Metformin as an Alternative Radiosensitizing Agent to 5-Fluorouracil During Neoadjuvant Treatment for Rectal Cancer

Abstract

BACKGROUND: Neoadjuvant chemoradiation for locally advanced rectal cancer combining 5-fluorouracil with radiation increases tumor regression compared with radiation alone. However, it occurs at the cost of significant treatment-related toxicity. Patients with rectal cancer using metformin have been associated with improved response to radiotherapy. OBJECTIVE: The purpose of this study was to evaluate the radiosensitizing effects of metformin in vitro and in vivo and compare it with a standard combination of radiation/5-fluorouracil. DESIGN: Colorectal cancer cell lines SW480, HT29, and HCT116 were used as models. Cell viability was compared under treatments with radiation, radiation/5-fluorouracil, metformin, radiation/metformin, and radiation/5-fluorouracil/metformin. Nude mice were injected subcutaneously with SW480 cells and treated for 1 week with radiation/5-fluorouracil, metformin, radiation/metformin, or radiation/5-fluorouracil/metformin. Tumor volume was evaluated for 4 weeks after treatment completion. The phosphorylation status of key proteins of the PI3K/Akt/mTOR pathway was determined by immunoblots. SETTINGS: This was an experimental study conducted in vitro and in vivo. PATIENTS: Animal models/cell lines were used. MAIN OUTCOME MEASURES: The end point was to investigate how metformin compares with 5-fluorouracil as a radiosensitizer. RESULTS: All cell lines significantly decreased cell viability after treatment with radiation/metformin when compared with radiation alone. Radiation/metformin was superior to radiation/5-fluorouracil in SW480 (37% vs 74%; p < 0.001). In HT29 and in HCT116, radiation/metformin was inferior to radiation/5-fluorouracil (40.0% vs 13.8%, p < 0.001 and 40.0% vs 7.0%, p < 0.001), mainly because of increased 5-fluorouracil toxicity (≤20% of cell viability). In vivo assays indicated that radiation/metformin treatment was comparable with radiation/5-fluorouracil (557 vs 398 mm3; p > 0.05) and that the addition of metformin to the standard radiation/5-fluorouracil did not improve tumor response (349 mm3; p > 0.05). Metformin exerted strong PI3K/Akt/mTOR pathway inactivation effects after 24-hour exposure (increasing pAMPK, p < 0.01; decreasing pAkt, p < 0.01; and pS6, p <0.05). LIMITATIONS: In vitro and in vivo chemoradiation regimens cannot be directly translated to human delivery methods. CONCLUSIONS: Metformin enhances tumor response to radiation in vitro and in vivo. Metformin is an attractive alternative radiosensitizing agent to be considered in future studies/trials. See Video Abstract at http://links.lww.com/DCR/B219. LA METFORMINA COMO AGENTE RADIOSENSIBILIZADOR ALTERNATIVO A 5FU DURANTE EL TRATAMIENTO NEOADYUVANTE PARA CÁNCER DE RECTO ANTECEDENTES: La quimiorradiación neoadyuvante para el cáncer de recto localmente avanzado que combina 5FU con radiación aumenta la regresión tumoral en comparación con la radiación sola. Sin embargo, se produce a costa de una toxicidad significativa relacionada con el tratamiento. Los pacientes con cáncer de recto que usan metformina se han asociado con una mejor respuesta a la radioterapia. OBJETIVO: Evaluar los efectos radiosensibilizantes de metformina in vitro e in vivo y compararlo con la combinación estándar de radiación / 5FU. DISEÑO: Se usaron como modelos las líneas celulares de cáncer colorrectal SW480, HT29 y HCT116. La viabilidad celular se comparó en tratamientos con radiación, radiación / 5FU, metformina, radiación / metformina y radiación / 5FU / metformina. A los ratones desnudos se les inyectó por vía subcutánea células SW480 y fueron tratados durante una semana con radiación / 5FU, metformina, radiación / metformina o radiación / 5FU / metformina. El volumen tumoral se evaluó durante 4 semanas después de la finalización del tratamiento. El estado de fosforilación de las proteínas clave de la vía PI3K / Akt / mTOR se determinó mediante inmunotransferencias. AJUSTES: Estudio experimental in vitro e in vivo. PACIENTES: Modelo animal / líneas celulares. PRINCIPALES MEDIDAS DE RESULTADO: El punto final fue investigar cómo la metformina se compara con 5FU como un radiosensibilizador. RESULTADOS: Todas las líneas celulares disminuyeron significativamente la viabilidad celular después del tratamiento con radiación / metformina en comparación con la radiación sola. La radiación / metformina fue superior a la radiación / 5FU en SW480 (37% frente a 74%; p <0,001). En el HT29 y el HCT116 la radiación / metformina fue inferior a la radiación / 5FU (40% vs 13.8%, p <0.001 y 40% vs 7%, p <0.001; respectivamente), debido principalmente al aumento de la toxicidad de 5FU (≤20% de la célula viabilidad). Los ensayos in vivo indicaron que el tratamiento con radiación / metformina era comparable a la radiación / 5FU (557 vs 398 mm3, p > 0.05), y que la adición de metformina a la radiación estándar / 5FU no mejoró la respuesta tumoral (349 mm3, p > 0.05). La metformina ejerció fuertes efectos de inactivación de la vía PI3K / Akt / mTOR después de 24 horas de exposición (aumentando pAMPK p < 0.01, disminuyendo pAkt, p < 0.01; y pS6, p < 0.05). LIMITACIONES: Los regímenes de CRT in vitro e in vivo no se pueden traducir directamente a los métodos de entrega en humanos. CONCLUSIONES: La metformina mejora la respuesta tumoral a la radiación in vitro e in vivo. La metformina es un agente alternativo de radiosensibilización atractivo para ser considerado en futuros estudios / ensayos. Consulte Video Resumen en http://links.lww.com/DCR/B219. (Traducción—Dr Gonzalo Hagerman)

Comprehensive analysis of DNA methylation and gene expression profiles in rectal cancer

“…However, research into the methylation regulation of TGFBI in RC has not been reported. Pathway analysis also revealed that these MeDEGs were enriched in the PI3K-Akt signaling pathway, which was involved in multiple types of malignancies [46,47] , including RC [48] . In the current study, we identi ed many aberrantly methylated and expressed genes participating in the PI3K-Akt signaling pathway, which could provide a foundation for experimental research in RC.…”

Pretreatment with metformin protects mice from whole-body irradiation

“…Recent studies have shown that metformin inhibits cell proliferation and increases apoptosis in various cancer cells [ 34 , 35 ]. Metformin could be as radiosensitizer that improves the sensitivity of several cancer cells to irradiation therapy [ 36 , 37 ]. Moreover, recent clinical data showed that colorectal carcinoma (CRC) patients treated with metformin due to coexisting diabetes developed fewer distant metastases and survived longer compared to those not treated with metformin [ 38 ].…”

Metformin with neoadjuvant chemoradiation to improve pathologic response in rectal cancer: A pilot phase I/II trial

“…In addition to inhibition of cancer cell proliferation, metformin might improve radiation response by decreasing tumor hypoxia-mediated radiation resistance [13]. There is preclinical evidence that metformin serves as a radiosensitizing agentand improves radiation treatment response in various cancer cell lines including colorectal cancer [13,23]. Metformin has thus been proposed as a novel radiation modifier [22,24].…”