NIBIB-funded biomedical engineers at the Ohio State University (OSU) have demonstrated a new method for delivering an anti-cancer drug in a study that tested the effect in animal models.
When formulated within a membrane sac, called an exosome, and when paired with the B-vitamin folate, the anti-cancer drug can enter the cell without being sealed off within the cell by another sac, called an endosome.
Endosome trapping has been a formidable challenge to overcome in drug delivery.
The approach, developed with support from the National Institute of Biomedical Imaging and Bioengineering (NIBIB) and the National Cancer Institute (NCI), both at NIH, works on the principle that receptors for folate are expressed in abundance on cancer cells, but to a more moderate degree on healthy cells.
In their report in the August 22, 2019 online Journal of Controlled Release, the authors suggest that their approach, tested on mice, will renew the interest in folate as a broad target for human cancer therapy.
“Folate targeting has been an elusive approach to cancer therapy,” said David Rampulla, Ph.D., director of the NIBIB Division of Discovery Science and Technology.
“This team has demonstrated an efficient drug delivery system and shown how a nanoparticle combined with folate can efficiently target cancer cells.
It is the kind of advance that could represent the basis for much-needed cancer therapies.”
Folate is a B-vitamin required for synthesis and cell division.
Because of the heightened expression of folate receptors on cancer cells, folate has been widely proposed for targeted cancer therapy for 25 years, having been tested extensively in studies with breast, lung, ovarian, colorectal, and head and neck cancers.
Typical approaches pair folate with an anti-cancer drug, such as a nanoparticle of interfering RNA, which has the potential to disrupt the genetic machinery within cancer cells.
Ideally, folate is recognized by receptors on the cell membrane, which allows the anti-cancer nanoparticle to gain access to the cell.
However, researchers have encountered the challenge that therapeutics delivered via the folate receptor pathway become trapped within the endosome sac.
Thus, in the past, the use of folate for specific drug delivery has not been successful.
The OSU team, led by senior author Peixuan Guo, Ph.D., the Sylvan G. Frank Endowed Chair in Pharmaceutical Drug Delivery, applied an alternate approach to delivering the interfering RNA to the cell.
They put interfering RNA nanoparticles into an exosome with folate on its surface. Upon contact with the cancer cell membrane, the exosome specifically binds to and fuses with the cancer cell’s membrane, releasing its therapeutic contents into the watery component of the cytoplasm (cytosol).
The research team had previously demonstrated that the approach could be effective in impeding breast, colorectal, and prostate cancers in mice. That study was published Dec. 11, 2017, in Nature Nanotechnology.
In their present study, the researchers took the next step, conducting tests to further elucidate the treatment delivery method.
To show that folate receptors enhance delivery of the interfering RNA nanoparticles when they are delivered as a component of the exosome, they paired folate with an interfering RNA called survivin siRNA, which disrupts a protein in cancer cells that can inhibit cell death.
Cancer occurs when cells do not die and proliferate out-of-control.
They used optical fluorescent imaging technology to capture the effect of the treatment delivery via exosome compared to delivery of the survivin siRNA without an exosome.
The imaging showed that the exosome delivery permitted the treatment to be distributed throughout the cell.
To determine whether folate receptors on cancer cells can be specifically targeted, the team applied the treatment in cervical cancer in mice.
Those mice treated with folate and survivin siRNA bound within an exosome had reduced tumor growth, confirming the effectiveness of the new cancer treatment approach.”
The therapeutic effect is surprisingly high,” Guo said. “This finding will be a revolution to renew an obsolete concept in using folate as a specific targeting agent in cancer therapy.”
Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable and biocompatible polymer which is widely used as a matrix to incorporate therapeutic agents. The anticancer activity of targeted folate-modified docetaxel-loaded PLGA nanoparticles (F–NP–Doc) was studied in vitro.
Nanoparticles were prepared by a single-emulsion solvent-evaporation technique and characterized by physico-chemical methods. Cell survival was measured by the MTT assay and the sulforhodamine B assay. Folate receptor α expression, particle uptake and apoptosis were assessed by flow cytometry.
Folate-modified docetaxel-loaded PLGA nanoparticles showed high anticancer activity in vitro against HeLa cervical carcinoma cells and MCF7 breast adenocarcinoma cells overexpressing folate receptors. Targeted F–NP–Doc nanoparticles were more active compared to free docetaxel and non-targeted NP–Doc nanoparticles; in contrast, the activity of targeted nanoparticles against human fibroblasts (negative control) was significantly lower. F–NP–Doc particles, like free docetaxel, induced apoptosis in cancer cells. F–NP–Doc, but not unmodified docetaxel-loaded PLGA nanoparticles, reversed multidrug resistance of MCF7R breast adenocarcinoma cells. High antitumor activity of F–NP–Doc has also been proven in in vivo experiments.
The summarized experimental data brought us to the conclusion that the incorporation of docetaxel into the targeted PLGA nanoparticles dramatically improves its selectivity against cancer cells.
Low selectivity of anticancer drugs results in a high incidence of side effects and remains one of the major problems in cancer chemotherapy. The high toxicity of anticancer drugs against proliferating cells is responsible for developing of numerous serious complications of hematopoietic system, gastrointestinal tract, immune and nervous systems. Over the past 3 decades, the targeted anticancer drugs have been actively developed to eliminate cancer cells. Targeted delivery of anticancer therapeutics is achieved by adding vector molecules to their composition. Such vector molecules include natural or synthetic ligands of receptors preferentially expressed in cancer cells, antibodies to these receptors, and aptamers. The interaction between vector and specific receptor triggers receptor-mediated endocytosis of targeted anticancer drug, thus increasing its selectivity.
Receptor-mediated endocytosis is an extremely effective cellular mechanism for rapid and controlled uptake of specific extracellular macromolecules such as low-density lipoproteins, growth factors, transport proteins as well as some low-molecular weight compounds, for example, folic acid (FA) (Bareford and Swaan 2007). FA is a low-molecular weight physiological ligand, which is non-immunogenic, inexpensive, stable, and readily available, and can be easily conjugated to other molecules through its carboxyl group. These properties have made FA one of the most popular ligands for targeted drug delivery. Actually, the unique properties of FA enable it to be near ideal vector for targeted liposomes, nanoparticles, quantum dots (Syu et al. 2012; Ye et al. 2014; Parveen and Sahoo 2010; Suriamoorthy et al. 2010; Chattopadhyay et al. 2013). This approach offers an opportunity to significantly enhance the efficacy of anticancer drugs. For example, the use of FA for targeted delivery of paclitaxel-loaded nanoparticles (Wang et al. 2012; Wu et al. 2012) resulted in a decrease in systemic toxicity and an increase in antitumor activity of the drug compared with free paclitaxel.
Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable and biocompatible polymer which is widely used as a matrix to incorporate a wide range of therapeutic agents, including hydrophilic and hydrophobic small molecules, nucleic acids, proteins, etc. (Kapoor et al. 2015). PLGA is approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA) for use in pharmaceutical products. Incorporation of poorly soluble cytostatic agents such as taxanes into polymeric nanoparticles is probably the most effective and simplest way to increase their therapeutic efficacy. At present, paclitaxel and docetaxel are widely used in the clinic to treat a variety of malignancies (Eisenhauer and Vermorken 1998; Montero et al. 2005). Both drugs exert cytostatic activity against cancer cells by binding to beta-tubulin and stabilizing cytoskeleton microtubules, resulting in cell cycle arrest at the G2/M phase, inhibition of mitosis and subsequent cell death (Hernandez-Vargas et al. 2007; Kraus et al. 2003). A serious disadvantage of taxanes is their extremely low solubility in aqueous solutions. When used in the clinic, solubilizers, such as Cremophor® EL for paclitaxel or polysorbate-80 for docetaxel, have to be added. These solubilizers often cause serious allergic and toxic reactions that limit the use of the drugs.
The aim of this study was to prepare targeted folate-modified docetaxel-loaded PLGA nanoparticles, to evaluate their cytostatic activity against human cancer cell lines in comparison with that of docetaxel, and to study the activity of targeted nanoparticles against cancer cells with multidrug resistance phenotype.
More information: Zhen Zheng et al. Folate-displaying exosome mediated cytosolic delivery of siRNA avoiding endosome trapping, Journal of Controlled Release (2019). DOI: 10.1016/j.jconrel.2019.08.021
Journal information: Nature Nanotechnology , Journal of Controlled Release
Provided by National Institutes of Health