HER2 isoforms co-expression differently tunes mammary tumor phenotypes affecting onset, vasculature and therapeutic response

Abstract

Full-length HER2 oncoprotein and splice variant Delta16 are co-expressed in human breast cancer. We studied their interaction in hybrid transgenic mice bearing human full-length HER2 and Delta16 (F1 HER2/Delta16) in comparison to parental HER2 and Delta16 transgenic mice. Mammary carcinomas onset was faster in F1 HER2/Delta16 and Delta16 than in HER2 mice, however tumor growth was slower, and metastatic spread was comparable in all transgenic mice. Full-length HER2 tumors contained few large vessels or vascular lacunae, whereas Delta16 tumors presented a more regular vascularization with numerous endothelium-lined small vessels. Delta16-expressing tumors showed a higher accumulation of i.v. injected doxorubicin than tumors expressing full-length HER2. F1 HER2/Delta16 tumors with high full-length HER2 expression made few large vessels, whereas tumors with low full-length HER2 and high Delta16 contained numerous small vessels and expressed higher levels of VEGF and VEGFR2. Trastuzumab strongly inhibited tumor onset in F1 HER2/Delta16 and Delta16 mice, but not in full-length HER2 mice. Addiction of F1 tumors to Delta16 was also shown by long-term stability of Delta16 levels during serial transplants, in contrast full-length HER2 levels underwent wide fluctuations. In conclusion, full-length HER2 leads to a faster tumor growth and to an irregular vascularization, whereas Delta16 leads to a faster tumor onset, with more regular vessels, which in turn could better transport cytotoxic drugs within the tumor, and to a higher sensitivity to targeted therapeutic agents. F1 HER2/Delta16 mice are a new immunocompetent mouse model, complementary to patient-derived xenografts, for studies of mammary carcinoma onset, prevention and therapy.

Virus-like particle display of HER2 induces potent anti-cancer responses

“…These F1 mice were used to benchmark the efficacy of the HER2-VLP vaccine against a HER2-based DNA vaccine (pHuRT), which previously has shown efficacy in various HER2 transgenic murine models, 36 including full-length HER2 transgenic mice, 37 in which DNA vaccination was more effective at preventing mammary carcinoma onset than passive administration of the anti-HER2 mAb trastuzumab. 38 In this study, vaccination with pHuRT had negligible preventive effect on the mammary carcinogenesis of F1 mice ( Fig. 3D–F ).…”

“…Cell line MAMBO89, established from a mammary carcinoma of huHER2 transgenic mouse, 38 was cultured in DMEM (Thermo Fisher Scientific) additioned with 20% fetal bovine serum (FBS, Thermo Fisher Scientific), 30 µg/ml bovine pituitary extract (Corning) and 5 µl/ml MITO+ SERUM EXTENDER (Corning). MAMBO89 cell line was monitored for murine origin by PCR and for full-length HER2 transgene expression by PCR and flow cytometry.…”

“… 35 , 63 Delta16 male mice and HER2 female mice were crossed to obtain a double transgenic human HER2/Delta16 progeny, here referred to as F1 mice. 38 All transgenic mice expressed human HER2 and/or Delta16 in the mammary glands under the transcriptional control of mouse mammary tumor virus long terminal repeats, leading to the development of mammary carcinomas. 62 , 63 Non-transgenic FVB female mice (FVB/NCrl) were purchased from Charles River Laboratories (Calco, Como, Italy).…”

“…i) Cell line MAMBO89 was previously established from a mammary carcinoma of a HER2 transgenic mouse. 38 MAMBO89 cells (5 × 10 6 cells) were subcutaneously ( s.c. ) injected in 10-20-week-old FVB female mice. Starting 5 weeks after cell injection, mice were immunized every second week with the HER2-VLP vaccine for the entire lifetime of the mouse.…”

HER2 splice variants in breast cancer: investigating their impact on diagnosis and treatment outcomes

“…Transgenic ∆16-HER2 mice suffer very rapid mammary carcinogenesis compared to HER2 WT mice. These tumours displayed altered vascularisation with HER2 WT-expressing tumours exhibiting a few large vessels and ∆16-HER2 mice numerous small vessels [89]. ∆16-HER2 mice also exhibit a distinct genetic profile and changes to the activation of various transcription factors [87].…”