Melanoma is one of the most aggressive solid tumors and includes a stromal microenvironment that regulates cancer growth and progression.,The components of stromal microenvironment such as fibroblasts, fibroblast aggregates and cancer-associated fibroblasts (CAFs) can differently influence the melanoma growth during its distinct stages.,In this work, we have developed and studied a stromal microenvironment model, represented by fibroblasts, proto-myofibroblasts, myofibroblasts and aggregates of inactivated myofibroblasts, such as spheroids.,In particular, we have generated proto-myofibroblasts from primary cutaneous myofibroblasts.,The phenotype of proto-myofibroblasts is characterized by a dramatic reduction of α-smooth muscle actin (α-SMA) and cyclooxygenase-2 (COX-2) protein levels, as well as an enhancement of cell viability and migratory capability compared with myofibroblasts.,Furthermore, proto-myofibroblasts display the mesenchymal marker vimentin and less developed stress fibers, with respect to myofibroblasts.,The analysis of crosstalk between the stromal microenvironment and A375 or A2058 melanoma cells has shown that the conditioned medium of proto-myofibroblasts is cytotoxic, mainly for A2058 cells, and dramatically reduces the migratory capability of both cell lines compared with the melanoma-control conditioned medium.,An array analysis of proto-myofibroblast and melanoma cell-conditioned media suggests that lower levels of some cytokines and growth factors in the conditioned medium of proto-myofibroblasts could be associated with their anti-tumor activity.,Conversely, the conditioned media of melanoma cells do not influence the cell viability, outgrowth, and migration of proto-myofibroblasts from spheroids.,Interestingly, the conditioned medium of proto-myofibroblasts does not alter the cell viability of both BJ-5ta fibroblast cells and myofibroblasts.,Hence, proto-myofibroblasts could be useful in the study of new therapeutic strategies targeting melanoma.
Since metastatic melanoma is deadly, early diagnosis thereof is crucial for managing the disease.,We recently developed α-melanocyte-stimulating hormone (αMSH) derivatives, [68Ga]Ga-CCZ01048 and [18F]CCZ01064, that target the melanocortin 1 receptor (MC1R) for mouse melanoma imaging.,In this study, we aim to evaluate [18F]CCZ01064 as well as a novel dual-ammoniomethyl-trifluoroborate (AmBF3) derivative, [18F]CCZ01096, for targeting human melanoma xenograft using μPET imaging.,The peptides were synthesized on solid phase using Fmoc chemistry.,Radiolabeling was achieved in a one-step 18F-19F isotope-exchange reaction. μPET imaging and biodistribution studies were performed in NSG mice bearing SK-MEL-1 melanoma xenografts.,The MC1R density on the SK-MEL-1 cell line was determined to be 972 ± 154 receptors/cell (n = 4) via saturation assays.,Using [18F]CCZ01064, moderate tumor uptake (3.05 ± 0.47%ID/g) and image contrast were observed at 2 h post-injection.,Molar activity was determined to play a key role.,CCZ01096 with two AmBF3 motifs showed comparable sub-nanomolar binding affinity to MC1R and much higher molar activity.,This resulted in improved tumor uptake (6.46 ± 1.42%ID/g) and image contrast (tumor-to-blood and tumor-to-muscle ratios were 30.6 ± 5.7 and 85.7 ± 11.3, respectively) at 2 h post-injection.,[18F]CCZ01096 represents a promising αMSH-based μPET imaging agent for human melanoma and warrants further investigation for potential clinical translation.