UVB-induced DHODH upregulation, which is driven by STAT3, is a promising target for chemoprevention and combination therapy of photocarcinogenesis.

The leading cause of cutaneous squamous cell carcinomas (cSCCs) is exposure to ultraviolet radiation (UV). Unlike most other cancers, the incidence rates of cSCCs are still on the rise and the treatment options currently available are limited. We have recently found that dihydroorotate dehydrogenase (DHODH), which is the rate-limiting enzyme in the de novo pyrimidine synthesis pathway, plays a critical role in UVB-induced energy metabolism reprogramming. Using a multistage model of UVB radiation-induced skin cancer, we show that UVB-induced DHODH upregulation is mainly regulated transcriptionally by STAT3. Our results indicate that chronic inhibition of DHODH by leflunomide (LFN) blocks UVB-induced tumor initiation. Human tumor xenograft studies showed that LFN treatment reduces growth of established tumors when used in combination with a genotoxic agent, 5-fluorouracil (5-FU). Our data suggest that DHODH is a promising target for chemoprevention and combination therapy of UVB-induced cSCCs.

NADPH Oxidase-1 Plays a Key Role in Keratinocyte Responses to UV Radiation and UVB-Induced Skin Carcinogenesis.

The nicotinamide adenine dinucleotide phosphate oxidase (NOX) family enzymes are involved in several physiological functions. However, their roles in keratinocyte responses to UV radiation have not been clearly elucidated. This study shows that, among other NOX family members, UVB irradiation results in a biphasic activation of NOX1 that plays a critical role in defining keratinocyte fate through the modulation of the DNA damage response network. Indeed, suppression of both bursts of UVB-induced NOX1 activation by using a specific peptide inhibitor of NOX1 (InhNOX1) is associated with increased nucleotide excision repair efficiency and reduction of apoptosis, which is finally translated into decreased photocarcinogenesis. On the contrary, when only the second peak of UVB-induced NOX1 activation is blocked, both nucleotide excision repair efficiency and apoptosis are decreased. Our results show that inhibition of NOX1 activation could be a promising target for the prevention and treatment of UVB-induced skin cancer in nucleotide excision repair-proficient and -deficient patients.