Abstract 2570: The mechanism of anti-tumor effect of metformin for gemcitabine-resistant pancreatic adenocarcinoma
Authors: Suzuki Keiichi , Takeuchi Osamu , Ishii Yoshiyuki , Osaku Masayoshi 
Published: August 2015

Abstract
Several epidemiological studies have revealed the anti-cancer effects of metformin (MET), first-line treatment for type-2 diabetes mellitus, including against pancreatic ductal carcinoma (PDC). Gemcitabine (GEM) has become the standard chemotherapy for PDC but tolerance to GEM becomes an important issue.
We evaluated the anti-tumor effects of MET for GEM-resistant PDC in a xenograft mouse model. For this in vivo study, wild-type BxPC-3 was implanted into both flanks of female BALB/c nude mice. Mice were divided into four groups: (i) control (without any treatment); (ii) GEM-treated group (100 mg/kg); (iii) MET-treated group (600 mg/kg); and (iv) combined treatment group (G+M). Mice were fed for 4 weeks. Estimated tumor volumes and body weights were measured each week. Treatments were initiated 2 weeks after implantation. MET was administrated orally every day. GEM was given by intraperitoneal injection every week.
In the final tumor volumes, the two groups treated with GEM had significantly reduced tumors compared with control, but there were no differences between control and MET groups. The anti-tumor effect of MET for BxG30 (the cell line for GEM-resistant PDC) was evaluated using the method described above. Tumor volumes were decreased significantly in GEM+MET groups compared with control. The treated control ratio (T/C%) was calculated: GEM, 80.2%; MET, 54.0%; GEM+MET, 47.2%. The anti-tumor effect of GEM for BxG30 was limited. The MET group showed satisfactory anti-tumor effects, but T/C% was &lt;50% only in the GEM+MET group. This result revealed that combination therapy had excellent anti-tumor effects even for GEM-resistant PDC.
Western blot analysis was performed to confirm mammalian target of rapamycin (mTOR) expression level was surely inhibited. The results revealed that the expression level of mTOR treated with MET was significantly decreased, but no in GEM group. Then the expression level of hypoxia-inducible factor 1 (HIF-1) was evaluated by western blot analysis also. The results showed significant inhibition of HIF-1 expression by MET treatment, but not by GEM, again.
Our results showed that MET has a partial anti-tumor effect for PDC. Combination therapy has an excellent effect not only for wild-type PDC but also for GEM-resistant PDC. mTOR is well known as an upstream activator of HIF-1 function in cancer cells. That is, the mechanism of anti-tumor effect of MET seems to be, at least partly, the inhibition of HIF-1 through the mTOR regulation. These data suggest that MET could be used to treat PDC.
Citation Format: Keiichi Suzuki, Osamu Takeuchi, Yoshiyuki Ishii, Masayoshi Osaku. The mechanism of anti-tumor effect of metformin for gemcitabine-resistant pancreatic adenocarcinoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2570. doi:10.1158/1538-7445.AM2015-2570