Human malignant melanoma is an aggressive cancer with high propensity for metastatic dissemination. Despite recent advances in melanoma therapy, most patients with metastatic disease do not experience durable benefit from current treatment options. Indeed, existing targeted and cancer immunotherapeutic modalities do not directly inhibit tumor metastasis, which accounts for most cancer-related deaths. Accordingly, the development of new agents that specifically target pro-metastatic pathways intrinsic to melanoma cells could greatly improve treatment outcomes and reduce off-target toxicities. The trafficking processes observed in disseminating metastatic cancers resemble, at least in part, the leukocyte homing paradigm, a sequential multistep adhesive cascade involving cell tethering and rolling on microvascular endothelium, followed by integrin-mediated arrest and transendothelial migration into secondary tissues. Leukocyte homing is dependent on specialized integrin heterodimers and their cognate ligands on endothelial cells. To date, however, expression of these distinct leukocytic homing integrin subsets has not been described in melanoma. Our preliminary studies demonstrate, for the first time, aberrant expression of integrin heterodimers, conventionally thought to be restricted to leukocytes, by melanoma cell subsets with high metastatic capacity. In patient primary melanomas, cancer cell-intrinsic integrin positivity correlated with sentinel lymph node metastases. Melanoma-specific inhibition of these integrin heterodimers suppressed endothelial adhesion and significantly blocked growth and metastasis formation in preclinical mouse models of human melanoma. These paradigm- shifting findings identify leukocytic homing integrins as novel mediators of tumor cell dissemination. While hematopoietic integrin targeting approaches, including humanized antibodies, have already been developed for the treatment of patients with inflammatory and autoimmune leukocyte trafficking disorders, they have never been examined in the context of cancer. In this proposal, we newly investigate the therapeutic utility of these validated and readily available integrin inhibitors in blocking metastatic dissemination in preclinical melanoma models.
Our specific aims are to 1) dissect mechanisms of melanoma cell-intrinsic homing integrin induction and functional activation, and define integrin glycosylation states and heterodimer composition in patient tumor biospecimens at various stages of progression, and 2) examine the therapeutic efficacy of CRISPR/Cas-9-mediated leukocytic integrin knockout or clinical-grade integrin inhibitors originally formulated for the treatment of immune trafficking disorders, in preclinical melanoma models. We have assembled a team of experts in the melanoma metastasis, leukocyte homing, gene editing, dermatopathology, and glycobiology fields, to bring to fruition the translationally relevant aims of this proposal. Results from our studies could establish melanoma cell-expressed leukocytic integrins and their glycostructural determinants as novel therapeutic targets for selective inhibition of metastatic dissemination.
This research project will provide insight into how a newly identified metastasis pathway, previously implicated only in blood cell trafficking, could be exploited to inhibit melanoma progression. Our studies will validate, in pre-clinical melanoma models, the potential therapeutic utility of commercially available pathway inhibitors used in other disease settings, for blocking cancer metastasis. Results from this project will yield the first in- depth target characterization in clinical tumor biospecimens and pave the way for the development of more potent and cancer-selective therapeutics targeting this cellular trafficking pathway.