Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Department of Urology, The James Buchanan Brady Urologic Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Prostate. 2021 Aug;81(11):745-753. doi: 10.1002/pros.24171. Epub 2021 May 25.
Current preclinical models of metastatic prostate cancer (PCa) require sophisticated technologies and/or genetically engineered cells for the noninvasive monitoring of tumors in remote sites, such as bone. Recent developments in circulating tumor DNA (ctDNA) analysis provide an alternative method for noninvasive tumor monitoring at a low cost. Here, we sought to evaluate human Alu and LINE-1 ctDNA for the longitudinal measurement of subcutaneous and intratibial human PCa xenograft growth and response to ionizing radiation (IR) through comparison with standard slide caliper and bioluminescence measurements.
Intratibial and subcutaneous xenografts were established in male athymic nude mice using LNCaP cells that stably express firefly luciferase. A subset of tumors was treated with a single dose of IR (CT-guided focal IR, 6 Gy). Tumor measurements were simultaneously taken by slide caliper (subcutaneous only), in vivo bioluminescence imaging, and quantitative real-time PCR (qPCR) of human-specific Alu and LINE-1 ctDNA for several weeks.
Levels of ctDNA and bioluminescence increased concordantly with subcutaneous and intratibial tumor growth. A statistically significant correlation (Spearman) was observed between ctDNA and subcutaneous tumor volume (LINE-1, r = .94 and Alu, r = .95, p < .0001), ctDNA and bioluminescence (LINE-1, r = .66 and Alu, r = .60, p < .002), and bioluminescence and tumor volume (r = .66, p = .0003). Bioluminescence and ctDNA were also significantly correlated in intratibial tumors (LINE-1, r = .82 and Alu, r = .81, p < .0001). Following external beam IR, the tumor responses varied briefly by method of measurement, but followed a similar trend. Statistically significant correlations were maintained between ctDNA and slide caliper measurement in irradiated subcutaneous tumors (LINE-1, r = .64 and Alu, r = .44, p < .02), and ctDNA and bioluminescence in intratibial tumors (LINE-1, r = .55, p = .018).
Real-time qPCR of circulating human Alu and LINE-1 DNA provides an accurate measurement of subcutaneous and intratibial xenograft burden that is comparable with conventional bioluminescence imaging and slide caliper measurement. Transient differences in measurements were observed following tumor-targeted IR, but overall all measurements mirrored tumor growth and response.
目前，转移性前列腺癌（PCa）的临床前模型需要复杂的技术和/或基因工程细胞来非侵入性地监测远处部位（如骨骼）的肿瘤。循环肿瘤 DNA（ctDNA）分析的最新进展为低成本的肿瘤非侵入性监测提供了一种替代方法。在这里，我们试图通过与标准测微计和生物发光测量的比较，评估人类 Alu 和 LINE-1 ctDNA 对皮下和胫骨内人前列腺癌异种移植物生长以及对电离辐射（IR）的反应的纵向测量。
使用稳定表达萤火虫荧光素酶的 LNCaP 细胞在雄性无胸腺裸鼠中建立胫骨内和皮下异种移植物。一部分肿瘤接受单次剂量的 IR（CT 引导的焦点 IR，6Gy）治疗。通过测微计（仅皮下）、体内生物发光成像和定量实时 PCR（qPCR）同时测量几种周内人类特异性 Alu 和 LINE-1 ctDNA 的肿瘤。
ctDNA 和生物发光水平与皮下和胫骨内肿瘤生长一致增加。ctDNA 与皮下肿瘤体积之间存在统计学显著相关性（Spearman）（LINE-1，r =.94 和 Alu，r =.95，p<.0001），ctDNA 与生物发光（LINE-1，r =.66 和 Alu，r =.60，p<.002），以及生物发光与肿瘤体积（r =.66，p =.0003）。胫骨内肿瘤的生物发光和 ctDNA 也有显著相关性（LINE-1，r =.82 和 Alu，r =.81，p<.0001）。接受外束 IR 后，测量方法略有短暂的肿瘤反应，但遵循相似的趋势。在照射的皮下肿瘤中，ctDNA 与测微计测量之间保持统计学显著相关性（LINE-1，r =.64 和 Alu，r =.44，p<.02），以及胫骨内肿瘤中的 ctDNA 和生物发光（LINE-1，r =.55，p =.018）。
循环人类 Alu 和 LINE-1 DNA 的实时 qPCR 提供了对皮下和胫骨内异种移植物负担的准确测量，与传统的生物发光成像和测微计测量相当。在肿瘤靶向 IR 后观察到测量值的瞬时差异，但总体上所有测量值均反映了肿瘤的生长和反应。
