Hedbrant Alexander, Erlandsson Ann, Delbro Dick, Wijkander Jonny
Department of Health Sciences, Karlstad University, Karlstad, Sweden.
School of Health and Medical Sciences, Örebro University, Örebro, Sweden.
Int J Oncol. 2015 Jan;46(1):37-46. doi: 10.3892/ijo.2014.2696. Epub 2014 Oct 7.
Resistance of tumor cells to chemotherapy, such as 5‑fluorouracil (5‑FU), is an obstacle for successful treatment of cancer. As a follow‑up of a previous study we have investigated the effect of conditioned media (CM) from macrophages of M1 or M2 phenotypes on 5‑FU cytotoxicity on the colon cancer cell lines HT‑29 and CACO‑2. HT‑29 cells, but not CACO‑2 cells, having been treated with a combination of M1 CM and 5‑FU recovered their cell growth to a much larger extent compared to cells having been treated with 5‑FU alone when further cultured for 7 days in fresh media. M1 CM treatment of HT‑29, but not CACO‑2 cells, induced cell cycle arrest in the G0/G1 and G2/M phases. 5‑FU treatment induced accumulation of cells in S‑phase in both HT‑29 and CACO‑2 cells. This accumulation of cells in S‑phase was attenuated by combined M1 CM and 5‑FU treatment in HT‑29 cells, but not in CACO‑2 cells. The mRNA expression of cell cycle regulatory proteins and 5‑FU metabolic enzymes were analyzed in an attempt to find possible mechanisms for the M1 CM induced attenuation of 5‑FU cytotoxicity in HT‑29. Thymidylate synthetase (TS) and thymidine phosphorylase (TP) were found to be substantially downregulated and upregulated, respectively, in HT‑29 cells treated with M1 CM, making them unlikely as mediators of reduced 5‑FU cytotoxicity. Among cell cycle regulating proteins, p21 was induced in HT‑29 cells, but not in CACO‑2 cells, in response to M1 CM treatment. However, small interfering RNA (siRNA) knockdown of p21 had no effect on the M1 CM induced cell cycle arrest seen in HT‑29 and neither did it change the growth recovery after combined treatment of HT‑29 cells with M1 CM and 5‑FU. In conclusion, treatment of HT‑29 cells with M1 CM reduces the cytotoxic effect of 5‑FU and this is mediated by a M1 CM induced cell cycle arrest in the G0/G1 and G2/M phases. So far, we lack an explanation why this action is absent in the CACO‑2 cells. The current findings may be important for optimization of chemotherapy in colon cancer.
肿瘤细胞对化疗药物（如5-氟尿嘧啶（5-FU））产生耐药性是癌症成功治疗的一大障碍。作为之前一项研究的后续，我们研究了M1或M2表型巨噬细胞的条件培养基（CM）对5-FU对结肠癌细胞系HT-29和CACO-2细胞毒性的影响。在用M1 CM和5-FU联合处理后，HT-29细胞（而非CACO-2细胞）在新鲜培养基中进一步培养7天时，其细胞生长恢复程度比仅用5-FU处理的细胞要大得多。M1 CM处理HT-29细胞（而非CACO-2细胞）可诱导细胞周期停滞在G0/G1期和G2/M期。5-FU处理可诱导HT-29和CACO-2细胞在S期积累。在HT-29细胞中，M1 CM和5-FU联合处理可减弱细胞在S期的这种积累，但在CACO-2细胞中则不然。为了寻找M1 CM诱导HT-29细胞中5-FU细胞毒性减弱的可能机制，我们分析了细胞周期调节蛋白和5-FU代谢酶的mRNA表达。结果发现，在用M1 CM处理的HT-29细胞中，胸苷酸合成酶（TS）显著下调，而胸苷磷酸化酶（TP）则显著上调，这使得它们不太可能是5-FU细胞毒性降低的介导因子。在细胞周期调节蛋白中，M1 CM处理可诱导HT-29细胞中p21表达，但不诱导CACO-2细胞中p21表达。然而，小干扰RNA（siRNA）敲低p21对HT-29细胞中M1 CM诱导的细胞周期停滞没有影响，也没有改变HT-29细胞用M1 CM和5-FU联合处理后的生长恢复情况。总之，用M1 CM处理HT-29细胞可降低5-FU的细胞毒性，这是由M1 CM诱导的细胞周期停滞在G0/G1期和G2/M期介导的。到目前为止，我们尚不清楚为何这种作用在CACO-2细胞中不存在。目前的研究结果可能对优化结肠癌化疗具有重要意义。
