title: Inhibition of melanocortin 1 receptor slows melanoma growth, reduces tumor heterogeneity and increases survival.
abstract: Melanoma risk is increased in patients with mutations of melanocortin 1 receptor (MC1R) yet the basis for the increased risk remains unknown. Here we report in vivo evidence supporting a critical role for MC1R in regulating melanoma tumor growth and determining overall survival time. Inhibition of MC1R by its physiologically relevant competitive inhibitor, agouti signaling protein (ASIP), reduced melanin synthesis and morphological heterogeneity in murine B16-F10 melanoma cells. In the lungs of syngeneic C57BL/6 mice, mCherry-marked, ASIP-secreting lung tumors inhibited MC1R on neighboring tumors lacking ASIP in a dose dependent manner as evidenced by a proportional loss of pigment in tumors from mice injected with 1:1, 3:1 and 4:1 mixtures of parental B16-F10 to ASIP-expressing tumor cells. ASIP-expressing B16-F10 cells formed poorly pigmented tumors in vivo that correlated with a 20% longer median survival than those bearing parental B16-F10 tumors (p=0.0005). Mice injected with 1:1 mixtures also showed survival benefit (p=0.0054), whereas injection of a 4:1 mixture showed no significant difference in survival. The longer survival time of mice bearing ASIP-expressing tumors correlated with a significantly slower growth rate than parental B16-F10 tumors as judged by quantification of numbers of tumors and total tumor load (p=0.0325), as well as a more homogeneous size and morphology of ASIP-expressing lung tumors. We conclude that MC1R plays an important role in regulating melanoma growth and morphology. Persistent inhibition of MC1R provided a significant survival advantage resulting in part from slower tumor growth, establishing MC1R as a compelling new molecular target for metastatic melanoma.
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Rita G
authors.initials: RG
authors.lastname: Kansal
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: McCravy
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Jacob H
authors.initials: JH
authors.lastname: Basham
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Earl
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Stacy L
authors.initials: SL
authors.lastname: McMurray
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Chelsey J
authors.initials: CJ
authors.lastname: Starner
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Whitt
authors.affiliation: Department of Microbiology, Immunology and Biochemistry, College of Medicine, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Lorraine M
authors.initials: LM
authors.lastname: Albritton
mesh_terms: D054366:Agouti Signaling Protein / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D008546:Melanoma, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008810:Mice, Inbred C57BL; D044102:Receptor, Melanocortin, Type 1 / Q000037:antagonists & inhibitors*
chemical_list: D054366:Agouti Signaling Protein; D044102:Receptor, Melanocortin, Type 1; C515183:a protein, mouse
keywords: B16-F10; GFP; MC1R; agouti; melanoma