ERBB3: Multifunctional enabler or primary actor in pancreatic cancer?

HER3 as biomarker and therapeutic target in pancreatic cancer: new insights in pertuzumab therapy in preclinical models

The anti-HER2 antibody pertuzumab inhibits HER2 dimerization and affects HER2/HER3 dimer formation and signaling. As HER3 and its ligand neuregulin are implicated in pancreatic tumorigenesis, we investigated whether HER3 expression could be a predictive biomarker of pertuzumab efficacy in HER2low-expressing pancreatic cancer. We correlated in vitro and in vivo HER3 expression and neuregulin dependency with the inhibitory effect of pertuzumab on cell viability and tumor progression. HER3 knockdown in BxPC-3 cells led to resistance to pertuzumab therapy. Pertuzumab treatment of HER3-expressing pancreatic cancer cells increased HER3 at the cell membrane, whereas the anti-HER3 monoclonal antibody 9F7-F11 down-regulated it. Both antibodies blocked HER3 and AKT phosphorylation and inhibited HER2/HER3 heterodimerization but affected differently HER2 and HER3 homodimers. The pertuzumab/9F7-F11 combination enhanced tumor inhibition and the median survival time in mice xenografted with HER3-expressing pancreatic cancer cells. Finally, HER2 and HER3 were co-expressed in 11% and HER3 alone in 27% of the 45 pancreatic ductal adenocarcinomas analyzed by immunohistochemistry. HER3 is essential for pertuzumab efficacy in HER2low-expressing pancreatic cancer and HER3 expression might be a predictive biomarker of pertuzumab efficacy in such cancers. Further studies in clinical samples are required to confirm these findings and the interest of combining anti-HER2 and anti-HER3 therapeutic antibodies.

Anti-tumor efficacy of naked siRNAs for ERBB3 or AKT2 against lung adenocarcinoma cell xenografts

The use of siRNAs against specific molecular targets has potential for cancer therapy but has been thought to be limited by the need for formulation to improve cellular uptake. Lung adenocarcinoma cells are markedly suppressed in culture by siRNAs to the receptor ERBB3 or its downstream signaling partner AKT2. We now demonstrate that naked, unformulated siRNAs to ERBB3 or AKT2, administered i.v. as saline solutions, 2 μg/g five times per week for 3 weeks (total dose 30 μg/g), were effective suppressors of growth of A549 human lung adenocarcinoma cell xenografts in athymic mice, 12 mice per group, in four different experiments. ERBB3 and AKT2 siRNAs each inhibited growth by 70-90% on average, compared to saline-treated or untreated controls; a nonsilencing siRNA was without significant effect. Lesser but significant effects were noted with a total dose of 12 μg/g. With the higher dose, effects persisted for several weeks after the end of treatment. Expected reductions of ERBB3 and AKT2 mRNAs and proteins occurred and correlated with decrease in tumor volume. There were no significant changes in serum cytokines. These results show that naked siRNAs to ERBB3 or AKT2 may have potential for lung cancer therapy.