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Gail M Seigel, Sharad Sharma, Abigail Hackam, Dhavalkumar Shah; HER2: A novel therapeutic target for retinoblastoma. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© ARVO (1962-2015); The Authors (2016-present)
HER2 (ERBB2), a member of the epidermal growth factor family, is overexpressed in variety of malignancies including breast, ovarian, gastric, colorectal, pancreatic and endometrial cancers. Overexpression and gene amplification of HER2 is associated with aggressive malignancies accompanied by chemoresistance and poor prognosis. HER2 has been successfully targeted in breast cancer therapy by humanized anti-HER2 antibody trastuzumab (Herceptin) and an antibody drug conjugate trastuzumab-DM1 (Kadcyla). In this study, we tested the hypothesis that HER2 is expressed in retinoblastoma (RB), a childhood malignancy of the retina, and can be targeted by anti-HER2 antibody based therapeutics.
To test the hypothesis that HER2 is expressed in retinoblastoma, we compared HER2 expression in four RB cell lines (Y79, WERI-RB27, RB143 and RB116) vs. breast cancer cell lines (BT474 and MDA-MB231), RB patient samples and breast cancer tumor arrays, as well as normal human ocular tissues by a variety of methods, including immunocytochemistry, flow cytometry, western immunoblot and RT-PCR. We utilized PCR primers that would detect all HER2 variants, as well as a variety of antibodies against HER2-specific epitopes. Once HER2 expression was confirmed, we tested the cytotoxic effect of trastuzumab and trastuzumab conjugates (T-vc-MMAE [DAR4 and DAR8]) on RB cells in vitro using an MTS assay.
HER2 expression was established in RB by flow cytometry, RT-PCR, immunohistochemistry of RB cell lines and an RB tumor tissue array. HER2 was not immunoreactive in normal ocular tissues.Western immunoblot analysis suggested a possible HER2 truncation in RB. This truncation spared the trastuzumab binding site and allowed us to test the cytotoxic effects of trastuzumab and its conjugates (T-vc-MMAE [DAR4 and DAR8]) on RB cells in vitro. Our data suggested that while trastuzumab itself was not cytotoxic in vitro, T-vc-MMAE was very effective in killing RB cells, where the DAR8 ADC (IC50=0.03-0.04 μM) was more potent than the DAR4 ADC (IC50=0.1-0.3 μM).
For the first time, we have reported on the expression of HER2 in retinoblastoma and the potential for anti-HER2 based therapy. Our discovery of HER2 expression in RB may lead to innovative and targeted drug treatment options with a wider therapeutic index and fewer systemic side effects, designed to spare the eye and preserve vision in RB patients.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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