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 6

Neuroendocrine and ASI-resistant prostate cancer cells upregulate cell surface CD46 expression, and exhibit enhanced sensitivity to CD46 ADC.

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Neuroendocrine and ASI-resistant prostate cancer cells upregulate cell s...
(A–E) CD46 is highly expressed on the surface of the NEPC cell line H660, and H660 is sensitive to CD46 ADC. (F–H) Upregulation of CD46 and enhanced sensitivity to CD46 ADC by ASI-resistant mCRPC cells. (A) FACS analysis of CD46 and PSMA expression on H660. (B) Antigen density (surface copy number per cell) for CD46 and PSMA on H660 cell (520,430 ± 52,020 for CD46 vs. 23,733 ± 8,591 for PSMA). ***P < 0.01 (P = 0.0007), Student’s t test, unpaired, 2-tailed; triplicate. (C) Western blot analysis showed CD46 protein expression as well as the neuroendocrine marker neuron-specific enolase (NSE). (D) YS5 IgG1 is internalized by H660 cells via macropinocytosis (colocalization with ND70) during 4-hour incubation at 37°C. The rate of colocalization was 83.33% (5/6). Scale bars: 30 μm. (E) CD46 ADC potently kills the neuroendocrine cancer line H660 in vitro (EC50 796 ± 460 pM). (F–H) CD46 antigen density increases in LNCaP-C4-2B cells following incubation with abiraterone (F) and enzalutamide (G) for 7 days, rising from 163,548 ± 6,402 before treatment to 336,690 ± 11,064 and 365,058 ± 42,168, respectively. ***P < 0.05 (P = 0.0002) (F) and **P < 0.01 (P = 0.0091) (G); Student’s t test, unpaired, 2-tailed; triplicate. The increased CD46 antigen density leads to increased sensitivity to CD46 ADC (H), with EC50 decreasing by 17-fold (226 ± 103 pM vs. 13 ± 1.8 pM). LNCaP C4-2B CD46 ADC: LNCaP-C4-2B cells treated with CD46 ADC. LNCaP C4-2B/Abi CD46 ADC: LNCaP-C4-2B cells with prior exposure to abiraterone were treated with CD46 ADC. LNCaP C4-2B Ctrl IgG ADC: LNCaP-C4-2B cells treated with the control ADC (Ctrl IgG-MC-vc-PAB-MMAF). LNCaP C4-2B/Abi Ctrl IgG ADC: LNCaP-C4-2B cells with prior exposure to abiraterone were treated with the control ADC (Ctrl IgG-MC-vc-PAB-MMAF).