由于血脑屏障的存在，许多神经中枢系统疾病的潜在治疗药物在应用中受到限制。

There existing blood-brain-barrier(BBB) problem, a variety of potential drugs for curing the illness of nerve center system(NCS) are restricted in the process of drug application.

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由于大部分化疗药物难以通过血脑屏障，脑部肿瘤的化疗效果不佳。

Since most of the chemotherapy drugs cannot pass the blood-brain barrier, the effect of chemotherapy for brain tumor is disappointing.

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