Si igf1r

miR-944 mimics, a miR-944 inhibitor, negative control miRNA mimics (miR-NC), and a negative control miRNA inhibitor (NC inhibitor) were provided by Shanghai GenePharma Co., Ltd. (Shanghai, China). A small interfering RNA (siRNA) used to knockdown IGF-1R expression (si-IGF-1R) and a control siRNA (si-ctrl) were chemically synthesized by Guangzhou RiboBio Co., Ltd. (Guangzhou, China).
The pcDNA3.1-IGF-1R (pc-IGF-1R) plasmid was employed to increase the expression of IGF-1R and an empty pcDNA3.1 plasmid was used as a control. Plasmids were chemically synthesized by the Chinese Academy of Sciences (Changchun, China).
For transfection, cells were plated into 6-well plates. Transfection was performed when the cells had grown to approximately 60–70% density. Lipofectamine™ 2000 (Invitrogen; Thermo Fisher Scientific) was used for transfections and assays were performed according to the product specifications. After 8 h of culture, culture medium was replaced with fresh DMEM containing 10% FBS.

American Type Culture Collection (ATCC, Manassas, VA, USA) provided the human MG-63, U2OS and 143B OS cell lines. The cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (Invitrogen; Thermo Fisher Scientific, Carlsbad, CA, USA) and maintained at 37°C in a humidified incubator with 5% CO^{2 (link)}. The miR-610 mimic, miR-610 inhibitor, and negative control were designed and synthesised by Guangzhou RiboBio Co., Ltd (Science City, Guangzhou, China), along with the small interfering RNA (siRNA) targeting FEN1 and IGF-1R (si-FEN1, si-IGF1R) and negative control (NC) siRNA. All plasmid constructs were verified by sequencing. Lipofectamine 2000 (Invitrogen, USA) was used for each miRNA or siRNA transfection according to the manufacturer’s protocol. Cells were harvested for subsequent experiments 48 h after transfection or anti-cancer drug treatment [Metformin 10 mM, ADM (0.7095 μM for MG-63, 0.9787 μM for U2OS), DDP (0.9731 μM for MG-63, 1.018 μM for U2OS), MTX (35.68 μM for MG-63, 33.54 μM for U2OS)]. Metformin, ADM, DDP and MTX were purchased from Sigma-Aldrich (St. Louis, MO, USA). The drugs were prepared immediately before use. The FEN1, IGF-1R, cleaved caspase-3, and GAPDH antibodies were obtained from Abcam (Cambridge, MA, USA).