Failure to progress: breast and prostate cancer cell lines in developing targeted therapies.

Developing anticancer drugs from preclinical to clinical takes approximately a decade in a cutting-edge biomedical lab and still 97% of most fail at clinical trials. Cell line usage is critical in expediting the advancement of anticancer therapies. Yet developing appropriate cell lines has been challenging and overcoming these obstacles whilst implementing a systematic approach of utilizing 3D models that recapitulate the tumour microenvironment is prudent. Using a robust and continuous supply of cell lines representing all ethnic groups from all locales is necessary to capture the evolving tumour landscape in culture. Next, the conversion of these models to systems on a chip that can by way of high throughput cytotoxic assays identify drug leads for clinical trials should fast-track drug development while markedly improving success rates. In this review, we describe the challenges that have hindered the progression of cell line models over seven decades and methods to overcome this. We outline the gaps in breast and prostate cancer cell line pathology and racial representation alongside their involvement in relevant drug development.

Racial disparities in breast cancer preclinical and clinical models.

Breast cancer (BCa) has long been a health burden to women across the globe. However, the burden is not equally carried across races. Though the manifestation and behavior of BCa differs among racial groups, the racial representation of models used in preclinical trials and clinical trial participants lacks this heterogeneity. Women of African Ancestry (WAA) are disproportionately afflicted by having an increased risk of developing BCas that are more aggressive in nature, and consequently suffer from poorer outcomes relative to women of European ancestry (WEA). Notwithstanding this, one of the most commonly used tools in studying BCa, cell lines, exhibit a sizeable gap in cell line derivatives of WEA relative to WAA. In this review, we summarize the available BCa cell lines grouped by race by major suppliers, American Type Culture Collection (ATCC) and the European Collection of Authenticated Cell Cultures (ECACC). Next, examined the enrollment of WAA in clinical trials for BCa. Of the cell lines found provided by ATCC and ECACC, those derived from WEA constituted approximately 80% and 94%, respectively. The disparity is mirrored in clinical trial enrollment where, on average, WEA made up more than 70% of participants in trials found where ancestry information was provided. As both experimental models and clinical trial participants primarily consist of WEA, results may have poorer translatability toward other races. This highlights the need for greater racial diversity at the preclinical and clinical levels to more accurately represent the population and strengthen the translatability of results.

Disparities in prostate cancer incidence and mortality rates: Solvable or not?

Prostate cancer (PCa) is recognized as a disease possessing not only great variation in its geographic and racial distribution but also tremendous variation in its potential to cause morbidity and death and it, therefore, ought not to be considered a homogenous disease entity. Morbidity and death from PCa are disproportionately higher in men of African ancestry (MAA) who are generally observed to have more aggressive disease and worse outcomes following treatment compared to men of European ancestry (MEA). The higher rates of PCa among MAA relative to MEA appear to be multifactorial and related to inherent differences in biological aggressiveness; a continued lack of awareness of the disease and methods of prevention; a lower prevalence of screen-detected PCa; comparatively lower access to quality healthcare as well as systemic and institutionalized disparities in the administration of optimal care to MAA in developed countries such as the United States of America where high-quality care is available. Even when access to quality healthcare is assured in equal access settings, it appears that MAA still have worse outcomes after PCa treatment stage-for-stage and grade-for-grade compared to MEA, suggesting that, inherent racial, ethnic and biological differences are paramount in predicting poor outcomes. This review has explored the different contributing factors to the current disparities in PCa incidence and mortality rates with emphasis on the incongruence in how research has been conducted in understanding the disease towards developing therapies.

Glaucarubulone glucoside from Castela macrophylla suppresses MCF-7 breast cancer cell growth and attenuates benzo[a]pyrene-mediated CYP1A gene induction.

Quassinoids often exhibit antioxidant and antiproliferative activity. Emerging evidence suggests that these natural metabolites also display chemopreventive actions. In this study, we investigated the potential for the quassinoid glaucarubulone glucoside (Gg), isolated from the endemic Jamaican plant Castela macrophylla (Simaroubaceae), to display potent cytotoxicity and inhibit human cytochrome P450s (CYPs), particularly CYP1A enzymes, known to convert polyaromatic hydrocarbons into carcinogenic metabolites. Gg reduced the viability of MCF-7 breast adenocarcinoma cells (IC50 = 121 nm) to a greater extent than standard of care anticancer agents 5-fluorouracil, tamoxifen (IC50 >10 µm) and the tamoxifen metabolite 4-hydroxytamoxifen (IC50 = 2.6 µm), yet was not cytotoxic to non-tumorigenic MCF-10A breast epithelial cells. Additionally, Gg induced MCF-7 breast cancer cell death. Gg blocked increases in reactive oxygen species in MCF-10A cells mediated by the polyaromatic hydrocarbon benzo[a]pyrene (B[a]P) metabolite B[a]P 1,6-quinone, yet downregulated the expression of genes that promote antioxidant activity in MCF-7 cells. This implies that Gg exhibits antioxidant and cytoprotective actions in non-tumorigenic breast epithelial cells and pro-oxidant, cytotoxic actions in breast cancer cells. Furthermore, Gg inhibited the activities of human CYP1A according to non-competitive kinetics and attenuated the ability of B[a]P to induce CYP1A gene expression in MCF-7 cells. These data indicate that Gg selectively suppresses MCF-7 breast cancer cell growth without impacting non-tumorigenic breast epithelial cells and blocks B[a]P-mediated CYP1A induction. Taken together, our data provide a rationale for further investigations of Gg and similar plant isolates as potential agents to treat and prevent breast cancer. Copyright © 2017 John Wiley & Sons, Ltd.

Marital Status, Living Arrangement, and Survival among Individuals with Advanced Prostate Cancer in the International Registry for Men with Advanced Prostate Cancer.

BACKGROUND: Studies have shown improved survival among individuals with cancer with higher levels of social support. Few studies have investigated social support and overall survival (OS) in individuals with advanced prostate cancer in an international cohort. We investigated the associations of marital status and living arrangements with OS among individuals with advanced prostate cancer in the International Registry for Men with Advanced Prostate Cancer (IRONMAN). METHODS: IRONMAN is enrolling participants diagnosed with advanced prostate cancer (metastatic hormone-sensitive prostate cancer, mHSPC; castration-resistant prostate cancer, CRPC) from 16 countries. Participants in this analysis were recruited between July 2017 and January 2023. Adjusting for demographics and tumor characteristics, the associations were estimated using Cox regression and stratified by disease state (mHSPC, CRPC), age (<70, ≥70 years), and continent of enrollment (North America, Europe, Other). RESULTS: We included 2,119 participants with advanced prostate cancer, of whom 427 died during up to 5 years of follow-up (median 6 months). Two-thirds had mHSPC. Most were married/in a civil partnership (79%) and 6% were widowed. Very few married participants were living alone (1%), while most unmarried participants were living alone (70%). Married participants had better OS than unmarried participants [adjusted HR: 1.44; 95% confidence interval (CI): 1.02-2.02]. Widowed participants had the worst survival compared with married individuals (adjusted HR: 1.89; 95% CI: 1.22-2.94). CONCLUSIONS: Among those with advanced prostate cancer, unmarried and widowed participants had worse OS compared with married participants. IMPACT: This research highlighted the importance of social support in OS within this vulnerable population.

Cycloartane-3,24,25-triol inhibits MRCKα kinase and demonstrates promising anti prostate cancer activity in vitro.

BACKGROUND: Given the high occurrence of prostate cancer worldwide and one of the major sources of the discovery of new lead molecules being medicinal plants, this research undertook to investigate the possible anti-cancer activity of two natural cycloartanes; cycloartane-3,24,25-diol (extracted in our lab from Tillandsia recurvata) and cycloartane-3,24,25-triol (purchased). The inhibition of MRCKα kinase has emerged as a potential solution to restoring the tight regulation of normal cellular growth, the loss of which leads to cancer cell formation. METHODS: Kinase inhibition was investigated using competition binding (to the ATP sites) assays which have been previously established and authenticated and cell proliferation was measured using the WST-1 assay. RESULTS: Cycloartane-3,24,25-triol demonstrated strong selectivity towards the MRCKα kinase with a Kd50 of 0.26 µM from a total of 451 kinases investigated. Cycloartane-3,24,25-triol reduced the viability of PC-3 and DU145 cell lines with IC50 values of 2.226 ± 0.28 µM and 1.67 ± 0.18 µM respectively. CONCLUSIONS: These results will prove useful in drug discovery as Cycloartane-3,24,25-triol has shown potential for development as an anti-cancer agent against prostate cancer.

Expanding the prostate cancer cell line repertoire with ACRJ-PC28, an AR-negative neuroendocrine cell line derived from an African-Caribbean patient.

Prostate cell lines from diverse backgrounds are important to addressing disparities in prostate cancer (PCa) incidence and mortality rates among Black men. ACRJ-PC28 was developed from a transrectal needle biopsy and established via inactivation of the CDKN2A locus and simultaneous expression of human telomerase. Characterization assays included growth curve analysis, immunoblots, IHC, 3D cultures, immunofluorescence imaging, confocal microscopy, flow cytometry, WGS, and RNA-Seq. ACRJ-PC28 has been passaged more than 40 times in vitro over 10 months with a doubling time of 45 hours. STR profiling confirmed the novelty and human origin of the cell line. RNA-Seq confirmed the expression of prostate specific genes alpha-methylacyl-CoA racemase (AMACR) and NKX3.1 and Neuroendocrine specific markers synaptophysin (SYP) and enolase 2 (ENO2) and IHC confirmed the presence of AMACR. Immunoblots indicated the cell line is of basal-luminal type; expresses p53 and pRB and is AR negative. WGS confirmed the absence of exonic mutations and the presence of intronic variants that appear to not affect function of AR, p53, and pRB. RNA-Seq data revealed numerous TP53 and RB1 mRNA splice variants and the lack of AR mRNA expression. This is consistent with retention of p53 function in response to DNA damage and pRB function in response to contact inhibition. Soft agar anchorage-independent analysis indicated that the cells are transformed, confirmed by principal component analysis (PCA) where ACRJ-PC28 cells cluster alongside other PCa tumor tissues, yet was distinct. The novel methodology described should advance prostate cell line development, addressing the disparity in PCa among Black men.

IRONMAN: A Novel International Registry of Men With Advanced Prostate Cancer.

PURPOSE: To describe a newly established international registry recruiting diverse patients with advanced prostate cancer across academic and community practices to address unmet needs in this population. PATIENTS AND METHODS: Initiated in 2017, IRONMAN (International Registry for Men with Advanced Prostate Cancer) is a prospective cohort of patients with advanced prostate cancer. The study will enroll 5,000 patients with metastatic hormone-sensitive prostate cancer (mHSPC) or castration-resistant prostate cancer (CRPC), recruited from Australia, the Bahamas, Barbados, Brazil, Canada, Ireland, Jamaica, Kenya, Nigeria, Norway, South Africa, Spain, Sweden, Switzerland, the United Kingdom, and the United States. The study is collecting datatypes to study variation in care and treatment of advanced prostate cancer across countries and across academic, community-based, and government practices with a focus on clinical outcomes, patient-reported outcomes, epidemiologic data, biologic subtypes, and clinician questionnaires. RESULTS: Through July 2022, 2,682 eligible patients were enrolled in 11 of 12 active countries. Sixty-six percent of patients have mHSPC, and 34% have CRPC. On the basis of self-report, 11% of patients are Black and 9% are Hispanic. Five Veterans Affairs Medical Centers are enrolling patients. Globally, 23% of patients report being veterans of military service. CONCLUSION: To our knowledge, this is the first international cohort of people newly diagnosed with advanced prostate cancer designed to describe variations in patient management, experiences, and outcomes. IRONMAN aims to identify optimal treatment sequences to improve survival, understand patient-reported outcomes, and explore novel biomarkers to understand treatment resistance mechanisms. Insights from IRONMAN will inform and guide future clinical management of people with mHSPC and CRPC. This cohort study will provide real-world evidence to facilitate a better understanding of the survivorship of people with advanced prostate cancer.

Immortalization of human primary prostate epithelial cells via CRISPR inactivation of the CDKN2A locus and expression of telomerase.

BACKGROUND: Immortalization of primary prostate epithelial cells (PrEC) with just hTERT expression is particularly inefficient in the absence of DNA tumor viral proteins or p16INK4A knockdown. MATERIALS AND METHODS: Here, we describe the establishment of immortalized normal prostate epithelial cell line models using CRISPR technology to inactivate the CDKN2A locus concomitantly with ectopic expression of an hTERT transgene. RESULTS: Using this approach, we have obtained immortal cell clones that exhibit fundamental characteristics of normal cells, including diploid genomes, near normal karyotypes, normal p53 and pRB cell responses, the ability to form non-invasive spheroids, and a non-transformed phenotype. Based on marker expression, these clones are of basal cell origin. CONCLUSIONS: Use of this approach resulted in the immortalization of independent clones of PrEC that retained normal characteristics, were stable, and non-transformed. Thus, this approach could be used for the immortalization of normal primary prostate cells. This technique could also be useful for establishing cell lines from prostate tumor tissues of different tumor grades and/or from patients of diverse ethnicities to generate cell line models that facilitate the study of the molecular basis of disease disparity.

Molecular Targets and Angiogenesis in Renal Cell Carcinoma, A Multitarget Approach: Mini Review.

BACKGROUND: Renal cell carcinoma (RCC) accounts for 2% of all adult malignancies and is associated with a case fatality rate as high as 40%. RCC has been on the rise for the last 6 decades at a steady increase of 2% per annum. Much work has been done to uncover the pathogenesis of the disease and the role of angiogenesis has been a recurrent denominator connected to vascular endothelial growth factor (VEGF) and its downstream effectors along with the mammalian target of rapamycin (mTOR) mediated signal transduction pathway. OBJECTIVE: This review will discuss relevant inhibitors of key biomarkers to the disease in hopes of paving the way for novel treatments geared towards improving RCC morbidity and mortality rates. RESULTS AND CONCLUSION: Currently, treatment of advanced RCC includes one or more of the following: partial or radical nephrectomy, systemic therapy, immunotherapy and targeted therapy. Still drug resistance continues to be a challenge to many of the approved drugs and those undergoing clinical trials. However, the inclusion of targeted therapies has improved advanced RCC treatment success rates over that of surgery alone, and over that of the use of traditional chemotherapy for this relatively chemo-resistant disease. In an era of personalized medicine, research utilizing a polypharmacology approach could enhance efficacy of drug leads to treating RCC.

Nitric oxide agents impair insulin-mediated signal transduction in rat skeletal muscle.

BACKGROUND: Evidence demonstrates that exogenously administered nitric oxide (NO) can induce insulin resistance in skeletal muscle. We have investigated the modulatory effects of two NO donors, S-nitroso-N-acetyl-D, L-penicillamine (SNAP) and S-nitrosoglutathione (GSNO) on the early events in insulin signaling in rat skeletal myocytes. RESULTS: Skeletal muscle cells from 6-8 week old Sprague-Dawley rats were treated with SNAP or GSNO (25 ng/ml) in the presence or absence of glucose (25 mM) and insulin (100 nM). Cellular insulin receptor-beta levels and tyrosine phosphorylation in IRS-1 were significantly reduced, while serine phosphorylation in IRS-1 was significantly increased in these cells, when compared to the insulin-stimulated control. Reversal to near normal levels was achieved using the NO scavenger, 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl 3-oxide (carboxy-PTIO). CONCLUSION: These data suggest that NO is a potent modulator of insulin-mediated signal transduction and may play a significant role in the pathogenesis of type 2 diabetes mellitus.

Potential for naturally derived therapeutics: the Caribbean as a model - insights from the conference on therapeutics and functional genomics.

The 2nd Annual Conference of the Society for Scientific Advancement (SoSA) was convened to integrate three research areas towards the development of therapies that will help to reduce disease burden in the Caribbean. Held in Kingston, the capital city of Jamaica, on November 22, 2013, the meeting assembled experts in the areas of genomics, stem cell research and natural medicine. The speakers represented the University of the West Indies, Mona and St. Augustine campuses, the University of Technology, and faculty from the USA and Africa. Sponsorship of this meeting supports SoSA's goal of stimulating translational research in the Caribbean.

In Vitro Anticancer Activity of the Crude Extract and two Dicinnamate Isolates from the Jamaican Ball Moss (Tillandsia Recurvata L.).

A crude chloroform extract from the Jamaican Ball Moss (Tillandsia recurvata L.) was tested for activity against three human cancer cell lines including; A375 (human melanoma), MCF-7 (human breast) and PC-3 (human prostate cancer) using the WST-1 assay. IC50s obtained against these cell lines; A375, MCF-7 and PC-3 in the presence of the crude extract are; 0.9µg/ml, 40.51µg/ml and 5.97µg/ml respectively indicating the promising anti-cancer activity of the ball moss extract. Further, preliminary phytochemical study was conducted in an attempt to identify and isolate the phytochemicals that could possibly be responsible for the observed bioactivity of the ball moss chloroform extract. As a result, two dicinnamates were isolated; 1,3-di-O-Cinnamoyl-glycerol (1) and (E)-3-(cinnamoyloxy)-2-hydroxypropyl 3-(3,4-dimethoxyphenyl)acrylate (2) and we report for the first time isolation of compound 2. Even though the bioactivity of these two islaotes were fairly weak against the cell lines, the results presented here will prove useful for further research aimed at identifying molecules that maybe effective against melanoma, breast and prostate cancers associated with fewer side-effects.

Antiproliferative activity and absolute configuration of zonaquinone acetate from the Jamaican alga Stypopodium zonale.

The chemical investigation of specimens of the Jamaican brown alga Stypopodium zonale led to the isolation of a cytotoxic compound, zonaquinone acetate (1), along with known compounds flabellinone, not previously identified in S. zonale, stypoldione, 5',7'-dihydroxy-2'-pentadecylchromone and sargaol. The structures of the metabolites were established by analysis of the spectral data including 1D and 2D NMR experiments while the stereochemistry of 1 was assessed by VCD measurements. Cytotoxic activity was reported in vitro for 1 against breast cancer and colon cancer cell lines at IC(50) values of 19.22-21.62 µM and 17.11-18.35 µM respectively, comparing favorably with standard treatments tamoxifen (17.22-17.32 µM) and fluorouracil (27.03-31.48 µM). When tested with liver cancer cells (Hep G2), no activity was observed. Weak antioxidant activity was observed with 1 but sargaol exhibited high activity.

Kinase inhibition by the Jamaican ball moss, Tillandsia recurvata L.

BACKGROUND: This research was undertaken in order to investigate the inhibitory potential of the Jamaican ball moss, Tillandsia recurvata against several kinases. The inhibition of these kinases has emerged as a potential solution to restoring the tight regulation of normal cellular growth, the loss of which leads to cancer cell formation. MATERIALS AND METHODS: Kinase inhibition was investigated using competition binding (to the ATP sites) assays, which have been previously established and authenticated. RESULTS: Four hundred and fifty one kinases were tested against the Jamaican ball moss extract and a dose-response was tested on 40 kinases, which were inhibited by more than 35% compared to the control. Out of the 40 kinases, the Jamaican ball moss selectively inhibited 5 (CSNK2A2, MEK5, GAK, FLT and DRAK1) and obtained Kd(50)s were below 20 µg/ml. CONCLUSION: Since MEK5 and GAK kinases have been associated with aggressive prostate cancer, the inhibitory properties of the ball moss against them, coupled with its previously found bioactivity towards the PC-3 cell line, makes it promising in the arena of drug discovery towards prostate cancer.

Cytotoxic and potent CYP1 inhibitors from the marine algae Cymopolia barbata.

BACKGROUND: Extracts from the marine algae Cymopolia barbata have previously shown promising pharmacological activity including antifungal, antitumor, antimicrobial, and antimutagenic properties. Even though extracts have demonstrated such bioactivity, isolated ingredients responsible for such bioactivity remain unspecified. In this study, we describe chemical characterization and evaluations of biological activity of prenylated bromohydroquinones (PBQ) isolated from the marine algae C. barbata for their cytotoxic and chemopreventive potential. METHODS: The impact of PBQs on the viability of cell lines (MCF-7, HT29, HepG, and CCD18 Co) was evaluated using the MTS assay. In addition, their inhibitory impact on the activities of heterologously expressed cytochrome P450 (CYP) enzymes (CYP1A1, CYP1A2, CYP1B1, CYP2C19, CYP2D6, and CYP3A4) was evaluated using a fluorescent assay. RESULTS: 7-Hydroxycymopochromanone (PBQ1) and 7-hydroxycymopolone (PBQ2) were isolated using liquid and column chromatography, identified using 1 H and 13 C NMR spectra and compared with the spectra of previously isolated PBQs. PBQ2 selectively impacted the viability of HT29, colon cancer cells with similar potency to the known chemotherapeutic drug, fluorouracil (IC50, 19.82 ± 0.46 µM compared to 23.50 ± 1.12 µM, respectively) with impact toward normal colon cells also being comparable (55.65 ± 3.28 compared to 55.51 ± 3.71 µM, respectively), while PBQ1 had no impact on these cells. Both PBQs had potent inhibition against the activities of CYP1A1 and CYP1B1, the latter which is known to be a universal marker for cancer and a target for drug discovery. Inhibitors of CYP1 enzymes by virtue of the prevention of activation of carcinogens such as benzo-a-pyrene have drawn attention as potential chemopreventors. PBQ2 potently inhibited the activity of CYP1B1 (IC50 0.14 ± 0.04 µM), while both PBQ1 and PBQ2 potently inhibited the activity of CYP1A1 (IC50s of 0.39 ± 0.05 µM and 0.93 ± 0.26 µM, respectively). Further characterizations showed partial noncompetitive enzyme kinetics for PBQ2 with CYP1B1 with a Ki of 4.7 × 10-3 ± 5.1 × 10-4 µM and uncompetitive kinetics with CYP1A1 (Ki = 0.84 ± 0.07 µM); while PBQ1 displayed partial non competitive enzyme kinetics with CYP1A1 (Ki of 3.07 ± 0.69 µM), noncompetitive kinetics with CYP1A2 (Ki = 9.16 ± 4.68 µM) and uncompetitive kinetics with CYP1B1 (Ki = 0.26 ± 0.03 µM) . CONCLUSIONS: We report for the first time, two isolated ingredients from C. barbata, PBQ1 and PBQ2, that show potential as valuable chemotherapeutic compounds. A hydroxyl moiety resident in PBQ2 appears to be critical for selectivity and potency against the cancer colon cells, HT29, in comparison to the three other malignant cell lines studied. PBQs also show potency against the activities of CYP1 enzyme which may be a lead in chemoprevention. This study, the first on isolates from these marine algae, exemplifies the value of searching within nature for unique structural motifs that can display multiple biological activities.

Inhibition of CYP1A1 by Quassinoids found in Picrasma excelsa.

Infusions of the plant Picrasma excelsa, known as Jamaican bitterwood tea, are commonly consumed to lower blood sugar levels in diabetics who are already on prescription medicines. We therefore investigated the inhibition properties of this tea against a panel of cytochrome P450 (CYP) enzymes, which are primarily responsible for the metabolism of a majority of drugs on the market. The two major ingredients, quassin and neoquassin, were then isolated and used for further characterization. Inhibition of the activities of heterologously expressed CYP microsomes (CYPs 2D6, 3A4, 1A1, 1A2, 2C9, and 2C19) was monitored, and the most potent inhibition was found to be against CYP1A1, with IC (50) values of 9.2 microM and 11.9 microM for quassin and neoquassin, respectively. The moderate inhibition against the CYP1A1 isoform by quassin and neoquassin displayed partial competitive inhibition kinetics, with inhibition constants ( K(i)) of 10.8 +/- 1.6 microM, for quassin and competitive inhibition kinetics, with a K(i) of 11.3 +/- 0.9 microM, for neoquassin. We then docked these two inhibitors into the active site of a model of CYP1A1, which provided insight at the atomic level into the structure-activity relationship of quassinoids with respect to this important CYP isoform known to be an activator of carcinogens, thus providing a useful basis for the search for more potent inhibitors of CYP1A1 that may have implications in chemoprotection.

Acute impairment of insulin signalling by dexamethasone in primary cultured rat skeletal myocytes.

In this study, we examined the cellular content of the insulin receptor substrate (IRS)-1, the levels of phosphorylated tyrosine (pY) and serine (pS) residues in IRS-1, and the glucose transporters GLUT-1 and GLUT-4 in primary cultured rat skeletal myocytes treated with the glucocorticoid, dexamethasone. Dexamethasone markedly increased basal and insulin-stimulated IRS-1 content 4 to 5-fold (p < 0.01). A similar level of increase was observed for IRS-1 pY content. However, dexamethasone treatment had no effect on IRS-1 pS content. Further, dexamethasone reduced the cellular content of GLUT-1 when insulin and glucose were absent (p < 0.05), but did not significantly affect the expression of GLUT-4 in the presence of insulin (p > 0.05). We conclude that dexamethasone treatment impairs insulin signalling by a mechanism independent of serine-phosphorylation-mediated IRS-1 depletion, or of impairment of GLUT-1 expression. Instead, dexamethasone-induced insulin resistance may be mediated via reduced cellular content of IRS-1 accompanied by parallel reduction in tyrosine phosphorylation in IRS-1.