Steve Bottega

Dissecting genetic requirements of human breast tumorigenesis in a tissue transgenic model of human breast cancer in mice

Breast cancer development is a complex pathobiological process involving sequential genetic alterations in normal epithelial cells that results in uncontrolled growth in a permissive microenvironment. Accordingly, physiologically relevant models of human breast cancer that recapitulate these events are needed to study cancer biology and evaluate therapeutic agents. Here, we report the generation and utilization of the human breast cancer in mouse (HIM) model, which is composed of genetically engineered primary human breast epithelial organoids and activated human breast stromal cells. By using this approach, we have defined key genetic events required to drive the development of human preneoplastic lesions as well as invasive adenocarcinomas that are histologically similar to those in patients. Tumor development in the HIM model proceeds through defined histological stages of hyperplasia, DCIS to invasive carcinoma. Moreover, HIM tumors display characteristic responses to targeted therapies, such as HER2 inhibitors, further validating the utility of these models in preclinical compound testing. The HIM model is an experimentally tractable human in vivo system that holds great potential for advancing our basic understanding of cancer biology and for the discovery and testing of targeted therapies.

Neuregulin 1 Expression Is a Predictive Biomarker for Response to AV-203, an ERBB3 Inhibitory Antibody, in Human Tumor Models

Purpose: ERBB3 is overexpressed in a broad spectrum of human cancers, and its aberrant activation is associated with tumor pathogenesis and therapeutic resistance to various anticancer agents. Neuregulin 1 (NRG1) is the predominant ligand for ERBB3 and can promote the heterodimerization of ERBB3 with other ERBB family members, resulting in activation of multiple intracellular signaling pathways. AV-203 is a humanized IgG1/κ ERBB3 inhibitory antibody that completed a first-in-human phase I clinical trial in patients with advanced solid tumors. The purpose of this preclinical study was to identify potential biomarker(s) that may predict response to AV-203 treatment in the clinic. Experimental Design: We conducted in vivo efficacy studies using a broad panel of xenograft models representing a wide variety of human cancers. To identify biomarkers that can predict response to AV-203, the relationship between tumor growth inhibition (TGI) by AV-203 and the expression levels of ERBB3 and NRG1 were evaluated in these tumor models. Results: A significant correlation was observed between the levels of NRG1 expression and TGI by AV-203. In contrast, TGI was not correlated with ERBB3 expression. The correlation between the levels of NRG1 expression in tumors and their response to ERBB3 inhibition by AV-203 was further validated using patient-derived tumor explant models. Conclusions: NRG1 is a promising biomarker that can predict response to ERBB3 inhibition by AV-203 in preclinical human cancer models. NRG1 warrants further clinical evaluation and validation as a potential predictive biomarker of response to AV-203. Clin Cancer Res; 21(5); 1106–14. ©2014 AACR.

Spontaneous Genomic Alterations in a Chimeric Model of Colorectal Cancer Enable Metastasis and Guide Effective Combinatorial Therapy

Colon cancer is the second most common cause of cancer mortality in the Western world with metastasis commonly present at the time of diagnosis. Screening for propagation and metastatic behavior in a novel chimeric-mouse colon cancer model, driven by mutant p53 and β-Catenin, led to the identification of a unique, invasive adenocarcinoma. Comparison of the genome of this tumor, CB42, with genomes from non-propagating tumors by array CGH and sequencing revealed an amplicon on chromosome five containing CDK6 and CDK14, and a KRAS mutation, respectively. Single agent small molecule inhibition of either CDK6 or MEK, a kinase downstream of KRAS, led to tumor growth inhibition in vivo whereas combination therapy not only led to regression of the subcutaneous tumors, but also near complete inhibition of lung metastasis; thus, genomic analysis of this tumor led to effective, individualized treatment.

Abstract 1228: AV-203, a fully humanized ERBB3 inhibitory antibody, reverses ERBB3-induced resistance to targeted therapies.

Targeted therapies have changed the treatment paradigm of cancer. Specifically, the use of tyrosine kinase inhibitors (TKIs) has improved therapeutic responses in a number of tumor types. However, initial response to TKIs is often followed by rapid relapse due to the acquisition of molecular features that lead to resistance. ERBB3, a receptor of the epidermal growth factor receptor (EGFR/ERBB1) family, has been linked to the development of resistance to multiple ERBB targeting TKIs. A proposed potential mechanism is the recruitment and activation of ERBB3 as a bypass mechanism to activate PI3K dependent pro-survival pathways. We investigated whether the inhibition of ERBB3 could reverse TKI resistance linked to ERBB3 activation. AV-203 is a humanized IgG1 antibody directed against ERBB3. AV-203 potently inhibits both ligand dependent and ligand independent activation of ERBB3. AV-203 was shown to inhibit the binding of NRG1 to ERBB3 and promote ERBB3 degradation. The tumor growth inhibitory activity of AV-203 was demonstrated in numerous xenograft models representing major human carcinomas (breast, lung, ovarian, kidney and pancreas). Here, we investigated the ability of AV-203 to restore TKI sensitivity in models with activated ERBB3. First, we demonstrated that ligand mediated (NRG1) activation of ERBB3 leads to acquired resistance to the EGFR TKI erlotinib in a lung cancer model bearing EGFR TKI sensitizing mutation, to the ERBB2/HER2 inhibitor lapatinib in a HER2 amplified breast cancer model, and to the EGFR inhibitory antibody cetuximab in head and neck cancer models. AV-203 was able to restore sensitivity to these RTK inhibitors. This data suggest that the combination of AV-203, with EGFR/HER2 targeted therapies could potentially extend the efficacy of these agents by preventing the emergence of ERBB3 mediated resistance. This hypothesis will be tested in future clinical trials. AV-203 is currently in Phase I development for the treatment of solid tumors. Citation Format: Steven M. Tyler, Sylvie Vincent, Christina Fleet, Steve Bottega, Donna McIntosh, Kristan Meetze, Jeno Gyuris. AV-203, a fully humanized ERBB3 inhibitory antibody, reverses ERBB3-induced resistance to targeted therapies. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1228. doi:10.1158/1538-7445.AM2013-1228

Abstract 2737: Spontaneous genomic alterations identified in a chimeric model of colorectal cancer guide effective combinatorial therapy.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Colon cancer is the second most common cause of cancer mortality in the western world. We generated a mouse model of colon cancer in which a conditional mutation of p53 is combined with inducible delta131-beta-Catenin over-expression in the intestinal epithelium. After 4-12 months of beta-Catenin induction, small adenomas and large solitary nodules of invasive adenocarcinomas developed in either the upper or lower intestinal tract, while the remainder of the intestine appeared normal. Molecular analysis revealed that EGFR and MET were expressed in advanced adenocarcinomas but not early stage adenomas. Although propagating mouse colon tumors has been very challenging, we nevertheless successfully established one tumor line through direct in vivo propagation in the kidney capsule. This tumor line, CB42, grew aggressively and metastasized to ancillary lymph nodes as well as the lung in a subcutaneous metastasis assay and grew in the liver when seeded there by intra splenic injection. Treatment with a MET inhibitor Crizotinib, had no effect on either primary tumor growth, or metastasis. By comparing the genome of CB42 with other colon tumors that did not propagate, we discovered an amplicon on chromosome five containing genes that correlated with propagation and metastasis. In addition, whole genome sequencing revealed that CB42 harbored a mutation in KRAS. Results from combination therapies against key genetic alterations will be presented. Citation Format: Yinghui Zhou, William M. Rideout, Angela Bressel, Sireesha Yalavarthi, Tong Zi, Anthony Monti, Steve Bottega, Bin Feng, M. Isabel Chiu, Marcus Bosenberg, Joerg Heyer. Spontaneous genomic alterations identified in a chimeric model of colorectal cancer guide effective combinatorial therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2737. doi:10.1158/1538-7445.AM2013-2737

Abstract 642: Novel EGFR inhibitory antibodies directed against EGFR mutants with potentially reduced toxicity

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Non-small cell lung cancers (NSCLC) driven by ligand-independent activating mutations in epidermal growth factor receptor (EGFR) often respond to treatment with EGFR tyrosine kinase inhibitors (TKIs). About half of acquired resistance to EGFR-TKI therapy results from a secondary point mutation in the EGFR tyrosine kinase domain at amino acid position 790 (T790M). T790M mutants also display reduced sensitivity to Cetuximab treatment. We have investigated the molecular mechanism responsible for the reduced Cetuximab sensitivity and found that T790M mutant receptors primarily exist and signal as monomers. We have exploited this characteristic of the T790M mutant to isolate novel EGFR inhibitory antibodies with activities against all EGFR variants. In addition, as opposed to other EGFR inhibitory antibodies, these novel antibodies have reduced ligand binding inhibitory activity and minimal inhibitory effect on EGF induced human primary keratinocyte proliferation, suggesting a potentially reduced skin toxicity profile. The broad activity profile, combined with potentially reduced skin toxicity, suggests that these antibodies will have great potential for combinability with other therapeutic agents. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 642. doi:10.1158/1538-7445.AM2011-642