Modulation of Therapeutic Response

为了改善癌症的治疗，对辐射损伤的调节已经引起了相当大的关注。目前正在研究各种化疗和/或分子靶向药物与辐射的相互作用，以确定是否可以使肿瘤更敏感或正常组织对放射治疗更有抵抗力。中心目标是确定将导致净治疗增益的方法，从而改善癌症放射治疗。该项目的一个目标是定义和更好地理解肿瘤生理学的这些方面，包括细胞和分子过程以及肿瘤微环境对治疗反应的影响。已经完成的两项独立研究表明，辐射诱导的基因表达谱在体外暴露的细胞与体内作为实体瘤生长的相同细胞之间存在显著差异，进一步强调了肿瘤微环境对辐射反应的影响。此外，我们已经表明，与单剂量放射治疗相比，多剂量放射治疗对基因的诱导更强。在肿瘤微环境方面，人们早就知道肿瘤细胞缺氧会引起放化疗的耐药。非侵入性成像可以识别出肿瘤缺氧的患者，这在临床上是有用的。采用动态正电子发射断层扫描（PET）对荷瘤小鼠进行了放射性缺氧标记物[64Cu]Cu-ATSM的评估。虽然这种PET示踪剂与肿瘤紧密结合，但当肿瘤的氧合水平被调节时，它无法预测地检测到不同程度的缺氧变化。相反，[18F]氟咪唑呈阳性趋势，随着肿瘤中氧水平的降低，肿瘤摄取更多。未来无创评估肿瘤缺氧的尝试将使用电子顺磁共振成像（放射生物学分支开发的仪器）结合氧敏感化学探针进行评估。在给定的治疗范围内，增强肿瘤对辐射的反应而不增强正常组织的能力是可取的。我们最近表明，氯雷他定和谷固酮增强肿瘤细胞的放射反应在体外。初步的机制研究表明，氯雷他定在细胞周期中施加G2/M阻滞（细胞周期的G2/M期对辐射非常敏感）和谷固酮，这似乎干扰辐射诱导的DNA损伤修复。目前正在对这两种药物联合辐射对荷瘤小鼠的影响进行评估。关于正常组织对辐射的反应，众所周知，TGF β信号通路是辐射诱导的晚期效应（纤维化）的主要参与者。我们之前的研究表明，TGF β信号缺失的小鼠（Smad3敲除小鼠- TGF β通路的下游信号中间体）在高剂量辐射治疗时具有纤维化抗性。我们最近表明，当暴露于辐射时，从这些动物中分离的成纤维细胞（与野生型成纤维细胞相比）增加了它们的DNA损伤感知机制，减少了促纤维化基因的诱导。这些基础研究表明，用分子靶向药物靶向TGF β通路可能对辐射诱导的纤维化（放射治疗的不良副作用）有显著的保护作用。最近的小鼠正常组织研究表明，使用靶向TGF β通路的几个点的halofuginone或TGF β 1型受体激酶抑制剂可以显著减少辐射诱导的软组织纤维化。目前的研究集中在确认这两种药物在体内影响它们的分子靶点。这些临床前研究的目标是获得足够的疗效数据，以便将这些药物引入人体临床试验。

Modulation of Therapeutic Response Summary In the interest of improving cancer treatment, considerable attention has been placed on the modification of radiation damage. The interaction of a variety of chemotherapy and/or molecularly targeted agents with radiation is under study to determine if tumors can be made more sensitive or normal tissues more resistant to radiation treatment. The central aim is to identify approaches that will result in a net therapeutic gain, thus improving cancer treatment with radiation. One goal of the project is to define and better understand those aspects of tumor physiology, including cellular and molecular processes and the influence of the tumor microenvironment on treatment response. Two independent studies have been completed showing that radiation-induced gene expression profiles differ significantly for cells exposed in vitro versus the same cells growing as a solid tumor in vivo further underscoring the influence of the tumor microenvironment on the radiation response. Further we have shown that multi-fraction radiation delivery results in a more robust induction of genes than single dose radiation treatment. With respect to the tumor microenvironment, it has long been known that tumor cell hypoxia can cause resistance to radiation and chemotherapy treatment. Non-invasive imaging that could identify patients whose tumors are hypoxic would be useful clinically. A putative radioactive hypoxia marker, [64Cu]Cu-ATSM, was evaluated in tumor-bearing mice using dynamic positron emission tomography (PET). While this PET tracer avidly bound to tumor, it was unable to predictably detect changes in varying amounts of hypoxia when oxygenation levels of the tumor were modulated. In contrast, [18F]fluoromisonidazole demonstrated a positive trend with more tumor uptake as oxygen levels were lowered in the tumor. Future attempts of non-invasively assessing tumor hypoxia will be evaluated using electron paramagnetic resonance imaging (instrumentation developed in the Radiation Biology Branch) in conjunction with oxygen sensitive chemical probes. The ability to enhance the response of the tumor to radiation, without enhancing normal tissue within a given treatment field is desirable. We have recently shown that loratadine and guggulsterone enhance tumor cell radiation response in vitro. Preliminary mechanistic studies indicate that loratadine imposes a G2/M block in cell cycle (G2/M phases of the cell cycle are very radiosensitive) and guggulsterone, which appears to interfere with radiation-induced DNA damage repair. Evaluation of both agents in combination with radiation in tumor bearing mice is currently underway. With respect to normal tissue response to radiation, it is widely known that the TGF beta signaling pathway is a major player in radiation-induced late effects (fibrosis). Our previous studies have shown that mice deficient in TGF beta signaling (Smad3 knock-out mice-downstream signaling intermediate in the TGF beta pathway) are resistant to fibrosis when treated with high dose radiation. We have recently shown that fibroblasts isolated from these animals (compared to wild type fibroblasts) when exposed to radiation increase their DNA damage sensing mechanisms and decrease induction of pro-fibrotic genes. These basic studies suggest that targeting the TGF beta pathway with molecularly targeted agents may provide significant protection against radiation-induced fibrosis, an untoward side effect of radiation treatment. Recent mouse normal tissue studies using halofuginone, which targets the TGF beta pathways at several points or a TGF beta type 1 receptor kinase inhibitor have shown marked reduction in radiation-induced soft tissue fibrosis. Current studies are centered in confirming that both agents impact their molecular targets in vivo. The goal of these pre-clinical studies is to gain enough efficacy data to introduce these agents into human clinical trials.