Dynamic Transitions of Virus Capsid (Cryo-electron micrographs)

Units of 3 CP subunits rotate to open a pore that can be used for loading of drugs at the production facility and for subsequent intracellular release in the clinic.

The natural first clinical application of this virus-based technology is oncology, where anti-tumor drugs can be delivered to the nuclei of tumor cells, dramatically increasing efficacy and tolerability while bypassing the main mechanism of resistance, cytosolic efflux pumps.  There are numerous additional clinical applications involving multiple therapeutic areas.  Potential nanoparticle cargo molecules may include: drugs (including those otherwise ineffective due to pharmacokinetic issues); dyes; peptides; nucleotides (such as siRNA or other gene silencing technologies); and possibly others.

Some more specific reasons as to why the anticancer therapy goal of various nanotechnologies has not yet been actualized include:  

 1)    Inadequate technologies enabling effective therapeutic cargo        loading in nanoparticles

            a.    Nanoparticle polydispersity

            b.    Poor nanoparticle reproducibility

            c.    Fundamental manufacturing issues

2)    Poor biological function

            a.    Inability to deliver cargo inside a cell

            b.    Premature release of cargo

            c.    Non-release of cargo

3)    Lack of oncology-specific advantages

            a.    Inability to differentiate healthy cells from cancer cells

            b.    Inability to overcome multidrug resistance (MDR)

            c.    Inability to achieve tumor penetration, and others.

We believe that the engineered plant virus we are using can adequately address all of these reasons for the serious difficulties presently encountered using nanoparticle-based therapies.  This plant virus survives in the soil and is one of the most robust of all known viruses.  It can survive the harshest of environments, including blood, while protecting its cargo.  It is nontoxic to humans; is found in the human food chain; and infects a variety of host plants, including cherries.  It appears to be nonimmunogenic. 

Our plant virus-based, multifunctional nanoparticle platform or “Plant Virus Nanoparticle” (PVN) may serve as a carrier for imaging agents as well as for therapeutics and is capable of cellular and sub-cellular targeting.  The PVN is stable, robustly protects its cargo, and may be lyophilized for long term storage.

The following figure shows how this platform may serve as a generalized test vehicle to establish the effectiveness of cell targeting strategies for many types of targets and targeting molecules.  The figure that follows shows the steps for preparing a PVN.  The loading mechanism is novel and results in a uniform population of identical nanoparticles that are identically loaded.  The loaded PVN in the left side of the figure below (A) carries a fluorophore inside and has targeting peptides on the outside, demonstrating the simplicity of proof-of-concept experiments.  Preliminary data demonstrate a highly controlled release of fluorophores inside the targeted cell and not externally.  The triggered release does not occur in the endosome due to the low pH and relatively high calcium ion concentration.  As shown in the right side of the figure (B) release occurs in the cytosol and is triggered by cytoplasmic entry.  Fluorescent dyes are quenched while inside the PVN, but they can be detected when they are released.  The PVN can also carry an internal payload of other types of imaging agents, chemotherapy agents, and small molecules in general.  This includes oligonucleotides, as well.

                                      NanoVector, Inc.• P.O. Box 98385 • Raleigh, NC27624

                                    Phone: 919.878.8464 • Fax: 919.676.5436

  

Although considerable progress has been made in the application of nanotechnology to cancer therapy, the goal of providing highly efficacious targeted drug delivery to tumors without adverse effects has not yet been achieved.  A general theory as to why this goal has not yet been actualized is that some of the inherent challenges associated with nanoparticles, for example: efficient manufacturing of nanoparticles; uniform loading; and timely cargo delivery; involve very difficult chemistry problems, some of which do not at this time have suitable solutions. 

Our nanoparticle inherently overcomes these problems because it is a biologic, specifically the product of natural replication of a unique plant virus in a well-controlled host plant system involving minimal human intervention.  This unusual virus brings with it some very interesting properties that turn out to be highly desired for a nanoscale drug delivery system.  Each nanoparticle is identical and can be filled with equal amounts of drug cargo using a simple process.  Moreover, the best chemistry-based technologies have been as yet unable to achieve the equivalent to what this plant virus has achieved through millions of years of evolution, such as the ability with the proper targeting to: form endosomes and enter cancer cells; sense the intracellular environment and initiate a process leading to the release of the contents of its “cargo chamber”; and delay this release long enough to enable the secondary targeting of intracellular structures, such as the nucleus.