PD03-07: Breast Cancer Heterogeneity and Treatment Resistance: Clues from Metaplastic Tumors

At late stage, nearly all breast cancers are heterogeneous and refractory to treatment, like metaplastic breast cancer is at an early stage. These rare carcinomas are highly aggressive and de-differentiated. They are enriched for mesenchymal and stem cell features and essentially fail current therapies. As metaplastic tumors provide a time-compressed picture of breast cancer progression early on, understanding these tumors will yield insight into mechanisms that drive breast cancer into advanced stages and treatment resistance.

To investigate a genetic basis for heterogeneity in metaplastic breast cancer, we established a progression model comprising three cell lines. The cell lines were derived from a primary tumor, a local recurrence and a pleural effusion of a 40-year old patient. The primary tumor was a stage III invasive metaplastic, triple negative, inflammatory breast cancer, resected after neoadjuvant chemotherapy (capecitabine and taxotere, then adriamycin and one cycle of bevacizumab). The local recurrence, biopsied seven months post mastectomy, developed after the patient received adjuvant carboplatin and gemcitabine for 3 cycles and then radiation to the chest wall. At this time, the patient had lung metastases and was treated with taxol and bevacizumab yielding a mixed response. Local invasive growth continued and a malignant pleural effusion developed four months later. Analyzing the genetic and molecular characteristics of this progression model in vitro, its tumorigenicity and metastasis in vivo, and interrogating lead findings in a growing collection of metaplastic tumors helps us to dissect the genetic heterogeneity in breast cancer, and potentially to identify the cell types that drive disease progression and treatment resistance. Our gene expression analyses and genomic evaluations identified epithelial to mesenchymal transition (EMT) as a key characteristic in the progression and treatment resistance of this cancer. Major changes in cytoskeletal genes, chemokines and their receptors, amplification of drug transporter proteins, metalloproteinases and matrix proteins seen with increasing motility and invasiveness along with recruitment of host inflammatory responses in the in vivo model, loss of chromosomal regions harboring known and putative tumor suppressors, and deletions of genes encoding proteins for metabolic inactivation of sex hormones in the breast tissue, along with specific loss of clusters of desmosomal genes are guiding our understanding of metaplastic breast cancer progression. The results provide insight into the development, the extremely invasive nature, and treatment resistance of these tumors. Our collaborative network of clinicians, pathologists, translational genomic researchers and bioinformatics specialists will enable us to identify and prioritize genetic events as disease drivers, prognostic biomarkers of disease progression, and determinants of treatment resistance. Our goal is to identify molecular and functional targets for effective therapy and evaluate them in the clinic. Lessons learned from metaplastic breast cancer will improve our understanding of breast cancer progression in general, and could translate into effective treatments for advanced breast cancer where current standard of care is failing.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD03-07.

In vitro assessment of the inflammatory breast cancer cell line SUM 149: Discovery of two single nucleotide polymorphisms in the RNase L gene

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Background: Inflammatory breast cancer (IBC) is a rare, aggressive form of breast cancer, accounting for 5% of breast cancers diagnosed annually in the United States. Understanding the distinct biology of IBC could help provide novel treatment targets. We sought to evaluate whether or not the IBC cell lines SUM 149 and SUM 190 demonstrated evidence of viral infection.

Methods: We performed single nucleotide polymorphism (SNP) genotyping for 2 variants of the ribonuclease (RNase) L gene that have been correlated with the risk of prostate cancer due to a possible viral etiology. We also performed proliferation assays; developed dose response curves to assess the treatment effect of interferon-alpha (IFN-a); and assayed for evidence of the putative human mammary tumor virus (HMTV, which has been implicated but not definitively associated with IBC,) in the DNA and RNA of SUM 149 cells.

Results: According to our allelic discrimination SNP assay, 2/2 IBC cell lines were homozygous for the 462 and 541 variants, whereas 0/10 non-IBC cell lines were homozygous positive for the 462 variant (p = 0.015) and 2/10 non-IBC cell lines contained homozygous alleles for the 541 variant (p = 0.52). We also found a dose and time-dependent decrease in the proliferation of SUM 149 IBC cells treated with IFN-a. In contrast, non-IBC cell lines did not show a dose-response decrease in cell proliferation. Our reverse transcriptase polymerase chain reaction (RT-PCR) and Southern blot analysis for the env/LTR and late LTR sequences of the putative HMTV revealed no evidence of the putative viral genome.

Conclusions: We discovered 2 SNPs, in the 462 and 541 variants of the RNase L gene, that were homozygously mutated in IBC cell lines but the 462 variant was absent in non-IBC lines. Our discovery of these mutated SNPs present in IBC cell lines suggests a possible genetic risk factor for IBC. In our study, the IBC cell line SUM 149 demonstrated a direct and specific response to treatment with IFN-a, an antiviral agent. We noted no evidence of HMTV infection in that cell line. Further studies of the prevalence and significance of the RNase L 462 and 541 variants in human IBC tissue specimens are warranted to validate our in vitro findings.

Primary renal hypoplasia in humans and mice with PAX2 mutations: evidence of increased apoptosis in fetal kidneys of Pax2(1Neu) +/- mutant mice

PAX2 mutations cause renal-coloboma syndrome (RCS), a rare multi-system developmental abnormality involving optic nerve colobomas and renal abnormalities. End-stage renal failure is common in RCS, but the mechanism by which PAX2 mutations lead to renal failure is unknown. PAX2 is a member of a family of developmental genes containing a highly conserved 'paired box' DNA-binding domain, and encodes a transcription factor expressed primarily during fetal development in the central nervous system, eye, ear and urogenital tract. Presently, the role of PAX2 during kidney development is poorly understood. To gain insight into the cause of renal abnormalities in patients with PAX2 mutations, kidney anomalies were analyzed in patients with RCS, including a large Brazilian kindred in whom a new PAX2 mutation was identified. In a total of 29 patients, renal hypoplasia was the most common congenital renal abnormality. To determine the direct effects of PAX2 mutations on kidney development fetal kidneys of mice carrying a Pax2 (1Neu)mutation were examined. At E15, heterozygous mutant kidneys were approximately 60% of the size of wild-type littermates, and the number of nephrons was strikingly reduced. Heterozygous 1Neu mice showed increased apoptotic cell death during fetal kidney development, but the increased apoptosis was not associated with random stochastic inactivation of Pax2 expression in mutant kidneys; Pax2 was shown to be biallelically expressed during kidney development. These findings support the notion that heterozygous mutations of PAX2 are associated with increased apoptosis and reduced branching of the ureteric bud, due to reduced PAX2 dosage during a critical window in kidney development.

Assessment of antibiotic aerosol generation using commercial jet nebulizers

The performance of 14 commercial jet nebulisers has been assessed; Unineb, Suremist (Unimed (UK) Ltd), Micro-Cirrus (Intersurgical Ltd), Pulmo-Neb (DeVilbiss Health Care UK Ltd), Side-Stream (Medic-Aid Ltd), Micro-Neb III (Lifecare Ltd), RespirGard (Marquest Medical Products Inc), Aeromist, Venticaire (S and W Vickers Ltd), Up-Draft II, Ava-Neb, Up-Draft (Hudson Respiratory Care Inc), Bennett/Twin, Raindrop (Puritan-Bennett Corporation). The units were operated with a high flow compressor (Maxi III, Medix Ltd) at 101/min. Performance was assessed by measuring the fraction of the initial mass of drug released as an aerosol and nebulisation time for initial drug volume of 2-6mls, and the mass median diameter and mass fraction of the aerosol in particles < 5.17 microns diameter. The Side-Stream nebuliser gave the best performance, although incorporation of a filter to trap exhaled antibiotic may prove difficult. The Micro-Cirrus generated a particularly fine aerosol. The Raindrop nebuliser performed well, while the Up-Draft II nebulised efficiently but was associated with extended nebulisation times which may limit its utility.

Measurement and prediction of drug solvent losses by evaporation from a jet nebuliser

The evaporative losses of solvent (water) from a commercial jet nebuliser (Unineb, Unimed Ltd) were estimated and found to be approximately 14% of total nebuliser output. A simple analysis of the nebulisation process then enabled the amount of the drug colomycin released as potentially respirable aerosol to be predicted from measurements of the total nebulisation time. Good agreement was found between the predicted (P) and measured (M) values such that P = 1.07 M (r2 = 0.98). The analysis also indicates that the proportion of the drug released as aerosol will increase as nebulisation proceeds provided nebuliser output is continuous and that for a given initial mass of drug a larger amount of drug is released as an aerosol if the volume of administration used in the nebuliser is as large as possible.