Genetic variation in low-dose UV-induced suppression of contact hypersensitivity and in the skin photocarcinogenesis response

Optimized nonclinical safety assessment strategies supporting clinical development of therapeutic monoclonal antibodies targeting inflammatory diseases

An increasing number of immunomodulatory monoclonal antibodies (mAbs) and IgG Fc fusion proteins are either approved or in early-to-late stage clinical trials for the treatment of chronic inflammatory conditions, autoimmune diseases and organ transplant rejection. The exquisite specificity of mAbs, in combination with their multi-functional properties, high potency, long half-life (permitting intermittent dosing and prolonged pharamcological effects), and general lack of off-target toxicity makes them ideal therapeutics. Dosing with mAbs for these severe and debilitating but often non life-threatening diseases is usually prolonged, for several months or years, and not only affects adults, including sensitive populations such as woman of child-bearing potential (WoCBP) and the elderly, but also children. Immunosuppression is usually a therapeutic goal of these mAbs and when administered to patients whose treatment program often involves other immunosuppressive therapies, there is an inherent risk for frank immunosuppression and reduced host defence which when prolonged increases the risk of infection and cancer. In addition when mAbs interact with the immune system they can induce other adverse immune-mediated drug reactions such as infusion reactions, cytokine release syndrome, anaphylaxis, immune-complex-mediated pathology and autoimmunity. An overview of the nonclinical safety assessment and risk mitigation strategies utilized to characterize these immunomodulatory mAbs and Fc fusion proteins to support first-in human (FIH) studies and futher clinical development in inflammatory disease indications is provided. Specific emphasis is placed on the design of studies to qualify animal species for toxicology studies, early studies to investigate safety and define PK/PD relationships, FIH-enabling and chronic toxicology studies, immunotoxicity, developmental, reproductive and juvenile toxicity studies and studies to determine the potential for immunosuppression and reduced host defence against infection and cancer. Nonclinical strategies to facilitate clinical and market entry in the most efficient timeframe are presented.

DNA damage, apoptosis and langerhans cells--Activators of UV-induced immune tolerance

Solar UVR is highly mutagenic but is only partially absorbed by the outer stratum corneum of the epidermis. UVR can penetrate into the deeper layers of the epidermis, depending on melanin content, where it induces DNA damage and apoptosis in epidermal cells, including those in the germinative basal layer. The cellular decision to initiate either cellular repair or undergo apoptosis has evolved to balance the acute need to maintain skin barrier function with the long-term risk of retaining precancerous cells. Langerhans cells (LCs) are positioned suprabasally, where they may sense UV damage directly, or indirectly through recognition of apoptotic vesicles and soluble mediators derived from surrounding keratinocytes. Apoptotic vesicles will contain UV-induced altered proteins that may be presented to the immune system as foreign. The observation that UVR induces immune tolerance to skin-associated antigens suggests that this photodamage response has evolved to preserve the skin barrier by protecting it from autoimmune attack. LC involvement in this process is not clear and controversial. We will highlight some basic concepts of photobiology and review recent advances pertaining to UV-induced DNA damage, apoptosis regulation, novel immunomodulatory mechanisms and the role of LCs in generating antigen-specific regulatory T cells.

Depletion of CD4+ Cells Exacerbates the Cutaneous Response to Acute and Chronic UVB Exposure

Solid organ transplant recipients have a 60-250-fold increased likelihood of developing sunlight-induced squamous cell carcinoma (SCC) compared with the general population. This increased risk is linked to the immunosuppressive drugs taken by these patients to modulate T cell function, thus preventing organ rejection. To determine the importance of T cells in the development of cutaneous SCC, we examined the effects of selectively depleting Skh-1 mice of systemic CD4+ or CD8+ T cells, using monoclonal antibodies, on ultraviolet B (UVB) radiation-induced inflammation and tumor development. Decreases in systemic CD4+ but not CD8+ T cells significantly increased and prolonged the acute UVB-induced cutaneous inflammatory response, as measured by neutrophil influx, myeloperoxidase activity, and prostaglandin E2 levels. Significantly more p53+ keratinocytes were observed in UVB-exposed CD4-depleted than in CD4-replete mice, and this difference was abrogated in mice depleted of neutrophils before UVB exposure. Increased acute inflammation was associated with significantly increased tumor numbers in CD4-depleted mice chronically exposed to UVB. Furthermore, topical treatment with the anti-inflammatory drug celecoxib significantly decreased tumor numbers in both CD4-replete and CD4-depleted mice. Our findings suggest that CD4+ T cells play an important role in modulating both the acute inflammatory and the chronic carcinogenic response of the skin to UVB.

Ultraviolet B exposure activates Stat3 signaling via phosphorylation at tyrosine705 in skin of SKH1 hairless mouse: a target for the management of skin cancer?

Understanding the molecular determinants of ultraviolet (UV) response may lead to the development of novel targets; and therefore, better approaches for the management of cancers, which mainly arise due to the exposure of skin to UV (particularly its UVB spectrum). Signal transducer and activator of transcription (Stat) proteins have been shown to activate multiple signaling pathways to contribute to oncogenesis. Here, we studied the regulation of Stat3 during UVB exposure-mediated responses in the skin of SKH-1 hairless mouse, a model regarded to possess relevance to human situations. Our data demonstrated that a single UVB (180 mJ/cm(2)) exposure to the skin of SKH-1 hairless mice resulted in significant upregulation in (i) protein levels of Stat3 and (ii) phosphorylation of Stat3 at tyrosine(705). Further, the activation of Stat3 was found to be associated with a decrease in apoptotic response of UVB and a gradual time-dependent increase in leukocyte infiltration and hyperplasia. In conclusion, we have demonstrated, for the first time, that UVB exposure to skin resulted in an activation of pro-survival protein Stat3. Based on our observation, we suggest that Stat3 could serve as a target for the management of UVB exposure-mediated damages including skin cancer.

Dose response for UV-induced immune suppression in people of color: differences based on erythemal reactivity rather than skin pigmentation

Ultraviolet radiation (UVR) is known to suppress immune responses in human subjects. The purpose of this study was to develop dose responses across a broad range of skin pigmentation in order to facilitate risk assessment. UVR was administered using FS 20 bulbs. Skin pigmentation and UVR sensitivity were evaluated using Fitzpatrick classifications, minimal erythemal dose (MED), slope of the erythemal dose response curve (sED), baseline pigmentation and tanning response. To assess immune responses dinitrochlorobenzene (DNCB) was applied to irradiated buttock skin 72 h after irradiation. Two weeks later DNCB was applied to the inside upper arm. Skin thickness was measured before and after challenge. Dose response was modeled (to obtain a regression line) for the entire group of 185 subjects. With the exception of sED none of the above-mentioned pigmentation indicators contributed significantly to variability around the regression line. Thus, differences in sensitivity for multiple skin types based on Fitzpatrick classification or MED were not observed. However, differences in immune sensitivity to UVR were detected between subjects with steep erythemal dose response curves and those with moderate or flat responses. For subjects with steep erythemal responses the dose calculated to suppress the immune response by 50% was 114 mJ/cm2. This group included individuals with Fitzpatrick skin types I-V, MED for these subjects ranged from 30 to 80 mJ/cm2. The 50% suppression dose for subjects with weak or no erythemal response could not be computed (the dose response was flat). This resistant group included subjects with skin types IV-VI and MED for these subjects ranged from 41 to > 105 mJ/cm2. This study provides a human dose response for UVR suppression of contact sensitivity that will be useful in risk assessment. It is the first study to provide this information using the FS sun lamp and is the first study to include people of color. The sED appears to be a new variable for identifying sensitive subjects at risk of UVR-induced immune suppression.

Topical application of a selective cyclooxygenase inhibitor suppresses UVB mediated cutaneous inflammation

Ultraviolet B (UVB) radiation causes much of the cutaneous damage after both acute and long-term exposure, and is also the most important etiologic agent in human skin cancer. UVB exposure initially induces an inflammatory response characterized by edema, dermal infiltration of leukocytes, sunburn cell formation, as well as the induction of cyclooxygenase-2 (COX-2) gene expression and subsequent increase in the production and release of prostaglandins. This process of inflammation induced by UVB exposure has been linked to tumor formation. Recently, a specific COX-2 inhibitor, Celecoxib, was developed, which inhibits COX-2-induced inflammation without inhibiting the cytoprotective function of cyclooxygenase-1 (COX-1). The present study compared the effects of topical treatment with Celecoxib (a specific COX-2 inhibitor) and Ibuprofen (a nonspecific COX inhibitor) on the acute UVB-induced cutaneous inflammatory response. We show that the specific inhibition of COX-2 effectively reduced many parameters of UVB-mediated inflammation, including edema, dermal neutrophil infiltration and activation, prostaglandin E2 (PGE2) levels and the formation of sunburn cells. By inhibiting this inflammatory response, topical Celecoxib treatment may ultimately be effective in preventing UVB-induced tumor development in the skin.

Sensitivity to sunburn is associated with susceptibility to ultraviolet radiation-induced suppression of cutaneous cell-mediated immunity

Skin cancer incidence is highest in white-skinned people. Within this group, skin types I/II (sun sensitive/tan poorly) are at greater risk than skin types III/IV (sun tolerant/tan well). Studies in mice demonstrate that ultraviolet radiation (UVR)-induced suppression of cell-mediated immune function plays an important role in the development of skin cancer and induces a susceptibility to infectious disease. A similar role is suspected in humans, but we lack quantitative human data to make risk assessments of ambient solar exposure on human health. This study demonstrates that ambient levels of solar UVR, typically experienced within 1 h of exposure to noonday summer sunlight, can suppress contact hypersensitivity (CHS) responses in healthy white-skinned humans in vivo (n = 93). There was a linear relationship between increase in erythema and suppression of CHS (P < 0.001), and a moderate sunburn (two minimal erythema doses [2 MED]) was sufficient to suppress CHS in all volunteers by 93%. However, a single suberythemal exposure of either 0.25 or 0.5 MED suppressed CHS responses by 50 and 80%, respectively, in skin types I/II, whereas 1 MED only suppressed CHS by 40% in skin types III/IV. The two- to threefold greater sensitivity of skin types I/II for a given level of sunburn may play a role in their greater sensitivity to skin cancer.

Health risks

The health risks associated with ozone depletion will principally be those due to increased ultraviolet B (UV-B) radiation in the environment, i.e., increased damage to the eyes, the immune system, and the skin. Some new risks may also be introduced with the increased use of alternatives to the ozone-depleting substances (ODSs). Quantitative risk estimates are available for some of the UV-B-associated effects, e.g., cataract and skin cancer; however, the data are insufficient to develop similar estimates for effects such as immunosuppression and the toxicity of alternatives. Ocular damage from UV exposures includes effects on the cornea, lens, iris, and associated epithelial and conjunctival tissues. The most common acute ocular effect of environmental ultraviolet radiation (UVR) is photokeratitis. Also known as snowblindness in skiers, this condition also occurs in other outdoor recreationists. Chronic eye conditions likely to increase with ozone depletion include cataract, squamous cell carcinoma, ocular melanoma, and a variety of corneal/conjunctival effects, e.g., pterygium and pinguecula. Suppression of local (at the site of UV exposure) and systemic (at a distant, unexposed site) immune responses to a variety of antigens has been demonstrated in both humans and animals exposed to UV-B. In experiments with animals these effects have been shown to worsen the course/outcome of some infectious diseases and cancers. There is reasonably good evidence that such immunosuppression plays a role in human carcinogenesis; however, the implications of such immunosuppression for human infectious diseases are still unknown. In light-skinned populations, exposure to solar UVR appears to be the most important environmental risk factor for basal and squamous cell carcinomas and cutaneous melanoma. Originally it was believed that total accumulated exposure to UVR was the most important environmental factor in determining risk for these tumors. Recent information now suggests that only squamous cell carcinoma risk is related to total exposure. In the cases of both basal cell carcinoma and melanoma, new information suggests that increases in risk are tied to early exposures (before about age 15), particularly those leading to severe sunburns. Testing of a number of the chlorofluorocarbon (CFC) alternatives indicates that most of these chemicals have low acute toxicity, and low to moderate chronic toxicity. Some chemicals that were originally proposed as alternatives have been dropped from consideration because these tests raised concerns about toxicity and/or manufacturing difficulties. In one instance, high accidental occupational exposure was associated with liver damage, underlining the need for care in the use of these substitutes. Recent quantitative risk estimates have been developed for cataract, melanoma, and all skin cancers combined. These estimates indicate that under the Montreal Adjustments, cataract and skin-cancer incidence will peak mid-century at additional incidences of just under 3 per 100,000 and about 7 per 100,000, respectively.