Novel Metformin Analogues for Treatment of Pancreatic Cancer

Abstract

Pancreatic ductal adenocarcinoma (PDCA) is a leading cause of cancer death in the US. Patients diagnosed with PDCA generally present with advanced disease with poor prognosis and limited treatment options. African American patients have higher incidence and mortality of PDCA than Caucasian American or any other ethnic group. Different factors have been attributed to contribute to this health disparity, among them higher incidence of Diabetes Mellitus type 2. To address the need for new therapeutic approaches, we note epidemiologic reports that patients with diabetes mellitus-type 2 treated with the biguanide drug metformin, but not other antidiabetic drugs, have a reduced risk of PDCA and an increased survival rate among those with PDCA. The main physiologic effect of metformin is to lower blood glucose and reduce hyperinsulinemia associated with insulin resistance. In the cell, metformin stimulates AMP-activated protein kinase (AMPK) that in turn inhibits mTORC1 which integrates signals from an array of intracellular pathways to regulate cell growth. Recent clinical trials describe modest antiproliferative effects from use of neoadjuvant metformin, but no significant clinical benefit occurred when metformin was dosed at glycemic control levels in patients with advanced cancers. These findings suggest that development of more potent anticancer analogues of metformin may help to boost clinical benefit and patient survival. Hence, we have designed new biguanide analogues of metformin, and screening of these compounds in preclinical PDCA models show that selected analogues are more efficacious in blocking tumor progression than parental metformin at lower doses. Using proliferation assays in vitro, PDCA cells (Panc 1, MIA Paca-2) were treated 72-hrs with metformin or analogues, and greater dose-dependent inhibition of PDCA cell proliferation was found with analogues as compared to metformin (P<0.001). Further, apoptosis was also markedly induced by metformin analogues as compared to parental metformin (P<0.01). Antitumor effects of metformin are attributed in part to activation LKB1-AMPK pathways and downstream blockade of mTOR signaling, which is often increased in PDCA cells. Using PDCA cells treated in vitro with analogues for 24-hrs, we find that analogues induce AMPK phosphorylation and suppression of mTOR signaling, thus blocking protein synthesis and tumor proliferation. With an in vivo PANC 1 xenograft model in nude mice, lead metformin analogues given by oral gavage daily significantly inhibited tumor progression over 28-days as compared to appropriate controls (P<0.0001). Our findings show that selected metformin analogues have potent anticancer activity in preclinical PDCA models and may have promise as new targeted therapeutics for patients afflicted with this deadly disease. [Funded by NIH/NCI R21CA176337 and NIH/NCI U54 CA143930]