Department of Genetics, Biology and Biochemistry, University of Turin, via Santena 5/bis, 10126 Turin, Italy.
Mol Cancer. 2009 Nov 19;8:108. doi: 10.1186/1476-4598-8-108.
Doxorubicin is one of the few chemotherapeutic drugs able to exert both cytotoxic and pro-immunogenic effects against cancer cells. Following the drug administration, the intracellular protein calreticulin is translocated with an unknown mechanism onto the plasma membrane, where it triggers the phagocytosis of tumour cells by dendritic cells. Moreover doxorubicin up-regulates the inducible nitric oxide (NO) synthase (iNOS) gene in cancer cells, leading to huge amounts of NO, which in turn acts as a mediator of the drug toxicity and as a chemosensitizer agent in colon cancer. Indeed by nitrating tyrosine on the multidrug resistance related protein 3, NO decreases the doxorubicin efflux from tumour cells and enhances the drug toxicity. It is not clear if NO, beside playing a role in chemosensitivity, may also play a role in doxorubicin pro-immunogenic effects. To clarify this issue, we compared the doxorubicin-sensitive human colon cancer HT29 cells with the drug-resistant HT29-dx cells and the HT29 cells silenced for iNOS (HT29 iNOS-).
In both HT29-dx and HT29 iNOS- cells, doxorubicin did not induce NO synthesis, had a lower intracellular accumulation and a lower toxicity. Moreover the drug failed to promote the translocation of calreticulin and the phagocytosis of HT29-dx and HT29 iNOS-cells, which resulted both chemoresistant and immunoresistant. However, if NO levels were exogenously increased by sodium nitroprusside, the chemosensitivity to doxorubicin was restored in HT29 iNOS-cells. In parallel the NO donor per se was sufficient to induce the exposure of calreticulin and to increase the phagocytosis of HT29 iNOS- cells by DCs and their functional maturation, thus mimicking the pro-immunogenic effects exerted by doxorubicin in the parental drug-sensitive HT29 cells.
Our data suggest that chemo- and immuno-resistance to anthracyclines are associated in colon cancer cells and rely on a common mechanism, that is the inability of doxorubicin to induce iNOS. Therefore NO donors might represent a promising strategy to restore both chemosensitivity and immunosensitivity to doxorubicin in resistant cells.
阿霉素是少数几种能够对癌细胞产生细胞毒性和促免疫原性作用的化疗药物之一。药物给药后，细胞内蛋白钙网蛋白通过未知机制易位到质膜上，在质膜上触发树突状细胞吞噬肿瘤细胞。此外，阿霉素上调癌细胞中的诱导型一氧化氮合酶（iNOS）基因，导致大量一氧化氮，一氧化氮反过来作为药物毒性的介质，并作为结肠癌的化疗增敏剂。事实上，通过硝化多药耐药相关蛋白 3 上的酪氨酸，NO 减少了肿瘤细胞中阿霉素的外排，增强了药物毒性。目前尚不清楚一氧化氮除了在化疗敏感性中发挥作用外，是否也在阿霉素的促免疫原性作用中发挥作用。为了澄清这一问题，我们比较了阿霉素敏感的人结肠癌细胞 HT29 与耐药的 HT29-dx 细胞和 iNOS 沉默的 HT29 细胞（HT29 iNOS-）。
在 HT29-dx 和 HT29 iNOS-细胞中，阿霉素均未诱导 NO 合成，细胞内积累减少，毒性降低。此外，药物未能促进 HT29-dx 和 HT29 iNOS-细胞中钙网蛋白的易位和吞噬作用，导致两者均具有化疗耐药性和免疫耐药性。然而，如果通过硝普酸钠外源性增加 NO 水平，则恢复了 HT29 iNOS-细胞对阿霉素的化疗敏感性。平行地，NO 供体本身足以诱导钙网蛋白的暴露，并增加 DC 对 HT29 iNOS-细胞的吞噬作用及其功能成熟，从而模拟阿霉素在亲本药物敏感的 HT29 细胞中发挥的促免疫原性作用。
我们的数据表明，结肠癌细胞的化疗和免疫耐药性相关，并依赖于一种共同的机制，即阿霉素不能诱导 iNOS。因此，NO 供体可能是恢复耐药细胞对阿霉素的化疗敏感性和免疫敏感性的一种有前途的策略。
