Search

Metastatic breast cancer is an obdurate cancer type that is not amenable to chemotherapy regimens currently used in clinic. There is a desperate need for alternative therapies to treat this resistant cancer type. Gene-Directed Enzyme Prodrug Therapy (GDEPT) is a superior gene therapy method when compared to chemotherapy and radiotherapy procedures, proven to be effective against many types of cancer in pre-clinical evaluations and clinical trials. Gene therapy that utilizes a single enzyme/prodrug combination targeting a single cellular mechanism needs significant overexpression of delivered therapeutic gene in order to achieve therapy response. Hence, to overcome this obstacle we recently developed a dual therapeutic reporter gene fusion that uses two different prodrugs, targeting two distinct cellular mechanisms in order to achieve effective therapy with a limited expression of delivered transgenes. In addition, imaging therapeutic reporter genes offers additional information that indirectly correlates gene delivery, expression, and functional effectiveness as a theranostic approach. In the present study, we evaluate the therapeutic potential of HSV1-sr39TK-NTR fusion dual suicide gene therapy system that we recently developed, in MDA-MB-231 triple negative breast cancer lung-metastatic lesions in a mouse model. We compared the therapeutic potential of HSV1-sr39TK-NTR fusion with respective dual prodrugs GCV-CB1954 with HSV1-sr39TK/GCV and NTR/CB1954 single enzyme prodrug system in this highly resistant metastatic lesion of the lungs. In vitro optimization of dose and duration of exposure to GCV and CB1954 was performed in MDA-MB-231 cells. Drug combinations of 1 μg/ml GCV and 10 μM CB1954 for 3 days was found to be optimal regimen for induction of significant cell death, as assessed by FACS analysis. In vivo therapeutic evaluation in animal models showed a complete ablation of lung metastatic nodules of MDA-MB-231 triple negative breast cancer cells following two consecutive doses of a combination of GCV (40 mg/kg) and CB1954 (40 mg/kg) administered at 5 day intervals. In contrast, the respective treatment condition in animals expressing HSV1-sr39TK or NTR separately, showed minimal or no effect on tumor reduction as measured by bioluminescence (tumor mass) and [(18)F]-FHBG microPET (TK expression) imaging. These highlight the strong therapeutic effect of the dual fusion prodrug therapy and its use in theranostic imaging of tumor monitoring in living animals by multimodality molecular imaging.

MicroRNAs (miRNAs) function as regulatory molecules of gene expression with multifaceted activities that exhibit direct or indirect oncogenic properties, which promote cell proliferation, differentiation, and the development of different types of cancers. Because of their extensive functional involvement in many cellular processes, under both normal and pathological conditions such as various cancers, this class of molecules holds particular interest for cancer research. MiRNAs possess the ability to act as tumor suppressors or oncogenes by regulating the expression of different apoptotic proteins, kinases, oncogenes, and other molecular mechanisms that can cause the onset of tumor development. In contrast to current cancer medicines, miRNA-based therapies function by subtle repression of gene expression on a large number of oncogenic factors, and therefore are anticipated to be highly efficacious. Given their unique mechanism of action, miRNAs are likely to yield a new class of targeted therapeutics for a variety of cancers. More than thousand miRNAs have been identified to date, and their molecular mechanisms and functions are well studied. Furthermore, they are established as compelling therapeutic targets in a variety of cellular complications. However, the notion of using them as therapeutic tool was proposed only recently, given that modern imaging methods are just beginning to be deployed for miRNA research. In this review, we present a summary of various molecular imaging methods, which are instrumental in revealing the therapeutic potential of miRNAs, especially in various cancers. Imaging methods have recently been developed for monitoring the expression levels of miRNAs and their target genes by fluorescence-, bioluminescence- and chemiluminescence-based imaging techniques. Mature miRNAs bind to the untranslated regions (UTRs) of the target mRNAs and regulate target genes expressions. This concept has been used for the development of fluorescent reporter-based imaging strategies to monitor the functional status of endogenous miRNAs, or the respective miRNAs transiently co-expressed in cells. Bioluminescence-based imaging strategies have been used to investigate various stages of miRNA processing and its involvement in different cellular processes. Similarly, chemiluminsecence methods were developed for in vitro miRNA imaging such as monitoring their therapeutic roles in various cancer cell lines.