Imiquimod, a Toll-like receptor 7 agonist, inhibits melanogenesis and proliferation of human melanocytes

Low-dose imiquimod induces melanogenesis in melanoma cells through an ROS-mediated pathway

BACKGROUND

Melanogenesis is the process of melanin maturation which not only protects skin from UV radiation but also plays an important role in antigenicity of melanomas. Imiquimod (IMQ) is a toll-like receptor 7 (TLR7) agonist that exhibits antiviral and anticancer activity.

OBJECTIVE

To explore whether IMQ could induce melanogenesis in melanoma cells.

METHODS

The mouse melanoma cell line B16F10, the mouse immortalized melanocyte Melan-A, and human melanoma cell lines MNT-1, C32 and A375 were utilized in this study. The pigmented level was observed by the centrifuged cell pellet. The intracellular and extracellular melanin levels were examined in the absorbance in NaOH-extracted cell lysate and cell-cultured medium, respectively. The expression of melanogenesis related proteins was examined by immunoblotting. The intracellular cyclic AMP amount was evaluated by the cAMP Glo assay kit. The activity of phosphodiesterase 4B (PDE4B) was investigated by CREB reporter assay with overexpressed PDE4B or not.

RESULTS

We demonstrated that a low dose of IMQ could trigger melanogenesis in B16F10 cells. IMQ induced microphthalmia-associated transcription factor (MITF) nuclear translocation, upregulated the expression of melanogenesis-related proteins, increased tyrosinase (TYR) activity, and led to pigmentation in B16F10 cells. Next, we found that IMQ-induced melanogenesis was activated by excessive intracellular cAMP accumulation, which was regulated through IMQ-mediated PDE4B inhibition. Finally, IMQ-induced ROS production was found to be involved in melanogenesis by its control of PDE4B activity.

CONCLUSIONS

Low dose of IMQ could activate melanogenesis through the ROS/PDE4B/PKA pathway in melanoma cells.

Novel Combination Treatment for Melanoma: FLASH Radiotherapy and Immunotherapy Delivered by a Radiopaque and Radiation Responsive Hydrogel

Immunotherapies have become the standard treatment for melanoma. To further improve patient responses, combinations of immunotherapies and radiotherapy (RT) are being studied, since radiotherapies can potentially provide additional immune stimulation, in addition to direct antitumor effects. FLASH-RT is a novel, ultrahigh dose rate, radiation delivery approach, with the potential of at least equivalent tumor control efficacy and reduced damage to healthy tissue. However, the effects of combining FLASH-RT and immunotherapy have not been extensively studied in melanoma. Toll-like receptor (TLR) agonists, such as imiquimod (IMQ), are potent immunostimulatory agents, although their utility is limited due to poor solubility and systemic side effects. We therefore developed a novel combination therapy for melanoma consisting of IMQ delivered to the tumor via a radiopaque and radiation responsive hydrogel combined with FLASH-RT. We found that FLASH was able to effectively stimulate IMQ release from the hydrogel. In addition, we found that the combination of FLASH and released IMQ resulted in synergistic melanoma cell killing in vitro. The combination therapy reduced tumor growth compared to controls, enhanced survival, and resulted in remarkable enhancements in certain tumor cytokine levels. CT imaging allowed the hydrogel to be monitored in vivo. In addition, no adverse effects of the treatment were observed. Overall, this IMQ-gel and FLASH-RT combination may have potential as an improved treatment for melanoma and indicates that the interactions of FLASH-RT and TLR agonists merit further study.

Uncoupling melanogenesis from proliferation in epidermal melanocytes responding to stimulation with psoriasis-related proinflammatory cytokines

BACKGROUND

Few studies have addressed the impact of the psoriasis-related proinflammatory cytokines on the proliferation and melanogenesis of melanocytes (MCs) in lesional psoriatic skin.

OBJECTIVE

We investigated the effects of TNFα, IL17A, and IL8 on the proliferation and melanin synthesis of MCs.

METHODS

Skin specimens were biopsied from patients with psoriasis vulgaris at the active stage, or from the tail skin of Dct-LacZ mice with imiquimod (IMQ)-induced psoriasiform dermatitis. Cultured keratinocytes (KCs), MCs, and human skin explants were used in this study. The numbers of MCs were measured via β-galactosidase staining, EdU incorporation and HMB45 immunohistochemical staining. The expression of human β-defensin 3 (hBD3) in KCs was silenced by siRNA, the conditioned medium (CM) from siRNA-transfected KCs was used to treat MCs, then followed by αMSH stimulation. The melanogenesis-related genes were examined by using qRT-PCR and western blotting.

RESULTS

The increased number of MCs and decreased melanin content were highly relevant to the enhanced expression of IL8 and BD3 both in human psoriatic skin and in IMQ-treated mouse tail skin. IL8 expression in KCs and CXCR2 expression in MCs was significantly increased by IL17A and TNFα, the αMSH-induced upregulations of microphthalmia-associated transcription factor (MITF) and tyrosinase in MCs were abrogated by the CM from hBD3-unsilenced KCs, but not from hBD3-silenced KCs.

CONCLUSION

Our results suggest the roles of IL8-CXCR2 activation in promoting MC proliferation and of BD3 upregulation in reducing melanogenesis. These findings have been implicated in the underlying mechanism that active psoriasis prefers hypopigmentation despite chronic inflammation.

Lipopolysaccharide reduces melanin synthesis in vitiligo melanocytes by regulating autophagy

Vitiligo is an autoimmune-related disease with a complex aetiology that involves innate immunity. Toll-like receptors (TLRs) are important parts of innate immunity and are related to a variety of autoimmune diseases, including vitiligo, through an unknown mechanism. In this study, we found that the TLR4 gene expression was increased in blood samples of patients with advanced stage vitiligo, and then we evaluated the effect of TLR4 ligand lipopolysaccharide (LPS) on melanin synthesis in a vitiligo melanocyte cell line PIG3V and along with its mechanism. LPS suppressed melanin synthesis, downregulated the expression of melanin synthesis-related proteins, and activated autophagy in vitiligo melanocytes. Inhibiting autophagy with 3-methyladenine or chloroquine blocked these effects. This suggests that LPS inhibits skin pigmentation by modulating autophagy, thus providing novel insights into the pathogenesis of vitiligo.

Imiquimod induced vitiligo-like lesions-A consequence of modified melanocyte function

INTRODUCTION

Imiquimod plays an important role in the management of condyloma and premalignant lesions. Successively, an increase of hypopigmented lesions following imiquimod application has been reported. However, the mechanisms of imiquimod on melanocytes remain unclear. This study was designed to assess the effect of Imiquimod on the functions of melanocytes in vitro.

METHODS

Primary cultured melanocytes were isolated from normal control skin tissue. After incubation with imiquimod for 48 h in vitro, cell viability was analyzed by cell counting kit-8 assay. Apoptosis was detected using the Annexin V-fluorescein-5-isothiocyanate flow cytometry assay. Melanin content and tyrosinase activity in melanocytes were measured by colorimetric method and the modified dopachrome method. The production of inflammatory cytokine interleukin 8 (IL-8), IL-6, and soluble ICAM-1 (soluble Intercellular Adhesion Molecule-1[sICAM-1]) in melanocytes were measured by enzyme-linked immunosorbent assay (ELISA). Toll-like receptor 7 (TLR7), toll-like receptor 9 (TLR9) protein, and autophagy-related proteins microtubule-associated protein 1A/1B-light chain 3 (LC3-II), p62, mechanistic target of rapamycin (mTOR), and Atg5 were assessed using western blot analysis.

RESULTS

Imiquimod significantly inhibited the activity of tyrosinase activity and decreased melanin content in melanocytes and significantly increased apoptosis and IL-6, IL-8, and sICAM-1 production in melanocytes. Moreover, the expression of TLR7 and TLR9 proteins were significantly increased, and the expression of mTOR, p62 protein were markedly decreased, but the expression of LC3II/I and Atg5 protein were significantly increased in melanocytes after incubating with imiquimod.

CONCLUSIONS

This study shows that imiquimod directly inhibits melanogenesis and increases melanocyte apoptosis rates. These effects combined with the upregulation of TLR7 and TLR9 together with increased autophagy activity and inflammatory cytokines production, might be the main reasons leading to hypopigmented lesions after imiquimod application.

Treating Melanoma in Situ During a Pandemic with Telemedicine and a Combination of Imiquimod, 5-Fluorouracil, and Tretinoin

The recent coronavirus disease 2019 (COVID-19) pandemic has created a quandary for the physician in terms of evaluating and treating cutaneous skin cancers, particularly melanomas. At the onset of the pandemic, many planned medical and surgical visits for skin cancers were postponed. Physicians and patients have had to balance the risk of exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with that of worsening morbidity and mortality due to delays in skin cancer treatments. We present a male patient who had two melanoma-in-situs (MISs) that were treated during the COVID-19 pandemic with a combination of topical imiquimod 5% cream, 5-fluorouracil 2% solution, and tretinoin 0.1% cream. The successful treatments occurred without in-person visits and with the aid of telemedicine. Although surgery is the standard for the treatment of melanoma in situ, this case demonstrates an effective viable treatment modality for MIS during a pandemic situation.

Melanogenesis Connection with Innate Immunity and Toll-Like Receptors

The epidermis is located in the outermost layer of the living body and is the place where external stimuli such as ultraviolet rays and microorganisms first come into contact. Melanocytes and melanin play a wide range of roles such as adsorption of metals, thermoregulation, and protection from foreign enemies by camouflage. Pigmentary disorders are observed in diseases associated with immunodeficiency such as Griscelli syndrome, indicating molecular sharing between immune systems and the machineries of pigment formation. Melanocytes express functional toll-like receptors (TLRs), and innate immune stimulation via TLRs affects melanin synthesis and melanosome transport to modulate skin pigmentation. TLR2 enhances melanogenetic gene expression to augment melanogenesis. In contrast, TLR3 increases melanosome transport to transfer to keratinocytes through Rab27A, the responsible molecule of Griscelli syndrome. TLR4 and TLR9 enhance tyrosinase expression and melanogenesis through p38 MAPK (mitogen-activated protein kinase) and NFκB signaling pathway, respectively. TLR7 suppresses microphthalmia-associated transcription factor (MITF), and MITF reduction leads to melanocyte apoptosis. Accumulating knowledge of the TLRs function of melanocytes has enlightened the link between melanogenesis and innate immune system.

Increased expression of Toll-like receptor 7 and 9 in vitiligo melanocytes: a pilot study

BACKGROUND

Toll-like receptors (TLRs) are expressed on human melanocytes, and play an important role in innate and acquired immunity. The role of TLRs in the pathogenesis of vitiligo has not been fully described.

AIM

To investigate the expression of TLRs in melanocytes from patients with vitiligo and healthy controls (HCs).

METHODS

Primary cultured vitiligo and control melanocytes were obtained from perilesional normal skin of patients with generalized vitiligo and HCs. TLRs mRNA expression in melanocytes were determined by real-time reverse transcription PCR and protein expression by western blotting. Apoptosis was analysed using an annexin V-fluorescein isothiocyanate apoptosis detection kit, and tyrosinase activity and melanin content were measured by a modified dopachrome and colorimetric method. Interleukin (IL)-6, IL-8 and soluble cell adhesion molecule (sICAM)-1 expression were measured by ELISA.

RESULTS

In vitiligo melanocytes, compared with control melanocytes, apoptosis rate, expression of TLR7 and TLR9 mRNA and protein, and production of IL-8, IL-6 and sICAM-1 were significantly increased, whereas tyrosinase activity and melanin content were significantly decreased.

CONCLUSIONS

Our results suggest that the increased expression of TLR7 and TLR9 might correlate with melanocyte dysfunction in vitiligo.

Toll-Like Receptors-2 and -4 in Graves' Disease-Key Players or Bystanders?

Graves’ disease (GD) is an autoimmune disease that affects the thyroid. The development of autoimmunity is associated with innate immune responses where the prominent role plays Toll-like receptors (TLRs). The aim of our study was to assess the relationship between the expression levels of TLR-2 and TLR-4 on CD4+ and CD8+ T as well as CD19+ B lymphocytes in patients with GD and selected clinical parameters. The study group consisted of 32 women with GD, the control group consisted of 20 healthy women. Immunophenotyping was performed using the flow cytometry and cytokines concentrations were assessed using ELISA assay. The mean percentage of CD4+/TLR-2+ and CD8+/TLR-2+ T cells in patients with GD was higher than in the control group (p < 0.0001). After obtaining euthyroidism, the mean percentage of CD4+/TLR-2+ T cells in patients with GD decreased (p < 0.0001). The expression level of TLR-2 on CD4+ T lymphocytes correlated with serum FT3 concentration in patients with GD (r = 0.47, p = 0.007). The mean percentage of CD8+/TLR-2+ T cells in patients with GD before treatment compared to patients with GD after obtaining euthyroidism was higher (p = 0.0163). Similar findings were found for TLR-4. Thus the TLR-2 and TLR-4 can be a prognostic marker for Graves’ disease.

Differential expression of inflammatory cytokines and chemokines in lipopolysaccharide-stimulated melanocytes from lightly and darkly pigmented skin

Increasing evidence suggests that human epidermal melanocytes play an important role in the skin immune system; however, a role of their pigmentation in immune and inflammatory responses is poorly examined. In the study, the expression of Toll-like receptor 4 (TLR4) and inflammatory cytokines and chemokines by cultured normal melanocytes derived from lightly and darkly pigmented skin was investigated after cell stimulation with lipopolysaccharide (LPS). The basal TLR4 mRNA level in heavily pigmented cells was higher as compared to their lightly pigmented counterparts. Melanocyte exposure to LPS upregulated the expression of TLR4 mRNA and enhanced the DNA-binding activity of NF-κB p50 and p65. We found substantial differences in the LPS-stimulated expression of numerous genes encoding inflammatory cytokines and chemokines between the cells with various melanin contents. In lightly pigmented melanocytes, the most significantly upregulated genes were nicotinamide phosphoribosyltransferase (NAMPT/visfatin), the chemokines CCL2 and CCL20, and IL6, while the genes for CXCL12, IL-16 and the chemokine receptor CCR4 were the most significantly upregulated in heavily pigmented cells. Moreover, the lightly pigmented melanocytes secreted much more NAMPT, CCL2 and IL-6. The results of our study suggest modulatory effect of melanogenesis on the immune properties of normal epidermal melanocytes.

Malignant Melanoma Treated with Topical Imiquimod: A Bespoke Treatment That Spared the Amputation

Surgical excision represents the primary treatment for malignant melanoma. On occasion, however, surgery may not be possible, and a different approach is required. Imiquimod is a Toll-like receptor 7 agonist involved in the activation of the innate immune system. We report the case of a 77-year-old female with a large, invasive, malignant melanoma of the malleolar area. Due to the size of the lesion, its location, and the patient's general condition, neither surgery nor radiotherapy were indicated. We offered topical treatment with 5% imiquimod to be applied once/day continuously over a 3-month period, pausing only when intense inflammation on the area of application occurred. Complete clinical and histological resolution of the lesion were observed. This case adds further merit to the growing body of evidence that imiquimod can be used to successfully treat malignant melanoma in cases where no other options are suitable.

A systematic review on the role of imiquimod in lentigo maligna and lentigo maligna melanoma: need for standardization of treatment schedule and outcome measures

Lentigo maligna (LM) is an in situ variant of melanoma. Our objective was to systematically review clinical and histological clearance and recurrence rates of imiquimod treatment of LM with emphasis on progression to lentigo maligna melanoma (LMM). PubMed, EMBASE and the Cochrane library were searched from inception to May 2015. Articles were included if they described histologically proven LM treated with imiquimod 5% monotherapy or combined with another topical therapy. Analysed outcomes were clinical and histological clearance, recurrence rates and number of LMM. The quality was assessed using the GRADE-like checklist, and results were reported according to the PRISMA Statement. Twenty-six case reports, 11 retrospective studies, three prospective studies and one randomized controlled trial were included. One case report of poor quality was excluded. Complete clinical clearance was seen in 369 of 471 patients (78.3%). Histological clearance was present in 285 of 370 (77%) patients. LMM was diagnosed in nine (1.8%) patients 3.9 months (range 0-11 months) post-treatment. Univariate multinominal logistic regression showed that 6-7 applications/week had a 6.47 greater odds (P = 0.017) of resulting in complete clinical clearance compared to 1-4 applications/week. An intensity of 6-7 applications/week showed a 8.85 greater odds (P = 0.003) of resulting in histological clearance compared to 1-4 applications. Applying imiquimod >60 times during a treatment period of 12 weeks (range 4-36) showed a 7.75 greater odds (P = 0.001) of resulting in histological clearance compared to <60 total applications. In conclusion, a treatment schedule using imiquimod 6-7 applications per week, with at least 60 applications, shows the greatest odds of complete clinical and histological clearance of LM. Imiquimod is an option for patients unfit for or not willing to undergo surgery or radiotherapy. Nine cases of LM progressed to LMM shortly after treatment. Our hypothesis is that these LMM may have been present before starting imiquimod.

Polymorphisms in Toll-like receptor genes are associated with vitiligo

Background: The members of Toll-like receptor (TLR) family are responsible for recognizing various molecular patterns associated with pathogens. Their expression is not confined to immune cells and have been detected in skin cells such as keratinocytes and melanocytes. As part of a generated response to pathogens, TLRs are involved in inducing inflammatory mediators to combat these threats. It is therefore not surprising that TLRs have been implicated in inflammatory skin diseases, including atopic dermatitis and psoriasis. Likewise, as key players in autoimmunity, they have been associated with a number of autoimmune diseases. Based on this, the role of TLRs in vitiligo could be suspected, but is yet to be clearly established.

Methods: In order to conduct a genetic association analysis, 30 SNPs were selected from TLR1-TLR8 and TLR10 regions to be genotyped in Estonian case-control cohort consisting of 139 vitiligo patients and 307 healthy control individuals. The patients were further analyzed in subgroups based on sex, age of onset, occurrence of vitiligo among relatives, extent of depigmented areas, vitiligo progression activity, appearance of Köbner's phenomenon, existence of halo naevi, and incidence of spontaneous repigmentation.

Results: The most notable finding came with SNP rs179020 situated in TLR7 gene, that was associated in entire vitiligo (Padj = 0.0065) and also several subgroup analyses. Other single marker and haplotype analyses pointed to TLR3, TLR4, and TLR10 genes.

Conclusions: This study investigated the genetic regions of nine TLR genes in relation to vitiligo susceptibility. The main results were the associations of TLR7 SNPs with vitiligo, while several other associations were obtained from the remaining TLR gene regions. This suggests that in addition to other inflammatory skin diseases, TLRs affect the development of vitiligo, thus making them interesting targets for future research.

Interventions for melanoma in situ, including lentigo maligna

BACKGROUND

Malignant melanoma is a form of skin cancer associated with significant mortality once it has spread beyond the skin. Melanoma in situ (MIS) is the earliest histologically recognisable stage of malignant melanoma and represents a precursor of invasive melanoma. Lentigo maligna (LM) represents a subtype of pre-invasive intraepidermal melanoma associated specifically with chronic exposure to ultraviolet (UV) radiation. Over the past two decades, the incidence of MIS has increased significantly, even more than the invasive counterpart. There are several treatment options for MIS, but no consensus exists on the best therapeutic management of this condition.

OBJECTIVES

To assess the effects of all available interventions, surgical and non-surgical, for the treatment of melanoma in situ, including LM.

SEARCH METHODS

We searched the following databases up to November 2014: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2014, Issue 10), MEDLINE (from 1946), Embase (from 1974), LILACS (from 1982), African Index Medicus (from inception), IndeMED of India (from inception), and Index Medicus for the South-East Asia Region (IMSEAR) (from inception). We scanned the references of included and excluded studies for further references to relevant trials and searched five trials registries. We checked the abstracts of major dermatology and oncology conference proceedings, and we shared our lists of included and excluded studies with industry contacts and other experts in the field of melanoma to try to identify further relevant trials.

SELECTION CRITERIA

We included randomised controlled trials (RCT) on the management of MIS, including LM, that compared any intervention to placebo or active treatment. We included individuals, irrespective of age and sex, diagnosed with MIS, including LM, based on histological examination.

DATA COLLECTION AND ANALYSIS

Two authors independently evaluated possible studies for inclusion; extracted data from the included study using a standard data extraction form modified for our review; assessed risk of bias; and analysed data on efficacy, safety, and tolerability. They resolved any disagreements by discussion with a third author. We collected adverse effects information from included studies.

MAIN RESULTS

Our search identified only 1 study eligible for inclusion (and 1 ongoing study in active recruitment stage), which was a single centre, open label, parallel group, 2-arm RCT with 90 participants, who had 91 histologically proven LM lesions.Forty-four participants, with 44 LM lesions, were treated with imiquimod 5% cream 5 days per week plus tazarotene 0.1% gel 2 days/week for 3 months, and 46 participants, with 47 LM lesions, were treated with imiquimod 5% cream 5 days per week for 3 months. Two months after cessation of topical treatment, the initial tumour footprint was excised using 2 mm margins via a staged excision. This study was open label, and analysis was not intention-to-treat, leading to a high risk of incomplete outcome data.Our primary outcome 'Histological or clinical complete response' was measured at 5 months in 29/44 participants (66%) treated with imiquimod plus tazarotene (combination therapy) and 27/46 participants (59%) treated with imiquimod (monotherapy). The difference was not statistically significant (risk ratio (RR) 1.12, 95% confidence interval (CI) 0.81 to 1.55, P value = 0.48).With regard to our secondary outcomes on recurrence and inflammation, after a mean follow up of 42 months, no local recurrences were observed among complete responders. Difference in overall inflammation score between the 2 groups was significant (mean difference (MD) 0.6, 95% CI 0.2 to 1, P value = 0.004), with the mean overall inflammation score being significantly higher in the combination group.The study authors did not clearly report on side-effects. Because of adverse effects, there was a dropout rate of 6/44 participants (13.7%) in the combination group compared with 1/46 (2.2%) in the imiquimod monotherapy group (due to excessive inflammation) before the cessation of topical treatment (first 3 months), but this was not statistically significant (RR 6.27, 95% CI 0.79 to 50.02, P value = 0.08).

AUTHORS' CONCLUSIONS

There is a lack of high-quality evidence for the treatment of MIS and LM.For the treatment of MIS, we found no RCTs of surgical interventions aiming to optimise margin control (square method, perimeter technique, 'slow Mohs', staged radial sections, staged "mapped" excisions, or Mohs micrographic surgery), which are the most widely used interventions recommended as first-line therapy. The use of non-surgical interventions in selected cases (patients with contraindications to surgical interventions) may be effective and may be considered preferable for experienced providers and under close and adequate follow up.For the treatment of LM, we found no RCTs of surgical interventions, which remain the most widely used and recommended available treatment. The use of non-surgical interventions, such as imiquimod, as monotherapy may be effective and may be considered in selected cases where surgical procedures are contraindicated and used preferentially by experienced providers under close and adequate follow up. The use of topical therapies, such as 5-fluorouracil and imiquimod, as neoadjuvant therapies warrants further investigation. There is insufficient evidence to support or refute the addition of tazarotene to imiquimod as adjuvant therapy; the current evidence suggests that it can increase topical inflammatory response and withdrawal of participants because of treatment-related side-effects.

Enhanced bleaching treatment: opportunities for immune-assisted melanocyte suicide in vitiligo

Depigmentation in vitiligo occurs by progressive loss of melanocytes from the basal layer of the skin, and can be psychologically devastating to patients. T cell-mediated autoimmunity explains the progressive nature of this disease. Rather than being confronted with periods of rapid depigmentation and bouts of repigmentation, patients with long-standing, treatment-resistant vitiligo can undergo depigmentation treatment. The objective is to remove residual pigmentation to achieve a cosmetically acceptable result--that of skin with a uniform appearance. In the United States, only the use of mono-benzyl ether of hydroquinone (MBEH) is approved for this purpose. However, satisfactory results can take time to appear, and there is a risk of repigmentation. MBEH induces necrotic melanocyte death followed by a cytotoxic T-cell response to remaining, distant melanocytes. As cytotoxic T-cell responses are instrumental to depigmentation, we propose that combining MBEH with immune adjuvant therapies will accelerate immune-mediated melanocyte destruction to achieve faster, more definitive depigmentation than with MBEH alone. As Toll-like Receptor (TLR) agonists--imiquimod, CpG, and Heat Shock Protein 70 (HSP 70)--all support powerful Th1 responses, we propose that using MBEH in combination with these agents can achieve superior depigmentation results for vitiligo patients.

Imiquimod and pulmonary embolism: a case report

Bilateral pulmonary embolism possibly related due to topically applied imiquimod is reported in a 47-year-old male patient with no evidence of risk factors.

In vivo reflectance confocal microscopy to monitor the response of lentigo maligna to imiquimod

BACKGROUND

Imiquimod has been used for treating lentigo maligna (LM) in selected cases when surgery is not an appropriate option because of functional or aesthetic impairment. Reflectance confocal microscopy (RCM) is a noninvasive method that has not been validated for monitoring the treatment of LM with imiquimod.

OBJECTIVE

We sought to evaluate the use of in vivo RCM to accurately monitor the response of LM to nonsurgical treatment with topical imiquimod.

METHODS

Twenty patients with confirmed facial LM, not amenable to surgical treatment or radiation therapy, were included prospectively. Clinical evaluation was performed by dermoscopy, RCM, and histopathology. Patients applied imiquimod 5% for 8 weeks. The affected area was assessed using the previously described LM score on RCM, and target sample biopsies were performed to confirm or discard RCM findings.

RESULTS

Fifteen of the 20 patients (75%) presented histologic tumor clearance. Confocal microscopy identified 70% of these responders with no false-negative results, and when compared with histopathology, there was no significant difference in evaluating the response to imiquimod.

LIMITATIONS

The impossibility of examining the entire lesion by means of histopathology is a limitation.

CONCLUSION

In vivo RCM evaluation was useful in accurately monitoring the response of LM to nonsurgical treatment with topical imiquimod in patients when surgery is contraindicated.

Expression of TLR3, 4, 7 and 9 in cutaneous malignant melanoma: relationship with clinicopathological characteristics and prognosis

Toll-like receptors (TLRs) have achieved an extraordinary amount of interest in cancer research due to their role in tumor progression. The aim of this study was to investigate the expression and clinical relevance of TLR3, 4, 7 and 9 in cutaneous malignant melanoma (CMM). The expression levels of TLR3, 4, 7 and 9 were analyzed in tumors from 30 patients with CMM. The analysis was performed by immunohistochemistry, and the results were correlated with various clinicopathological findings and with relapse-free survival. Our results indicate that there was a wide variability in the immunostaining score values for each receptor. Positive staining for TLRs was generally found in tumor cells, especially for TLR4 and TLR9. Nevertheless, a significant percentage of tumors also showed TLR4 expression in mononuclear inflammatory cells (62.1 %) and in fibroblast-like cells (34.5 %). Our results showed no significant association between score values for each TLR and clinicopathological characteristics of patients. However, our results demonstrated that high TLR4 expression was significantly associated with a shortened relapse-free survival (p = 0.001). Therefore, TLR4 expression may be a new prognostic factor of unfavorable evolution in cutaneous malignant melanoma.

Identification of genes related to white and black plumage formation by RNA-Seq from white and black feather bulbs in ducks

To elucidate the genes involved in the formation of white and black plumage in ducks, RNA from white and black feather bulbs of an F(2) population were analyzed using RNA-Seq. A total of 2,642 expressed sequence tags showed significant differential expression between white and black feather bulbs. Among these tags, 186 matched 133 annotated genes that grouped into 94 pathways. A number of genes controlling melanogenesis showed differential expression between the two types of feather bulbs. This differential expression was confirmed by qPCR analysis and demonstrated that Tyr (Tyrosinase) and Tyrp1 (Tyrosinase-related protein-1) were expressed not in W-W (white feather bulb from white dorsal plumage) and W-WB (white feather bulb from white-black dorsal plumage) but in B-B (black feather bulb from black dorsal plumage) and B-WB (black feather bulb from white-black dorsal plumage) feather bulbs. Tyrp2 (Tyrosinase-related protein-2) gene did not show expression in the four types of feather bulbs but expressed in retina. C-kit (The tyrosine kinase receptor) expressed in all of the samples but the relative mRNA expression in B-B or B-WB was approximately 10 fold higher than that in W-W or W-WB. Additionally, only one of the two Mitf isoforms was associated with plumage color determination. Downregulation of c-Kit and Mitf in feather bulbs may be the cause of white plumage in the duck.

Double-stranded RNA induces melanocyte death via activation of Toll-like receptor 3

As cutaneous pigment-producing cells, melanocytes can become targets of primary and secondary immune response as can be seen in diseases like vitiligo and Vogt-Koyanagi-Harada (VKH) syndrome. Viral infections have previously been implicated as a possible precipitating factor in the destruction of melanocytes in these disorders. During viral replication, double-stranded RNA (dsRNA) is produced as an intermediate metabolite, which induces antiviral and inflammatory responses through Toll-like receptor 3 (TLR3) in cells of innate immune system. The functional responses of melanocytes to dsRNA, however, remain unclear. Herein, we demonstrated that human melanocytes expressed TLR3 at a constitutive and inducible level. Stimulation with poly(I:C), a synthetic dsRNA analogue, triggered apoptosis of melanocytes. The apoptosis-inducing effect was shown by RNA interference to be largely dependent on TLR3, but occurred independently of NF-κB activation since treatment with specific NF-κB inhibitor Bay 11-7082 failed to prevent the process. In contrast, IFN-β neutralizing Ab blocked the apoptosis-inducing effect of dsRNA, indicating the involvement of IFN-β autocrine signalling. Furthermore, studies on the intracellular signal transduction pathways revealed that dsRNA induces the activation of p38, ERK1/2 and JNK1/2 in melanocytes. Using specific inhibitors, we demonstrated that activation of p38 and ERK1/2 controlled both IFN-β secretion and IFN-β mediated cell death. Taken together, these data suggest that viral dsRNA stimulates TLR3 in human melanocytes and triggers the cellular apoptosis through autocrine of IFN-β.

Managing melanoma in situ

Melanoma is a highly aggressive skin cancer with an increasing incidence. Melanoma in situ is an early, non-invasive form in which the tumor is confined to the epidermis. Treatment of melanoma in situ is challenging due to the frequent subclinical microscopic spread and to the presentation on the head and neck in cosmetically sensitive areas with chronic sun damage. Optimizing tumor eradication is imperative to reduce the potential progression into invasive disease and metastasis, all while maintaining cosmesis. Multiple treatment regimens have been implemented for managing difficult melanoma in situ tumors. We provide a thorough review of surgical, and non-surgical, management of melanoma in situ which can pose therapeutic dilemmas due to size, anatomic location, and subclinical spread.

Activation of Toll-like Receptors 1, 2, 4, 5, and 7 on Human Melanocytes Modulate Pigmentation

Human melanocytes are not simply pigment-producing cells. It may be part of the inflammatory response, during which the pigmentary system may produce more melanin or suppress melanization. Toll-like receptors (TLRs) have been implicated in both innate host defense against pathogens and inflammatory response. Therefore, it may be possible that activation of TLRs in melanocytes may play a role in the modulation of melanogenesis. In this study, we investigated whether normal human melanocytes expressed TLRs and analyzed pigmentation changes upon TLR stimulation. The expression of TLR1~10 mRNA in cultured human melanocyte was analyzed using RT-PCR, Western blotting and immunocytochemistry. Human melanocytes constitutively express mRNA and protein for TLR2, 3, 4, 5, 7, 9 and 10. Stimulation of TLR1/2 and 4 with Pam3CSK4 and lipopolysaccharide induced pigmentation of melanocytes. Activation of TLR5 and 7 with flagellin and imiquimod treatments reduced pigmentation of melanocytes and zebrafish. In summary, the results provided evidence for TLRs expression in normal human melanocytes. It is speculated that a response of melanocyte to TLR ligands may play a role in the pigmentary change in the skin.

Inhibition of DNA synthesis in mouse epidermis by topical imiquimod is dependent on opioid receptors

The imidazoquinolines are immune response modifiers that have potent antiviral and antitumor properties. The mechanism by which they exert their effects on cell replication has been investigated in vitro and is related to the upregulation of the opioid growth factor receptor (OGFr) and modulation of opioid growth factor (OGF; [Met5]-enkephalin). The OGF–OGFr axis regulates cell proliferative events through a cyclin-dependent kinase inhibitory pathway. The present study examined the mechanism whereby imiquimod repressed cell proliferation in vivo. Using a nude mouse model that has a compromised T-cell immune system, as well as C57BL/6 mice with an intact immune system, the effects of topical imiquimod (Aldara®) on DNA synthesis of basal epithelial cells in skin were examined. Imiquimod's effects on DNA synthesis were detected 24 h after application, and could be observed for one week after a single treatment. The magnitude of change in DNA synthesis following imiquimod was similar for one, three or six applications. Naloxone, an opioid antagonist, blocked the inhibitory effect of imiquimod. Imiquimod in combination with OGF or a low dose of naltrexone (LDN; known to upregulate the OGF–OGFr axis) had no greater inhibitory response on DNA synthesis than either OGF or LDN alone. Both OGF and OGFr were upregulated in basal epithelium after imiquimod treatment. Both nude and C57BL/6 mice exhibited the same repressive action of imiquimod on epithelial DNA synthesis. Imiquimod was neither an opioid agonist nor antagonist using nociceptive testing, and did not induce apoptosis or necrosis. Exposure to imiquimod was found to depress DNA synthesis in cells located in distant epithelium from day 3 and lasted until day 5. These results suggest that the target of imiquimod on DNA synthesis is dependent on an opioid receptor-mediated pathway, and infers that imiquimod is reliant on the OGF–OGFr axis for modulating cell proliferation.

Toll-like receptors: role in dermatological disease

Toll-like receptors (TLRs) are a class of conserved receptors that recognize pathogen-associated molecular patterns (PAMPs) present in microbes. In humans, at least ten TLRs have been identified, and their recognition targets range from bacterial endotoxins to lipopeptides, DNA, dsRNA, ssRNA, fungal products, and several host factors. Of dermatological interest, these receptors are expressed on several skin cells including keratinocytes, melanocytes, and Langerhans cells. TLRs are essential in identifying microbial products and are known to link the innate and adaptive immune systems. Over the years, there have been significant advances in our understanding of TLRs in skin inflammation, cutaneous malignancies, and defence mechanisms. In this paper, we will describe the association between TLRs and various skin pathologies and discuss proposed TLR therapeutics.

Imiquimod induces apoptosis of human melanocytes

Development of vitiligo-like hypopigmentary lesions associated with topical imiquimod has been reported. We hypothesized that mode of action of imiquimod in melanocytes may include triggering of apoptosis resulted in loss of cells, which may be a possible mechanism of imiquimod-induced hypopigmentary lesions. Therefore, we investigated whether imiquimod induces apoptosis of human melanocytes and also whether it modulates expression of apoptosis-related molecules in human melanocytes. Imiquimod treatment induced apoptosis of melanocytes, which was observed by TUNEL assay and Hoechst 33258 staining. Imiquimod-induced apoptosis was further shown by measuring mitochondrial membrane potential in melanocytes. The apoptotic activity of imiquimod was associated with caspase-3, Bcl-2 and mitogen-activated protein kinase expression in melanocytes. These results indicated that imiquimod induces apoptosis of melanocytes. These findings may provide a clue to understand pathogenesis of imiquimod-induced vitiligo-like hypopigmentary lesions.

Cultured human melanocytes express functional toll-like receptors 2-4, 7 and 9

BACKGROUND

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPs), which have been evolutionarily conserved in microbes. Human melanocytes are not simply pigment-producing cells but also have the phagocytic capacity and can produce pro-inflammatory mediators. However, the mechanisms of recognition of microbes by melanocytes have not yet been fully established.

OBJECTIVE

We investigated the TLRs 1-10 expression profile in human epidermal melanocytes and assessed their functions after triggering by their specific ligands.

METHODS

TLRs mRNA expression was determined by RT-PCR, and the TLR protein expression was measured by flow cytometry and immunofluorescence assays. After stimulation with various TLR ligands, the production of inflammatory cytokine IL-8 and IL-6 was measured by ELISA and the mRNA for chemokine CCL2, CCL3 and CCL5 was analyzed by real-time PCR. Phosphorylation of IkappaBalpha in TLR ligands-triggered melanocytes was determined by Western blot and the nucleus translocation of NF-kappaBp65 was analyzed by immunofluorescence.

RESULTS

Human melanocytes constitutively expressed TLRs 1-4, 6, 7 and 9 mRNA. Ample amounts of TLRs 2-4, 7 and 9 were confirmed at protein level. Stimulation of melanocytes with TLRs ligands resulted in the release of cytokines (IL-8 and IL-6) and the mRNA accumulation of chemokines (CCL2, CCL3 and CCL5). Triggering of TLRs in melanocytes resulted in the up-regulation of phosphorylated IkappaBalpha and in the nucleus translocation of NF-kappaBp65.

CONCLUSION

Present study indicates human melanocytes express a panel of functional TLRs. The ligation of TLRs can turn these cells into active players of the skin innate immunity.

Quantitation of imidazo[1,2-a]quinoxaline derivatives in human and rat plasma using LC/ESI-MS

Since several years, our group developed quinoxalinic compounds. Among the synthesized compounds, in the imidazo[1,2-a]quinoxaline series, EAPB0203 has shown interesting activities both on melanoma and lymphoma. The structure of EAPB0203 has been modulated and a new compound, EAPB0503, exhibits an in vitro cytotoxic activity on melanoma cancer cell line 7-9 times higher than EAPB0203. We validated an LC/ESI-MS method to simultaneously quantify EAPB0503 and its metabolite EAPB0603 in human and rat plasma. Chromatography was performed on a C8 Zorbax eclipse XDB column with a mobile phase consisting of acetronitrile and formate buffer gradient elution. LC-MS data were acquired in SIM mode at m/z 305, 291, and 303 for EAPB0503, EAPB0603, and the internal standard, respectively. The drug/internal standard peak area ratios were linked via quadratic relationships to concentrations (low range: 5-300 microg/L, high range: 100-1000 microg/L). The method is precise (precision, < or = 14%) and accurate (recovery, 92-113%). Mean extraction efficiencies, > 72% for each analyte, were obtained. The lower LOQs were 5 microg/L. This highly specific and sensitive method was successfully used to investigate plasma concentrations of EAPB0503 and EAPB0603 in a pharmacokinetic study carried out in rat and would also be useful in clinical trials at a later stage.