Projects for Human Health

Targeted Drug and Nucleic Acid Delivery

Introduction. Targeting therapies only to specific cells in our bodies -- and thereby increasing efficacy and avoiding side effects – is an exciting idea first proposed by Erlich in 1900. Strikingly, a 2016 review revealed that the average delivery efficiency for more than 200 attempts was less than 1%. The overriding reason for these failures is that many distinct challenges (Figure 1) must be simultaneously addressed. The Swartz lab is now building upon more than ten years of their own design and testing experience to produce a “smart” virus-like particle that answers these challenges.

Our approach. The initial disease focus is end stage prostate cancer using the heavily over-expressed PSMA cell surface marker as our target. The vehicle is produced as shown in Figure 2. The virus-like particle (VLP) is composed of 240 copies of a single multiple-mutated protein. The protein immediately forms the dimers shown, and 120 of these are triggered, simply by adding salt, to spontaneously assemble into hollow spherical particles filled with toxic cargo. After assembly, the nanoparticles are stabilized by stimulating disulfide bond formation between the VLP subunits. The shell then becomes a single covalently stabilized molecule. These bonds will dissolve inside the targeted cells to release the toxin and kill the cancer cells.

Figure 1. Challenges for Targeted Drug Delivery

Figure 2. General Production Process

The VLPs display 120 protruding surface spikes; each decorated with uniquely reactive non-natural amino acids that facilitate precise surface modification. An anti-PSMA nanobody is attached so the particles will bind to the cancer cells with high avidity and trigger internalization into the same cells.

To avoid immediate immune system removal of the particle, we are pioneering the production and attachment of the extracellular domain (ECD) of the CD47 receptor that tells immune cells “don’t eat me”.

Progress and plans. Feasibility has now been demonstrated for the major design features, and we are studying how the type and number of each VLP surface modification affects nanoparticle pharmacokinetics. We plan to optimize the delivery vehicle design with an objective of delivering at least 90% of the injected (or infused) toxin (mertansine) to the tumors for effective cancer destruction using nanobodies to target the VLP. 

Precisely Designed Vaccines for Stopping Pandemics and General Applications

Introduction. The COVID-19 global pandemic has been extremely costly in lives lost, physical suffering, and economic disruption. This is truly a global challenge, and we are learning that the most effective deterrent is almost certainly a widely distributed, efficacious vaccine. While anti-COVID progress is now encouraging in the US, unfortunately, a new pandemic threat could emerge at any time. We are therefore working toward a new vaccine technology to address this critical dilemma.

We have therefore designed a program with the objective of providing six billion doses of a safe and effective vaccine within two months of discovering the new pandemic pathogen. Such a response requires highly productive as well as inexpensive production technologies. Our objective is to increase productivity and to reduce costs by at least 100-fold relative to current technologies. 

Vaccine Design. Because our immune systems have evolved to fight viral invaders, our new vaccine design mimics a natural virus. On its surface will be attached a protein antigen capable of eliciting protective responses and one or more adjuvant molecules to both stimulate and direct a potent response. The general design is indicated in Figure 3.

Figure 3. Vaccine Design

Most of the vaccine nanoparticle can be produced in advance of the pandemic threat and stockpiled. This will help tremendously in rapidly producing the vaccine when needed.

Proposed Pandemic Suppression. When a potential pandemic-causing pathogen emerges, the probability is high that enough will be known about the virus to identify a surface antigen suitable for an effective vaccine. Cell-free protein synthesis (CFPS) methods allow us to test thousands of different antigen production protocols in parallel to identify an optimal production process in only a few days. Using dried or frozen cell extracts that have also been stored, commercial scale production would then begin only about 10 days after antigen identification. 500 L CFPS bioreactors could then produce about 500 million doses a week at very low cost.

Progress and plans. Initial feasibility for such a vaccine has been demonstrated in mice using a lymphoma cancer model. High levels of neutralizing antibodies were elicited, and the antibodies protected against an otherwise lethal cancer challenge. Going forward, we plan to further optimize the vaccine design in mice while testing vaccine candidates for at least three different diseases. The program is further described in this article: https://news.stanford.edu/2021/03/16/rapid-response-vaccine-stop-pandemics/ .