Development of prostate specific membrane antigen targeted ultrasound microbubbles using bioorthogonal chemistry

PLoS One. 2017 May 4;12(5):e0176958. doi: 10.1371/journal.pone.0176958. eCollection 2017.

Abstract

Prostate specific membrane antigen (PSMA) targeted microbubbles (MBs) were developed using bioorthogonal chemistry. Streptavidin-labeled MBs were treated with a biotinylated tetrazine (MBTz) and targeted to PSMA expressing cells using trans-cyclooctene (TCO)-functionalized anti-PSMA antibodies (TCO-anti-PSMA). The extent of MB binding to PSMA positive cells for two different targeting strategies was determined using an in vitro flow chamber. The initial approach involved pretargeting, where TCO-anti-PSMA was first incubated with PSMA expressing cells and followed by MBTz, which subsequently showed a 2.8 fold increase in the number of bound MBs compared to experiments performed in the absence of TCO-anti-PSMA. Using direct targeting, where TCO-anti-PSMA was linked to MBTz prior to initiation of the assay, a 5-fold increase in binding compared to controls was observed. The direct targeting approach was subsequently evaluated in vivo using a human xenograft tumor model and two different PSMA-targeting antibodies. The US signal enhancements observed were 1.6- and 5.9-fold greater than that for non-targeted MBs. The lead construct was also evaluated in a head-to-head study using mice bearing both PSMA positive or negative tumors in separate limbs. The human PSMA expressing tumors exhibited a 2-fold higher US signal compared to those tumors deficient in human PSMA. The results demonstrate both the feasibility of preparing PSMA-targeted MBs and the benefits of using bioorthogonal chemistry to create targeted US probes.

MeSH terms

  • Animals
  • Antibodies / immunology
  • Antigens, Surface / immunology
  • Antigens, Surface / metabolism*
  • Glutamate Carboxypeptidase II / immunology
  • Glutamate Carboxypeptidase II / metabolism*
  • Heterografts
  • Humans
  • Male
  • Mice
  • Mice, Nude
  • Microbubbles*
  • Prostatic Neoplasms / immunology*
  • Prostatic Neoplasms / pathology
  • Ultrasonics*

Substances

  • Antibodies
  • Antigens, Surface
  • FOLH1 protein, human
  • Glutamate Carboxypeptidase II

Grants and funding

This study was supported by the Natural Sciences and Engineering Research Council of Canada (#227514), http://www.nserc-crsng.gc.ca/, recipient JFV; Ontario Institute for Cancer Research (# P.SI.015.8), https://oicr.on.ca/, recipient JFV; Canadian Cancer Society (# 703857), http://www.cancer.ca, recipients JFV and FSF; Terry Fox Research Institute, http://www.tfri.ca, recipient FSF. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.