title: Intracellular activation of SGN-35, a potent anti-CD30 antibody-drug conjugate.
abstract: OBJECTIVE
  SGN-35 is an antibody-drug conjugate (ADC) containing the potent antimitotic drug, monomethylauristatin E (MMAE), linked to the anti-CD30 monoclonal antibody, cAC10. As previously shown, SGN-35 treatment regresses and cures established Hodgkin lymphoma and anaplastic large cell lymphoma xenografts. Recently, the ADC has been shown to possess pronounced activity in clinical trials. Here, we investigate the molecular basis for the activities of SGN-35 by determining the extent of targeted intracellular drug release and retention, and bystander activities.
  
  
  METHODS
  SGN-35 was prepared with (14)C-labeled MMAE. Intracellular ADC activation on CD30(+) and negative cell lines was determined using a combination of radiometric and liquid chromatograhpy/mass spectrometry-based assays. The bystander activity of SGN-35 was determined using mixed tumor cell cultures consisting of CD30(+) and CD30(-) lines.
  
  
  RESULTS
  SGN-35 treatment of CD30(+) cells leads to efficient intracellular release of chemically unmodified MMAE, with intracellular concentrations of MMAE in the range of 500 nmol/L. This was due to specific ADC binding, uptake, MMAE retention, and receptor recycling or resynthesis. MMAE accounts for the total detectable released drug from CD30(+) cells, and has a half-life of retention of 15 to 20 h. Cytotoxicity studies with mixtures of CD30(+) and CD30(-) cell lines indicated that diffusible released MMAE from CD30(+) cells was able to kill cocultivated CD30(-) cells.
  
  
  CONCLUSIONS
  MMAE is efficiently released from SGN-35 within CD30(+) cancer cells and, due to its membrane permeability, is able to exert cytotoxic activity on bystander cells. This provides mechanistic insight into the pronounced preclinical and clinical antitumor activities observed with SGN-35.
authors.affiliation: Seattle Genetics, Inc., Bothell, Washington, USA. nokeley@seagen.com
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Okeley
authors.forename: Jamie B
authors.initials: JB
authors.lastname: Miyamoto
authors.forename: Xinqun
authors.initials: X
authors.lastname: Zhang
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Sanderson
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Benjamin
authors.forename: Eric L
authors.initials: EL
authors.lastname: Sievers
authors.forename: Peter D
authors.initials: PD
authors.lastname: Senter
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Alley
mesh_terms: D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000079963:Brentuximab Vedotin; D024201:Bystander Effect / Q000187:drug effects; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D006801:Humans; D018796:Immunoconjugates / Q000378:metabolism / Q000494:pharmacology*; D017730:Ki-1 Antigen / Q000276:immunology*; D009842:Oligopeptides / Q000378:metabolism
chemical_list: D000888:Antibodies, Anti-Idiotypic; D018796:Immunoconjugates; D017730:Ki-1 Antigen; D009842:Oligopeptides; D000079963:Brentuximab Vedotin; C495575:monomethyl auristatin E