Adjuvant Anti-PD-1 Antibody Therapy for Advanced Melanoma: A Multicentre Study of 78 Japanese Cases.

Anti-PD-1 antibodies (Abs) are among the optimal adjuvant therapies for melanoma at high risk of recurrence, especially BRAF wild-type melanoma, but the anti-tumour effects of anti-PD-1 Abs in the adjuvant setting for acral melanoma have not been evaluated previously. The aim of this study was to analyse the efficacy and safety profiles of anti-PD-1 Ab monotherapy in the adjuvant setting in an Asian population including a high ratio of acral melanoma. The efficacy and safety profiles of anti-PD-1 Ab monotherapy in the adjuvant setting were retrospectively analysed in 78 Japanese patients with advanced melanoma, including 31 cases (40%) of acral melanoma. Overall relapse-free survival was 60.3% (47 of 78 cases, 95% confidence interval (CI) 49.2-70.4%), and 39.7% of patients (31 of 78 patients, 95% CI 29.6-50.8%) relapsed during the adjuvant PD-1 Ab treatment. Six cases (7.9%) discontinued the protocol due to serious adverse events. One case (1.3%) discontinued the protocol due to trauma. The relapse-free survival of acral melanoma was 25.8%, whereas that of high cumulative sun damage was 60.0%, and that of low cumulative sun damage was 57.1%. The acral type had a significantly lower 12-month relapse-free survival than other cutaneous types (p = 0.029). The acral type appeared to be an independent prognostic factor on multivariate analysis (p = 0.015). Adverse events due to anti-PD-1 antibody were observed in 37.1% overall. The results of this study suggest that anti-PD-1 Ab therapy in the adjuvant setting is less effective for acral melanoma than for other cutaneous types.

Long-term follow up of nivolumab in previously untreated Japanese patients with advanced or recurrent malignant melanoma.

The immune checkpoint inhibitor nivolumab inhibits the programmed death 1 receptor and suppresses the immune resistance of cancer cells. This is a long-term follow up of a single-arm, open-label, multicenter, phase II study of nivolumab in untreated Japanese patients with stage III/IV or recurrent melanoma. In addition, a post-hoc subgroup analysis stratified by melanoma types was performed. Nivolumab was administered intravenously at a dose of 3 mg/kg every 2 weeks. The primary endpoint was the overall response rate (ORR), and secondary endpoints included overall survival (OS), progression-free survival (PFS), best overall response, the disease control rate and change in tumor diameter. Safety was assessed by recording treatment-related adverse events (TRAE), including select immune-related adverse events. Of the 24 patients initially included in the primary phase II study, 10 survived for over 3 years (41.7%). The ORR was 34.8% (90% confidence interval [CI]: 20.8, 51.9) for all patients. When analyzing by melanoma type, the ORR was 66.7% (90% CI: 34.7, 88.3) for superficial spreading, 33.3% (90% CI: 11.7, 65.3) for mucosal, and 28.6% (90% CI: 10.0, 59.1) for acral lentiginous tumors. The median OS was 32.9 months, the 3-year OS rate was 43.5%, and the 3-year PFS rate was 17.2%. A long-term response was observed in all the tumor types. The most common TRAE included skin toxicity (45.8%) and endocrine disorders (29.2%). This study demonstrated the long-term efficacy and tolerability of nivolumab in patients with advanced or recurrent melanoma, irrespective of melanoma type.

Variable indoleamine 2,3-dioxygenase expression in acral/mucosal melanoma and its possible link to immunotherapy.

Immune checkpoint inhibitors have improved the prognosis of advanced melanoma. Although anti-programmed death ligand-1 (PD-L1) is a well-studied biomarker for response to anti-programmed death-1 PD-1 therapy in melanoma, its clinical relevance remains unclear. It has been established that the high expression of indoleamine 2,3-dioxygenase (IDO) is correlated to a response to anti-CTLA-4 treatment in melanoma. However, it is still unknown whether the IDO expression is associated with response to anti-PD-1 therapy in advanced melanoma. In addition, acral and mucosal melanomas, which comprise a great proportion of all melanomas in Asians, are genetically different subtypes from cutaneous melanomas; however, they have not been independently analyzed due to their low frequency in Western countries. To evaluate the association of IDO and PD-L1 expression with response to anti-PD-1 antibody in acral and mucosal melanoma patients, we analyzed 32 Japanese patients with acral and mucosal melanomas treated with anti-PD-1 antibody from the perspective of IDO and PD-L1 expression levels by immunohistochemistry (IHC). Multivariate Cox regression models showed that the low expression of IDO in tumors was associated with poor progression-free survival (HR = 0.33, 95% CI = 0.13-0.81, P = 0.016), whereas PD-L1 expression on tumors was not associated with progression-free survival. Significantly lower expression of IDO in tumors was found in non-responders compared to responders. Assessment of the IDO expression could be useful for the identification of suitable candidates for anti-PD-1 therapy among acral and mucosal melanomas patients. Further validation study is needed to estimate the clinical utility of our findings.

Dioxin-induced increase in leukotriene B4 biosynthesis through the aryl hydrocarbon receptor and its relevance to hepatotoxicity owing to neutrophil infiltration.

Dioxin and related chemicals alter the expression of a number of genes by activating the aryl hydrocarbon receptors (AHR) to produce a variety of disorders including hepatotoxicity. However, it remains largely unknown how these changes in gene expression are linked to toxicity. To address this issue, we initially examined the effect of 2,3,7,8-tetrachrolodibenzo-p-dioxin (TCDD), a most toxic dioxin, on the hepatic and serum metabolome in male pubertal rats and found that TCDD causes many changes in the level of fatty acids, bile acids, amino acids, and their metabolites. Among these findings was the discovery that TCDD increases the content of leukotriene B4 (LTB4), an inducer of inflammation due to the activation of leukocytes, in the liver of rats and mice. Further analyses suggested that an increase in LTB4 comes from a dual mechanism consisting of an induction of arachidonate lipoxygenase-5, a rate-limiting enzyme in LTB4 synthesis, and the down-regulation of LTC4 synthase, an enzyme that converts LTA4 to LTC4. The above changes required AHR activation, because the same was not observed in AHR knock-out rats. In agreement with LTB4 accumulation, TCDD caused the marked infiltration of neutrophils into the liver. However, deleting LTB4 receptors (BLT1) blocked this effect. A TCDD-produced increase in the mRNA expression of inflammatory markers, including tumor-necrosis factor and hepatic damage, was also suppressed in BLT1-null mice. The above observations focusing on metabolomic changes provide novel evidence that TCDD accumulates LTB4 in the liver by an AHR-dependent induction of LTB4 biosynthesis to cause hepatotoxicity through neutrophil activation.

Activation of central/effector memory T cells and T-helper 1 polarization in malignant melanoma patients treated with anti-programmed death-1 antibody.

Human anti-programmed death-1 (PD-1) antibody possesses the capability to revitalize host T cells and has been an effective therapy for metastatic malignant melanoma (MM). The precise subsets of T cells predominantly activated by anti-PD-1, however, have not yet been clarified. In this study, peripheral blood mononuclear cells obtained from MM patients scheduled to receive anti-PD-1 (nivolumab) therapy, and healthy subjects (HS), were systematically examined on flow cytometry to identify changes in the proportion of immune cell subsets. Compared with HS, MM patients prior to therapy had an increased proportion of activated CD8+ T cells with effector memory phenotypes (Tem), and PD-1 positive subsets of CD4+ central memory T cells (Tcm) and T-helper (Th)17 cells. After a single course of anti-PD-1 therapy, MM patients had an increase in activated Tem and Tcm subsets of CD4+ and CD8+ T cells, and activated Th1 plus T-helper follicular 1 cells. There was no consistent change in the proportion of Tfh cells, B cells, natural killer cells, or dendritic cells. The observed activated phenotypes were attenuated during the course of therapy, but regulatory T cells belonging to the CD3+CD4+CD45RO+CD25high fraction increased at disease progression. Taken together, anti-PD-1 therapy modulates systemic immune reactions and exerts anti-tumor effects, not only by revitalizing Tem and Tcm of CD4+ and CD8+ T cells, but also via a shift to a Th1 phenotype.

Evaluation of mapping biopsies for extramammary Paget disease: A retrospective study.

BACKGROUND: Extramammary Paget disease (EMPD) sometimes shows an ill-defined border and an unexpectedly extended tumor spread beyond the clinical borders. Mapping biopsy is 1 approach for complete surgical removal, but its efficacy has remained controversial. OBJECTIVE: We sought to evaluate mapping biopsies for EMPD. METHODS: We performed a retrospective review of 133 patients with 150 primary EMPD lesions. We histopathologically examined 1182 skin biopsy specimens (975 from mapping biopsy and 207 from lesional biopsy). RESULTS: Only 1.6% of mapping biopsy specimens from well-defined EMPD (13 of 810) were positive. Moreover, 4.6% of mapping biopsy specimens from ill-defined EMPD (8 of 165) were positive, whereas all specimens taken from sites 2 cm or more from the clinical border were negative. For both well-defined and ill-defined EMPD, there was no significant difference in the margin status of surgical resection regardless of mapping biopsy. LIMITATIONS: This was a retrospective study. CONCLUSIONS: Mapping biopsies are unnecessary for well-defined EMPD or when 2-cm margins can be achieved, whereas surgical removal with predetermined margins (1 cm for well-defined EMPD and 2 cm for ill-defined EMPD) appears to be safe. Mapping biopsies can be considered when shortening of the safe surgical margin to less than 2 cm is required in ill-defined EMPD.

Melanoma and Immune Checkpoint Inhibitors.

PURPOSE OF REVIEW: Prognosis of patients with advanced melanoma is dismal with a median overall survival of about 8 months and 5-year overall survival from a diagnosis of metastatic disease of roughly 10%. However, immune checkpoint inhibitors have brought indispensable benefits to melanoma patients. Here we will review the recent clinical efficacy and adverse events of immune checkpoint inhibitors for melanoma patients. RECENT FINDINGS: The immune checkpoint inhibitors increase confirmed objective response and prolong progression-free and overall survival of the afflicted patients in association with maintaining their quality of life. Although diverse immune-related adverse events occur, most of them are manageable by appropriate immunomodulating agents. Clinical efficacy of immune checkpoint inhibitors continues even after discontinuation of drugs. Compared with conventional therapeutic options, the immune checkpoint inhibitors appear to prolong the survival of patients with advanced melanoma. Further clinical trials are warranted to determine whether their combinatory use with other treatment options may augment benefits or not.

Nivolumab-induced thyroid dysfunction lacking antithyroid antibody is frequently evoked in Japanese patients with malignant melanoma.

BACKGROUND: Nivolumab, an anti-programmed cell death-1 monoclonal antibody, has improved the survival of patients with malignant melanoma. Despite its efficacy, nivolumab inconsistently induces thyroid dysfunction as an immune-related adverse event (irAE). This study aimed to evaluate nivolumab-induced thyroid dysfunction to determine the risks and mechanisms of thyroid irAEs. METHODS: After excluding 10 patients, data of 24 patients with malignant melanoma (aged 17-85 years; 54% female) were retrospectively analyzed. RESULTS: Thyroid irAEs were observed in seven patients (29%). Three patients had hypothyroidism after preceding transient thyrotoxicosis, and the other four patients had hypothyroidism without thyrotoxicosis. Levothyroxine-Na replacement was required in three patients. Antithyroid antibody (ATA) titer was elevated in one of four assessable patients. The average (±SD) time to onset of thyroid irAE was 33.6 (±21.9) weeks. The administration period of nivolumab was longer in patients with thyroid irAEs than in those without thyroid irAEs (P < 0.01). There were no significant differences between patients with and without thyroid irAEs regarding age, sex, tumor stage, response to nivolumab therapy, baseline thyroid function, antithyroid peroxidase antibody (anti-TPO Ab) and antithyroglobulin antibody (anti-Tg Ab). CONCLUSIONS: Thyroid dysfunction was a common irAE of nivolumab in malignant melanoma. Neither anti-TPO Ab nor anti-Tg Ab was associated with the risk for nivolumab-induced thyroid dysfunction. A conventional ATA-independent mechanism might be involved in thyroid irAEs. Further studies are required to clarify the mechanism and identify the predictive factors of thyroid irAEs.

Highlighting Interleukin-36 Signalling in Plaque Psoriasis and Pustular Psoriasis.

Plaque psoriasis and pustular psoriasis are overlapping, but distinct, disorders. The therapeutic response to biologics supports the pivotal role of the tumour necrosis alpha (TNF-?)/ interleukin (IL)-23/IL-17/IL-22 axis in the pathogenesis of these disorders. Recently, functional activation of the IL-36 receptor (IL-36R) was discovered to be another driving force in the pathogenesis of psoriasis. This was first highlighted by the discovery that a loss-of-function mutation of the IL-36R antagonist (IL-36Ra) causes pustular psoriasis. Although the TNF-?/IL-23/IL-17/IL-22 axis and the functional activation of IL-36R are fundamentally involved in plaque psoriasis and pustular psoriasis, respectively, the 2 pathways are closely related and mutually reinforced, resulting in full-blown clinical manifestations. This review summarizes current topics on how IL-36 agonists (IL-36?, IL-36?, IL-36?) signal IL-36R, the pathological expression of IL-36 agonists and IL-36Ra in plaque and pustular psoriatic lesions, and the cross-talk between the TNF-?/IL-23/IL-17/IL-22 axis and the functional activation of IL-36R in the epidermal milieu.

Long-Term Health Effects of PCBs and Related Compounds: A Comparative Analysis of Patients Suffering from Yusho and the General Population.

Yusho, which refers to a mass poisoning caused by the ingestion of rice bran oil contaminated with polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans, was first reported in October 1968 in Japan. Yusho patients suffer from various symptoms; however, after 40 years, some emerging symptoms have been attributed to aging. The prevalence of symptoms and diseases among Yusho patients and the general population was compared in this study. The data obtained from the survey among Yusho patients (1131 patients) by the Ministry of Health, Labour, and Welfare of Japan in 2008 were compared with the data from a survey conducted among the general population. When selecting the comparison group, the age and residential area (prefecture) were taken into account to match the baseline characteristics of Yusho patients. A logistic regression analysis was performed to identify the association between Yusho and the prevalence of symptoms and was adjusted for various potential confounding factors (age, sex, body mass index, cigarette smoking, frequency of drinking, and walking time). Skin pigmentation and acneiform eruption were found to be characteristic symptoms of Yusho and were more prevalent in these patients. Other symptoms and diseases associated with Yusho included orthostatic hypotension, hypohidrosis, dysgeusia, Basedow's disease, hoarseness, cardiac insufficiency, tachycardia, eczema, and hair loss. Symptoms related to aging, such as general fatigue, arthralgia, and numbness in the extremities, were significantly higher in Yusho patients after adjusting for age and lifestyle. This study demonstrated that, 40 years after the outbreak of Yusho, the prevalence of various symptoms and diseases in Yusho patients, including age-related diseases, was higher than that in the general population.

Efficacy and safety of nivolumab in Japanese patients with previously untreated advanced melanoma: A phase II study.

Treating advanced or recurrent melanoma remains a challenge. Cancer cells can evade the immune system by blocking T-cell activation through overexpression of the inhibitory receptor programmed death 1 (PD-1) ligands. The PD-1 inhibitor nivolumab blocks the inhibitory signal in T cells, thus overcoming the immune resistance of cancer cells. Nivolumab has shown promising anticancer activity in various cancers. We carried out a single-arm, open-label, multicenter, phase II study to investigate the efficacy and safety of nivolumab in previously untreated Japanese patients with advanced melanoma. Twenty-four patients with stage III/IV or recurrent melanoma were enrolled and received i.v. nivolumab 3 mg/kg every 2 weeks until disease progression or unacceptable toxicity. The primary endpoint was overall response rate evaluated by an independent radiology review committee. The independent radiology review committee-assessed overall response rate was 34.8% (90% confidence interval, 20.8-51.9), and the overall survival rate at 18 months was 56.5% (90% confidence interval, 38.0-71.4). Treatment-related adverse events (AEs) of grade 3 or 4 only occurred in three patients (12.5%). Two patients discontinued nivolumab because of AEs, but all AEs were considered manageable by early diagnosis and appropriate treatment. Subgroup analyses showed that nivolumab was clinically beneficial and tolerable regardless of BRAF genotype, and that patients with treatment-related select AEs and with vitiligo showed tendency for better survival. In conclusion, nivolumab showed favorable efficacy and safety profiles in Japanese patients with advanced or recurrent melanoma, with or without BRAF mutations. (Trial registration no. JapicCTI-142533.).

Cytokine biomarkers to predict antitumor responses to nivolumab suggested in a phase 2 study for advanced melanoma.

Promising antitumor activities of nivolumab, a fully humanized IgG4 inhibitor antibody against the programmed death-1 protein, were suggested in previous phase 1 studies. The present phase 2, single-arm study (JAPIC-CTI #111681) evaluated the antitumor activities of nivolumab and explored its predictive correlates in advanced melanoma patients at 11 sites in Japan. Intravenous nivolumab 2 mg/kg was given repeatedly at 3-week intervals to 35 of 37 patients enrolled from December 2011 to May 2012 until they experienced unacceptable toxicity, disease progression, or complete response. Primary endpoint was objective response rate. Serum levels of immune modulators were assessed at multiple time points. As of 21 October 2014, median response duration, median progression-free survival, and median overall survival were 463 days, 169 days, and 18.0 months, respectively. The overall response rate and 1- and 2-year survival rates were 28.6%, 54.3%, and 42.9%, respectively. Thirteen patients remained alive at the end of the observation period and no deaths were drug related. Grade 3-4 drug-related adverse events were observed in 31.4% of patients. Pretreatment serum interferon-γ, and interleukin-6 and -10 levels were significantly higher in the patients with objective tumor responses than in those with tumor progression. In conclusion, giving repeated i.v. nivolumab had potent and durable antitumor effects and a manageable safety profile in advanced melanoma patients, strongly suggesting the usefulness of nivolumab for advanced melanoma and the usefulness of pretreatment serum cytokine profiles as correlates for predicting treatment efficacy.

Potential role of the OVOL1-OVOL2 axis and c-Myc in the progression of cutaneous squamous cell carcinoma.

OVOL1 and OVOL2 are ubiquitously conserved genes encoding C2H2 zinc-finger transcription factors in mammals. They promote epithelial cell proliferation, differentiation, and mesenchymal-to-epithelial transition, coordinately mediated via the Wnt signaling pathway. We previously reported that human OVOL1 and OVOL2 were preferentially expressed in the normal epidermis and hair follicles as well as their tumors, and found that OVOL1 is upregulated in Bowen's disease and downregulated in cutaneous squamous cell carcinoma. The aims of this study were to elucidate the potential role of the OVOL1-OVOL2 axis in Bowen's disease and squamous cell carcinoma, and to reveal the relationship between OVOL and c-Myc, a proto-oncogene that plays a pivotal role in the malignancy of epithelial tumors. We investigated 20 Bowen's disease and 20 squamous cell carcinoma clinical samples and a human squamous cell carcinoma cell line (A431) using immunohistochemical staining and molecular biological approaches. Immunohistochemical analysis revealed that OVOL1 was upregulated in Bowen's disease and markedly downregulated in squamous cell carcinoma; conversely, c-Myc was downregulated in Bowen's disease and upregulated in squamous cell carcinoma. OVOL2 was markedly upregulated in the nucleus of Bowen's disease cells, but the distribution of OVOL2 expression in squamous cell carcinoma varied widely; OVOL2 was typically expressed in the cytoplasm, but only sporadically in the nucleus. Furthermore, knockdown of OVOL1 using a specific small interfering RNA increased the mRNA and protein levels of c-Myc and OVOL2. Knockdown of OVOL2 did not significantly affect the mRNA and protein levels of either c-Myc or OVOL1. These results suggest that OVOL1 is an upstream suppressor of c-Myc and OVOL2, and the OVOL1-OVOL2 axis is a modulator of c-Myc, coordinately regulating the invasiveness of cutaneous squamous cell carcinoma. Taken together, this study suggests that the OVOL1-OVOL2 axis is a key modulator of c-Myc expression in the shift from in situ epidermal malignancy (Bowen's disease) to invasive squamous cell carcinoma.

Activation of the OVOL1-OVOL2 Axis in the Hair Bulb and in Pilomatricoma.

OVOL1 and OVOL2, ubiquitously conserved genes encoding C2H2 zinc finger transcription factors in mammals, control epithelial cell proliferation, and differentiation, including those in skin. OVOL1 and OVOL2 expression is coordinately mediated via the Wnt signaling pathway, and OVOL1 negatively regulates OVOL2 expression in a transcriptional manner. Our previous study of OVOL1 expression in human skin revealed that OVOL1 is preferentially expressed in the inner root sheath of the hair follicle. Therefore, we hypothesized that the OVOL1-OVOL2 axis is involved in normal and neoplastic follicular differentiation. Immunohistochemical analysis showed that OVOL1 and OVOL2 were strongly expressed in a mutually exclusive manner in the cytoplasm of inner root sheath cells and matrix cells, respectively, in normal follicles. OVOL2 was also expressed in pilomatricoma, with only partial expression of OVOL1. Cultured human keratinocytes expressed OVOL1 and OVOL2 on both the mRNA and protein levels. The expression of OVOL2 was higher in keratinocytes transfected with siRNA of OVOL1. Ketoconazole, a hair growth stimulant, up-regulated the expression of OVOL1 but did not affect OVOL2 expression. These results indicated that the OVOL1-OVOL2 axis may actively contribute to cell differentiation and proliferation in the hair bulb, suggesting that the OVOL1 and OVOL2 may be therapeutic targets of hair disorders, including alopecia, and play important roles in the tumorigenesis of pilomatricoma.

Randomized phase III trial of adjuvant therapy with locoregional interferon beta versus surgery alone in stage II/III cutaneous melanoma: Japan Clinical Oncology Group Study (JCOG1309, J-FERON).

The Dermatologic Oncology Group of Japan Clinical Oncology Group has started a randomized phase III trial to confirm the superiority of adjuvant therapy with locoregional interferon beta in overall survival over surgery alone for patients with pathological stage II/III cutaneous melanoma (JCOG1309). Patients in the interferon beta arm receive intra- or subcutaneous injections of interferon beta directly into the surgical site at a flat dose of 3 million units once per day. Treatment is repeated for 10 consecutive days every 8 weeks for a total of 3 courses during the induction phase, then 1-day injection every 4 weeks for 2.5 years. A total of 240 patients will be accrued from 17 Japanese institutions within 6.5 years. Primary endpoint is overall survival. Secondary endpoints are relapse-free survival, distant metastasis-free survival, pattern of recurrence, and adverse events. This trial has been registered at the UMIN Clinical Trials Registry as UMIN000017494 [http://www.umin.ac.jp/ctr/index.htm].

Isolated ACTH deficiency probably induced by autoimmune-related mechanism evoked with nivolumab.

Nivolumab, an anti-programmed death-1 antibody, is a breakthrough treatment for several malignancies. Its specific adverse effects caused by autoimmunity are termed immune-related adverse events, which involve several endocrine dysfunctions. Herein, we report two cases of isolated adrenocorticotropic hormone (ACTH) deficiency induced by nivolumab for the treatment of metastatic malignant melanoma. Case 1 was a 39-year-old man and Case 2 was a 50-year-old woman, both of whom presented with progressive melanoma. After 13 courses of nivolumab administration, both cases were diagnosed with adrenal insufficiency. Despite their basal serum ACTH and cortisol levels being low with little response to corticotropin-releasing hormone loading, other anterior pituitary hormone levels were preserved. Based on these endocrinological data, isolated ACTH deficiency was diagnosed. Magnetic resonance imaging showed normal pituitary glands, excluding hypophysitis. Finally, hydrocortisone replacement enabled the patients to continue nivolumab treatment. Therefore, it is important to consider isolated ACTH syndrome as a possible and potentially severe immune-related adverse event of nivolumab, even when head magnetic resonance imaging of affected cases does not show enlargement. We should not misdiagnose hidden immune-related adverse events behind general complaints of malignancies such as general malaise and appetite loss, to allow successful treatment using this beneficial immune checkpoint inhibitor.

The leukotriene B4 receptor BLT2 protects barrier function via actin polymerization with phosphorylation of myosin phosphatase target subunit 1 in human keratinocytes.

Leukotriene B4 (LTB4 ) receptor type 2 (BLT2) is a novel G-protein-coupled receptor, which selectively binds to 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid (12-HHT) with stronger affinity than to LTB4 . Recently, 12-HHT has been shown to have a protective effect on the epidermal barrier in human keratinocytes or transfectant cells overexpressing BLT2. Because the protective activity of BLT2 in high-calcium conditions, which occurs in well-differentiated cells, is exerted through increasing the integrity of tight junctions, we investigated the effects of 12-HHT on the barrier function of human keratinocytes in low-calcium conditions that mimic the basal layer; to our knowledge, this has not been reported previously. After stimulation with or without 12-HHT, barrier function was measured using transepithelial electrical resistance (TER) and dextran permeability assay. Expression levels of adhesion molecules and actin polymerization were also evaluated. Treatment with 12-HHT increased TER, along with decreased epidermal permeability of dextran in human keratinocytes. Furthermore, 12-HHT induced actin polymerization with phosphorylation of myosin phosphatase target subunit 1. These results suggest that the ligation of BLT2 protects permeability barrier function by enhancing cell-cell contact, even under low-calcium conditions, and indicate that a BLT2 agonist could be a novel therapeutic target for barrier-disrupted skin diseases.