Cai Weijing, Ratnayake Ranjala, Wang Mengxiong, Chen Qi-Yin, Raisch Kevin P, Dang Long H, Law Brian K, Luesch Hendrik
Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, 32610, USA.
Center for Natural Products, Drug Discovery and Development (CNPD3), University of Florida, Gainesville, FL, 32610, USA.
Curr Res Pharmacol Drug Discov. 2021 Sep 8;2:100053. doi: 10.1016/j.crphar.2021.100053. eCollection 2021.
Receptor tyrosine kinases (RTKs) have become major targets for anticancer therapy. However, resistance and signaling pathway redundancy has been problematic. The marine-derived apratoxins act complementary to direct kinase inhibitors by downregulating the levels of multiple of these receptors and additionally prevent the secretion of growth factors that act on these receptors by targeting Sec61α, therefore interfering with cotranslational translocation. We have profiled the synthetic, natural product-inspired apratoxin S4 against panels of cancer cells characterized by differential sensitivity to RTK inhibitors due to receptor mutations, oncogenic KRAS mutations, or activation of compensatory pathways. Apratoxin S4 was active at low-nanomolar to sub-nanomolar concentrations against panels of lung, head and neck, bladder, and pancreatic cancer cells, concomitant with the downregulation of levels of several RTKs, including EGFR, MET and others. However, the requisite concentration to inhibit certain receptors varied, suggesting some differential substrate selectivity in cellular settings. This selectivity was most pronounced in breast cancer cells, where apratoxin S4 selectively targeted HER3 over HER2 and showed greater activity against ER+ and triple negative breast cancer cells than HER2+ cancer cells. Depending on the breast cancer subtype, apratoxin S4 differentially downregulated transmembrane protein CDCP1, which is linked to metastasis and invasion in breast cancer and modulates EGFR activity. We followed the fate of CDCP1 through proteomics and found that nonglycosylated CDCP1 associates with chaperone HSP70 and HUWE1 that functions as an E3 ubiquitin ligase and presumably targets CDCP1, as well as potentially other substrates inhibited by apratoxins, for proteasomal degradation. By preventing cotranslational translocation of VEGF and other proangiogenic factors as well as VEGFR2 and other receptors, apratoxins also possess antiangiogenic activity, which was validated in endothelial cells where downregulation of VEGFR2 was observed, extending the therapeutic scope to angiogenic diseases.
受体酪氨酸激酶（RTK）已成为抗癌治疗的主要靶点。然而，耐药性和信号通路冗余一直是个问题。海洋来源的阿普拉毒素通过下调多种此类受体的水平，对直接激酶抑制剂起互补作用，此外还通过靶向Sec61α来阻止作用于这些受体的生长因子的分泌，从而干扰共翻译转运。我们已对合成的、受天然产物启发的阿普拉毒素S4针对一系列癌细胞进行了分析，这些癌细胞因受体突变、致癌KRAS突变或补偿途径的激活而对RTK抑制剂具有不同的敏感性。阿普拉毒素S4在低纳摩尔至亚纳摩尔浓度下对肺癌、头颈癌、膀胱癌和胰腺癌细胞系具有活性，同时伴随着几种RTK水平的下调，包括表皮生长因子受体（EGFR）、间质-上皮转化因子（MET）等。然而，抑制某些受体所需的浓度有所不同，这表明在细胞环境中存在一些底物选择性差异。这种选择性在乳腺癌细胞中最为明显，在乳腺癌细胞中，阿普拉毒素S4选择性地靶向HER3而非HER2，并且对雌激素受体阳性（ER+）和三阴性乳腺癌细胞的活性比对HER2阳性癌细胞的活性更高。根据乳腺癌亚型的不同，阿普拉毒素S4对跨膜蛋白CDCP1的下调存在差异，CDCP1与乳腺癌的转移和侵袭有关，并调节EGFR活性。我们通过蛋白质组学追踪CDCP1的命运，发现非糖基化的CDCP1与伴侣蛋白热休克蛋白70（HSP70）和具有E3泛素连接酶功能的HUWE1相关联，推测其靶向CDCP1以及可能被阿普拉毒素抑制的其他底物进行蛋白酶体降解。通过阻止血管内皮生长因子（VEGF）和其他促血管生成因子以及血管内皮生长因子受体2（VEGFR2）和其他受体的共翻译转运，阿普拉毒素还具有抗血管生成活性，这在内皮细胞中得到了验证，在内皮细胞中观察到了VEGFR2的下调，从而将治疗范围扩展到血管生成性疾病。
