Binding and internalization of the melanocyte stimulating hormone receptor ligand [Nle4, D-Phe7] alpha-MSH in B16 melanoma cells

Nanoparticles for Topical Application in the Treatment of Skin Dysfunctions-An Overview of Dermo-Cosmetic and Dermatological Products

Nanomaterials (NM) arouse interest in various fields of science and industry due to their composition-tunable properties and the ease of modification. They appear currently as components of many consumer products such as sunscreen, dressings, sports clothes, surface-cleaning agents, computer devices, paints, as well as pharmaceutical and cosmetics formulations. The use of NPs in products for topical applications improves the permeation/penetration of the bioactive compounds into deeper layers of the skin, providing a depot effect with sustained drug release and specific cellular and subcellular targeting. Nanocarriers provide advances in dermatology and systemic treatments. Examples are a non-invasive method of vaccination, advanced diagnostic techniques, and transdermal drug delivery. The mechanism of action of NPs, efficiency of skin penetration, and potential threat to human health are still open and not fully explained. This review gives a brief outline of the latest nanotechnology achievements in products used in topical applications to prevent and treat skin diseases. We highlighted aspects such as the penetration of NPs through the skin (influence of physical-chemical properties of NPs, the experimental models for skin penetration, methods applied to improve the penetration of NPs through the skin, and methods applied to investigate the skin penetration by NPs). The review summarizes various therapies using NPs to diagnose and treat skin diseases (melanoma, acne, alopecia, vitiligo, psoriasis) and anti-aging and UV-protectant nano-cosmetics.

Enhancing the Efficacy of Melanocortin 1 Receptor-Targeted Radiotherapy by Pharmacologically Upregulating the Receptor in Metastatic Melanoma

Melanocortin 1 receptor (MC1R) is under investigation as a target for drug delivery for metastatic melanoma therapy and imaging. The purpose of this study was to determine the potential of using BRAF inhibitors (BRAF_i) and histone deacetylase inhibitors (HDAC_i) to enhance the delivery of MC1R-targeted radiolabeled peptide ([²¹²Pb]DOTA-MC1L) by pharmacologically upregulating the MC1R expression in metastatic melanoma cells and tumors. MC1R expression was analyzed in de-identified melanoma biopsies by immunohistochemical staining. Upregulation of MC1R expression was determined in BRAF^V600E cells (A2058) and BRAF wild-type melanoma cells (MEWO) by quantitative real-time polymerase chain reaction, flow cytometry, and receptor-ligand binding assays. The role of microphthalmia-associated transcription factor (MITF) in the upregulation of MC1R was also examined in A2058 and MEWO cells. The effectiveness of [²¹²Pb]DOTA-MC1L α-particle radiotherapy in combination with BRAF_i and/or HDAC_i was determined in athymic nu/nu mice bearing A2058 and MEWO human melanoma xenografts. High expression of MC1R was observed in situ in clinical melanoma biopsies. BRAF_i and HDAC_i significantly increased the MC1R expression (up to 10-fold in mRNA and 4-fold in protein levels) via MITF-dependent pathways, and this increase led to enhanced ligand binding on the cell surface. Inhibition of MITF expression antagonized the upregulation of MC1R in both BRAF^V600E and BRAF^WT cells. Combining [²¹²Pb]DOTA-MC1L with BRAF_i and/or HDAC_i improved the tumor response by increasing the delivery of ²¹²Pb α-particle emissions to melanoma tumors via augmented MC1R expression. These data suggest that FDA-approved HDAC_i and BRAF_i could improve the effectiveness of MC1R-targeted therapies by enhancing drug delivery via upregulated MC1R.

Melanocortin-1 Receptor-Targeting Ultrasmall Silica Nanoparticles for Dual-Modality Human Melanoma Imaging

The poor prognosis associated with malignant melanoma has not changed substantially over the past 30 years. Targeted molecular therapies, such as immunotherapy, have shown promise but suffer from resistance and off-target toxicities, underscoring the need for alternative therapeutic strategies that can be used in combination with existing protocols. Moreover, peptides targeting melanoma-specific markers, like the melanocortin-1 receptor (MC1-R), for imaging and therapy exhibit high renal uptake that limits clinical translation. In the current study, the application of ultrasmall fluorescent (Cy5) silica nanoparticles (C' dots), conjugated with MC1-R targeting alpha melanocyte stimulating hormone (αMSH) peptides on the polyethylene glycol (PEG) coated surface, is examined for melanoma-selective imaging. αMSH peptide sequences, evaluated for conjugation to the PEG-Cy5-C' dot nanoparticles, bound to MC1-R with high affinity and targeted melanoma in syngenetic and xenografted melanoma mouse models. Results demonstrated a 10-fold improvement in MC1-R affinity over the native peptide alone following surface attachment of the optimal αMSH peptide. Systematic in vivo studies further demonstrated favorable in vivo renal clearance kinetics as well as receptor-mediated tumor cell internalization of as-developed radiolabeled particle tracers in B16F10 melanoma bearing mice. These findings highlight the ability of αMSH-PEG-Cy5-C' dots to overcome previous hurdles that prevented clinical translation of peptide and antibody-based melanoma probes and reveal the potential of αMSH-PEG-Cy5-C' dots for melanoma-selective imaging, image-guided surgery, and therapeutic applications.

Evaluation of the Relationship between Alopecia Areata and Viral Antigen Exposure

BACKGROUND

Alopecia areata (AA) is an autoimmune disease characterized by non-scarring alopecia with T-cell infiltration at the affected hair follicle.

OBJECTIVE

Our aim was to study the potential link between hepatitis B virus (HBV) antigen exposure and AA.

METHODS

Two pediatric patients with AA following hepatitis B vaccination were identified in a general dermatology clinic. A bioinformatics analysis and an electronic medical record (EMR) database query were performed at the University of Rochester Medical Center to identify patients with AA, coexisting viral infections, vaccinations, or interferon (IFN) therapy in order to determine if the presence of AA and these conditions was higher than in AA patients without these associated conditions or therapy.

RESULTS

An increased frequency of AA among those who received the HBV surface protein antigen [odds ratio (OR) 2.7, p < 0.0001] was identified, and an independent analysis revealed an increased frequency of AA in those receiving IFN-β treatment (OR 8.1, p < 0.05). One potential antigenic target identified was SLC45A2, a melanosomal transport protein important in skin and hair pigmentation. The longest potential vaccine peptide fragment match (8-mer) was to a segment of natural killer (NK) cell inhibitory receptors, KIR3DL2 and KIR3DL1. Predictive modeling of major histocompatibility complex (MHC)-peptide binding demonstrated potential binding of this peptide to MHC relevant to AA.

LIMITATIONS

The results will need to be verified in additional patient databases allowing analysis of temporal relationships, and with molecular experiments of the identified antigens.

CONCLUSIONS

Our data confirm associations between viral infection and IFN treatment with AA. It establishes that the hepatitis B surface protein antigen has shared epitopes with human killer immunoglobulin-like receptors.

MC1R, the cAMP pathway, and the response to solar UV: extending the horizon beyond pigmentation

The melanocortin 1 receptor (MC1R) is a G protein-coupled receptor crucial for the regulation of melanocyte proliferation and function. Upon binding melanocortins, MC1R activates several signaling cascades, notably the cAMP pathway leading to synthesis of photoprotective eumelanin. Polymorphisms in the MC1R gene are a major source of normal variation of human hair color and skin pigmentation, response to ultraviolet radiation (UVR), and skin cancer susceptibility. The identification of a surprisingly high number of MC1R natural variants strongly associated with pigmentary phenotypes and increased skin cancer risk has prompted research on the functional properties of the wild-type receptor and frequent mutant alleles. We summarize current knowledge on MC1R structural and functional properties, as well as on its intracellular trafficking and signaling. We also review the current knowledge about the function of MC1R as a skin cancer, particularly melanoma, susceptibility gene and how it modulates the response of melanocytes to UVR.

Malignant melanoma and melanocortin 1 receptor

The conventional chemotherapeutic treatment of malignant melanoma still remains poorly efficient in most cases. Thus the use of specific features of these tumors for development of new therapeutic modalities is highly needed. Melanocortin 1 receptor (MC1R) overexpression on the cell surface of the vast majority of human melanomas, making MC1R a valuable marker of these tumors, is one of these features. Naturally, MC1R plays a key role in skin protection against damaging ultraviolet radiation by regulating eumelanin production. MC1R activation is involved in regulation of melanocyte cell division. This article reviews the peculiarities of regulation and expression of MC1R, melanocytes, and melanoma cells, along with the possible connection of MC1R with signaling pathways regulating proliferation of tumor cells. MC1R is a cell surface endocytic receptor, thus considered perspective for diagnostics and targeted drug delivery. A number of new therapeutic approaches that utilize MC1R, including endoradiotherapy with Auger electron and α- and β-particle emitters, photodynamic therapy, and gene therapy are now being developed.

Applications of nanotechnology in dermatology

What are nanoparticles and why are they important in dermatology? These questions are addressed by highlighting recent developments in the nanotechnology field that have increased the potential for intentional and unintentional nanoparticle skin exposure. The role of environmental factors in the interaction of nanoparticles with skin and the potential mechanisms by which nanoparticles may influence skin response to environmental factors are discussed. Trends emerging from recent literature suggest that the positive benefit of engineered nanoparticles for use in cosmetics and as tools for understanding skin biology and curing skin disease outweigh potential toxicity concerns. Discoveries reported in this journal are highlighted. This review begins with a general introduction to the field of nanotechnology and nanomedicine. This is followed by a discussion of the current state of understanding of nanoparticle skin penetration and their use in three therapeutic applications. Challenges that must be overcome to derive clinical benefit from the application of nanotechnology to skin are discussed last, providing perspective on the significant opportunity that exists for future studies in investigative dermatology.

Nanostructured assemblies for dental application

Millions of teeth are saved each year by root canal therapy. Although current treatment modalities offer high levels of success for many conditions, an ideal form of therapy might consist of regenerative approaches in which diseased or necrotic pulp tissues are removed and replaced with healthy pulp tissue to revitalize teeth. Melanocortin peptides (alpha-MSH) possess anti-inflammatory properties in many acute and chronic inflammatory models. Our recent studies have shown that alpha-MSH covalently coupled to poly-l-glutamic acid (PGA-alpha-MSH) retains anti-inflammatory properties on rat monocytes. This study aimed to define the effects of PGA-alpha-MSH on dental pulp fibroblasts. Lipopolysaccharide (LPS)-stimulated fibroblasts incubated with PGA-alpha-MSH showed an early time-dependent inhibition of TNF-alpha, a late induction of IL-10, and no effect on IL-8 secretion. However, in the absence of LPS, PGA-alpha-MSH induced IL-8 secretion and proliferation of pulp fibroblasts, whereas free alpha-MSH inhibited this proliferation. Thus, PGA-alpha-MSH has potential effects in promoting human pulp fibroblast adhesion and cell proliferation. It can also reduce the inflammatory state of LPS-stimulated pulp fibroblasts observed in gram-negative bacterial infections. These effects suggest a novel use of PGA-alpha-MSH as an anti-inflammatory agent in the treatment of endodontic lesions. To better understand these results, we have also used the multilayered polyelectrolyte films as a reservoir for PGA-alpha-MSH by using not only PLL (poly-l-lysine) but also the Dendri Graft poly-l-lysines (DGL(G4)) to be able to adsorb more PGA-alpha-MSH. Our results indicated clearly that, by using PGA-alpha-MSH, we increase not only the viability of cells but also the proliferation. We have also analyzed at the nanoscale by atomic force microscopy these nanostructured architectures and shown an increase of thickness and roughness in the presence of PGA-alpha-MSH incorporated into the multilayered film (PLL-PGA-alpha-MSH)(10) or (DGL(G4)-PGA-alpha-MSH)(10) in accordance with the increase of the proliferation of the cells growing on the surface of these architectures. We report here the first use of nanostructured and functionalized multilayered films containing alpha-MSH as a new active biomaterial for endodontic regeneration.

The melanocortin-1 receptor gene polymorphism and association with human skin cancer

The melanocortin-1 receptor (MC1R) is a key gene involved in the regulation of melanin synthesis and encodes a G-protein coupled receptor expressed on the surface of the melanocyte in the skin and hair follicles. MC1R activation after ultraviolet radiation exposure results in the production of the dark eumelanin pigment and the tanning process in humans, providing physical protection against DNA damage. The MC1R gene is highly polymorphic in Caucasian populations with a number of MC1R variant alleles associated with red hair, fair skin, freckling, poor tanning, and increased risk of melanoma and nonmelanoma skin cancer. Variant receptors have shown alterations in biochemical function, largely due to intracellular retention or impaired G-protein coupling, but retain some signaling ability. The association of MC1R variant alleles with skin cancer risk remains after correction for pigmentation phenotype, indicating regulation of nonpigmentary pathways. Notably, MC1R activation has been linked to DNA repair and may also contribute to the regulation of immune responses.

Peptide-targeted radionuclide therapy for melanoma

Melanocortin-1 receptor (MC1-R) and melanin are two attractive melanoma-specific targets for peptide-targeted radionuclide therapy for melanoma. Radiolabeled peptides targeting MC1-R/melanin can selectively and specifically target cytotoxic radiation generated from therapeutic radionuclides to melanoma cells for cell killing, while sparing the normal tissues and organs. This review highlights the recent advances of peptide-targeted radionuclide therapy of melanoma targeting MC1-R and melanin. The promising therapeutic efficacies of 188Re-(Arg(11))CCMSH (188Re-[Cys(3,4,10), D-Phe(7),Arg(11)]-alpha-MSH(3-13)), 177Lu- and 212Pb-labeled DOTA-Re(Arg(11))CCMSH (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-[ReO-(Cys(3,4,10), D-Phe(7), Arg(11))]-alpha-MSH(3-13)) and 188Re-HYNIC-4B4 (188Re-hydrazinonicotinamide-Tyr-Glu-Arg-Lys-Phe-Trp-His-Gly-Arg-His) in preclinical melanoma-bearing models demonstrate an optimistic outlook for peptide-targeted radionuclide therapy for melanoma. Peptide-targeted radionuclide therapy for melanoma will likely contribute in an adjuvant setting, once the primary tumor has been surgically removed, to treat metastatic deposits and for treatment of end-stage disease. The lack of effective treatments for metastatic melanoma and end-stage disease underscores the necessity to develop and implement new treatment strategies, such as peptide-targeted radionuclide therapy.

Melanocortin-1 receptor signaling markedly induces the expression of the NR4A nuclear receptor subgroup in melanocytic cells

The melanocortin-1 receptor (MCIR) is a G-protein-coupled receptor expressed primarily in melanocytes and is known to play a pivotal role in the regulation of pigmentation in mammals. In humans MC1R has been found to be highly polymorphic with several functional variants associated with the phenotype of red hair color and fair skin, cutaneous UV sensitivity, and increased risk of developing melanoma and non-melanoma skin cancer. Recent evidence suggests that MC1R plays a photo-protective role in melanocytes in response to UV irradiation. Relatively few genetic targets of MC1R signaling have been identified independent of the pigmentation pathway. Here we show that MC1R signaling in B16 mouse melanoma cells and primary human melanocytes rapidly, and transiently, induces the transcription of the NR4A subfamily of orphan nuclear receptors. Furthermore, primary human melanocytes harboring homozygous RHC variant MC1R alleles exhibited an impaired induction of NR4A genes in response to the potent MC1R agonist (Nle4,D-Phe7)-alpha-melanocyte-stimulating hormone. Using small interference RNA-mediated attenuation of NR4A1 and NR4A2 expression in melanocytes, the ability to remove cyclobutane pyrimidine dimers following UV irradiation appeared to be impaired in the context of MC1R signaling. These data identify the NR4A receptor family as potential mediators of an MC1R-coordinated DNA damage response to UV exposure in melanocytic cells.

Regulation of human melanocortin 1 receptor signaling and trafficking by Thr-308 and Ser-316 and its alteration in variant alleles associated with red hair and skin cancer

The melanocortin 1 receptor (MC1R), a G protein-coupled receptor (GPCR) positively coupled to adenylyl cyclase, is a key regulator of melanocyte proliferation and differentiation and a determinant of pigmentation, skin phototype, and skin cancer risk. MC1R activation stimulates melanogenesis and increases the ratio of black, strongly photoprotective eumelanins to yellowish and poorly photoprotective pheomelanin pigments. Desensitization and internalization are key regulatory mechanisms of GPCR signaling. Agonist-induced desensitization usually depends on phosphorylation by a GPCR kinase (GRK) followed by receptor internalization in endocytic vesicles. We have shown that MC1R desensitization is mediated by two GRKs expressed in melanocytes and melanoma cells, GRK2 and GRK6. Here we show that in contrast with this dual specificity for desensitization, GRK6 but not GRK2 mediated MC1R internalization. Mutagenesis studies suggested that the targets of GRK6 are two residues located in the MC1R cytosolic C terminus, Thr-308 and Ser-316. A T308D/S316D mutant mimicking their phosphorylated state was constitutively desensitized and associated with endosomes, whereas a T308A/S316A mutant was resistant to desensitization and internalization. We studied the desensitization and internalization of three variant MC1R forms associated with red hair and increased skin cancer risk: R151C, R160W, and D294H. These variants showed a less efficient desensitization. Moreover, D294H was resistant to internalization, thus accounting for its abnormally high surface expression. Co-expression of variant and wild type MC1R modified its desensitization and internalization behavior. These data suggest that MC1R might be regulated by novel mechanisms including differential effects of GRKs and altered desensitization rates of certain allelic combinations.

Melanocortin-1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin-1 receptor (MC1R). MC1R is a member of the G-protein-coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or alpha-melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist-independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.

Altered cell surface expression of human MC1R variant receptor alleles associated with red hair and skin cancer risk

The human melanocortin-1 receptor gene (MC1R) encodes a G-protein coupled receptor that is primarily expressed on melanocytes, where it plays a key role in pigmentation regulation. Variant alleles are associated with red hair colour and fair skin, known as the RHC phenotype, as well as skin cancer risk. The R151C, R160W and D294H alleles, designated 'R', are strongly associated with the RHC phenotype and have been proposed to result in loss of function receptors due to impaired G-protein coupling. We recently provided evidence that the R151C and R160W variants can efficiently couple to G-proteins in response to alpha-melanocyte stimulating hormone. The possibility that altered cellular localization of the R151C and R160W variant receptors could underlie their association with RHC was therefore considered. Using immunofluorescence and ligand binding studies, we found that melanocytic cells exogenously or endogenously expressing MC1R show strong surface localization of the wild-type and D294H alleles but markedly reduced cell surface expression of the R151C and R160W receptors. In additional exogenous expression studies, the R variant D84E and the rare I155T variant, also demonstrated a significant reduction in plasma membrane receptor numbers. The V60L, V92M and R163Q weakly associated RHC alleles, designated 'r', were expressed with normal or intermediate cell surface receptor levels. These results indicate that reduced receptor coupling activity may not be the only contributing factor to the genetic association between the MC1R variants and the RHC phenotype, with MC1R polymorphisms now linked to a change in receptor localization.

Agonist-dependent internalization of the human melanocortin-4 receptors in human embryonic kidney 293 cells

A chimeric protein comprised of melanocortin-4 receptor (MC4R) and the green fluorescent protein (GFP) was created for studying receptor/ligand localization and trafficking. The ligand binding affinities and second messenger stimulation induced by MC4R-GFP closely resembled those of the wild-type receptor, suggesting functional integrity of the chimeric protein. As observed with a confocal microscope, in human embryonic kidney (HEK)-293 cells MC4R/GFP was distributed evenly along the cell membrane. Addition of [Nle4-d-Phe7]-alpha-melanocyte-stimulating hormone (NDP-MSH), a peptide MC4R agonist, induced receptor translocation into intracellular compartments in a time- and concentration-dependent manner. [Ac-Nle-c[Asp-His-d-Nal(2')-Arg-Trp-Lys]-NH2] (SHU9119), a potent MC4R antagonist, completely inhibited NDP-MSH-mediated internalization. MC4R-GFP internalization was unaffected by a protein kinase A inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89), but was impaired by pretreatment with inhibitors of endocytosis through clathrin-coated pits, hypertonic sucrose, or concanavalin A. Time-dependent colocalization of MC4R-GFP with rhodamine-transferrin, an early endosome marker, and with LysoTraker, a lysosome marker, was observed after short-term (45 min) and prolonged (20 h) agonist exposure, respectively. Rhodamine-[AcNle-c[Asp-His-d-Phe-Arg-Trp-Lys]-NH2] (MTII), a fluorescent derivative of an MC4R agonist, was found to cointernalize with MC4R-GFP into intracellular vesicles. No significant receptor recycling or segregation from the ligand was observed 60 min after removal of the agonist. In contrast, an antagonist rhodamine-Ac-Cys-Glu-His-(d-Nal)-Arg-Trp-Gly-Cys-Pro-Pro-Lys-Asp-NH2 (HS014) bound to and colocalized with MC4R-GFP on the cell surface and did not stimulate receptor internalization. In sum, these results suggest that MC4R is subject to agonist-dependent endocytosis via clathrin-coated pits. Prolonged agonist exposure directs MC4R into lysosomes, possibly for degradation. Receptor and ligand recycling is not efficient for MC4R in HEK-293 cells.

Peptide receptors as molecular targets for cancer diagnosis and therapy

During the past decade, proof of the principle that peptide receptors can be used successfully for in vivo targeting of human cancers has been provided. The molecular basis for targeting rests on the in vitro observation that peptide receptors can be expressed in large quantities in certain tumors. The clinical impact is at the diagnostic level: in vivo receptor scintigraphy uses radiolabeled peptides for the localization of tumors and their metastases. It is also at the therapeutic level: peptide receptor radiotherapy of tumors emerges as a serious treatment option. Peptides linked to cytotoxic agents are also considered for therapeutic applications. The use of nonradiolabeled, noncytotoxic peptide analogs for long-term antiproliferative treatment of tumors appears promising for only a few tumor types, whereas the symptomatic treatment of neuroendocrine tumors by somatostatin analogs is clearly successful. The present review summarizes and critically evaluates the in vitro data on peptide and peptide receptor expression in human cancers. These data are considered to be the molecular basis for peptide receptor targeting of tumors. The paradigmatic peptide somatostatin and its receptors are extensively reviewed in the light of in vivo targeting of neuroendocrine tumors. The role of the more recently described targeting peptides vasoactive intestinal peptide, gastrin-releasing peptide, and cholecystokinin/gastrin is discussed. Other emerging and promising peptides and their respective receptors, including neurotensin, substance P, and neuropeptide Y, are introduced. This information relates to established and potential clinical applications in oncology.

Recombinant modular transporters for cell-specific nuclear delivery of locally acting drugs enhance photosensitizer activity

The search for new pharmaceuticals that are specific for diseased rather than normal cells in the case of cancer and viral disease has raised interest in locally acting drugs that act over short distances within the cell and for which different cell compartments have distinct sensitivities. Thus, photosensitizers (PSs) used in anti-cancer therapy should ideally be transported to the most sensitive subcellular compartments in order for their action to be most pronounced. Here we describe the design, production, and characterization of the effects of bacterially expressed modular recombinant transporters for PSs comprising 1) alpha-melanocyte-stimulating hormone as an internalizable, cell-specific ligand; 2) an optimized nuclear localization sequence of the SV40 large T-antigen; 3) an Escherichia coli hemoglobin-like protein as a carrier; and 4) an endosomolytic amphipathic polypeptide, the translocation domain of diphtheria toxin. These modular transporters delivered PSs into the nuclei, the most vulnerable sites for the action of PSs, of murine melanoma cells, but not non-MSH receptor-overexpressing cells, to result in cytotoxic effects several orders of magnitude greater than those of nonmodified PSs. The modular fusion proteins described here for the first time, capable of cell-specific targeting to particular subcellular compartments to increase drug efficacy, represent new pharmaceuticals with general application.

In vivo evaluation of 188Re-labeled alpha-melanocyte stimulating hormone peptide analogs for melanoma therapy

The purpose of our study was to optimize melanoma tumor uptake of 188Re-CCMSH and reduce its nonspecific kidney retention. Nephrotoxicity is often a serious problem associated with targeted radiotherapy, therefore, increasing the tumor/kidney uptake ratio of 188Re-CCMSH is crucial for optimizing its therapeutic efficacy. Structural modification of the peptide and amino acid co-infusion were investigated as strategies to improve the tumor/kidney uptake ratio of 188Re-CCMSH. The substitution of Lys11 with Arg11 was examined to determine if removal of lysine from the peptide would improve kidney clearance without sacrificing tumor uptake. The pharmacokinetics of 188Re-CCMSH and 188Re-(Arg(11))CCMSH were determined in B16/F1 murine melanoma-bearing C57 mice. Tumor uptake values of (188)Re-CCMSH and 188Re-(Arg(11))CCMSH were 15.03 +/- 5.20% ID/g and 20.44 +/- 1.91% ID/g at 1 hr postinjection and 1.94 +/- 0.47% ID/g and 3.50 +/- 2.32% ID/g at 24 hr postinjection. Renal retention of 188Re-(Arg(11))CCMSH was 11.79 +/- 1.29 ID/g and 3.67 +/- 0.51 ID/g at 1 hr and 4 hr postinjection, which was a greater than 50% reduction compared to 188Re-CCMSH. The Arg for Lys substitution in 188Re-(Arg(11))CCMSH resulted in improved tumor uptake and reduced kidney retention. Renal retention of both 188Re-CCMSH and 188Re-(Arg(11))CCMSH were significantly reduced by co-injection of 20 mg of L-lysine, L-arginine and a combination of L-lysine:L-arginine. Tumor/kidney uptake values for 188Re-CCMSH and 188Re-(Arg(11))CCMSH were maximally reduced by 52.9% and 46.3%, respectively. However, even with amino acid co-injection, the tumor/kidney ratio of 188Re-CCMSH was lower than that of 188Re-(Arg(11))CCMSH. Improved tumor uptake and reduced kidney retention of 188Re-(Arg(11))CCMSH will facilitate targeted irradiation of melanoma tumors while minimizing the dose to the kidneys.

Skin colour and skin cancer - MC1R, the genetic link

Pigmentary traits such as red hair, fair skin, lack of tanning ability and propensity to freckle (the RHC phenotype) have been identified as genetic risk factors for both melanoma and non-melanocytic skin cancers when combined with the environmental risk factor of high ultraviolet light exposure. The human melanocortin-1 receptor (MC1R) is a key determinant of the pigmentation process and can account in large part for the diverse range of variation in human pigmentation phenotypes and skin phototypes. The coding sequence is highly polymorphic in human populations, with several of these variant forms of the receptor now known to be associated with the RHC phenotype. We have examined variant allele frequencies in the general population and in a collection of adolescent dizygotic and monozygotic twins with defined pigmentation characteristics. Variant allele frequencies have also been determined in several case-control studies of sporadic melanoma, basal cell carcinoma and squamous cell carcinoma, and in familial melanoma kindreds collected within Australia. These studies have shown that three RHC alleles - Arg151Cys, Arg160Trp and Asp294His - were associated with increased risk in all forms of skin cancer and with penetrance and age of onset in familial melanoma in mutation carriers. There is a significant RHC allele heterozygote carrier effect on skin phototype and skin cancer risk, which indicates that variant alleles do not behave in a strictly recessive manner. Ultimately, the genetic and chemical assessment of melanin synthesis rather than skin colour will be the best indicator for skin cancer risk, and such genetic association studies combined with functional analysis of variant alleles should provide the link to understanding skin phototypes.

Homologous regulation of melanocortin-1 receptor (MC1R) expression in melanoma tumor cells in vivo

As G protein-coupled receptors (GPCRs) are the target of numerous signaling molecules, including about half of the therapeutic drugs currently used, it is important to understand the consequences of homologous (ligand-induced) receptor regulation. Continuous exposure of GPCRs to agonist in vitro most frequently results in receptor down-regulation, but receptor up-regulation may occur as well. These phenomena are expected to play a role in the physiological adaptation to endogenous ligands and also in the response to repetitive administration of drugs in the clinic. However, there is little information on homologous regulation of GPCRs in vivo. Here, we report on the regulation of melanocortin-1 receptor (MC1R) expression in melanoma cells implanted into mice. Two melanoma cell lines were investigated, D10 and B16F1, which in vitro had previously been shown to undergo homologous receptor up- and down-regulation, respectively. After implantation into mice and exposure to the natural MC1R agonist alpha-melanocyte-stimulating hormone (alpha-MSH), cell-surface MC1R expression was evaluated by competition binding experiments in tumor membrane preparations. In B 16F1 cells, a single injection of 50 to 500 microg alpha-MSH induced a rapid but moderate dose-dependent MC1R down-regulation which could be totally reverted within 16-24 h. By continuous administration of alpha-MSH via osmotic minipumps, MC1R down-regulation was considerably amplified and reached the level observed in vitro, demonstrating that prolonged receptor interaction was necessary to induce a maximal effect in vivo. Similar results were obtained in vitro, which demonstrates that homologous MC1R regulation in B16F1 cells is essentially independent of the physiological environment. In D10 cells, however, up-regulation could not be reproduced in vivo, suggesting that MC1R up-regulation is more dependent on the physiological environment. These results demonstrate the importance of in vivo receptor regulation studies, in particular in view of the potential use of MC1R as a target for melanoma therapy.

Expression of melanocortin-1 receptor in normal, malformed and neoplastic skin glands and hair follicles

Melanocortin receptors (MC-Rs) are G-protein coupled receptors that mediate pleiotropic actions of melanocyte-stimulating hormones and adrenocorticotropin. There is increasing evidence that one of the five so far identified melanocortin receptors, i.e. melanocortin-1 receptor (MC-1R), has a more ubiquitous distribution in the skin than originally expected. In the present study, the expression of MC-1R in normal skin glands and hair follicles, various malformations and neoplasms with adnexal differentiation is described. Using an anti-MC-1R antibody directed against the amino acids 2-18 of the human MC-1R, specimens of normal healthy skin (n = 10) as well as hamartomas, cysts, hyperplasias, and benign or malignant neoplasms with eccrine, apocrine, sebaceous gland, and hair follicle differentiation (n = 98) were immunostained. MC-1R expression was widely preserved in various adnexal malformations and neoplasms as compared with normal skin and did not show major differences with regard to maturation of the neoplasms. The majority of adnexal epithelia showed an intracytoplasmically granular staining and, to a lesser extent, an intercellular staining pattern. Immunoelectron microscopical investigations revealed expression of MC-1R both along the cell surface and intracytoplasmically within tubular endosomes, the latter suggesting internalisation of the receptor. In conclusion, preserved MC-1R expression in adnexal epithelia suggests a functional role of proopiomelanocortin (POMC) in various malformations and neoplasms of the skin.

Radiometallated receptor-avid peptide conjugates for specific in vivo targeting of cancer cells

New receptor-avid radiotracers are being developed for site-specific in vivo targeting of a myriad of receptors expressed on cancer cells. This review exemplifies strategies being used to design radiometallated peptide conjugates that maximize uptake in tumors and optimize their in vivo pharmacokinetic properties. Efforts to produce synthetic peptide analogues that target the following three receptor systems are highlighted: Gastrin releasing peptide (GRP), alpha-melanocyte stimulating hormone (alpha-MSH), and guanylate cyclase-C (GC-C) receptors.

Enhancement of gene delivery by an analogue of alpha-MSH in a receptor-independent fashion

In order to transfect melanoma specifically by receptor-mediated endocytosis we prepared dioctadecyl aminoglycylspermine (lipospermine)--DNA complexes with [Nle(4),D-Phe(7)]-alpha-MSH(4--10), a pseudo-peptide analogue of alpha-melanocyte stimulating hormone (alpha-MSH) linked to a thiol-reactive phospholipid. With these complexes we obtained an up to 70-fold increase of transfection with B16-F1 melanoma cells. However when B16-G4F, an alpha-MSH receptor negative melanoma cell line was transfected, an up to 700-fold increased transfection efficiency was observed. The peptide hormone analogue was equally efficient when it was only mixed with lipospermine--DNA complexes without covalent coupling. In addition to melanoma cells we also obtained up to 30-fold increased transfection with BN cells (embryonic liver cells). Our data show that an alpha-MSH analogue increased transfection independently of the MSH receptor expression but reaches efficiencies approaching those obtained with peptides derived from viral fusion proteins. The absence of targeting of constructs containing [Nle(4),D-Phe(7)]-alpha-MSH(4-10) can probably be attributed due to the relatively modest number of MSH receptors at the surface of melanoma. We suggest, however, that the peptide hormone analogue used in this study has membrane-active properties and could be of interest as helper agent to enhance non-viral gene delivery presumably by endosomal-destabilizing properties.