Targeting CD46 for both adenocarcinoma and neuroendocrine prostate cancer
Yang Su, … , Eric J. Small, Bin Liu
Yang Su, … , Eric J. Small, Bin Liu
Published September 6, 2018
Citation Information: JCI Insight. 2018;3(17):e121497. https://doi.org/10.1172/jci.insight.121497.
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Research Article Oncology Therapeutics

Targeting CD46 for both adenocarcinoma and neuroendocrine prostate cancer

Abstract

Although initially responsive to androgen signaling inhibitors (ASIs), metastatic castration-resistant prostate cancer (mCRPC) inevitably develops and is incurable. In addition to adenocarcinoma (adeno), neuroendocrine prostate cancer (NEPC) emerges to confer ASI resistance. We have previously combined laser capture microdissection and phage antibody display library selection on human cancer specimens and identified novel internalizing antibodies binding to tumor cells residing in their tissue microenvironment. We identified the target antigen for one of these antibodies as CD46, a multifunctional protein that is best known for negatively regulating the innate immune system. CD46 is overexpressed in primary tumor tissue and CRPC (localized and metastatic; adeno and NEPC), but expressed at low levels on normal tissues except for placental trophoblasts and prostate epithelium. Abiraterone- and enzalutamide-treated mCRPC cells upregulate cell surface CD46 expression. Genomic analysis showed that the CD46 gene is gained in 45% abiraterone-resistant mCRPC patients. We conjugated a tubulin inhibitor to our macropinocytosing anti-CD46 antibody and showed that the resulting antibody-drug conjugate (ADC) potently and selectively kills both adeno and NEPC cell lines in vitro (sub-nM EC50) but not normal cells. CD46 ADC regressed and eliminated an mCRPC cell line xenograft in vivo in both subcutaneous and intrafemoral models. Exploratory toxicology studies of the CD46 ADC in non-human primates demonstrated an acceptable safety profile. Thus, CD46 is an excellent target for antibody-based therapy development, which has potential to be applicable to both adenocarcinoma and neuroendocrine types of mCRPC that are resistant to current treatment.

Authors

Yang Su, Yue Liu, Christopher R. Behrens, Scott Bidlingmaier, Nam-Kyung Lee, Rahul Aggarwal, Daniel W. Sherbenou, Alma L. Burlingame, Byron C. Hann, Jeffry P. Simko, Gayatri Premasekharan, Pamela L. Paris, Marc A. Shuman, Youngho Seo, Eric J. Small, Bin Liu

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Figure 3

Internalization by macropinocytosis and tumor-selective killing by CD46 ADC.

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Internalization by macropinocytosis and tumor-selective killing by CD46 ...
(A) Confocal microscopy study of YS5 IgG1 internalization into mCRPC lines (DU145, LNCaP-C4-2B, and PC3M) and primary human T cells. Colocalization between the macropinocytosis marker ND70 and YS5 IgG1 is analyzed in a single confocal slice. The rate of colocalization, calculated as the percentage of double-positive intracellular spots relative to antibody-positive intracellular spots, was 93.75% (15 of 16) for DU145, 94.44% (LNCaP-C4-2B), and 92.68% (38 of 41) for PC3M. There was no internalization and no colocalization for primary T cells. In the above experiment, the BPH-1 cell line was used as a negative control (no YS5 binding and no fluorescence signal; data not shown). Nuc, nuclei. Scale bars: 30 μm. (B) In vitro tumor killing assay by CD46 ADC. YS5-MC-vc-PAB-MMAF was incubated with a panel of mCRPC lines (LNCaP-C4-2B, DU145, and PC3M) and control normal human cells (BPH-1, CD3+ T cells, and CD14-depleted PBMCs, and the normal human primary prostate epithelial cell line HPrEpC). A nonbinding human IgG1 was conjugated to MMAF and used as a control. EC50 values were 275 ± 98 pM for LNCaP-C4-2B; 1.13 ± 0.45 nM for DU145; and 607 ± 172 pM for PC3M. No cytotoxic effects were observed on the panel of control normal cells studied across the ADC concentration (conc.) range.