99mTechnetium- or Cy7-Labeled Fab(Tocilizumab) as Potential Multiple Myeloma Imaging Agents

Anticancer Agents Med Chem. 2021;21(14):1883-1893. doi: 10.2174/1871520621999210104181238.

Abstract

Background: Multiple Myeloma (MM) is a malignant hematologic disorder and the second most common blood cancer. Interleukin-6 (IL-6) has been identified as a crucial factor for the proliferation and survival of MM cells and the overexpression of IL-6 receptor is being studied as a molecular target for therapeutic and diagnostic use in myelomas and other comorbidities. Tocilizumab is a humanized monoclonal antibody that binds IL-6R.

Objective: We aim to label and evaluate Fab(Tocilizumab) with 99mTechnetium or Cy7 as potential MM imaging agents.

Methods: IL-6R distribution was analyzed by Laser Confocal Microscopy (LCM) in MM cell lines. Fab(Tocilizumab) was produced by the digestion of Tocilizumab with papain for 24h at 37°C, derivatized with NHS-HYNIC-Tfa and radiolabeled with 99mTc. Radiochemical stability and in vitro cell assays were evaluated. Biodistribution and SPECT/CT were performed. Also, Fab(Tocilizumab) was labeled with Cy7 for in vivo fluorescence imaging up to 72h.

Results: LCM analysis demonstrates IL-6R distribution on MM cell lines. Incubation with papain resulted in complete digestion of Tocilizumab and exhibited a good purity and homogeneity. Radiolabeling with 99mTc via NHS-HYNIC-Tfa was found to be fast, easy, reproducible and stable, revealing high radiochemical purity and without interfering with IL-6R recognition. Biodistribution and SPECT/CT studies showed a quick blood clearance and significant kidney and MM engrafted tumor uptake. Cy7-Fab(Tocilizumab) fluorescent imaging allowed MM1S tumor identification up to 72h p.i.

Conclusion: These new molecular imaging agents could potentially be used in the clinical setting for staging and follow-up of MM through radioactive whole-body IL-6R expression visualization in vivo. The fluorescent version could be used for tissue sample evaluation and to guide surgical excision, if necessary.

Keywords: 99mTechnetium- or Cy7-lableled Fab(Tocilizumab).; Fab(Tocilizumab); IL-6R; molecular imaging; multiple myeloma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal, Humanized / chemistry*
  • Carbocyanines / chemistry*
  • Humans
  • Molecular Imaging*
  • Multiple Myeloma / diagnostic imaging*
  • Organotechnetium Compounds / chemistry*
  • Radiopharmaceuticals / chemistry*
  • Receptors, Interleukin-6 / analysis

Substances

  • Antibodies, Monoclonal, Humanized
  • Carbocyanines
  • IL6R protein, human
  • Organotechnetium Compounds
  • Radiopharmaceuticals
  • Receptors, Interleukin-6
  • indotricarbocyanine
  • tocilizumab