1, 9-pyrazoloanthrones downregulate hif-1α and sensitize cancer cells to cetuximab-mediated anti-egfr therapy1,9-pyrazoloanthrones下调hif-1α和提高癌细胞对cetuximab-mediated anti-egfr疗法.pdfVIP

1, 9-Pyrazoloanthrones Downregulate HIF-1a and Sensitize Cancer Cells to Cetuximab-Mediated Anti-EGFR Therapy Yang Lu, Xinqun Li, Haiquan Lu, Zhen Fan* Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America Abstract Cetuximab, a monoclonal antibody that blocks the epidermal growth factor receptor (EGFR), is currently approved for the treatment of several types of solid tumors. We previously showed that cetuximab can inhibit hypoxia-inducible factor-1 alpha (HIF-1a) protein synthesis by inhibiting the activation of EGFR downstream signaling pathways including Erk, Akt, and mTOR. 1, 9-pyrazoloanthrone (1, 9 PA) is an anthrapyrazolone compound best known as SP600125 that specifically inhibits c-jun N-terminal kinase (JNK). Here, we report 1, 9 PA can downregulate HIF-1a independently of its inhibition of JNK. This downregulatory effect was abolished when the oxygen-dependent domain (ODD) of HIF-1a (HIF-1a-DODD, the domain responsible for HIF-1a degradation) was experimentally deleted or when the activity of HIF-1a prolyl hydroxylase (PHD) or the 26S proteasomal complex was inhibited, indicating that the 1, 9 PA downregulates HIF-1a by promoting PHD- dependent HIF-1a degradation. We found that the combination of 1, 9 PA and cetuximab worked synergistically to induce apoptosis in cancer cells in which cetuximab or 1, 9 PA alone had no or only weak apoptotic activity. This synergistic effect was substantially decreased in cancer cells transfected with HIF-1a-DODD, indicating that downregulation of HIF-1a was the mechanism of this synergistic effect. More importantly, 1, 9 PA can downregulate HIF-1a in cancer cells that are insensitive to cetuximab-induced inhibition of HIF-1a expression due to overexpression of oncogenic Ras (RasG