Project 4: Therapeutic Immune Targeting of EphA2 Expressed by Melanoma and Its Tumor-Associated Vasculature
We have recently determined that more than 90% of melanomas overexpress the receptor tyrosine kinase (RTK) EphA2, with the EphA2 level of overexpression associated with metastic phenotype and an adverse clinical prognosis. Cross-linking of tumor cell-expressed EphA2 molecules using either ligand Ephrin A1-Ig fusion proteins or activating anti-EphA2 antibodies results in RTK phosphorylation, followed by receptor internalization, c-CbI-dependent ubiquitination and proteasome-dependent degradation. As a consequence, agonist-treated tumor cells acquire a more benign phenotype, and based on our preliminary data, they conditionally up-regulate their expression of EphA2-derived epitopes presented in MHC class I complexes.
Using Eph-A2-specific CTL lines and clones, we have shown in preliminary data that treatment with these EphA2 ligand agonists results in improved recognition and killing of tumor cells by anti-EphA2 CD8+ T cells in vitro and in vivo in Hu-SCID models. We have also recently observed that pharmacologic inhibition of protein tyrosine phosphatases (PTP) or HSP90 function also serves to increase EPhA2 proteasomal processing, theoretically making Eph-A2 peptides accessible to the MHC class I biosynthetic pathway. We hypothesize that EphA2 ligand agonists and PTP/HSP90 inhibitors may act synergistically in promoting enhanced tumor cell recognition by CTLs. As a consequence, we hypothesize that combinational immunotherapies consisting of 1) EphA2-based vaccines designed to elicit specific CTLs and 2) the conditional activation of EphA2 degradation and proteasomal processing via locoregional administration of EphA2 ligand agonists or PTP/HSP90 inhibitors will result in improved anti-melanoma efficacy.
Specific Aim 1: Evaluate the ability of agonists that promote EphA2 proteasomal processing to sensitize melanoma cells to anti-EphA2 CD8+ T cell recognition in vitro.
Specific Aim 2: Test the hypothesis that combinational immunotherapies targeting the conditional proteasomal processing of EphA2 are safe and more effective than single modality therapies in mouse models in vivo.
Specific Aim 3: Design and perform a phase I clinical trial of a combinational therapy involving DC1/EphA2 peptide immunization and conditional augmentation of tumor presentation of EphA2-derived epitopes in HLA-A2+ patients with advanced-stage melanoma.