Abstract P1-07-03: Reproductive factors and subtype specific breast cancer risk

Introduction: Reproductive history and breast cancer risk reportedly differ by the estrogen receptor (ER±) and by the joint expression of ER and the human epidermal growth factor-2 receptor (ER±/HER2±). However, large sample sizes are needed to identify risk factor associations for the relatively less common ER- subtypes.

Material and Methods: We, therefore, linked two large-scale and population-based Danish registries to assess the associations for parity, number of live births, and age at first live birth (AFLB) with receptor-specific breast cancer risk. Relative risks (RRs) and 95% confidence intervals (CIs) for associations were estimated with Poisson regression models.

Results: With nearly 31 million women-years of follow-up, there were 45786 Danish women between the ages 20-84 years who developed an invasive breast cancer during the study period 1992-2011. Parity significantly reduced risk for ER+ and ER+/HER2- subtypes (RR for ER+/HER2- = 0.92; 0.87, 0.98) and suggestively increased risk for ER- and ER-/HER2- subtypes (RR for ER-/HER2- = 1.16; 0.99, 1.36). RRs increased with advancing AFLB for ER+ cancers, especially among premenopausal women; and were elevated for ER- cancers among age groups 12-19 years and 30-34 years compared to the reference age group 20-24 years.

Conclusion: Associations of breast cancer risk and reproductive history varied among Danish women by ER± and by ER±/HER2±, consistent with receptor-specific etiological heterogeneity. Risk estimates for ER+ and ER+/HER2- cancers were similar to the well-established associations for breast cancer overall, whereas relative risks for ER- and ER/HER2- cancers tended to be null or the inverse of ER+ associations.

Citation Format: Anderson WF, Pfeiffer RM, Wohlfahrt J, Ejlertsen B, Jensen M-B, Kroman NT. Reproductive factors and subtype specific breast cancer risk. [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 P1-07-03.

Abstract P1-07-04: Etiologic heterogeneity in breast cancer across quantitative levels of estrogen receptor expression

Introduction: The clinical classification of breast cancer into at least four intrinsic subtypes has advanced targeted therapy and improved prognosis. However, for etiological classification, it has been proposed that breast cancer is comprised of just two main subtypes: basal-like and non-basal-like. Evidence for these two etiologic subtypes emerges strongly from bimodal age frequency distributions at diagnosis. In the absence of RNA-based intrinsic subtyping, estrogen receptor (ER) expression is a useful surrogate for these two distinct etiologic classes. Using data from the population-based Carolina Breast Cancer Study (CBCS), we examined evidence for a two-component (ER-positive vs. ER-negative) mixture model for breast cancer biologic/etiologic heterogeneity.

Methods: Automated digital scoring of ER expression was performed on immunohistochemistry-stained tissue microarrays comprising 1,920 invasive breast cancer cases from CBCS. Clinical classification of ER status has changed over time as new data have emerged regarding optimal treatment-relevant thresholds, but optimal etiologic thresholds have not been established. Therefore, we considered ER status as a quantitative, categorical variable with cut points of <1% (ER-negative) vs. ≥1% (ER-positive), with ER-positive cases further categorized as highly positive (≥80-100%), intermediate (≥40-<80%), low (≥10-<40%) or borderline (≥1-<10%). Smoothed age frequency distributions at diagnosis (i.e., density plots) were constructed and logistic regression adjusted for age and race was conducted to assess associations between patient and tumor characteristics and level of ER positivity.

Results: As expected for etiologically-distinct entities, ER-negative and highly ER-positive tumors showed predominantly unimodal early-onset and late-onset age distributions at diagnosis with peak frequencies near ages 50 and 70 years, respectively. However, tumors with low and intermediate positivity showed bimodal patterns, consistent with a mixture of two main subtypes. Consistent with these age distribution patterns, young age (<40 years) at diagnosis was associated with an elevated odds ratio (OR) for low positive (OR 1.8; 95% CI 1.1-2.9), borderline (OR 1.9; 95% CI 1.1-3.3) and ER-negative disease (OR 2.2; 95% CI 1.5-3.2). Relative to highly ER-positive tumors, low ER-positive tumors were more likely to be node-positive (OR 1.4; 95% CI 1.0-1.9), higher grade (combined grade III; OR 1.9; 95% CI 1.3-2.9), and were more likely to harbor a p53 mutation (OR 2.0; 95% CI 1.2-3.5).

Conclusions: While etiologic differences between dichotomized ER-negative and ER-positive breast cancer categories have been well described in many epidemiologic studies, differences in breast cancer etiology across quantitative levels of ER expression have not been so well-characterized. In this study, we report that ER-positive tumors with low positivity share etiologic features of ER-negative tumors, including young age at diagnosis and aggressive tumor characteristics. These data provide additional support for a two-component breast cancer mixture model, with quantitative level of ER positivity reflecting the relative distributions of ER-positive and ER-negative tumor populations.

Citation Format: Allott EH, Tse C-K, Carey L, Anderson WF, Olshan AF, Troester MA. Etiologic heterogeneity in breast cancer across quantitative levels of estrogen receptor expression. [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 P1-07-04.

Crystal structures of the components of the Staphylococcus aureus leukotoxin ED

Staphylococcal leukotoxins are a family of β-barrel, bicomponent, pore-forming toxins with membrane-damaging functions. These bacterial exotoxins share sequence and structural homology and target several host-cell types. Leukotoxin ED (LukED) is one of these bicomponent pore-forming toxins that Staphylococcus aureus produces in order to suppress the ability of the host to contain the infection. The recent delineation of the important role that LukED plays in S. aureus pathogenesis and the identification of its protein receptors, combined with its presence in S. aureus methicillin-resistant epidemic strains, establish this leukocidin as a possible target for the development of novel therapeutics. Here, the crystal structures of the water-soluble LukE and LukD components of LukED have been determined. The two structures illustrate the tertiary-structural variability with respect to the other leukotoxins while retaining the conservation of the residues involved in the interaction of the protomers in the bipartite leukotoxin in the pore complex.

Abstract ES05-2: Divergent trends in breast cancer subtypes, a manifestation of cancer heterogeneity

Recent studies in the United States show an unexpected divergence of ER positive and ER negative breast cancer incidence rates (JNCI 103: 1397-1402, 2011). ER positive cancers have risen while ER negative cancers have declined over the long-term. Divergent ER-specific trends might reflect statistical anomalies, lower assay thresholds for classifying breast cancers as ER positive, and/or the implementation of widespread screening mammography with increased sensitivity for ER positive cancers. However, the analysis of secular trends in Denmark, where there was better control of these potentially confounding factors, showed similar trends as in the United States (IJC 133: 2201-2206, 2013). ER positive cancers had increased among middle-aged and older Danish women in earlier birth-cohorts (or generations), implying a confluence of risk factor exposures during the peri- and the post-menopausal time periods of a woman's lifetime. In contrast, ER negative cancers had decreased among younger women in more recent birth-cohorts during the premenopausal time periods.

Divergent ER-specific trends among different birth-cohorts in younger and older generations is consistent with breast cancer heterogeneity due to distinct etiologic pathways for ER positive and ER negative breast cancers, which could be due to trends in environmental and lifestyle risk factors with dual effects by ER expression. Two such possible risk factors are pregnancy (or parity) and obesity, which are decreasing and increasing, respectively, in both the United States and Denmark. For example, parity tends to reduce breast cancer risk for ER positive cancer and to increase risk for ER negative cancers. In fact, new breast cancer cases appear to be rising worldwide due to the consequences of changing reproductive, hormonal, and dietary risk factors. For this reason, it is plausible that the same risk factors or at the least risk factors acting through common mechanisms in the United States and Denmark may foreshadow a common pattern worldwide. This is good news since ER negative breast cancers are the most difficult to treat subtypes of breast cancer, especially the so-called triple negative cancers.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr ES05-2.

Crystal structure of the novel PaiA N-acetyltransferase from Thermoplasma acidophilum involved in the negative control of sporulation and degradative enzyme production

GCN5-related N-acetyltransferases (GNATs) are the most widely distributed acetyltransferase systems among all three domains of life. GNATs appear to be involved in several key processes, including microbial antibiotic resistance, compacting eukaryotic DNA, controlling gene expression, and protein synthesis. Here, we report the crystal structure of a putative GNAT Ta0374 from Thermoplasma acidophilum, a hyperacidophilic bacterium, that has been determined in an apo-form, in complex with its natural ligand (acetyl coenzyme A), and in complex with a product of reaction (coenzyme A) obtained by cocrystallization with spermidine. Sequence and structural analysis reveals that Ta0374 belongs to a novel protein family, PaiA, involved in the negative control of sporulation and degradative enzyme production. The crystal structure of Ta0374 confirms that it binds acetyl coenzyme A in a way similar to other GNATs and is capable of acetylating spermidine. Based on structural and docking analysis, it is expected that Glu53 and Tyr93 are key residues for recognizing spermidine. Additionally, we find that the purification His-Tag in the apo-form structure of Ta0374 prevents binding of acetyl coenzyme A in the crystal, though not in solution, and affects a chain-flip rotation of "motif A" which is the most conserved sequence among canonical acetyltransferases.

Structural genomics and drug discovery for infectious diseases

The application of structural genomics methods and approaches to proteins from organisms causing infectious diseases is making available the three dimensional structures of many proteins that are potential drug targets and laying the groundwork for structure aided drug discovery efforts. There are a number of structural genomics projects with a focus on pathogens that have been initiated worldwide. The Center for Structural Genomics of Infectious Diseases (CSGID) was recently established to apply state-of-the-art high throughput structural biology technologies to the characterization of proteins from the National Institute for Allergy and Infectious Diseases (NIAID) category A-C pathogens and organisms causing emerging, or re-emerging infectious diseases. The target selection process emphasizes potential biomedical benefits. Selected proteins include known drug targets and their homologs, essential enzymes, virulence factors and vaccine candidates. The Center also provides a structure determination service for the infectious disease scientific community. The ultimate goal is to generate a library of structures that are available to the scientific community and can serve as a starting point for further research and structure aided drug discovery for infectious diseases. To achieve this goal, the CSGID will determine protein crystal structures of 400 proteins and protein-ligand complexes using proven, rapid, highly integrated, and cost-effective methods for such determination, primarily by X-ray crystallography. High throughput crystallographic structure determination is greatly aided by frequent, convenient access to high-performance beamlines at third-generation synchrotron X-ray sources.

Population profiles of extra-ovarian and ovarian serous adenocarcinomas: Comparisons with grade stratification

e16506

Background: Molecular studies of ovarian serous adenocarcinomas (OSC) have linked distinct patterns of gene expression or mutations to high or low tumor grade. This heterogeneity appears to be mirrored in two population subgroups delineated by age-specific incidence rates (ASIR) stratified by grade. We aimed to determine whether serous adenocarcinomas of the peritoneum (PSC) or fallopian tubes (FSC) comprised grade-related subgroups comparable to OSC. Methods: Data for women with invasive OSC (25,997 cases), PSC (2,157), and/or FSC (618) registered in the NCI's Surveillance, Epidemiology, and End Results program (1976–2005) were analyzed. Incidence rates (IR) stratified by grade were compared by year or age of diagnosis. Descriptive analyses were supplemented with tests for trend or age interaction by grade. Cancer-specific survival also was compared by grade (Kaplan-Meier estimator). Results: We observed trend interactions by grade for OSC, PSC, and FSC (p < 0.001); age-adjusted incidence rates rose more rapidly for high than low grade tumors over time. ASIR for OSC/PSC were higher for low than high grade tumors prior to age 40 years, after which rates became higher for high grade (p < 0.001 for age interaction by grade). ASIR were similar for FSC but interpretation was limited by small sample sizes. Unilateral carcinomas were far more common for FSC than OSC (90.9% versus 40.6%). Actuarial cancer-specific cumulative survival was worse for high than low grade tumors (all anatomic sites). Conclusions: Trend and survival analyses both were consistent with a biologically significant high/low grade stratification of OSC, PSC, and FSC. For PSC, significant correlations to ASIR by high/low grade were consistent with two population subgroups as defined for OSC; and also appeared congruent with molecular models that project dual pathways of carcinogenesis. For FSC, definitive correlations will require larger sample sizes.

No significant financial relationships to disclose.

Divergent cancer pathways for early-onset and late-onset cutaneous malignant melanoma

9079

Background: Emerging data suggest that cutaneous malignant melanomas (CMM) may arise through divergent cancer pathways, linked to intermittent versus accumulated sun exposure. However, numerous questions remain regarding the timing and/or age of exposure. Methods: We, therefore, systematically examined the effect of aging upon CMM incidence in the Surveillance, Epidemiology, and End Results program of the National Cancer Institute. Standard descriptive epidemiology was supplemented with mathematical models. The impact of advancing age upon CMM incidence was assessed by gender, histopathological subtype (superficial spreading melanoma (SSM) or lentigo maligna melanoma [LMM]), and anatomic site (face, head, and neck [FHN] or lower extremity [LE]). Results: Gender, histopathological and anatomic site were age-specific effect modifiers for CMM, showing divergent (or bimodal) early- and late-onset cancer pathways. Early-onset melanomas were predominantly associated with female gender, SSM, and LE. Late- onset melanomas were correlated with male gender, LMM, and FHN. Early- and late-onset melanoma populations were confirmed with age-period-cohort models (adjusted for period and cohort effects) and two-component mixture models. Conclusions: These results are consistent with a divergent and age-dependent solar hypothesis for CMM. Early-onset melanomas may represent gene-sun exposure interactions occurring early (and/or intermittently) in life among susceptible individuals. Late-onset melanomas possibly reflect accumulated lifelong sun exposure in comparatively less susceptible individuals. Future analytical studies should be adequately powered to account for this age-dependent effect modification for acknowledged (gender, histopathology, and anatomic site) as well as suspected melanoma risk factors such as constituent genetic variants.

No significant financial relationships to disclose.

The black to white breast cancer incidence rate crossover

Abstract #2086

Background: Although breast cancer incidence rates are higher among Blacks than Whites prior to age 40 years, the reverse is true after age 40 years. This so-called Black to White ethnic crossover has been described but never systematically studied.&#x2028; Materials and Methods: To further assess the Black to White incidence rate crossover, we obtained data from the National Cancer Institute's Surveillance, Epidemiology, and End Results program. Invasive female breast cancers were stratified by Black and White race and estrogen receptor (ER) expression. Standard descriptive epidemiology was supplemented with “comparative” age-period-cohort (APC) models.&#x2028; Results:]We observed “qualitative” (reversing or crossing) age-interactions by race, stratified by birth-cohort and adjusted for calendar-period. For example, APC fitted age-at-onset curves were higher among Blacks than Whites prior to age 40 years, and then rates crossed, after which age-specific rates were higher for Whites (p ∼ 0 for difference). In contrast to age-related differences, secular trends were similar for Blacks and Whites (net drifts, p = 0.85 for difference). For all time periods and age groups, ER negative incidence rates were higher among Blacks, whereas ER positive rates were higher among Whites.&#x2028; Conclusion: When viewed as a qualitative (crossing) age-interaction, the Black to White ethnic crossover reflects the reversal of incidence rate ratios for early-onset/poor prognosis and late-onset/good prognosis breast cancer types. Blacks have more early-onset and ER-negative tumors, even after adjustment for calendar-period (screening) and birth-cohort (exposure) effects.&#x2028; &#x2028;

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2086.

Human epidermal growth factor receptor-2 and estrogen receptor expression, a demonstration project using the residual tissue repository of the Surveillance, Epidemiology, and End Results (SEER) program

BACKGROUND

In 2001, the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program established Residual Tissue Repositories (RTR) in the Hawaii, Iowa, and Los Angeles Tumor Registries to collect discarded tissue blocks from pathologic laboratories within their catchment areas. To validate the utility of the RTR for supplementing SEER's central database, we assessed human epidermal growth factor receptor-2 (HER2) and estrogen receptor expression (ER) in a demonstration project.

MATERIALS

Using a prepared set of tissue microarrays (TMAs) residing in the Hawaii Tumor Registry (HTR), we performed standard immunohistochemistry. Breast cancers in the TMA were diagnosed in 1995, followed through 2006, and linked to SEER's main database.

RESULTS

The TMA included 354 cases, representing 51% of 687 breast cancers in the HTR (1995). The HTR and TMA cases were similar with respect to patient demographics and tumor characteristics. Seventy-six percent (76%, 268 of 354) of TMA cases were HER2+ and/or ER+, i.e., 28 HER2+ER-, 12 HER2+ER+, and 228 HER2-ER+. There were 67 HER2-ER- cases and 19 were unclassified. Age distributions at diagnosis were bimodal with dominant early-onset modes for HER2+ER- tumors and dominant late-onset modes for HER2-ER+ breast cancers. Epidemiologic patterns for concordant HER2+ER+ (double-positive) and HER2-ER- (double-negative) were intermediate to discordant HER2+ER- and HER2-ER+.

CONCLUSION

Results showed contrasting incidence patterns for HER2+ (HER2+ER-) and ER+ (HER2-ER+) breast cancers, diagnosed in 1995. Though sample sizes were small, this demonstration project validates the potential utility of the RTR for supplementing the SEER program.

Qualitative age interactions (or effect modification) suggest divergent pathways for early-onset and late-onset breast cancers

21036

Background: Notwithstanding some recent declines, breast cancer incidence rates have risen for decades, though not equally for all age groups. We used the National Cancer Institute's SEER program to further explore the effect of aging upon breast cancer incidence. Materials and Methods: The SEER program collected data on n=494,543 in-situ + invasive female breast cancer cases, newly diagnosed during 1974–2003. Temporal trends by race, stage, and grade were stratified by age at diagnosis in decades: 20–29 to 80+ years. Results: We observed age interactions over time. For example, as the specification of grade improved from 1974–2003, temporal trends for high and low grade tumors varied with age. Among women ages <40 years, high grade lesions were more common than low grade tumors for all time periods. Among women ages 40+ years, high grade lesions were more common during the early years, and then rates crossed, after which low-grade tumors were more common than high grade lesions. Conclusion: Age at diagnosis was both a quantitative (non- crossover) and qualitative (crossover) effect modifier. The crossing of rates from high to low grade tumors among women ages 40+ years in the 1980s is consistent with more aggressive breast cancer screening, with mammography preferentially detecting low grade tumors among women targeted for screening, i.e., ages 40–80 years. Though once thought to be rare or artifactual, qualitative interactions or effect modification suggest etiologic heterogeneity in an otherwise homogeneous disease process. Indeed, if true, qualitative age interactions imply divergent pathways for early-onset and late-onset breast cancers.

No significant financial relationships to disclose.

Bimodal breast cancer incidence patterns provide support for a dualistic model of mammary carcinogenesis

595

Background: Although breast cancers are extremely heterogeneous with respect to clinical presentation, histopathological appearance, and molecular alterations; breast cancer is often viewed as a single biologic entity with common etiology and unified pathogenesis. Accumulating data has challenged this view, demonstrating that the stratification of tumors by gene expression profiles, immunohistochemical (IHC) staining patterns, and other techniques may permit the categorization of breast cancers into two main pathways of mammary carcinogenesis. Based upon cellular origin and/or estrogen receptor (ER) expression there are 1) tumors from stem cells committed to luminal differentiation and ER expression and 2) neoplasms from stem cells programmed to display basal differentiation and lacking ER expression. If confirmed, these observations may form the basis for revised conceptual frameworks. Methods:: We applied age-at-diagnosis density plots and a two component statistical mixture model to breast cancer cases overall (n=270,124) in the SEER program. These age distributions were reevaluated after stratification by histopathologic type, race, and ER. Results: A bimodal distribution provided a better fit for the age distribution patterns than a single distribution for breast cancers overall and for all histologic types, except medullary carcinoma. However, the proportion of early-onset and late-onset tumors varied: ductal and tubular carcinomas demonstrated relatively equal proportions; lobular, papillary and mucinous tumors were associated with late-onset populations; and inflammatory and medullary tumors were more related to early-onset disease. Medullary carcinomas were exceptional in showing a single distribution irrespective of race and/or ER status. Of note, medullary breast carcinomas are rare tumors that are associated with germline mutations in BRCA1. Conclusion: Most histopathologic types of breast carcinomas demonstrated a bimodal mixture of early- and late-onset cancer populations, possibly representing two major age-related causal pathways. These population-based results seem consistent with emerging molecular data, showing two main classes of breast cancer based upon cellular origin and ER expression.

No significant financial relationships to disclose.

Established breast cancer risk factors by clinically important tumour characteristics

Breast cancer is a morphologically and clinically heterogeneous disease; however, it is less clear how risk factors relate to tumour features. We evaluated risk factors by tumour characteristics (histopathologic type, grade, size, and nodal status) in a population-based case-control of 2386 breast cancers and 2502 controls in Poland. Use of a novel extension of the polytomous logistic regression permitted simultaneous modelling of multiple tumour characteristics. Late age at first full-term birth was associated with increased risk of large (> 2 cm) tumours (odds ratios (95% confidence intervals) 1.19 (1.07-1.33) for a 5-year increase in age), but not smaller tumours (P for heterogeneity adjusting for other tumour features (Phet) = 0.007). On the other hand, multiparity was associated with reduced risk for small tumours (0.76 (0.68-0.86) per additional birth; Phet = 0.004). Consideration of all tumour characteristics simultaneously revealed that current or recent use of combined hormone replacement therapy was associated with risk of small (2.29 (1.66-3.15)) and grade 1 (3.36 (2.22-5.08)) tumours (Phet = 0.05 for size and 0.0008 for grade 1 vs 3), rather than specific histopathologic types (Phet = 0.63 for ductal vs lobular). Finally, elevated body mass index was associated with larger tumour size among both pre- and postmenopausal women (Phet = 0.05 and 0.0001, respectively). None of these relationships were explained by hormone receptor status of the tumours. In conclusion, these data support distinctive risk factor relationships by tumour characteristics of prognostic relevance. These findings might be useful in developing targeted prevention efforts.

Reproduction of Meloidogyne spp. on Resistant Peanut Genotypes from Three Breeding Programs

Three described species of root-knot nematode parasitize peanut (Arachis hypogaea): Meloidogyne arenaria race 1 (Ma), M. hapla (Mh), and M. javanica (Mj). Peanut cultivars with broad resistance to Meloidogyne spp. will be useful regardless of the species present in the field. The objective of this study was to determine whether peanut genotypes with resistance to M. arenaria originating from three different breeding programs were also resistant to M. hapla and M. javanica. The experiment used a factorial arrangement (completely randomized) with peanut genotype and nematode population as the factors. The five peanut genotypes were 'COAN' and AT 0812 (highly resistant to Ma), C209-6-13 (moderately resistant to Ma), and 'Southern Runner' and 'Georgia Green' (susceptible to Ma). The four nematode populations were two isolates of Ma (Gibbs and Gop) and one isolate each of Mh and Mj. On COAN or AT 0812, both Ma and Mj produced <10% of the eggs produced on Georgia Green. On the peanut genotype C209-6-13, Ma and Mj produced about 50% of the eggs produced on Georgia Green. None of the resistant genotypes exhibited a high level of resistance to Mh. The lack of resistance to Mh in any cultivars or advanced germplasm is a concern because the identity of a Meloidogyne sp. in a particular peanut field is generally not known. Breeding efforts should focus on moving genes for resistance to M. hapla into advanced peanut germplasm, and combining genes for resistance to the major Meloidogyne spp. in a single cultivar.

Geographic variation in breast cancer mortality for white and black women: 1986-1995

Breast cancer mortality rates have decreased during the last 20 years in the United States overall. However, declines in breast cancer mortality rates differ among individual states. This analysis ranked states from the highest to the lowest percentage change in mortality between 1986 to 1990 and 1991 to 1995. Data on white and black females were analyzed separately. Among white women, the 10 states showing the greatest percentage change in mortality during those two periods had the greatest baseline mortality in the 1986-to-1990 period. Similarly, the 10 states with the lowest percentage change in mortality had the lowest mortality rate in 1986 to 1990. In contrast, among black women, the top 10 states ranked by percentage change in mortality included either a decline or an increase. The disparities in mortality rates by state likely depend on the stage of disease at diagnoses, socioeconomic status, access to care, and adequacy of medical care.

Retroviral vectors bearing IgG-binding motifs for antibody-mediated targeting of vascular endothelial growth factor receptors

Targeting retroviral vectors to tumor vasculature is an important goal of cancer gene therapy. In this study, we report a novel targeting approach wherein IgG-binding peptides were inserted into the Moloney murine leukemia virus (MuLV) envelope (env) protein. The modifications on the viral env included replacement of the entire receptor binding region of the viral env with protein A (or ZZ) domains. The truncated env incorporating IgG-binding motifs (known as proteins) provided the targeting function, while the co-expressed wild-type (WT) env protein enabled viral fusion and cell entry. An anti-human VEGF receptor (Flk-1/KDR) antibody served as a molecular bridge, directing the retroviral vector to the endothelial cell. Hence, the IgG-targeted vectors bound to the Flk-1/KDR antibody which in turn bound to VEGF receptors on Kaposi sarcoma, KSY1, endothelial cells. The net effect was increased viral fusion and infectivity of IgG-bound retroviral vectors when compared to non-targeted vectors bearing WT env alone. These data provide the proof of concept that IgG-binding vector/VEGF receptor antibody complexes may be used to enhance retroviral gene delivery to activated endothelial cells.

Recent advances in retrovirus vector-mediated gene therapy: teaching an old vector new tricks

Oncoretrovirus-based vectors have been shown to be a safe and reliable vector system that can achieve permanent integration of delivered transgenes. Successful application of these vectors for gene therapy has proven difficult due to their relatively low transduction efficiency; however, cumulative improvements in methodology have recently yielded promising clinical results. Furthermore, significant improvements in basic retrovirus vector technology now promise to revitalize the field. This review focuses on these important recent developments in the field of retrovirus-mediated gene transfer technology and its application to human diseases.

Quantitation of retroviral-mediated transfer using luciferase in living and lysed cells

We have developed a murine retroviral vector containing an improved luciferase gene for the study of retroviral gene transfer and expression in living or lysed cells. We used a cytosolic form of luciferase gene (luc+) with transcriptional enhancements that yielded greater expression levels. The luc+ gene was subcloned into the retroviral plasmids pDON-AI, in which almost the entire U3 region has been replaced with the heterologous human cytomegalovirus immediate-early promoter A stable ecotropic and amphotropic retrovirus-producing cell line was generated with a titer 1 x 10(6) cfu/mL. NIH/3T3(tk-) cells transduced with ecotropic luciferase retrovirus demonstrated a high level of luminescence on the third day. Lysed NIH/3T3(tk-) cells demonstrated a 10-fold increase in activity as compared to living cultures. The creation of a new retroviral system allowed a substantial decrease to 5 days from the 10-14 days previously needed to evaluate viral transfer using the standard neomycin method. Our assay also provides a quantitative assessment in contrast to the beta-galactosidase detection method, which also takes 5-6 days but lacks quantitative evaluation. Thus, the expression of an integrated luc+ gene in eukaryotic cells provides a powerful tool for the study of retroviral gene transfer and will greatly facilitate functional studies in both living and lysed cells.

Lesion-targeted injectable vectors for vascular restenosis

Pathologic lesions caused by catheter-based revascularization procedures for occlusive artery disease include disruption of the endothelium, exposure of extracellular matrix (ECM) proteins, and proliferation of vascular smooth muscle cells, which lead to neointima formation and restenosis. We have developed matrix-collagen-targeted retroviral vectors that are able to accumulate at sites of vascular injury (Hall et al., Hum. Gene Ther. 1997;8:2183-2192; Hall et al., Hum. Gene Ther. 2000;11:983-993). The primary tissue-targeting motif, adapted from the physiological surveillance sequence found in von Willebrand factor, served to localize and concentrate the vector within vascular lesions. In the present study, we evaluated the efficiency of this vector-targeting system in rats with nonligated balloon-injured carotid arteries. Both intraarterial (by retrograde femoral artery catheterization) and intravenous (via femoral vein) injection of a matrix-targeted vector enhanced transduction of neointimal cells ( approximately 20%) at severely denuded areas when compared with the nontargeted vector (<1%). Further, intraarterial instillation of a matrix-targeted, but not a nontargeted, vector bearing an antisense cyclin G1 construct inhibited neointima lesion formation in the injured carotid arteries. Taken together, these data indicate that strategic targeting of retroviral vectors to vascular lesions would have therapeutic potential in the management of vascular restenosis and many other disorders of uncontrolled proliferation where endothelial disruption, ECM remodeling, and collagen deposition form the nexus for preferential vector localization and concentration in vivo.

Frequency distributions of breast cancer characteristics classified by estrogen receptor and progesterone receptor status for eight racial/ethnic groups

BACKGROUND

The National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) cancer registries have been collecting data regarding estrogen receptor (ER) and progesterone receptor (PR) status in breast cancer since 1990. The current study reports on some of these data for eight racial/ethnic groups.

METHODS

Stratified by ER and PR status, the frequency distributions of 112,588 breast cancer cases diagnosed between 1992--1997 in 11 SEER cancer registries were examined by age at diagnosis, stage at diagnosis, histologic grade, and tumor type for white, black, Hispanic, Japanese, Chinese, Filipino, Native Hawaiian, and American Indian and Alaska Native (AI/AN) females.

RESULTS

For each racial/ethnic group, the percentage of ER positive (+)/PR+ was > ER-PR- > ER+PR- > ER-PR+ tumors. For the two major ER/PR groups, the ER+PR+ tumors were different from the ER-PR- tumors in several ways. For white females, there were differences in the age distributions, stage at diagnosis, and histologic grade. For black females, the differences involved the age distributions and tumor grades. For Hispanic and Japanese females, there were differences with regard to the age distributions and tumor grades. For Filipino, Chinese, and AI/AN females, the tumor stages and grades differed. For Native Hawaiians, the histologic tumor grades were different.

CONCLUSIONS

For each racial/ethnic group, the ER/PR status appeared to divide breast cancer patients into two or more subgroups with unique tumor characteristics. In general, ER status appeared to have the greatest impact on delineating these subgroups, whereas in some cases, PR status was able to modify the subgroups further. It is hoped that reporting these tumor characteristics by ER/PR status for each racial/ethnic group will spur more investigation into the significance of ER/PR status in each racial/ethnic group.

Induction of stable prenatal tolerance to beta-galactosidase by in utero gene transfer into preimmune sheep fetuses

The successful transduction of hematopoietic stem cells and long-term (28 months) transgene expression within the hematopoietic system following the direct injection of high-titer retroviral vectors into preimmune fetal sheep was previously demonstrated. The present studies extended these analyses for 40 months postinjection and evaluated whether the longevity of transgene expression in this model system was the result of induction of prenatal tolerance to the transgene product. The intraperitoneal injection of retroviral vectors into preimmune sheep fetuses transduces thymic epithelial cells thought to present antigen and thus define self during immune system development. To directly demonstrate induction of tolerance, postnatal sheep were boosted with purified beta-galactosidase and showed that the peripheral blood lymphocytes from in utero-transduced sheep exhibited significantly lower stimulation indices to transduced autologous cells than did control animals and that the in utero-transduced sheep had a reduced ability to mount an antibody response to the vector-encoded beta-galactosidase protein compared with control sheep. Collectively, our results provide evidence that the direct injection of retroviral vectors into preimmune sheep fetuses induces cellular and humoral tolerance to the vector/transgene products and provide an explanation for the duration and stability of transgene expression seen in this model. These results also suggest that even relatively low levels of gene transfer in utero may render the recipient tolerant to the exogenous gene and thus potentially permit the successful postnatal treatment of the recipient. (Blood. 2001;97:3417-3423)

Infectious entry by amphotropic as well as ecotropic murine leukemia viruses occurs through an endocytic pathway

Infectious entry of enveloped viruses is thought to proceed by one of two mechanisms. pH-dependent viruses enter the cells by receptor-mediated endocytosis and are inhibited by transient treatment with agents that prevent acidification of vesicles in the endocytic pathway, while pH-independent viruses are not inhibited by such agents and are thought to enter the cell by direct fusion with the plasma membrane. Nearly all retroviruses, including amphotropic murine leukemia virus (MuLV) and human immunodeficiency virus type 1, are classified as pH independent. However, ecotropic MuLV is considered to be a pH-dependent virus. We have examined the infectious entry of ecotropic and amphotropic MuLVs and found that they were equally inhibited by NH4Cl and bafilomycin A. These agents inhibited both viruses only partially over the course of the experiments. Agents that block the acidification of endocytic vesicles also arrest vesicular trafficking. Thus, partial inhibition of the MuLVs could be the result of virus inactivation during arrest in this pathway. In support of this contention, we found that that the loss of infectivity of the MuLVs during treatment of target cells with the drugs closely corresponded to the loss of activity due to spontaneous inactivation at 37 degrees C in the same period of time. Furthermore, the drugs had no effect on the efficiency of infection under conditions in which the duration of infection was held to a very short period to minimize the effects of spontaneous inactivation. These results indicate that the infectious processes of both ecotropic and amphotropic MuLVs were arrested rather than aborted by transient treatment of the cells with the drugs. We also found that infectious viruses were efficiently internalized during treatment. This indicated that the arrest occurred in an intracellular compartment and that the infectious process of both the amphotropic and ecotropic MuLVs very likely involved endocytosis. An important aspect of this study pertains to the interpretation of experiments in which agents that block endocytic acidification inhibit infectivity. As we have found with the MuLVs, inhibition of infectivity may be secondary to the block of endocytic acidification. While this strongly suggests the involvement of an endocytic pathway, it does not necessarily indicate a requirement for an acidic compartment during the infectious process. Likewise, a lack of inhibition during transient treatment with the drugs would not preclude an endocytic pathway for viruses that are stable during the course of the treatment.

A uniquely stable replication-competent retrovirus vector achieves efficient gene delivery in vitro and in solid tumors

A major obstacle in cancer gene therapy is the limited efficiency of in vivo gene transfer by replication-defective retrovirus vectors in current use. One strategy for circumventing this difficulty would be to use vectors capable of replication within tumor tissues. We have developed a replication-competent retrovirus (RCR) vector derived from murine leukemia virus (MuLV). This vector utilizes a unique design strategy in which an internal ribosome entry site-transgene cassette is positioned between the env gene and the 3' long terminal repeat (LTR). The ability of this vector to replicate and transmit a transgene was examined in culture and in a solid tumor model in vivo. The RCR vector exhibited replication kinetics similar to those of wildtype MuLV and mediated efficient delivery of the transgene throughout an entire population of cells in culture after an initial inoculation with 1 plaque-forming unit (PFU) of vector per 2000 cells. After injection of 6 x 10(3) PFU of vector into established subcutaneous tumors, highly efficient spread of the transgene was observed over a period of 7 weeks, in some cases resulting in spread of the transgene throughout the entire tumor. MuLV-based RCR vectors show significant advantages over standard replication-defective vectors in efficiency of gene delivery both in culture and in vivo. This represents the first example of the use of an RCR vector in an adult mammalian host, and their first application to transduction of solid tumors.

Receptor-specific targeting mediated by the coexpression of a targeted murine leukemia virus envelope protein and a binding-defective influenza hemagglutinin protein

The entry of retroviral vectors into cells requires two events: binding to a cell surface receptor and the subsequent fusion of viral and cellular membranes. The host range of a vector is therefore determined largely by the receptor specificity of the fusion protein contained in the outer viral envelope. Previous attempts to generate targeted retroviral vectors have included the addition of targeting ligands to the murine leukemia virus envelope protein (MuLV Env). Although such proteins frequently display modified cell-binding characteristics, the interaction with the targeted receptors fails to trigger virus-cell fusion. Here, we report the use of a binding-defective but fusion-competent hemagglutinin (HA) protein to complement the fusion defect in a chimeric MuLV Env targeted to the Flt-3 receptor. Retroviral vectors containing both proteins showed enhanced transduction of cells expressing Flt-3, which was abrogated by preincubating the target cells with soluble Flt-3 ligand. Furthermore, the fusion function of HA was absolutely required. These data demonstrate that it is possible to separate the binding and fusion events of retroviral entry, using two separate proteins, and suggest that varying the binding protein component in this scheme may allow a general strategy for targeting retroviral vectors.

Secondary chemoprevention of upper aerodigestive tract tumors

Patients with successfully treated upper aerodigestive tract (UADT) tumors commonly develop second primary tumors (SPTs). These tumors occur more often than chance would predict, arise in both the upper or lower aerodigestive tracts, are frequently preceded by leukoplakia, and are a major cause of treatment-related failure. Measures to control SPTs include primary prevention with tobacco and alcohol abstinence, surveillance endoscopy, and secondary chemoprevention. Chemoprevention is the administration of natural or synthetic substances to suppress or reverse the malignant process. Secondary chemoprevention of the UADT is the suppression or reversal of leukoplakia and/or SPTs. Classic antioxidant micronutrients such as retinoids, carotenoids, and certain other agents have been effective in nonrandomized and randomized clinical trials, but treatment is uncertain and recurrences common. These facts, coupled with recent harmful effects of beta-carotene in two clinical trials, stress the need for additional basic science, translational, and clinical research. Chemoprevention is a promising new technology, but is not currently standard therapy for the secondary prevention of UADT tumors.

Systemic administration of a matrix-targeted retroviral vector is efficacious for cancer gene therapy in mice

Targeting cytocidal vectors to tumors and associated vasculature in vivo is a long-standing goal of human gene therapy. In the present study, we demonstrated that intravenous infusion of a matrix (i.e., collagen)-targeted retroviral vector provided efficacious gene delivery of a cytocidal mutant cyclin G1 construct (designated Mx-dnG1) in human cancer xenografts in nude mice. A nontargeted CAE-dnG1 vector (p = 0.014), a control matrix-targeted vector bearing a marker gene (Mx-nBg; p = 0.004), and PBS served as controls (p = 0.001). Enhanced vector penetration and transduction of tumor nodules (35.7 +/- 1.4%, mean +/- SD) correlated with therapeutic efficacy without associated toxicity. Kaplan-Meier survival studies were conducted in mice treated with PBS placebo, the nontargeted CAE-dnG1 vector, and the matrix-targeted Mx-dnG1 vector. Using the Tarone log-rank test, the overall p value for comparing all three groups simultaneously was 0.003, with a trend that was significant to a level of 0.004, indicating that the probability of long-term control of tumor growth was significantly greater with the matrix-targeted Mx-dnG1 vector than with the nontargeted CAE-dnG1 vector or PBS placebo. The present study demonstrates that a matrix-targeted retroviral vector deployed by peripheral vein injection (1) accumulated in angiogenic tumor vasculature within 1 hr, (2) transduced tumor cells with high-level efficiency, and (3) enhanced therapeutic gene delivery and long-term efficacy without eliciting appreciable toxicity.

Tumor variants by hormone receptor expression in white patients with node-negative breast cancer from the surveillance, epidemiology, and end results database

PURPOSE

Hormone receptor expression (presence-positive or absence-negative) may reflect different stages of one disease or different breast cancer types. Determining whether hormone receptor expression represents one or more breast cancer phenotypes would have important paradigmatic and practical implications.

METHODS

Breast cancer records were obtained from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database. The study included 19,541 non-Hispanic white women with node-negative breast cancer. Standard tumor cell characteristics and breast cancer-specific survival were analyzed by independent estrogen receptor (ER+ and ER-), independent progesterone receptor (PR+ and PR-), and joint ERPR expression (ER+PR+, ER+PR-, ER-PR+, and ER-PR-).

RESULTS

Age frequency density plots by hormone receptor expression showed two overlapping breast cancer populations with early-onset and/or late-onset etiologies. Independent ER+ and PR+ phenotype were associated with smaller tumor sizes, better grade, and better cancer-specific survival than ER- and PR- breast cancer types. Joint ERPR phenotype exhibited biologic gradients for tumor size, grade, and cancer-specific survival, which ranked from good to worse for ER+PR+ to ER+PR- to ER-PR+ to ER-PR-.

CONCLUSION

Variations of standard tumor cell characteristics and breast cancer-specific survival by hormone receptor expression in white patients with node-negative breast cancer suggested two breast cancer phenotypes with overlapping etiologies and distinct clinical features.

The structure of the yrdC gene product from Escherichia coli reveals a new fold and suggests a role in RNA binding

The yrdC family of genes codes for proteins that occur both independently and as a domain in proteins that have been implicated in regulation. An example for the latter case is the sua5 gene from yeast. SuaS was identified as a suppressor of a translation initiation defect in cytochrome c and is required for normal growth in yeast (Na JG, Pinto I, Hampsey M, 1992, Genetics 11:791-801). However, the function of the Sua5 protein remains unknown; Sua5 could act either at the transcriptional or the posttranscriptional levels to compensate for an aberrant translation start codon in the cyc gene. To potentially learn more about the function of YrdC and proteins featuring this domain, the crystal structure of the YrdC protein from Escherichia coli was determined at a resolution of 2.0 A. YrdC adopts a new fold with no obvious similarity to those of other proteins with known three-dimensional (3D) structure. The protein features a large concave surface on one side that exhibits a positive electrostatic potential. The dimensions of this depression, its curvature, and the fact that conserved basic amino acids are located at its floor suggest that YrdC may be a nucleic acid binding protein. An investigation of YrdC's binding affinities for single- and double-stranded RNA and DNA fragments as well as tRNAs demonstrates that YrdC binds preferentially to double-stranded RNA. Our work provides evidence that 3D structures of functionally uncharacterized gene products with unique sequences can yield novel folds and functional insights.

Murine hematopoietic stem cell characterization and its regulation in BM transplantation

Using 5-color fluorescence-activated cell sorting, we isolated a subset of murine pluripotent hematopoietic stem cells (PHSC) with the phenotype Lin(-) Sca(+) kit(+) CD38(+) CD34(-) that appears to fulfill the criteria for most primitive PHSC. In the presence of whole bone marrow (BM) competitor cells, these cells produced reconstitution in lethally irradiated primary, secondary, and tertiary murine transplant recipients over the long term. However, these cells alone could not produce reconstitution in lethally irradiated recipients. Rapid proliferation of these cells after BM transplantation required the assistance of another BM cell subset, which has the phenotype Lin(-) Sca(+) kit(+) CD38(-) CD34(+).

Functional implications from crystal structures of the conserved Bacillus subtilis protein Maf with and without dUTP

Three-dimensional structures of functionally uncharacterized proteins may furnish insight into their functions. The potential benefits of three-dimensional structural information regarding such proteins are particularly obvious when the corresponding genes are conserved during evolution, implying an important function, and no functional classification can be inferred from their sequences. The Bacillus subtilis Maf protein is representative of a family of proteins that has homologs in many of the completely sequenced genomes from archaea, prokaryotes, and eukaryotes, but whose function is unknown. As an aid in exploring function, we determined the crystal structure of this protein at a resolution of 1.85 A. The structure, in combination with multiple sequence alignment, reveals a putative active site. Phosphate ions present at this site and structural similarities between a portion of Maf and the anticodon-binding domains of several tRNA synthetases suggest that Maf may be a nucleic acid-binding protein. The crystal structure of a Maf-nucleoside triphosphate complex provides support for this hypothesis and hints at di- or oligonucleotides with either 5'- or 3'-terminal phosphate groups as ligands or substrates of Maf. A further clue comes from the observation that the structure of the Maf monomer bears similarity to that of the recently reported Methanococcus jannaschii Mj0226 protein. Just as for Maf, the structure of this predicted NTPase was determined as part of a structural genomics pilot project. The structural relation between Maf and Mj0226 was not apparent from sequence analysis approaches. These results emphasize the potential of structural genomics to reveal new unexpected connections between protein families previously considered unrelated.

Incorporation of tumor vasculature targeting motifs into moloney murine leukemia virus env escort proteins enhances retrovirus binding and transduction of human endothelial cells

Adhesion receptors expressed on the surfaces of tumor-activated endothelial cells provide an advantageous locus for targeting gene therapy vectors to angiogenic tissues and/or tumor vasculature. In this study, we engineered a series of Asn-Gly-Arg (NGR)-containing congeners of the presumptive cell binding motif contained within the ninth type III repeat of fibronectin and displayed these tumor vasculature targeting motifs (TVTMs) within the context of Moloney murine leukemia envelope "escort" proteins. Comparative studies of envelope incorporation into viral particles and evaluation of the cell binding properties of the targeted vectors revealed critical structural features, thus identifying a subset of optimal TVTMs. Utilizing a modified ELISA to evaluate viral binding to target cells, we observed a significant down-regulation of TVTM-virion binding to human endothelial cells following sustained (48-h) exposure to VEGF. Normalized for equivalent titers (10(6) CFU/ml), as assayed on NIH 3T3 cells, vectors displaying TVTM escort proteins significantly enhanced the transduction efficiency from 12.2 to 37.4% in human KSY-1 endothelial cell cultures (P < 0.001) and from 0.4 to 4.1% in human umbilical vein endothelial cell (HUVEC) cultures (P < 0.001). In summary, these studies utilized an engineering approach to identify a subset of TVTMs that are stably incorporated as envelope "escort" proteins into retroviral vectors and that, by functioning to improve the binding efficiency and transduction of both HUVEC and KSY1 endothelial cells, may have therapeutic potential for targeting gene delivery to the tumor-associated vasculature.

Neonatal gene therapy. transfer and expression of exogenous genes in neonatal sheep following direct injection of retroviral vectors into the bone marrow space

We investigated whether gene transfer into hematopoietic cells could be achieved by direct injection of retroviral vector supernatant into the bone marrow space of newborn sheep. Six sheep (5 weeks old) were injected bilaterally with either 1 mL of G1nBgSvNa8.1 vector supernatant (titer: 1 x 10(7)) in each hip (n = 5) or with 3 mL of the same vector preparation/hip (n = 1). In addition, one 3-month-old sheep was injected unilaterally with 1 mL of the same vector preparation. Blood and marrow of these animals were analyzed for the transgene before injection and at intervals thereafter. At 1 week postinjection, an average of 11.6% of the lymphocytes and 25.5% of the granulocytes/monocytes in the marrow, and an average of 0.9% of the lymphocytes and 1.8% of the granulocytes/monocytes in the blood contained and expressed the LacZ gene. The presence/expression of the transgene has persisted for at least 13 months within the blood and bone marrow of these animals. These findings demonstrate that the direct injection of small volumes of high-titer retroviral supernatant into the bone marrow of newborn sheep results in transduction of hematopoietic cells that persists for at least 13 months postinjection.