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Research Overview 

The central working hypothesis of the Arap/Pasqualini research program is that differential protein expression in the human vascular endothelium, associated with normal or diseased tissues, offers the potential for developing novel diagnostic, imaging, and therapeutic strategies. Our program uses peptide- and antibody-based combinatorial library selection to discover, validate, and exploit the vascular biochemical diversity of endothelial cell surfaces towards identifying new vascular targeted pharmacologics for clinical translation.

Funded Programs in the Arap/Pasqualini Laboratory

Radiation therapy (RT) is an integral therapeutic modality for treating non-small cell lung cancer (NSCLC). However, lung cancer is often refractory to RT and molecular mechanisms mediating treatment resistance and tumor repopulation remain poorly defined. We have determined that the receptor tyrosine kinase EphA5 is highly expressed in lung cancer and, more importantly, its expression in patients negatively correlates with RT success and survival, thus suggesting its involvement in the regulation of cellular responses to genotoxic insult. We have assembled multiple lines of evidence to support a potential mechanism underlying EphA5-mediated radioresistance (reported by Staquicini et al. JBC 2015). In order to translate these findings, we plan to utilize a combined in vitro and in vivo screening approach based on phage and yeast antibody display to select and characterize antibodies with radiosensitizing properties and recognize targets in vivo. This work is supported by NIH grant R01CA218853.

We reported that ligand-directed targeting of lymphatic vessels could reveal mechanistic insights in melanoma metastasis formation (Christianson et al. PNAS, 2015). We discovered a functional ligand-receptor system by selecting, isolating, and validating a new homophilic protein-protein interaction between malignant melanoma cells and lymphatic endothelial cells. This unique and previously unrecognized finding provides the foundation for the development and optimization of a new platform for ligand-directed imaging of the lymphatic system. We are interrogating previously identified peptide ligands that bind to the surface of the lymphatic endothelium during disease progression to develop a novel, ligand-directed, non-invasive in vivo lymphatic imaging platform. Peptides that home to PPP2R1A, a new powerful lymphatic marker, will be prioritized. This work is supported by NIH award R01CA204517.

We have pioneered and developed an in vivo screening system in which peptide-targeted particles capable of homing to tumors are recovered from a phage display random library following intravenous administration. In an unbiased screening of an established patient-derived xenograft (PDX) with several biological attributes reminiscent of human metastatic prostate cancer, we first isolated and validated tumor-homing peptides targeting the cell surface-associated glucose-regulated protein-78 kD (GRP78); we also screened a patient directly to isolate and validate ligands targeting the interleukin-11 receptor (IL-11R). Work from our group (among others) shows that overexpression of GRP78 and IL-11R is related to disease progression. As such, promoters for these genes will be evaluated in new hybrid AAV/phage (AAVP) constructs for tumor imaging and suicide gene therapy in preclinical models of prostate cancer. This work is supported by NIH grant R01CA240516.

Treatment failure and acquired drug resistance mechanisms are major concerns in oncology. One method to stabilize poorly soluble and/or highly toxic drugs, and potentially overcome resistance, is to encapsulate drugs in nanoparticles (NPs) to prevent their degradation and enhance their circulation time. We will generate GRP78-targeted NPs against enzalutamide-resistant prostate cancer using the modular “protocell” platform developed by collaborators in New Mexico. Protocells consist of a porous silica core, which can be engineered to accommodate varied and combination cargos, encapsulated within a supported lipid bilayer that protects and retains the cargo, and provides a biocompatible surface for conjugation to targeting and/or trafficking ligands. Our modular GRP78-targeted protocells will be designed to package small interfering RNAs (siRNAs) directed against the long non-coding RNA PCA3 to selectively bind to GRP78-expressing prostate cancer cells, and deliver PCA3 siRNA intracellularly to inhibit tumor growth. This project is supported by NIH grant R01CA226537.

Our group has recently developed targeted strategies for the development of vaccine candidates for COVID-19. Our vaccine program combines an attractive and highly effective delivery system of targeted phage particles that can be safely administered, including via a pulmonary delivery mechanism, to induce robust immunity against the spike protein of SARS-CoV-2. Engineered phage particles have great potential as a vaccine due to their inherent immunogenicity, genetic plasticity, stability, and proven safety profile in humans. We recently reported the design, development, and testing of two phage-based vaccine candidate approaches for severe acute respiratory syndrome virus 2 (SARS-CoV-2): dual-display phage and adeno-associated virus phage (AAVP) particles (Staquicini et al. PNAS 2021). This work is supported by a Sponsored Research Agreement and has been licensed for further development.

We developed a novel and robust antibody discovery methodology, termed selection of phage-displayed accessible recombinant targeted antibodies (SPARTA) that combines an in vitro screening step of a naive human antibody library against known tumor targets and an in vivo selection based on tumor-homing capabilities of the pre-enriched antibody pool. We used SPARTA on two well-established tumor cell surface targets, EphA5 and GRP78, to develop antibodies that showed tumor-targeting selectivity in mouse models and had potential as antibody-drug conjugates (ADCs). This program is ongoing under a Sponsored Research Agreement and has been licensed for commercial development.