Cancer screening by systemic administration of a gene delivery vector encoding tumor-selective secretable biomarker expression.

Andrew W Browne,Jennifer L Leddon,Mark A Currier,Timothy P Cripe,Jason S Frischer,Margaret H Collins,Jon P Williams,Chong H Ahn

doi:10.1371/journal.pone.0019530

Abstract

Cancer biomarkers facilitate screening and early detection but are known for only a few cancer types. We demonstrated the principle of inducing tumors to secrete a serum biomarker using a systemically administered gene delivery vector that targets tumors for selective expression of an engineered cassette. We exploited tumor-selective replication of a conditionally replicative Herpes simplex virus (HSV) combined with a replication-dependent late viral promoter to achieve tumor-selective biomarker expression as an example gene delivery vector. Virus replication, cytotoxicity and biomarker production were low in quiescent normal human foreskin keratinocytes and high in cancer cells in vitro. Following intravenous injection of virus >90% of tumor-bearing mice exhibited higher levels of biomarker than non-tumor-bearing mice and upon necropsy, we detected virus exclusively in tumors. Our strategy of forcing tumors to secrete a serum biomarker could be useful for cancer screening in high-risk patients, and possibly for monitoring response to therapy. In addition, because oncolytic vectors for tumor specific gene delivery are cytotoxic, they may supplement our screening strategy as a “theragnostic” agent. The cancer screening approach presented in this work introduces a paradigm shift in the utility of gene delivery which we foresee being improved by alternative vectors targeting gene delivery and expression to tumors. Refining this approach will usher a new era for clinical cancer screening that may be implemented in the developed and undeveloped world.

Highlights

Cancer detection is vital to improve cure rates because cancer stage predicts prognosis
In vitro characterization of mutant Herpes simplex virus (HSV) rQ-M38G rQ-M38G-mediated Gaussia luciferase (GLuc) transduction, replication and cytotoxicity were tested by infecting a range of cell types with various virus concentrations and assessing GLuc levels in culture media (Fig. 2a, Fig. S1), virus genome copy number (Fig. 2b, Fig. S2) and cytotoxicity (Fig. 2c, Fig. S3) on days 2, 4, and 6 after infection
Cell replication-dependent cytotoxicity was observed in replicating human foreskin keratinocytes (HFK-r) while cytotoxicity was attenuated or absent in differentiated/quiescent human foreskin keratinocytes (HFK-q) (Fig. S3)

Summary

Introduction

Cancer detection is vital to improve cure rates because cancer stage predicts prognosis. Cancer-associated blood biomarkers have been identified in a few cancers such as prostate specific antigen (PSA) in prostate cancer and alpha fetoprotein in some liver and germline cancers. New innovations in systemic gene transfer raise the prospect of selectively delivering and activating genes encoding detectable biomarkers into tumor cells that do not produce known serum biomarkers. We sought to develop a prototypical cancer screening strategy whereby genetic information encoding a universal serum biomarker for cancer would be injected into a patient systemically, delivered to and expressed within tumor cells in a tumor-selective manner. Tumors would effectively be forced to secrete a serum biomarker, which could be measured in the blood or urine as a screening test while tumor-free patients would show no or only low levels of biomarker following systemic administration of the gene delivery vector (Fig. 1a)

Methods

Results

Conclusion