Effect of the plantar skin microenvironment on tumor metastasis and drug tolerance - Project Summary Patients with advanced acral melanoma (AM) suffer worse outcomes relative to patients with cutaneous melanoma (CM), in part, because they do not respond as well to treatments approved for CM including immune checkpoint blockade and BRAFV600E inhibitor strategies. Tailored therapies are warranted for patients with advanced AM given that AMs differ from CMs in a) cell of origin (volar melanocytes versus non-volar melanocytes, respectively) and b) mutational frequencies in targetable driver genes (e.g., BRAF hotspot mutations in 18% of AMs versus 46% of CMs). In this application, we focus on the unique biological dynamics induced by the plantar skin microenvironment of the foot where AMs most commonly arise in. The plantar microenvironment is mechanically stiffer relative to non-plantar skin sites (e.g., arm) where CMs arise, and the resident dermal fibroblasts in plantar skin display cancer associated fibroblast (CAF)-like markers in the absence of cancer cells. In the first aim, we will mechanistically define how matrix stiffness impacts AM metabolism. Our preliminary data identify elevated lysosome catabolism and collagen degradation gene signatures in AM cells grown in the stiffer plantar skin of the foot versus softer non-plantar skin of the flank in mice. We will track changes in lysosomal catabolism in a panel of in vitro and in vivo AM model systems using a) live cell reporters (e.g., mCherry-eGFP-LC3), b) Western blotting of protein markers of lysosome activity (e.g., LC3B, p62, NBR1), and c) bulk and single cell RNA sequencing analyses. In the second aim, we are testing the hypothesis that matrix stiffness-induced lysosomal catabolism promotes metastasis to the liver and insensitivity to CDK4/6 inhibitor therapy. These studies will not only determine whether liver metastasis and therapy resistance emerge via elevated lysosomal catabolism, but will also provide us with information on the relationship between matrix stiffness and lysosomal catabolism that will extend to other tumor types including breast and pancreatic where tissue stiffening is associated with poorer survival. In the third aim, we are testing the hypothesis that plantar fibroblasts promote AM metastasis and therapy resistance through the secretion of factors including matrix gla protein (MGP). We expect that targeting separate aspects of the plantar skin microenvironment in a rationally designed way (in vitro and then in preclinical in vivo models) will enable the reduction of resistance onset and metastatic disease in patients.
