Andrea Valentine

A Novel FK506-Like Binding Protein Interacts with the Glucocorticoid Receptor and Regulates Steroid Receptor Signaling

FKBP-like (FKBPL) protein is a novel immunophilin-like protein that plays a role in the cellular stress response. Its three tetratricopeptide repeat motifs are homologous to the heat shock protein 90 interaction sites of other immunophilins that have roles in steroid hormone receptor signaling. In this study, using biomolecular complementation and coimmunoprecipitation techniques, we show that FKBPL also colocalizes and interacts with the components of the heat shock protein 90-glucocorticoid receptor (GR) complex and demonstrate that the PPIase domain of FKBPL is important for the interaction between this complex and the dynein motor protein, dynamitin. Treatment of DU145 cells with the GR ligand, dexamethasone, induced a rapid and coordinated translocation of both GR and FKBPL to the nucleus; this response was perturbed when FKBPL was knocked down with a targeted small interfering RNA. Furthermore, overexpression of FKBPL increased GR protein levels and transactivation of a luciferase reporter gene in response to dexamethasone in DU145 cells. However, these responses were cell line dependent. In summary, these data suggest that FKBPL can be classed as a new member of the FKBP protein family with a role in steroid receptor complexes and signaling.

FKBPL Regulates Estrogen Receptor Signaling and Determines Response to Endocrine Therapy

The HSP90 chaperone and immunophilin FKBPL is an estrogen-responsive gene that interacts with estogen receptor alpha (ERalpha) and regulates its levels. In this study, we explored the effects of FKBPL on breast cancer proliferation. Breast cancer cells stably overexpressing FKBPL became dependent on estrogen for their growth and were dramatically more sensitive to the antiestrogens tamoxifen and fulvestrant, whereas FKBPL knockdown reverses this phenotype. FKBPL knockdown also decreased the levels of the cell cycle inhibitor p21WAF1 and increased ERalpha phosphorylation on Ser(118) in response to 17beta-estradiol and tamoxifen. In support of the likelihood that these effects explained FKBPL-mediated cell growth inhibition and sensitivity to endocrine therapies, FKBPL expression was correlated with increased overall survival and distant metastasis-free survival in breast cancer patients. Our findings suggest that FKBPL may have prognostic value based on its impact on tumor proliferative capacity and sensitivity to endocrine therapies, which improve outcome.

FKBPL and Peptide Derivatives: Novel Biological Agents That Inhibit Angiogenesis by a CD44-Dependent Mechanism

Purpose: Antiangiogenic therapies can be an important adjunct to the management of many malignancies. Here we investigated a novel protein, FKBPL, and peptide derivative for their antiangiogenic activity and mechanism of action. Experimental Design: Recombinant FKBPL (rFKBPL) and its peptide derivative were assessed in a range of human microvascular endothelial cell (HMEC-1) assays in vitro. Their ability to inhibit proliferation, migration, and Matrigel-dependent tubule formation was determined. They were further evaluated in an ex vivo rat model of neovascularization and in two in vivo mouse models of angiogenesis, that is, the sponge implantation and the intravital microscopy models. Antitumor efficacy was determined in two human tumor xenograft models grown in severe compromised immunodeficient (SCID) mice. Finally, the dependence of peptide on CD44 was determined using a CD44-targeted siRNA approach or in cell lines of differing CD44 status. Results: rFKBPL inhibited endothelial cell migration, tubule formation, and microvessel formation in vitro and in vivo. The region responsible for FKBPLs antiangiogenic activity was identified, and a 24-amino acid peptide (AD-01) spanning this sequence was synthesized. It was potently antiangiogenic and inhibited growth in two human tumor xenograft models (DU145 and MDA-231) when administered systemically, either on its own or in combination with docetaxel. The antiangiogenic activity of FKBPL and AD-01 was dependent on the cell-surface receptor CD44, and signaling downstream of this receptor promoted an antimigratory phenotype. Conclusion: FKBPL and its peptide derivative AD-01 have potent antiangiogenic activity. Thus, these agents offer the potential of an attractive new approach to antiangiogenic therapy. Clin Cancer Res; 17(5); 1044–56. ©2011 AACR.

Identification of RBCK1 as a novel regulator of FKBPL: implications for tumor growth and response to tamoxifen

FKBPL has been implicated in processes associated with cancer, including regulation of tumor growth and angiogenesis with high levels of FKBPL prognosticating for improved patient survival. Understanding how FKBPL levels are controlled within the cell is therefore critical. We have identified a novel role for RBCK1 as an FKBPL-interacting protein, which regulates FKBPL stability at the post-translational level via ubiquitination. Both RBCK1 and FKBPL are upregulated by 17-β-estradiol and interact within heat shock protein 90 chaperone complexes, together with estrogen receptor-α (ERα). Furthermore, FKBPL and RBCK1 associate with ERα at the promoter of the estrogen responsive gene, pS2, and regulate pS2 levels. MCF-7 clones stably overexpressing RBCK1 were shown to have reduced proliferation and increased levels of FKBPL and p21. Furthermore, these clones were resistant to tamoxifen therapy, suggesting that RBCK1 could be a predictive marker of response to endocrine therapy. RBCK1 knockdown using targeted small interfering RNA resulted in increased proliferation and increased sensitivity to tamoxifen treatment. Moreover, in support of our in vitro data, analysis of mRNA microarray data sets demonstrated that high levels of FKBPL and RBCK1 correlated with increased patient survival, whereas high RBCK1 predicted for a poor response to tamoxifen. Our findings support a role for RBCK1 in the regulation of FKBPL with important implications for estrogen receptor signaling, cell proliferation and response to endocrine therapy.

Evaluation of the Antiangiogenic Potential of AQ4N

Purpose: A number of cytotoxic chemotherapy agents tested at low concentrations show antiangiogenic properties with limited cytotoxicity, e.g., cyclophosphamide, tirapazamine, and mitoxantrone. AQ4N is a bioreductive alkylaminoanthraquinone that is cytotoxic when reduced to AQ4; hence, it can be used to target hypoxic tumor cells. AQ4N is structurally similar to mitoxantrone and was evaluated for antiangiogenic properties without the need for bioreduction. Experimental Design: The effect of AQ4N and fumagillin on human microvascular endothelial cells (HMEC-1) was measured using a variety of in vitro assays, i.e., 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, wound scrape, tubule formation, rat aortic ring, and invasion assays. Low-dose AQ4N (20 mg/kg) was also given in vivo to mice bearing a tumor in a dorsal skin flap. Results: AQ4N (10−11 to 10−5 mol/L) had no effect on HMEC-1 viability. AQ4N (10−9 to 10−5mol/L) caused a sigmoidal dose-dependent inhibition of endothelial cell migration in the wound scrape model. Fumagillin showed a similar response over a lower dose range (10−13 to 10−9 mol/L); however, the maximal inhibition was less (25% versus 43% for AQ4N). AQ4N inhibited HMEC-1 cell contacts on Matrigel (10−8 to 10−5 mol/L), HMEC-1 cell invasion, and sprouting in rat aorta explants. Immunofluorescence staining with tubulin, vimentim, dynein, and phalloidin revealed that AQ4N caused disruption to the cell cytoskeleton. When AQ4N (20 mg/kg) was given in vivo for 5 days, microvessels disappeared in LNCaP tumors grown in a dorsal skin flap. Conclusions: This combination of assays has shown that AQ4N possesses antiangiogenic effects in normoxic conditions, which could potentially contribute to antitumor activity.

Prognostic Role of P27 kip1 and Epidermal Growth Factor Receptor in Transitional Cell Carcinoma of the Bladder

Objective : Presently, there is no reliable method that allows accurate prediction of the clinical course of an individual superficial bladder tumour. As 10-20% of superficial bladder tumours will become invasive, the discovery of a single or combination of prognostic markers would allow the early establishment of appropriate treatment regimens that could potentially prolong patient life. The aim of this study was to evaluate the potential of both p27 and epidermal growth factor receptor (EGFR), individually and in combination as prognostic markers for bladder cancer. Patients and methods : Immunohistochemistry was used to assess bladder tumours for p27 (54 samples), nuclear EGFR (65 samples) and 49 biopsies for both markers. Results : To assess p27 expression, a cut-off value of 30% was employed. Associations were found between p27 status and grade, stage, disease recurrence and progression ( p =0.0113, 0.0001, 0.0167 and 0.0024, respectively). Patients presenting with p27 positive tumours had longer dis...

Identification and Characterization of Dual Inhibitors of the USP25/28 Deubiquitinating Enzyme Subfamily

The ubiquitin proteasome system is widely postulated to be a new and important field of drug discovery for the future, with the ubiquitin specific proteases (USPs) representing one of the more attractive target classes within the area. Many USPs have been linked to critical axes for therapeutic intervention, and the finding that USP28 is required for c-Myc stability suggests that USP28 inhibition may represent a novel approach to targeting this so far undruggable oncogene. Here, we describe the discovery of the first reported inhibitors of USP28, which we demonstrate are able to bind to and inhibit USP28, and while displaying a dual activity against the closest homologue USP25, these inhibitors show a high degree of selectivity over other deubiquitinases (DUBs). The utility of these compounds as valuable probes to investigate and further explore cellular DUB biology is highlighted by the demonstration of target engagement against both USP25 and USP28 in cells. Furthermore, we demonstrate that these inhibitors are able to elicit modulation of both the total levels and the half-life of the c-Myc oncoprotein in cells and also induce apoptosis and loss of cell viability in a range of cancer cell lines. We however observed a narrow therapeutic index compared to a panel of tissue-matched normal cell lines. Thus, it is hoped that these probes and data presented herein will further advance our understanding of the biology and tractability of DUBs as potential future therapeutic targets.

Abstract 3288: The anti-tumour efficacy of the novel peptide inhibitor of angiogenesis ALM-201

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Neovascularization is critical to tumour growth and metastasis and this has led to the development of a number of marketed anti-angiogenic agents which target VEGF/VEGFR2 receptors, for clinical use in specific types of cancer. However, incomplete responses and/or resistance to these therapies has highlighted the need for new agents targeting alternative pathways. Here we describe the characterisation of a novel peptide derived from the natural protein FKBP-like binding protein (FKBPL), which has extremely potent anti-angiogenic activity, is very effective in mouse xenograft models at low doses, and exerts its effects through microtubule binding using CD44 as a cell-entry mechanism. ALM-201 has been profiled in a range of human microvascular endothelial cell (HMEC-1) assays and potently inhibited migration, tubule formation and microvessel formation in vitro and in vivo. Although the peptide has a marked effect on migration, ALM-201 does not inhibit proliferation in a range of growth factor stimulated proliferation assays. Importantly, there is a significant disconnect between the pharmacokinetic and pharmacodynamic profiles of ALM-201 which allows for 3 q.d. dosing in mouse xenograft models. The peptide is well tolerated with no signs of toxicity observed in mouse xenograft models up to 80 days of dosing. The mechanism by which ALM-201 inhibits angiogenesis involves the cell surface receptor CD44, as determined by siRNA depletion of the receptor in migration assays. Furthermore, the peptide potently inhibits microtubule assembly and downstream signalling, thus promoting the anti-migratory phenotype. In summary, ALM-201 is a novel, targeted microtubule binding agent which exhibits potent anti-angiogenic activity in vitro and in vivo. Pre-clinical development is in progress with a Phase 1 clinical study planned for 2011. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3288. doi:10.1158/1538-7445.AM2011-3288

Role of the Hsp90 cochaperone, FKBPL, in oestrogen receptor signalling and breast cancer growth and survival

Hsp90 chaperone complexes are involved in maintaining the stability and signalling of Hsp90 client proteins such as the oestrogen receptor (ER). The ER is the primary mediator of breast cancer proliferation in response to oestrogen. Since increased ER levels and transcriptional activation are associated with over 50% of breast cancers, the ER is an attractive target for cancer treatment strategies. Hsp90 inhibitors such as 17AAG are known to destabilize these complexes by promoting proteasome-mediated degradation of the steroid hormone receptor leading to tumour growth inhibition [1] and sensitization to chemotherapy [2] and radiotherapy [3]. Using protein interaction assays, we have identified FKBPL, a novel gene that codes for an immunophilin-like protein, as an Hsp90 cochaperone associated with the ER and dynein motor protein complex. Overexpression studies have demonstrated that FKBPL modulates ER signalling and affects breast cancer growth and survival. Since most tumours become refractory to current hormonal therapies within a year of starting treatment, FKBPL represents a novel drug target that would enable the disruption of signalling pathways integral in maintaining ER-mediated tumour growth and survival.