Characterization of Site-Specifically Conjugated Monomethyl Auristatin E- and Duocarmycin-Based Anti-PSMA Antibody-Drug Conjugates for Treatment of PSMA-Expressing Tumors

J Nucl Med. 2018 Mar;59(3):494-501. doi: 10.2967/jnumed.117.196279. Epub 2017 Nov 16.


Prostate cancer (PCa) is the most common cancer in men worldwide. In general, PCa responds poorly to chemotherapy. Therefore, antibody-drug conjugates (ADCs) have been developed to specifically deliver highly cytotoxic drugs to the tumor. Because the prostate-specific membrane antigen (PSMA) is overexpressed in PCa, it represents a promising target for ADC-based therapies. The aim of this study was to evaluate the therapeutic efficacy of site-specifically conjugated duocarmycin- and monomethyl auristatin E (MMAE)-based anti-PSMA ADCs with drug-to-antibody ratios (DARs) of 2 and 4. Methods: The glycan group of the anti-PSMA antibody D2B was chemoenzymatically conjugated with duocarmycin or MMAE. Preservation of the immunoreactivity of the antibody on site-specific conjugation was investigated in vitro. Biodistribution and small-animal SPECT/CT imaging (18.5 ± 2.6 MBq) with 25 μg of 111In-labeled ADCs were performed on BALB/c nude mice with subcutaneous PSMA-positive LS174T-PSMA xenografts. Finally, the therapeutic efficacy of the 4 different ADCs was assessed in mice with LS174T-PSMA tumors. Results: The immunoreactivity of the anti-PSMA antibody was preserved on site-specific conjugation. Biodistribution revealed high tumor uptake of all agents. The highest tumor uptake was observed in mice administered with 111In-D2B-DAR2-MMAE, reaching 119.7 ± 37.4 percentage injected dose per gram at 3 d after injection. Tumors of mice injected with 111In-D2B, 111In-D2B-DAR2-duocarmycin, 111In-D2B-DAR4-duocarmycin, 111In-D2B-DAR2-MMAE, and 111In-D2B-DAR4-MMAE could clearly be visualized with small-animal SPECT/CT. In contrast to unconjugated D2B or vehicle, treatment with either of the MMAE-based ADCs, but not with a duocarmycin-based ADC, significantly impaired tumor growth and prolonged median survival from 13 d (phosphate-buffered saline) to 20 and 29 d for DAR2 and DAR4 ADC, respectively. Tumor-doubling time increased from 3.5 ± 0.5 d to 5.2 ± 1.8 and 9.2 ± 2.1 d after treatment with D2B-DAR2-MMAE and D2B-DAR4-MMAE, respectively. Conclusion: The site-specifically conjugated anti-PSMA ADCs D2B-DAR2-MMAE and D2B-DAR4-MMAE efficiently targeted PSMA-expressing xenografts, effectively inhibited tumor growth of PSMA-expressing tumors, and significantly prolonged survival of mice.

Keywords: antibody–drug conjugate; duocarmycin; monomethyl auristatin E (MMAE); prostate cancer; prostate-specific membrane antigen (PSMA).

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Cell Transformation, Neoplastic
  • Duocarmycins
  • Gene Expression Regulation, Neoplastic*
  • Glutamate Carboxypeptidase II / metabolism*
  • Immunoconjugates / chemistry*
  • Immunoconjugates / pharmacokinetics
  • Immunoconjugates / therapeutic use*
  • Indoles / chemistry*
  • Male
  • Mice
  • Mice, Nude
  • Oligopeptides / chemistry*
  • Prostatic Neoplasms / diagnostic imaging
  • Prostatic Neoplasms / drug therapy*
  • Prostatic Neoplasms / metabolism
  • Prostatic Neoplasms / pathology
  • Pyrrolidinones / chemistry
  • Single Photon Emission Computed Tomography Computed Tomography
  • Tissue Distribution


  • Duocarmycins
  • Immunoconjugates
  • Indoles
  • Oligopeptides
  • Pyrrolidinones
  • Glutamate Carboxypeptidase II
  • duocarmycin A
  • monomethyl auristatin E