Abstract LB-41: Histone deacetylase (HDAC) inhibition induces a resistance mechanism via the insulin-like growth factor-1 receptor (IGF-1R) signaling pathway: Rational basis for cotargeting of IGF-1R and HDAC in non-small cell lung cancer

Background: Histone deacetylase (HDAC), which modulate chromatin structure and gene expression, has attracted attention as a promising therapeutic target for hematologic and solid tumors including non-small cell lung cancer (NSCLC). However, the mechanisms resulting in the resistance to HDAC inhibitors are not yet well-known. In the current study, we investigated the involvement of insulin-like growth factor 1 receptor (IGF-1R) signaling in resistance to HDAC inhibitor in NSCLC.]\ Material and Methods: We assessed response of a panel of 14 NSCLC cells to vorinostat-based treatment by MTT assay. Because cells growing in monolayer on standard tissue culture plates could have different response to drug treatment compared with cells growing in vivo in three-dimensional environment, we also tested the effects of vorinostat on the cells cultured as spheroids on poly-HEMA coated plate or in soft agar. The antitumor effects of vorinostat, either alone or in combination with a novel anti-IGF-1R antibody, MK0646 (Merck) were evaluated in vitro using representative vorinostat-resistant NSCLC cell lines. The antitumor potency of the combination was evaluated in vivo using xenograft tumor models established in nude mice. The mice were treated twice a week with vorinostat (50 mg/kg), MK0646 (15 mg/kg) or their combination by intraperitoneal (IP) injection. Western blot, real time quantitative PCR, and immunohistochemical analyses were performed to assess biochemical changes, especially those related with IGF-1R signaling components. Results: Treatment with vorinostat at doses ranging from 0.5 to 50 μ M exhibited a range of sensitivities after 3-day treatment. IGF-1R expression remained unchanged or increased by vorinostat treatment in relatively resistant cells while relatively sensitive cells showed decreased expression of IGF-1R after the drug treatment. Addition of MK0646 enhanced cytotoxic activities of vorinostat in relatively resistant cells. In xenograft model, combined treatment of vorinostat and MK0646 significantly delayed the growth of H1299 and H226Br xenograft tumors compared with vehicle or single agent treatment. Conclusions: Our results suggested that (a) resistance to vorinostat is related to induction expression and subsequent activation of IGF-1R and (b) integration of IGF-IR-targeted agents is needed to the treatment regimens with vorinostat for patients with lung cancer. Results from this study provide a proof-of principle for clinical trials of MK0646 and vorinostat combination in patients with vorinostat-resistant NSCLC. Background: Histone deacetylase (HDAC), which modulate chromatin structure and gene expression, has attracted attention as a promising therapeutic target for hematologic and solid tumors including non-small cell lung cancer (NSCLC). However, the mechanisms resulting in the resistance to HDAC inhibitors are not yet well-known. In the current study, we investigated the involvement of insulin-like growth factor 1 receptor (IGF-1R) signaling in resistance to HDAC inhibitor in NSCLC. Materials and Methods: We assessed response of a panel of 14 NSCLC cells to vorinostat-based treatment by MTT assay. Because cells growing in monolayer on standard tissue culture plates could have different response to drug treatment compared with cells growing in vivo in three-dimensional environment, we also tested the effects of vorinostat on the cells cultured as spheroids on poly-HEMA coated plate or in soft agar. The antitumor effects of vorinostat, either alone or in combination with a novel anti-IGF-1R antibody, MK0646 (Merck) were evaluated in vitro using representative vorinostat-resistant NSCLC cell lines. The antitumor potency of the combination was evaluated in vivo using xenograft tumor models established in nude mice. The mice were treated twice a week with vorinostat (50 mg/kg), MK0646 (15 mg/kg) or their combination by intraperitoneal (IP) injection. Western blot, real time quantitative PCR, and immunohistochemical analyses were performed to assess biochemical changes, especially those related with IGF-1R signaling components. Results: Treatment with vorinostat at doses ranging from 0.5 to 50 μ M exhibited a range of sensitivities after 3-day treatment. IGF-1R expression remained unchanged or increased by vorinostat treatment in relatively resistant cells while relatively sensitive cells showed decreased expression of IGF-1R after the drug treatment. Addition of MK0646 enhanced cytotoxic activities of vorinostat in relatively resistant cells. In xenograft model, combined treatment of vorinostat and MK0646 significantly delayed the growth of H1299 and H226Br xenograft tumors compared with vehicle or single agent treatment. Conclusions: Our results suggested that (a) resistance to vorinostat is related to induction expression and subsequent activation of IGF-1R and (b) integration of IGF-IR-targeted agents is needed to the treatment regimens with vorinostat for patients with lung cancer. Results from this study provide a proof-of principle for clinical trials of MK0646 and vorinostat combination in patients with vorinostat-resistant NSCLC. Supported by the National Institutes of Health Grants R01 CA109520 (to H-Y. Lee) and CA100816 (to H-Y. Lee) and a Study Agreement with Merck and Company. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-41.