Tyrosine transport in a human melanoma cell line as a basis for selective transport of cytotoxic analogues

A Sulfur Containing Melanogenesis Substrate, N-Pr-4-S-CAP as a Potential Source for Selective Chemoimmunotherapy of Malignant Melanoma

N-propionyl-4-S-cysteaminylphenol (N-Pr-4-S-CAP) is a substrate for tyrosinase, which is a melanin biosynthesis enzyme and has been shown to be selectively incorporated into melanoma cells. It was found to cause selective cytotoxicity against melanocytes and melanoma cells after selective incorporation, resulting in the induction of anti-melanoma immunity. However, the underlying mechanisms for the induction of anti-melanoma immunity remain unclear. This study aimed to elucidate the cellular mechanism for the induction of anti-melanoma immunity and clarify whether N-Pr-4-S-CAP administration could be a new immunotherapeutic approach against melanoma, including local recurrence and distant metastasis. A T cell depletion assay was used for the identification of the effector cells responsible for N-Pr-4-S-CAP-mediated anti-melanoma immunity. A cross-presentation assay was carried out by using N-Pr-4-S-CAP-treated B16-OVA melanoma-loaded bone marrow-derived dendritic cells (BMDCs) and OVA-specific T cells. Administration of N-Pr-4-S-CAP induced CD8+ T cell-dependent anti-melanoma immunity and inhibited the growth of challenged B16F1 melanoma cells, indicating that the administration of N-Pr-4-S-CAP can be a prophylactic therapy against recurrence and metastasis of melanoma. Moreover, intratumoral injection of N-Pr-4-S-CAP in combination with BMDCs augmented the tumor growth inhibition when compared with administration of N-Pr-4-S-CAP alone. BMDCs cross-presented a melanoma-specific antigen to CD8+ T cells through N-Pr-4-S-CAP-mediated melanoma cell death. Combination therapy using N-Pr-4-S-CAP and BMDCs elicited a superior anti-melanoma effect. These results suggest that the administration of N-Pr-4-S-CAP could be a new strategy for the prevention of local recurrence and distant metastasis of melanoma.

Molecular Events in the Melanogenesis Cascade as Novel Melanoma-Targeted Small Molecules: Principle and Development

Malignant melanoma is one of the most malignant of all cancers. Melanoma occurs at the epidermo-dermal interface of the skin and mucosa, where small vessels and lymphatics are abundant. Consequently, from the onset of the disease, melanoma easily metastasizes to other organs throughout the body via lymphatic and blood circulation. At present, the most effective treatment method is surgical resection, and other attempted methods, such as chemotherapy, radiotherapy, immunotherapy, targeted therapy, and gene therapy, have not yet produced sufficient results. Since melanogenesis is a unique biochemical pathway that functions only in melanocytes and their neoplastic counterparts, melanoma cells, the development of drugs that target melanogenesis is a promising area of research. Melanin consists of small-molecule derivatives that are always synthesized by melanoma cells. Amelanosis reflects the macroscopic visibility of color changes (hypomelanosis). Under microscopy, melanin pigments and their precursors are present in amelanotic melanoma cells. Tumors can be easily targeted by small molecules that chemically mimic melanogenic substrates. In addition, small-molecule melanin metabolites are toxic to melanocytes and melanoma cells and can kill them. This review describes our development of chemo-thermo-immunotherapy based on the synthesis of melanogenesis-based small-molecule derivatives and conjugation to magnetite nanoparticles. We also introduce the other melanogenesis-related chemotherapy and thermal medicine approaches and discuss currently introduced targeted therapies with immune checkpoint inhibitors for unresectable/metastatic melanoma.

Immunomodulation of Melanoma by Chemo-Thermo-Immunotherapy Using Conjugates of Melanogenesis Substrate NPrCAP and Magnetite Nanoparticles: A Review

A major advance in drug discovery and targeted therapy directed at cancer cells may be achieved by the exploitation and immunomodulation of their unique biological properties. This review summarizes our efforts to develop novel chemo-thermo-immunotherapy (CTI therapy) by conjugating a melanogenesis substrate, N-propionyl cysteaminylphenol (NPrCAP: amine analog of tyrosine), with magnetite nanoparticles (MNP). In our approach, NPrCAP provides a unique drug delivery system (DDS) because of its selective incorporation into melanoma cells. It also functions as a melanoma-targeted therapeutic drug because of its production of highly reactive free radicals (melanoma-targeted chemotherapy). Moreover, the utilization of MNP is a platform to develop thermo-immunotherapy because of heat shock protein (HSP) expression upon heat generation in MNP by exposure to an alternating magnetic field (AMF). This comprehensive review covers experimental in vivo and in vitro mouse melanoma models and preliminary clinical trials with a limited number of advanced melanoma patients. We also discuss the future directions of CTI therapy.

Development of Radiofluorinated Nicotinamide/Picolinamide Derivatives as Diagnostic Probes for the Detection of Melanoma

Regarding the increased incidence and high mortality rate of malignant melanoma, practical early-detection methods are essential to improve patients’ clinical outcomes. In this study, we successfully prepared novel picolinamide–benzamide (¹⁸F-FPABZA) and nicotinamide–benzamide (¹⁸F-FNABZA) conjugates and determined their biological characteristics. The radiochemical yields of ¹⁸F-FPABZA and ¹⁸F-FNABZA were 26 ± 5% and 1 ± 0.5%, respectively. ¹⁸F-FPABZA was more lipophilic (log P = 1.48) than ¹⁸F-FNABZA (log P = 0.68). The cellular uptake of ¹⁸F-FPABZA in melanotic B16F10 cells was relatively higher than that of ¹⁸F-FNABZA at 15 min post-incubation. However, both radiotracers did not retain in amelanotic A375 cells. The tumor-to-muscle ratios of ¹⁸F-FPABZA-injected B16F10 tumor-bearing mice increased from 7.6 ± 0.4 at 15 min post-injection (p.i.) to 27.5 ± 16.6 at 3 h p.i., while those administered with ¹⁸F-FNABZA did not show a similarly dramatic increase throughout the experimental period. The results obtained from biodistribution studies were consistent with those derived from microPET imaging. This study demonstrated that ¹⁸F-FPABZA is a promising melanin-targeting positron emission tomography (PET) probe for melanotic melanoma.

Evaluation of Radioiodinated Fluoronicotinamide/Fluoropicolinamide-Benzamide Derivatives as Theranostic Agents for Melanoma

Malignant melanoma is the most harmful type of skin cancer and its incidence has increased in this past decade. Early diagnosis and treatment are urgently desired. In this study, we conjugated picolinamide/nicotinamide with the pharmacophore of ¹³¹I-MIP-1145 to develop ¹³¹I-iodofluoropicolinamide benzamide (¹³¹I-IFPABZA) and ¹³¹I-iodofluoronicotiamide benzamide (¹³¹I-IFNABZA) with acceptable radiochemical yield (40 ± 5%) and high radiochemical purity (>98%). We also presented their biological characteristics in melanoma-bearing mouse models. ¹³¹I-IFPABZA (Log P = 2.01) was more lipophilic than ¹³¹I-IFNABZA (Log P = 1.49). B16F10-bearing mice injected with ¹³¹I-IFNABZA exhibited higher tumor-to-muscle ratio (T/M) than those administered with ¹³¹I-IFPABZA in planar γ-imaging and biodistribution studies. However, the imaging of ¹³¹I-IFNABZA- and ¹³¹I-IFPABZA-injected mice only showed marginal tumor uptake in A375 amelanotic melanoma-bearing mice throughout the experiment period, indicating the high binding affinity of these two radiotracers to melanin. Comparing the radiation-absorbed dose of ¹³¹I-IFNABZA with the melanin-targeted agents reported in the literature, ¹³¹I-IFNABZA exerts lower doses to normal tissues on the basis of similar tumor dose. Based on the in vitro and in vivo studies, we clearly demonstrated the potential of using ¹³¹I-IFNABZA as a theranostic agent against melanoma.

Development of radioiodine-labeled 4-hydroxyphenylcysteamine for specific diagnosis of malignant melanoma

INTRODUCTION

A specific diagnosis for melanoma is strongly desired because malignant melanoma has poor prognosis. In a previous study, although radioiodine-125-labeled 4-hydroxyphenyl-L-cysteine ((125)I-L-PC) was found to have good substrate affinity for tyrosinase enzyme in the melanin metabolic pathway, (123/131)I-L-PC had insufficient substrate affinity for tyrosinase to diagnose melanoma. In this study, we synthesized 4-hydroxyphenylcysteamine (4-PCA) and developed a novel radioiodine-125-labeled 4-hydroxyphenylcysteamine ((125)I-PCA) to increase affinity for the melanin biosynthesis pathway.

METHODS

4-PCA was separated with 2-hydroxyphenylcysteamine (2-PCA), which is an isomer of 4-PCA, and was examined using melting point, proton nuclear magnetic resonance, mass spectrometry and elemental analysis. (125)I-PCA was prepared using the chloramine-T method under no-carrier added conditions. We performed biodistribution experiments using B16 melanoma-bearing mice using (125)I-PCA, (125)I-L-PC, (125)I-α-methyl-L-tyrosine, (123)I-m-iodobenzylguanidine and (67)Ga-citrate. In vitro assay was performed with B16 melanoma cells, and affinity for tyrosinase, DNA polymerase and amino acid transport was evaluated using phenylthiourea, thymidine, ouabine and L-tyrosine inhibitor. In addition, partition coefficients of (125)I-PCA were evaluated.

RESULTS

In the synthesis of 4-PCA, analysis values did not differ between calculated and reported values, and 4-PCA was separated from 2-PCA at high purity. In biodistribution experiments, (125)I-PCA was accumulated and retained in B16 melanoma cells when compared with (125)I-L-PC. (125)I-PCA showed the highest values at 60 min after radiotracer injection in melanoma-to-muscle ratios, melanoma-to-blood ratios and melanoma-to-skin ratios. Accumulation of (125)I-PCA was significantly inhibited by phenylthiourea and thymidine. Partition coefficients of (125)I-PCA were lower than those of N-isopropyl-p-[(123)I]iodoamphetamine and were not significantly different from (125)I-L-PC.

CONCLUSIONS

(125)I-PCA is a better substrate for tyrosinase and DNA polymerase and has higher uptake and longer retention in B16 melanoma cells when compared with (125)I-L-PC. Therefore, (123/131)I-PCA has good potential for diagnosis for malignant melanoma.

ADVANCE IN KNOWLEDGE

(125)I-PCA will be a specific diagnosis tool for malignant melanoma.

IMPLICATIONS FOR PATIENT CARE

(123/131)I-PCA has good potential for the diagnosis of malignant melanoma when compared with other SPECT tracers, as well as anti-melanoma chemotherapeutic drugs.

Efficacy of hydroquinone-free skin-lightening cream for photoaging

BACKGROUND

Hyperpigmentation and solar damage remains a difficult problem to treat with topical agents.

AIMS

To evaluate a novel skin-lightening complex (SLC) comprising four actives targeting melanin formation at multiple levels, namely disodium glycerophosphate, L-leucine, phenylethyl resorcinol, and undecylenoyl phenylalanine, in an oil-in-water emulsion cream.

PATIENTS/METHODS

Skin-lightening complex was evaluated in 80 female subjects of skin types I-III with at least moderate mottled hyperpigmentation. After a wash-out period of 1 month with a sunscreen, the subjects added a cream containing the SLC for 12 weeks twice daily to entire face and continued the sunscreen use.

RESULTS

Whereas there was no significant change during the wash-out period, the primary endpoint mottled hyperpigmentation decreased by 32% after the 12-week treatment period with the SLC cream. Secondary endpoints such as severity and number of lentigines, skin tone, and skin brightness also improved. In all, 57% of the subjects showed at least a moderate response, 17% did not improve, and 3% got worse after the treatment.

CONCLUSIONS

The SLC cream was well tolerated, in particular when comparing with exfoliating or peeling agent containing skin-lightening products. When used with a daily sunscreen, this study confirms that the SLC represents an alternative to hydroquinone, retinoids, and many other skin-lightening actives.

Melanoma-Targeted Chemothermotherapy and In Situ Peptide Immunotherapy through HSP Production by Using Melanogenesis Substrate, NPrCAP, and Magnetite Nanoparticles

Exploitation of biological properties unique to cancer cells may provide a novel approach to overcome difficult challenges to the treatment of advanced melanoma. In order to develop melanoma-targeted chemothermoimmunotherapy, a melanogenesis substrate, N-propionyl-4-S-cysteaminylphenol (NPrCAP), sulfur-amine analogue of tyrosine, was conjugated with magnetite nanoparticles. NPrCAP was exploited from melanogenesis substrates, which are expected to be selectively incorporated into melanoma cells and produce highly reactive free radicals through reacting with tyrosinase, resulting in chemotherapeutic and immunotherapeutic effects by oxidative stress and apoptotic cell death. Magnetite nanoparticles were conjugated with NPrCAP to introduce thermotherapeutic and immunotherapeutic effects through nonapoptotic cell death and generation of heat shock protein (HSP) upon exposure to alternating magnetic field (AMF). During these therapeutic processes, NPrCAP was also expected to provide melanoma-targeted drug delivery system.

Growth inhibition of re-challenge B16 melanoma transplant by conjugates of melanogenesis substrate and magnetite nanoparticles as the basis for developing melanoma-targeted chemo-thermo-immunotherapy

Melanogenesis substrate, N-propionyl-cysteaminylphenol (NPrCAP), is selectively incorporated into melanoma cells and inhibits their growth by producing cytotoxic free radicals. Magnetite nanoparticles also disintegrate cancer cells and generate heat shock protein (HSP) upon exposure to an alternating magnetic field (AMF). This study tested if a chemo-thermo-immunotherapy (CTI therapy) strategy can be developed for better management of melanoma by conjugating NPrCAP on the surface of magnetite nanoparticles (NPrCAP/M). We examined the feasibility of this approach in B16 mouse melanoma and evaluated the impact of exposure temperature, frequency, and interval on the inhibition of re-challenged melanoma growth. The therapeutic protocol against the primary transplanted tumor with or without AMF exposure once a day every other day for a total of three treatments not only inhibited the growth of the primary transplant but also prevented the growth of the secondary, re-challenge transplant. The heat-generated therapeutic effect was more significant at a temperature of 43°C than either 41°C or 46°C. NPrCAP/M with AMF exposure, instead of control magnetite alone or without AMF exposure, resulted in the most significant growth inhibition of the re-challenge tumor and increased the life span of the mice. HSP70 production was greatest at 43°C compared to that with 41°C or 46°C. CD8⁺T cells were infiltrated at the site of the re-challenge melanoma transplant.

Melanin-targeted preclinical PET imaging of melanoma metastasis

Dialkylamino-alkyl-benzamides possess an affinity for melanin, suggesting that labeling of such benzamides with (18)F could potentially produce melanin-targeted PET probes able to identify melanotic melanoma metastases in vivo with high sensitivity and specificity.

METHODS

In this study, N-[2-(diethylamino)ethyl]-4-(18)F-fluorobenzamide ((18)F-FBZA) was synthesized via a 1-step conjugation reaction. The sigma-receptor binding affinity of (19)F-FBZA was determined along with the in vitro cellular uptake of radiofluorinated (18)F-FBZA in B16F10 cells. In vivo distribution and small-animal PET studies were conducted on mice bearing B16F10 melanoma, A375M amelanotic melanoma, and U87MG tumors, and comparative studies were performed with (18)F-FDG PET in the melanoma models.

RESULTS

In vitro, uptake of (18)F-FBZA was significantly higher in B16F10 cells treated with l-tyrosine (P < 0.001). In vivo, (18)F-FBZA displayed significant tumor uptake; at 2 h, 5.94 +/- 1.83 percentage injected dose (%ID) per gram was observed in B16F10 tumors and only 0.75 +/- 0.09 %ID/g and 0.56 +/- 0.13 %ID/g was observed in amelanotic A375M and U87MG tumors, respectively. Lung uptake was significantly higher in murine lungs bearing melanotic B16F10 pulmonary metastases than in normal murine lungs (P < 0.01). Small-animal PET clearly identified melanotic lesions in both primary and pulmonary metastasis B16F10 tumor models. Coregistered micro-CT with small-animal PET along with biopsies further confirmed the presence of tumor lesions in the mouse lungs.

CONCLUSION

(18)F-FBZA specifically targets primary and metastatic melanotic melanoma lesions with high tumor uptake and may have translational potential.

Differentiation of tumour and inflammation: characterisation of [methyl-3H]methionine (MET) and O-(2-[18F]fluoroethyl)-L-tyrosine (FET) uptake in human tumour and inflammatory cells

PURPOSE

Previous studies suggest that radiolabelled amino acids could be superior to FDG in differentiating tumour and inflammation. Therefore the aim of this study was to investigate the uptake of FET and MET in human tumour and inflammatory cells and to investigate their uptake kinetics.

METHODS

For uptake studies, cells were incubated with 370 kBq FET or 3.7 kBq MET for 15 min. Kinetic studies were performed at variable concentrations of FET and MET. Competitive inhibition studies were done with BCH, MeAIB and L: -serine.

RESULTS

All inflammatory cells incorporated more MET than the tumour cells. The uptake of FET, in contrast, was significantly lower in all inflammatory cells than in the tumour cells. In tumour cells the uptake of MET was about five times the uptake of FET. The competitive inhibitors reduced uptake of both tracers to 20-40% in tumour cells and to 70% in inflammatory cells. Kinetic studies showed that MET and FET transport was saturable in all cells except macrophages and followed a Michaelis-Menten kinetic. Highest capacity (V (max)) and affinity (K (m)) for the uptake of MET was observed in granulocytes. Capacity and affinity for FET uptake were highest in the DHL-4 cells.

CONCLUSION

In contrast to MET, FET accumulated to a significantly greater extent in tumour cells than in inflammatory cells. The marked differences between tumour and inflammatory cells concerning FET and MET uptake suggest that FET and MET are substrates of different subtypes of the L system.

In vitro characterization of the influx of 3-[125I]iodo-L-alpha-methyltyrosine and 2-[125I]iodo-L-tyrosine into U266 human myeloma cells: evidence for system T transport

The aim of this study was to investigate the cellular uptake mechanisms responsible for the accumulation of 3-[(125)I]iodo-L-alpha-methyltyrosine ((125)I-3-IMT) and 2-[(125)I]iodo-L-tyrosine ((125)I-2-IT), two radiotracers for metabolic tumor imaging, using single-photon emission tomography, into U266 human myeloma cancer cells. Time course and concentration dependency of (125)I-3-IMT uptake was assessed. Kinetic parameters were calculated using an Eadie Hofstee plot. A set of competitive inhibitors of the main amino acid transport systems was used for the discrimination of the transporters responsible for the uptake of (125)I-3-IMT and (125)I-2-IT. Protein incorporation of both tracers was determined using acid precipitation. The measured maximum velocity for (125)I-3-IMT transport was 4.199 nmol per mg protein 20 s(-1), and the Michaelis constant was 107.9 microM. Addition of 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH), a competitive inhibitor of System L, reduced the influx by 39.0+/-3.3% for (125)I-3-IMT and 66.3+/-0.9% for (125)I-2-IT. The BCH-insensitive influx was further reduced by Tryptophan (Trp) by 43.8+/-3.5% for (125)I-3-IMT and 15.3+/-1.3% for (125)I-2-IT. This suggests involvement of System T transport. We measured <2% of radioactivity in the acid precipitable fractions of both tracers with no increase in time. We conclude that the influx of (125)I-3-IMT and (125)I-2-IT into U266 human myeloma cells is mediated by both System L and System T amino acid transporters. The kinetic parameters suggest that elevated plasma levels of aromatic amino acids will reduce (123)I-3-IMT uptake in myeloma patients. Both tracers do not enter protein synthesis significantly.

Changes in the levels of integrin and focal adhesion kinase (FAK) in human melanoma cells following 532 nm laser treatment

Despite the increase in laser therapy, concern remains that sublethal treatment of pre-malignant lesions may adversely affect the biological behaviour of surviving cells. Integrin receptors mediate interaction of cells with the extracellular matrix and their occupation leads to focal adhesion kinase (FAK) activation. Using our previously established model we have now investigated subcellular changes and compared integrin and FAK concentrations, the degree of FAK phosphorylation and its association with the beta1 integrin in laser vs. non-laser treated cells. We treated cells with laser generated from a frequency doubled Q-switched (Nd:YAG) laser system (532 nm) at 0.4 J/cm2 twice per week for 4 weeks. Using cell lysates we performed Western immunoblotting 24 hr later to detect integrin subunits and FAK proteins and immunoprecipitation to investigate FAK phosphorylation and its association with beta1. Cell morphology was examined using electron microscopy. SK23 and G361 cells exhibited an 3.4- and 11.2-fold increase, respectively, in FAK protein following laser treatment. FAK phosphorylation in SK23 cells was increased by 82%, whereas FAK phosphorylation in G361 cells was reduced slightly (2%). Furthermore, both alpha3 and 4 integrins were up-regulated, by approximately 4-fold and 7- to 9-fold, respectively. In addition, the beta1 integrin was proteolysed in both cell lines and the levels of FAK associated with beta1 was increased (2.1- and 2.7-fold, respectively). Finally, laser treatment of SK23 cells caused an increased number of cell processes. Sublethal 532 nm laser light thus induces changes in integrin and FAK concentrations and subsequently influences cellular attachment and morphology.

Sub-lethal effects of exposing the human melanoma cell line SKmel-23 to 532 nm laser light

The human melanoma cell line SKmel-23 has been used to investigate the sub-lethal damage that can occur as a result of exposing melanin containing cells to light (532 nm) from a frequency doubled Q-switched (Nd:YAG) laser. A dose response curve was obtained, which indicates that at energy levels of 0.6 J/cm2 and below no effect on either the viability or growth rate of the cell line was observed. Above this, cells rapidly died and at an energy level of 2.0 J/cm2, only approximately 15% of cells survived. This contrasts with the effects on the G361 melanoma line, which contains far less melanosomes, as an LD50 for this cell line was approximately 5.5 J/cm2. Exposing SKmel-23 cells to 0.4 J/cm2 of 532 nm light results in a diminution of the number of melanosomes within cells as well as a marked decrease in melanin content, as determined by spectrophotometric assay and electron microscopy. Using the reverse transcriptase polymerase chain reaction technique, the reduction in melanin content of the cells was accompanied by a selective decrease in mRNA coding for tyrosinase, the first enzyme in the biosynthetic pathway for melanin. No decrease in the mRNA coding for the GAPDH protein was observed. Our finding has implications for understanding the control processes that regulate the melanin content of cells and suggests that the model described can be used to further investigate changes that may occur in cells as a result of their exposure to sub-lethal levels of laser light.