title: Targeting both IGF-1R and mTOR synergistically inhibits growth of renal cell carcinoma in vitro.
abstract: BACKGROUND
  Advanced or metastatic renal cell carcinoma (RCC) has a poor prognosis, because it is relatively resistant to conventional chemotherapy or radiotherapy. Treatments with human interferon-α2b alone or in combination with mammalian target of rapamycin (mTOR) inhibitors have led to only a modest improvement in clinical outcome. One observation made with mTOR inhibitors is that carcinomas can overcome these inhibitory effects by activating the insulin-like growth factor-I (IGF-I) signaling pathway. Clinically, there is an association of IGF-I receptor (IGF-IR) expression in RCC and poor long-term patient survival. We have developed a humanized anti-IGF-IR monoclonal antibody, hR1, which binds to RCC, resulting in effective down-regulation of IGF-IR and moderate inhibition of cell proliferation in vitro. In this work, we evaluate the anti-tumor activity of two novel IGF-1R-targeting agents against renal cell carcinoma given alone or in combination with an mTOR inhibitor.
  
  
  METHODS
  hR1 was linked by the DOCK-AND-LOCK™ (DNL™) method to four Fabs of hR1, generating Hex-hR1, or to four molecules of interferon-α2b, generating 1R-2b. Eight human RCC cell lines were screened for IGF-1R expression and sensitivity to treatment with hR1 in vitro. Synergy with an mTOR inhibitor, temsirolimus, was tested in a cell line (ACHN) with low sensitivity to hR1.
  
  
  RESULTS
  Hex-hR1 induced the down-regulation of IGF-IR at 10-fold lower concentrations compared to the parental hR1. Sensitivity to growth inhibition mediated by hR1 and Hex-hR1 treatments correlated with IGF-1R expression (higher expression was more sensitive). The potency of 1R-2b to inhibit the in vitro growth of RCC was also demonstrated in two human cell lines, ACHN and 786-O, with EC50-values of 63 and 48 pM, respectively. When combined with temsirolimus, a synergistic growth-inhibition with hR1, Hex-hR1, and 1R-2b was observed in ACHN cells at concentrations as low as 10 nM for hR1, 1 nM for Hex-hR1, and 2.6 nM for 1R-2b.
  
  
  CONCLUSIONS
  Both Hex-hR1 and 1R-2b proved to be more potent than parental hR1 in inhibiting growth of RCC in vitro. Synergy was achieved when each of the three hR1-based agents was combined with temsirolimus, suggesting a new approach for treating RCC.
authors.affiliation: Immunomedics, Inc, 300 American Rd, Morris Plains, NJ 07950, USA. tcardillo@immunomedics.com
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Cardillo
authors.forename: Preeti
authors.initials: P
authors.lastname: Trisal
authors.forename: Roberto
authors.initials: R
authors.lastname: Arrojo
authors.forename: David M
authors.initials: DM
authors.lastname: Goldenberg
authors.forename: Chien-Hsing
authors.initials: CH
authors.lastname: Chang
mesh_terms: D000818:Animals; D002292:Carcinoma, Renal Cell / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D006801:Humans; D007680:Kidney Neoplasms / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D047428:Protein Kinase Inhibitors; D017526:Receptor, IGF Type 1; D058570:TOR Serine-Threonine Kinases
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