Title

The role of PI3K and ERBB family gene mutations and other abnormalities in resistance to HER2-targeted therapies in HER2-positive breast cancer

Author

Naomi Elster, Royal College of Surgeons in IrelandFollow

Date of Award

2016

Document type

Thesis

Degree Name

PhD (Doctor of Philosophy)

First Supervisor

Professor Bryan T Hennessy

Second Supervisor

Dr Alex J Eustace

Funder/Sponsor

Irish Cancer Society Research Scholarship Award CRS11ELS.

Keywords

Breast Cancer, PI3K Pathway, Herceptin Resistance, HER2-Targeted Therapies, Kinome Mutations, ERBB Family Mutations

Abstract

Trastuzumab resistance remains a challenge in the treatment of the 15-20% of breast cancers which are HER2-positive (HER2+ BC). Known mechanisms, including the PI3K pathway, account for some but not all cases of trastuzumab resistance.

The novel, pan-class I PI3K inhibitor copanlisib was tested alone and in combination with HER2-targeted therapies in a panel of HER2+BC cell lines, including models of acquired trastuzumab and/or lapatinib resistance. Reverse phase protein array was used to determine the effect of copanlisib on expression and activation of PI3K pathway components. 227 HER2+ BC tumours were assayed for ERBB family mutations using a custom-designed Sequenom panel. Two ERBB4 mutations, S303F and V721I, were created by site-directed mutagenesis and stably expressed in HER2+ BC cell lines to determine their effect on growth, invasiveness, signalling and response to HER2-targeted therapies.

Copanlisib is highly effective in HER2+ BC cell lines, including those with resistance to HER2-targeted therapies. The combination of HER2-targeted therapies and copanlisib is synergistic, and restores sensitivity to trastuzumab and lapatinib in cells with acquired resistance. Novel, somatic ERBB family mutations are present in 7.05% of HER2+BCs. There is a nonsignificant trend towards a survival effect after trastuzumab. The ERBB4 S303F mutation has increased HER4 kinase activity and is lethal to 2/3 cell lines. ERBB4 V721I increases HER4 overexpression, growth rate, and 3D colony formation. Both ERBB4 mutations studied alter sensitivity to copanlisib and the pan-HER inhibitor afatinib. The combination of copanlisib with HER2-targeted therapies is potentially an improved treatment for trastuzumab resistant HER2-positive breast cancer, which, due to our work presented herein, is now being evaluated in a Phase Ib/II clinical trial (Panther, ICORG 15-02). ERBB family mutations are present in 7.05% of HER2-positive breast cancers. ERBB4 S303F and V721I affect the biology of HER2+ BC and are potential predictive biomarker for copanlisib and afatinib.

Link to this item at

https://epubs.rcsi.ie/phdtheses/213/

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

File Size

5.23 MB

Comments

A thesis submitted for the degree of Doctor of Philosophy from the Royal College of Surgeons in Ireland in 2016.

Citation

Elster N. The role of PI3K and ERBB family gene mutations and other abnormalities in resistance to HER2-targeted therapies in HER2-positive breast cancer [PhD Thesis]. Dublin: Royal College of Surgeons in Ireland; 2016.