MCL1 inhibition targets Myeloid Derived Suppressors Cells, promotes antitumor immunity and enhances the efficacy of immune checkpoint blockade

Immune checkpoint inhibitors (ICIs) are now the first-line treatment for patients with advanced melanoma. Despite promising clinical results, many patients fail to respond to these therapies. BH3 mimetics, a novel class of small molecule inhibitors that bind and inhibit anti-apoptotic members of the BCL2 family proteins such as BCL2 or MCL1, have been very successful in treating hematologic malignancies. However, there are limited studies on the immunomodulatory role of the BH3 mimetics. Several factors contribute to ICI resistance including myeloid-derived suppressor cells (MDSCs) that exert immunosuppressive effects through direct and indirect inhibition of antitumor immunity. Thus, targeting MDSCs to enhance antitumor immunity has the potential to enhance the efficacy of ICIs. In this study, we show that the MCL1 inhibitor S64315 reduces melanoma tumor growth in an immune cell-dependent manner in mice. Specifically, S64315 enhances antitumor immunity by reducing MDSC frequency and by promoting the activity of CD8+T cells. Additionally, human MDSCs are 10 times more sensitive to S64315 than cutaneous melanoma lines. Further, we found that a higher expression of MCL1 is associated with poor survival for patients treated with anti-PD-1. Finally, combining S64315 and anti-PD-1 significantly slowed tumor growth compared to either agent alone. Together, this proof-of-concept study demonstrates the potential of combining an MCL1 inhibitor with anti-PD-1 in the treatment of melanoma. It justifies the further development of next generation MCL1 inhibitors to improve efficacy of ICIs in treating malignant melanoma.

SASH1 interacts with TNKS2 and promotes human melanocyte stem cell maintenance

Both aging spots (hyperpigmentation) and hair graying (lack of pigmentation) are associated with aging, two seemingly opposite pigmentation phenotypes. It is not clear how they are mechanistically connected. This study investigated the underlying mechanism in a family with an inherited pigmentation disorder. Clinical examinations identified accelerated hair graying and skin dyspigmentation (intermixed hyper and hypopigmentation) in the family members carrying the SASH1 S519N variant. Cell assays indicated that SASH1 promoted stem-like characteristics in human melanocytes, and SASH1 S519N was defective in this function. Multiple assays showed that SASH1 binds to tankyrase 2 (TNKS2), which is required for SASH1's promotion of stem-like function. Further, the SASH1 S519N variant is in a bona fide Tankyrase-binding motif, and SASH1 S519N alters the binding kinetics and affinity. Results here indicate SASH1 as a novel protein regulating the appropriate balance between melanocyte stem cells (McSC) and mature melanocytes (MCs), with S519N variant causing defects. We propose that dysfunction of McSC maintenance connects multiple aging-associated pigmentation phenotypes in the general population.

Expression Differences in BCL2 Family Members between Uveal and Cutaneous Melanomas Account for Varying Sensitivity to BH3 Mimetics

Uveal melanoma (UM) is a subtype of melanoma. Although they share a melanocytic origin with cutaneous melanoma (CM), patients with UM have few treatment options. BCL2 homologous 3 mimetics are small-molecule drugs that mimic proapoptotic BCL2 family members. We compared BCL2 family member expression between UM and CM using immunoblot and The Cancer Genome Atlas transcriptomic analysis. UM has a unique signature of low BFL1 and high PUMA proteins compared with CM and 30 other cancer types, making them an attractive candidate for BCL2 homologous 3 protein mimetics. We tested the efficacy of a BCL2 inhibitor and MCL1 inhibitor (MCL1i) in UM, with viability assays, live-cell imaging, sphere assays, and mouse xenograft models. UM had a higher sensitivity to MCL1i than CM. Overexpression of BFL1 or knockdown of PUMA made the UM more resistant to MCL1i. In contrast, MAPK/extracellular signal‒regulated kinase inhibitor treatment in CM made them more sensitive to MCL1i. However, MCL1i-alone treatment was not very effective to reduce the UM initiating cells; to overcome this, we employed a combination of MCL1i with BCL2 inhibitor that synergistically inhibited UM initiating cell's capacity to expand. Overall, we identify a distinct expression profile of BCL2 family members for UM that makes them susceptible to BCL2 homologous 3 mimetics.

Loss of prdm1a accelerates melanoma onset and progression

Melanoma is an aggressive, deadly skin cancer derived from melanocytes, a neural crest cell derivative. Melanoma cells mirror the developmental program of neural crest cells in that they exhibit the same gene expression patterns and utilize similar cellular mechanisms, including increased cell proliferation, epithelial-mesenchymal transition, and migration. Here we studied the role of neural crest regulator PRDM1 in melanoma onset and progression. In development, Prdm1a functions to promote neural crest progenitor fate, and in melanoma, we found that PRDM1 has reduced copy number and is recurrently deleted in both zebrafish and humans. When examining expression of neural crest and melanocyte development genes, we show that sox10 progenitor expression is high in prdm1a-/- mutants, while more differentiated melanocyte markers are reduced, suggesting that normally Prdm1a is required for differentiation. Data mining of human melanoma datasets indicates that high PRDM1 expression in human melanoma is correlated with better patient survival and decreased PRDM1 expression is common in metastatic tumors. When one copy of prdm1a is lost in the zebrafish melanoma model Tg(mitfa:BRAFV600E );p53-/- ;prdm1a+/- , melanoma onset occurs more quickly, and the tumors that form have a larger area with increased expression of sox10. These data demonstrate a novel role for PRDM1 as a tumor suppressor in melanoma.

Melanocyte Precursors in the Hair Follicle Bulge of Repigmented Vitiligo Skin Are Controlled by RHO-GTPase, KCTD10, and CTNNB1 Signaling

In repigmentation of human vitiligo, the melanocyte (MC) precursors in the hair follicle bulge proliferate, migrate, and differentiate to repopulate the depigmented epidermis. Here, we present a comprehensive characterization of pathways and signals in the bulge that control the repigmentation process. Using biopsies from patients with vitiligo, we have selectively harvested, by laser capture microdissection, MC and keratinocyte precursors from the hair follicle bulge of untreated vitiligo skin and vitiligo skin treated with narrow-band UVB. The captured material was subjected to whole transcriptome RNA-sequencing. With this strategy, we found that repigmentation in the bulge MC precursors is driven by KCTD10, a signal with unknown roles in the skin, and CTNNB1 (encoding β-catenin) and RHO guanosine triphosphatase [RHO GTPase, RHO], two signaling pathways previously shown to be involved in pigmentation biology. Knockdown studies in cultured human MCs of RHOJ, the upmost differentially expressed RHO family component, corroborated with our findings in patients with vitiligo, identified RHOJ involvement in UV response and melanization, and confirmed previously identified roles in melanocytic cell migration and apoptosis. A better understanding of mechanisms that govern repigmentation in MC precursors will enable the discovery of molecules that induce robust repigmentation phenotypes in vitiligo.

Simultaneously Inhibiting BCL2 and MCL1 Is a Therapeutic Option for Patients with Advanced Melanoma

There is an urgent need to develop treatments for patients with melanoma who are refractory to or ineligible for immune checkpoint blockade, including patients who lack BRAF-V600E/K mutations. This is often the case in patients diagnosed with rare melanoma subtypes such as mucosal and acral melanoma. Here, we analyzed data from the cutaneous melanoma The Cancer Genome Atlas Network (TCGA) transcriptomic and proteomic databases for differential expression of apoptosis molecules between melanomas with or without BRAF hotspot mutations. Our data indicated higher B-cell CLL/lymphoma 2 (BCL2) expression in melanoma without BRAF hotspot mutations, suggesting that BH3 mimetics, such as ABT-199 (venetoclax, a small molecule against BCL2), may be a potential therapeutic option for these patients. We explored the efficacy of combining two BH3 mimetics, ABT-199 and a myeloid cell leukemia sequence 1 (MCL1) inhibitor (S63845 or S64315/MIK665) in cutaneous, mucosal and acral melanomas, in vitro and in vivo. Our data indicate this combination induced cell death in a broad range of melanoma cell lines, including melanoma initiating cell populations, and was more potent in melanoma cells without BRAF-V600E/K mutations. Our knockdown/knockout experiments suggest that several pro-apoptotic BCL2 family members, BCL2-like 11 (apoptosis facilitator) (BIM), phorbol-12-myristate-13-acetate-induced protein 1 (NOXA) or BID, play a role in the combination-induced effects. Overall, our study supports the rationale for combining an MCL1 inhibitor with a BCL2 inhibitor as a therapeutic option in patients with advanced melanoma.

MCL1 inhibitors S63845/MIK665 plus Navitoclax synergistically kill difficult-to-treat melanoma cells

Current treatment for patients with metastatic melanoma include molecular-targeted therapies and immune checkpoint inhibitors. However, a subset of melanomas are difficult-to-treat. These melanomas include those without the genetic markers for targeted therapy, non-responsive to immunotherapy, and those who have relapsed or exhausted their therapeutic options. Therefore, it is necessary to understand and explore other biological processes that may provide new therapeutic approaches. One of most appealing is targeting the apoptotic/anti-apoptotic system that is effective against leukemia. We used genetic knockdown and pharmacologic approaches of BH3 mimetics to target anti-apoptotic BCL2 family members and identified MCL1 and BCLXL as crucial pro-survival members in melanoma. We then examined the effects of combining BH3 mimetics to target MCL1 and BCLXL in vitro and in vivo. These include clinical-trial-ready compounds such as ABT-263 (Navitoclax) and S63845/S64315 (MIK655). We used cell lines derived from patients with difficult-to-treat melanomas. In vitro, the combined inhibition of MCL1 and BCLXL resulted in significantly effective cell killing compared to single-agent treatment (p < 0.05) in multiple assays, including sphere assays. The combination-induced cell death was independent of BIM, and NOXA. Recapitulated in our mouse xenograft model, the combination inhibited tumor growth, reduced sphere-forming capacity (p < 0.01 and 0.05, respectively), and had tolerable toxicity (p > 0.40). Taken together, this study suggests that dual targeting of MCL1 and BCLXL should be considered as a treatment option for difficult-to-treat melanoma patients.

Residential greenness and allergic respiratory diseases in children and adolescents - A systematic review and meta-analysis

BACKGROUND

The aetiology of allergic respiratory disease in children is not yet fully understood. Environmental factors are believed to play a major part. The amount of green vegetation surrounding the home (residential greenness) has been recently identified as a potentially important exposure OBJECTIVES: Our goal was to provide a systematic review and quantitative summary of the evidence regarding the relationship between residential greenness and allergic respiratory diseases in children.

METHODS

Peer-reviewed literature published prior to 1 March 2017 was systematically searched using nine electronic databases. Meta-analyses were conducted if at least three studies published risk estimates for the same outcome and exposure measures.

RESULTS

We included 11 articles across broad outcomes of asthma and allergic rhinitis. Reported effects were inconsistent with varying measures to define residential greenness. Only limited meta-analysis could be conducted, with the pooled odds ratios for asthma (OR 1.01 95%CI 0.93, 1.09; I² 68.1%) and allergic rhinitis (OR 0.99 95%CI 0.87, 1.12; I² 72.9%) being significantly heterogeneous.

CONCLUSIONS

Inconsistencies between the studies were too large to accurately assess the association between residential greenness and allergic respiratory disease. A standardised global measure of greenness which accounts for seasonal variation at a specific relevant buffer size is needed to create a more cohesive body of evidence and for future examination of the effect of residential greenness on allergic respiratory diseases.

Repigmentation of Human Vitiligo Skin by NBUVB Is Controlled by Transcription of GLI1 and Activation of the β-Catenin Pathway in the Hair Follicle Bulge Stem Cells

Vitiligo repigmentation is a complex process in which the melanocyte-depleted interfollicular epidermis is repopulated by melanocyte precursors from hair follicle bulge that proliferate, migrate, and differentiate into mature melanocytes on their way to the epidermis. The strongest stimulus for vitiligo repigmentation is narrow-band UVB (NBUVB), but how the hair follicle melanocyte precursors are activated by UV light has not been extensively studied. To better understand this process, we developed an application that combined laser capture microdissection and subsequent whole transcriptome RNA sequencing of hair follicle bulge melanocyte precursors and compared their gene signatures to that of regenerated mature epidermal melanocytes from NBUVB-treated vitiligo skin. Using this strategy, we found up-regulation of TNC, GJB6, and THBS1 in the hair follicle bulge melanocytes and of TYR in the epidermal melanocytes of the NBUVB-treated vitiligo skin. We validated these results by quantitative real-time-PCR using NBUVB-treated vitiligo skin and untreated normal skin. We also identified that GLI1, a candidate stem cell-associated gene, is significantly up-regulated in the melanocytes captured from NBUVB-treated vitiligo bulge compared with untreated vitiligo bulge. These signals are potential key players in the activation of bulge melanocyte precursors during vitiligo repigmentation.

Acute effects of cell isolation on InsP profiles in adult rat cardiomyocytes

The isolation and culture of adult rat cardiomyocytes was shown to cause major changes in the contents of [3H]-labeled inositol phosphates and inositol phospholipids. Undigested heart tissue contained high levels of [3H]Ins(1,4,5)P3 (5364+/-800 ct/min/g tissue, 80+/-12 ct/min/mg protein) and mass content averaged 13.8 nmol/g tissue or 208+/-36 pmol/mg protein (mean+/-S.E.M., n=4). After collagenase digestion, [3H]Ins(1,4,5)P3 was undetectable and the mass content of Ins(1,4,5)P3 had decreased to 0.8+/-0.2 pmol/mg protein (mean+/-S.E.M., n=4, P<0.01). [3H]Ins(1,4)P2 was reduced by 80% and [3H]PtdIns(4,5)P2 by 90%. These profiles remained essentially unchanged when the isolated cells were maintained in culture for up to 24 h, even though the inositol phosphate response remained sensitive to norepinephrine. Similar to findings in intact tissue, the inositol phosphate response to norepinephrine in these cells was inhibited by neither U-73122 (5 microM) nor by neomycin (5 mM). By 48 h in culture, the relative levels of [3H]Ins(1,4,5)P3 and [3H]Ins(1,4)P2 had increased in relation to the total inositol phosphate content and responses appeared to better reflect intact tissue. However, while retaining insensitivity to neomycin, cells at 48 h were fully sensitive to U-73122 (5 microM). These data demonstrate that altered inositol phosphate responses are observed in adult cardiomyocytes from the time of isolation and that while the profiles change over time in culture, a pattern similar to that in intact heart is not re-established.

Inositol phosphate metabolism during myocardial ischemia

Inositol phosphate release in intact heart in response to norepinephrine involves primarily release of inositol(1,4)bisphosphate (Ins(1,4)P2) rather than inositol(1,4,5)trisphosphate (Ins(1,4,5)P3) but Ins(1,4,5)P3 release predominates under conditions of post-ischemic reperfusion. In the current study, effects of myocardial ischemia on inositol phosphate responses were examined. Global myocardial ischemia in rat ventricle caused a reduction in the content of [3H]Ins(1,4)P3 (70-90%) and [3H]Ins(1,4,5)P3 (46%) and altered the pattern of norepinephrine stimulation such that increases in [3H]Ins(1,4,5)P3 were observed. Simulated ischemia in isolated right atria or isolated ventricular myocytes (P alpha 2 16-20 mmHg. pH 6.7. KCl 10 mM) produced similar changes. Reduction in O2 in the absence of other changes reduced the content of [3H]Ins (1,4)P2 (79%) in right atria whereas hypoxia and reduced pH were required to alter the [3H]Ins(1,4,5)P3 response. Progressive reduction in atrial ATP content using metabolic inhibitors caused a parallel decrease in [3H]Ins(1,4,5)P3 content (r = 0.96) without affecting [3H]Ins(1,4)P2 or the isomers of InsP1, showing that levels of Ins(1,4)P2 and Ins(1,4,5)P3 are regulated differently in the heart. These findings show that effects of ischemia on inositol phosphates in heart are complex and multifactorial, with Ins(1,4)P2 being affected under more moderately ischemic conditions than required for alterations in Ins(1,4,5)P3. These studies also demonstrate that ischemia produces similar effects on the release and metabolism of inositol phosphates in heart regardless of the ischemic model or the myocardial preparation used.

Ins(1,4,5)P3 during myocardial ischemia and its relationship to the development of arrhythmias

Reperfusion of globally ischemic rat hearts in vitro causes release of inositol(1,4,5) trisphosphate (Ins(1,4,5)P3) which is associated with the development of reperfusion arrhythmias. Both of these responses require the presence of a receptor agonist, either norepinephrine or thrombin, and both responses are inhibited by the aminoglycoside, gentamicin and the polyamine, spermine. In the current study, the role of Ins(1,4,5)P3 in the development of arrhythmias under ischemic conditions was addressed. Arrhythmias [ventricular premature beats, ventricular tachycardia and ventricular fibrillation (VF)] occurring over 25 min subsequent to coronary artery ligation were shown to be independent of endogenous norepinephrine or adrenergic receptor stimulation but were effectively inhibited by gentamicin (0.15-1.5 mM, 95% VF in controls compared with 0% VF, at 1.5 mM, P < 0.01) and spermine (5 mM, 40% VF, P < 0.01). Depletion of Ca2+ stores, including Ins(1,4,5)P3-sensitive Ca2+ stores, with thapsigargin (300 nM) reduced the incidence of ischemic arrhythmias (40% VF, P < 0.01). [3H]-Inositol-labeled right atria incubated under conditions of simulated ischemia retained the ability to respond to norepinephrine by releasing inositol phosphates. Under ischemic conditions, gentamicin (1.5 mM) caused a reduction in [3H]Ins(1,4,5)P3 without any effect on the other inositol phosphates. Similar effects of gentamicin were observed under ischemic conditions in the absence of norepinephrine (95 +/- 8 cpm/mg, mean +/- S.E.M., n = 4, v 29 +/- 4, P < 0.0] for 1.5 mM gentamicin). Agonist independent release of [3H]Ins(1,4,5)P3 under ischemic conditions required extracellular Ca2+ suggesting the operation of a Ca(2+)-activated phospholipase C. In agreement with this, release of [3H]Ins(1,4,5)P3 could be initiated by Ca2+ overload under normoxic conditions and this was inhibited by gentamicin. These findings show that Ca2+ overload can enhance release of Ins(1,4,5)P3 under ischemic conditions and provide evidence that this release is involved in the genesis of arrhythmias under these conditions.

Arrhythmogenic action of thrombin during myocardial reperfusion via release of inositol 1,4,5-triphosphate

BACKGROUND

Cardiac reperfusion initiates release of inositol 1,4,5-triphosphate [Ins(1,4,5)P3] and arrhythmogenesis via norepinephrine stimulation of alpha1-adrenergic receptors. The present study examines arrhythmogenic effects of thrombin-stimulated Ins(1,4,5)P3 release under these conditions.

METHODS AND RESULTS

[3H]Ins(1,4,5)P3 release was measured in [3H]inositol-labeled rat hearts by high-performance liquid chromatography. Arrhythmia studies were performed in buffer-perfused rat hearts. Two-minute reperfusion after 20 minutes of global ischemia increased [3H]Ins(1,4,5)P3 from 1123 +/- 77 to 2238 +/- 44 cpm/mg tissue. No increase was observed in catecholamine-depleted hearts (755 +/- 89 cpm/mg). The addition of thrombin (5 IU/mL) or thrombin receptor agonist peptide (TRAP(1-6), 50 micromol/L) restored the reperfusion Ins(1,4,5)P3 response (thrombin, 1518 +/- 68 cpm/mg and TRAP(1-6), 1755 +/- 128 cpm/mg). Ins(1,4,5)P3 release initiated by norepinephrine or thrombin was inhibited by gentamicin (150 micromol/L; 986 +/- 52 and 868 +/- 125 cpm/mg, respectively). The thrombin response was inhibited by the phospholipase C inhibitor U-73122 (5 micromol/L; 394 +/- 59 cpm/mg) but not by its inactive isomer U-73343. The norepinephrine response was not inhibited by U-73122 (2126 +/- 74 cpm/mg). Ventricular tachycardia and ventricular fibrillation were observed in intact hearts but not in hearts from catecholamine-depleted rats (ventricular fibrillation duration, 110 +/- 19 versus 0 +/- 0 seconds). The addition of thrombin or TRAP(1-6) increased arrhythmias in catecholamine-depleted hearts (112 +/- 32 and 89 +/- 28 seconds, respectively). Gentamicin and U-73122 but not U-73343 prevented thrombin-induced arrhythmias. Gentamicin inhibited norepinephrine-initiated arrhythmias, but U-73122 was ineffective.

CONCLUSIONS

This study demonstrates that the development of reperfusion arrhythmias under these conditions depends on the release of Ins(1,4,5)P3.

The inositol phosphate response to thrombin in rat right atria differs from the response to noradrenaline

Addition of thrombin to isolated [3H]inositol-labelled rat right atria stimulated the release of 3H-labelled inositol phosphates. The thrombin response was smaller than the response to noradrenaline and generated a different spectrum of inositol phosphates. Unlike the inositol phosphate response to noradrenaline, the thrombin response was inhibited by pertussis toxin treatment and by the phospholipase C inhibitor U-73122 (1-(6-((17 beta-3- methoxyestra-1,3,5(10)-trien-17-yl)amino)amino)hexyl)-1H- pyrrole-2, 5-dione). The data indicate that the thrombin stimulation involves different G-proteins and phospholipase C isoforms from those which couple alpha 1-adrenoceptors in the myocardium.

The norepinephrine-stimulated inositol phosphate response in human atria

Inositol phosphate release and metabolism were studied in right atrial appendages obtained from 18 patients undergoing coronary artery bypass surgery and/or mitral valve replacement. [3H]Inositol-labeled human atria contained inositol(1,4. 5)trisphosphate, inositol(1,4)bisphosphate and the 1- (or 3) and 4-isomers of inositol monophosphate. Addition of norepinephrine (100 mumol/l) activated the release of inositol phosphates, as indicated by increased [3H]inositol label in all of these inositol phosphates. However, the phosphorylation product of inositol (1.4.5)trisphosphate, inositol-(1,3,4,5)tetrakisphosphate, and its metabolic products were not detected, either in control or stimulated atria. Similar inositol phosphate profiles were observed in rat right atria. Furthermore, both human and rat atria contained high concentrations of inositol(1,4,5)trisphosphate, which were not observed to increase with norepinephrine stimulation. The inositol phosphate responses to norepinephrine in rat and human cardiac tissue appear to be similar, except for the generally lower activity observed in human tissue. Thus, the rat provides a suitable model for the study of cardiac phosphatidylinositol turnover.