Marini A M, Fridman R, Kanemoto T, Martin G R, Guo Y, Passaniti A
Clinical Neuroscience Branch, National Institute of Mental Health, Alcohol, Drug Abuse and Mental Health Administration, Bethesda, MD 20892.
J Natl Cancer Inst. 1992 Oct 21;84(20):1582-7. doi: 10.1093/jnci/84.20.1582.
Small-cell lung cancer (SCLC) is a common malignancy that is usually fatal, since it metastasizes and recurs even after aggressive chemotherapy. While the cellular origin of this cancer is not well established, the cells of certain tumors exhibit neuroendocrine markers, including L-dopa decarboxylase.
We designed in vitro and in vivo studies to investigate whether the neuroendocrine features in classic SCLC cell lines were sufficient to make them sensitive to 1-methyl-4-phenylpyridinium (MPP+), a known neurotoxin that destroys nigrostriatal dopaminergic neurons.
Both classic SCLC cell lines (NCI-H345, NCI-H510, NCI-H187, and NCI-H146) and variant SCLC cell lines (NCI-H417, NCI-H82, NCI-H446, and NCI-H524) were exposed to MPP+ (0-512 microM) for 3 days. Inhibition of DNA synthesis was determined by [3H]thymidine incorporation assays. In a related experiment, MPP+ was removed from the classic cell line culture, and the incorporation of [3H]thymidine was determined. In the in vivo study, male athymic nude mice received subcutaneous injections of 0.5 mL tumor cells with matrigel for 10 days to enhance tumor growth, followed by MPP+ at doses of 100-400 micrograms/d given intraperitoneally for 2 days.
All four classic SCLC cell lines showed great sensitivity to MPP+, with detachment from laminin substrates and inhibition of DNA synthesis. MPP+ interfered with [3H]thymidine incorporation and, thus, with DNA synthesis in classic SCLC cell lines at low doses (median +/- SD, 12 +/- 4 microM), whereas much higher doses (median, > 512 microM) were required to inhibit [3H]thymidine incorporation in the variant lines. Treated cells excluded trypan blue dye, showing that inhibition of DNA synthesis was not due to cytotoxicity, and the cells incorporated [3H]thymidine when MPP+ was removed from the culture medium, demonstrating that the inhibition was reversible. MPP+ inhibited the growth of the classic NCI-H187 and variant NCI-H417 cell lines implanted in nude mice.
These results suggest that MPP+ differentially interferes with DNA synthesis in SCLC cell lines in vitro; the selective inhibitory effect on classic cell lines suggests that the neuroendocrine properties expressed by classic SCLC cells may be responsible for the differential effect.
MPP+ exerts a cytostatic effect on these cell lines, and the differential sensitivity observed in vitro is maintained in vivo, suggesting that MPP+ or other pyridinium compounds may be of therapeutic value in SCLC.
小细胞肺癌（SCLC）是一种常见的恶性肿瘤，通常是致命的，因为即使经过积极的化疗，它仍会发生转移和复发。虽然这种癌症的细胞起源尚未完全明确，但某些肿瘤细胞表现出神经内分泌标志物，包括L-多巴脱羧酶。
我们设计了体外和体内研究，以调查经典SCLC细胞系中的神经内分泌特征是否足以使其对1-甲基-4-苯基吡啶鎓（MPP+）敏感，MPP+是一种已知的神经毒素，可破坏黑质纹状体多巴胺能神经元。
将经典SCLC细胞系（NCI-H345、NCI-H510、NCI-H187和NCI-H146）和变异SCLC细胞系（NCI-H417、NCI-H82、NCI-H446和NCI-H524）暴露于MPP+（0-512微摩尔）3天。通过[3H]胸苷掺入试验测定DNA合成的抑制情况。在一项相关实验中，从经典细胞系培养物中去除MPP+，并测定[3H]胸苷的掺入情况。在体内研究中，雄性无胸腺裸鼠皮下注射0.5毫升含有基质胶的肿瘤细胞，持续10天以促进肿瘤生长，随后腹腔注射剂量为100-400微克/天的MPP+，持续2天。
所有四种经典SCLC细胞系对MPP+均表现出高度敏感性，出现从层粘连蛋白底物上脱离以及DNA合成受到抑制的情况。MPP+在低剂量（中位数±标准差，12±4微摩尔）时干扰经典SCLC细胞系中的[3H]胸苷掺入，进而干扰DNA合成，而在变异细胞系中则需要更高得多的剂量（中位数，>512微摩尔）才能抑制[3H]胸苷掺入。处理后的细胞排斥台盼蓝染料，表明DNA合成的抑制并非由于细胞毒性，并且当从培养基中去除MPP+时，细胞会掺入[3H]胸苷，这表明抑制是可逆的。MPP+抑制了植入裸鼠体内的经典NCI-H187和变异NCI-H417细胞系的生长。
这些结果表明，MPP+在体外对SCLC细胞系中的DNA合成有不同程度的干扰；对经典细胞系的选择性抑制作用表明，经典SCLC细胞所表达的神经内分泌特性可能是造成这种差异效应的原因。
MPP+对这些细胞系具有细胞生长抑制作用，并且在体外观察到的差异敏感性在体内也得以维持，这表明MPP+或其他吡啶鎓化合物可能在SCLC治疗中具有一定价值。
