Targeting mutant p53 shows promise for sunscreens and skin cancer

Drugs Targeting p53 Mutations with FDA Approval and in Clinical Trials

Mutations in the tumor suppressor p53 (p53) promote cancer progression. This is mainly due to loss of function (LOS) as a tumor suppressor, dominant-negative (DN) activities of missense mutant p53 (mutp53) over wild-type p53 (wtp53), and wtp53-independent oncogenic activities of missense mutp53 by interacting with other tumor suppressors or oncogenes (gain of function: GOF). Since p53 mutations occur in ~50% of human cancers and rarely occur in normal tissues, p53 mutations are cancer-specific and ideal therapeutic targets. Approaches to target p53 mutations include (1) restoration or stabilization of wtp53 conformation from missense mutp53, (2) rescue of p53 nonsense mutations, (3) depletion or degradation of mutp53 proteins, and (4) induction of p53 synthetic lethality or targeting of vulnerabilities imposed by p53 mutations (enhanced YAP/TAZ activities) or deletions (hyperactivated retrotransposons). This review article focuses on clinically available FDA-approved drugs and drugs in clinical trials that target p53 mutations and summarizes their mechanisms of action and activities to suppress cancer progression.

Belinostat (PXD101) resists UVB irradiation-induced cellular senescence and skin photoaging

Belinostat (PXD101), a new histone deacetylase inhibitor, has shown good performance in various cancer treatments and has been approved by the FDA for the treatment of recurrent or refractory peripheral T-cell lymphoma (PTCL) in patients with drugs. PXD101 is considered to have certain anti-allergic and anti-inflammatory properties, but its beneficial effects in UVB-induced skin photoaging have not been reported. In a recent study, HacaT cells and C57BL6 mice were used to study the impact of PXD101 on UVB-induced cellular senescence and skin photoaging and to explore their potential mechanisms of action. Studies have shown that PXD101 inhibits UVB-induced HacaT cell senescence, which appears to be achieved by inhibiting activation of the UVB-induced NF-κB/p65 signaling pathway. At the same time, PXD101 inhibits the expression of MMPs. In addition, PXD101 alleviated skin damage on the dorsal skin of mice, reduced skin aging and inflammation, increased collagen fiber synthesis, and restored UVB-induced epidermal thickening. In short, we believe that PXD101 effectively inhibits cellular senescence and skin photoaging caused by UVB exposure, a potential method for developing clinical prevention and treatment of skin aging.

Testing the validity of a proposed dermal cancer slope factor for Benzo[a]pyrene

In 2014, the United States Environmental Protection Agency (EPA) proposed a Dermal Slope Factor (DSF) for benzo[a]pyrene (BaP) of 0.006 (μg/day)^-1 (USEPA 2014a). It would make cancer risk estimates associated with soil contact 100 times greater than those from soil ingestion and would predict that a large fraction of skin Basal Cell Carcinomas (BCCs) and Squamous Cell Carcinomas (SCCs) worldwide are caused by low level dermal exposures to PAHs, such as BaP. This is not logical given that sunlight (ultraviolet radiation (UV)) exposure is the generally recognized cause of BCCs and SCCs. This paper critically evaluates the proposed DSF. First, a reality check is performed using EPA standard risk assessment methods and comparing the results to actual BCC and SCC rates in the U.S. population. Then, the biological plausibility of the mechanism by which PAHs might cause human skin cancer is evaluated by exploring the generally recognized etiology of human skin cancer and comparing the genetic mutation signatures of rodent skin tumors caused by PAH exposures to those of human skin cancers. It is concluded that scientific flaws resulted in a proposed DSF value that greatly overestimates the skin cancer risk for humans dermally exposed to BaP in soil.

Squamous Cell Carcinoma - Similarities and Differences among Anatomical Sites

Squamous cell carcinoma (SCC) is an epithelial malignancy involving many anatomical sites and is the most common cancer capable of metastatic spread. Development of early diagnosis methods and novel therapeutics are important for prevention and mortality reduction. In this effort, numerous molecular alterations have been described in SCCs. SCCs share many phenotypic and molecular characteristics, but they have not been extensively compared. This article reviews SCC as a disease, including: epidemiology, pathology, risk factors, molecular characteristics, prognostic markers, targeted therapy, and a new approach to studying SCCs. Through this comparison, several themes are apparent. For example, HPV infection is a common risk factor among the four major SCCs (NMSC, HNSC, ESCC, and NSCLC) and molecular abnormalities in cell-cycle regulation and signal transduction predominate. These data reveal that the molecular insights, new markers, and drug targets discovered in individual SCCs may shed light on this type of cancer as a whole.

Targeting the p53 pathway

This article summarizes data on translational studies to target the p53 pathway in cancer. It describes the functions of the p53 and Mdm-2 signaling pathways, and discusses current therapeutic approaches to target p53 pathways, including reactivation of p53. In addition, direct interaction and colocalization of the p53 and focal adhesion kinase proteins in cancer cells have been demonstrated, and different approaches to target this interaction are reviewed. This is a broad review of p53 function as it relates to the diagnosis and treatment of a wide range of cancers.

Sunlight UV-induced skin cancer relies upon activation of the p38α signaling pathway

The activation of cellular signal transduction pathways by solar ultraviolet (SUV) irradiation plays a vital role in skin tumorigenesis. Although many pathways have been studied using pure ultraviolet A (UVA) or ultraviolet B (UVB) irradiation, the signaling pathways induced by SUV (i.e., sunlight) are not understood well enough to permit improvements for prevention, prognosis, and treatment. Here, we report parallel protein kinase array studies aimed at determining the dominant signaling pathway involved in SUV irradiation. Our results indicated that the p38-related signal transduction pathway was dramatically affected by SUV irradiation. SUV (60 kJ UVA/m(2)/3.6 kJ UVB/m(2)) irradiation stimulates phosphorylation of p38α (MAPK14) by 5.78-fold, MSK2 (RPS6KA4) by 6.38-fold, and HSP27 (HSPB1) by 34.56-fold compared with untreated controls. By investigating the tumorigenic role of SUV-induced signal transduction in wild-type and p38 dominant-negative (p38 DN) mice, we found that p38 blockade yielded fewer and smaller tumors. These results establish that p38 signaling is critical for SUV-induced skin carcinogenesis.

Role of vitamin D metabolism in cutaneous tumour formation and progression

OBJECTIVES

Very limited information is available on the role of vitamin D in skin carcinogenesis. For most individuals, skin cancer can be readily managed with surgery; however, some patients may face life-threatening neoplasia. Sun exposure, specifically UV radiation, is a causative agent for development of skin cancer, though, somewhat ironically, sunlight through the production of vitamin D may have protective effect against some skin cancers. This review focuses on the development and progression of cutaneous carcinogenesis and the role of vitamin D in the prevention of the initiation and progression of lethal skin cancers.

KEY FINDINGS

Vitamin D is involved in regulation of multiple signalling pathways that have implications in carcinogenesis. Skin cancer metastasis depends on the tumour microenvironment, where vitamin D metabolites play a key role in prevention of certain molecular events involved in tumour progression. The vitamin D receptor (VDR) is a well-known potent regulator of cellular growth and differentiation.

SUMMARY

The VDR's possible involvement in cell death, tumour microenvironment and angiogenesis makes it a candidate agent for cancer regulation.

Alterations of ubiquitylation and sumoylation in conventional renal cell carcinomas after the Chernobyl accident: a comparison with Spanish cases

We determined whether ubiquitylation and sumoylation processes are involved in conventional renal cell carcinogenesis associated with chronic, long-term, persistent low doses of ionizing radiation (IR) in patients living for more than 20 years in cesium-137 ((137)Cs)-contaminated areas after the Chernobyl accident in Ukraine. To this end, we assessed the immunohistochemical expression of ubiquitin (Ub), SUMO1, SUMO E2 conjugating enzyme Ubc9, and the cell cycle regulators p53, mdm2, and p14(ARF) in 38 conventional renal cell carcinomas from Ukrainian patients with different degrees of radiation exposure after the Chernobyl accident. As control cases, 18 conventional renal carcinoma (cRCC) tissues from a Spanish cohort were analyzed. No significant differences between the Ukrainian and Spanish groups were found regarding Ub overexpression, although being higher in the Ukrainian cases. Furthermore, this expression was inversely associated with SUMO1 and Ubc9, with no correlation with tumor nuclear grade. There was also a direct relationship between Ubc9 and inflammatory response. These findings do not allow us to consider the immunohistochemical expression of ubiquitylation and sumoylation as valuable markers for discriminating the effects of long-term, low-dose IR exposure in cRCC carcinogenesis.

Squamous Cell Carcinoma - Similarities and Differences among Anatomical Sites

Squamous cell carcinoma (SCC) is an epithelial malignancy involving many anatomical sites and is the most common cancer capable of metastatic spread. Development of early diagnosis methods and novel therapeutics are important for prevention and mortality reduction. In this effort, numerous molecular alterations have been described in SCCs. SCCs share many phenotypic and molecular characteristics, but they have not been extensively compared. This article reviews SCC as a disease, including: epidemiology, pathology, risk factors, molecular characteristics, prognostic markers, targeted therapy, and a new approach to studying SCCs. Through this comparison, several themes are apparent. For example, HPV infection is a common risk factor among the four major SCCs (NMSC, HNSC, ESCC, and NSCLC) and molecular abnormalities in cell-cycle regulation and signal transduction predominate. These data reveal that the molecular insights, new markers, and drug targets discovered in individual SCCs may shed light on this type of cancer as a whole.

p53-based cancer therapy

Inactivation of p53 functions is an almost universal feature of human cancer cells. This has spurred a tremendous effort to develop p53 based cancer therapies. Gene therapy using wild-type p53, delivered by adenovirus vectors, is now in widespread use in China. Other biologic approaches include the development of oncolytic viruses designed to replicate and kill only p53 defective cells and also the development of siRNA and antisense RNA's that activate p53 by inhibiting the function of the negative regulators Mdm2, MdmX, and HPV E6. The altered processing of p53 that occurs in tumor cells can elicit T-cell and B-cell responses to p53 that could be effective in eliminating cancer cells and p53 based vaccines are now in clinical trial. A number of small molecules that directly or indirectly activate the p53 response have also reached the clinic, of which the most advanced are the p53 mdm2 interaction inhibitors. Increased understanding of the p53 response is also allowing the development of powerful drug combinations that may increase the selectivity and safety of chemotherapy, by selective protection of normal cells and tissues.

UV-induced squamous cell carcinoma--a role for antiapoptotic signalling pathways

The incidence of nonmelanoma skin cancer including squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) has dramatically increased in the last decades, and chronic sun exposure was identified as a main etiologic agent. UV radiation may produce DNA damage either directly or through reactive oxygen species (ROS). As mutations caused by UV may lead to skin cancer due to oncogene activation and tumor suppressor gene inactivation, efficient safeguard mechanisms have been developed during evolution. These enclose induction of apoptosis and formation sunburn cells aiming at the removal of premalignant cells. The keratinocyte apoptotic machinery in response to UV consists of both intrinsic/mitochondrial and extrinsic/death receptor-mediated cell-death pathways, which are particularly regulated by mitogen-activated protein kinases (MAPKs, JNK and p38) and the tumor-suppressor protein p53. For development of skin cancer, it appears that critical steps in apoptosis control are dysregulated leading to resistance both to death ligand-mediated and intrinsic proapoptotic pathways. These particularly include inactivation of p53, as well as activation of EGFR, COX-2 and MAPKs, which result in specific regulation of Bcl-2 proteins, death ligands and death receptors. The final unravelling of apoptosis regulation in epithelial skin cancer may allow the development of new targeted therapeutic strategies.