title: Targeting HER2-positive cancer with dolastatin 15 derivatives conjugated to trastuzumab, novel antibody-drug conjugates.
abstract: OBJECTIVE
  Targeting tubulin binders to cancer cells using antibody-drug conjugates (ADCs) has great potential to become an effective cancer treatment with low normal tissue toxicity. The nature of the linker used to tether the tubulin binder to the antibody and the conjugation sites on the antibody and the small molecule are important factors in the ADC stability and effectiveness.
  
  
  METHODS
  We explored the use of tubulin-targeting dolastatin 15 derivatives (Dol15) tethered covalently to a representative antibody, trastuzumab, via cleavable and non-cleavable linkers at varying antibody reactive sites (i.e., lysine residues, partially reduced hinge region disulfide bonds) and drug coupling sites (i.e., C-terminus, N-terminus), to investigate which constructs were more effective in killing HER2-positive cells in vitro and in vivo.
  
  
  RESULTS
  We found that Dol15 conjugated to trastuzumab via lysine residues at the drug C-terminus using a non-cleavable linker (trastuzumab-amide-C-term-Dol15) produced target-dependent growth inhibition of cells endogenously expressing high HER2 levels (i.e., SK-BR-3, SK-OV-3) in vitro. This ADC was effective at varying doses (i.e., 10 and 20 mg/kg) in the SK-OV-3 human ovarian cancer xenograft.
  
  
  CONCLUSIONS
  Tethering Dol15 via partially reduced disulfide bonds at the drug C-terminus via a non-cleavable linker (trastuzumab-MC-C-term-Dol15) resulted in an equally effective ADC in vitro, showing that site of antibody conjugation did not influence ADC activity. However, tethering Dol15 at the drug N-terminus using non-cleavable and cleavable linkers (trastuzumab-MC-N-term-Dol15 and trastuzumab-MC-VC-PABC-N-term-Dol15, respectively) resulted in ineffective ADCs. Thus, Dol15 tethered at the C-terminus may be a useful tubulin-targeting agent for conjugation at various antibody reactive sites.
authors: Drugs and Biomaterials R&D, Genzyme a Sanofi Company, Cambridge, MA 02142, USA. diego.gianolio@genzyme.com
authors: Diego A
authors: DA
authors: Gianolio
authors: Cecile
authors: C
authors: Rouleau
authors: William E
authors: WE
authors: Bauta
authors: Dennis
authors: D
authors: Lovett
authors: William R
authors: WR
authors: Cantrell
authors: Antonio
authors: A
authors: Recio
authors: Paul
authors: P
authors: Wolstenholme-Hogg
authors: Michelle
authors: M
authors: Busch
authors: Peng
authors: P
authors: Pan
authors: James E
authors: JE
authors: Stefano
authors: Hildegard M
authors: HM
authors: Kramer
authors: James
authors: J
authors: Goebel
authors: Roy D
authors: RD
authors: Krumbholz
authors: Stephanie
authors: S
authors: Roth
authors: Steven M
authors: SM
authors: Schmid
authors: Beverly A
authors: BA
authors: Teicher
mesh_terms: D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage* / Q000737:chemistry / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D047630:Depsipeptides / Q000008:administration & dosage* / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016503:Drug Delivery Systems; D005260:Female; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000473:pathology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000276:immunology*; D000068878:Trastuzumab; D014404:Tubulin / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D047630:Depsipeptides; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; D014404:Tubulin; C075610:dolastatin 15