PIK3CA oncogenic mutations represent a major mechanism of resistance to trastuzumab in HER2/neu overexpressing uterine serous carcinomas.
OBJECTIVE
We evaluated the role of PIK3CA-mutations as mechanism of resistance to trastuzumab in primary HER2/neu-amplified uterine-serous-carcinoma (USC) cell lines.


METHODS
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.


RESULTS
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.


CONCLUSIONS
Oncogenic PIK3CA mutations are common in HER2/neu-amplified USC and may constitute a major mechanism of resistance to trastuzumab treatment.
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Jonathan D
JD
Black
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.|Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, University Campus Bio-Medico of Rome, Via Alvaro del Portillo 21, 00128 Rome, Italy.
Salvatore
S
Lopez
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Emiliano
E
Cocco
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Stefania
S
Bellone
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Gary
G
Altwerger
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Carlton L
CL
Schwab
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Diana P
DP
English
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Elena
E
Bonazzoli
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Federica
F
Predolini
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Francesca
F
Ferrari
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Elena
E
Ratner
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Dan-Arin
DA
Silasi
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Masoud
M
Azodi
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Peter E
PE
Schwartz
Department of Obstetrics, Gynecology and Reproductive Sciences Yale University School of Medicine, Yale, CT 06520, USA.
Alessandro D
AD
Santin
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage* / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects; D058534:Class I Phosphatidylinositol 3-Kinases; D018284:Cystadenocarcinoma, Serous / Q000188:drug therapy* / Q000235:genetics; D005260:Female; D005784:Gene Amplification; D006801:Humans; D051379:Mice; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D000068878:Trastuzumab / Q000008:administration & dosage* / Q000627:therapeutic use; D014594:Uterine Neoplasms / Q000188:drug therapy* / Q000235:genetics; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D058534:Class I Phosphatidylinositol 3-Kinases; D019869:Phosphatidylinositol 3-Kinases; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C484760:PIK3CA protein, human; C508053:ERBB2 protein, human