Department of Biological Sciences, University of Texas at Dallas, Richardson, Texas.
Mol Cancer Ther. 2021 Dec;20(12):2506-2518. doi: 10.1158/1535-7163.MCT-21-0033. Epub 2021 Sep 22.
Heme is an essential nutritional, metabolic, and signaling molecule in living organisms. Pathogenic microbes extract heme from hosts to obtain metallonutrient, while heme fuels mitochondrial respiration and ATP generation in lung tumor cells. Here, we generated small heme-sequestering proteins (HeSPs) based on bacterial hemophores. These HeSPs contain neutral mutations in the heme-binding pocket and hybrid sequences from hemophores of different bacteria. We showed that HeSPs bind to heme and effectively extracted heme from hemoglobin. They strongly inhibited heme uptake and cell proliferation and induced apoptosis in non-small cell lung cancer (NSCLC) cells, while their effects on nontumorigenic cell lines representing normal lung cells were not significant. HeSPs strongly suppressed the growth of human NSCLC tumor xenografts in mice. HeSPs decreased oxygen consumption rates and ATP levels in tumor cells isolated from treated mice, while they did not affect liver and blood cell functions. IHC, along with data from Western blotting and functional assays, revealed that HeSPs reduced the levels of key proteins involved in heme uptake, as well as the consumption of major fuels for tumor cells, glucose, and glutamine. Further, we found that HeSPs reduced the levels of angiogenic and vascular markers, as well as vessel density in tumor tissues. Together, these results demonstrate that HeSPs act via multiple mechanisms, including the inhibition of oxidative phosphorylation, to suppress tumor growth and progression. Evidently, heme sequestration can be a powerful strategy for suppressing lung tumors and likely drug-resistant tumors that rely on oxidative phosphorylation for survival.
血红素是生物体内必需的营养、代谢和信号分子。病原体从宿主中提取血红素以获取金属营养物质，而血红素则为肺肿瘤细胞的线粒体呼吸和 ATP 生成提供燃料。在这里，我们基于细菌血影蛋白生成了小的血红素结合蛋白（HeSP）。这些 HeSP 在血红素结合口袋中含有中性突变，并且具有来自不同细菌的血影蛋白的混合序列。我们表明，HeSP 与血红素结合并有效地从血红蛋白中提取血红素。它们强烈抑制血红素摄取和细胞增殖，并诱导非小细胞肺癌（NSCLC）细胞凋亡，而对代表正常肺细胞的非肿瘤细胞系的影响则不显著。HeSP 在小鼠中强烈抑制人 NSCLC 肿瘤异种移植物的生长。HeSP 降低了从接受治疗的小鼠中分离出的肿瘤细胞的耗氧率和 ATP 水平，而对肝脏和血细胞功能没有影响。免疫组化结合 Western blot 和功能测定的数据表明，HeSP 降低了参与血红素摄取的关键蛋白的水平，以及肿瘤细胞的主要燃料（葡萄糖和谷氨酰胺）的消耗。此外，我们发现 HeSP 降低了肿瘤组织中血管生成和血管标记物以及血管密度的水平。总之，这些结果表明 HeSP 通过多种机制发挥作用，包括抑制氧化磷酸化，从而抑制肿瘤生长和进展。显然，血红素螯合可以成为抑制肺肿瘤和可能依赖氧化磷酸化生存的耐药肿瘤的有效策略。
