Drugs such as gemcitabine that increase replication stress are effective chemotherapeutics in a range of cancer settings. These drugs effectively block replication and promote DNA damage, triggering a cell cycle checkpoint response through the ATR-CHK1 pathway. Inhibiting this signalling pathway sensitises cells to killing by replication stress-inducing drugs. Here, we investigated the effect of low-level replication stress induced by low concentrations (> 0.2 mm) of the reversible ribonucleotide reductase inhibitor hydroxyurea (HU), which slows S-phase progression but has little effect on cell viability or proliferation. We demonstrate that HU effectively synergises with CHK1, but not ATR inhibition, in > 70% of melanoma and non-small-cell lung cancer cells assessed, resulting in apoptosis and complete loss of proliferative potential in vitro and in vivo. Normal fibroblasts and haemopoietic cells retain viability and proliferative potential following exposure to CHK1 inhibitor plus low doses of HU, but normal cells exposed to CHK1 inhibitor combined with submicromolar concentrations of gemcitabine exhibited complete loss of proliferative potential. The effects of gemcitabine on normal tissue correlate with irreversible ATR-CHK1 pathway activation, whereas low doses of HU reversibly activate CHK1 independently of ATR. The combined use of CHK1 inhibitor and subclinical HU also triggered an inflammatory response involving the recruitment of macrophages in vivo. These data indicate that combining CHK1 inhibitor with subclinical HU is superior to combination with gemcitabine, as it provides equal anticancer efficacy but with reduced normal tissue toxicity. These data suggest a significant proportion of melanoma and lung cancer patients could benefit from treatment with this drug combination.

中文翻译：

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与吉西他滨相比，亚临床羟基脲和CHK1抑制剂的联合使用可有效控制黑色素瘤和肺癌的进展，同时降低正常组织的毒性。

吉西他滨等可增加复制压力的药物在多种癌症环境中都是有效的化学疗法。这些药物有效阻止复制并促进DNA损伤，从而通过ATR-CHK1途径触发细胞周期检查点反应。抑制该信号传导途径使细胞对复制应激诱导药物的杀伤敏感。在这里，我们研究了低浓度（> 0.2 mm）可逆核糖核苷酸还原酶抑制剂羟基脲（HU）引起的低水平复制应激的影响，该反应减慢了S期进程，但对细胞生存力或增殖的影响很小。我们证明，在评估的> 70％的黑色素瘤和非小细胞肺癌细胞中，HU有效地与CHK1协同作用，但对ATR抑制不起作用，导致细胞凋亡，并在体外和体内完全丧失增殖潜能。正常的成纤维细胞和造血细胞在暴露于CHK1抑制剂加低剂量的HU后仍保持活力和增殖潜能，但暴露于CHK1抑制剂与亚微摩尔浓度的吉西他滨组合的正常细胞表现出完全丧失增殖潜能。吉西他滨对正常组织的作用与不可逆的ATR-CHK1途径激活相关，而低剂量的HU则独立于ATR可逆地激活CHK1。CHK1抑制剂和亚临床HU的组合使用也引发了炎症反应，涉及体内巨噬细胞的募集。这些数据表明，将CHK1抑制剂与亚临床HU联合使用优于与吉西他滨联合使用，因为它提供相同的抗癌功效，但正常组织毒性降低。这些数据表明，相当大比例的黑色素瘤和肺癌患者可以从这种药物联合治疗中受益。