Identification of the B-Raf/Mek/Erk MAP kinase pathway as a target for all-trans retinoic acid during skin cancer promotion

OSBPL2 compound heterozygous variants cause dyschromatosis, ichthyosis, deafness and atopic disease syndrome

PURPOSE

In this study, we identified and diagnosed a novel inherited condition called Dyschromatosis, Ichthyosis, Deafness, and Atopic Disease (DIDA) syndrome. We present a series of studies to clarify the pathogenic variants and specific mechanism.

METHODS

Exome sequencing and Sanger sequencing was conducted in affected and unaffected family members. A variety of human and cell studies were performed to explore the pathogenic process of keratosis.

RESULTS

Our finding indicated that DIDA syndrome was caused by compound heterozygous variants in the oxysterol-binding protein-related protein 2 (OSBPL2) gene. Furthermore, our findings revealed a direct interaction between OSBPL2 and Phosphoinositide phospholipase C-beta-3 (PLCB3), a key player in hyperkeratosis. OSBPL2 effectively inhibits the ubiquitylation of PLCB3, thereby stabilizing PLCB3. Conversely, OSBPL2 variants lead to enhanced ubiquitination and subsequent degradation of PLCB3, leading to epidermal hyperkeratosis, characterized by aberrant proliferation and delayed terminal differentiation of keratinocytes.

CONCLUSIONS

Our study not only unveiled the association between OSBPL2 variants and the newly identified DIDA syndrome but also shed light on the underlying mechanism.

ALDH1A1 confers resistance to RAF/MEK inhibitors in melanoma cells by maintaining stemness phenotype and activating PI3K/AKT signaling

The mitogen-activated protein kinase (MAPK/ERK) pathway is pivotal in controlling the proliferation and survival of melanoma cells. Several mutations, including those in BRAF, exhibit an oncogenic effect leading to increased cellular proliferation. As a result, the combination therapy of a MEK inhibitor with a BRAF inhibitor demonstrated higher efficacy and lower toxicity than BRAF inhibitor alone. This combination has become the preferred standard of care for tumors driven by BRAF mutations. Aldehyde dehydrogenase 1A1 (ALDH1A1) is a known marker of stemness involved in drug resistance in several type of tumors, including melanoma. This study demonstrates that melanoma cells overexpressing ALDH1A1 displayed resistance to vemurafenib and trametinib through the activation of PI3K/AKT signaling instead of MAPK axis. Inhibition of PI3K/AKT signaling partially rescued sensitivity to the drugs. Consistently, pharmacological inhibition of ALDH1A1 activity downregulated the activation of AKT and partially recovered responsiveness to vemurafenib and trametinib. We propose ALDH1A1 as a new potential target for treating melanoma resistant to MAPK/ERK inhibitors.

Jagged1 contained in MSC-derived small extracellular vesicles promotes squamous differentiation of cervical cancer by activating NOTCH pathway

PURPOSE

Cervical cancer is the fourth most common cancer in women and poses a major threat to women's health, urgently requiring new treatment methods.

METHODS

This study first successfully extracted and identified small extracellular vesicles secreted by human umbilical cord-derived mesenchymal stem cells. We studied the effects of MSC-sEV on the squamous differentiation levels of cervical cancer CaSki cells in vitro, and explored the effects of MSC-sEV on the NOTCH pathway, the growth, proliferation, migration abilities and squamous differentiation levels of cervical cancer cells. The roles of MSC-sEV were also verified in human keratinocyte HaCaT cells.

RESULTS

The results showed that Jagged1 protein on MSC-sEV can bind to NOTCH1 on cervical cancer cells, activate NOTCH signaling, and promote squamous differentiation levels in CaSki cells, thus inhibiting the growth, proliferation and migration abilities of CaSki cells. MSC-sEV can also activate the NOTCH pathway in HaCaT cells, but promote the viability of HaCaT cells.

CONCLUSION

MSC-sEV can activate the NOTCH pathway to promote squamous differentiation of CaSki cells and inhibit the growth proliferation and migration abilities of CaSki cells which may be a new mechanism for cervical cancer treatment.

The Use of Retinoids for the Prevention and Treatment of Skin Cancers: An Updated Review

Retinoids are natural and synthetic vitamin A derivatives that are effective for the prevention and the treatment of non-melanoma skin cancers (NMSC). NMSCs constitute a heterogenous group of non-melanocyte-derived skin cancers that impose substantial burdens on patients and healthcare systems. They include entities such as basal cell carcinoma and cutaneous squamous cell carcinoma (collectively called keratinocyte carcinomas), cutaneous lymphomas and Kaposi’s sarcoma among others. The retinoid signaling pathway plays influential roles in skin physiology and pathology. These compounds regulate diverse biological processes within the skin, including proliferation, differentiation, angiogenesis and immune regulation. Collectively, retinoids can suppress skin carcinogenesis. Both topical and systemic retinoids have been investigated in clinical trials as NMSC prophylactics and treatments. Desirable efficacy and tolerability in clinical trials have prompted health regulatory bodies to approve the use of retinoids for NMSC management. Acceptable off-label uses of these compounds as drugs for skin cancers are also described. This review is a comprehensive outline on the biochemistry of retinoids, their activities in the skin, their effects on cancer cells and their adoption in clinical practice.

Pterygium-The Good, the Bad, and the Ugly

Pterygium is a multifaceted pathology that displays apparent conflicting characteristics: benign (e.g., self-limiting and superficial), bad (e.g., proliferative and potentially recurrent) and ugly (e.g., signs of preneoplastic transformation). The natural successive question is: why are we lacking reports showing that pterygium lesions become life-threatening through metastasis, especially since pterygium has considerable similarities with UV-related malignancies on the molecular level? In this review, we consider how our pathophysiological understanding of the benign pterygium pathology overlaps with ocular surface squamous neoplasia and skin cancer. The three UV-related disorders share the same initial insult (i.e., UV radiation) and responsive repair mechanisms to the ensuing (in)direct DNA damage. Their downstream apoptotic regulators and other cellular adaptations are remarkably alike. However, a complicating factor in understanding the fine line between the self-limiting nature of pterygium and the malignant transformation in other UV-related diseases is the prominent ambiguity in the pathological evaluation of pterygium biopsies. Features of preneoplastic transformation (i.e., dysplasia) are used to define normal cellular reactions (i.e., atypia and metaplasia) and vice versa. A uniform grading system could help in unraveling the true nature of this ancient disease and potentially help in identifying the earliest intervention point possible regarding the cellular switch that drives a cell’s fate towards cancer.

Trifarotene: A Current Review and Perspectives in Dermatology

Retinoids have numerous applications in inflammatory, dyskeratotic, and oncohematology diseases. Retinoids have now reached the fourth generation, progressively reducing toxicity whilst increasing their efficacy. Trifarotene is a new fourth-generation retinoid with a selective action on RAR-γ. In this review, we reported the trials—both concluded and in progress—including the use of trifarotene in dermatological diseases. Studies were identified by searching electronic databases (MEDLINE, EMBASE, PubMed, Cochrane, Trials.gov) from 2012 to today and reference lists of respective articles. Only articles published in English language were included. Randomized trials evaluating trifarotene tolerability, safety, and efficacy in congenital ichthyosis and acne have demonstrated great results and mild side effects, leading to the approval by the FDA of trifarotene for the treatment of lamellar ichthyosis in 2014, and of acne vulgaris in October 2019. No high-quality randomized clinical trials have evaluated the treatment of primary cutaneous lymphomas with trifarotene. Finally, we are hypothesizing future perspectives in the treatment of non-melanoma skin cancers, fungal infections, photoaging, and hand-foot skin reactions with trifarotene.

Retinoids in Cutaneous Squamous Cell Carcinoma

Animal studies as early as the 1920s suggested that vitamin A deficiency leads to squamous cell metaplasia in numerous epithelial tissues including the skin. However, humans usually die from vitamin A deficiency before cancers have time to develop. A recent long-term cohort study found that high dietary vitamin A reduced the risk of cutaneous squamous cell carcinoma (cSCC). cSCC is a form of nonmelanoma skin cancer that primarily occurs from excess exposure to ultraviolet light B (UVB). These cancers are expensive to treat and can lead to metastasis and death. Oral synthetic retinoids prevent the reoccurrence of cSCC, but side effects limit their use in chemoprevention. Several proteins involved in vitamin A metabolism and signaling are altered in cSCC, which may lead to retinoid resistance. The expression of vitamin A metabolism proteins may also have prognostic value. This article reviews what is known about natural and synthetic retinoids and their metabolism in cSCC.

Consensus on the use of oral isotretinoin in dermatology - Brazilian Society of Dermatology

BACKGROUND

Isotretinoin is a synthetic retinoid, derived from vitamin A, with multiple mechanisms of action and highly effective in the treatment of acne, despite common adverse events, manageable and dose-dependent. Dose-independent teratogenicity is the most serious. Therefore, off-label prescriptions require strict criteria.

OBJECTIVE

To communicate the experience and recommendation of Brazilian dermatologists on oral use of the drug in dermatology.

METHODS

Eight experts from five universities were appointed by the Brazilian Society of Dermatology to develop a consensus on indications for this drug. Through the adapted DELPHI methodology, relevant elements were listed and an extensive analysis of the literature was carried out. The consensus was defined with the approval of at least 70% of the experts.

RESULTS

With 100% approval from the authors, there was no doubt about the efficacy of oral isotretinoin in the treatment of acne, including as an adjunct in the correction of scars. Common and manageable common adverse events are mucocutaneous in nature. Others, such as growth retardation, abnormal healing, depression, and inflammatory bowel disease have been thoroughly investigated, and there is no evidence of a causal association; they are rare, individual, and should not contraindicate the use of the drug. Regarding unapproved indications, it may represent an option in cases of refractory rosacea, severe seborrheic dermatitis, stabilization of field cancerization with advanced photoaging and, although incipient, frontal fibrosing alopecia. For keratinization disorders, acitretin performs better. In the opinion of the authors, indications for purely esthetic purposes or oil control are not recommended, particularly for women of childbearing age.

CONCLUSIONS

Approved and non-approved indications, efficacy and adverse effects of oral isotretinoin in dermatology were presented and critically evaluated.

A Conserved Amino Acid in the C Terminus of Human Papillomavirus E7 Mediates Binding to PTPN14 and Repression of Epithelial Differentiation

The human papillomavirus (HPV) E7 oncoprotein is a primary driver of HPV-mediated carcinogenesis. The E7 proteins from diverse HPVs bind to the host cellular nonreceptor protein tyrosine phosphatase type 14 (PTPN14) and direct it for degradation through the activity of the E7-associated host E3 ubiquitin ligase UBR4. Here, we show that a highly conserved arginine residue in the C-terminal domain of diverse HPV E7 mediates the interaction with PTPN14. We found that disruption of PTPN14 binding through mutation of the C-terminal arginine did not impact the ability of several high-risk HPV E7 proteins to bind and degrade the retinoblastoma tumor suppressor or activate E2F target gene expression. HPVs infect human keratinocytes, and we previously reported that both PTPN14 degradation by HPV16 E7 and PTPN14 CRISPR knockout repress keratinocyte differentiation-related genes. Now, we have found that blocking PTPN14 binding through mutation of the conserved C-terminal arginine rendered both HPV16 and HPV18 E7 unable to repress differentiation-related gene expression. We then confirmed that the HPV18 E7 variant that could not bind PTPN14 was also impaired in repressing differentiation when expressed from the complete HPV18 genome. Finally, we found that the ability of HPV18 E7 to extend the life span of primary human keratinocytes required PTPN14 binding. CRISPR/Cas9 knockout of PTPN14 rescued keratinocyte life span extension in the presence of the PTPN14 binding-deficient HPV18 E7 variant. These results support the model that PTPN14 degradation by high-risk HPV E7 leads to repression of differentiation and contributes to its carcinogenic activity.IMPORTANCE The E7 oncoprotein is a primary driver of HPV-mediated carcinogenesis. HPV E7 binds the putative tumor suppressor PTPN14 and targets it for degradation using the ubiquitin ligase UBR4. PTPN14 binds to a C-terminal arginine highly conserved in diverse HPV E7. Our previous efforts to understand how PTPN14 degradation contributes to the carcinogenic activity of high-risk HPV E7 used variants of E7 unable to bind to UBR4. Now, by directly manipulating E7 binding to PTPN14 and using a PTPN14 knockout rescue experiment, we demonstrate that the degradation of PTPN14 is required for high-risk HPV18 E7 to extend keratinocyte life span. Our data show that PTPN14 binding by HPV16 E7 and HPV18 E7 represses keratinocyte differentiation. HPV-positive cancers are frequently poorly differentiated, and the HPV life cycle depends upon keratinocyte differentiation. The finding that PTPN14 binding by HPV E7 impairs differentiation has significant implications for HPV-mediated carcinogenesis and the HPV life cycle.

Retinoic acid receptor γ activation promotes differentiation of human induced pluripotent stem cells into esophageal epithelium

BACKGROUND

The esophagus is known to be derived from the foregut. However, the mechanisms regulating this process remain unclear. In particular, the details of the human esophagus itself have been poorly researched. In this decade, studies using human induced pluripotent stem cells (hiPSCs) have proven powerful tools for clarifying the developmental biology of various human organs. Several studies using hiPSCs have demonstrated that retinoic acid (RA) signaling promotes the differentiation of foregut into tissues such as lung and pancreas. However, the effect of RA signaling on the differentiation of foregut into esophagus remains unclear.

METHODS

We established a novel stepwise protocol with transwell culture and an air-liquid interface system for esophageal epithelial cell (EEC) differentiation from hiPSCs. We then evaluated the effect of all-trans retinoic acid (ATRA), which is a retinoic acid receptor (RAR)α, RARβ and RARγ agonist, on the differentiation from the hiPSC-derived foregut. Finally, to identify which RAR subtype was involved in the differentiation, we used synthetic agonists and antagonists of RARα and RARγ, which are known to be expressed in esophagus.

RESULTS

We successfully generated stratified layers of cells expressing EEC marker genes that were positive for lugol staining. The enhancing effect of ATRA on EEC differentiation was clearly demonstrated with quantitative reverse transcription polymerase chain reaction, immunohistology, lugol-staining and RNA sequencing analyses. RARγ agonist and antagonist enhanced and suppressed EEC differentiation, respectively. RARα agonist had no effect on the differentiation.

CONCLUSION

We revealed that RARγ activation promotes the differentiation of hiPSCs-derived foregut into EECs.

A, Bava SV, Sundaram S, Retnakumari AP, Chittalakkottu S, Anto RJ. Pre-clinical evidences for the efficacy of tryptanthrin as a potent suppressor of skin cancer

OBJECTIVE

Clinical trials have demonstrated the efficacy of indigo naturalis, a traditional Chinese medicine ingredient, against psoriasis, a skin disease characterized by keratinocyte hyperproliferation and inflammation. The present study investigates the efficacy of tryptanthrin, a bioactive compound in indigo naturalis, against non-melanoma skin cancer (NMSC) and the signalling events involved.

METHODS

Efficacy of tryptanthrin against NMSC was assessed using DMBA/PMA-induced skin carcinogenesis model in Swiss albino mice. Immunostaining for PCNA and ki-67 was used to mark proliferating cells in tissues. Haematoxylin and eosin staining and toluidine staining were employed to assess inflammation, and TUNEL assay was used to detect apoptosis in tissues. The signalling events were evaluated using Western blot, imunohistochemistry and immunofluorescence staining. MTT assay and clonogenic assay were performed to assess the viability and proliferation of cancer cells, in vitro.

RESULTS

In mice, topical application of tryptanthrin suppressed skin carcinogenesis. It attenuated inflammation, impeded the proliferation of hair follicle (HF) cells and suppressed the activation of β-catenin, a major driver of HF cell proliferation. Additionally tryptanthrin suppressed the activation of ERK1/2 and p38, both of which promote β-catenin activation and lowered the expression of c-Myc and cyclin-D1. Tryptanthrin suppressed the proliferation of the human NMSC cell line, A431 and abrogated EGF-induced activation of β-catenin and subsequent cytoskeletal rearrangement.

CONCLUSION

The study demonstrates with molecular evidence that tryptanthrin is an effective suppressor of NMSC.

A new regulatory mechanism for Raf kinase activation, retinoic acid-bound Crabp1

The rapidly accelerated fibrosarcoma (Raf) kinase is canonically activated by growth factors that regulate multiple cellular processes. In this kinase cascade Raf activation ultimately results in extracellular regulated kinase 1/2 (Erk1/2) activation, which requires Ras binding to the Ras binding domain (RBD) of Raf. We recently reported that all-trans retinoic acid (atRA) rapidly (within minutes) activates Erk1/2 to modulate cell cycle progression in stem cells, which is mediated by cellular retinoic acid binding protein 1 (Crabp1). But how atRA-bound Crabp1 regulated Erk1/2 activity remained unclear. We now report Raf kinase as the direct target of atRA-Crabp1. Molecularly, Crabp1 acts as a novel atRA-inducible scaffold protein for Raf/Mek/Erk in cells without growth factor stimulation. However, Crabp1 can also compete with Ras for direct interaction with the RBD of Raf, thereby negatively modulating growth factor-stimulated Raf activation, which can be enhanced by atRA binding to Crabp1. NMR heteronuclear single quantum coherence (HSQC) analyses reveal the 6-strand β-sheet face of Crabp1 as its Raf-interaction surface. We identify a new atRA-mimicking and Crabp1-selective compound, C3, that can also elicit such an activity. This study uncovers a new signal crosstalk between endocrine (atRA-Crabp1) and growth factor (Ras-Raf) pathways, providing evidence for atRA-Crabp1 as a novel modulator of cell growth. The study also suggests a new therapeutic strategy by employing Crabp1-selective compounds to dampen growth factor stimulation while circumventing RAR-mediated retinoid toxicity.

Manipulation of Epithelial Differentiation by HPV Oncoproteins

Papillomaviruses replicate and cause disease in stratified squamous epithelia. Epithelial differentiation is essential for the progression of papillomavirus replication, but differentiation is also impaired by papillomavirus-encoded proteins. The papillomavirus E6 and E7 oncoproteins partially inhibit and/or delay epithelial differentiation and some of the mechanisms by which they do so are beginning to be defined. This review will outline the key features of the relationship between HPV infection and differentiation and will summarize the data indicating that papillomaviruses alter epithelial differentiation. It will describe what is known so far and will highlight open questions about the differentiation-inhibitory mechanisms employed by the papillomaviruses.

UAB30, a novel RXR agonist, decreases tumorigenesis and leptomeningeal disease in group 3 medulloblastoma patient-derived xenografts

BACKGROUND

Group 3 tumors account for approximately 25-30% of medulloblastomas and have the worst prognosis. UAB30 is a novel synthetic rexinoid shown to have limited toxicities in humans and significant efficacy in the pediatric neuroectodermal tumor, neuroblastoma. We hypothesized that treatment with UAB30 would decrease tumorigenicity in medulloblastoma patient-derived xenografts (PDXs).

METHODS

Three group 3 medulloblastoma PDXs (D341, D384 and D425) were utilized. Cell viability, proliferation, migration and invasion assays were performed after treatment with UAB30 or 13-cis-retinoic acid (RA). Cell cycle analysis was completed using flow cytometry. A flank model, a cerebellar model, and a model of leptomeningeal metastasis using human medulloblastoma PDX cells was used to assess the in vivo effects of UAB30 and RA.

RESULTS

UAB30 treatment led to cell differentiation and decreased medulloblastoma PDX cell viability, proliferation, migration and invasion and G1 cell cycle arrest in all three PDXs similar to RA. UAB30 and RA treatment of mice bearing medulloblastoma PDX tumors resulted in a significant decrease in tumor growth and metastasis compared to vehicle treated animals.

CONCLUSIONS

UAB30 decreased viability, proliferation, and motility in group 3 medulloblastoma PDX cells and significantly decreased tumor growth in vivo in a fashion similar to RA, suggesting that further investigations into the potential therapeutic application of UAB30 for medulloblastoma are warranted.

A novel retinoid X receptor agonist, UAB30, inhibits rhabdomyosarcoma cells in vitro

BACKGROUND

While patients with early-stage rhabdomyosarcoma (RMS) have seen steady improvement in prognosis over the last 50 y, those with advanced-stage or high-grade disease continue to have a dismal prognosis. Retinoids have been shown to cause growth suppression and terminal differentiation in RMS cells, but the toxicities associated with retinoic acid limit its use. Rexinoids provide an alternative treatment approach to retinoic acid. Rexinoids primarily bind the retinoid X receptor with minimal retinoic acid receptor binding, the entity responsible for many of the toxicities of retinoid therapies. UAB30 is a novel rexinoid with limited toxicities. We hypothesized that UAB30 would lead to decreased cell survival in RMS.

MATERIALS AND METHODS

Two RMS cell lines, one embryonal (RD) subtype and one alveolar (St. Jude Cancer Research Hospital 30) subtype, were used. Cells were treated with UAB30, and cytotoxicity, proliferation, mobility, and apoptosis were evaluated.

RESULTS

UAB30 significantly decreased RMS tumor cell viability and proliferation. Invasion, migration, and attachment-independent growth were reduced following UAB30 treatment. UAB30 also resulted in apoptosis and G1 cell cycle arrest. UAB30 affected both the alveolar and embryonal RMS cell lines in a similar fashion.

CONCLUSIONS

The results of these studies suggest a potential therapeutic role for the low-toxicity synthetic retinoid X receptor selective agonist, UAB30, in RMS treatment.

Molecular signaling cascades involved in nonmelanoma skin carcinogenesis

Nonmelanoma skin cancer (NMSC) is the most common cancer worldwide and the incidence continues to rise, in part due to increasing numbers in high-risk groups such as organ transplant recipients and those taking photosensitizing medications. The most significant risk factor for NMSC is ultraviolet radiation (UVR) from sunlight, specifically UVB, which is the leading cause of DNA damage, photoaging, and malignant transformation in the skin. Activation of apoptosis following UVR exposure allows the elimination of irreversibly damaged cells that may harbor oncogenic mutations. However, UVR also activates signaling cascades that promote the survival of these potentially cancerous cells, resulting in tumor initiation. Thus, the UVR-induced stress response in the skin is multifaceted and requires coordinated activation of numerous pathways controlling DNA damage repair, inflammation, and kinase-mediated signal transduction that lead to either cell survival or cell death. This review focuses on the central signaling mechanisms that respond to UVR and the subsequent cellular changes. Given the prevalence of NMSC and the resulting health care burden, many of these pathways provide promising targets for continued study aimed at both chemoprevention and chemotherapy.

Lgr4 is crucial for skin carcinogenesis by regulating MEK/ERK and Wnt/β-catenin signaling pathways

Lgr4 is a member of the leucine-rich, G protein-coupled receptor family of proteins, and has recently been shown to augment Wnt/β-catenin signaling via binding to Wnt agonists R-spondins. It plays an important role in skin development, but its involvement in skin tumorigenesis is unclear. Here, we report that mice deficient for Lgr4 are resistant to 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced keratinocyte proliferation and papilloma formation. We show that TPA treatment activates MEK1, ERK1/2 and downstream effector AP-1 in wild-type (WT) epidermal cells and mice, but not in cells or mice where Lgr4 is depleted. Wnt/β-catenin signaling is also dramatically activated by TPA treatment, and this activation is abolished when Lgr4 is deleted. We provide evidences that blocking both MEK1/ERK1/2 and Wnt/β-catenin pathways prevents TPA-induced increase in the expression of Ccnd1 (cyclin D1), a known Wnt/β-catenin target gene, and that the activation of MEK1/ERK1/2 pathway lies upstream of Wnt/β-catenin signal pathway. Collectively, our findings identify Lgr4 as a critical positive factor for skin tumorigenesis by mediating the activation of MEK1/ERK1/2 and Wnt/β-catenin pathways.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

All-trans retinoic acid induces cell-cycle arrest in human cutaneous squamous carcinoma cells by inhibiting the mitogen-activated protein kinase-activated protein 1 pathway

BACKGROUND

All-trans retinoic acid (ATRA) has been tried for the treatment and prevention of a number of epithelial cancers. However, the precise mechanism by which ATRA inhibits the growth of cutaneous squamous cell carcinoma (cSCC) remains elusive.

AIMS

To determine the suppressive effects of ATRA on the human cSCC cell line SCL-1, and explore the possible mechanisms involved.

METHODS

SCL-1 cells were treated with ATRA, then cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, while apoptosis and cell cycle progression were analysed by flow cytometry. Protein levels of cell-cycle regulatory proteins and the activation of extracellular signal-regulated kinase (ERK) and Jun kinase (JNK) were detected by western blotting analysis. Transcriptional activity of activator protein (AP)-1 was examined by luciferase reporter assay.

RESULTS

ATRA inhibited the proliferation of SCL-1 cells and had modest proapoptotic effects. ATRA also induced G1 cell-cycle arrest, inhibited the expression of cyclin D1/cyclin-dependent kinase (CDK)4 and cyclinE/CDK2, and increased the expression of the cyclin-dependent kinase inhibitors p21 and p27. In addition, ATRA significantly decreased the phosphorylation of ERK1/2 and JNK1/2, and inhibited AP-1 transcriptional activity.

CONCLUSIONS

ATRA induces cell-cycle arrest in human cSCC cells by inhibiting the mitogen-activated protein kinase (MAPK)-AP1 pathway, and could be effective in the prevention and chemotherapy of human cSCC.

In vivo long-term effects of retinoic acid exposure in utero on induced tumours in adult mouse skin

BACKGROUND

Retinoic acid (RA) and its analogues (retinoids) are promising agents in skin cancer prevention following either topical application or oral administration. However, long-term in vivo effects of RA on chemically induced hyperplastic epidermal foci in adult mouse skin have also been described, casting some doubt with regard to its chemopreventive activity.

HYPOTHESIS/OBJECTIVES

To characterize chemically induced skin tumours and to investigate the in vivo long-term action and preventive effect of RA on adult mouse skin carcinogenesis.

ANIMALS

Fifty-six adult Naval Medical Research Institute mice, exposed (n = 28) or not exposed (n = 28) to RA in utero.

METHODS

Mice were treated with a standard two-stage skin carcinogenesis protocol, which included an initiating application of 7,12-dimethylbenz(a)anthracene followed by promotion with 12-O-tetradecanoylphorbol 13-acetate.

RESULTS

Retinoic acid administered to pregnant mice showed a long-term inhibitory action on cell differentiation and development of chemically induced tumours on the adult skin of their offspring, as well as a stimulatory effect on cell proliferation and expression of an early marker of malignant progression (keratin 13).

CONCLUSIONS AND CLINICAL IMPORTANCE

The results suggest that RA exposure in utero confers long-lasting effects on adult mouse skin carcinogenesis. These include chemopreventive activity (reduced number of tumours), as well as enhancement of squamous papilloma progression, which appears to be due to enhanced keratinocyte proliferation and suppression of epidermal maturation. The clinical significance of these findings is not known for other routes of RA administration at this time.

Retinoids for prevention and treatment of actinic keratosis

Actinic keratosis is a common cause of dermatological consultations and it presents a strong association with squamous cell carcinoma. Many substances are used for treatment and prevention, such as retinoids. Nevertheless, many studies on retinoids emphasize their application in treating and preventing non melanoma skin cancers. In this article, we reviewed studies about systemic and topical retinoids used with immunocompetent patients and organ transplant recipients with actinic keratosis, as primary or secondary outcomes. The majority of these papers pointed to a reduction in actinic keratosis count after treatment with retinoids. However, studies need to be better-defined in order to address the lack of a standardized dose, the absence of control groups, the low number of patients and short follow-up periods. Blind, randomized and controlled clinical trials with adequate sample sizes, specifically focused on actinic keratosis, are needed to clarify the real benefit of topical and/or oral retinoids. Comparison of efficacy and safety between oral and topical retinoids in the prevention and treatment of non-melanoma skin cancers and actinic keratosis is an essential pre requisite to establish new strategies to control these conditions.

NGAL can alternately mediate sunitinib resistance in renal cell carcinoma

PURPOSE

Serum NGAL is highly expressed in patients with advanced renal cancer treated with sunitinib. We investigated the role of NGAL in sunitinib resistance in renal cell carcinoma to identify potential tactics to overcome it.

MATERIALS AND METHODS

NGAL expression was correlated with sunitinib sensitivity. Vascular endothelial growth factor related upstream Ras, Erk1/2 and STAT1 phosphorylation activity in Caki-1 and NGAL transfected Caki-1 cells after sunitinib treatment was analyzed using Western blot. NGAL and vascular endothelial growth factor-A interaction with sunitinib therapeutic efficacy was monitored in renal cell carcinoma tumor xenografted mice by tumor growth inhibition, serum NGAL and vascular endothelial growth factor-a levels, and microscopic examination of tumor microvascular density.

RESULTS

Sunitinib cytotoxicity in various renal cell carcinoma cell lines was reversibly related to NGAL expression. Sunitinib showed the lowest 50% inhibitory concentration (5.53 μM) in Caki-1 cells, which had the lowest NGAL expression of these renal cell carcinoma cell lines. After sunitinib treatment adding NGAL inhibited Ras and Erk1/2 phosphorylation but activated STAT1α phosphorylation in Caki-1 cells and Caki-1 cells transfected with NGAL. In a xenograft mouse model sunitinib significantly inhibited tumor growth in Caki-1 mice. NGAL transfected Caki-1 mice had higher serum NGAL and lower vascular endothelial growth factor-A than Caki-1 mice. Microvascular density was decreased in Caki-1 mice with sunitinib treatment.

CONCLUSIONS

NGAL in tumor cells may show crosstalk with vascular endothelial growth factor-a and alternative activation in stimulating tumor growth during sunitinib treatment. It may become a therapeutic target to reverse sunitinib resistance in renal cell carcinoma.

Eruptive squamous cell carcinomas after vemurafenib therapy

BACKGROUND

Vemurafenib is an oral BRAF inhibitor recently approved for the treatment of metastatic melanoma. Patients treated with this medication have been reported to have the occurrence of squamous cell carcinoma (SCC) and/or actinic keratosis (AK).

OBJECTIVE

We report the case of a patient treated with vemurafenib for papillary thyroid carcinoma who subsequently developed multiple SCCs and AK of the skin. The lesions were deemed related to the medication and treated with excision. In addition, subsequent development of SCCs and AK was successfully prevented with a combination of isotretinoin and 5-fluorouracil in this patient. We discuss postulated mechanisms for these findings, as well as potential preventive therapy with the aforementioned combination regimen in patients undergoing treatment with vemurafenib.

All-trans retinoic acid modulates mitogen-activated protein kinase pathway activation in human scleral fibroblasts through retinoic acid receptor beta

PURPOSE

All-trans retinoic acid (ATRA) is known to inhibit the proliferation of human scleral fibroblasts (HSFs) and to modulate the scleral intercellular matrix composition, and may therefore serve as a mediator for controlling eye growth. Cell proliferation is regulated by the mitogen-activated protein kinase (MAPK) pathway. The aim of the current study was to investigate whether changed activation of the MAPK pathway could be involved in the response of HSFs exposed to ATRA.

METHODS

HSFs were cultured in Dulbecco Modified Eagle's Medium/F12 (DMEM/F12) and exposed to 1 μmol/l ATRA for 10 min, 30 min, 1 h, 8 h, or 24 h. The activation of extracellular signal-regulated kinase (ERK 1/2), p38, and c-Jun N-terminal kinase (JNK) in HSFs was assessed with western blot analysis and immunocytofluorescence.

RESULTS

After exposure to ATRA for 24 h, the HSFs appeared shrunken and thinner than the control cells. The intercellular spaces were wider, and the HSFs appeared less numerous than in the control culture. Western blot showed decreased activation of ERK 1/2 in the HSFs from 30 min (p=0.01) to 24 h (p<0.01) after the start of exposure to ATRA, and increased activation of the JNK protein from 10 to 30 min (p<0.01) after the start of exposure to ATRA. Indirect immunofluorescence confirmed changes in activation of ERK 1/2 and JNK in HSFs exposed to ATRA. No change in activation of p38 in HSFs was observed after exposure to ATRA. Pretreatment of the HSFs with LE135, an antagonist of retinoic acid receptor beta (RARβ), abolished the ATRA-induced changes inactivation of ERK 1/2 and JNK.

CONCLUSIONS

ATRA inhibits HSF proliferation by a mechanism associated with modulation of ERK 1/2 and JNK activation and depends on stimulation of retinoic acid receptor beta.

Blood glucose fluctuation affects skin collagen metabolism in the diabetic mouse by inhibiting the mitogen-activated protein kinase and Smad pathways

BACKGROUND

We recently reported that in mice, blood glucose fluctuations (BGF) produced more detrimental effects on skin structure and function than did diabetes alone.

AIM

To determine whether treatment of BGF changes the collagen metabolism in the skin of diabetic mice, and to explore its possible molecular mechanism further.

METHODS

The study used diabetic and BGF animal models. Immunohistochemistry, western blotting and real-time PCR analysis were used to detect the expression of type I collagen, matrix metalloproteinase (MMP)-1, MMP-2 and MMP-13, tissue inhibitor of metalloproteinase (TIMP)-1, extracellular signal-regulated kinase, p38, and Smad2/3. The activities of mitogen-activated protein kinase (MAPK) and Smad signal molecules were also detected by western blotting, and the skin fibroblast ultrastructure was examined using an electron microscope.

RESULTS

BGF treatment produced a twofold reduction in type I collagen synthesis compared with diabetes-only mice. Expression of MMP-1, MMP-2 and MMP-13 increased markedly in the BGF-treated mice, but TIMP-1 expression was strongly downregulated by the BGF treatment. There was also evidence of higher levels of apoptosis of skin fibroblasts after BGF treatment.

CONCLUSIONS

BGF treatment can affect collagen production in the skin of diabetic BGF mice by inhibiting collagen synthesis and increasing collagen degradation. Furthermore, both MAPK and Smad signalling pathways seem to play a role in the inhibition of collagen production in diabetic mice treated with BGF.

In vivo SILAC-based proteomics reveals phosphoproteome changes during mouse skin carcinogenesis

Cancer progresses through distinct stages, and mouse models recapitulating traits of this progression are frequently used to explore genetic, morphological, and pharmacological aspects of tumor development. To complement genomic investigations of this process, we here quantify phosphoproteomic changes in skin cancer development using the SILAC mouse technology coupled to high-resolution mass spectrometry. We distill protein expression signatures from our data that distinguish between skin cancer stages. A distinct phosphoproteome of the two stages of cancer progression is identified that correlates with perturbed cell growth and implicates cell adhesion as a major driver of malignancy. Importantly, integrated analysis of phosphoproteomic data and prediction of kinase activity revealed PAK4-PKC/SRC network to be highly deregulated in SCC but not in papilloma. This detailed molecular picture, both at the proteome and phosphoproteome level, will prove useful for the study of mechanisms of tumor progression.

Effects of the tropical ginger compound,1'-acetoxychavicol acetate, against tumor promotion in K5.Stat3C transgenic mice

The purpose of the current study was to determine whether a tropical ginger derived compound 1'-acetoxychavicol acetate (ACA), suppresses skin tumor promotion in K5.Stat3C mice. In a two-week study in which wild-type (WT) and K5.Stat3C mice were co-treated with either vehicle, ACA, galanga extract, or fluocinolone acetonide (FA) and tetradecanoyl phorbol acetate (TPA), only the galanga extract and FA suppressed TPA-induced skin hyperproliferation and wet weight. None of these agents were effective at suppressing p-Tyr705Stat3 expression. However, ACA and FA showed promising inhibitory effects against skin tumorigenesis in K5.Stat3C mice. ACA also suppressed phospho-p65 NF-κB activation, suggesting a potential mechanism for its action.

JWA deficiency suppresses dimethylbenz[a]anthracene-phorbol ester induced skin papillomas via inactivation of MAPK pathway in mice

Our previous studies indicated that JWA plays an important role in DNA damage repair, cell migration, and regulation of MAPKs. In this study, we investigated the role of JWA in chemical carcinogenesis using conditional JWA knockout (JWA^Δ2/Δ2) mice and two-stage model of skin carcinogenesis. Our results indicated that JWA^Δ2/Δ2 mice were resistant to the development of skin papillomas initiated by 7, 12-dimethylbenz(a)anthracene (DMBA) followed by promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). In JWA^Δ2/Δ2 mice, the induction of papilloma was delayed, and the tumor number and size were reduced. In primary keratinocytes from JWA^Δ2/Δ2 mice, DMBA exposure induced more intensive DNA damage, while TPA-promoted cell proliferation was reduced. The further mechanistic studies showed that JWA deficiency blocked TPA-induced activation of MAPKs and its downstream transcription factor Elk1 both in vitro and in vivo. JWA^Δ2/Δ2 mice are resistance to tumorigenesis induced by DMBA/TPA probably through inhibition of transcription factor Elk1 via MAPKs. These results highlight the importance of JWA in skin homeostasis and in the process of skin tumor development.

Array-based pharmacogenomics of molecular-targeted therapies in oncology

The advent of microarrays over the past decade has transformed the way genome-wide studies are designed and conducted, leading to an unprecedented speed of acquisition and amount of new knowledge. Microarray data have led to the identification of molecular subclasses of solid tumors characterized by distinct oncogenic pathways, as well as the development of multigene prognostic or predictive models equivalent or superior to those of established clinical parameters. In the field of molecular-targeted therapy for cancer, in particular, the application of array-based methodologies has enabled the identification of molecular targets with 'key' roles in neoplastic transformation or tumor progression and the subsequent development of targeted agents, which are most likely to be active in the specific molecular setting. Herein, we present a summary of the main applications of whole-genome expression microarrays in the field of molecular-targeted therapies for solid tumors and we discuss their potential in the clinical setting. An emphasis is given on deciphering the molecular mechanisms of drug action, identifying novel therapeutic targets and suitable agents to target them with, and discovering molecular markers/signatures that predict response to therapy or optimal drug dose for each patient.

ATRA in combination with nedaplatin inhibits cell proliferation but promotes apoptosis in human hepatoma cell line Huh-7

AIM: To observe the effects of all-trans retinoic acid (ATRA) and nedaplatin, alone or in combination, on cell proliferation and apoptosis in human hepatoma cell line Huh-7, and to determine whether the two drugs in combination have a synergistic effect in treating hepatocarcinoma.

METHODS: After Huh-7 cells were incubated with different concentrations of ATRA (10^-4, 10^-5 and 10^-6 mol/L) and nedaplatin (1, 2 and 5 mg/L), alone or in combination, for 24, 48 and 72 h, cell morphology changes were observed using an inverted microscope; cell proliferation was evaluated by MTT assay; and apoptosis was evaluated by flow cytometry.

RESULTS: Both ATRA and nedaplatin could markedly inhibit cell proliferation in a time- and concentration-dependent manner (all P < 0.01). ATRA and nedaplatin in combination had a significant synergistic effect on cell proliferation compared with ATRA or nedaplatin alone (both P < 0.01). Both ATRA and nedaplatin promoted the apoptosis of Huh-7 cells. The apoptosis rate was significantly lower in Huh-7 cells treated with ATRA and nedaplatin alone for 48 h than in those treated with the two drugs in combination (28.49% ± 0.6%, 42.57% ± 1.03% vs 55.35% ± 1.30%, both P < 0.01), suggesting a synergistic effect of combined nedaplatin and ATRA on the apoptosis of Huh-7 cells.

CONCLUSION: Both ATRA and nedaplatin can inhibit cell proliferation and promote apoptosis in human hepatoma cell line Huh-7. ATRA combined with nedaplatin has a significant synergistic effect on the proliferation and apoptosis of Huh-7 cells.

Effects of ATRA combined with citrus and ginger-derived compounds in human SCC xenografts

BACKGROUND

NF-kappaB is a survival signaling transcription factor complex involved in the malignant phenotype of many cancers, including squamous cell carcinomas (SCC). The citrus coumarin, auraptene (AUR), and the ethno-medicinal ginger (Alpinia galanga) phenylpropanoid, 1'-acetoxychavicol acetate (ACA), were previously shown to suppress 12-O-tetradecanoylphorbol-13-acetate (TPA) induced mouse skin tumor promotion. The goal of the present study was to determine whether AUR and ACA are effective either alone or in combination with all-trans retinoic acid (ATRA) for suppressing SCC tumor growth.

METHODS

We first determined the effects of orally administered ACA (100 mg/kg bw) and AUR (200 mg/kg bw) on lipopolysaccharide (LPS)-induced NF-kappaB activation in NF-kappaB-RE-luc (Oslo) luciferase reporter mice. Dietary administration of AUR and ACA +/- ATRA was next evaluated in a xenograft mouse model. Female SCID/bg mice were fed diets containing the experimental compounds, injected with 1 x 106 SRB12-p9 cells s.c., palpated and weighed twice a week for 28 days following injection.

RESULTS

Both ACA and AUR suppressed LPS-induced NF-kappaB activation in the report mice. In the xenograft model, AUR (1000 ppm) and ACA (500 ppm) modestly suppressed tumor volume. However, in combination with ATRA at 5, 10, and 30 ppm, ACA 500 ppm significantly inhibited tumor volume by 56%, 62%, and 98%, respectively. The effect of ATRA alone was 37%, 33%, and 93% inhibition, respectively. AUR 1000 ppm and ATRA 10 ppm were not very effective when administered alone, but when combined, strongly suppressed tumor volume by 84%.

CONCLUSIONS

Citrus AUR may synergize the tumor suppressive effects of ATRA, while ACA may prolong the inhibitory effects of ATRA. Further studies will be necessary to determine whether these combinations may be useful in the control of human SCC.

Identification of genes correlated with early-stage bladder cancer progression

Transitional cell carcinoma (TCC) of the bladder ranks fourth in incidence of all cancers in the developed world, yet the mechanisms of its origin and progression remain poorly understood. There are also few useful diagnostic or prognostic biomarkers for this disease. We have combined a transgenic mouse model for invasive bladder cancer (UPII-SV40Tag mice) with DNA microarray technology to determine molecular mechanisms involved in early TCC development and to identify new biomarkers for detection, diagnosis, and prognosis of TCC. We have identified genes that are differentially expressed between the bladders of UPII-SV40Tag mice and their age-matched wild-type littermates at 3, 6, 20, and 30 weeks of age. These are ages that correspond to premalignant, carcinoma in situ, and early-stage and later stage invasive TCC, respectively. Our preliminary analysis of the microarray data sets has revealed approximately 1,900 unique genes differentially expressed (> or =3-fold difference at one or more time points) between wild-type and UPII-SV40Tag urothelium during the time course of tumor development. Among these, there were a high proportion of cell cycle regulatory genes and a proliferation signaling genes that are more strongly expressed in the UPII-SV40Tag bladder urothelium. We show that several of the genes upregulated in UPII-SV40Tag urothelium, including RacGAP1, PCNA, and Hmmr, are expressed at high levels in superficial bladder TCC patient samples. These findings provide insight into the earliest events in the development of bladder TCC as well as identify several promising early-stage biomarkers.

The promise of natural products for blocking early events in skin carcinogenesis

This perspective on Stratton et al. (beginning on p. 160), Kowalczyk et al. (beginning on p. 170), and Katiyar et al. (beginning on p. 179) highlights the common theme of translational investigation of natural substances and their molecular effects and mechanisms in preventing skin squamous cell carcinoma, which has potentially severe clinical consequences. These studies comprise results of naturally occurring phytochemicals and green tea polyphenols in mouse models of UV-induced and chemically induced skin carcinogenesis and results of perillyl alcohol in a phase IIa clinical trial-all pointing to the great promise of this exciting approach for better understanding of and preventing skin cancer.

All-trans retinoic acid suppresses Stat3 signaling during skin carcinogenesis

Squamous cell carcinoma (SCC) of the skin is the most clinically aggressive form of nonmelanoma skin cancer. We have determined the effects of all-trans retinoic acid (ATRA), a naturally occurring chemopreventive retinoid, on signal transducer and activator of transcription 3 (Stat3) signaling during the development of skin SCC. Stat3 is a transcription factor that plays a critical role in cell proliferation and survival, and it is constitutively active in several malignant cell types. We have previously shown that Stat3 is required for the initiation, promotion, and progression of skin SCC. ATRA is a highly efficient suppressor of tumor formation in the two-stage mouse skin carcinogenesis model and we have shown that this effect correlates with the suppression of the B-Raf/Mek/Erk signaling pathway. In this study, we have determined the pattern of Stat3 phosphorylation throughout the course of the two-stage protocol, both in the presence and absence of ATRA. We have used both SENCAR mice and K5.Stat3C transgenic mice, which express the Stat3C protein, a constitutively active form of Stat3, in the skin. Using Western blotting and immunohistochemical staining with phosphospecific antibodies, we show that coadministration of ATRA suppressed the 12-O-tetradecanoylphorbol-13-acetate-induced phosphorylation of Stat3 in both models, but was only able to suppress tumor formation in the SENCAR mice. Surprisingly, ATRA actually enhanced tumor formation in 12-O-tetradecanoylphorbol-13-acetate-treated K5.Stat3C mice. We hypothesize that ATRA blocks tumor formation, at least in part, by targeting events upstream of Stat3, such as the B-Raf/Mek/Erk pathway, and that in the K5.Stat3C mice, in which Stat3 activity is constitutive, it cannot suppress tumor formation.