Christenson Jessica L, Denny Erin C, Kane Susan E
Department of Cancer Biology, Beckman Research Institute at City of Hope, Duarte, CA 91010, USA.
Current address: Department of Pathology, University of Colorado Denver, Aurora, CO 80045, USA.
Oncotarget. 2015 Oct 20;6(32):33134-45. doi: 10.18632/oncotarget.5311.
Drug resistance is a major barrier to successful cancer treatment. For patients with HER2-positive breast cancer who initially respond to therapy, the majority develop resistance within one year of treatment. Patient outcomes could improve significantly if we can find and exploit common mechanisms of acquired resistance to different targeted therapies. Overexpression of t-Darpp, a truncated form of the dual kinase/phosphatase inhibitor Darpp-32, has been linked to acquired resistance to trastuzumab, a front-line therapy for HER2-positive breast cancer. Darpp-32 reverses t-Darpp's effect on trastuzumab resistance. In this study, we examined whether t-Darpp could be involved in resistance to lapatinib, another HER2-targeted therapeutic. Lapatinib-resistant SKBR3 cells (SK/LapR) showed a marked change in the Darpp-32:t-Darpp ratio toward a predominance of t-Darpp. Overexpression of t-Darpp alone was not sufficient to confer lapatinib resistance, but cells that overexpress t-Darpp partially mimicked the molecular resistance phenotype observed in SK/LapR cells exposed to lapatinib. SK/LapR cells failed to down-regulate Survivin and failed to induce BIM accumulation in response to lapatinib; cells overexpressing t-Darpp exhibited only the failed BIM accumulation. t-Darpp knock-down reversed this phenotype. Using a fluorescence-based co-culture system, we found that cells overexpressing t-Darpp formed colonies in lapatinib within 3-4 weeks, whereas parental cells in the same co-culture did not. Overall, t-Darpp appears to mediate a survival advantage in lapatinib, possibly linked to failed lapatinib-induced BIM accumulation. t-Darpp might also be relevant to acquired resistance to other cancer drugs that rely on BIM accumulation to induce apoptosis.
耐药性是癌症治疗成功的主要障碍。对于最初对治疗有反应的HER2阳性乳腺癌患者，大多数人在治疗一年内就会产生耐药性。如果我们能够找到并利用对不同靶向治疗获得性耐药的共同机制，患者的治疗效果可能会显著改善。t-Darpp是双激酶/磷酸酶抑制剂Darpp-32的截短形式，其过表达与曲妥珠单抗（HER2阳性乳腺癌的一线治疗药物）的获得性耐药有关。Darpp-32可逆转t-Darpp对曲妥珠单抗耐药性的影响。在本研究中，我们研究了t-Darpp是否参与对另一种HER2靶向治疗药物拉帕替尼的耐药性。对拉帕替尼耐药的SKBR3细胞（SK/LapR）显示Darpp-32:t-Darpp比值有明显变化，t-Darpp占主导地位。单独过表达t-Darpp不足以赋予拉帕替尼耐药性，但过表达t-Darpp的细胞部分模拟了在暴露于拉帕替尼的SK/LapR细胞中观察到的分子耐药表型。SK/LapR细胞在接触拉帕替尼时未能下调Survivin，也未能诱导BIM积累；过表达t-Darpp的细胞仅表现出BIM积累失败。敲低t-Darpp可逆转这种表型。使用基于荧光的共培养系统，我们发现过表达t-Darpp的细胞在3-4周内在拉帕替尼中形成集落，而同一共培养中的亲代细胞则没有。总体而言，t-Darpp似乎介导了对拉帕替尼的生存优势，可能与拉帕替尼诱导的BIM积累失败有关。t-Darpp也可能与对其他依赖BIM积累来诱导细胞凋亡的癌症药物的获得性耐药有关。
