The molecular phenotype of heart transplant biopsies: relationship to histopathological and clinical variables

Histopathology of endomyocardial biopsies (EMB) is the standard rejection surveillance for heart transplants. However, ISHLT consensus criteria for interpreting biopsies are arbitrarily defined. Gene expression offers an independent re-evaluation of existing diagnostic systems. We performed histologic and microarray analysis on 105 EMB from 45 heart allograft recipients. Histologic lesions, diagnosis and transcripts were compared to one another, time posttransplantation, indication for biopsy and left ventricular ejection fraction (LVEF). Histologic lesions presented in two groups: myocyte-interstitial and microcirculation lesions. Expression of transcript sets reflecting T cell and macrophage infiltration, and γ-interferon effects correlated strongly with each other and with transcripts indicating tissue/myocardium injury. This molecular phenotype correlated with Quilty (p < 0.005), microcirculation lesions (p < 0.05) and decreased LVEF (p < 0.007), but not with the histologic diagnosis of rejection. In multivariate analysis, LVEF was associated (p < 0.03) with γ-interferon inducible transcripts, time posttransplantation, ischemic injury and clinically indicated biopsies, but not the diagnosis of rejection. The results indicate that (a) the current ISHLT system for diagnosing rejection does not reflect the molecular phenotype in EMB and lacks clinical relevance; (b) the interpretation of Quilty lesions has to be revisited; (c) the assessment of molecules in heart biopsy can guide improvements of current diagnostics.

Effect of tricalcium aluminate on the properties of tricalcium silicate-tricalcium aluminate mixtures: setting time, mechanical strength and biocompatibility

AIM

To prepare biphasic mixtures by adding Ca(3) Al(2) O(6) into Ca(3) SiO(5) and to evaluate the effect of Ca(3) Al(2) O(6) on physical and ex vivo biological properties of the Ca(3) SiO(5) /Ca(3) Al(2) O(6) mixtures derived from mineral trioxide aggregate (MTA).

METHODOLOGY

Combinations of Ca(3) SiO(5) and Ca(3) Al(2) O(6) (0, 5%, 10% and 15%) powders were mixed with deionized water. After hydration, setting time, compressive strength, ex vivo bioactivity and biocompatibility of each mixture were investigated and compared to pure Ca(3) SiO(5) .

RESULTS

With the addition of Ca(3) Al(2) O(6) from 0% to 15%, the initial setting time and final setting time of the Ca(3) SiO(5) /Ca(3) Al(2) O(6) mixtures decreased from 110 to 43min and from 220 to 97min, respectively (P≤0.05). However, the compressive strength increased from 6.75 to 16.20MPa after one day (P≤0.05) and from 17.73 to 29.13 Mpa after 28 days. Furthermore, the mixtures with 10% Ca(3) Al(2) O(6) or less had similar bioactivity and biocompatibility when compared to the pure Ca(3) SiO(5).

CONCLUSIONS

The addition of Ca(3) Al(2) O(6) into Ca(3) SiO(5) accelerated the hydration process, reduced the setting time and improved the compressive strength. Furthermore, these mixtures were bioactive and biocompatible and had a stimulatory effect on the L929 cell growth when the content of Ca(3) Al(2) O(6) was below 10%. Therefore, the mixtures with 10% Ca(3) Al(2) O(6) produced the best compromise between hydration and ex vivo biological properties.

NK cell transcripts and NK cells in kidney biopsies from patients with donor-specific antibodies: evidence for NK cell involvement in antibody-mediated rejection

To explore the mechanisms of antibody-mediated rejection (ABMR) in kidney transplants, we studied the transcripts expressed in clinically indicated biopsies from patients with donor-specific antibody (DSA). Comparison of biopsies from DSA-positive versus DSA-negative patients revealed 132 differentially expressed transcripts: all were associated with class II DSA but none with class I DSA. Many transcripts were expressed in DSA-positive ABMR but were also expressed in T-cell-mediated rejection (TCMR), reflecting shared molecular features. Removal of shared transcripts created 23 DSA selective transcripts (DSASTs). Some DSASTs (6/23) showed selective high expression in NK cells, whereas others (8/23) were expressed in endothelium or in endothelium plus other cell types (7/23). Of 145 biopsies ranked by DSAST expression, the 25 with highest DSAST expression primarily consisted of ABMR (22/25, 88%), either C4d-positive or C4d-negative. By immunostaining, CD56+ and CD68+ cells in peritubular capillaries, but not CD3+ cells, were increased in ABMR compared to TCMR, compatible with a role for NK cells, as well as macrophages, as effectors in endothelial injury during ABMR. Thus, the strategy of using DSASTs in the biopsy to identify mechanism-related transcripts in biopsies from patients with clinical phenotypes indicates the selective involvement of NK cells in ABMR.

TRAF6 knockdown promotes survival and inhibits inflammatory response to lipopolysaccharides in rat primary renal proximal tubule cells

AIM

TRAF6 is a unique adaptor protein of the tumour necrosis factor receptor-associated factor family that mediates both tumour necrosis factor receptor (TNFR) and interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) signalling. Activation of IL-1R/TLR and TNFR pathways in renal tubular cells contributes to renal injury. This study aimed to investigate if blockade of lipopolysaccharide (LPS)-triggered TLR4 signalling by small interfering RNA (siRNA) targeting TRAF6 protects survival and inhibits inflammatory response in isolated rat renal proximal tubular cells (PTCs).

METHODS

PTCs isolated from F344 rat kidneys were transfected with chemically synthesized siRNA targeting TRAF6 mRNA. Real-time quantitative PCR was applied to measure mRNA level of TRAF6, TNF-alpha, IL-6 and monocyte chemoattractant protein-1 (MCP-1). Protein levels of extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase, caspase 3 and cleaved caspase 3 were evaluated by Western blotting. Cell viability was analysed with XTT reagents.

RESULTS

We found that the TRAF6 gene was effectively silenced in PTCs using siRNA. TRAF6 knockdown resulted in reduced TNF-alpha and IL-6 mRNA expression upon LPS challenge. LPS-induced phosphorylation of JNK and p38 was attenuated in TRAF6 siRNA-transfected cells while the change in the phosphorylation of ERK was not remarkable. TRAF6 knockdown was associated with increased cell viability and reduced protein level of cleaved caspase-3, both, in the absence and presence of LPS.

CONCLUSION

Our studies suggest that TRAF6 knockdown may inhibit inflammatory response and promote cell survival upon LPS challenge in primary rat proximal renal tubular cells.

Improving the privacy of optical steganography with temporal phase masks

Temporal phase modulation of spread stealth signals is proposed and demonstrated to improve optical steganography transmission privacy. After phase modulation, the temporally spread stealth signal has a more complex spectral-phase-temporal relationship, such that the original temporal profile cannot be restored when only dispersion compensation is applied to the temporally spread stealth signals. Therefore, it increases the difficulty for the eavesdropper to detect and intercept the stealth channel that is hidden under a public transmission, even with a correct dispersion compensation device. The experimental results demonstrate the feasibility of this approach and display insignificant degradation in transmission performance, compared to the conventional stealth transmission without temporal phase modulation. The proposed system can also work without a clock transmission for signal synchronization. Our analysis and simulation results show that it is difficult for the adversary to detect the existence of the stealth transmission, or find the correct phase mask to recover the stealth signals.

Nernst and Seebeck coefficients of the cuprate superconductor YBa2Cu3O6.67: a study of Fermi surface reconstruction

The Seebeck and Nernst coefficients S and nu of the cuprate superconductor YBa{2}Cu{3}O{y} (YBCO) were measured in a single crystal with doping p=0.12 in magnetic fields up to H=28 T. Down to T=9 K, nu becomes independent of field by H approximately 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and nu/T are both large and negative in the T-->0 limit, with the magnitude and sign of S/T consistent with the small electronlike Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T approximately 50 K is remarkably similar to that observed in La2-xBaxCuO4, La{2-x-y}Nd{y}Sr_{x}CuO{4}, and La{2-x-y}Eu{y}Sr{x}CuO{4}, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO.

Cluster analysis of lesions in nonselected kidney transplant biopsies: microcirculation changes, tubulointerstitial inflammation and scarring

Banff classification empirically established scoring of histologic lesions, but the relationships of lesions to each other and to underlying biologic processes remain unclear. We hypothesized that class discovery tools would reveal new relationships between individual lesions, and relate lesions to C4d staining, anti-HLA donor-specific antibody (DSA) and time posttransplant. We studied 234 nonselected renal allograft biopsies for clinical indications from 173 patients. Silhouette plotting and principal component analysis revealed three groups of lesions: microcirculation changes, including inflammation (glomerulitis, capillaritis) and deterioration (double contours, mesangial expansion); scarring/hyalinosis; and tubulointerstitial inflammation. DSA and C4d grouped with microcirculation inflammation, whereas time posttransplant grouped with scarring/hyalinosis lesions. Intimal arteritis clustered with DSA, C4d and microcirculation inflammation, but also showed correlations with tubulitis. Fibrous intimal thickening in arteries clustered with scarring/hyalinosis. Capillary basement membrane multilayering showed intermediary relationships between microcirculation deterioration and time-dependent scarring. Correlation analysis and hierarchical clustering confirmed the lesion relationships. Thus, we propose that the pathologic lesions in biopsies are not independent but are members of groups that represent distinct pathogenic forces: microcirculation changes, reflecting the stress of DSA; scarring, hyalinosis and arterial fibrosis, reflecting the cumulative burden of injury over time; and tubulointerstitial inflammation. Interpretation of lesions should reflect these associations.

Strontium borate glass: potential biomaterial for bone regeneration

Boron plays important roles in many life processes including embryogenesis, bone growth and maintenance, immune function and psychomotor skills. Thus, the delivery of boron by the degradation of borate glass is of special interest in biomedical applications. However, the cytotoxicity of borate glass which arises with the rapid release of boron has to be carefully considered. In this study, it was found that the incorporation of strontium into borate glass can not only moderate the rapid release of boron, but also induce the adhesion of osteoblast-like cells, SaOS-2, thus significantly increasing the cyto-compatibility of borate glass. The formation of multilayers of apatite with porous structure indicates that complete degradation is optimistic, and the spread of SaOS-2 covered by apatite to form a sandwich structure may induce bone-like tissue formation at earlier stages. Therefore, such novel strontium-incorporated borosilicate may act as a new generation of biomaterial for bone regeneration, which not only renders boron as a nutritious element for bone health, but also delivers strontium to stimulate formation of new bones.

High IGF-IR Activity in Triple-Negative Breast Cancer Cell Lines Correlates with Sensitivity to IGF-IR Inhibitor BMS-754807 in This Subtype of Human Breast Cancer

BACKGROUND: Evidence implicates insulin-like growth factor-I (IGF-I) signaling in the development and progression of breast cancer. Within the last few years several drugs targeting IGF-I receptor (IGF-IR) have entered clinical trials and are showing promising early results. BMS-754807 is a new small molecule inhibitor of IGF-IR in Phase 1 clinical trials.METHODS: Minimal and maximal IC50 to BMS-754807 for monolayer proliferation was determined for a panel of 30 breast cancer cell lines. Comparative gene expression analysis was performed using publicly available gene expression among the most resistant and sensitive cell lines. Q-RT-PCR was used to validate gene expression differences. Using the IGF gene signature, we scored each expression profile in a panel of cell lines and tumorgrafts, for correlation with the IGF-induced patterns. IGF-IR and pY-IGF-IR levels were determined in human tumorgrafts by immunohistochemistry.RESULTS: Among the different tumor cell lines, sensitivity to BMS-754807 varied widely from 0.1µM to 25µM. When defining cell lines as sensitive or resistant based on the median IC50, there was a strong enrichment for triple negative (TN; ERa-/PR-/HER2-) breast cancer cell lines in the sensitive group (11/15), while luminal breast cancer cell lines were generally resistant (11/15). We identified 136 differentially expressed genes between sensitive and resistance cell lines. Sensitive breast cancer cell lines preferentially express genes such as CAV1, and CAV2 while resistant cell lines were associated with high expression of ErbB3, and SPDEF. As luminal breast cancer cell lines were generally resistant to BMS-754807, we examined the role of estrogen and ERa on the sensitivity to BMS-754807. ERa mRNA levels strongly correlated with resistance to BMS-754807. Consistent with this, estrogen-withdrawal sensitized luminal breast cancer cells to BMS-754807. Previously, we developed an IGF-I gene signature that was derived from breast cancer cells stimulated with IGF-I, and reported that the signature strongly correlated with the TN subtype of human breast cancer. Consistent with this observation, we found that the IGF-I signature was high in TN breast cancer cell lines, and the IGF-I signature correlated with sensitivity to BMS-754807. To examine this further, we measured IGF-IR and pY-IGF-IR levels in four recently developed tumorgraft models of TN human breast cancer and found strong reactivity in half of the models. Interestingly, the tumorgraft (MC1) with the highest IGF-IR levels and activity showed the strongest enrichment for the IGF-I gene signature.CONCLUSIONS: In summary, our data indicates that the IGF-I pathway is highly active in TN breast cancer and this study provides the preclinical rationale for targeting IGF-IR in this subtype of human breast cancer.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1132.

Transcriptional and Post-Translational Upregulation of HER3 (ErbB3) Counteracts Antitumor Effect of HER2 Tyrosine Kinase Inhibitors

We hypothesized that sustained inhibition of HER3 and its output to PI3K/Akt is required for the optimal antitumor effect of HER2 inhibitors. Therefore, we examined the temporal effect of the HER2 tyrosine kinase inhibitor (TKI) lapatinib (lap) on feedback upregulation of active HER3 in HER2-overexpressing breast cancer cells. A time course with lap-treated cells showed 3 to 5-fold upregulation of HER3 RNA and protein, beginning at 4 h and increasing through 48 h. P-Tyr immunoblot of HER3 immunoprecipitates revealed recovery of HER3 phosphorylation at and beyond 13 h of treatment. Site-specific antibodies revealed HER3 phosphorylation at Y1197 and Y1289, two of the six p85 binding sites in HER3. Recovery of P-HER3 correlated temporally with recovery of T308 P-Akt. The upregulation of HER3 RNA upon treatment with lap suggested that inhibition of active HER2 and PI3K/Akt derepresses the transcription factor FoxO3a. Putative FoxO3a binding sites were identified within the 5' flanking region upstream of the HER3 transcription start site. Transfection with FoxO3a siRNA reduced basal and lap-induced HER3 RNA levels 2 to 5-fold compared to control cells. Conversely, overexpression of FoxO3a increased HER3 RNA 2.5-fold, which could be further enhanced by lap treatment. In addition to these transcriptional mechanisms, the recovery of P-HER3 upon lap-induced inhibition of HER2 suggested engagement of another tyrosine kinase transactivating HER3 and/or that HER2 had been incompletely inhibited by the TKI. However, IGF-IR, Src, and MET TKIs did not inhibit the recovery of P-HER3. On the other hand, the addition of trastuzumab (tz) to lap-treated cells prevented recovery of P-HER3, suggesting that disruption of a ligand-independent HER2-HER3 interaction was involved in partial maintenance of HER3 phosphorylation.The upregulation of HER3 RNA and partial maintenance of P-HER3 and P-Akt suggested that combined inhibition of HER2 and HER3 will synergistically inhibit tumor cell viability. Transfection with HER3 siRNA sensitized HER2+ breast cancer cells to each lap and tz as assessed by Apo-BrdU (apoptosis) and 3D-Matrigel growth assays. Further, treatment with AMG-888, a HER3 monoclonal antibody (AMGEN-U3), sensitized cells to each lap and tz. Ongoing studies include the treatment of BT474 xenografts in athymic mice with lap ± AMG-888 using [18F]-FDG-PET as a non-invasive imaging biomarker to predict treatment outcome. Finally, we examined HER3 levels by immunohistochemistry in sections from tumor blocks of patients enrolled in a neoadjuvant trial where lap was given alone during the first 6 weeks of therapy. The percent and intensity of tumor cell staining was calculated as a histoscore (Human Pathol. 26:291, 1995). On week 2 of therapy, HER3 levels increased 135% above pre-therapy levels (n=8; p=0.03, Mann-Whitney). These data suggest that upon inhibition of the HER2 tyrosine kinase, HER2+ breast cancers 1) upregulate HER3 by transcriptional mechanisms and partially maintain HER3 function by post-translational mechanisms; 2) this compensatory phosphorylation of HER3 partially maintains PI3K/Akt; and 3) inhibition of HER3 sensitizes HER2-dependent breast cancer cells to HER2 inhibitors.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 63.

Estrogen Deprivation Results in Altered DNA Methylation Profile in Breast Cancer Cells – Role in Endocrine Resistance?

Postmenopausal breast cancer patients benefit from aromatase inhibitors (AIs) that reduce the levels of estrogens which are critical for tumor growth. To date, epigenetic contributions to hormonal therapy resistance have not been well characterized, with only a limited understanding of antiestrogen mediated epigenetic modification of chromatin and altered gene expression. Furthermore, no genome-wide studies have been undertaken to identify altered DNA methylation patterns due to estrogen deprivation, which mimic AI therapy. We hypothesized that estrogen deprivation results in altered methylation, and therefore altered expression of critical target genes in breast cancer cells, which ultimately helps the cell to survive in the absence of estrogen and thus would contribute to acquire AI resistance in breast cancer patients.We used previously established MCF-7 cell clones, termed C4-12 and LTED (Long Term Estrogen Deprivation) that were isolated after being cultured in estrogen-free media for 9 months and 18-24 months, respectively. A genome-wide methylation screen was done using Methyl CpG binding Domain (MBD) pull down assay followed by hybridization into Affymetrix Human Promoter 1.0R Array. Altered DNA methylations were validated by bisulfite genomic sequencing assays and gene expression of some selected genes were studied by qRT PCR.From the array, we found that long term estrogen deprivation results in widespread genomic hyper- and hypomethylation events. 267 and 301 genes were hypermethylated in C4-12 and LTED respectively. In both resistant cell lines, the number of hypermethyled genes was more prominent than hypomethylated genes since only 82 and 97 genes were hypomethylated in C4-12 and LTED respectively. While hypomethylation of genes generally correlated with increased gene expression, hypermethylation did not in many cases. A gene which was heavily methylated in both cell line system, possibly reflecting a more general and important pathway in estrogen-deprivation, was HOXC10. Transient and stable silencing of HOXC10 in MCF-7 cells resulted in increased cell proliferation in estrogen deprived medium, suggesting a potential role of HOXC10 in developing resistance to endocrine therapy.This is the first genome-wide approach to identify gene-specific epigenetic alterations, and the functional consequences of these changes in developing resistance to estrogen deprivation therapy. This approach allows the development of epigenetic signatures of therapeutic resistance to be used concurrently with genomic signatures to better understand the molecular mechanism of endocrine resistance. This study might provide the basis for future clinical trials such as combination therapy of DNA demethylating agents and aromatase inhibitors.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5127.

Novel Stably Transplantable Xenograft Models of Human Breast Cancer for Evaluation of Experimental Therapeutics

In translational breast cancer research, our ability to evaluate clinical responses of human tumors to new therapeutic agents is severely limited experimentally. For example, it is not possible to evaluate the response of a single tumor to multiple candidate therapeutic agents. Conversely, the limited number of well-characterized in vivo preclinical human tumor models currently available precludes evaluation of multiple clinically relevant tumors with candidate therapeutic agents. These limitations severely impinge on our ability to develop and test novel therapeutic agents, particularly those that may target tumor-initiating “cancer stem cells”, which are relatively resistant to chemotherapy and radiation and may be responsible for disease recurrence and metastases.Historically, in vivo experimental therapeutic research has relied on either genetically engineered animal models, or “xenograft” transplantation models in which established human cancer cell lines are transplanted into immunocompromised host mice. However, each type of model has significant limitations. We sought to circumvent some of these limitations by propagating a cohort of human tumors as stably transplantable xenograft tissue lines grown in the absence of engineered or immortalized fibroblasts by transplanting clinical biopsies directly into the mammary fat pad of SCID/Beige immunocompromised mice (lacking B-cell, T-cell, and NK cell function) without intervening culture in vitro.Thus far, we have established 13 independent stably transplantable xenograft lines representing nine “triple-negative” (ER-PR-HER2-), two HER2+, and two ER+ breast cancers. Established xenograft lines show phenotypic similarity to the primary tumor with respect to histology and gene expression. Xenografts are being characterized genetically by whole genome sequencing as well as for the diversity of tumor-initiating cell types present. These models are proving useful for the evaluation of experimental therapeutics for their ability to inhibit tumor growth, and for their ability to target the subset cancer cells capable of regenerating tumors upon transplantation, with the goals of overcoming chemoresistance, preventing disease recurrence, and eliminating metastases.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1159.

A BRCA1-Like, 25-Gene Assay Predicts for Anthracycline-Chemosensitivity in Sporadic Triple-Negative Breast Cancer

Background Studies have shown higher chemosensitivity to anthracyclines in BRCA1-associated breast cancer (BABC) when compared to sporadic triple-negative breast cancers (TNBC), possibly due to differences in DNA repair function. We hypothesized that a subset of TNBC with acquired BRCA1 deficiency and defective DNA repair function will benefit most from DNA-damaging agents, such as anthracyclines. Methods We applied a previously published BRCA1 gene expression signature that differentiates BABC from sporadic TNBC to three datasets of sporadic TNBC from Baylor College of Medicine (BCM, n=68), GSE2034 (n=49), and the Netherlands Cancer Institute (NKI2, n=40). The signature separated the sporadic TNBC samples into those with a gene expression profile similar to BABC, or BRCA1-like, versus those with an expression pattern similar to sporadic TNBC, nonBRCA1-like. A list of 92 genes was obtained from the overlap of the most differentially expressed genes between the BRCA1-like samples and nonBRCA1-like samples in each of the three datasets. We then confirmed a subset of the 25 most differentially expressed genes by quantitative RTPCR. We validated the predictive value of this BRCA1-based, 25-gene assay in anthracycline response in three neoadjuvant studies of fluorouracil, epirubicin, and cyclophosphamide (FEC 6 cycles, n=53), doxorubicin and cyclophosphamide (AC 4 cycles, n=12), and T-FAC (paclitaxel-FAC, n=16). Results We determined gene expression of the 92 candidate genes by RT-PCR on 30 available samples of the BCM database. 25 genes were found to have the highest correlation between the microarray and RTQPCR gene expression. Gene expression profile using these 25-gene assay was obtained for three databases which included neoadjuvant anthracycline response data. The 25-gene assay predicted for anthracycline response in sporadic triple-negative breast cancers. In a neoadjuvant FEC study, this assay predicted for pathologic complete response (pCR) in 14/25 patients with BRCA1-like pattern, vs. 7/25 with sporadic-like pattern, p&lt;0.05. In the AC study, 6/9 patients in the BRCA1-like group achieved pCR, vs. 0/3 in nonBRCA1-like group, p&lt;0.05. Finally, in the T-FAC study, 5/7 patients in the BRCA1-like group achieved pCR vs. 3/9 patients in the nonBRCA1-like group, p=0.15. Analysis of the microarray data of triple negative breast cancer revealed higher PARP1 expression levels in the BRCA1-like group when compared to nonBRCA1-like group. Conclusion We present a promising BRCA1-based 25-gene assay that can be used on formalin-fixed paraffin-embedded tissue that may guide therapy in triple- negative breast cancer. The assay differentiates TNBC that are very sensitive to anthracyclines, and it should now be tested and validated prospectively in clinical trials with anthracyclines, other DNA-damaging agents, and PARP1 inhibitors.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 110.

Lentiviral shRNA Screen To Test the Validity of a Gene Signature of Breast Cancer Stem Cells Using High Throughput Mammosphere Assays

Background Conventional chemotherapies are effective initially in controlling growth of many tumors, yet, many patients relapse over time. A possible explanation for relapse is that a rare sub-population of cancer stem cells (CSCs) with tumorigenic potential is intrinsically resistant to conventional therapy. We have identified a gene signature which is derived from human breast cancer biopsies that is the overlap between CD44+/CD24-/low vs. all other cell subpopulations, and cancer-derived mammospheres (MS) vs. bulk tumor. Both the CD44+/CD24-/low subpopulation and mammospheres are typically enriched for tumor-initiating “cancer stem cells” and their division-competent descendents. We found that 477 genes were differentially expressed in the combination group of which 185 of these were highly expressed in CD44+/CD24-/low cells and in MS, a highly significant overlap (p&lt;1.0E-9).The rest of the 292 genes demonstrated a reduction in expression in the CD44+/CD24-/low cells and cancer-derived MS vs. all other cells and bulk tumors, respectively (p&lt;5.0E-5, one-sided Fisher's exact). We hypothesized that a subset of these genes may have functional significance in decreasing MS formation efficiency (MSFE).MethodsWe then tested this gene signature by screening the entire list of 477 genes for their ability to increase or decrease MS formation using lentiviral shRNA knockdown vectors (OpenBiosystems, Inc). We created a sub-library comprised of fourteen 96-well plates containing approximately ∼1200 unique shRNA constructs, with an average of 3-4 shRNA constructs per gene, thereby targeting ∼500 unique genes.The library was designed and constructed on a “one gene, one well” structure, such that each sequence validated lentiviral shRNA construct targeting an individual gene is located in a unique well of a 96-well plate. Next, we transduced SUM159 cells with each of the lentiviruses individually, along with a positive control lentivirus targeting Bmi1, a polycomb group gene known to be required for self-renewal of many stem cell types, a non-specific negative control lentivirus, as well as untreated cells. Each transduced cell population was plated into individual wells of a 96-well low-attachment plate and allowed to form MS over 4 days. MS formation was quantified using Gelcount (Oxford Optornix, Inc). ResultsEfficacy of the lentivirus transfection was ∼80%. Of the 477 genes, we identified 151 shRNAs that demonstrated significant change (p≤0.05) in MS formation with respect to median MSFE and controls. ConclusionsWe have developed a high throughput lentiviral shRNA screening method to test the validity of CSC targets using MS assays. These data suggest intricate interactions between MS-initiating cells and downstream progenitors in MS formation and provides a set of ideal candidate genes. Inhibitors to these targets may decrease MS self renewal, as well as eliminate cancer stem cells, and may be important to test as pharmaceutical interventions.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 1158.

Targeting Intrinsically-Resistant Breast Cancer Stem Cells with Gamma-Secretase Inhibitors

Background: We showed previously that tumorigenic, mammosphere-forming human breast cancer cells characterized by high CD44 and low or undetectable CD24 levels (CD44+/CD24-/low) are intrinsically resistant to conventional chemotherapy, and therefore may be responsible for cancer relapse. Our goal is identify novel drugs that selectively target these chemotherapy-resistant, tumor-initiating cells. Gene expression analysis of CD44+/CD24-/low cells vs. non-tumorigenic cells implicated the Notch, PI3K, and Hedgehog signaling pathways in regulating CD44+/CD24-/low cells. Thus, Notch, PI3K-AKT, and/or Hedgehog inhibitors may eliminate this unique subpopulation of cancer cells, either alone or in combination with chemotherapy, and could improve patient outcome. To test this hypothesis, we are carrying out a series of preclinical and clinical studies using a gamma-secretase inhibitor (GSI) to target the Notch pathway. Methods: For preclinical studies, stable xenograft lines were generated by transplantation of human tumor biopsy fragments into immunocompromised mice. Mice with tumors (n = 32, 150-300 mm3) were randomized to four treatment groups: 1) vehicle control, 2) chemotherapy: docetaxel 3) drug: GSI (MRK-003, Merck) or 4) combination: docetaxel + MRK-003. During treatment, mice were monitored for tumor volume and body weight. At the end of the treatment cycle, residual tumors were characterized by FACS for the percentage of CD44+/CD24-/low cells, as well as for mammosphere-forming efficiency (MSFE) and tumor-initiating capacity. In a complementary clinical trial, breast cancer biopsies taken before and after treatment with GSI (MK-0752, Merck) were characterized for expression of CD44, CD24, and ALDH by FACS and for MSFE. Results and Conclusions: In preclinical studies using two independent triple negative xenograft lines, Notch pathway inhibition reduced mammosphere formation but did not affect tumor volume, with no consistent change in marker expression by FACS. In patient samples, MSFE also declined after the first cycle of GSI/chemotherapy and remained low after subsequent cycles. This response corresponded with a stasis of metastatic growth during five cycles of treatment, but metastatic burden began to increase coincident with the sixth cycle of treatment. Marker analysis suggests that GSI treatment chemo-sensitizes a significant proportion of the otherwise chemo-resistant CD44+/CD24-/low cell population indicating that they are dependent on the Notch pathway for survival. The decrease of MSFE in both preclinical and clinical studies suggests that inhibition of the Notch pathway by GSI may reduce the number of tumorigenic cancer cells that would otherwise remain after chemotherapy.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 48.