Abstract 4402: The anti-tumor effects of two novel multivalent/multifunctional agents derived from hR1, a humanized anti-insulin-like growth factor receptor-I monoclonal antibody, are enhanced in renal cell carcinoma and synergistic with an mTOR inhibitor

Abstract

Abstract Among kidney cancer types, approximately 90% are renal cell carcinomas (RCC). Advanced or metastatic RCC, which presents in about one third of the patients, has a poor prognosis as it is resistant to conventional chemotherapy or radiotherapy. Treatments with human interferon-α2b (IFN-γ2b) alone or in combination with mammalian target of rapamycin (mTOR) inhibitors have led to only modest improvements in clinical outcomes. One observation made with mTOR inhibitors is that cancer cells can overcome the effects of the inhibitor by activating the insulin-like growth factor-I (IGF-I) signaling pathways. Clinically, there is an association of IGF-I receptor (IGF-IR) expression in RCC and poor long-term patient survival, particularly among patients with high-grade tumors. We have developed a humanized anti-IGF-IR monoclonal antibody, hR1, which binds to multiple tumor types, including RCC, resulting in effective down-regulation of IGF-IR and moderate inhibition of cell proliferation in vitro. To enhance the anti-tumor activity of hR1, we applied the Dock-and-Lock (DNL) platform technology to generate 1R-2b, comprising a conjugate of hR1 IgG with two dimers of interferon-α2b, and Hex-hR1, comprising 6 Fab fragments of hR1 tethered onto a common Fc. There was no loss in cell binding for both 1R-2b and Hex-hR1 when compared to parental hR1 as determined by flow cytometry. Units of activity for 1R-2b as measured by a luciferase reporter gene fused to a promoter containing the interferon-stimulated response element (iLite kit), yielded a specific activity of 3750 U/pmole versus 180 U/pmole and 3255 U/pmole for two different forms of peginterferon alpha-2a (60 and 31 kDa), respectively. An in vitro cytotoxicity assay with1R-2b demonstrated growth inhibition of two different RCC cell lines, 786-0 and ACHN with EC50-values of 0.049 and 0.062 pmole/mL, respectively. In terms of receptor down-regulation, Hex-hR1 could effectively down-regulate IGF-IR at concentrations 10-fold lower than parental hR1 IgG. In soft-agar growth assays, all three agents (hR1, Hex-hR1 and 1R-2b) could significantly inhibit colony formation of 786-0 and ACHN (P<0.038 and P<0.0022, respectively). When combined with temsirolimus, an mTOR inhibitor, in vitro cytotoxicity assays demonstrated a synergistic interaction with hR1, Hex-hR1, and 1R-2b. This synergy occurred at concentrations as low as 10 nM for hR1, 1 nM for Hex-hR1, and 2.6 nM for 1R-2b. Experimental therapeutic efficacy studies are currently underway to determine if these in vitro observations will translate to the in vivo setting. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4402. doi:1538-7445.AM2012-4402