Abstract PO1-25-12: Metformin enhances response to chemotherapy combined with immunotherapy in a triple negative breast cancer in vivo model
Authors: Zamora Pilar , Pozo Angelo Gamez , Vega-Clemente Luz , Lopez-Camacho Elena , Trilla-Fuertes Lucia , Alonso-Martin David , Vara Juan Angel Fresno , Garcia-Arranz Mariano , Espinosa Enrique 
Published: May 2024

Abstract
Background
Triple-negative breast cancer (TNBC) is a heterogeneous group comprising several well-defined molecular subtypes. Classical chemotherapy remains the standard of care for advanced TNBC, although blockade of the PD-1/PD-L1 axis has emerged as a promising therapeutic option to enhance antitumor immunity. Atezolizumab is an immune checkpoint inhibitor targeting PD-L1 that has been approved for use in combination with paclitaxel for the treatment of advanced TNBC. Metformin (MTF) is a prescribed drug for type 2 diabetes with well-tolerated side-effects and has been reported to have anticancer effects. Xenograft mouse models studies of breast, lung and prostate cancer, have reveal a synergistic effect of MTF when combined with paclitaxel, carboplatin or doxorubicin and has been reported to enhance the efficacy of immunotherapy. In this work we want to explore the effect of including MTF in a chemo-immunotherapy scheme using an in vivo model. Methods 1x106 EMT6 TNBC cell line (ATCC® CRL-2755™) were implanted subcutaneously in the back of immunocompetent BALB/c mice. Treatment began when tumours reached a volume size of 30-100 mm3. At that moment, mice received the drug, or drugs combinations, for 21 days. All drugs were administered intraperitoneally, except for MTF, which was given orally in drinking water at a concentration of 1g/L. The anti PD-L1 drug anti-hPD-L1-mIgG1 (mATZ, 300 mg/week) was administered twice per week and doxorubicin (DOXO) every three days (0.3 mg/Kg or 6 mg/kg). The primary outcome will be tumour response. Tumour size was measured using a digital caliper every day until mice were euthanized. For tumour volume determination (mm3), two measures were taken (length and width). Volume was calculated as (length x wide2)/2. We tested three different arms: DOXO(0,3mg/Kg)+m-ATZ, DOXO(0,3mg/Kg)+m-ATZ+MTF, and DOXO(6mg/Kg)+m-ATZ. Each arm included 10 mice. Differences in tumour volume and mice weight were assessed by Kruskall-Wallis analysis. Results EMT6 cells produced a tumour mass in twenty seven out of thirty mice. Follow-up in mice in the DOXO(0.3mg/Kg)+m-ATZ and DOXO(6mg/Kg)+m-ATZ arms was interrupted in two weeks due to extended tumour growth and quality of live criteria, respectively. Mice in the DOXO(0.3mg/Kg)+m-ATZ+MTF arm were followed for three weeks. Increase of tumoral volume was assessed at 14 days. Mean increase was 205, 1096 and 365 mm3in the DOXO(6mg/Kg)+m-ATZ, DOXO(0,3mg/Kg)+m-ATZ, and DOXO(0,3mg/Kg)+m-ATZ+MTF arms respectively, being the volume increase between DOXO(0,3mg/Kg)+m-ATZ treated mice significantly higher. Regarding mice, mean weight at the beginning of the treatments was 19.8 gr for the complete mice population, whereas mean weight after 14 days of treatment was 15.4, 20.9 and 21.7 gr in the DOXO(6mg/Kg)+m-ATZ, DOXO(0,3mg/Kg)+m-ATZ, and DOXO(0,3mg/Kg)+m-ATZ+MTF arms respectively, showing a significant decrease of body weight in mice receiving a high dose of DOX, while no differences associated to the inclusion of MTF in the treatment scheme was found. Conclusions MTF addition to a combination of chemotherapy and immunotherapy in the treatment of TNBC increased therapy efficacy, with no added side effects. These result paves the way to explore treatment schemes with lower chemotherapy doses, decreasing toxicity side effects.
Citation Format: Pilar Zamora, Angelo Gamez Pozo, Luz Vega-Clemente, Elena Lopez-Camacho, Lucia Trilla-Fuertes, David Alonso-Martin, Juan Angel Fresno Vara, Mariano Garcia-Arranz, Enrique Espinosa. Metformin enhances response to chemotherapy combined with immunotherapy in a triple negative breast cancer in vivo model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-25-12.