UVR-induced Tumors Research Articles

Milestones in Photoimmunology

Photoimmunology started almost 40 years ago with the discovery of a link between UVR and immunosuppression during experimental photocarcinogenesis. Cutaneous UVR-induced tumors appeared to be highly antigenic, as they were rejected upon inoculation into syngeneic mice (Kripke, 1986). Recipients treated with immunosuppressive drugs did not reject the transplanted tumors, similar to recipients who had received low doses of UVR instead of pharmacological immunosuppression, indicating that UVR suppresses cellular immunity. The most effective UVR spectrum to alter an immune response turned out to be the mid-wave range (UVB, 290–320 nm). Thus, most of the photoimmunologic studies were conducted with UVB, although UVA (320–400 nm) certainly has an effect on immune reactions as well. Besides the development of skin tumors, UVR was found to inhibit contact hypersensitivity (Toews et al., 1980). As mice that received the contact allergen through UVR-exposed skin could not be resensitized against the same antigen a few weeks later, it was concluded that UVR induces long-term suppression. This appeared to be antigen specific, as no other immune responses were altered. As UVR exposure and sensitization affect the same skin area, this model is also referred to as local immunosuppression. Later studies showed that UVR, although at higher doses, can also affect the immune system in a systemic manner via the release of soluble mediators (IL-10, tumor necrosis factor) from the skin (Ullrich and Schmitt, 2000). Whether the alarmin (endogenous mediators released upon cellular injury) IL-33 contributes to UVR-induced immunosuppression awaits further investigation, although the fact that neutralization of IL-33 blocks UVR-induced immunosuppression is quite convincing (Byrne et al., 2011).

Infrared radiation does not enhance the frequency of ultraviolet radiation-induced skin tumors, but their growth behaviour in mice

There is increasing concern about the interaction between infrared radiation (IR) and ultraviolet radiation (UVR) with regard to carcinogenesis because prolonged solar exposure is associated with an increased cumulative load not only of UVR but also of IR. We recently demonstrated that IR-pretreatment reduces UVR-induced apoptosis. As this might support the survival of UVR-damaged cells and thus carcinogenesis, we performed an in vivo photocarcinogenesis study. One group of mice were treated with IR prior to each UVR exposure; additional groups were treated with IR or UVR alone. IR alone did not induce skin cancer. UVR-induced tumor formation was not enhanced in IR-pretreated mice, but, in contrast, seemed to occur with delay. This correlated with a reduction of p53 mutated clones in the skin. However, once developed, tumors in IR-pretreated mice grew faster which was confirmed by their enhanced Ki-67 expression. The enhanced aggressiveness of tumors derived from IR-pretreated mice was associated with a higher prevalence of sarcomas than epithelial tumors. Hence, the impact of IR on UVR-induced carcinogenesis has to be interpreted with caution. Although IR may delay the onset of UVR-induced tumors, it might contribute to a worse outcome by shifting these tumors into a more aggressive phenotype.

The p53 tumor suppressor gene of the marsupial Monodelphis domestica: cloning of exons 411 and mutations in exons 58 in ultraviolet radiation-induced corneal sarcomas

Inactivating p53 mutations are found in many ultraviolet radiation (UVR)-induced skin tumors. We examined 12 UVR-induced corneal tumors of the marsupial Monodelphis domestica for mutations in exons 5-8 of p53 and compared their mutational spectrum with that of UVR-induced skin tumors of other species. First we cloned and characterized a cDNA extending from the middle of exon 4 through exon 11 of the Monodelphis p53 gene. Based on the sequence information obtained, primers were designed to amplify introns 4-9 of the gene; intron primers to amplify individually exons 5-8 were subsequently developed. 'Cold' single strand conformational polymorphism analysis followed by reamplification of DNA with altered mobility and cycle sequencing revealed single p53 mutations in four of 12 tumors (33%), including one mutation in exon 5, two identical mutations in exon 7 and one mutation in exon 8. All mutations were at dipyrimidine sites and occurred on the non-transcribed strand. Three of the four were hallmark UVR-induced C-->T alterations. Three of the mutations were found at sites corresponding to human codons 248 and 273, which are mutational hotspots in human and murine UVR-induced squamous cell carcinomas. Our findings suggest that UVR-induced corneal sarcomas in Monodelphis will be valuable in studying mechanisms of p53 mutation in UVR-induced tumors.

Ability of cyclosporine to promote the growth of transplanted ultraviolet radiation-induced tumors in mice.

The use of immunosuppressive agents (primarily azathioprine and prednisone) to promote human allograft survival is known to be associated with an enhanced rate of skin cancer development by ultraviolet radiation (UVR). These observations raise the question of whether the immunosuppressive agents are functioning as cocarcinogen or whether they augment UVR-induced tumors by their successive influence on normal tumor-directed immune responses. In this report we have examined the effect of cyclosporine (CsA) on the capacity of murine UVR-induced tumors to grow following their transplantation to syngeneic recipients. We found that transplanted UVR tumors, selected for their inability to grow in normal recipients, were capable of progressive growth following implantation into CsA-treated recipients. This CsA-induced tumor-susceptible state could be reversed by treatment of prospective recipients with the drug cyclophosphamide (CY), supporting the concept that CsA was functioning in vivo by its capacity to promote suppressor cell generation. Further studies established that CsA treatment needed to be given at or near the time of tumor transplantation for susceptibility to occur. Our findings support the possibility that CsA is capable of promoting the survival and progression of UVR-induced skin tumors via its capacity to enhance the dominance of suppressor-cell-controlled immune responses.

Cross-Reactive Tumor Antigens in the Skin of Mice Exposed to Subcarcinogenic Doses of Ultraviolet Radiation

This study suggests that cross-reactive tumor-associated antigens (TAA) are induced in the epidermis of mice exposed to subcarcinogenic doses of ultraviolet radiation (UVR). Foot-pad immunization of C3H mice with viable epidermal cells from syngeneic UVR-exposed mice induced cytotoxic cells in the draining lymph nodes (DLN). These cells were capable of lysing a battery of UVR-induced tumor targets in a short-term chromium release assay. In contrast, the DLN cells of mice immunized with epidermal cells from normal non-UVR-exposed mice did not mature into effector cells with antitumor activity. The spectrum of tumor recognition of cytotoxic cells induced by immunization with UVR-exposed epidermal cells was identical to that of cytotoxic T cells obtained from animals that were foot-pad immunized with UVR-induced tumor cells. Both cytotoxic cell populations were shown to lyse tumors of diverse origin, including syngeneic UVR- and methylcholanthrene-induced tumors, as well as allogeneic UVR-induced tumors. These cells displayed minimal lytic activity against YAC-1 lymphoma cells, peritoneal exudate cells, and concanavalin A-stimulated splenocytes. The results from this study demonstrate that antigens are expressed on UVR-exposed mouse epidermal cells prior to the emergence of skin tumors, and these antigens can induce cytotoxic cells with specificity for TAA. We conclude that the early antigenic changes observed in UVR-exposed epidermis and their effect on the host's immune system may influence the emergence and progression of UVR-induced skin cancers.

Clonal Origin of Tumors Induced by Ultraviolet Radiation<xref ref-type="fn" rid="FN2">2</xref>

Skin tumors were induced in (C3H/HeN X C3H/HeN-PGK-1a)F1 female mice, heterozygous at the X-linked phosphoglycerate kinase-1 (PGK-1) locus, by exposure to the carcinogenic influence of ultraviolet radiation (UVR), 3-methylcholanthrene [(MCA) CAS: 56-49-5], or benz[a]pyrene [(BP) CAS: 50-32-8]. An assessment of the clonal origin of these tumors was accomplished through an analysis of the PGK-1 enzyme phenotype expressed by the transformed cells. In vitro culture was employed as a means of depleting nontransformed cells of host origin from the induced tumors. Cultured lines derived from tumors induced by each of the above agents were found to express only one of the two enzyme forms encoded by the host genotype, consistent with the probability that all the UVR-, MCA-, and BP-induced tumors examined in this study were monoclonal in origin. For further substantiation of the monoclonality of UVR-induced tumors, 2 UVR-induced tumors were enzymatically dissociated immediately following excision from the primary hosts, and the resulting cell suspensions were cloned in soft agar. Upon analysis, each set of clones selected in soft agar expressed only a single PGK-1 enzyme form. To rule out the possibility that the apparent monoclonality of culture-adapted tumor lines was due to in vitro selection, tumors that arose in UVR-treated PGK-1a/b female heterozygote mice were transplanted into PGK-1a and PGK-1b homozygous recipients. These transplanted tumors expressed a single PGK-1 allozyme following growth in recipients that were genetically homozygous for the major PGK-1 enzyme form expressed by the tumor prior to transplantation. These data strongly support the concept that most, if not all, UVR-induced tumors are derived from the progeny of a single transformed cell. This observation is important to the understanding of the nature of tumor-specific transplantation antigens expressed by individual UVR-induced tumors and indicates that such antigens also are clone specific. In addition, the results of this study indicate that polyclonality does not play a significant role in the generation of cellular and phenotypic heterogeneity known to be present within individual UVR-induced tumors.