Immune-based biomarker accurately predicts response to imiquimod immunotherapy in cervical high-grade squamous intraepithelial lesions.

BACKGROUND: The complete response rate of cervical high-grade squamous intraepithelial lesion (cHSIL) patients to imiquimod immunotherapy is approximately 60%. Consequently, many patients are exposed to unnecessary adverse effects of imiquimod. On the other hand, conventional surgical large loop excision therapy is associated with increased risk of premature births in subsequent pregnancies. An in-depth analysis of the cHSIL immune microenvironment was performed in order to identify and develop a predictive biomarker for response to imiquimod, to maximize therapy efficacy and to avoid adverse effects in patients unlikely to respond. METHODS: Biopsies of 35 cHSIL patients, before and 10 weeks on imiquimod treatment, were analyzed by two multispectral seven-color immunofluorescence panels for T cell and myeloid cell composition in relation to treatment response. Based on these results a simplified immunohistochemical detection protocol was developed. Samples were scanned with the Vectra multispectral imaging system and cells were automatically identified using machine learning. RESULTS: The immune microenvironment of complete responders (CR) is characterized by a strong and coordinated infiltration by T helper cells (activated PD1+/type 1 Tbet+), M1-like macrophages (CD68+CD163-) and dendritic cells (CD11c+) prior to imiquimod. The lesions of non-responders (NRs) displayed a high infiltration by CD3+FOXP3+ regulatory T cells. At 10 weeks on imiquimod, a strong influx of intraepithelial and stromal CD4+ T cells was observed in CR but not NR patients. A steep decrease in macrophages occurred both in CR and NR patients, leveling the pre-existing differences in myeloid cell composition between the two groups. Based on the pre-existing immune composition differences, the sum of intraepithelial CD4 T cell, macrophage and dendritic cell counts was used to develop a quantitative simplified one color immunohistochemical biomarker, the CHSIL immune biomarker for imiquimod (CIBI), which can be automatically and unbiasedly quantified and has an excellent predictive capacity (receiver operating characteristic area under the curve 0.95, p<0.0001). CONCLUSION: The capacity of cHSIL patients to respond to imiquimod is associated with a pre-existing coordinated local immune process, fostering an imiquimod-mediated increase in local T cell infiltration. The CIBI immunohistochemical biomarker has strong potential to select cHSIL patients with a high likelihood to experience a complete response to imiquimod immunotherapy.

BRCA1-associated mammary tumorigenesis is dependent on estrogen rather than progesterone signaling.

Hereditary breast cancers in BRCA1 mutation carriers are mostly estrogen receptor α (ERα)-negative and progesterone receptor (PR)-negative; however, hormone depletion via bilateral oophorectomy does result in a marked reduction in breast cancer risk, suggesting that BRCA1-associated breast tumorigenesis is dependent on hormone signaling. We used geneticaly engineered mouse models to determine the individual influences of ERα and PR signaling on the development of BRCA1-deficient breast cancer. In line with the human data, BRCA1-deficient mouse mammary tumors are ERα-negative, and bilateral ovariectomy leads to abrogation of mammary tumor development. Hormonal replacement experiments in ovariectomized mice showed that BRCA1-deficient mammary tumor formation is promoted by estrogen but not by progesterone. In line with these data, mammary tumorigenesis was significantly delayed by the selective ERα downregulator fulvestrant, but not by the selective PR antagonist Org33628. Together, our results illustrate that BRCA1-associated tumorigenesis is dependent on estrogen signaling rather than on progesterone signaling, and call into question the utility of PR antagonists as a tumor prevention strategy for BRCA1 mutation carriers. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cutaneous squamous cell carcinomas (SCC) associated with cosmetic skin whitening: 8 cases reported in Senegal.

BACKGROUND: The cosmetic use of bleaching products is common among women from sub-Saharan Africa. The most frequently used products are highly potent corticosteroids (clobetasol propionate) and hydroquinone. Herein, we report 8 cases of SCC in women using skin bleaching products for cosmetic purposes. Our aim is to describe the epidemiological, clinical and pathological aspects of the carcinomas observed during the course of skin lightening. METHODS: We conducted a descriptive multicentre study from August 2005 to January 2016 in three dermatology units in Senegal. We included all patients consulting for cutaneous squamous cell carcinoma associated with skin bleaching. Sociodemographic, clinical, paraclinical and therapeutic data were recorded. RESULTS: A total of 8 female patients were included. The mean age was 48.1 years (37-63 years). Topical hydroquinone and highly potent corticosteroids were the main products used over the whole body, for an average duration of 20.3 years. No pre-neoplastic skin disease was found in our patients. The clinical aspects of tumours were as follows: cauliflower-like (n=4), ulcerated (n=3) and nodular (n=1). The average development time before consultation was 6.75 months. All the cutaneous squamous cell carcinomas were localized to lichenoid lesions or exogenous ochronotic lesions on photo-exposed areas: face (n=1), neck (n=3) or upper back (n=4). The most common histopathological type was the infiltrating form and there was one case of in situ carcinoma. The outcome was favourable in six of eight patients after surgical resection. Two deaths occurred: one through tumour recurrence and the other through haemorrhagic shock. CONCLUSIONS: From 2005 to 2016, eight cases of cutaneous squamous cell carcinomas associated with cosmetic use of bleaching products were reported in Senegal. The mechanism was not fully elucidated and further studies are necessary. These observations provide an additional argument for combating this practice and including skin bleaching among known risk factors for squamous cell carcinoma.

Anthocyanins Prevent Colorectal Cancer Development in a Mouse Model.

BACKGROUND: Colorectal cancer is the main leading cause of cancer-related deaths worldwide. Present data suggest that plant-derived anthocyanins have anti-inflammatory and chemopreventive properties. This study was aimed at evaluating the effect of an anthocyanin-rich extract from bilberries on colorectal tumour development and growth in the administration of azoxymethan (AOM)/dextran sodium sulfate (DSS) mouse model. METHODS: Colonic carcinogenesis was induced by AOM and DSS 3 or 5%, respectively, in 50 female Balb/c mice. Mice received either normal food (controls) or a diet containing either 10 or 1% anthocyanin-rich bilberry extract. Colonoscopy took place at week 4 and 9 after initiation of carcinogenesis. After termination at week 9, colon samples were analysed macroscopically and microscopically. RESULTS: Mice receiving 10% anthocyanins showed significantly (p < 0.004) less reduced colon length (12.1 cm [8.5-14.4 cm]) as compared to controls (11.2 cm [9.8-12.3]) indicating less inflammation. Mice fed with 10% anthocyanin-rich extract revealed significantly less mean tumour numbers (n = 1.2) compared to control (n = 14) and anthocyanin 1% treated mice (n = 10.6, p < 0.001). CONCLUSION: Anthocyanins prevented the formation and growth of colorectal cancer in AOM/DSS-treated Balb/c mice. Further studies should investigate the mechanisms of how anthocyanins influence the development of colorectal cancer.

The role of Ly49E receptor expression on murine intraepithelial lymphocytes in intestinal cancer development and progression.

Ly49E is a member of the Ly49 family of NK receptors and is distinct from other members of this family on the basis of its structural properties, expression pattern and ligand recognition. Importantly, Ly49E receptor expression is high on small intestinal and colonic intraepithelial lymphocytes (IELs). Intestinal IELs are regulators of the mucosal immune system and contribute to front-line defense at the mucosal barrier, including anti-tumor immune response. Whereas most Ly49 receptors have MHC class-I ligands, we showed that Ly49E is instead triggered by urokinase plasminogen activator (uPA). uPA has been extensively implicated in tumor development, where increased uPA expression correlates with poor prognosis. As such, we investigated the role of Ly49E receptor expression on intestinal IELs in the anti-tumor immune response. For this purpose, we compared Ly49E wild-type mice to Ly49E knockout mice in two established tumor models: ApcMin/+-mediated and azoxymethane-induced intestinal cancer. Our results indicate that Ly49E expression on IELs does not influence the development or progression of intestinal cancer.

HDAC3 mediates smoking-induced pancreatic cancer.

Smoking is a major risk factor for developing pancreatic adenocarcinoma (PDAC); however, little is known about the mechanisms involved. Here we employed a genetic animal model of early stages of PDAC that overexpresses oncogenic Kras in the pancreas to investigate the mechanisms of smoking-induced promotion of the disease in vivo. We confirmed the regulation of the interactions between the tumor microenvironment cells using in vitro cellular systems. Aerial exposure to cigarette smoke stimulated development of pancreatic intraepithelial neaoplasia (PanIN) lesions associated with a tumor microenvironment-containing features of human PDAC including fibrosis, activated stellate cells, M2-macrophages and markers of epithelial-mesenchymal transition (EMT). The pro-cancer effects of smoking were prevented by Histone Deacetylase HDAC I/II inhibitor Saha. Smoking decreased histone acetylation associated with recruitment of and phenotypic changes in macrophages; which in turn, stimulated survival and induction of EMT of the pre-cancer and cancer cells. The interaction between the cancer cells and macrophages is mediated by IL-6 produced under the regulation of HDAC3 translocation to the nucleus in the cancer cells. Pharmacological and molecular inhibitions of HDAC3 decreased IL-6 levels in cancer cells. IL-6 stimulated the macrophage phenotype change through regulation of the IL-4 receptor level of the macrophage. This study demonstrates a novel pathway of interaction between cancer cells and tumor promoting macrophages involving HDAC3 and IL-6. It further demonstrates that targeting HDAC3 prevents progression of the disease and could provide a strategy for treating the disease considering that the HDAC inhibitor we used is FDA approved for a different disease.

Characterization of Mouse Models of Early Pancreatic Lesions Induced by Alcohol and Chronic Pancreatitis.

OBJECTIVE: We describe the first mouse model of pancreatic intraepithelial neoplasia (PanIN) lesions induced by alcohol in the presence and absence of chronic pancreatitis. METHODS: Pdx1-Cre;LSL-K-ras mice were exposed to Lieber-DeCarli alcohol diet for 6 weeks with cerulein injections. The PanIN lesions and markers of fibrosis, inflammation, histone deacetylation, epithelial-to-mesenchymal transition (EMT), and cancer stemness were measured by immunohistochemistry and Western. RESULTS: Exposure of Pdx1-Cre;LSL-K-ras mice to an alcohol diet significantly stimulated fibrosis and slightly but not significantly increased the level of PanIN lesions associated with an increase in tumor-promoting M2 macrophages. Importantly, the alcohol diet did not increase activation of stellate cells. Alcohol diet and cerulein injections resulted in synergistic and additive effects on PanIN lesion and M2 macrophage phenotype induction, respectively. Cerulein pancreatitis caused stellate cell activation, EMT, and cancer stemness in the pancreas. Pancreatitis caused histone deacetylation, which was promoted by the alcohol diet. Pancreatitis increased EMT and cancer stemness markers, which were not further affected by the alcohol diet. CONCLUSIONS: The results suggest that alcohol has independent effects on promotion of PDAC associated with fibrosis formed through a stellate cell-independent mechanism and that it further promotes early PDAC and M2 macrophage induction in the context of chronic pancreatitis.

Mutations in the p16 gene in DMBA-induced pancreatic intraepithelial neoplasia and pancreatic cancer in rats.

BACKGROUND: 7, 12-dimethylbenzanthracene (DMBA)-induced pancreatic intraepithelial neoplasia (PanIN) and pancreatic cancer in rats provide a classic model for uncovering the molecular mechanisms underlying pancreatic cancer. However, this model has not been characterized genetically, and in particular, the major genetic alterations in the p16 gene are unknown. METHODS: Lesions of PanIN and pancreatic cancer were induced with DMBA implantation in 40 rats, and control pancreatic tissue was obtained from 10 age-matched rats without exposure to DMBA. Pancreatic tissue was harvested three months after DMBA implantation and DNA was extracted. Homozygous deletions and point mutations of the p16 (exons 1 and 2) gene were detected by PCR amplification and direct sequencing. RESULTS: DMBA implantation in the 40 rats induced 26 PanINs and 9 carcinomas. The overall frequency of p16 alterations in the pancreatic tissue of these rats was 42.86% (15/35), and the changes were point mutations, not homozygous deletions. p16 mutations were present in 30.77% (8/26) of the rats with PanIN and 77.78% (7/9) of the rats with carcinoma (P<0.05). The increasing incidence of p16 alterations was detected in 20.00% (1/5) of PanIN-1, 28.57% (2/7) of PanIN-2 and 35.71% (5/14) of PanIN-3 lesions. CONCLUSION: Our findings indicated that p16 alteration is a common event in the carcinogenesis of this model and that the mutation pattern is analogous to that of human lesions.

Dietary exposure in utero and during lactation to a mixture of genistein and an anti-androgen fungicide in a rat mammary carcinogenesis model.

Endocrine disruptors may play substantial roles in the high incidence of breast cancer. We previously described how early exposure to the mixture of phytoestrogen genistein (G) and the anti-androgen vinclozolin (V) affects peripubertal mammary development. This study evaluates the carcinogenic potential of exposure to V alone or associated with G from conception until weaning in Wistar rats. Dams were exposed to V, G or GV during pregnancy/lactation. At PND50 offspring were treated with DMBA[7,12-dimethylbenz(a)anthracene]. V or GV maternal exposure decreased number of DMBA-induced mammary tumors in the offspring, without significant modifications in tumor incidence, multiplicity and latency. G exposure decreased number of tumors, incidence and multiplicity. Unexpectedly, GV exposure increased tumor volume (p=0.04 vs controls) and epithelial proliferation (p=0.001 vs controls; p=0.005 vs G,V only). All tumors were in situ carcinomas. Concluding, maternal gestation/lactation exposure to a vinclozolin and genistein mixture significantly increases offspring tumor growth without changes in carcinogenesis susceptibility.

Melatonin potentiates the anti-tumour effect of pravastatin in rat mammary gland carcinoma model.

Previous studies in the field of cancer research have suggested a possible role for statins in the reduction of risk in certain malignancies. The purpose of these studies was to examine the chemopreventive effects of pravastatin alone and in combination with pineal hormone melatonin in the N-methyl-N-nitrosourea-induced mammary carcinogenesis model. Pravastatin was given orally (1 00 mg/kg) and melatonin was added to the water (20 µg/ml). Chemoprevention began seven days prior to carcinogen administration and subsequently continued for 15 weeks until autopsy. At autopsy, mammary tumours were removed and prepared for histopathological and immunohistochemical analysis. Parameters of experimental carcinogenesis, mechanism of action (biomarkers of apoptosis, angiogenesis and proliferation) and side effects after long-term treatment in animals were assessed. Pravastatin alone suppressed tumour frequency by 20.5% and average tumour volume by 15% compared with controls. Combined administration of the drugs decreased tumour frequency by 69% and lengthened tumour latency by nine days compared with control animals. The ration between high and low grade carcinomas was apparently reduced in both treated groups. The analysis of carcinoma cells showed significant expression increase in caspase-3 and caspase-7 after pravastatin treatment; however, combined treatment even more pronounced increase in the expression of both caspases. Regarding VEGFR-2 expression, a small effect in carcinomas of both treated groups was found. In plasma metabolism evaluation, pravastatin alone significantly decreased levels of glucose and triacylglycerols. Our results suggest a mild anti-neoplastic effect of pravastatin in this rat mammary gland carcinoma model. Statins co-administered with other suitable drug (e.g. melatonin) should be further evaluated for tumour-preventive properties.

Bladder cancers arise from distinct urothelial sub-populations.

Bladder cancer is the sixth most common cancer in humans. This heterogeneous set of lesions including urothelial carcinoma (Uca) and squamous cell carcinoma (SCC) arise from the urothelium, a stratified epithelium composed of K5-expressing basal cells, intermediate cells and umbrella cells. Superficial Uca lesions are morphologically distinct and exhibit different clinical behaviours: carcinoma in situ (CIS) is a flat aggressive lesion, whereas papillary carcinomas are generally low-grade and non-invasive. Whether these distinct characteristics reflect different cell types of origin is unknown. Here we show using lineage tracing in a murine model of carcinogenesis that intermediate cells give rise primarily to papillary lesions, whereas K5-basal cells are likely progenitors of CIS, muscle-invasive lesions and SCC depending on the genetic background. Our results provide a cellular and genetic basis for the diversity in bladder cancer lesions and provide a possible explanation for their clinical and morphological differences.

Focused ultrasound therapy for vulvar intraepithelial neoplasia in a mice model.

BACKGROUND: The purpose of this study was to determine the effectiveness and safety of focused ultrasound (FU) for the treatment of vulvar intraepithelial neoplasia (VIN) in a mice model. METHODS: Estradiol benzoate was subcutaneously injected into the abdomens of eighty 129/J mice. VIN was successfully induced in 56 mice and was divided into the FU group and the control group. Pathologic features and changes in vascular endothelial growth factor expression in the lesions were analyzed before and after treatment. RESULTS: Two months after treatment, lesions in 25 of the 56 mice showed restoration of normal skin. Nineteen of the 21 VINI and VINII lesions returned to normal and the other 2 VINII lesions were down graded to VINI, yielding a curative rate of 90.1%. In the control group, all 21 mice had persistent VIN (P < 0.0001). In the 14 mice with VINIII lesions, 6 returned to normal skin histology representing a curative rate of 42.9%, 5 were reclassified as VINI and 3 were reclassified as VINII. Thus, the total effectiveness rate was 100%. CONCLUSIONS: The present study suggests that FU therapy is effective, noninvasive and safe in treating VIN in a mice model.

An unusual cause of cancer mimicry following liver transplantation.

Sirolimus is an approved anti-rejection agent following liver or kidney transplantation that works through inhibition of the mammalian target of rapamycin (mTOR). As sirolimus functions through a pathway independent of calcineurin inhibition, it may have less potential for nephrotoxicity and carcinogenesis. That being said, there are a myriad of potential adverse effects reported with sirolimus, many of which are severe and unknown or poorly understood. Herein we present a case of sirolimus causing a serious but uncommon adverse event in an adult liver transplant recipient; the adverse event in this instance unfortunately resulted in significant medical testing and morbidity. The adverse event profile of sirolimus is summarized through review of available evidence.

Proteomic analysis of pancreatic intraepithelial neoplasia and pancreatic carcinoma in rat models.

AIM: To detect the proteomic variabilities of pancreatic intraepithelial neoplasia (PanIN) and pancreatic carcinoma (PC) induced by 7,12-dimethylbenzanthracene (DMBA) in rat models and to identify potential biomarkers. METHODS: Sixty adult male Sprague Dawley rats were randomized into three groups. The rats had DMBA implanted into their pancreas for one (n = 20) or two months (n = 20) or assigned to the normal group (n = 20). The rats were killed after one or two months, and were evaluated histopathologically. Three tissue samples from each group of rats with either normal pancreas, PanIN (PanIN-2) or PC were examined by 2D-DIGE. The different expression spot features were analyzed by matrix-assisted laser desorption/ionization-time of flight/time of flight (MALDI-TOF/TOF) tandem mass spectrometry. The expression of enolase 1, a differentially expressed protein, was identified by immunohistochemistry. RESULTS: There was significant difference in the proportions of neoplastic changes between the 1- and 2-mogroups (P = 0.0488). There was an increase in the frequency of adenocarcinomas in the 2-mo group compared with the 1-mo group (P = 0.0309). No neoplastic changes were observed in any of the animals in the normal group. Enolase 1, pancreatic ELA3B, necdin, Hbp23, CHD3, hnRNP A2/B1, Rap80, and Gnb2l1 were up-regulated in the PanIN and PC tissues, and CEL, TPT1, NME2, PCK2, an unnamed protein product, and glycine C-acetyltransferase were down-regulated in the PanIN and PC tissues. The immunohistochemical results showed that enolase 1 expression was up-regulated in the pancreatic cancer tissues of rats and humans. CONCLUSION: The pancreatic protein expression changes induced by DMBA suggest potential molecular targets for the early diagnosis and treatment of PC.

Histological and immunohistochemical evaluation of the chemopreventive role of lycopene in tongue carcinogenesis induced by 4-nitroquinoline-1-oxide.

OBJECTIVE: Increasing attention has been given to the potential protective roles of specific antioxidant nutrients found in fruits and vegetables. However, there are relatively few reports on the cancer chemopreventive effects of lycopene or tomato carotenoids in animal models. Therefore, the chemopreventive efficacy of lycopene with regard to oral carcinogenesis was investigated using 4-nitroquinoline-1-oxide (4-NQO) induced tongue squamous cell carcinoma. MATERIALS AND METHODS: Twenty albino rats were equally divided into 2 groups. 4-NQO was dissolved in the drinking water (20 ppm) for rats of both groups. Rats in group 2 were administered lycopene at a dose of 2.5mg/kg body weight by intragastric intubation once a day. Incidence of oral neoplasms and histopathological changes were microscopically evaluated after 32 weeks of administration of the specific treatments. Moreover, immunohistochemical expressions of proliferating cell nuclear antigen (PCNA), E-cadherin and ß-catenin were analysed in tongue specimens using an image analyser computer system. RESULTS: Lycopene treatment significantly decreased the incidence of 4-NQO induced tongue carcinogenesis. A decreased percentage of PCNA-positive nuclei was associated with lycopene treatment. Proliferating cells were mainly confined to the basal and parabasal epithelial cell layers. Increased E-cadherin and ß-catenin immunoexpression was recorded in the lycopene treated group in comparison to the carcinogen group. CONCLUSION: Results of the present study indicate that lycopene can exert protective effects against 4-NQO induced tongue carcinogenesis through reduction in cell proliferation and enhanced cellular adhesion, suggesting a new mechanism for the anti-invasive effect of lycopene. Further studies are needed to provide more definitive answers to the question of the anticancer effects of lycopene.

Computer-assisted morphometric analysis of lymphatic vessel changes in hamster tongue carcinogenesis.

BACKGROUND: To characterize lymphangiogenesis in early-stage hamster tongue carcinoma development, morphological features and spatial relationships of lymphatic vessels. METHODS: Lymphatic vessels were examined histochemically, using 5'-Nase-ALPase enzyme and combined light and electron microscopy to measure lymphatic vessel area (LVA) and lymphatic vessel density (LVD). RESULTS: In atypical hyperplastic tissues, LVA was found to be 1429.97 and LVD was found to be 39, in carcinoma in situ LVA was 2538.33 and LVD was 48, and in micro-invasive carcinoma LVA was 5733.74 and LVD was 59. Increased lymphangiogenesis was seen in pre-neoplastic states and in early-stage oral squamous cell carcinoma (OSCC). Small regular lymphatic vessels predominated in atypical hyperplasia, and large, irregular lymphatic vessels in early-stage OSCC. Lymphatic endothelial vessels were stretched and porous over large areas. CONCLUSIONS: Newly formed lymphatics and patulous intercellular junctions may be optimally suited for tumor cell metastasis through lymphatic channels in early- and middle-phase carcinogenesis. Lymphatic capillary LVA and LVD became enlarged, and positively correlated, with malignancy, but show no correlation with 7,12-dimethylbenz[a]anthracene-induced time.

Fluorescent imaging of high-grade bladder cancer using a specific antagonist for chemokine receptor CXCR4.

We previously reported that the expression of CXC chemokine receptor-4 (CXCR4) was upregulated in invasive bladder cancers and that the small peptide T140 was a highly sensitive antagonist for CXCR4. In this study, we identified that CXCR4 expression was induced in high-grade superficial bladder tumors, including carcinoma in situ and invasive bladder tumors. To visualize the bladder cancer cells using urinary sediments from the patients and chemically induced mouse bladder cancer model, a novel fluorescent CXCR4 antagonist TY14003 was developed, that is a T140 derivative. TY14003 could label bladder cancer cell lines expressing CXCR4, whereas negative-control fluorescent peptides did not label them. When labeling urinary sediments from patients with invasive bladder cancer, positive-stained cells were identified in all patients with bladder cancer and positive urine cytology but not in controls. Although white blood cells in urine were also labeled with TY14003, they could be easily discriminated from urothelial cells by their shape and size. Finally, intravesical instillation of TY14003 into mouse bladder, using N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced bladder cancer model, demonstrated that fluorescent signals were detected in the focal areas of bladder of all mice examined at 12 weeks of BBN drinking by confocal microscopy and fluorescent endoscopy. On the contrary, all the normal bladders were found to be negative for TY14003 staining. In conclusion, these results indicate that TY14003 is a promising diagnostic tool to visualize small or flat high-grade superficial bladder cancer.

Specific overexpression of cyclin E·CDK2 in early preinvasive and primary breast tumors in female ACI rats induced by estrogen.

Overexpressed Aurora A, amplified centrosomes, and aneuploidy are salient features of estrogen-induced mammary preinvasive lesions and tumors in female August--Copenhagen Irish (ACI) rats. Intimately involved in these events are cyclins and their associated cyclin-dependent kinase (CDK) partners. Cyclin E1·CDK2 overexpression plays an important dual role in late G1/S phase of the cell cycle in cancer cells. It increases DNA replication providing growth advantage to cancer cells and facilitates aberrant centrosome duplication, generating chromosomal instability and aneuploidy leading to tumor development. Presented herein, a 24.0- and 45.0-fold elevation in cyclin E1 and CDK2 was found in 17ß-estradiol (E(2))-induced ACI rat mammary tumors (MTs), respectively. Cyclin E·CDK2 positive staining was confined to the large round cells found within focal dysplasias, ductal carcinomas in situ, and invasive MTs. Co-immunoprecipitation and in vitro kinase activity of these tumors revealed that these cell cycle entities are functional. When mammary tissue derived from untreated normal, E(2)-induced hyperplasia and primary tumors were normalized to cyclin E1 levels, low molecular weight (LMW) cyclin E1 forms (33- and 45-kDa) were detected in all of these tissue groups. Moreover, increasing concentrations of protease inhibitor in tissue lysates resulted in a marked reduction of LMW forms, indicating that the presence of cyclin E1 LMW forms can be markedly reduced. Significant increases in cyclin E1 mRNA (2.1-fold) were detected in primary ACI rat E(2)-induced breast tumors, and quantitative real-time polymerase chain reaction revealed a 20% amplification of the cyclin E1 gene (CCNE1). Collectively, these results support the involvement of cyclin E1·CDK2 in centrosome overduplication during each stage of E(2)-induced mammary tumorigenesis.