Corresponding Author: Ira Pastan, Laboratory of Molecular Biology, 37 Convent Drive, Room 5106, National Cancer Institute, Bethesda, MD 20892-4264.
Mol Cancer Ther. 2014 Jan;13(1):82-9. doi: 10.1158/1535-7163.MCT-13-0726. Epub 2013 Oct 21.
Recombinant immunotoxins (RIT) are agents being developed for cancer treatment. They are composed of an Fv that binds to a cancer cell, fused to a 38-kDa fragment of Pseudomonas exotoxin A. SS1P is a RIT that targets mesothelin, a protein expressed on mesothelioma as well as pancreatic, ovarian, lung, and other cancers. Because the protein tyrosine kinase family regulates a variety of cellular processes and pathways, we hypothesized that tyrosine kinases might regulate susceptibility to immunotoxin killing. To investigate their role, we used siRNAs to lower the level of expression of the 88 known tyrosine kinases. We identified five tyrosine kinases, INSR, HCK, SRC, PDGFRβ, and BMX that enhance the activity of SS1P when their level of expression is lowered by siRNAs. We further investigated the Src family member HCK in this study. Knocking down of SRC slightly increased SS1P killing in A431/H9 cells, but knocking down HCK substantially enhanced killing by SS1P. We investigated the mechanism of enhancement and found that HCK knockdown enhanced SS1P cleavage by furin and lowered levels of Mcl-1 and raised Bax. We then found that Src inhibitors mimic the stimulatory effect of HCK knockdown; both SU6656 and SKI-606 (bosutinib) enhanced immunotoxin killing of mesothelin-expressing cells by SS1P and CD22-expressing cells by HA22 (moxetumomab pasudotox). SU6656 also enhanced the antitumor effects of SS1P and HA22 in mouse xenograft tumor models. Our data suggest that the combination of immunotoxin with tyrosine kinase inhibitors may be an effective way to treat some cancers.
重组免疫毒素（RIT）是正在开发用于癌症治疗的药物。它们由与癌细胞结合的 Fv 组成，融合到假单胞菌外毒素 A 的 38 kDa 片段上。SS1P 是一种针对间皮素的 RIT，间皮素是间皮瘤以及胰腺、卵巢、肺和其他癌症中表达的一种蛋白质。由于蛋白酪氨酸激酶家族调节多种细胞过程和途径，我们假设酪氨酸激酶可能调节对免疫毒素杀伤的敏感性。为了研究它们的作用，我们使用 siRNA 降低 88 种已知的酪氨酸激酶的表达水平。我们鉴定出五种酪氨酸激酶，胰岛素受体（INSR）、HCK、Src、PDGFRβ 和 BMX，当它们的表达水平被 siRNA 降低时，它们增强 SS1P 的活性。在这项研究中，我们进一步研究了 Src 家族成员 HCK。SRC 的敲低略微增加了 A431/H9 细胞中 SS1P 的杀伤，但 HCK 的敲低大大增强了 SS1P 的杀伤作用。我们研究了增强的机制，发现 HCK 的敲低增强了 SS1P 通过 furin 的切割，并降低了 Mcl-1 的水平并提高了 Bax。然后我们发现 Src 抑制剂模拟了 HCK 敲低的刺激作用；SU6656 和 SKI-606（博舒替尼）都增强了 SS1P 对表达间皮素的细胞和 HA22（莫昔妥莫单抗 pasudotox）对表达 CD22 的细胞的免疫毒素杀伤作用。SU6656 还增强了 SS1P 和 HA22 在小鼠异种移植肿瘤模型中的抗肿瘤作用。我们的数据表明，免疫毒素与酪氨酸激酶抑制剂的联合使用可能是治疗某些癌症的有效方法。
