Targeted drug delivery is critical for the success of many therapeutic efforts including immunology, immuno-oncology and gene therapy. It has been largely an unmet need and challenge to target and deliver therapeutic agents such as immune-modulating agents, antigens, adjuvants and nucleic acids to immune cells. Phosphorex’s approach is to engineer the surface of nanoparticles or microparticles so they can target and enter cells via receptor-mediated endocytosis.

To address this challenge, we created Zetafinity®, an enabling platform that can deliver therapeutic agents to immune cells.


Zetafinity® particles, which can be either nanoparticles or microparticles, are designed to bind receptors on the surface of certain immune cells. The particles have the following unique features:

  • Safety – made of FDA-approved biodegradable polymers
  • Superior colloidal stability – less likely to aggregate during or after dosing compared with ordinary polymeric particles
  • Durability – Phosphorex’s patented process ensures manufacturing robustness and durability of targeting entity on the surface.
  • Feasibility – no antibody is needed in the particle formulation and process for cell-targeting, making it economically feasible.
  • Versatility – can be dosed intravenously, subcutaneously, intraperitoneally, intrathecally, intratumorally, topically and orally
  • Efficient in vitro cell uptake – Our data show Zetafinity® particles are effectively taken up by certain immune cells, much more efficiently than ordinary polymeric particles
  • In vivo cell targeting – Our data show Zetafinity® particles effectively target antigen-presenting cells, especially dendritic cells, when systemically dosed in tumor-bearing rodents