Imaging cancer response and resistance to therapy using the chick CAM and isolated perfused tumour

耐药是高级别转移性癌症患者有效治疗的主要障碍。目前，还没有令人满意的方法来确定哪些患者对标准治疗有反应，哪些患者对标准治疗无效。正电子发射断层扫描（PET）成像通过对支持耐药性的分子过程进行无创评估，为这一临床问题提供了一个潜在的解决方案。采用多学科方法，我们正在开发具有开创性的新型PET显像剂，以识别耐药肿瘤（图1）[1-3]。早期发现耐药性将有助于选择替代疗法，从而改善这种疾病的预后。目前的鸡CAMA癌症耐药临床前模型的相当大的局限性是无法概括肿瘤微环境的复杂性，进化的遗传景观和肿瘤-免疫细胞相互作用。小鼠癌症模型在药物和显像剂开发中显示出广泛的效用和采用。然而，小鼠模型价格昂贵，有很高的维护和饲养成本，并且受到有关动物福利的伦理问题的影响。在这里，我们将开发鸡绒毛膜尿囊膜（CAM）作为一种替代的，高通量的方法来开发新的癌症显像剂。CAM是鸡胚的一种高度血管化的胚外膜。CAM可以很容易地进入胚胎，对胚胎的侵袭最小，使培养的癌细胞和患者来源的异种移植物生长，并完成增选的血管系统[4]。小鸡CAM是一种成熟的抗癌药物疗效评估模型。它也被用于量化带有PET[5]的胶质母细胞瘤异种移植物的肿瘤代谢。因此，该实验模型将能够以类似于标准小鼠异种移植工作的方式高通量筛选新型放射性示踪剂，但时间和成本都很低。利用小鸡CAM作为体内肿瘤生长和血管化的载体，我们将开发一种全新的癌症治疗评估模型和新型放射性示踪剂：“孤立的灌注肿瘤”。灌注肿瘤将具有体内小鼠肿瘤模型的生物学复杂性，具有体外培养实验的通用性、可控性和可重复性。基于Langendorff分离的灌注大鼠心脏，我们有丰富的经验[6-8]，小鸡CAM肿瘤将被切除，并通过大的喂养血管灌注，从而首次在完整的肿瘤中精确控制氧气、能量基质和药物的输送。为了利用我们开发的离体灌注组织装置的力量，我们在灌注装置周围构建了一个三重检测器系统，使我们能够评估离体灌注肿瘤中的放射性示踪剂选择性、敏感性和药代动力学。我们有一个平行灌注装置，在9.4T核磁共振磁体内工作，使我们能够进行平行光谱实验，以评估组织活力和代谢[7]。结合小鸡CAM，分离的灌注肿瘤和我们的各种生物物理技术，将允许使用新型放射性示踪剂以前所未有的精度评估复杂的肿瘤微环境，以成像肿瘤对治疗的反应和耐药性。

Drug-resistance is a major obstacle for the effective treatment of patients with high grade metastatic cancer. Currently, there is no satisfactory way to identify patients that will respond and those that will fail standard-of-care therapy. Positron emission tomography (PET) imaging offers a potential solution to this clinical problem through the non-invasive assessment of molecular processes that underpin drug-resistance. Using a multidisciplinary approach, we are developing pioneering new PET imaging agents to identify drug-resistant tumours (Fig. 1) [1-3]. Early detection of drug resistance will enable the selection of alternative therapies, thereby improving outcomes in this disease.The chick CAMA considerable limitation of current preclinical models of cancer drug resistance is the inability to recapitulate the complexity of the tumour microenvironment, evolving genetic landscape and tumour-immune cell interactions. Mouse models of cancer have shown wide-spread utility and adoption for both drug and imaging agent development. However, mouse models are expensive, have high maintenance and husbandry costs, and are subject to ethical issues surrounding animal welfare. Here, we will develop the chick chorioallantoic membrane (CAM) as an alternative, high-throughput method for the development of novel cancer imaging agents. The CAM is a highly vascularised extra-embryonic membrane of the chick embryo. The CAM can be accessed easily with minimal invasion to the embryo, enabling the growth of cultured cancer cell and patient-derived xenografts, complete with a co-opted vascular system [4].The chick CAM is a well-established model for the assessment of anti-cancer drug efficacy. It has also been adapted to quantify tumour metabolism in a glioblastoma xenograft with PET [5]. This experimental model will therefore enable high throughput screening of novel radiotracers in a way analogous to standard mouse xenograft work but at the fraction of the time and cost.The perfused tumourUsing the chick CAM as a vehicle for in vivo tumour growth and vascularisation, we will develop an entirely new model for the assessment of cancer therapies and novel radiotracers: the 'isolated perfused tumour'. The perfused tumour will have the biological complexity of in vivo mouse models of cancer, with the versatility, control and reproducibility of in vitro culture experiments. Based on the Langendorff isolated perfused rat heart, with which we have extensive experience [6-8], the chick CAM tumour will be excised and perfused through the large feeding vessels to allow precise control over the delivery of oxygen, energy substrates and drugs in an intact tumour for the very first time.To exploit the power of the isolated perfused tissue apparatus that we have developed, we have constructed a triple-detector system around our perfusion rig which allows us to evaluate radiotracer selectivity, sensitivity and pharmacokinetics in the isolated perfused tumour. We have a parallel perfusion setup which works within a 9.4T NMR magnet which allows us to perform parallel spectroscopy experiments to assess tissue viability and metabolism [7]. Together, the chick CAM, the isolated perfused tumour and our assorted biophysical technologies will allow the evaluation of the complex tumour microenvironment with unprecedented precision using novel radiotracers developed to image tumour response and resistance to therapy.