Landslides on Ceres: Diversity and Geologic Context

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first-order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta-like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice.

Abstract P5-03-03: Antitumor Activity and Cancer Stem Cells Effect of Cetuximab in Combination with Ixabepilone in Triple Negative Breast Cancers (TNBC)

Purpose: The ErbB family, including EGFR, has been demonstrated to play key roles in metastasis, tumorigenesis, cell proliferation, and drug resistance. Recently, these characteristics have been linked to a small subpopulation of cells classified as cancer stem cells (CSCs) which are believed to be responsible for tumor initiation and maintenance. Ixabepilone is the microtubule-stabilizing agent has been expected to be more sensitive than the conventional taxanes. The aim of this study was to investigate whether the EGFR monoclonocal antibody cetuximab, in combination with ixabepilone is a more effective treatment, and kill cancer stem cells more effectively as compared to chemotherapy alone in TNBC.

Experimental Design and Results: Breast CSC populations were evaluated with FACS analysis (CD44+ and CD24−/low, or Aldefluor+) and mammosphere formation efficiency (MSFE). In vitro, we demonstrated that in triple negative cell lines (MDA-MB-231 and SUM159), cancer stem cell populations were decreased after treatment of cetuximab, or cetuximab plus ixabepilone. In vivo, cetuximab in combination with ixabepilone treatment caused significant tumor regression (cetuximab vs. cetuximab+ ixabepilone; tumor volume fold change P <0.05 (MDA-MB-231), P <0.0001 (SUM159) in triple negative breast cancer xenografts. Thus, cetuximab decreased CSC population in xenograft tumors. Decrease in autophagy (LC3b, p62 and autophagosomes) were seen in cetuximab-treated tumors.

Conclusions: These studies demonstrate that cetuximab in combination with ixabepilone is more effective than chemotherapy alone in TNBC by affecting CSCs, as well as bulk tumor. These data support a neoadjuvant phase II study comparing ixabepilone vs. ixabepilone +cetuximab in TNBC patients.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-03-03.

P3-17-02: Targeting the Autophagy Pathway for Drug Resistance of Breast Tumor-Initiating Cells

Background: Our clinical data and experimental evidence reveal that the tumor-initiating cells (TICs) in the original tumor are intrinsically resistant to conventional chemotherapy and radiation therapy and greatly enriched in residual breast cancers after such treatments. We have published a gene expression signature of such breast TICs, and our pathway analysis on the gene signature suggests that the activation of autophagy pathway may be an intrinsic characteristic of the TICs. This motivates us to further investigate the role of the autophagy pathway in TICs self-maintenance and their resistance to hormonal and chemo therapies, as well as their response to TIC-targeted therapies.

Methods: A collective 84 well-documented autophagy pathway genes were used to compare the activation of autophagy pathway in different microarray datasets, 1) flow-sorted CD44+/CD24−/low cancer cells vs. all other cells (representing 20 patients), and cancer-derived MSs vs. corresponding primary bulk tumors (representing 17 patients), 2) before vs. after letrozole and doxetaxel treatments (representing 30 patient pairs), 3) before vs. after letrozole treatment (representing 176 patient pairs), and 4) before vs. after lapatinib treatment (representing 115 patient pairs). We applied the Significance Analysis of Microarrays (SAM) algorithm to analyze the expression data of 211 normalized probes for the 84 genes. Low-density RTPCR array for the 84 genes was used to confirm the differential expressed genes on tumor tissues of 18 letrozol treated patient pairs. Two human-cancer-in-mouse triple-negative xenograft tumor lines were treated with Notch pathway inhibitor alone or in combining with docetaxel. The tumor growth, mammosphere formation efficiency, and the expression of autophagy marker proteins were evaluated.

Results: Overall, the enrichment analysis of the 84-gene set in all the above microarray datasets showed that the autophagy genes are significantly enriched in the differential expressed genes. In particular, 28 out of the 84 autophagy genes are significantly up-regulated in the TICs populations while 5 other autophagy genes are down-regulated with the false discovery rate (FDR) less than 0.05. For the letrozole and doxetaxel treatment microarray analysis, 34 out of the 84 autophagy genes are significantly up-regulated in the after-treatment group (p<0.01), and only 3 out of the 84 autophagy genes are down-regulated (FDR<0.05). Interestingly, significantly more autophagy genes (15 out of the 84) are down-regulated in the after-lapatinib treatment group (p<0.05), and less genes (13 out of 84) are up-regulated after lapatinib treatment, thus confirming previous observations that lapatinib may affect TICs. We confirmed these findings in two human cancer xenograft studies of Notch pathway inhibitor (GSI) to target TICs, which showed significantly reduced expressions of LC3 and p62, two autophagic markers. In both xenograft models, GSI reduced mammosphere formation efficiency compared to vehicle control (p<0.05).

Conclusion: Activation of the autophagy pathway in TICs is a promising target to combat the drug resistance of breast cancer to conventional systemic therapy.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-17-02.

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<0.05. In the AC study, 6/9 patients in the BRCA1-like group achieved pCR, vs. 0/3 in nonBRCA1-like group, p<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.

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.

Effect of preoperative donation of autologous blood on deep-vein thrombosis following total joint arthroplasty of the hip or knee

The effect of preoperative donation of autologous blood on postoperative deep-vein thrombosis was retrospectively studied in men who had been managed consecutively with elective total joint replacement of the hip or knee because of osteoarthrosis. The patients had, on the average, two of nine considered risk factors for deep-vein thrombosis. Two hundred and thirty-seven patients were evaluated postoperatively with ascending venography, and they form the basis of this study. Fifty-four patients had venographic evidence of deep-vein thrombosis of the lower extremity, with most having asymptomatic clots distal to the knee. The prevalence of deep-vein thrombosis was nineteen (16 per cent) of 116 after total hip arthroplasty, compared with thirty-five (29 per cent) of 121 after total knee arthroplasty (chi square=4.6, p=0.03). Deep-vein thrombosis developed in twenty-eight (17 per cent) of the 161 patients who had donated blood preoperatively, compared with twenty-six (34 per cent) of the seventy-six patients who had not donated blood preoperatively (chi square=7.7, p=0.006). Through logistic regression analysis, the donation of autologous blood was shown to reduce significantly the development of postoperative deep-vein thrombosis for patients managed with total knee arthroplasty (p<0.01) but not for patients managed with total hip arthroplasty. Additional neural network analysis showed the donation of autologous blood to be the most important prognostic factor in predicting the absence of postoperative deep-vein thrombosis. In addition to diminishing the need for transfusion of homologous blood after total joint arthroplasty, preoperative donation of autologous blood appears to protect against postoperative deep-vein thrombosis after total knee arthroplasty.

Removal of excess nuclear protein from cells heated in different physiological states

The relationship between heat-induced cell kill and alterations in nuclear protein content was investigated by heating quiescent 66 mouse mammary adenocarcinoma cells in three different physiological states: (1) quiescent, nutrient deprived cells (Q); (2) Q cells placed in fresh medium 2 h prior to heating (QM); and (3) Q cells made thermotolerant by a previous heat treatment (QTT). Although cell survival varied by a factor of 80, the increase in nuclear protein after a 30 min exposure to 45 degrees C was similar in Q, QM and QTT cells. Removal of the excess nuclear protein from cells in the three physiological states differed both in the percentage of the population that could remove the protein and the rate at which the protein was removed. While all of the QM and QTT cells removed the excess nuclear protein, approximately 30% of the Q cells did not remove the excess nuclear protein, and continued to accumulate protein over the 48 h after the heat treatment. The time for complete removal of the excess protein (Q, 32 h: QM, 18 h: QTT, 8 h) was directly correlated with cell survival. Therefore, these data support the hypothesis that the removal of excess nuclear protein after heat treatment is related to and, perhaps, a determinant of, cell survival.