Inhibition of Importin β1 Augments the Anticancer Effect of Agonistic Anti-Death Receptor 5 Antibody in TRAIL-resistant Tumor Cells

TNF-related apoptosis-inducing ligand (TRAIL) and an agonistic antibody against the death-inducing TRAIL receptor 5, DR5, are thought to selectively induce tumor cell death and therefore, have gained attention as potential therapeutics currently under investigation in several clinical trials. However, some tumor cells are resistant to TRAIL/DR5-induced cell death, even though they express DR5. Previously, we reported that DR5 is transported into the nucleus by importin beta 1, and knockdown of importin beta 1 upregulates cell surface expression of DR5 resulting in increased TRAIL sensitivity in vitro. Here, we examined the impact of importin beta 1 knockdown on agonistic anti-human DR5 (hDR5) antibody therapy. Drug-inducible importin beta 1 knockdown sensitizes HeLa cells to TRAIL-induced cell death in vitro, and exerts an antitumor effect when combined with agonistic anti-hDR5 antibody administration in vivo. Therapeutic importin beta 1 knockdown, administered via the atelocollagen delivery system, as well as treatment with the importin beta inhibitor, importazole, induced regression and/or eradication of two human TRAIL-resistant tumor cells when combined with agonistic anti-hDR5 antibody treatment. Thus, these findings suggest that the inhibition of importin beta 1 would be useful to improve the therapeutic effects of agonistic anti-hDR5 antibody against TRAIL-resistant cancers.

肿瘤坏死因子相关凋亡诱导配体（TRAIL）以及一种针对诱导死亡的TRAIL受体5（DR5）的激动性抗体，被认为可选择性地诱导肿瘤细胞死亡，因此，作为潜在的治疗药物受到关注，目前正在多项临床试验中进行研究。然而，一些肿瘤细胞对TRAIL/DR5诱导的细胞死亡具有抗性，即便它们表达DR5。此前我们曾报道，DR5由输入蛋白β1转运至细胞核，并且输入蛋白β1的敲低会上调DR5的细胞表面表达，从而导致体外对TRAIL的敏感性增加。在此，我们研究了输入蛋白β1敲低对激动性抗人DR5（hDR5）抗体治疗的影响。药物诱导的输入蛋白β1敲低使HeLa细胞在体外对TRAIL诱导的细胞死亡敏感，并且在体内与激动性抗hDR5抗体联合使用时发挥抗肿瘤作用。通过去端肽胶原递送系统进行的治疗性输入蛋白β1敲低，以及使用输入蛋白β抑制剂——输入蛋白唑进行治疗，在与激动性抗hDR5抗体治疗联合使用时，可诱导两种人源TRAIL抗性肿瘤细胞的消退和/或根除。因此，这些发现表明，抑制输入蛋白β1有助于提高激动性抗hDR5抗体对TRAIL抗性癌症的治疗效果。