The challenge of targeting metastasis.

Metastases that are resistant to conventional therapy are the major cause of death from cancer. In most patients, metastasis has already occurred by the time of diagnosis. Thus, the prevention of metastasis is unlikely to be of therapeutic benefit. The biological heterogeneity of metastases presents a major obstacle to treatment. However, the growth and survival of metastases depend on interactions between tumor cells and host homeostatic mechanisms. Targeting these interactions, in addition to the tumor cells, can produce synergistic therapeutic effects against existing metastases.

Reflections on the field of photoimmunology.

Photoimmunology evolved from experiments carried out in the 1970s on the immunology of cancer. In studying the antigenic properties of skin cancers induced in mice by UV radiation, I found that most of these tumors failed to grow when transplanted into normal, syngeneic mice but grew progressively in immunosuppressed mice. Thus, these UV-induced skin cancers were highly antigenic. The critical question was, how can these antigenic skin cancers escape immune rejection in their primary host? The answer was that exposing their skin to UV radiation prevented mice from triggering an immune response against their tumors. The failure to reject these tumors was owing to the development of UV tumor-specific regulatory T cells during the course of irradiation. In unraveling the mechanisms of this effect of UV, much has been learned about the immunology of the skin, including the function of Langerhans cells, the migration of immune cells in skin, the role of antigen-presenting cells in directing the immune response, and the role of keratinocytes as producers of immunological mediators. Thus, photoimmunology helped demonstrate that skin is an important immunological organ, and that the immune system can be influenced by the external environment via the skin.

Reducing death from cancer: what will it take?

In spite of advances in cancer diagnosis and treatment, cancer remains a serious problem for most societies. It is unlikely that cancer can ever be eliminated entirely; therefore, we must continue to seek ways to reduce the incidence, morbidity, and mortality from this devastating disease. Although most cancer research is devoted to finding new treatments, there are many other obstacles to reducing death from cancer that will need to be addressed if significant progress is to be made. These include growth in the number of cancer cases owing to the increasing longevity of populations, unequal access to cancer care, the increasing number of cancer survivors, limited resources including human resources, and our inability to deal with preventable cancers. To address these challenges, we must make cancer a national and international priority. We must focus our attention on prevention, not just on treatment, including elimination of tobacco use and reduction in exposure to environmental carcinogens. Finally, we must improve the accessibility of cancer care and ensure that there will be new generations of oncologists, health-care providers, and biomedical researchers by investing in medical research and education.

p53 tumor suppressor gene: a critical molecular target for UV induction and prevention of skin cancer.

The relationship between exposure to UV radiation and development of skin cancer has been well established. Several studies have shown that UVB induces unique mutations (C-->T and CC-->TT transitions) in the p53 tumor suppressor gene that are not commonly induced by other carcinogens. Our studies have demonstrated that UV-induced mouse skin cancers contain p53 mutations at a high frequency and that these mutations can be detected in UV-irradiated mouse skin well before the appearance of skin tumors. This observation suggested that it might be possible to use p53 mutations as a biologic endpoint for testing the efficacy of sunscreens in photoprotection studies. Indeed, application of SPF 15 sunscreens to mouse skin before each UVB irradiation resulted in reduction in the number of p53 mutations. Because p53 mutations represent an early essential step in photocarcinogenesis, these results imply that inhibition of this event may protect against skin cancer development. This hypothesis was confirmed by our finding that sunscreens used in p53 mutation inhibition experiments also protected mice against UVB-induced skin cancer.

Repair capacity for UV light induced DNA damage associated with risk of nonmelanoma skin cancer and tumor progression.

PURPOSE: To examine the role of suboptimal DNA repair capacity (DRC) for UV light-induced DNA damage in the development of nonmelanoma skin cancer (NMSC) and tumor progression. EXPERIMENTAL DESIGN: We conducted a hospital-based case-control study of 255 patients with newly diagnosed NMSC [146 with basal cell carcinoma (BCC) and 109 with squamous cell carcinoma (SCC)] and 333 cancer-free controls. We collected information on demographic variables and risk factors from questionnaires, tumor characteristics from medical records, and lymphocytic DRC phenotype by the host-cell reactivation assay. Multivariable logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: Overall, there was a relative 16% reduction in DRC in NMSC patients compared with controls (P < 0.001 for BCC and for SCC, respectively). DRC below the controls' median value was associated with increased risk significantly for BCC (OR, 1.62; 95% CI, 1.07-2.45) but borderline for SCC (OR, 1.63; 95% CI, 0.95-2.79) after adjustment for age, sex, and other assay-related covariates. When the highest tertile of controls' DRC was used as the reference, the intermediate and low DRC were associated with a statistically significant trend for increasing risk for both BCC (P(trend) = 0.007) and SCC (P(trend) = 0.020). However, patients with aggressive or multiple SCC tended to have a higher DRC than those with nonaggressive or single SCC. CONCLUSIONS: Reduced DRC is an independent risk factor for BCC and single or nonaggressive SCC but not for multiple primaries, local aggressiveness, or recurrence of NMSC.

Mortality risk from squamous cell skin cancer.

PURPOSE: To identify nonmelanoma skin cancer patients with squamous cell carcinoma (SCC) who are at greatest risk of disease-specific mortality. PATIENTS AND METHODS: Prospectively enrolled patients with a minimum of one pathologically confirmed skin SCC lesion, definitive treatment of the SCC lesion(s) resulting in no evidence of disease, and at least 2 months of follow-up after definitive treatment were eligible for the present longitudinal analysis. They received comprehensive clinical, pathologic evaluations and follow-up for patterns of failure and mortality. RESULTS: We enrolled 210 patients (187 men and 23 women) with a total of 277 skin SCC lesions and a median enrollment age of 68 years (range, 34 to 95 years). Median follow-up of surviving patients was 22 months. Three-year overall and disease-specific survival (DSS) rates were 70% and 85%, respectively. In univariate analyses, the clinical-pathologic factors associated with adverse DSS were local recurrence at presentation (P = .05), invasion beyond subcutaneous tissues (P = .009), perineural invasion (P = .002), lesion size (P = .0003), and depth of invasion (P = .05). Statistical models identified a homogeneous high-risk group of patients with lesions > or = 4 cm, perineural invasion, and deep invasion beyond subcutaneous structures. Three-year DSS was 100% for patients with no risk factors versus 70% for patients with at least one risk factor. CONCLUSION: Lesion size > or = 4 cm and histologic evidence of perineural invasion and deep invasion beyond subcutaneous structures were the clinical-pathologic factors most significantly associated with disease-specific mortality in skin SCC.

Viability of the antigen determines whether DNA or urocanic acid act as initiator molecules for UV-induced suppression of delayed-type hypersensitivity.

UV radiation suppresses the immune response, and UV-induced immune suppression contributes to UV-induced photocarcinogenesis. For UV-induced immune suppression to occur, electromagnetic energy (i.e. UV radiation) must be converted to a biological signal. Two photoreceptors have been identified in the skin that serves this purpose, epidermal DNA and trans-urocanic acid (UCA). Although compelling evidence exists to support a role for each pathway (UV-induced DNA damage or photoisomerization of UCA) in UV-induced immune suppression, it is not clear what determines which photoreceptor pathway is activated. To address this question, we injected UV-irradiated mice with a monoclonal antibody with specificity for cis-UCA or applied liposomes containing DNA repair enzymes to the skin of UV-irradiated mice. The effect that each had on UV-induced suppression of delayed-type hypersensitivity was measured. We asked whether the light source used (FS-40 sunlamps vs solar-simulated UV radiation) altered whichever pathway of immune suppression was activated. Different doses of UV radiation and the viability of the antigen were also considered. Neither the dose of UV nor the light source had any influence on determining which pathway was activated. Rather, we found that the viability of the antigen was the critical determinant. When live antigens were used, UV-induced immune suppression was blocked with monoclonal anti-cis-UCA but not with T4 endonuclease V-containing liposomes. The reverse was observed when formalin-fixed or killed antigens were used. Our findings indicate that antigen viability dictates which photoreceptor pathway predominates after UV exposure.

Advantages of using hairless mice versus haired mice to test sunscreen efficacy against photoimmune suppressions.

We tested the hypothesis that the strain of mice used in sunscreen protection experiments may influence immune protection. Ultraviolet (UV) dose-response curves were done in the presence or absence of a sun protection factor (SPF) 15 sunscreen using SKH1:hrBR or C3H/HeN mice. SKH1:hrBR mice showed a higher sensitivity to the suppressive effects of UV radiation (50% immune suppression equal to 5.2 kJ/m2 UVB in SKH1:hrBR mice versus 18.5 kJ/m2 in C3H mice). Immune protection factors (IPF) and an erythema protection factor (Ery-PF) for SKH1:hr mice were derived. The Ery-PF in hairless mice was 13.5, which was similar to the SPF of 15 measured in humans. When IPF were calculated as a ratio of minimal immune suppressive doses, the IPF for the SKH1:hrBR mice was 8.23 and the IFP for the C3H/HeN mice was 1.92. When IPF were estimated using the entire UV dose-response range, they were equal to 9.01 for SKH1:hrBR mice and 1.79 for the C3H/HeN mice. Because IPF and SPF can be measured directly in hairless mice, we suggest that the use of hairless mice may provide a better model to measure sunscreen efficacy, especially when the use of human volunteers is inappropriate, unethical or impossible.

Health effects from stratospheric ozone depletion and interactions with climate change.

The potential health effects of elevated levels of ambient UV-B radiation are diverse, and it is difficult to quantify the risks, especially as they are likely to be considerably modified by human behaviour. Nevertheless epidemiological and experimental studies have confirmed that UV radiation is a definite risk factor for certain types of cataract, with peak efficacy in the UV-B waveband. The causal link between squamous cell carcinoma and cumulative solar UV exposure has been well established. New findings regarding the genetic basis of skin cancer, including studies on genetically modified mice, have confirmed the epidemiological evidence that UV radiation contributes to the formation of basal cell carcinomas and cutaneous melanomas, For the latter, animal models have demonstrated that UV exposure at a very young age is more detrimental than exposure in adulthood. Although suppression of certain immune responses has been recognised following UV exposure, the impact of this suppression on the control of infectious and autoimmune diseases is largely unknown. However, studies on several microbial infections have indicated significant consequences in terms of symptoms or reactivation of disease. The possibility that the immune response to vaccination could be depressed by UV-B exposure is of considerable concern. Newly emerging possibilities regarding interactions between ozone depletion and global climate change further complicate the risk assessments for human health but might result in an increased incidence of cataracts and skin cancer, plus alterations in the patterns of certain categories of infectious and other diseases.

p53 mutations in human aggressive and nonaggressive basal and squamous cell carcinomas.

PURPOSE: The purpose is to investigate whether aggressive basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) differ from nonaggressive BCC and SCC with respect to the p53 mutation spectrum and whether specific mutations can serve as prognostic indicators of tumor aggressiveness. EXPERIMENTAL DESIGN: We analyzed 342 tissues from patients with aggressive and nonaggressive BCCs and SCCs for p53 mutations by single-strand conformation polymorphism and nucleotide sequencing. RESULTS: p53 mutations were detected in 33 of 50 aggressive BCCs (66%), 37 of 98 nonaggressive BCCs (38%), 28 of 80 aggressive SCCs (35%), 28 of 56 nonaggressive SCCs (50%), and 3 of 29 samples of sun-exposed skin (10%). About 71% of the p53 mutations detected in aggressive and nonaggressive BCCs and SCCs were UV signature mutations. The frequency of CC to TT mutations in aggressive (36%) and nonaggressive SCCs (39%) was 2-fold higher than in aggressive (18%) and nonaggressive (14%) BCCs. In contrast, aggressive BCCs had a higher frequency (24%) of transversions than nonaggressive BCCs (8%) and aggressive (14%) and nonaggressive (11%) SCCs did. CONCLUSIONS: Our results indicate that UV radiation is responsible for the induction of p53 mutations and perhaps for the initiation of both aggressive and nonaggressive BCCs and SCCs. Although some differences in p53 mutation frequency, types of mutation, and hot spots were seen between aggressive and nonaggressive BCCs and SCCs, these factors do not constitute as clear-cut diagnostic or prognostic indicators of tumor aggressiveness. Tumor aggressiveness may be attributable to other genetic changes or events that occur during tumor progression.

Systemic alteration induced in mice by ultraviolet light irradiation and its relationship to ultraviolet carcinogenesis. 1977.

Chronic irradiation of mice with ultraviolet (UV) light produces a systemic alteration of an immunologic nature. This alteration is detectable in mice long before primary skin cancers induced by UV light begin to appear. The alteration results in the failure of UV-irradiated mice to reject highly antigenic, transplanted UV-induced tumors that are rejected by unirradiated syngeneic recipients. The immunologic aspect of this systemic alteration was demonstrated by transferring lymphoid cells from UV-irradiated mice to lethally x-irradiated recipients. These recipients were unable to resist a later challenge with a syngeneic UV-induced tumor, whereas those given lymphoid cells from normal donors were resistant to tumor growth. Parabiosis of normal mice with UV-irradiated mice, followed by tumor challenge of both parabionts with a UV-induced tumor, resulted in the growth of the challenge tumors in both WV-irradiated and unirradiated mice. Splenic lymphocytes from tumor-implanted UV-treated mice were not cytotoxic in vitro against UV-induced tumors, whereas under identical conditions cells from tumor-implanted, unirradiated mice were highly cytotoxic. Our findings suggest that repeated UV irradiation can circumvent an immunologic mechanism that might otherwise destroy nascent UV-induced primary tumors that are strongly antigenic.

Mechanisms underlying UV-induced immune suppression: implications for sunscreen design.

The ultraviolet (UV) radiation present in sunlight is immune-suppressive. Recently we showed that solar-simulated UV radiation (UVA + UVB; 295-400 nm), applied after immunization, suppressed immunological memory and the elicitation of delayed-type hypersensitivity to the common opportunistic pathogen, Candida albicans. Further, we found that wavelengths in the UVA region of the solar spectrum (320-400 nm), devoid of UVB, were equally effective in activating immune suppression as UVA + UVB radiation. Here we report on the mechanisms involved. No immune suppression was found in UV-irradiated mice injected with monoclonal anti-interleukin (IL)-10 antibody, or mice exposed to solar-simulated UV radiation and injected with recombinant IL-12. Antigen-specific suppressor T cells were found in the spleens of mice exposed to UVA + UVB radiation. Applying liposomes containing bacteriophage T4N5 to the skin of mice exposed to solar-simulated UVA + UVB radiation or mice exposed to UVA radiation blocked immune suppression, demonstrating an essential role for UV-induced DNA damage in the suppression of established immune reactions. These findings indicate that UV radiation activates similar immunological pathways to suppress the induction, or the elicitation, of the immune response.

Inhibition of UV-induced p53 mutations and skin cancers by sunscreens: implication for skin cancer prevention.

The relationship between exposure to UVB radiation and development of skin cancer has been well established. Several studies have shown that UVB induces unique mutations (C to T and CC to TT transitions) in the p53 tumor suppressor gene that are not commonly induced by other carcinogens. Our studies have demonstrated that UV-induced mouse skin cancers contain p53 mutations at a high frequency and that these mutations can be detected in UV-irradiated mouse skin well before the appearance of skin tumors. This observation suggested that it might be possible to use p53 mutations as a biological endpoint for testing the efficacy of sunscreens in photoprotection studies. Indeed, application of SPF 15 sunscreens to mouse skin before each UVB irradiation resulted in 88-92% reduction in the number of p53 mutations. Because p53 mutations represent an early essential step in photocarcinogenesis, these results imply that inhibition of this event may protect against skin cancer development. This hypothesis is confirmed by our finding that sunscreens used in p53 mutation inhibition experiments also protected mice against UVB-induced skin cancer.

Mechanisms underlying the suppression of established immune responses by ultraviolet radiation.

The ultraviolet radiation present in sunlight is immune suppressive. Recently we showed that solar-simulated ultraviolet radiation (ultraviolet A + B; 295-400 nm), applied after immunization, suppressed immunologic memory and the elicitation of delayed-type hypersensitivity to the common opportunistic pathogen, Candida albicans. Further, we found that wavelengths in the ultraviolet A region of the solar spectrum (320-400 nm), devoid of ultraviolet B, were equally effective in activating immune suppression as ultraviolet A + B radiation. Here we report on the mechanisms involved. Maximal immune suppression was found when mice were exposed to solar-simulated ultraviolet radiation 7-9 d post immunization. No immune suppression was found in ultraviolet-irradiated mice injected with monoclonal anti-interleukin-10 antibody, or mice exposed to solar-simulated ultraviolet radiation and injected with recombinant interleukin-12. Suppressor lymphocytes were found in the spleens of mice exposed to ultraviolet A + B radiation. In addition, antigen-specific suppressor T cells (CD3+, CD4+, DX5+) were found in the spleens of mice exposed to ultraviolet A radiation. Applying liposomes containing bacteriophage T4N5 to the skin of mice exposed to solar-simulated ultraviolet A + B radiation, or mice exposed to ultraviolet A radiation, blocked immune suppression, demonstrating an essential role for ultraviolet-induced DNA damage in the suppression of established immune reactions. These findings indicate that overlapping immune suppressive mechanisms are activated by ultraviolet A and ultraviolet A + B radiation. Moreover, our findings demonstrate that ultraviolet radiation activates similar immunologic pathways to suppress the induction of, or the elicitation of, the immune response.