Demers, Laurence M.

3587 Background: The Insulin like Growth Factor I receptor (IGF-IR), a tyrosine kinase, is widely expressed in human tissues. IGF- IR and its ligands (IGF-I and IGF-II) are expressed by many human cancers (e.g., breast, prostate, colorectal and non-small cell lung). Binding of the ligands to the IGF-IR activates key cellular signaling pathways important for stimulating cellular proliferation and inhibiting apoptosis. IGF- I and IGF-II are present in the circulation, but also locally expressed in neoplastic tissue. Bioavailability of these ligands is regulated by a family of IGF binding proteins (IGFBPs1–6). CP-751,871, a fully human monoclonal antibody, is a highly specific and potent inhibitor of IGF-IR activation. In vitro experiments show that binding of CP 751,871 to IGF-IR induces receptor internalization and degradation. This antibody has been shown to have antineoplastic activity using both in vivo and in vitro pre-clinical models. Methods: Blood samples were collected for characterization of the pharmacokinetic and pharmacodynamic properties of CP-751,871 in phase 1 trials of this agent given to cancer patients either alone or in combination with chemotherapy. The endpoints assessed included among others: CP-751,871 plasma concentrations, total and free IGF-I, IGFBP-3, soluble IGF-IR and IGF-IR expression on granulocytes and tumor cells. Results: CP 751,871 exposure increased with dose over the 800-fold dose range investigated. Pharmacokinetic profiles were consistent with target-mediated disposition. A dose-dependent downregulation of soluble IGF-IR serum concentration and IGF-IR expression was observed, with sustained inhibition for the entire dosing period (3–4 week cycles) observed at doses ≥ 1.5 mg/kg. As predicted for an agent that interferes with IGF-I action, IGF-I and IGFBP-3 serum levels were up-regulated in a similar dose-dependent manner. Conclusions: The pharmacodynamic endpoints of clinical trials provide evidence that CP-751,871 targets IGF-IR in granulocytes, tumor cells and tissues involved in regulation of the growth hormone -IGF-I axis. These data provide proof of principle for the use of CP-751,871 as a first-in-class therapeutic approach to inhibit the IGF-IR pathway in cancer patients. No significant financial relationships to disclose.

Abstract The effects of castration on bone histomorphometry and mineral homeostasis were compared in male and female rats. Measurements were performed 4 weeks after sham operation or gonadectomy. Orchiectomy produced increases in serum calcium and decreases in serum testosterone and androstenedione, whereas ovariectomy produced decreases in serum estradiol and testosterone. Orchiectomy did not alter static bone histomorphometric measurements of the tibial diaphysis, whereas ovariectomy increased cross-sectional and medullary areas, lowered endosteal tetracycline-labeled surface length, and markedly increased endosteal nonlabeled surface length. Orchiectomy decreased mean periosteal bone formation rate and mean periosteal bone apposition rate, whereas ovariectomy increased both measurements. Orchiectomy and ovariectomy markedly diminished trabecular area and trabecular surface length at the tibial metaphysis. Orchiectomy did not alter the number of osteoclasts per mm trabecular surface or the percentage of trabecular surface covered by osteoclasts, whereas ovariectomy increased both measurements. These findings indicate that gonadal hormones produce separate and distinct effects on bone metabolism as determined by histomorphometry in male and female rats.