Purpose: Obesity is associated with increased risk and worse outcomes for endometrial cancer (EC). Metformin, a frontline therapy for type 2 diabetes, is thought to have both indirect and direct anti-cancer effects via decreasing circulating insulin/glucose and activating AMPK/inhibiting mTOR signaling, respectively. Due to its positive charge (pKa 12.4) and hydrophilicity (logD -6.13 at pH 7.4), metformin requires cation transporters for cellular uptake where it can then activate AMPK; and thus, variation in transporter expression may be critical for response to metformin for cancer treatment. Thus, we explored the inter-relationship of obesity, cation transporter expression and the anti-tumorigenic efficacy of metformin in a genetically engineered endometrioid EC mouse model.
Methods: LKB1fl/fl p53fl/fl mice were fed a low-fat diet (10% calories from fat) vs. a high-fat diet (60% calories from fat) to mimic diet-induced obesity, starting at 3 weeks of age (n=10 mice/group). AdCre was injected at 6 weeks of age to induce EC. Mice were treated for four weeks with placebo or metformin (200 mg/kg/day, oral gavage) following tumor onset. Cell proliferation/apoptotic markers and downstream targets of AMPK/mTOR signaling were evaluated in the ECs by immunohistochemistry. Cation transporter expression was assessed in the ECs by Western blotting and RNA sequencing.
Results: Obesity led to a doubling of endometrial tumor size in obese vs. lean mice (1.469g vs. 0.75g). Metformin was more potent in inhibiting tumor growth in obese vs. lean mice (78% vs. 60%) compared to the respective controls (p<0.05). Metformin (i) decreased expression of Ki-67 and cyclin D1 (cell proliferation markers) by 65% and 15%, respectively, in tumors from obese mice and by 18% and 5%, respectively, in tumors from lean mice vs. their respective controls (p<0.05); (ii) increased cleaved caspase-3 (marker of apoptosis) in tumors from obese and lean mice (2.3 fold and 2.1 fold) vs. their respective controls (p<0.05); (iii) increased phosphorylated AMPK expression and decreased expression of phosphorylated S6 in ECs from obese and lean mice vs. their respective controls (p<0.05); (iv) increased cation transporter OCT3 and PMAT gene expression in only tumors from obese mice, with a trend towards higher protein expression of OCT1 and 3 and MATE1 and 2 with metformin treatment in ECs from both lean and obese mice.
Conclusion: Our data suggest that metformin has greater anti-tumorigenic efficacy in obese vs. lean mice with EC. In addition, cation transporters were expressed in the endometrial tumors and were affected by metformin treatment. Studies are underway in EC patients to understand the impact of obesity and transporter expression on response rates to metformin in the clinic.
Note: This abstract was not presented at the meeting.
Citation Format: Aruljothi Muralidharan, Hui Guo, Jianjun Han, Lu Zhang, Wenchuan Sun, Yajie Yin, Chunxiao Zhou, Ruth S. Everett, Dhiren R. Thakker, Victoria L. Bae-Jump. Metformin treatment outcomes in relation to obesity and cation transporter expression in mouse models of endometrial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3609.