The chemical composition, size, shape and surface characteristics of nanoparticles affect the way proteins bind to these particles, and this in turn influences the way in which nanoparticles interact with cells and tissues. Nanomaterials bound with proteins can result in physiological and pathological changes, including macrophage uptake, blood coagulation, protein aggregation and complement activation, but the mechanisms that lead to these changes remain poorly understood. Here, we show that negatively charged poly(acrylic acid)-conjugated gold nanoparticles bind to and induce unfolding of fibrinogen, which promotes interaction with the integrin receptor, Mac-1. Activation of this receptor increases the NF-κB signalling pathway, resulting in the release of inflammatory cytokines. However, not all nanoparticles that bind to fibrinogen demonstrated this effect. Our results show that the binding of certain nanoparticles to fibrinogen in plasma offers an alternative mechanism to the more commonly described role of oxidative stress in the inflammatory response to nanomaterials.

A single nanoparticle platform has been developed through the modular and controlled layer-bylayer process to co-deliver siRNA that knocks down a drug-resistance pathway in tumor cells and a chemotherapy drug to challenge a highly aggressive form of triple-negative breast cancer. Layer-by-layer films were formed on nanoparticles by alternately depositing siRNA and poly-L-arginine; a single bilayer on the nanoparticle surface could effectively load up to 3,500 siRNA molecules, and the resulting LbL nanoparticles exhibit an extended serum half-life of 28 hours. In animal models, one dose via intravenous administration significantly reduced the target gene expression in the tumors by almost 80%. By generating the siRNA-loaded film atop a doxorubicin-loaded liposome, we identified an effective combination therapy with siRNA targeting multidrug resistance protein 1, which significantly enhanced doxorubicin efficacy by 4 fold in vitro and led to up to an 8-fold decrease in tumor volume compared to the control treatments with no observed toxicity. The results indicate that the use of layer-by-layer films to modify a simple liposomal doxorubicin delivery construct with a synergistic siRNA can lead to significant tumor reduction in the cancers that are otherwise nonresponsive to treatment with Doxil or other common chemotherapy drugs. This approach provides a potential strategy to treat aggressive and resistant cancers, and a modular platform for a broad range of controlled multidrug therapies customizable to the cancer type in a singular nanoparticle delivery system.

Nanoparticles rapidly interact with the proteins present in biological fluids, such as blood. The proteins that are adsorbed onto the surface potentially dictate the biokinetics of the nanomaterials and their fate in vivo. Using nanoparticles with different sizes and surface characteristics, studies have reported the effects of physicochemical properties on the composition of adsorbed plasma proteins. However, to date, few studies have been conducted focusing on the nanoparticles that are commonly exposed to the general public, such as the metal oxides. Using previously established ultracentrifugation approaches, two-dimensional gel electrophoresis and mass spectrometry, the current study investigated the binding of human plasma proteins to commercially available titanium dioxide, silicon dioxide and zinc oxide nanoparticles. We found that, despite these particles having similar surface charges in buffer, they bound different plasma proteins. For TiO2, the shape of the nanoparticles was also an important determinant of protein binding. Agglomeration in water was observed for all of the nanoparticles and both TiO2 and ZnO further agglomerated in biological media. This led to an increase in the amount and number of different proteins bound to these nanoparticles. Proteins with important biological functions were identified, including immunoglobulins, lipoproteins, acute-phase proteins and proteins involved in complement pathways and coagulation. These results provide important insights into which human plasma proteins bind to particular metal oxide nanoparticles. Because protein absorption to nanoparticles may determine their interaction with cells and tissues in vivo, understanding how and why plasma proteins are adsorbed to these particles may be important for understanding their biological responses.

Active targeting of nanoscale drug carriers can improve tumor-specific delivery; however, cellular heterogeneity both within and among tumor sites is a fundamental barrier to their success. Here, we describe a tumor microenvironment-responsive layer-by-layer (LbL) polymer drug carrier that actively targets tumors based on two independent mechanisms: pH-dependent cellular uptake at hypoxic tumor pH and hyaluronan-directed targeting of cell-surface CD44 receptor, a well-characterized biomarker for breast and ovarian cancer stem cells. Hypoxic pH-induced structural reorganization of hyaluronan-LbL nanoparticles was a direct result of the nature of the LbL electrostatic complex, and led to targeted cellular delivery in vitro and in vivo, with effective tumor penetration and uptake. The nanoscale drug carriers selectively bound CD44 and diminished cancer cell migration in vitro, while co-localizing with the CD44 receptor in vivo. Multimodal targeting of LbL nanoparticles is a powerful strategy for tumor-specific cancer diagnostics and therapy that can be accomplished using a single bilayer of polyamine and hyaluronan that, when assembled, produce a dynamic and responsive cell–particle interface.

The binding of fibrinogen to various nanoparticles can result in protein unfolding and exposure of cryptic epitopes that subsequently interact with cell surface receptors. This response is dependent on the size, charge, and concentration of the nanoparticle. Here we examine the binding kinetics of human fibrinogen to negatively charged poly(acrylic acid)-coated gold nanoparticles ranging in size from 7 to 22 nm. These particles have previously been shown to elicit an inflammatory response in human cells. The larger nanoparticles bound fibrinogen with increasing affinity and a slower dissociation rate. Each fibrinogen molecule could accommodate two 7 nm nanoparticles but only one when the diameter increased to 10 nm. Nanoparticles larger than 12 nm bound multiple fibrinogen molecules in a positively cooperative manner. However, in the presence of excess nanoparticle, fibrinogen induced aggregation of the larger particles that could bind more than one protein molecule. This is consistent with interparticle bridging by the fibrinogen. Taken together, these results demonstrate that subtle changes in nanoparticle size can influence protein binding both with the surface of the nanoparticle and within the protein corona.

Exposure to the EGFR (epidermal growth factor receptor) inhibitor erlotinib promotes the dynamic rewiring of apoptotic pathways, which sensitizes cells within a specific period to subsequent exposure to the DNA-damaging agent doxorubicin. A critical challenge for translating this therapeutic network rewiring into clinical practice is the design of optimal drug delivery systems. We report the generation of a nanoparticle delivery vehicle that contained more than one therapeutic agent and produced a controlled sequence of drug release. Liposomes, representing the first clinically approved nanomedicine systems, are well-characterized, simple, and versatile platforms for the manufacture of functional and tunable drug carriers. Using the hydrophobic and hydrophilic compartments of liposomes, we effectively incorporated both hydrophobic (erlotinib) and hydrophilic (doxorubicin) small molecules, through which we achieved the desired time sequence of drug release. We also coated the liposomes with folate to facilitate targeting to cancer cells. When compared to the time-staggered application of individual drugs, staggered release from tumor-targeted single liposomal particles enhanced dynamic rewiring of apoptotic signaling pathways, resulting in improved tumor cell killing in culture and tumor shrinkage in animal models.

While plasma proteins can influence the physicochemical properties of nanoparticles, the adsorption of protein to the surface of nanomaterials can also alter the structure and function of the protein. Here, we show that plasma proteins form a hard corona around synthetic layered silicate nanoparticles (LSN) and that one of the principle proteins is serum albumin. The protein corona was required for recognition of the nanoparticles by scavenger receptors, a major receptor family associated with the mononuclear phagocyte system (MPS). Albumin alone could direct nanoparticle uptake by human macrophages, which involved class A but not class B scavenger receptors. Upon binding to LSN, albumin unfolded to reveal a cryptic epitope that could also be exposed by heat denaturation. This work provides an understanding of how albumin, and possibly other proteins, can promote nanomaterial recognition by the MPS without albumin requiring chemical modification for scavenger receptor recognition. These findings also demonstrate an additional function for albumin in vivo.

The binding of proteins to nanoparticles is an important event that can determine the biological effect of nanoparticles in the body. We examined plasma protein binding to gold nanoparticles (5-20 nm) with different surface charge. Positively and negatively charged nanoparticles bound a range of proteins whereas neutral nanoparticle bound very little. As little as 25% neutral polymer on the surface of the charged nanoparticles inhibited protein binding, with only slight change in surface charge. Fibrinogen bound with high affinity to both of the charged nanoparticles. However, binding kinetics and protease digestion suggested that the binding orientation for each nanoparticle was different. Only the negatively charged nanoparticles induced cytokine release from THP-1 cells. While common proteins can bind to different nanoparticles, the biological outcome may not be the same. Consequently, knowledge about the composition of the protein corona is not sufficient to predict biological effects of nanoparticles.