EXTH-25. Highly potent drug candidate for the treatment of brain metastatic lung cancer and melanoma

Abstract Several cancers metastasize preferentially to the brain, including lung cancer and melanoma, where their prognosis is dismal. Previously, we found four receptors that are over-expressed in glioblastoma (GBM) and more recently, in breast cancer brain metastases (BCBM): EphA2, EphA3, EphB2, and interleukin 13 receptor alpha 2 (IL-13RA2). A multivalent ligand, termed QUAD, targets all these four receptors and can be conjugated with DM1, a microtubule-disrupting agent (QUAD-DM1). This conjugate demonstrates specific potency and receptor-dependent killing of GBM and BCBM cells/tumors. We have thus examined whether lung cancer and melanoma that frequent brain metastases, express these receptors. We found that the four targeted receptors are over-expressed in nine types of brain metastatic lung cancers by immunohistochemical staining. The most prominently over-expressed receptors were IL-13RA2 and EphA3 and only one tumor out of 18 studied was negative for all four receptors. The genes for epha2, epha3, and ephb2 were most prominently expressed using cancer heatmaps from The Cancer Genome Atlas (TCG). The four receptors were readily detected using Western blots in A549, SK-LU-1, SK-MES-1 and NCI-H358 established primary lung cancer cells. These cells were killed potently by QUAD-DM1 (IC50 of 10-8M or less). In continuation of this study in melanoma, we found general over-expression of the genes for epha2, epha3, and ephb2, and less so for il-13ra2. We observed robust over-expression of IL-13RA2, EphA2, EphA3 and EphB2 receptors in a brain metastatic melanoma tissue microarray available (four patients). Potent cell killing was observed in 7/8 melanoma cells lines by QUAD-DM1 (IC50 of 10-8M - 10-11M). The cells over-expressed at least one of the targeted receptors. Specific binding to the individual four receptors was detected in the A-375 human melanoma cell line. A novel multivalent drug conjugate QUAD-DM1 should be further explored for the treatment of brain metastatic lung cancer and melanoma.