Fighting cancer with plant-expressed pharmaceuticals

Cancer biologics made in plants

Plants are routinely utilized as efficient production platforms for the development of anti-cancer biologics leading to novel anti-cancer vaccines, immunotherapies, and drug-delivery modalities. Various biosimilar/biobetter antibodies and immunogens based on tumor-associated antigens have been produced and optimized for plant expression. Plant virus nanoparticles, including those derived from cowpea mosaic virus or tobacco mosaic virus in particular have shown promise as immunotherapies stimulating tumor-associated immune cells and as drug carriers delivering conjugated chemotherapeutics effectively to tumors. Advancements have also been made toward the development of lectins that can selectively recognize cancer cells. The ease at which plant systems can be utilized for the production of these products presents an opportunity to further develop novel and exciting anti-cancer biologics.

Co-Delivery Nanosystems for Cancer Treatment: A Review

Massive data available on cancer therapy more than ever lead our mind to the general concept that there is no perfect treatment for cancer. Indeed, the biological complexity of this disease is too excessive to be treated by a single therapeutic approach. Current delivery systems containing a specific drug or gene have their particular opportunities and restrictions. It is worth noting that a considerable number of studies suggest that single- drug delivery systems result in insufficient suppression of cancer growth. Therefore, one of the main ideas of co-delivery system designing is to enhance the intended response or to achieve the synergistic/combined effect compared to the single drug strategy. This review focuses on various strategies for co-delivery of therapeutic agents in the treatment of cancer. The primary approaches within the script are categorized into co-delivery of conventional chemotherapeutics, gene-based molecules, and plant-derived materials. Each one is explained in examples with the recent researches. In the end, a brief summary is provided to conclude the gist of the review.

Engineering Plants for the Future: Farming with Value-Added Harvest

Plants and their rich variety of natural compounds are used to maintain and to improve health since the earliest stages of civilization. Despite great advances in synthetic organic chemistry, one fourth of present-day drugs have still a botanical origin, and we are currently living a revival of interest in new pharmaceuticals from plant sources.

Modern biotechnology has defined the potential of plants to be systems able to manufacture not only molecules naturally occurring in plants but also newly engineered compounds, from small to complex protein molecules, which may originate even from non-plant sources. Among these compounds, pharmaceuticals such as vaccines, antibodies and other therapeutic or prophylactic entities can be listed. For this technology, the term plant molecular farming has been coined with reference to agricultural applications due to the use of crops as biofactories for the production of high-added value molecules. In this perspective, edible plants have also been thought as a tool to deliver by the oral route recombinant compounds of medical significance for new therapeutic strategies. Despite many hurdles in establishing regulatory paths for this “novel” biotechnology, plants as bioreactors deserve more attention when considering their intrinsic advantages, such as the quality and safety of the recombinant molecules that can be produced and their potential for large-scale and low-cost production, despite worrying issues (e.g. amplification and diffusion of transgenes) that are mainly addressed by regulations, if not already tackled by the plant-made products already commercialized. The huge benefits generated by these valuable products, synthesized through one of the safest, cheapest and most efficient method, speak for themselves.

Milestone for plant-based recombinant protein production for human health use was the approval in 2012 by the US Food and Drug Administration of plant-made taliglucerase alfa, a therapeutic enzyme for the treatment of Gaucher’s disease, synthesized in carrot suspension cultures by Protalix BioTherapeutics.

In this review, we will go through the various approaches and results for plant-based production of proteins and recent progress in the development of plant-made pharmaceuticals (PMPs) for the prevention and treatment of human diseases. An analysis on acceptance of these products by public opinion is also tempted.

Simply and sensitively simultaneous detection hepatocellular carcinoma markers AFP and miRNA-122 by a label-free resonance light scattering sensor

In this study, an intelligent and label-free sensor is utilized for the first time to one-spot simultaneous detection hepatocellular carcinoma markers AFP and miRNA-122 by a resonance light scattering (RLS) sensor. cDNA1 hybridizes with cDNA2 to form double-stranded DNA (dsDNA). The construction of dsDNA and methyl violet is used to form the RLS sensor via the electronic interaction. When AFP or miRNA-122 is present, the cDNA (cDNA1 or cDNA2) can bindings of target, thereby RLS intensity changed proportionally with the concentration of AFP or that of miRNA-122. The detection limits of AFP and miRNA-122 are 0.94 μg/L and 98 pM respectively, and their good linear which ranges from 5 to 100 μg/L and 200 pM to 10 nM are achieved using the assay. In the presence of miRNA-122 and AFP mixtures, AFP bound to the AFP aptamer to increase the RLS signal, and miRNA-122 bound to the miRNA-122 complementary strand to decrease the RLS signal. The RLS signal changed in response to changing AFP and miRNA-122 concentrations, so that one-spot simultaneous detection of alpha fetal protein and miRNA-122 is achieved. This method has potential practical applications in the research of hepatocellular carcinoma.

Theobroma cacao: Review of the Extraction, Isolation, and Bioassay of Its Potential Anti-cancer Compounds

Plants have been a good source of therapeutic agents for thousands of years; an impressive number of modern drugs used for treating human diseases are derived from natural sources. The Theobroma cacao tree, or cocoa, has recently garnered increasing attention and become the subject of research due to its antioxidant properties, which are related to potential anti-cancer effects. In the past few years, identifying and developing active compounds or extracts from the cocoa bean that might exert anti-cancer effects have become an important area of health- and biomedicine-related research. This review provides an updated overview of T. cacao in terms of its potential anti-cancer compounds and their extraction, in vitro bioassay, purification, and identification. This article also discusses the advantages and disadvantages of the techniques described and reviews the processes for future perspectives of analytical methods from the viewpoint of anti-cancer compound discovery.

Production and secretion of a heterologous protein by turnip hairy roots with superiority over tobacco hairy roots

A fully contained and efficient heterologous protein production system was designed using Brassica rapa rapa (turnip) hairy roots. Two expression cassettes containing a cauliflower mosaic virus (CaMV) 35S promoter with a duplicated enhancer region, an Arabidopsis thaliana sequence encoding a signal peptide and the CaMV polyadenylation signal were constructed. One cassette was used to express the green fluorescent protein (GFP)-encoding gene in hairy roots grown in flasks. A stable and fast-growing hairy root line secreted GFP at >120 mg/l culture medium. GFP represented 60 % of the total soluble proteins in the culture medium. Turnip hairy roots retained sustainable growth and stable GFP production over 3 years. These results were superior to those obtained using tobacco hairy roots.

Tobacco as biofactory for biologically active hPL production: a human hormone with potential applications in type-1 diabetes

Human placental lactogen (hPL) is a peptidic hormone that belongs to the short list of growth factors that could treat type-1 diabetes through pancreatic islet transplantation. Placental lactogen has the capacity to improve islet survival and function before or after transplantation. In this study, transgenic tobacco plants were used as a novel expression system for the production of recombinant hPL protein (rhPL). The expression vector pNEKhPL2 containing hPL cDNA was introduced into tobacco plants; the transcriptional activity was confirmed by real-time PCR, and the rhPL levels reached 1% of the total soluble protein (TSP) content in plants cultivated in the greenhouse. In vitro bioassays using the rat insulinoma (INS-1) cell line showed that recombinant protein was able to induce cell proliferation and activate the JAK-2/STAT-5 signal transduction pathway, demonstrating that plant cells can produce the biologically active hPL protein. To further characterize the plant expression system for hPL production, we analyzed the stability of the protein during the life cycle of tobacco plants as well as the transmission of the transgenic trait to the progeny. The recombinant protein was stably accumulated in young leaves, reaching the maximum level in the first month (6.51 μg/g of fresh weight), but showing a decreasing trend of 26% from the initial sampling time until the end of plant's life cycle. The progeny of the selected pNEKhPL2 plant showed in vitro expression levels of up to 1.1% of TSP. Our results therefore indicate that transgenic plants are a suitable expression system for hPL production.

Plant-made trastuzumab (herceptin) inhibits HER2/Neu+ cell proliferation and retards tumor growth

BACKGROUND

Plant biotechnology provides a valuable contribution to global health, in part because it can decrease the cost of pharmaceutical products. Breast cancer can now be successfully treated by a humanized monoclonal antibody (mAb), trastuzumab (Herceptin). A course of treatment, however, is expensive and requires repeated administrations of the mAb. Here we used an Agrobacterium-mediated transient expression system to produce trastuzumab in plant cells.

METHODOLOGY/PRINCIPAL FINDINGS

We describe the cloning and expression of gene constructs in Nicotiana benthamiana plants using intron-optimized Tobacco mosaic virus- and Potato virus X-based vectors encoding, respectively, the heavy and light chains of trastuzumab. Full-size antibodies extracted and purified from plant tissues were tested for functionality and specificity by (i) binding to HER2/neu on the surface of a human mammary gland adenocarcinoma cell line, SK-BR-3, in fluorescence-activated cell sorting assay and (ii) testing the in vitro and in vivo inhibition of HER-2-expressing cancer cell proliferation. We show that plant-made trastuzumab (PMT) bound to the Her2/neu oncoprotein of SK-BR-3 cells and efficiently inhibited SK-BR-3 cell proliferation. Furthermore, mouse intraperitoneal PMT administration retarded the growth of xenografted tumors derived from human ovarian cancer SKOV3 Her2+ cells.

CONCLUSIONS/SIGNIFICANCE

We conclude that PMT is active in suppression of cell proliferation and tumor growth.

The production of biopharmaceuticals in plant systems

Biopharmaceuticals present the fastest growing segment in the pharmaceutical industry, with an ever widening scope of applications. Whole plants as well as contained plant cell culture systems are being explored for their potential as cheap, safe, and scalable production hosts. The first plant-derived biopharmaceuticals have now reached the clinic. Many biopharmaceuticals are glycoproteins; as the Golgi N-glycosylation machinery of plants differs from the mammalian machinery, the N-glycoforms introduced on plant-produced proteins need to be taken into consideration. Potent systems have been developed to change the plant N-glycoforms to a desired or even superior form compared to the native mammalian N-glycoforms. This review describes the current status of biopharmaceutical production in plants for industrial applications. The recent advances and tools which have been utilized to generate glycoengineered plants are also summarized and compared with the relevant mammalian systems whenever applicable.

Generation of plant-derived recombinant DTP subunit vaccine

The current diphtheria-tetanus-pertussis (DTP) pediatric vaccine is produced from the corresponding pathogenic bacteria Corynebacterium diphtheriae, Clostridium tetani and Bordetella pertussis; five injected doses of DTaP (acellular) vaccine are required for every child in the standard US vaccination schedule. Because the vaccine is derived from native live sources, adverse effects are possible and production is complex and costly. To address issues of safety, ease of renewability and expense, we used recombinant technology in an effort to develop a subunit DPT vaccine derived in non-pathogenic plant expression systems. Expression of diphtheria toxin (DT), tetanus fragment-C (TetC) and the non-toxic S1 subunit of pertussis toxin (PTX S1) antigenic proteins in soluble form in low-alkaloid tobacco plants and carrot cell cultures allowed efficient downstream purification to levels suitable for intramuscular injection in BALB/c mice. At working concentrations of 5mug per dose, these preparations induced high levels of antigen-specific IgGs in mouse sera. Our results clearly support the feasibility of producing recombinant pediatric vaccine components in plants.

Investigating recombinant protein exudation from roots of transgenic tobacco

It is widely acknowledged that plant-made pharmaceuticals (PMPs) offer numerous benefits, including inexpensive production, biological safety and the facility for production at agricultural scale. At the same time, it is important to minimize any potential risk associated with this new technology, including the potential release of bioactive proteins into the environment. To address this issue, we studied transgenic Nicotiana benthamiana and Nicotiana tabacum plants expressing two recombinant single-chain variable fragment (scFv) antibodies, respectively scFvB9 and scFvH10. ScFvB9 was raised against glycoprotein G1 of Tomato spotted wilt virus (TSWV), and scFvH10 was raised against human tumor-associated antigen tenascin-C. Both antibodies were targeted to the secretory pathway using the N-terminal signal peptide from Phaseolus vulgaris polygalacturonase-inhibiting protein (PGIP), and scFvH10 carried in addition a C-terminal KDEL tetrapeptide for retention in the endoplasmic reticulum (ER). Sterile hydroponic cultures were established, allowing us to investigate whether scFvB9 and scFvH10 were present in root exudates. Intercellular fluids extracted from different plant tissues were analyzed by western blotting revealing the presence of scFvB9. Successful secretion of scFvB9 in hydroponic medium was also demonstrated, whereas no scFvH10 could be detected in the leaf, stem or root apoplast, nor secreted into the hydroponic medium. Our results show that scFvH10 release or diffusion from the roots of transgenic plants was not occurring, suggesting that the KDEL signal might contribute to the environmental biosafety of crops producing PMPs.