along with two known sterols, 24 S-methyl cholesterol and 24-methylene cholesterol, were isolated from the Palau soft coral Sinularia dura. The structures of the new metabolites were determined on the basis of spectroscopic methods and by comparison of NMR data with those of related metabolites. Sinulodurin A (1) and sinulodurin B (2) showed antiproliferative activity against highly malignant +SA mammary epithelial cells with an IC 50 range of 20-30 microM. They also displayed anti-invasive activity against human highly metastatic prostate cancer PC-3M-CT+ cells in the spheroid disaggregation assay. Furthermore, the antimicrobial activities of the isolates were tested.

Semisynthetic and biotransformation studies of (1S,2E,4S,6R,7E,11E)-2,7,11-cembratriene-4,6-diol

Tobacco-derived (1 S,2 E,4 S,6 R,7 E,11 E)-2,7,11-cembratriene-4,6-diol (1) and (1 S,2 E,4 R,6 R,7 E,11 E)-2,7,11-cembratriene-4,6-diol (2) were first shown to display potential antitumor-promoting activity in the mid-1980s. However, very little is currently understood regarding the structural activity relationships of tobacco cembranoids. The aim of this present study was to explore antiproliferative activity of various derivatives of (1 S,2 E,4 S,6 R,7 E,11 E)-2,7,11-cembratriene-4,6-diol (1) using semisynthetic and biotransformation approaches. Derivatives of 1 include esterified, oxidized, halogenated, and nitrogen- and sulfur-containing compounds (3-17). Biotransformation of 1 using Mucor ramannianus ATCC 9628 and Cunninghamella elegans ATCC 7929 afforded the known 10 S,11 S-epoxy analogue of 1 (4) as the main metabolite. Biotransformation of the 6-O-acetyl analogue (3) using the marine symbiotic Bacillus megaterium strain MO31 afforded (1 S,2 E,4 S,6 R,7 E,11 E,10 R)-2,7,11-cembratriene-4,6,10-triol (18). (1 S,2 E,4 S,6 R,7 E,11 E,13 R)-2,7,11-Cembratriene-4,6,13-triol-6-O-acetate (6), (1 S,2 E,4 S,6 R,7 E,11 E,13 S)-2,7,11-cembratriene-4,6,13-triol-6-O-acetate (7), the rearranged alpha-ketol (1 S,2 E,4 S,7 Z,11 E)-2,7,11-cembratrien-4-ol-6-one (11), and the secocembranoid 12 showed antiproliferative activity against highly malignant +SA mammary epithelial cells with an IC50 range of 15-30 microM.

Synergistic antiproliferative effects of gamma-tocotrienol and statin treatment on mammary tumor cells

Statins are potent inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMGCoA) reductase and display anticancer activity, but their clinical use is limited by their high-dose toxicity. Similarly, gamma-tocotrienol, an isoform of vitamin E, also reduces HMGCoA reductase activity and displays potent anticancer activity. Studies were conducted to determine if combined low dose treatment of gamma-tocotrienol with individual statins resulted in a synergistic antiproliferative effect on neoplastic mouse +SA mammary epithelial cells. Treatment with 3-4 microM gamma-tocotrienol or 2-8 microM simvastatin, lovastatin or mevastatin alone resulted in a significant decrease, whereas treatment with 10-100 microM pravastatin had no effect on +SA cell growth. However, combined treatment of subeffective doses (0.25 or 10 microM) of individual statins with 0.25-2.0 microM gamma-tocotrienol resulted in a dose-responsive synergistic inhibition in +SA cell proliferation. Additional studies showed that treatment with subeffective doses of individual statins or gamma-tocotrienol alone had no effect, whereas combined treatment of these compounds resulted in a relatively large decrease in intracellular levels of phosphorylated (activated) MAPK, JNK, p38, and Akt. These findings strongly suggest that combined low dose treatment of gamma-tocotrienol with individual statins may have potential value in the treatment of breast cancer without causing myotoxicity that is associated with high dose statin treatment.