Detecting cancers through tumor-activatable minicircles that lead to a detectable blood biomarker

Abstract

Earlier detection of cancers can dramatically improve the efficacy of available treatment strategies. However, despite decades of effort on blood-based biomarker cancer detection, many promising endogenous biomarkers have failed clinically because of intractable problems such as highly variable background expression from nonmalignant tissues and tumor heterogeneity. In this work we present a tumor-detection strategy based on systemic administration of tumor-activatable minicircles that use the pan-tumorspecific Survivin promoter to drive expression of a secretable reporter that is detectable in the blood nearly exclusively in tumor-bearing subjects. After systemic administration we demonstrate a robust ability to differentiate mice bearing human melanoma metastases from tumor-free subjects for up to 2 wk simply by measuring blood reporter levels. Cumulative change in reporter levels also identified tumor-bearing subjects, and a receiver operator-characteristic curve analysis highlighted this test's performance with an area of 0.918 ± 0.084. Lung tumor burden additionally correlated (r 2 = 0.714; P < 0.05) with cumulative reporter levels, indicating that determination of disease extent was possible. Continued development of our system could improve tumor detectability dramatically because of the temporally controlled, high reporter expression in tumors and nearly zero background from healthy tissues. Our strategy's highly modular nature also allows it to be iteratively optimized over time to improve the test's sensitivity and specificity. We envision this system could be used first in patients at high risk for tumor recurrence, followed by screening high-risk populations before tumor diagnosis, and, if proven safe and effective, eventually may have potential as a powerful cancer-screening tool for the general population.cancer | minicircles | tumor-specific promoter | reporter gene | blood test

Towards clinically translatable in vivo nanodiagnostics

“…Unfortunately, because nanoworms passively target and attach to tumours, their delivery may suffer from low yield. Alternatively, we introduced tumour-activatable minicircles 197 that greatly improve tumour detectability by detecting unique blood biomarkers for cancers 198 . Tumour-activatable minicircles encoding a secretable biomarker downstream of the tumour-specific survivin promoter are packaged in nanocomplexes and delivered systemically.…”

Mathematical framework for activity-based cancer biomarkers

“…Recent mathematical studies showed that tumors may remain undetectable with blood biomarkers for an entire decade following tumorigenesis, reaching 1-2.5 cm in diameter (4,5). To increase sensitivity, major research areas include the development of ultrasensitive in vitro diagnostic platforms (6)(7)(8)(9)(10)(11), as well as methods to increase biomarker production by solid tumors (12,13). These approaches are designed to measure the quantity, or abundance, of a disease biomarker.…”

Detecting Tumor Metastases

“…A blood-based tumor-activatable microcircle approach was devised for detection of tumors and metastases (Ronald, Chuang, Dragulescu-Andrasi, Hori, & Gambhir, 2015). Nonviral tumor-activatable minicircles encoding human SEAP (secreted embryonic alkaline phosphatase) under the transcriptional control of the tumor-specific survivin promoter along with a transfection agent was introduced systemically via the tail vein of the mouse.…”

“…The reporter SEAP was only produced in tumor cells and was secreted into the blood stream of the mice. Blood samples collected from mice and plasma were screened for the presence of SEAP, which was indicative of the presence of tumors in the mouse (Ronald et al, 2015). …”

“…This study also showed that the minicircle vector enabled prolonged expression of the reporter and conferred reduced inflammatory response. A practical use of minicircle expression for cancer detection used the survivin promoter upstream of a reporter protein, human SEAP (Ronald et al, 2015). Because SEAP is orthogonal to proteins normally expressed in adult tissue it could be used in a sensitive way to detect cancer in body fluids.…”