LB-1 Exerts Antitumor Activity in Pancreatic Cancer by Inhibiting HIF-1α and Stat3 Signaling.

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Hypoxia is widely present in pancreatic cancer and subsequently causes the overexpression of hypoxia-inducible factor-1α (HIF-1α) and signal transducer and activator of transcription-3 (Stat3). HIF-1α and Stat3 function cooperatively to regulate a number of downstream genes that are implicated in tumorigenesis. Thus, inhibition of HIF-1α and Stat3 is a potential therapeutic strategy for pancreatic cancer. In this study, we explored how LB-1, a novel triptolide (LA) derivative, exerted its antitumor effect through blockade of HIF-1α and Stat3 signaling. Our data showed that LB-1 was able to inhibit the proliferation and colony formation of Mia-PaCa2 and SW1990 cells. LB-1 suppressed HIF-1α protein accumulation by promoting its proteasome degradation and reducing transactivation. Moreover, the silence of HIF-1α by shRNA partially prevented the proliferation inhibition triggered by LB-1. As expected, LB-1 also decreased Stat3 protein accumulation and blocked the physical interactions between HIF-1α/p300/phosphor-Stat3 (p-Stat3) at the pharmacological concentration to reduce VEGF expression, thereby hypoxia-induced angiogenesis. In the Mia-PaCa2 nude xenograft model, therapeutic treatment with LB-1 significantly inhibited tumor growth and had minimal systemic toxicity compared to the mother drug LA. Furthermore, in accordance with in vitro results, HIF-1α activation and Stat3 expression in tumors were blocked by LB-1 through mTOR-dependent pathway. Taken together, these results illustrate that, as a potent inhibitor of HIF-1α and Stat3 signaling, LB-1 exhibits antitumor effect and could be potentially used to treat pancreatic cancer.