Tumor-targeted gene therapy using Adv-AFP-HRPC/IAA prodrug system suppresses growth of hepatoma xenografted in mice

Smart nanocarriers for enzyme-activated prodrug therapy

Exogenous enzyme-activated prodrug therapy (EPT) is a potential cancer treatment strategy that delivers non-human enzymes into or on the surface of the cell and subsequently converts a non-toxic prodrug into an active cytotoxic substance at a specific location and time. The development of several pharmacological pairs based on EPT has been the focus of anticancer research for more than three decades. Numerous of these pharmacological pairs have progressed to clinical trials, and a few have achieved application in specific cancer therapies. The current review highlights the potential of enzyme-activated prodrug therapy as a promising anticancer treatment. Different microbial, plant, or viral enzymes and their corresponding prodrugs that advanced to clinical trials have been listed. Additionally, we discuss new trends in the field of enzyme-activated prodrug nanocarriers, including nanobubbles combined with ultrasound (NB/US), mesoscopic-sized polyion complex vesicles (PICsomes), nanoparticles, and extracellular vesicles (EVs), with special emphasis on smart stimuli-triggered drug release, hybrid nanocarriers, and the main application of nanotechnology in improving prodrugs.

Horseradish Peroxidase-Functionalized Gold Nanoconjugates for Breast Cancer Treatment Based on Enzyme Prodrug Therapy

Introduction

Breast cancer has the highest mortality rate among cancers in women. Patients suffering from certain breast cancers, such as triple-negative breast cancer (TNBC), lack effective treatments. This represents a clinical concern due to the associated poor prognosis and high mortality. As an approach to succeed over conventional therapy limitations, we present herein the design and evaluation of a novel nanodevice based on enzyme-functionalized gold nanoparticles to efficiently perform enzyme prodrug therapy (EPT) in breast cancer cells.

Results

In particular, the enzyme horseradish peroxidase (HRP) – which oxidizes the prodrug indole-3-acetic acid (IAA) to release toxic oxidative species – is incorporated on gold nanoconjugates (HRP-AuNCs), obtaining an efficient nanoplatform for EPT. The nanodevice is biocompatible and effectively internalized by breast cancer cell lines. Remarkably, co-treatment with HRP-AuNCs and IAA (HRP-AuNCs/IAA) reduces the viability of breast cancer cells below 5%. Interestingly, 3D tumor models (multicellular tumor spheroid-like cultures) co-treated with HRP-AuNCs/IAA exhibit a 74% reduction of cell viability, whereas the free formulated components (HRP, IAA) have no effect.

Conclusion

Altogether, our results demonstrate that the designed HRP-AuNCs nanoformulation shows a remarkable therapeutic performance. These findings might help to bypass the clinical limitations of current tumor enzyme therapies and advance towards the use of nanoformulations for EPT in breast cancer.

Enzyme prodrug therapy: cytotoxic potential of paracetamol turnover with recombinant horseradish peroxidase

Targeted cancer treatment is a promising, less invasive alternative to chemotherapy as it is precisely directed against tumor cells whilst leaving healthy tissue unaffected. The plant-derived enzyme horseradish peroxidase (HRP) can be used for enzyme prodrug cancer therapy with indole-3-acetic acid or the analgesic paracetamol (acetaminophen). Oxidation of paracetamol by HRP in the presence of hydrogen peroxide leads to N-acetyl-p-benzoquinone imine and polymer formation via a radical reaction mechanism. N-acetyl-p-benzoquinone imine binds to DNA and proteins, resulting in severe cytotoxicity. However, plant HRP is not suitable for this application since the foreign glycosylation pattern is recognized by the human immune system, causing rapid clearance from the body. Furthermore, plant-derived HRP is a mixture of isoenzymes with a heterogeneous composition. Here, we investigated the reaction of paracetamol with defined recombinant HRP variants produced in E. coli, as well as plant HRP, and found that they are equally effective in paracetamol oxidation at a concentration ≥ 400 µM. At low paracetamol concentrations, however, recombinant HRP seems to be more efficient in paracetamol oxidation. Yet upon treatment of HCT-116 colon carcinoma and FaDu squamous carcinoma cells with HRP-paracetamol no cytotoxic effect was observed, neither in the presence nor absence of hydrogen peroxide.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00706-021-02848-x.

Potential of unglycosylated horseradish peroxidase variants for enzyme prodrug cancer therapy

Fighting cancer still relies on chemo- and radiation therapy, which is a trade-off between effective clearance of malignant cells and severe side effects on healthy tissue. Targeted cancer treatment on the other hand is a promising and refined strategy with less systemic interference. The enzyme horseradish peroxidase (HRP) exhibits cytotoxic effects on cancer cells in combination with indole-3-acetic acid (IAA). However, the plant-derived enzyme is out of bounds for medical purposes due to its foreign glycosylation pattern and resulting rapid clearance and immunogenicity. In this study, we generated recombinant, unglycosylated HRP variants in Escherichia coli using random mutagenesis and investigated their biochemical properties and suitability for cancer treatment. The cytotoxicity of the HRP-IAA enzyme prodrug system was assessed in vitro with HCT-116 human colon, FaDu human nasopharyngeal squamous cell carcinoma and murine colon adenocarcinoma cells (MC38). Extensive cytotoxicity was shown in all three cancer cell lines: the cell viability of HCT-116 and MC38 cells treated with HRP-IAA was below 1% after 24 h incubation and the surviving fraction of FaDu cells was ≤ 10% after 72 h. However, no cytotoxic effect was observed upon in vivo intratumoral application of HRP-IAA on a MC38 tumor model in C57BL/6J mice. However, we expect that targeting of HRP to the tumor by conjugation to specific antibodies or antibody fragments will reduce HRP clearance and thereby enhance therapy efficacy.

Potential Alternatives to Conventional Cancer Therapeutic Approaches: The Way Forward

onventional cancer therapeutic approaches broadly include chemotherapy, radiation therapy and surgery. These established approaches have evolved over several decades of clinical experience. For a complex disease like cancer, satisfactory treatment remains an enigma for the simple fact that the causal factors for cancer are extremely diverse. In order to overcome existing therapeutic limitations, consistent scientific endeavors have evolved several potential therapeutic approaches, majority of which focuses essentially on targeted drug delivery, minimal concomitant ramification, and selective high cytotoxicity. The current review focuses on highlighting some of these potential alternatives that are currently in various stages of in vitro, in vivo, and clinical trials. These include physical, chemical and biological entities that are avidly being explored for therapeutic alternatives. Some of these entities include suicide gene, micro RNA, modulatory peptides, ultrasonic waves, free radicals, nanoparticles, phytochemicals, and gene knockout, and stem cells. Each of these techniques may be exploited exclusively and in combination with conventional therapeutic approaches thereby enhancing the therapeutic efficacy of the treatment. The review intends to briefly discuss the mechanism of action, pros, and cons of potential alternatives to conventional therapeutic approaches.

Interaction of indole-3-acetic acid with horseradish peroxidase as a potential anticancer agent: from docking to molecular dynamics simulation

The oxidation process, catalyzed by the peroxidase enzymes, occurs in all domains of life to detoxify the hydrogen peroxide toxicity. The most well-known, applicable and vastly studied member of the peroxidases family is horseradish peroxidase (HRP), especially the isoenzyme C (HRP C). HRP (primarily HRP C) is commercially available and applicable in biotechnology and diagnosis. Recently, a novel application of HRP has been introduced in cancer therapy as the combination of HRP with indole-3-acetic acid (IAA). The anticancer activity of HRP/IAA complex is through oxidation of IAA by HRP in hypoxic tumor condition, which leads to apoptosis and cancerous cell death. However, the molecular interaction of HRP/IAA has not been elucidated. Identifying the interaction of IAA with HRP would provide a better insight into its function and applications. In this study, molecular docking and molecular dynamics (MD) simulation were applied to determine the molecular interaction of the IAA/HRP complex. The docking study represented that IAA bound at the 'exposed' heme edge of the HRP enzyme, and the IAA entrance to the enzyme was situated at the carboxymethyl side-chain of the selected structure. Our computational results showed the HRP/IAA complex structure stability. While hydrogen bond formation with ARG38 and HIS42 stabilized the substrate, hydrophobic interactions with Phe68, Gly69, Leu138, Pro139, Pro141 and Phe179 contributed to IAA/HRP complex stability. The results can help to better understand peroxidase enzyme activity and would pave the way for future development of new therapeutics with improved anticancer efficacy.Communicated by Ramaswamy H. Sarma.

Efficient enzyme-activated therapy based on the different locations of protein and prodrug in nanoMOFs

Enzyme-activated prodrug therapy (EAPT) is an effective cancer treatment strategy able to transport non-toxic prodrugs and subsequently convert them into drugs at specific times and locations. However, due to the limitation of easy biodegradability and the membrane-impermeable characteristic of exogenous enzymes, there is a need to exploit suitable carriers for the effective protection and simultaneous delivery of activating enzymes into cancer cells. Herein, hierarchically porous MOFs were employed for the loading of enzyme and prodrug in a single nanocarrier thanks to their different cavity sizes. The simple loading process allows entrapping of horseradish peroxidase (HRP) and a monocarboxyl-containing indole-3-acetic acid (IAA) prodrug with high loading capacities in different spaces, which keeps the catalytic activity of the enzyme perfectly intact and avoids the premature activation of the prodrug. The encapsulated HRP and IAA exhibit sustained and synchronized release behaviors. Compared to the native HRP enzyme, the current MOF nanocarriers not only facilitate enzyme delivery into cellular lysosomes and subsequent endosomal escape, but also effectively release enzyme and prodrug in the intracellular environment within 48 h. Eventually, HRP and IAA loaded MOF nanocarriers cause significant cell death with a low IC₅₀ of 4.2 mg L^-1, while the IAA prodrug alone is non-toxic even at high concentrations. Thus, hierarchically porous MOFs might offer a promising platform for EAPT with a highly consistent spatiotemporal distribution of enzymes and prodrugs in target tissues.

Improving the Performance of Horseradish Peroxidase by Site-Directed Mutagenesis

Horseradish peroxidase (HRP) is an intensely studied enzyme with a wide range of commercial applications. Traditionally, HRP is extracted from plant; however, recombinant HRP (rHRP) production is a promising alternative. Here, non-glycosylated rHRP was produced in Escherichia coli as a DsbA fusion protein including a Dsb signal sequence for translocation to the periplasm and a His tag for purification. The missing N-glycosylation results in reduced catalytic activity and thermal stability, therefore enzyme engineering was used to improve these characteristics. The amino acids at four N-glycosylation sites, namely N13, N57, N255 and N268, were mutated by site-directed mutagenesis and combined to double, triple and quadruple enzyme variants. Subsequently, the rHRP fusion proteins were purified by immobilized metal affinity chromatography (IMAC) and biochemically characterized. We found that the quadruple mutant rHRP N13D/N57S/N255D/N268D showed 2-fold higher thermostability and 8-fold increased catalytic activity with 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as reducing substrate when compared to the non-mutated rHRP benchmark enzyme.

Origins of Suicide Gene Therapy

"Tumor chemosensitivity" can be achieved by the expression of the herpes simplex virus thymidine kinase gene in cells, followed by the conversion of the "prodrug" ganciclovir into the therapeutic drug inside the cells. This system presaged other combinations of suicide genes and prodrugs, including cytosine deaminase/5-fluorocytosine, purine nucleoside phosphorylase/6-methylpurine deoxyriboside, and horseradish peroxidase/indole-3-acetic acid.

Enzyme/Prodrug Systems for Cancer Gene Therapy

The use of enzyme/prodrug system has gained attention because it could help improve the efficacy and safety of conventional cancer chemotherapies. In this approach, cancer cells are first transfected with a gene that can express an enzyme with ability to convert a non-toxic prodrug into its active cytotoxic form. As a result, the activated prodrug could kill the transfected cancer cells. Despite the significant progress of different suicide gene therapy protocols in preclinical studies and early clinical trials, none has reached the clinic due to several shortcomings. These include slow prodrug-drug conversion rate, low transfection/transduction efficiency of the vectors and nonspecific toxicity/immunogenicity related to the delivery systems, plasmid DNA, enzymes and/or prodrugs. This mini review aims at providing an overview of the most widely used enzyme/prodrug systems with emphasis on reporting the results of the recent preclinical and clinical studies.

Recombinant horseradish peroxidase variants for targeted cancer treatment

Cancer is a major cause of death. Common chemo‐ and radiation‐therapies damage healthy tissue and cause painful side effects. The enzyme horseradish peroxidase (HRP) has been shown to activate the plant hormone indole‐3‐acetic acid (IAA) to a powerful anticancer agent in in vitro studies, but gene directed enzyme prodrug therapy (GDEPT) studies showed ambivalent results. Thus, HRP/IAA in antibody directed enzyme prodrug therapy (ADEPT) was investigated as an alternative. However, this approach has not been intensively studied, since the enzyme preparation from plant describes an undefined mixture of isoenzymes with a heterogenic glycosylation pattern incompatible with the human system. Here, we describe the recombinant production of the two HRP isoenzymes C1A and A2A in a Pichia pastoris benchmark strain and a glyco‐engineered strain with a knockout of the α‐1,6‐mannosyltransferase (OCH1) responsible for hypermannosylation. We biochemically characterized the enzyme variants, tested them with IAA and applied them on cancer cells. In the absence of H₂O₂, HRP C1A turned out to be highly active with IAA, independent of its surface glycosylation. Subsequent in vitro cytotoxicity studies with human T24 bladder carcinoma and MDA‐MB‐231 breast carcinoma cells underlined the applicability of recombinant HRP C1A with reduced surface glycoslyation for targeted cancer treatment. Summarizing, this is the first study describing the successful use of recombinantly produced HRP for targeted cancer treatment. Our findings might pave the way for an increased use of the powerful isoenzyme HRP C1A in cancer research in the future.

Production and removal of superoxide anion radical by artificial metalloenzymes and redox-active metals

Generation of reactive oxygen species is useful for various medical, engineering and agricultural purposes. These include clinical modulation of immunological mechanism, enhanced degradation of organic compounds released to the environments, removal of microorganisms for the hygienic purpose, and agricultural pest control; both directly acting against pathogenic microorganisms and indirectly via stimulation of plant defense mechanism represented by systemic acquired resistance and hypersensitive response. By aiming to develop a novel classes of artificial redox-active biocatalysts involved in production and/or removal of superoxide anion radicals, recent attempts for understanding and modification of natural catalytic proteins and functional DNA sequences of mammalian and plant origins are covered in this review article.

Nitroreductase gene-directed enzyme prodrug therapy: insights and advances toward clinical utility

This review examines the vast catalytic and therapeutic potential offered by type I (i.e. oxygen-insensitive) nitroreductase enzymes in partnership with nitroaromatic prodrugs, with particular focus on gene-directed enzyme prodrug therapy (GDEPT; a form of cancer gene therapy). Important first indications of this potential were demonstrated over 20 years ago, for the enzyme-prodrug pairing of Escherichia coli NfsB and CB1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide]. However, it has become apparent that both the enzyme and the prodrug in this prototypical pairing have limitations that have impeded their clinical progression. Recently, substantial advances have been made in the biodiscovery and engineering of superior nitroreductase variants, in particular development of elegant high-throughput screening capabilities to enable optimization of desirable activities via directed evolution. These advances in enzymology have been paralleled by advances in medicinal chemistry, leading to the development of second- and third-generation nitroaromatic prodrugs that offer substantial advantages over CB1954 for nitroreductase GDEPT, including greater dose-potency and enhanced ability of the activated metabolite(s) to exhibit a local bystander effect. In addition to forging substantial progress towards future clinical trials, this research is supporting other fields, most notably the development and improvement of targeted cellular ablation capabilities in small animal models, such as zebrafish, to enable cell-specific physiology or regeneration studies.

An updated view on horseradish peroxidases: recombinant production and biotechnological applications

Horseradish peroxidase has been the subject of scientific research for centuries. It has been used exhaustively as reporter enzyme in diagnostics and histochemistry and still plays a major role in these applications. Numerous studies have been conducted on the role of horseradish peroxidase in the plant and its catalytic mechanism. However, little progress has been made in its recombinant production. Until now, commercial preparations of horseradish peroxidase are still isolated from plant roots. These preparations are commonly mixtures of various isoenzymes of which only a small fraction has been described so far. The composition of isoenzymes in these mixed isolates is subjected to uncontrollable environmental conditions. Nowadays, horseradish peroxidase regains interest due to its broad applicability in the fields of medicine, life sciences, and biotechnology in cancer therapy, biosensor systems, bioremediation, and biocatalysis. These medically and commercially relevant applications, the recent discovery of new natural isoenzymes with different biochemical properties, as well as the challenges in recombinant production render this enzyme particularly interesting for future biotechnological solutions. Therefore, we reviewed previous studies as well as current developments with biotechnological emphasis on new applications and the major remaining biotechnological challenge—the efficient recombinant production of horseradish peroxidase enzymes.

Salicylic acid-induced superoxide generation catalyzed by plant peroxidase in hydrogen peroxide-independent manner

It has been reported that salicylic acid (SA) induces both immediate spike and long lasting phases of oxidative burst represented by the generation of reactive oxygen species (ROS) such as superoxide anion radical (O2(•-)). In general, in the earlier phase of oxidative burst, apoplastic peroxidase are likely involved and in the late phase of the oxidative burst, NADPH oxidase is likely involved. Key signaling events connecting the 2 phases of oxidative burst are calcium channel activation and protein phosphorylation events. To date, the known earliest signaling event in response to exogenously added SA is the cell wall peroxidase-catalyzed generation of O2(•-) in a hydrogen peroxide (H2O2)-dependent manner. However, this model is incomplete since the source of the initially required H2O2 could not be explained. Based on the recently proposed role for H2O2-independent mechanism for ROS production catalyzed by plant peroxidases (Kimura et al., 2014, Frontiers in Plant Science), we hereby propose a novel model for plant peroxidase-catalyzed oxidative burst fueled by SA.

Hydrogen peroxide-independent generation of superoxide by plant peroxidase: hypotheses and supportive data employing ferrous ion as a model stimulus

When plants are threaten by microbial attacks or treated with elicitors, alkalization of extracellular space is often induced and thus pH-dependent extracellular peroxidase-mediated oxidative burst reportedly takes place, especially at the site of microbial challenge. However, direct stimulus involved in activation of peroxidase-catalyzed oxidative burst has not been identified to date. Here, we would like to propose a likely role for free ferrous ion in reduction of ferric native peroxidase into ferrous enzyme intermediate which readily produces superoxide anion via mechanism involving Compound III, especially under alkaline condition, thus, possibly contributing to the plant defense mechanism. Through spectroscopic and chemiluminescence (CL) analyses of reactions catalyzed by horseradish peroxidase (HRP), the present study proposed that plant peroxidase-catalyzed production of superoxide anion can be stimulated in the absence of conventional peroxidase substrates but in the presence of free ferrous ion.

Suicide gene therapy in cancer: where do we stand now?

Suicide gene therapy is based on the introduction into tumor cells of a viral or a bacterial gene, which allows the conversion of a non-toxic compound into a lethal drug. Although suicide gene therapy has been successfully used in a large number of in vitro and in vivo studies, its application to cancer patients has not reached the desirable clinical significance. However, recent reports on pre-clinical cancer models demonstrate the huge potential of this strategy when used in combination with new therapeutic approaches. In this review, we summarize the different suicide gene systems and gene delivery vectors addressed to cancer, with particular emphasis on recently developed systems and associated bystander effects. In addition, we review the different strategies that have been used in combination with suicide gene therapy and provide some insights into the future directions of this approach, particularly towards cancer stem cell eradication.