Grb7 knockout mice develop normally but litters born to knockout females fail to thrive.

BACKGROUND: Growth factor receptor-bound 7 (Grb7) is an adaptor protein involved in signal transduction downstream of multiple receptor tyrosine kinases, including ERBB, FGFR, and PDGFR pathways. Experimental studies have implicated Grb7 in regulating cell proliferation, survival, migration, and invasion through its large repertoire of protein-protein interactions. RESULTS: Here, we describe the generation and characterization of a Grb7 knockout mouse. These mice are viable and fertile. A lacZ knock-in reporter was used to visualize Grb7 promoter activity patterns in adult tissues, indicating widespread Grb7 expression in glandular epithelium, the central nervous system, and other tissues. The sole defect observed in these animals was a failure of Grb7 knockout females to successfully raise pups to weaning age, a phenotype that was independent of both paternal and pup genotypes. CONCLUSIONS: These data suggest a regulatory role for Grb7 in mammary lactational physiology.

Amphiregulin deletion strongly attenuates the development of estrogen receptor-positive tumors in p53 mutant mice.

PURPOSE: The epidermal growth factor receptor ligand, Amphiregulin, is a transcriptional target of estrogen receptor alpha and is required for pubertal mammary gland development. Previous studies using immortalized human breast cancer cell line xenografts have suggested that Amphiregulin may be an important effector of estrogen receptor alpha during breast cancer development, at least in immune-compromised animals. Here, we evaluate the requirement for Amphiregulin in an immune-competent mouse model which is prone to developing estrogen receptor-positive tumors. METHODS: We have intercrossed mice with mammary-specific mutation of p53 with mice deficient in Amphiregulin in order to assess the requirement for Amphiregulin in the initiation and progression of both estrogen receptor-positive and estrogen receptor-negative mammary tumors. RESULTS: Deletion of Amphiregulin significantly delayed the onset of palpable mammary tumors and also strongly reduced the proportion of estrogen receptor alpha-positive tumors formed. Upon necropsy, no substantial differences in the prevalence of non-palpable lesions were observed between cohorts, suggesting that the importance of Amphiregulin in mammary tumorigenesis is limited to the post-initiation phase. CONCLUSIONS: This study underlines the importance of the EGFR ligand, Amphiregulin, as a key mediator of estrogen receptor action in breast cancer.

Adaptation of an amplicon-based human cancer next-generation sequencing panel assay for murine tumors.

Unlike humans, inbred genetically engineered mice have minimal inter-individual variation and, consequently, offer substantially increased statistical power for robust definition of recurrent cooperating cancer mutations. While technically feasible, whole exome sequencing is expensive and extremely data-intensive. Somatic mutation analysis using panels of 25-75 genes now provides detailed insight into the biology of human tumors. Here we report an adaptation for mouse tumors of a human PCR amplicon-based panel (Ion Torrent Cancer Hotspot Panel v2) allowing analysis of 18 cancer genes, including Kras, Nras, Hras, Pten, Pik3ca and Smad4, and encompassing regions homologous to more than 2000 known human cancer mutations.

Genomic analysis of melanoma evolution following a 30-year disease-free interval.

Ultra-late melanoma recurrence is infrequent, poorly understood and, in most cases, difficult to unambiguously distinguish from a new primary melanoma. We identified a patient with a second melanoma diagnosed after a 30-year disease-free interval, and sought to determine if this new lesion was a recurrence of the original melanoma. Here we report the genomic sequence analysis of the exomes of 2 melanoma lesions isolated from the same individual in 1985 and 2015, and their comparison to each other and to the germline DNA of the patient. Identification of many shared somatic mutations between these lesions proves a lineal relationship spanning 30 years. Unlike prior reports of ultra-late melanoma recurrence, the availability of the original tumor and the use of comprehensive genomic analysis allowed us to confirm that the second lesion is truly a recurrence. We demonstrate the acquisition of numerous additional mutations during the 3 decade asymptomatic period. These data highlight the low but very long-lasting risk of recurrence in this patient population.

Gemcitabine combination therapies induce apoptosis in uterine carcinosarcoma patient-derived organoids.

Uterine carcinosarcoma (UCS) is a rare but aggressive endometrial cancer. Survival outcomes for women diagnosed with UCS remain poor with lower survival than those of endometrioid or high-grade serous uterine cancers. The histopathological hallmark of carcinosarcoma is the presence of both sarcomatous and carcinomatous elements. The survival rates for UCS have not improved for over 40 years; therefore, there is a profound need to identify new treatments. To investigate novel chemotherapy treatment combinations for UCS, we generated a UCS patient-derived organoid (PDO) cell line from a patient that received neoadjuvant treatment with paclitaxel and carboplatin. The PDO cell line (UCS1) was grown in three-dimensional domes. The PDO domes were treated with six individual chemotherapies or nine combinations of those six drugs. Cell death in response to chemotherapy was assessed. We found that the six monotherapies had minimal effectiveness at inducing cell death after 48 h of treatment. The combination of paclitaxel and carboplatin (which is the standard-of-care chemotherapy treatment for UCS) led to a small increase in apoptosis compared with the monotherapies. Importantly, when either carboplatin or paclitaxel was combined with gemcitabine, there was an appreciable increase in cell death. In conclusion, for the UCS1 patient-derived tumor cells, gemcitabine combinations were more effective than carboplatin/paclitaxel. Our data support the use of PDOs to predict responses to second-line chemotherapy.

Pan-cancer distribution of cleaved cell-surface amphiregulin, the target of the GMF-1A3 antibody drug conjugate.

Amphiregulin is a transmembrane protein which, when cleaved by the TACE/ADAM17 protease, releases a soluble epidermal growth factor receptor ligand domain that promotes proliferation of normal and malignant cells. We previously described a rabbit monoclonal antibody, GMF-1A3, that selectively recognizes the cell-associated cleaved amphiregulin epitope. Antibody-drug conjugates had anti-tumor activity against human breast cancer xenografts. Several tumor types express amphiregulin, but evidence for a functional requirement for amphiregulin in these malignancies is limited. By directly evaluating amphiregulin cleavage with immunohistochemistry, GMF-1A3 provides a more direct measure of amphiregulin activity. Using 370 specimens from 10 tumor types (as well as normal controls), we demonstrate that cleaved amphiregulin is widely expressed in solid tumors and is especially common (> 50% of cases) in breast, prostate, liver and lung cancer. As a potential companion diagnostic for this antibody-drug conjugate, this assay allows identification of tumors with high levels of the cleaved amphiregulin target.

Mammary gland specific expression of Brk/PTK6 promotes delayed involution and tumor formation associated with activation of p38 MAPK.

INTRODUCTION: Protein tyrosine kinases (PTKs) are frequently overexpressed and/or activated in human malignancies, and regulate cancer cell proliferation, cellular survival, and migration. As such, they have become promising molecular targets for new therapies. The non-receptor PTK termed breast tumor kinase (Brk/PTK6) is overexpressed in approximately 86% of human breast tumors. The role of Brk in breast pathology is unclear. METHODS: We expressed a WAP-driven Brk/PTK6 transgene in FVB/n mice, and analyzed mammary glands from wild-type (wt) and transgenic mice after forced weaning. Western blotting and immunohistochemistry (IHC) studies were conducted to visualize markers of mammary gland involution, cell proliferation and apoptosis, as well as Brk, STAT3, and activated p38 mitogen-activated protein kinase (MAPK) in mammary tissues and tumors from WAP-Brk mice. Human (HMEC) or mouse (HC11) mammary epithelial cells were stably or transiently transfected with Brk cDNA to assay p38 MAPK signaling and cell survival in suspension or in response to chemotherapeutic agents. RESULTS: Brk-transgenic dams exhibited delayed mammary gland involution and aged mice developed infrequent tumors with reduced latency relative to wt mice. Consistent with delayed involution, mammary glands of transgenic animals displayed decreased STAT3 phosphorylation, a marker of early-stage involution. Notably, p38 MAPK, a pro-survival signaling mediator downstream of Brk, was activated in mammary glands of Brk transgenic relative to wt mice. Brk-dependent signaling to p38 MAPK was recapitulated by Brk overexpression in the HC11 murine mammary epithelial cell (MEC) line and human MEC, while Brk knock-down in breast cancer cells blocked EGF-stimulated p38 signaling. Additionally, human or mouse MECs expressing Brk exhibited increased anchorage-independent survival and resistance to doxorubicin. Finally, breast tumor biopsies were subjected to IHC analysis for co-expression of Brk and phospho-p38 MAPK; ductal and lobular carcinomas expressing Brk were significantly more likely to express elevated phospho-p38 MAPK. CONCLUSIONS: These studies illustrate that forced expression of Brk/PTK6 in non-transformed mammary epithelial cells mediates p38 MAPK phosphorylation and promotes increased cellular survival, delayed involution, and latent tumor formation. Brk expression in human breast tumors may contribute to progression by inducing p38-driven pro-survival signaling pathways.

Anti-tumor efficacy of an MMAE-conjugated antibody targeting cell surface TACE/ADAM17-cleaved Amphiregulin in breast cancer.

BACKGROUND: The Epidermal Growth Factor Receptor (EGFR) ligand, Amphiregulin (AREG), is a key proliferative effector of estrogen receptor signaling in breast cancer and also plays a role in other malignancies. AREG is a single-pass transmembrane protein proteolytically processed by TACE/ADAM17 to release the soluble EGFR ligand, leaving a residual transmembrane stalk that is subsequently internalized. METHODS: Using phage display, we identified antibodies that selectively recognize the residual transmembrane stalk of cleaved AREG. Conjugation with fluorescence labels and monomethyl auristatin E (MMAE) was used to study their intracellular trafficking and anti-cancer effects, respectively. RESULTS: We report the development of an antibody-drug conjugate (ADC), GMF-1A3-MMAE, targeting an AREG neo-epitope revealed following ADAM17-mediated cleavage. The antibody does not interact with uncleaved AREG, providing a novel means of targeting cells with high rates of AREG shedding. Using fluorescent dye conjugation, we demonstrated that the antibody is internalized by cancer cells in a manner dependent on the presence of cell surface cleaved AREG. Antibodies conjugated with MMAE were cytotoxic in vitro and induced rapid regression of established breast tumor xenografts in immunocompromised mice. We further demonstrate that these antibodies recognize the AREG neo-epitope in formalin-fixed, paraffin-embedded tumor tissue, suggesting their utility as a companion diagnostic for patient selection. CONCLUSIONS: This ADC targeting AREG has potential utility in the treatment of breast and other tumors in which proteolytic AREG shedding is a frequent event.

Acquisition of Cabozantinib-Sensitive MET D1228N Mutation During Progression on Crizotinib in MET-Amplified Triple-Negative Breast Cancer.

BACKGROUND: Targeting of somatic MET mutations using crizotinib has led to strong clinical responses, most frequently in patients with lung cancer, raising the possibility of adopting similar treatment strategies in patients with MET alterations in other cancer types. PATIENT AND METHODS: We describe a patient with advanced triple-negative breast cancer with a 30-fold amplification of MET. Next-generation sequencing of pre- and postprogression biopsies was performed to identify the resistance mechanism emerging after an initial exceptional response to crizotinib. The response of the resistance mutant to type I and II MET inhibitors was assessed in cultured cells. RESULTS: After progressing on crizotinib, a MET-D1228N mutation was detected, which is located in the crizotinib-binding region of the MET kinase domain. Experimental studies demonstrated that this mutation confers complete resistance to crizotinib yet retains cabozantinib sensitivity. Treatment of the patient with cabozantinib led to a subjective improvement in clinical symptoms, but the patient progressed after 7 weeks. CONCLUSION: Although MET mutations are rare in breast cancer, these patients may experience substantial clinical benefit from crizotinib treatment. Nevertheless, drug resistance owing to on-target MET mutations will likely be frequently encountered and comprehensive mechanistic studies to assess sensitivity of these mutants to a series of potential second-line therapies may help guide subsequent treatment for these patients.

Mutant GATA3 Actively Promotes the Growth of Normal and Malignant Mammary Cells.

BACKGROUND/AIM: GATA3, a transcription factor expressed in luminal breast epithelial cells, is required for mammary gland development. Heterozygous GATA3 mutations occur in up to 15% of estrogen receptor (ER)-positive breast tumors and have been proposed to be null alleles resulting in haploinsufficiency; however, the mutation spectrum of GATA3 in breast cancer is in sharp contrast to that found in HDR syndrome, a true GATA3 haploinsufficiency disease. MATERIALS AND METHODS: Transgenic mice, 3D cultures and xenografts were used to examine the effect of mutant GATA3 expression on mammary cell proliferation. RESULTS: Mutant GATA3 accelerated tumor growth of ZR751 cell xenografts and promoted precocious lobuloalveolar development in transgenic mouse mammary glands. CONCLUSION: GATA3 mutations, recently observed in breast cancer, encode active transcription factors, which elicit proliferative phenotypes in normal mammary epithelium and promote the growth of ER-positive breast cancer cell lines.

Amphiregulin Is a Critical Downstream Effector of Estrogen Signaling in ERα-Positive Breast Cancer.

Estrogen stimulation promotes epithelial cell proliferation in estrogen receptor (ERα)-positive breast cancer. Many ERα target genes have been enumerated, but the identities of the key effectors mediating the estrogen signal remain obscure. During mouse mammary gland development, the estrogen growth factor receptor (EGFR) ligand amphiregulin acts as an important stage-specific effector of estrogen signaling. In this study, we investigated the role of amphiregulin in breast cancer cell proliferation using human tissue samples and tumor xenografts in mice. Amphiregulin was enriched in ERα-positive human breast tumor cells and required for estrogen-dependent growth of MCF7 tumor xenografts. Furthermore, amphiregulin levels were suppressed in patients treated with endocrine therapy. Suppression of EGF receptor signaling appeared necessary for the therapeutic response in this setting. Our findings implicate amphiregulin as a critical mediator of the estrogen response in ERα-positive breast cancer, emphasizing the importance of EGF receptor signaling in breast tumor pathogenesis and therapeutic response.

Breast tumor kinase (Brk/PTK6) is a mediator of hypoxia-associated breast cancer progression.

Basal-type triple-negative breast cancers (TNBC) are aggressive and difficult to treat relative to luminal-type breast cancers. TNBC often express abundant Met receptors and are enriched for transcriptional targets regulated by hypoxia-inducible factor-1α (HIF-1α), which independently predict cancer relapse and increased risk of metastasis. Brk/PTK6 is a critical downstream effector of Met signaling and is required for hepatocyte growth factor (HGF)-induced cell migration. Herein, we examined the regulation of Brk by HIFs in TNBC in vitro and in vivo. Brk mRNA and protein levels are upregulated strongly in vitro by hypoxia, low glucose, and reactive oxygen species. In HIF-silenced cells, Brk expression relied upon both HIF-1α and HIF-2α, which we found to regulate BRK transcription directly. HIF-1α/2α silencing in MDA-MB-231 cells diminished xenograft growth and Brk reexpression reversed this effect. These findings were pursued in vivo by crossing WAP-Brk (FVB) transgenic mice into the MET(Mut) knockin (FVB) model. In this setting, Brk expression augmented MET(Mut)-induced mammary tumor formation and metastasis. Unexpectedly, tumors arising in either MET(Mut) or WAP-Brk × MET(Mut) mice expressed abundant levels of Sik, the mouse homolog of Brk, which conferred increased tumor formation and decreased survival. Taken together, our results identify HIF-1α/2α as novel regulators of Brk expression and suggest that Brk is a key mediator of hypoxia-induced breast cancer progression. Targeting Brk expression or activity may provide an effective means to block the progression of aggressive breast cancers.

Mechanisms of HGF/Met signaling to Brk and Sam68 in breast cancer progression.

Signal transduction pathways downstream of receptor tyrosine kinases (RTKs) are often deregulated during oncogenesis, tumor progression, and metastasis. In particular, the peptide growth factor hormone, hepatocyte growth factor (HGF), and its specific receptor, Met tyrosine kinase, regulate cancer cell migration, thereby conferring an aggressive phenotype (Nakamura et al., J Clin Invest 106(12):1511-1519, 2000; Huh et al., Proc Natl Acad Sci U S A 101:4477-4482, 2004). Additionally, overexpression of Met is associated with enhanced invasiveness of breast cancer cells (Edakuni et al., Pathol Int 51(3):172-178, 2001; Jin et al., Cancer 79(4):749-760, 1997; Tuck et al., Am J Pathol 148(1):225-232, 1996). Here, we review the regulation of recently identified novel downstream mediators of HGF/Met signaling, Breast tumor kinase (Brk/PTK6), and Src-associated substrate during mitosis of 68 kDa (Sam68), and discuss their relevance to mechanisms of breast cancer progression.