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PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas.

ABSTRACT: We evaluated the role of PIK3CA-mutations as mechanism of resistance to trastuzumab in primary HER2/neu-amplified uterine-serous-carcinoma (USC) cell lines.Fifteen whole-exome-sequenced USC cell lines were tested for HER2/neu-amplification and PIK3CA-mutations. Four HER2/neu-amplified USC (2-harbouring wild-type-PIK3CA-genes and 2-harbouring oncogenic-PIK3CA-mutations) were evaluated in in vitro dose-titration-proliferation-assays, cell-viability and HER2 and S6-protein-phosphorylation after exposure to trastuzumab. USC harbouring wild-type-PIK3CA were transfected with plasmids encoding oncogenic PIK3CA-mutations (i.e., H1047R/R93Q) and exposed to trastuzumab. Finally, trastuzumab efficacy was tested by using two USC xenograft mouse models.Seven out of fifteen (46%) of the USC cell lines were HER2/neu-amplified by fluorescence in situ hybridisation. Within these tumours four out of seven (57%) were found to harbour oncogenic PIK3CA-mutations vs two out of eight (25%) of the HER2/neu not amplified cell lines (P=0.01). HER2/neu-amplified/PIK3CA-mutated USC were highly resistant to trastuzumab when compared with HER2/neu-amplified/wild-type-PIK3CA cell lines (P=0.02). HER2/neu-amplified/PIK3CA wild-type cell lines transfected with oncogenic PIK3CA-mutations increased their resistance to trastuzumab (P<0.0001). Trastuzumab was effective in reducing tumour growth (P=0.001) and improved survival (P=0.0001) in mouse xenografts harbouring HER2-amplified/PIK3CA wild-type USC but not in HER2-amplified/PIK3CA-mutated tumours.Oncogenic PIK3CA mutations are common in HER2/neu-amplified USC and may constitute a major mechanism of resistance to trastuzumab treatment.

SUBMITTER: Black JD

PROVIDER: S-EPMC4651122 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas.

Black Jonathan D JD Lopez Salvatore S Cocco Emiliano E Bellone Stefania S Altwerger Gary G Schwab Carlton L CL English Diana P DP Bonazzoli Elena E Predolini Federica F Ferrari Francesca F Ratner Elena E Silasi Dan-Arin DA Azodi Masoud M Schwartz Peter E PE Santin Alessandro D AD

British journal of cancer 20150901 7

<h4>Objectives</h4>We evaluated the role of PIK3CA-mutations as mechanism of resistance to trastuzumab in primary HER2/neu-amplified uterine-serous-carcinoma (USC) cell lines.<h4>Methods</h4>Fifteen whole-exome-sequenced USC cell lines were tested for HER2/neu-amplification and PIK3CA-mutations. Four HER2/neu-amplified USC (2-harbouring wild-type-PIK3CA-genes and 2-harbouring oncogenic-PIK3CA-mutations) were evaluated in in vitro dose-titration-proliferation-assays, cell-viability and HER2 and S ...[more]

PMID: 26325104

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Project description:ObjectiveAberrant expression of HER2/neu and PIK3CA gene products secondary to amplification/mutations are common in high-grade-serous-endometrial (USC) and ovarian-cancers (HGSOC). Because scant information is currently available in the literature on the potential negative effect of PIK3CA mutations on the activity of afatinib, in this study we evaluate for the first time the role of oncogenic PIK3CA mutations as a potential mechanism of resistance to afatinib in HGSOC and USC overexpressing HER2/neu.MethodsWe used six whole-exome-sequenced primary HGSOC/USC cell-lines and three xenografts overexpressing HER2/neu and harboring mutated or wild-type PIK3CA/PIK3R1 genes to evaluate the role of PI3K-mutations as potential mechanism of resistance to afatinib, an FDA-approved pan-c-erb-inhibitor in clinical trials in USC. Primary-USC harboring wild-type-PIK3CA gene was transfected with plasmids encoding oncogenic PIK3CA-mutations (H1047R/E545K). The effect of afatinib on HER2/PI3K/AKT/mTOR pathway was evaluated by immunoblotting.ResultsWe found PI3K wild-type cell-lines to be significantly more sensitive (lower IC50) than PI3K-mutated cell-lines p = 0.004). In vivo, xenografts of primary cell-line USC-ARK2, transfected with the PIK3CA-H1047R or E545K hotspot-mutations, exhibited significantly more rapid tumor growth when treated with afatinib, compared to mice harboring ARK2-tumors transfected with wild-type-PIK3CA (p = 0.041 and 0.001, respectively). By western-blot, afatinib effectively reduced total and phospho-HER2 proteins in all cell-lines. However, H1047R/E545K-PIK3CA-transfected-ARK2-cells demonstrated a greater compensatory increase in phosphorylated-AKT proteins after afatinib exposure when compared to controls ARK2.ConclusionsOncogenic PI3K mutations may represent a major mechanism of resistance to afatinib. Combinations of c-erb with PIK3CA, AKT or mTOR inhibitors may be necessary to more efficiently block the PIK3CA/AKT/mTOR pathway.

Project description:HER2 overexpression/amplification is identified in up to 40% of uterine serous carcinomas (USC) and 10% of ovarian serous carcinomas (OSC). However, clinical trials using various HER2-targeted agents failed to show significant responses. FDA-approved HER2 assays target only the protein's intracellular domain (ICD) and not the extracellular domain (ECD). Previous quantitative studies in breast cancer by our group have shown that ICD of HER2 is expressed in some cases that do not express the HER2 ECD. We measured HER2 ICD and ECD in USC and OSC samples, and determined their relationship with clinico-pathologic characteristics and survival.We measured HER2 ICD and ECD levels in 2 cohorts of USC and OSC comprising 102 and 175 patients, respectively. HER2 antibodies targeting ICD (CB11) and ECD (SP3) were validated and standardized using the AQUA® method of quantitative immunofluorescence (QIF) and a previously reported HER2 standardization tissue microarray (TMA). Objective, population-based cut-points were used to stratify patients according to HER2 ICD/ECD status.In USC, 8% of patients with high HER2 ICD had low ECD levels (6/75 patients). In OSC, 42% of patients with high HER2 ICD had low ECD levels (29/69 patients). HER2 ICD/ECD status in USC and OSC was not significantly associated with major clinico-pathological features or survival.Using objective, domain-specific HER2 measurement, 8% of USC and 42% of OSC patients with high HER2 ICD levels do not show uniform overexpression of the ECD. This may be related to the presence of p95 HER2, an oncogenic fragment generated by full protein cleavage or alternative initiation of translation. These observations raise the possibility that USC/OSCs expressing low ECD despite being HER2-positive by ICD measurement, may benefit from therapies directed against the intracellular domain (e.g. lapatinib or afatinib) alone or in combination with extracellular domain-directed drugs (e.g. trastuzumab, pertuzumab, T-DM1).

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PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas.

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PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas.

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