Targeted enzyme prodrug therapy for metastatic prostate cancer - a comparative study of L-methioninase, purine nucleoside phosphorylase, and cytosine deaminase.

Katrin P Guillen,Carla Kurkjian,Roger G Harrison

doi:10.1186/s12929-014-0065-3

Katrin P Guillen, Carla Kurkjian + Show 1 more

Open Access

https://doi.org/10.1186/s12929-014-0065-3

Copy DOI

Abstract

BackgroundEnzyme prodrug therapy shows promise for the treatment of solid tumors, but current approaches lack effective/safe delivery strategies. To address this, we previously developed three enzyme-containing fusion proteins targeted via annexin V to phosphatidylserine exposed on the tumor vasculature and tumor cells, using the enzymes L-methioninase, purine nucleoside phosphorylase, or cytosine deaminase. In enzyme prodrug therapy, the fusion protein is allowed to bind to the tumor before a nontoxic drug precursor, a prodrug, is introduced. Upon interaction of the prodrug with the bound enzyme, an anticancer compound is formed, but only in the direct vicinity of the tumor, thereby mitigating the risk of side effects while creating high intratumoral drug concentrations. The applicability of these enzyme prodrug systems to treating prostate cancer has remained unexplored. Additionally, target availability may increase with the addition of low dose docetaxel treatment to the enzyme prodrug treatment, but this effect has not been previously investigated. To this end, we examined the binding strength and the cytotoxic efficacy (with and without docetaxel treatment) of these enzyme prodrug systems on the human prostate cancer cell line PC-3.ResultsAll three fusion proteins exhibited strong binding; dissociation constants were 0.572 nM for L-methioninase-annexin V (MT-AV), 0.406 nM for purine nucleoside phosphorylase-annexin V (PNP-AV), and 0.061 nM for cytosine deaminase-annexin V (CD-AV). MT-AV produced up to 99% cell death (p < 0.001) with limited cytotoxicity of the prodrug alone. PNP-AV with docetaxel created up to 78% cell death (p < 0.001) with no cytotoxicity of the prodrug alone. CD-AV with docetaxel displayed up to 60% cell death (p < 0.001) with no cytotoxicity of the prodrug alone. Docetaxel treatment created significant increases in cytotoxicity for PNP-AV and CD-AV.ConclusionsStrong binding of fusion proteins to the prostate cancer cells and effective cell killing suggest that the enzyme prodrug systems with MT-AV and PNP-AV may be effective treatment options. Additionally, low-dose docetaxel treatment was found to increase the cytotoxic effect of the annexin V-targeted therapeutics for the PNP-AV and CD-AV systems.

Highlights

Enzyme prodrug therapy shows promise for the treatment of solid tumors, but current approaches lack effective/safe delivery strategies
To improve upon the clinical applicability, efficacy, and safety of enzyme prodrug therapy, we previously developed three fusion proteins (FPs), each targeted to primary tumors, their metastases, and the tumor vasculature
To address the vascular targeting capabilities of these enzyme prodrug systems, we have previously shown that all three FPs bind tightly to PS expressing human abdominal aorta endothelial cells (HAAE-1) in vitro, with dissociation constants ranging from 0.5-1.5 nM [23,24,25]

Summary

Introduction

Enzyme prodrug therapy shows promise for the treatment of solid tumors, but current approaches lack effective/safe delivery strategies. Upon interaction of the prodrug with the bound enzyme, an anticancer compound is formed, but only in the direct vicinity of the tumor, thereby mitigating the risk of side effects while creating high intratumoral drug concentrations The applicability of these enzyme prodrug systems to treating prostate cancer has remained unexplored. To improve upon the clinical applicability, efficacy, and safety of enzyme prodrug therapy, we previously developed three fusion proteins (FPs), each targeted to primary tumors, their metastases, and the tumor vasculature This dual targeting strategy allows for two distinct mechanisms of killing: (i) via the direct action of the cytotoxic drug on the tumor cells, and (ii) by killing tumor vasculature endothelial cells and thereby effectively cutting off the tumor blood supply. The efficacy of these targeted enzyme prodrug systems on PC has remained unexplored

Methods

Results

Discussion

Conclusion