Janni Mirosevich

Action of the Src Family Kinase Inhibitor, Dasatinib (BMS-354825), on Human Prostate Cancer Cells

Src family kinases (SFK) are currently being investigated as targets for treatment strategies in various cancers. The novel SFK/Abl inhibitor, dasatinib (BMS-354825), is a promising therapeutic agent with oral bioavailability. Dasatinib has been shown to inhibit growth of Bcr-Abl-dependent chronic myeloid leukemia xenografts in nude mice. Dasatinib also has been shown to have activity against cultured human prostate and breast cancer cells. However, the molecular mechanism by which dasatinib acts on epithelial tumor cells remains unknown. In this study, we show that dasatinib blocks the kinase activities of the SFKs, Lyn, and Src, in human prostate cancer cells at low nanomolar concentrations. Moreover, focal adhesion kinase and Crk-associated substrate (p130(CAS)) signaling downstream of SFKs are also inhibited at similar concentrations of dasatinib. Consistent with inhibition of these signaling pathways, dasatinib suppresses cell adhesion, migration, and invasion of prostate cancer cells at low nanomolar concentrations. Therefore, dasatinib has potential as a therapeutic agent for metastatic prostate cancers harboring activated SFK and focal adhesion kinase signaling.

Forkhead box A1 regulates prostate ductal morphogenesis and promotes epithelial cell maturation

We have previously shown that a forkhead transcription factor Foxa1 interacts with androgen signaling and controls prostate differentiated response. Here, we show the mouse Foxa1 expression marks the entire embryonic urogenital sinus epithelium (UGE), contrasting with Shh and Foxa2, which are restricted to the basally located cells during prostate budding. The Foxa1-deficient mouse prostate shows a severely altered ductal pattern that resembles primitive epithelial cords surrounded by thick stromal layers. Characterization of these mutant cells indicates a population of basal-like cells similar to those found in the embryonic UGE, whereas no differentiated or mature luminal epithelial cells are found in Foxa1-deficient epithelium. These phenotypic changes are accompanied with molecular aberrations, including focal epithelial activation of Shh and elevated Foxa2 and Notch1 in the null epithelium. Perturbed epithelial-stromal interactions induced by Foxa1-deficient epithelium is evident, as demonstrated by the expansion of surrounding smooth muscle and elevated levels of stromal factors (Bmp4, Fgf7, Fgf10 and Gli). The prostatic homeobox protein Nkx3.1, a known proliferation inhibitor, was downregulated in Foxa1-deficient epithelial cells, while several prostate-specific androgen-regulated markers, including a novel Foxa1 target, are absent in the null prostate. These data indicate that Foxa1 plays a pivotal role in controlling prostate morphogenesis and cell differentiation.

Sorafenib inhibits signal transducer and activator of transcription 3 signaling associated with growth arrest and apoptosis of medulloblastomas

Medulloblastomas are the most frequent malignant brain tumors in children. Sorafenib (Nexavar, BAY43-9006), a multikinase inhibitor, blocks cell proliferation and induces apoptosis in a variety of tumor cells. Sorafenib inhibited proliferation and induced apoptosis in two established cell lines (Daoy and D283) and a primary culture (VC312) of human medulloblastomas. In addition, sorafenib inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) in both cell lines and primary tumor cells. The inhibition of phosphorylated STAT3 (Tyr705) occurs in a dose- and time-dependent manner. In contrast, AKT (protein kinase B) was only decreased in D283 and VC312 medulloblastoma cells and mitogen-activated protein kinases (extracellular signal-regulated kinase 1/2) were not inhibited by sorafenib in these cells. Both D-type cyclins (D1, D2, and D3) and E-type cyclin were down-regulated by sorafenib. Also, expression of the antiapoptotic protein Mcl-1, a member of the Bcl-2 family, was decreased and correlated with apoptosis induced by sorafenib. Finally, sorafenib suppressed the growth of human medulloblastoma cells in a mouse xenograft model. Together, our data show that sorafenib blocks STAT3 signaling as well as expression of cell cycle and apoptosis regulatory proteins, associated with inhibition of cell proliferation and induction of apoptosis in medulloblastomas. These findings provide a rationale for treatment of pediatric medulloblastomas with sorafenib. [Mol Cancer Ther 2008;7(11):3519–26]

Foxa1 and Foxa2 Interact with the Androgen Receptor to Regulate Prostate and Epididymal Genes Differentially

Abstract: Previous studies from our group have shown that Foxa1 is expressed in the prostate and interacts with the androgen receptor (AR) to regulate prostate‐specific genes such as prostate‐specific antigen (PSA) and probasin (PB). We report here that Foxa2 but not Foxa1 is expressed in the epididymis. Further, Foxa2 interacts with the AR to regulate the mouse epididymal retinoic acid binding protein (mE‐RABP) gene, an epididymis‐specific gene. Binding of Foxa2 to the mE‐RABP promoter was confirmed by gel‐shift and chromatin immunoprecipitation (ChIP) assays. Overexpression of Foxa2 suppresses androgen activation of the mE‐RABP promoter while overexpression of Foxa2 with prostate‐specific promoters activates gene expression in an androgen‐independent manner. GST pull‐down assays determined that both Foxa1 and Foxa2 physically interact with the DNA binding domain of the AR. The interaction between Foxa proteins and AR was further confirmed by gel‐shift assays where Foxa protein was recruited to AR binding oligomers even when Foxa binding sites were not present, and AR was recruited to Foxa binding oligomers even in the absence of an AR binding site. Given that Foxa1 and Foxa2 proteins are expressed differentially in the prostate and epididymis, these data suggest that the Foxa proteins have distinct effects on AR‐regulated genes in different male reproductive accessory organs.

Prostate epithelial cell fate.

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with its own unique character.

The Role of Foxa Proteins in the Regulation of Androgen Receptor Activity

Activation of the androgen receptor is required for normal prostate physiology and in controlling the growth prostate cancer. However, the fact that multiple target organs express androgen receptor and are exposed to circulating androgens, yet fail to express prostate-specific markers and fail to develop androgen-dependent cancers, indicates that androgen receptor alone is not sufficient to dictate normal function and progression to cancer. Therefore, androgen action can be restricted in a given tissue by transcription factors that serve as co-regulators of androgen receptor. How androgen signaling acts in concert with other transcription factors, resulting in tissue-specific gene expression needs to be understood. The establishment of unique transcription factor regulatory networks is responsible, at least in part, to control androgen receptor action (1) in tissue-specific gene expression; (2) organ determination; and (3) cell differentiation. The identification of TF networks involved in these disparate events will allow researchers to elucidate the mechanisms that control prostate development, function, and pathology. Experimental evidence generated by our laboratory and others indicates that members of the Foxa subfamily of transcription factors play an important role in (1) normal prostate development; (2) the determination of prostatic cell fate; and (3) specific types of prostate pathology. This chapter reviews evidence generated by our laboratory and others regarding the important role of the Foxa transcription factors in the regulation of prostate-specific gene regulatory networks.

Synthesis of heterobifunctional polyethylene glycols with azide functionality suitable for “click” chemistry

A heterobifunctional polyethylene glycol (PEG) derivative possessing both “click” and electrophilic functionalities was prepared for use in bioconjugation applications. We utilized a dibenzyl-protected amine functional initiator to prepare high purity amino-PEG-alcohol by the polymerization of ethylene oxide. Subsequent chain-end modification of the heterobifunctional PEG afforded the desired N-hydroxy succinimidyl-PEG-azide derivative in 33% overall yield. This PEG derivative allows for versatile bioconjugation chemistry where activated ester chemistry and “click” chemistry can be selectively performed, an area of orthogonal bioconjugation that has not previously been accessible.

Activation of GRP/GRP-R signaling contributes to castration-resistant prostate cancer progression

Numerous studies indicate that androgen receptor splice variants (ARVs) play a critical role in the development of castration-resistant prostate cancer (CRPC), including the resistance to the new generation of inhibitors of androgen receptor (AR) action. Previously, we demonstrated that activation of NF-κB signaling increases ARVs expression in prostate cancer (PC) cells, thereby promoting progression to CRPC. However, it is unclear how NF-κB signaling is activated in CRPC. In this study, we report that long-term treatment with anti-androgens increases a neuroendocrine (NE) hormone — gastrin-releasing peptide (GRP) and its receptor (GRP-R) expression in PC cells. In addition, activation of GRP/GRP-R signaling increases ARVs expression through activating NF-κB signaling. This results in an androgen-dependent tumor progressing to a castrate resistant tumor. The knock-down of AR-V7 restores sensitivity to antiandrogens of PC cells over-expressing the GRP/GRP-R signaling pathway. These findings strongly indicate that the axis of Androgen-Deprivation Therapy (ADT) induces GRP/GRP-R activity, activation NF-κB and increased levels of AR-V7 expression resulting in progression to CRPC. Both prostate adenocarcinoma and small cell NE prostate cancer express GRP-R. Since the GRP-R is clinically targetable by analogue-based approach, this provides a novel therapeutic approach to treat advanced CRPC.

Abstract 599: Development of poly(Asp-DET) cationic polymers for nonviral gene delivery

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Cationic polymers have received much attention as promising non-viral vectors for gene transfer. However, identification of polymers able to systemically deliver nucleic acids continues to be a significant hurdle to the success of this methodology. The purpose of this study was to develop a new biocompatible and biodegradable cationic polymer system as a non-viral gene delivery agent for plasmid DNA. Poly-aspartate-diethylene triamine (“P(Asp-DET)”) polymers were synthesized and utilized to complex plasmid DNA. The resulting polymer/DNA complexes, also known as “polyplexes,” were further modified by covalent coupling with polyethylene glycol (PEG), known as “PEGylation,” and characterized. Polyplexes were evaluated for efficiency of encapsulation, particle size, zeta potential and morphology by TEM. Stability of the complexed plasmid DNA was assessed by challenging polyplexes with nucleases. Efficacy of DNA delivery and gene expression was examined by performing transfection experiments using HCT-116 cells. In vivo DNA delivery was also investigated using tumor-bearing nude mice. Asp-DET polymers were found to bind to plasmid DNA with polymer to DNA (+/-) charge ratios of above 1.5. In addition, these polymers formed polyplex particles of approximately 50-150 nm with zeta potentials between neutral and +40 mV. TEM showed that the polyplexes were uniform and spherical in shape. It was also demonstrated that the polyplexes maintained the structural integrity of DNA following incubation in nucleases. The polyplexes were also capable of transfecting HCT-116 culture cells, with non-PEG complexes having significantly higher GFP and luciferase expression. Tail vein injections of post-PEGylated polyplexes into tumor bearing nude mice did not reveal any observable toxicities. Notably, nucleic acid accumulation was found in tumors with expression detected in lymph nodes. P(Asp-DET) cationic polymers show enormous potential as non-viral drug delivery agents. Further, the surface modification of described polyplexes with PEG allowed for systemic delivery of nucleic acids to tumors. The characterization of post-PEGylated Asp-DET/DNA polyplexes provides insights that can be used to design vectors for targeted nucleic acid delivery. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 599.