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

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.</p

The impact of ERBB-family germline single nucleotide polymorphisms on survival response to adjuvant trastuzumab treatment in HER2-positive breast cancer.

BACKGROUND: Trastuzumab treatment for women with HER2-positive breast cancer (BC) resulted in the significant improvement of both relapse free survival (RFS) and overall survival (OS). However, many women who are classified as HER2-positive do not respond. Many studies have focused on the role of somatic mutations rather than germline polymorphisms in trastuzumab resistance. RESULTS: We completed an Agena MassArray screen of 10 ERBB-family single nucleotide polymorphisms (SNPs) in 194 adjuvant trastuzumab treated HER2-positive BC patients. SNPs in EGFR genes have a significant association with RFS and OS. Patients with the minor allele of EGFR N158N had significantly worse OS (hazard ratio (HR) = 4.01, (confidence interval (CI) = 1.53- 10.69), p = 0.05) relative to those with either the heterozygous or wild-type (WT) allele. Patients with the minor allele of EGFR T903T (HR = 3.52, (CI = 1.38- 8.97), p = 0.05) had worse RFS relative to those with either the heterozygous or WT allele. PATIENTS AND METHODS: Using next generation sequencing (NGS) we identified ERBB-family (EGFR, HER2, HER3 and HER4) single nucleotide polymorphisms (SNPs) that occurred in 2 or more patients of a 32 HER2-positive BC patient cohort. Agena MassArray analysis confirmed the frequency of these SNPs in 194 women with HER2-positive BC who received trastuzumab in the adjuvant setting. Using Kaplan-Meier estimates and Cox regression analysis we correlated the presence of ERBB-family SNPs with both RFS and OS. CONCLUSIONS: The presence of germline ERBB-family SNPs may play an important role in how a patient responds to adjuvant trastuzumab, and clinical assessment of these SNPs by targeted genetic screening of patients' blood may be important to stratify patients for treatment.</p

Supplementary_material – Supplemental material for Frequency, impact and a preclinical study of novel ERBB gene family mutations in HER2-positive breast cancer

<p>Supplemental material, Supplementary_material for Frequency, impact and a preclinical study of novel ERBB gene family mutations in HER2-positive breast cancer by Naomi Elster, Sinead Toomey, Yue Fan, Mattia Cremona, Clare Morgan, Karolina Weiner Gorzel, Una Bhreathnach, Malgorzata Milewska, Madeline Murphy, Stephen Madden, Jarushka Naidoo, Joanna Fay, Elaine Kay, Aoife Carr, Sean Kennedy, Simon Furney, Janusz Mezynski, Oscar Breathhnach, Patrick Morris, Liam Grogan, Arnold Hill, Susan Kennedy, John Crown, William Gallagher, Bryan Hennessy and Alex Eustace in Therapeutic Advances in Medical Oncology</p