Human Skin Carcinoma Research Articles

Bioactivity-guided Study of Antiproliferative Activities of Salvia Extracts

The cytotoxic activities of the n-hexane, chloroform and aqueous methanolic fractions prepared from the methanolic extract of the leaves of 23 Salvia taxa were studied for their cell growth-inhibitory activity against human cervix adenocarcinoma (HeLa), skin carcinoma (A431) and breast adenocarcinoma (MCF7) cells using the MTT assay. The n-hexane fractions of six Salvia taxa (S. hispanica, S. nemorosa, S. nemorosa 1. albiflora, S. pratensis, S. recognita and S. ringens) and the chloroform fraction ofS. officinalis 1. albiflora produced over 50% growth inhibition of the skin carcinoma cell line. None of the tested extracts showed substantial (above 50%) antiproliferative effects against HeLa and MCF7 cells. S. ringens was the most powerful among the studied Salvia species with a 61.8% cell growth inhibitory activity on A431 cells. In the case of S. ringens, other plant parts were also tested for antiproliferative effect, and the highest activities were recorded for the root extract. This was subjected to bioactivity-guided fractionation, which yielded four abietane diterpenes (royleanone, horminone, 7-O-methyl-horminone and 7-acetyl-horminone), one triterpene (erythrodiol-3-acetate) and beta-sitosterol. Horminone, 7-acetyl-horminone and erythrodiol-3-acetate displayed marked concentration-dependent antiproliferative effects, while royleanone and 7-O-methyl-horminone produced weaker activities.

Antiproliferative Constituents of the Roots ofConyza canadensis

Bioassay-guided fractionation of the N-hexane and CHCl₃ phases of the methanol extract of the roots of Conyza canadensis (L.) Cronquist led to the isolation of two new dihydropyranones named conyzapyranone A (1) and B (2), and the known 4 Z,8 Z-matricaria- γ-lactone (3), 4 E,8 Z-matricaria- γ-lactone (4), 9,12,13-trihydroxy-10(E)-octadecenoic acid (5), epifriedelanol (6), friedeline (7), taraxerol (8), simiarenol (9), spinasterol (10), stigmasterol, β-sitosterol, and apigenin. The structures were determined by means of ESIMS and 1D and 2D NMR spectroscopy, including ¹H-¹H COSY, NOESY, HSQC, and HMBC experiments. The isolated compounds were evaluated for their antiproliferative activities and were demonstrated to exert considerable cell growth-inhibitory activity against human cervix adenocarcinoma (HeLa), skin carcinoma (A431), and breast adenocarcinoma (MCF-7) cells. Some of the active components, including 2, 4, and 10, proved to be substantially more potent against these cell lines than against noncancerous human foetal fibroblasts (MRC-5) and can therefore be considered selective antiproliferative natural products.

IL‐6 promotes malignant growth of skin SCCs by regulating a network of autocrine and paracrine cytokines

Cytokines play a crucial role in tumor initiation and progression. Here, we demonstrate that interleukin (IL)-6 is a key factor by driving tumor progression from benign to malignant, invasive tumors in the HaCaT-model of human skin carcinoma. IL-6 activates STAT3 and directly stimulates proliferation and migration of the benign noninvasive HaCaT-ras A-5 cells in vitro. Furthermore, IL-6 induces a complex, reciprocally regulated cytokine network in the tumor cells that includes inflammatory and angiogenic factors such as IL-8, GM-CSF, VEGF and MCP-1. These IL-6 effects lead to tumor cell invasion in organotypic cultures in vitro and to the formation of malignant and invasive s.c. tumors in vivo. Tumor invasion is supported by the IL-6 induced overexpression of MMP-1 in vitro and in vivo. These data demonstrate a key function of IL-6 in the progression of skin SCCs by regulating a complex cytokine and protease network and suggest new therapeutic approaches to target this central player in skin carcinogenesis.

Mitochondrial Mix: Combined Approach to Visualizing Oxidative Stress in Real Time

Oxidative stress resulting from mitochondrial dysfunction may play a role in toxicity caused by many different environmental contaminants, including aromatic hydrocarbons and metal ions, but it has been difficult to evaluate the role of mitochondria in oxidative stress using currently available methods. A new study combining new and established imaging techniques to document mitochondrial dysfunction now indicates this integrated approach to real-time imaging in live cells can be useful for studying the role of oxidative stress in toxicologic responses [EHP 118(7):902–908; Cheng et al.]. Real-time imaging in live cells to detect products of oxidative stress known as reactive oxygen species (ROS) offers superior temporal and spatial resolution compared with traditional methods such as detecting oxidized lipids, proteins, or DNA. But the accuracy and utility of the fluorescent indicator H2DCF-DA, a reagent commonly used for directly detecting ROS in living cells, is limited. The authors conducted a set of experiments in which they exposed cultured human skin carcinoma cells to zinc (Zn2+), a ubiquitous contaminant known to induce oxidative stress. Three different fluorescent imaging techniques were used to study effects of Zn2+ on mitochondria. The first used the fluorophore PG1 to measure production of the ROS hydrogen peroxide. The scientists found that hydrogen peroxide increased within the cells upon Zn2+ exposure and that its production was inhibited with the addition of the mitochondrial inhibitor CCCP, implicating mitochondria as the source of the Zn2+-induced hydrogen peroxide. A second experiment used the fluorescent indicator JC-1 to measure changes in mitochondrial membrane potential (the difference in electrical potential between the inside and outside of the mitochondrial membrane) following exposure to Zn2+. When Zn2+ was administered, loss of JC-1 fluorescence emission indicated a loss of membrane potential consistent with impaired mitochondrial function. A third experiment used the genetically encoded fluorescent sensor MTroGFP1 to measure the redox potential of mitochondria after Zn2+ exposure. MTroGFP1 associates with mitochondria in transfected cells, causing the mitochondria to fluoresce. However, the investigators observed a change in the fluorescent signals following exposure to Zn2+ consistent with a loss of redox potential. In a fourth experiment on mitochondria isolated from live mouse hearts, the authors demonstrated that administering Zn2+ resulted in rapid mitochondrial swelling, another indication of a loss of mitochondrial function. The study shows the value of combining multiple imaging techniques to constitute an integrated approach that permits real-time monitoring of the mechanisms behind oxidative stress within living cells. The results also add to the evidence that oxidative stress induced by Zn2+ originates in mitochondria and sheds light on some of the mechanisms that may be involved. Further study is under way to determine the exact sequence of cellular events by which toxicants induce generation of ROS and mitochondrial dysfunction.

Gene Expression Patterns of Normal Human Skin, Actinic Keratosis, and Squamous Cell Carcinoma

To identify and compare the gene expression profiles of actinic keratosis (AK) and squamous cell carcinoma (SCC) and to further clarify critical genetic alterations in the evolution of SCC from normal sun-damaged human skin. Observational study. University practice. Skin biopsy specimens were obtained from 16 patients. The specimens included 14 normal non-sun-exposed skin samples, 14 normal sun-exposed skin samples, 5 AKs, and 15 cutaneous SCCs. Gene expression profiles from normal non-sun-exposed skin, normal sun-exposed skin, AKs, and SCCs. Using a highly astringent shrunken centroid threshold of 6.52 and the prediction analysis of microarrays, we identified 89 unique genes that most likely contribute to the molecular evolution of SCC. Our model was cross-validated using data from a separate study and clearly distinguishes between skin tumors (AK and SCC) and normal skin independent of sun exposure. Genes that were upregulated in AK and SCC were downregulated in normal skin, and genes that were downregulated in AK and SCC were upregulated in normal skin. The finding of similar differentially expressed genes in AK and SCC confirms that AK is a precursor lesion of SCC and indicates that they are closely related genetically. Clear elucidation of these relationships will be critical to improving therapeutic approaches.

Antiproliferative, Cytotoxic, Antioxidant Activity and Polyphenols Contents in Leaves of Four Staphylea L. Species

Staphylea has been used for long time in Traditional Chinese Medicine (TCM) and by Native Americans in a number of therapeutical indications. The present study describes in vitro antiproliferative, cytotoxic properties (MTT and LDH test) and antioxidant activities (reduction of DPPH radical and peroxynitrite radical) of Staphylea colchica Stev. (SC), S. elegans Zab. (SC), S. holocarpa Hemsl. (SH) and S. pinnata L. (SP) leave water extracts. Time- (24 and 72 h) and dose- (1-150 μg/mL) dependent effects of the above extracts were tested at the mitochondrial (MTT test) and plasma membrane level (LDH leakage) in A431 human skin carcinoma cells. Screening of these properties has shown time and dose dependent increase of harmful effects, the highest activity was observed for the SE, while the less active was the SH extract. The ED50 values for the mitochondrial and membrane damage were nearly identical for the SE and very similar for SH extract. These findings indicate simultaneous injury of both cell compartments by SE and SH extracts. The highest antioxidant potential of SE species is accompanied by the highest content of flavones/flavonols and polyphenols. Only flavonoid contents are associated with antiproliferative effects and cell membrane injury, while antioxidant properties are the result of polyphenol content. The data clearly demonstrate that individual Staphylea L. species differ, not only in the amount of biologically active compounds, but also by the extent of harmful and beneficial effects.

Xanthanolides with Antitumour Activity from Xanthium italicum

Bioassay-guided fractionation of a CHCl3 extract of the leaves of Xanthium italicum Moretti led to the isolation of four xanthanolides: xanthatin (1), 4-epixanthanol (2), 4-epi-isoxanthanol (3), and 2-hydroxyxanthinosin (4). Their structures were determined by means of 1D and 2D NMR spectroscopy, including 1H-1H COSY, NOESY, HSQC and HMBC experiments, which resulted in complete and unambiguous 1H and 13C NMR chemical shift assignments. The isolated compounds 1-4 were evaluated for their antiproliferative activities, and were demonstrated to exert significant cell growth inhibitory activity against human cervix adenocarcinoma (HeLa), skin carcinoma (A431), and breast adenocarcinoma (MCF7) cells.

Synthesis and in vitro antiproliferative activity of diphenyl(sulphonylpiperidin-4-yl)methanol derivatives

A series of novel diphenyl(piperidin-4-yl)methanol derivatives 10(a–n) were synthesized and characterized by 1H NMR, LC/MS, FTIR, and elemental analyses. All the synthesized compounds were evaluated for cell proliferation by MTT assay. The antiproliferative effects of the synthesized compounds were tested against viable human skin fibroblast cell line and carcinoma cell lines, namely HeLa cells, HT-29 cells, MCF-7 cells, and HepG-2 cells in comparing the positive and negative control. Among the synthesized compounds, (10b) and (10g) have been identified as potent antiproliferative agents.

Molecular Signature of HPV-Induced Carcinogenesis: pRb, p53 and Gene Expression Profiling

The infection by mucosal human papillomavirus (HPV) is causally associated with tumor development in cervix and oropharynx. The mechanisms responsible for this oncogenic potential are mainly due to the product activities of two early viral oncogenes: E6 and E7. Although a large number of cellular targets have been described for both oncoproteins, the interaction with tumor suppressors p53 and retinoblastoma protein (pRb) emerged as the key functional activities. E6 degrades tumor suppressor p53, thus inhibiting p53-dependent functions, whereas E7 binds and degrades pRb, allowing the transcription of E2F-dependent genes. Since these two tumor suppressors exert their actions through transcriptional modulation, functional genomics has provided a large body of data that reflects the altered gene expression of HPVinfected cells or tissues. Here we will review the similarities and differences of these findings, and we also compare them with those obtained with transgenic mouse models bearing the deletion of some of the viral oncogene targets. The comparative analysis supports molecular evidences about the role of oncogenes E6 and E7 in the interference with the mentioned cellular functions, and also suggests that the mentioned transgenic mice can be used as models for HPV-associated diseases such as human cervical, oropharynx, and skin carcinomas.

Synthesis of novel 6-fluoro-3-(4-piperidinyl)-1,2-benzisoxazole derivatives as antiproliferative agents: A structure–activity relationship study

A series of novel 6-fluoro-3-(4-piperidinyl)-1,2-benzisoxazole derivatives 5(a-m) were synthesized with different substituted aromatic/heterocyclic acid chlorides (R-CO-Cl) and characterized by (1)H NMR, LC/MS, FTIR and elemental analyses. All the compounds synthesised were evaluated for their antiproliferative activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The antiproliferative effects of the synthesised compounds were tested against viable human skin fibroblast cells and carcinoma cells namely HeLa cells, HT-29 cells, MCF-7 cells, HepG-2 cells by adopting positive and negative control. The importance of the aromatic and heterocyclic moiety was confirmed. From the SAR studies, it reveals that, the substitution at N-terminal of 6-fluoro-3-(4-piperidinyl)-1,2-benzisoxazole by the heterocyclic ring plays a dominant role and was responsible for the antiproliferative activity. Among the synthesized compounds 5a, 5d and 5k have showed potent antiproliferative activity on all the carcinoma cells tested.

Zinc oxide nanoparticles as novel alpha-amylase inhibitors

Amylase inhibitors, also known as starch blockers, contain substances that prevent dietary starches from being absorbed by the body via inhibiting breakdown of complex sugars to simpler ones. In this sense, these materials are projected as having potential applications in diabetes control. In this context, we report on zinc oxide nanoparticles as possible alpha-amylase inhibitors. Zinc oxide nanoparticles have been synthesized using soft-chemistry approach and 1-thioglycerol was used as a surfactant to yield polycrystalline nanoparticles of size ∼18 nm, stabilized in wurtzite structure. Conjugation study and structural characterization have been done using x-ray diffraction technique, Fourier transform infrared spectroscopy, UV-visible spectroscopy, and transmission electron microscopy. Cytotoxicity studies on human fibrosarcoma (HT-1080) and skin carcinoma (A-431) cell lines as well as mouse primary fibroblast cells demonstrate that up to a dose of 20 μg/ml, ZnO nanoparticles are nontoxic to the cells. We report for the first time the alpha-amylase inhibitory activity of ZnO nanoparticles wherein an optimum dose of 20 μg/ml was sufficient to exhibit 49% glucose inhibition at neutral pH and 35 °C temperature. This inhibitory activity was similar to that obtained with acarbose (a standard alpha-amylase inhibitor), thereby projecting ZnO nanoparticles as novel alpha-amylase inhibitors.

Synthesis and In Vitro Antiproliferative Activity of Diphenyl(piperidin-4- yl)thioamide Methanol Derivatives

A series of novel diphenyl(piperidin-4-yl)methanol derivatives 10(a-j) were synthesized and characterized by 1H NMR, LC/MS, FTIR and elemental analyses. All the compounds synthesised were evaluated for their cell antiproliferation activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The antiproliferative effects of the synthesised compounds were tested against viable human skin fibroblast cell line and carcinoma cell lines namely HeLa, HT-29, MCF-7, HepG-2 by adopting positive and negative control. The importance of the methoxy and fluorine group on diphenyl(piperidin-4-yl)methanol moiety was confirmed and it was noted that, the substitution at 4th position of the aryl ring plays a dominant role and was responsible for the antiproliferative activity. Among the synthesized compounds, only (10a) and (10b) have potent antiproliferative activity on all the carcinoma cell lines tested.

Comparison of ALA- and ALA hexyl-ester-induced PpIX depth distribution in human skin carcinoma

Photodynamic therapy (PDT) based on the use of photoactivable porphyrins, such as protoporphyrin IX (PpIX), induced by the topical application of amino-levulinic acid (ALA) or its derivatives, ALA methyl-ester (m-ALA), is a treatment for superficial basal cell carcinoma (BCC), with complete response rates of over 80%. However, in the case of deep, nodular-ulcerative lesions, the complete response rates are lower, possibly related to a lower bioavailability of PpIX. Previous in vitro skin permeation studies demonstrated an increased penetration of amino-levulinic acid hexyl-ester (h-ALA) over ALA. In this study, we tested the validity of this approach in vivo on human BCCs. An emulsion containing 20% ALA (w/w) and preparations of h-ALA at different concentrations were applied topically to the normal skin of Caucasian volunteers to compare the PpIX fluorescence intensities with an optical fiber-based spectrofluorometer. In addition, the PpIX depth distribution and fluorescence intensity in 26 BCCs were investigated by fluorescence microscopy following topical application of 20% ALA and 1% h-ALA. We found that, for application times up to 24 h, h-ALA is identical to ALA as a PpIX precursor with respect to PpIX fluorescence intensity, depth of penetration, and distribution in basal cell carcinoma, but has the added advantage that much smaller h-ALA concentrations can be used (up to a factor 13). We observed a non-homogenous distribution in BCCs with both precursors, independent of the histological type and depth of invasion in the dermis.

Antiproliferative and cytotoxic activity of infusions from four Staphylea L. species

Water infusions from some Staphylea L. species (Staphyleaceae) are used in Traditional Chinese Medicine. Based on this fact, time (24 and 72h) and dose (1–150µg/ml) dependent antiproliferative and toxic effects of water leaf infusions from S. colchica (SC), S. elegans (SE), S. holocarpa (SH) and S. pinnata (SP) were investigated. Human skin carcinoma cells A431 were used for determination of antiproliferative activity/cell viability (MTT test) and cytotoxic effects were measured by LDH leakage (representing membrane integrity). Screening of these activities has shown time dependent increase of destructive effects, with SE performing the best. The ED50 values for the mitochondrial and membrane integrity damage were quite similar for SE extract. This finding indicates simultaneous harmful effect on both cell compartments. SC, SH and SP infusions display similar ED50 values for intracellular and membrane damage as well as the extent of cell growth inhibition and LDH leakage. The values represent mean±SE of 4 separate experiments performed in duplicate. Statistical significance was calculated using Student's t-test and the one-way ANOVA test, when *p<0.05; **p<0.01; ***p<0.0001 (24h vs. 72h).

Synthesis and in vitro antiproliferative activity against human cancer cell lines of novel 5-(4-methyl-benzylidene)-thiazolidine-2,4-diones

A series of novel 5-(4-methyl-benzylidene)-thiazolidine-2,4-dione derivatives 6 (a-d) and 7 (a-g) were synthesized with different substituted aromatic sulfonyl chlorides (R-SO(2)-Cl) and alkyl halides (R-X) and were characterized by (1)H NMR, LC/MS, FTIR and elemental analyses. All the compounds synthesised were evaluated for their cell antiproliferation activity by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The antiproliferative effects of the synthesised compounds were tested against viable human skin fibroblast cell line and carcinoma cell lines namely HeLa cells, HT-29 cells, MCF-7 cells, HepG-2 cells by adopting positive and negative control. The importance of the nitro group on thiazolidinone moiety was confirmed and it was concluded that the fourth position of the substituted aryl ring plays a dominant role and was responsible for the antiproliferative activity. Among the synthesized compounds only 6a, 7e and 7g have potent antiproliferative activity on all the carcinoma cell lines tested.

UVA radiation causes DNA strand breaks, chromosomal aberrations and tumorigenic transformation in HaCaT skin keratinocytes

The role of UVA-radiation-the major fraction in sunlight-in human skin carcinogenesis is still elusive. We here report that different UVA exposure regime (4 x 5 J/cm(2) per week or 1 x 20 J/cm(2) per week) caused tumorigenic conversion (tumors in nude mice) of the HaCaT skin keratinocytes. While tumorigenicity was not associated with general telomere shortening, we found new chromosomal changes characteristic for each recultivated tumor. Since this suggested a nontelomere-dependent relationship between UVA irradiation and chromosomal aberrations, we investigated for alternate mechanisms of UVA-dependent genomic instability. Using the alkaline and neutral comet assay as well as gamma-H2AX foci formation on irradiated HaCaT cells (20-60 J/cm(2)), we show a dose-dependent and long lasting induction of DNA single and double (ds) strand breaks. Extending this to normal human skin keratinocytes, we demonstrate a comparable damage response and, additionally, a significant induction and maintenance of micronuclei (MN) with more acentric fragments (indicative of ds breaks) than entire chromosomes particularly 5 days post irradiation. Thus, physiologically relevant UVA doses cause long-lasting DNA strand breaks, a prerequisite for chromosomal aberration that most likely contribute to tumorigenic conversion of the HaCaT cells. Since normal keratinocytes responded similarly, UVA may likewise contribute to the complex karyotype characteristic for human skin carcinomas.

Agelastatin A: a novel inhibitor of osteopontin-mediated adhesion, invasion, and colony formation

Effective inhibitors of osteopontin (OPN)-mediated neoplastic transformation and metastasis are still lacking. (-)-Agelastatin A is a naturally occurring oroidin alkaloid with powerful antitumor effects that, in many cases, are superior to cisplatin in vitro. In this regard, past comparative assaying of the two agents against a range of human tumor cell lines has revealed that typically (-)-agelastatin A is 1.5 to 16 times more potent than cisplatin at inhibiting cell growth, its effects being most pronounced against human bladder, skin, colon, and breast carcinomas. In this study, we have investigated the effects of (-)-agelastatin A on OPN-mediated malignant transformation using mammary epithelial cell lines. Treatment with (-)-agelastatin A inhibited OPN protein expression and enhanced expression of the cellular OPN inhibitor, Tcf-4. (-)-Agelastatin A treatment also reduced beta-catenin protein expression and reduced anchorage-independent growth, adhesion, and invasion in R37 OPN pBK-CMV and C9 cell lines. Similar effects were observed in MDA-MB-231 and MDA-MB-435s human breast cancer cell lines exposed to (-)-agelastatin A. Suppression of Tcf-4 by RNA interference (short interfering RNA) induced malignant/invasive transformation in parental benign Rama 37 cells; significantly, these events were reversed by treatment with (-)-agelastatin A. Our study reveals, for the very first time, that (-)-agelastatin A down-regulates beta-catenin expression while simultaneously up-regulating Tcf-4 and that these combined effects cause repression of OPN and inhibition of OPN-mediated malignant cell invasion, adhesion, and colony formation in vitro. We have also shown that (-)-agelastatin A inhibits cancer cell proliferation by causing cells to accumulate in the G(2) phase of cell cycle.

99mTc-Labeled Nanobodies: A New Type of Targeted Probes for Imaging Antigen Expression

Introduction: The development of specific radiolabeled probes towards molecular markers in vivo has gained interest as targeted imaging allows for a more accurate detection of diseases. We investigate the feasibility of targeted imaging of cancer antigens using the variable domain of single chain camelid antibodies (Nanobodies®) labeled with 99mTechnetium. Nanobodies against carcinoembryonic antigen (CEA) were used as a model. Methods: His6-CEA1 Nanobodies were generated and labeled with 99mTc at their His-tag using Tc(I)-tricarbonyl (Isolink, Mallinckrodt, B.V., Petten, The Netherlands). The normal biodistribution was assessed in healthy athymic mice by ex vivo analysis at 1 and 3 h. In vivo targeting was evaluated in the same mouse model bearing the CEA-positive LS174T tumour or a CEA-negative A431 (human skin carcinoma) control tumour. Pinhole SPECT imaging was performed at 3 hours after intravenous injection of 90 MBq 99mTc-His6-CEA1 using a dual-headed gamma camera equipped with pinhole collimators. Results: Radiolabeling efficiency was > 95%. General biodistribution showed intense renal uptake and marked liver accumulation. Using pinhole-SPECT, the average uptake of 99mTc- His6-CEA1 in LS174T (CEA positive) was significantly higher compared to the A431 (CEA negative) control tumour: respectively 3.2 ± 0.6 %IA/cm3 and 1.1 ± 0.2 %IA/cm3 (p < 0.05). Conclusion: This study presents effective labeling of Nanobodies with 99mTc using Tc(I)-carbonyl chemistry and shows their potential as a new type of specific probes for imaging antigen expression.

Targeting mutant p53 shows promise for sunscreens and skin cancer

Chronic exposure to UV light is a risk factor for skin cancer in which signature mutations in the p53 tumor suppressor gene occur due to DNA damage and contribute to cancer development. In this issue of the JCI, Tang et al. report on their study of a nonimmunodeficient mouse model of UVB-induced skin cancer and human skin carcinoma cells and show that the mutant p53 conformation-modifying drug CP-31398 not only treats these tumors but also prevents them (see the related article beginning on page 3753). These studies have important implications for chemoprevention as well as therapy of common, mutant p53-driven tumors.

CP-31398 restores mutant p53 tumor suppressor function and inhibits UVB-induced skin carcinogenesis in mice.

Mutations in the tumor suppressor p53 are detectable in over 50% of all human malignancies. Mutant p53 protein is incapable of transactivating its downstream target genes that are required for DNA repair and apoptosis. Chronic exposure to UVB induces p53 mutations and is carcinogenic in both murine and human skin. CP-31398, a styrylquinazoline compound, restores the tumor suppressor functions of mutant forms of p53 in tumor cells. However, its effectiveness in vivo remains unclear. Here, we demonstrate that CP-31398 blocked UVB-induced skin carcinogenesis and was associated with increases in p53, p21, and BclXs. CP-31398 downregulated Bcl2, proliferating nuclear cell antigen, and cyclin D1. Activation of caspase-3 and cleavage of poly (ADP-ribose) polymerase also occurred in both tumor and perilesional skin following treatment. CP-31398 induced the expression of p53-dependent target proteins, and this was followed by apoptosis in UVB-irradiated wild-type mice but not in their p53-deficient littermates. Similar effects were observed in human skin carcinoma A431 cells expressing mutant p53. In addition, CP-31398 induced mitochondrial translocation of p53, leading to changes in mitochondrial membrane permeability pore transition (MPT) and consequent cytochrome c release in these cells. Blocking MPT diminished p53 translocation and apoptosis. These studies indicate that reconstituting p53 tumor suppressor functions in vivo by small molecular weight compounds may block the pathogenesis and progression of skin cancer.