Tumor Melanin Research Articles

Contrast mechanisms in pump-probe microscopy of melanin.

Pump-probe microscopy of melanin in tumors has been proposed to improve diagnosis of malignant melanoma, based on the hypothesis that aggressive cancers disaggregate melanin structure. However, measured signals of melanin are complex superpositions of multiple nonlinear processes, which makes interpretation challenging. Polarization control during measurement and data fitting are used to decompose signals of melanin into their underlying molecular mechanisms. We then identify the molecular mechanisms that are most susceptible to melanin disaggregation and derive false-coloring schemes to highlight these processes in biological tissue. We demonstrate that false-colored images of a small set of melanoma tumors correlate with clinical concern. More generally, our systematic approach of decomposing pump-probe signals can be applied to a multitude of different samples.

Clinical analysis of 29 cases of nasal mucosal malignant melanoma.

The present study aimed to investigate the clinical features of nasal mucosa malignant melanoma, including the histopathological features and factors affecting prognosis. A retrospective analysis of the clinical data obtained from the Department of Otolaryngology Head and Neck Surgery, Tianjin Huanhu Hospital (Tianjin, China) between October 1999 and June 2013 was performed using the Kaplan-Meier method. In total, 29 cases of nasal mucosal malignant melanoma were analyzed. The overall 3- and 5-year survival rates were 48.3 and 27.6%, respectively. The study group consisted of 18 males and 11 females, with a median age of 61.5 years. Overall, 19 patients underwent surgery, 28 received radiotherapy and 17 received chemotherapy. The American Joint Committee on Cancer staging system (AJCC) was used to retrospectively stage the tumors. In total, 8 were tumor stage (T)1, 10 were T2, 6 were T3 and 5 were T4. The results revealed that the T stage, surgical treatment, location of the tumor and the presence of black pigmentation affected the 5-year survival rate of the patients. By contrast, radiotherapy and chemotherapy had no effect on the overall survival rate. Overall, endoscopic or endoscopic-assisted surgery were the preferred methods of treatment, and histological features, including the presence of tumor melanin pigmentation, affected the prognosis of the patients. This study indicated that the AJCC staging system is able to effectively predict the prognosis of patients with nasal mucosa malignant melanoma.

¹²³I]ICF01012 melanoma imaging and [¹³¹I]ICF01012 dosimetry allow adapted internal targeted radiotherapy in preclinical melanoma models.

Melanin-targeting radiotracers are interesting tools for imaging and treatment of pigmented melanoma metastases. However, variation of the pigment concentration may alter the efficiency of such targeting. A clear assessment of both tumor melanin status and dosimetry are therefore prerequisites for internal radiotherapy of disseminated melanoma. The melanin tracer ICF01012 was labelled with iodine-123 for melanoma imaging in pigmented murine B16F0 and human SK-Mel 3 melanomas. In vivo imaging showed that the uptake of [(123)I]ICF01012 to melanomas correlated significantly with melanin content. Schedule treatment of 3 × 25 MBq [(131)I]ICF01012 significantly reduced SK-Mel 3 tumor growth and significantly increased the median survival in treated mice. For this protocol, the calculated delivered dose was 53.2 Gy. Radio-iodinated ICF01012 is a good candidate for both imaging and therapeutic purposes for patients with metastatic pigmented melanomas.

Pre-clinical evaluation and efficacy studies of a melanin-binding IgM antibody labeled with 188Re against experimental human metastatic melanoma in nude mice

Purpose. Currently there is no satisfactory treatment for metastatic melanoma. Radioimmunotherapy (RIT) uses the antigen-antibody interaction to deliver lethal radiation to target cells. Recently we established the feasibility of targeting melanin in tumors with 188-Rhenium (188Re)-labeled 6D2 mAb to melanin. Here we carried out pre-clinical development of 188Re-6D2 to accrue information necessary for Phase I trial in patients with metastatic melanoma. Experimental design. Tris(2-Carboxyethyl) Phosphine Hydrochloride (TCEP) was evaluated as potential agent for generation of –SH groups on 6D2 mAb. TCEP-treated 6D2 mAb was radiolabeled with 188Re and its radiochemical purity and stability was measured by ITLC and HPLC and its immunoreactivity – by melanin-binding ELISA. The pharmacokinetics, therapeutic efficacy and acute hematologic toxicity studies were performed in nude mice bearing lightly pigmented A2058 human metastatic melanoma tumors. Results. TCEP proved to be effective in generating sufficient number of -SH groups on 6D2 to ensure high radiolabeling yields with 188Re and preserved its structural integrity. 188Re-6D2 was quickly cleared from the blood with the half-life of approximately 5 hrs and from the body – with the half-life of 10 hr. The doses of 0.5, 1.0 and 1.5 mCi significantly (P

Phage Display Library Derived Peptides that Bind to Human Tumor Melanin as Potential Vehicles for Targeted Radionuclide Therapy of Metastatic Melanoma

Metastatic melanoma remains an incurable disease, and there is a great need for novel therapeutic modalities. We have recently identified melanin as a target for radionuclide therapy of melanoma and demonstrated the feasibility of this approach using a 188-rhenium ( (188)Re)-radiolabeled melanin-binding decapeptide to fungal melanin known as 4B4. Although the results indicated that radiolabeled melanin-binding decapeptide had activity against melanoma, that peptide also manifested high kidney uptake and this might become a concern during clinical trials. We hypothesized that by identifying peptides with different amino acid composition against tumor melanin we might be able to decrease their kidney uptake. Using the Heptapeptide Ph.D.-7 Phage Display Library, we identified three heptapeptides that bind to human tumor melanin. These peptides were radiolabeled with (188)Re via HYNIC ligand, and their comprehensive biodistribution in A2058 human metastatic melanoma tumor-bearing nude mice was compared to that of (188)Re-4B4 decapeptide. While tumor uptake of heptapeptides was quite similar to that of (188)Re-4B4 decapeptide, there was dramatically less uptake in the kidneys at both 3 h (6% ID/g vs 38%) and 24 h (2% ID/g vs 15%) postinjection. Administration of one of the generated heptapeptides, (188)Re-HYNIC-AsnProAsnTrpGlyProArg, to A2058 human metastatic melanoma-bearing nude mice resulted in significant retardation of the tumor growth. Immunofluorescence showed that in spite of their relatively small size heptapeptides were not able to penetrate through the membranes of viable melanoma cells and bound only to extracellular melanin, which provides assurance that they will be safe to healthy melanin-containing tissues during radionuclide therapy. Thus, these heptapeptides appear to have potentially significant advantages for targeted therapy of melanoma relative to existing melanin-binding peptides.

Computational model predicts effective delivery of 188-Re-labeled melanin-binding antibody to metastatic melanoma tumors with wide range of melanin concentrations

Metastatic melanoma is almost always deadly and new methods of treatment are urgently needed. Recently, we established the feasibility of radioimmunotherapy (RIT) for experimental melanoma in mice using a 188-rhenium (188Re)-labeled monoclonal antibody (mAb) 6D2 (IgM) to melanin. Our objective was to determine the effects of varying tumor melanin concentration and of different diffusivities and lymphatic clearance rates of the normal tissue, on the absorbed dose to the tumor in simulated therapy, in preparation for a clinical trial of RIT for melanoma. Using finite element analysis (FEA), we created a pharmacokinetic model that describes melanin-targeting RIT of a melanoma micrometastasis (1.3-mm radius) imbedded in normal tissue (14.3-mm radius). Our method incorporates antibody plasma kinetics, transcapillary transport, interstitial diffusion, and lymphatic clearance. Michaelis-Menten kinetics was used to model mAb binding to tumor melanin for melanin concentrations of 76, 7.6, 0.76, 0.076, and 0.0076 micromol/l. An absorbed dose was calculated, after accounting for direct and crossfire irradiation, on the basis of a 7.4-GBq intravenous dose of 188Re-6D2. The results showed that penetration of mAb into the tumor was inversely proportional to tumor melanin concentration. Decreased diffusivity and increased lymphatic clearance of the surrounding normal tissue decreased the dose to the tumor. The formation of mAb-melanin complex was remarkably similar within a 1000-fold range of melanin concentration, resulting in total doses of 2840, 2820, 2710, and 1990 cGy being delivered to tumors with melanin concentrations of 76, 7.6, 0.76, and 0.076 micromol/l, respectively. In conclusion, RIT of metastatic melanoma can be effective over a wide range of tumor melanin concentrations. The results can be useful in the design of a clinical trial of melanin-targeting RIT in patients with metastatic melanoma.

Radiolabeled Melanin-Binding Peptides Are Safe and Effective in Treatment of Human Pigmented Melanoma in a Mouse Model of Disease

The incidence of melanoma is rising, and therapeutic options for metastatic melanoma are limited. We report the results of experimental melanoma therapy with 188-Rhenium-labeled melanin-binding decapeptide ((188)RE-HYNIC-4B4) and a comprehensive safety evaluation of this treatment. (188)RE-HYNIC- 4B4 bound only to nonviable eumelanotic MNT1 and pheomelanotic SK-28-MEL human melanoma cells in vitro, as determined by immunofluorescence, which is consistent with the inaccessibility of intracellular melanin in live cells, and suggests specificity for tumors with a significant amount of extracellular melanin. Administration of 1 mCi (188)RE-HYNIC-4B4 to MNT1 tumor-bearing mice significantly slowed tumor growth, with the therapeutic effect being a result of specific binding to tumor melanin, as irrelevant (188)RE-labeled decapeptide did not produce therapeutic gain. Repeated doses of (188)RE-HYNIC-4B4 had a more profound effect on tumor growth than a single dose. Treatment of tumors with 0.3-0.4 cm diameter was more effective than of larger ones (0.5-0.7 cm). There was no difference in uptake of (188)REHYNIC- 4B4 in melanized tissues of black C57BL6 mice and no histologically apparent damage to these tissues in comparison with white BALB/C mice. Treatment of C57BL6 mice with (188)RE-HYNIC-4B4 did not change their behavior, as established by SHIRPA protocol, and did not cause damage to neurons and glial cells. These results indicate that radiolabeled melanin-binding peptides are efficient and safe in treatment of melanoma and could be potentially useful against this tumor.

Dead cells in melanoma tumors provide abundant antigen for targeted delivery of ionizing radiation by a mAb to melanin.

Melanoma is a cancer with a rising incidence, and metastatic disease is almost always lethal. We investigated the feasibility of targeting melanin, an intracellular melanocyte pigment, to deliver cytotoxic radiation to human melanoma cells in vivo by using a melanin-binding mAb (6D2). Nude mice bearing MNT1 pigmented human melanoma tumors were treated with mAb 6D2 labeled with 1.5 mCi (1 Ci = 37 GBq) of the beta-emitter 188-Rhenium (188Re) and manifested inhibition of tumor growth and prolonged survival. mAb 6D2 bound tumor melanin and demonstrated no crossreactivity with normal melanized tissues in black mice. The mechanism of melanin targeting involved Ab binding to extracellular melanin released during tumor cell turnover or to dying cells with permeable membranes. In this approach, the cytotoxic radiation emanating from labeled Ab bound to melanin is presumably delivered by "crossfire" effect to the adjacent viable tumor cells. Our results establish the feasibility of targeting melanin released from dead melanoma cells in tumors with radiolabeled Abs to achieve a therapeutic effect. In contrast to conventional tumor antigens, melanin is insoluble, resistant to degradation, and can be expected to accumulate in targeted tissues, suggesting that the efficacy of therapy could increase with each subsequent treatment cycle.

Role of melanin as a scavenger of active oxygen species.

The protective role of melanin, either synthetic or derived from a metastatic lung melanoma nodule, was studied in terms of its ability to interact with active oxygen species (O2., H2O2, RO., ROO., etc.). Both melanins showed the ability to react with O2.. The superoxide dismutase-like activity corresponds to 21 and 10 U/mg for synthetic and tumor melanin, respectively. The latter value accounts for about 8% of the superoxide dismutase activity of cultured melanoma cells. Neither type of melanin showed catalase-like or glutathione peroxidase-like activity. Both types of melanin reacted with RO. and ROO. radicals as determined by inhibition of the lipid peroxidation reaction of rat liver homogenates. The spontaneous lipid peroxidation of rat liver homogenate was inhibited up to 90% and 80% by synthetic and tumor melanin with half-maximal effects at 2.5 and 5.5 micrograms melanin/ml, respectively. The 2,2-azo-bis-(2 amidino propane) (AAPH)-initiated lipid peroxidation of rat liver homogenate was inhibited up to 30% and 20% by synthetic and tumor melanin, with half maximal effect at 120 and 500 micrograms melanin/ml, respectively. Both types of melanin were able to protect the in vitro inactivation of glucose oxidase, which occurs in the presence of AAPH-generated radicals.

Metal reduction reactions of the melanins: histochemical studies.

In general the melanins are argentaffin and, except in hair cortex, reduce ferric ferricyanide. Cutaneous and ocular melanins reduce acid silver nitrate, more promptly in guinea pigs than in man and rhesus monkeys. This reduction is slower than that of ammoniacal silver nitrate. It may be accelerated so as to occur in one or two minutes by prior reduction of the melanins by sodium hydrosulfite. Neuromelanin reduces acid silver nitrate very slowly (2-3 days) and prior hydrosulfite reduction does not induce rapid reductivity for acid silver. Acetylation has no influence on the reductivity of melanin for acid or ammoniacal silver or ferric ferricyanide. But, if applied to cutaneous and ocular melanins after reduction with hydrosulfite, it then greatly impairs the reduction of acid silver nitrate, but not of ammoniacal silver. Acetylation similarly influences the reductivity of catechol toward the acid and ammoniacal silver solutions. Oxidation has two general effects on the melanins, an irreversible bleaching by the more drastic oxidants, and a reversible abolition or impairment of their reducing capacity toward acid and ammoniacal silver solutions and ferric ferri cyanide. The oxidants vary in their effect on the silver and ferric ferricyanide reactions, so that some are more effective against the argentaffin reactions, others against the ferric ferricyanide reaction. Likewise the cutaneous, ocular and nerve cell melanins show differences in loss of reductivity with the various oxidants. Tumor melanins seem somewhat less reactive to silver than adjacent normal tissue melanins. Ocular tumor melanin resembles chorioidal melanin more than the epithelial melanins of the retina, ciliary and iris. The argentaffin reaction of cutaneous and ocular melanin is probably assignable to the presence of quinhydrone groupings which may be reversibly oxidized to quinones and reduced to diphenols. This type of grouping does not appear to be present in neuromelanin. Neuromelanin, from this and from the other recorded differences, appears to be a distinct substance, perhaps not even closely related chemically to the other melanins.