Department of Surgery, University of Texas Southwestern Medical Center/Dallas VA Medical Center, Dallas, TX 75216, USA.
Surgery. 2010 Aug;148(2):346-53. doi: 10.1016/j.surg.2010.05.006.
The response to neoadjuvant chemoradiation in rectal cancer is variable and unpredictable. Resistance to chemoradiation has been directly correlated with the levels of the inhibitors of apoptosis (IAPs) in several malignancies. Because smac-DIABLO is a pro-apoptotic gene product that directly inhibits the activity of the IAPs, molecules with similar activity might radiosensitize rectal tumors with phenotypes that express high levels of IAPs. This study was undertaken to assess the radiosensitizing properties of the smac mimetic JP-1201 in radioresistant HT-29 colorectal cancer cells in vitro and established xenografts in SCID mice.
Survival was determined by clonogenic assays. PARP-1, caspase-8 cleavage, and IAP levels were assessed by Western blot analysis. SCID mice bearing HT-29 xenografts were treated with ionizing radiation: 2.0 Gy x 5; (n = 6), JP-1201 (5.0 mg/Kg i.p., n = 5) or combination treatment (n = 7) and compared to control (n = 8). DNA repair mechanisms were interrogated by gammaH2AX positive foci.
Pretreatment of HT-29 cells with JP-1201 (5.0 microM) prior to ionizing radiation (IR) significantly decreased the survival of these cells. SCID mice bearing HT-29 xenografts demonstrated no difference in tumor load in the group receiving exclusively JP-1201 versus control. At the end of the treatment (day 40), a 46% reduction of tumor load was observed in the IR+JP-1201-treated group compared to the IR-only treated group. Radiosensitization was achieved with a substantial elevation of cleaved PARP-1 in JP-1201- treated HT-29 cells versus control cells with a concomitant decrease of XIAP, but not of survivin or cIAP1/2. JP-1201-treated HT-29 cells had a reduced ability to repair double-stranded DNA breaks (DSBs).
The smac mimetic JP-1201 decreased the survival of HT-29 cells and tumor growth by an additive effect in apoptosis and a reduction in the level of XIAP and an impairment of DNA repair mechanisms. The pathways leading to this response need to be further investigated.
新辅助放化疗在直肠癌中的反应是多变且不可预测的。在几种恶性肿瘤中，化疗耐药性与凋亡抑制剂（IAPs）的水平直接相关。由于 smac-DIABLO 是一种促凋亡基因产物，可直接抑制 IAPs 的活性，因此具有类似活性的分子可能会使表型表达高水平 IAPs 的直肠肿瘤对放疗敏感。本研究旨在评估 smac 模拟物 JP-1201 在体外对 HT-29 结直肠癌细胞和 SCID 小鼠建立的异种移植瘤的放射增敏作用。
通过集落形成试验测定存活率。通过 Western blot 分析评估 PARP-1、caspase-8 切割和 IAP 水平。用离子辐射（2.0 Gy x 5；n = 6）、JP-1201（5.0 mg/kg ip，n = 5）或联合治疗（n = 7）处理荷 HT-29 异种移植瘤的 SCID 小鼠，并与对照组（n = 8）进行比较。通过γH2AX 阳性焦点来检测 DNA 修复机制。
在 HT-29 细胞接受离子辐射（IR）之前，用 JP-1201（5.0 μM）预处理可显著降低这些细胞的存活率。仅接受 JP-1201 的组与对照组相比，荷 HT-29 异种移植瘤的 SCID 小鼠的肿瘤负荷无差异。在治疗结束时（第 40 天），与仅接受 IR 治疗的组相比，IR+JP-1201 治疗组的肿瘤负荷减少了 46%。与对照组相比，JP-1201 处理的 HT-29 细胞中 cleaved PARP-1 的水平显著升高，同时 XIAP 降低，但 survivin 或 cIAP1/2 没有降低，从而实现了放射增敏。JP-1201 处理的 HT-29 细胞修复双链 DNA 断裂（DSBs）的能力降低。
smac 模拟物 JP-1201 通过凋亡的附加作用和 XIAP 水平的降低以及 DNA 修复机制的损伤，降低了 HT-29 细胞的存活率和肿瘤生长。需要进一步研究导致这种反应的途径。
