Selective stimulation of prostatic carcinoma cell proliferation by transferrin

Preclinical and Clinical Research Models of Prostate Cancer: A Brief Overview

The incidence and mortality from prostate cancer (PCa) are on the rise which poses a major public health concern worldwide. In this narrative review, we have summarized the characteristics of major in vitro and in vivo PCa models including their utility in developing treatment strategies. Androgens, particularly, testosterone and dihydrotestosterone (DHT) activate the androgen receptor (AR) signaling pathway that facilitates the development and progression of castration resistant PCa. Several enzymes namely, CYP17A1, HSD17B, and SRD5A are essential to furnishing DHT from dehydroepiandrosterone in the classical pathway while DHT is formed from androstanediol in the backdoor pathway. The advancement in delineating the molecular heterogeneity of PCa has been possible through the development of several in vitro and in vivo research models. Generally, tissue culture models are advantageous to understand PCa biology and investigate the efficacy and toxicity of novel agents; nevertheless, animal models are indispensable to studying the PCa etiology and treatment since they can simulate the tumor microenvironment that plays a central role in initiation and progression of the disease. Moreover, the availability of several genetically engineered mouse models has made it possible to study the metastasis process. However, the conventional models are not devoid of limitations. For example, the lack of heterogeneity in tissue culture models and the variation of metastatic characteristics in xenograft models are obviously challenging. Additionally, due to the racial and ethnic disparities in PCa pathophysiology, a new model that can represent PCa encompassing different ethnicities is urgently needed. New models should continue to evolve to address the genetic and molecular complexities as well as to further elucidate the finer details of the steroidogenic pathway associated with PCa.

Prostate-specific membrane antigen-targeted theranostics: past, present, and future approaches

Although prostate cancer is the type of cancer most commonly survived by men in the United States, it remains the second most common cause of death from cancer, largely owing to metastatic disease. Patients with metastatic castration-resistant prostate cancer (mCRPC) whose disease has progressed on standard-of-care therapies have few options and a poor prognosis. Prostate-specific membrane antigen (PSMA) is a type II integral membrane protein that is commonly expressed in prostate cancer. Expression is limited on extra-prostatic tissues other than the salivary glands, lacrimal glands, duodenal epithelium, Kupffer cells, and renal tubules. PSMA-directed theranostics has emerged to exploit the specificity of PSMA for prostate cancer cells and has demonstrated promising results in the clinic. Radionuclides linked to PSMA inhibitors/binders have resulted in US Food and Drug Administration (FDA) approval of 2 radiodiagnostics for PSMA-directed positron emission tomography/computed tomography. In addition, these radionuclides have led to the development of lutetium Lu 177PSMA-617 therapy, which is currently under priority FDA review. Multiple novel PSMA-targeted modalities have been developed and are currently under clinical investigation, including ligand-drug and cellular immune therapies. In this review, we discuss the development of PSMA-directed theranostics, along with its clinical implications, limitations, and future directions.

Metallofullerenol Inhibits Cellular Iron Uptake by Inducing Transferrin Tetramerization

Herein, A549 tumor cell proliferation was confirmed to be positively dependent on the concentration of Fe³⁺ or transferrin (Tf). Gd@C₈₂ (OH)₂₂ or C₆₀ (OH)₂₂ effectively inhibited the iron uptake and the subsequent proliferation of A549 cells. The conformational changes of Tf mixed with FeCl₃ , GdCl₃ , C₆₀ (OH)₂₂ or Gd@C₈₂ (OH)₂₂ were obtained by SAXS. The results demonstrate that Tf homodimers can be decomposed into monomers in the presence of FeCl₃ , GdCl₃ or C₆₀ (OH)₂₂ , but associated into tetramers in the presence of Gd@C₈₂ (OH)₂₂ . The larger change of SAXS shapes between Tf+C₆₀ (OH)₂₂ and Tf+FeCl₃ implies that C₆₀ (OH)₂₂ is bound to Tf, blocking the iron-binding site. The larger deviation of the SAXS shape from a possible crystal structure of Tf tetramer implies that Gd@C₈₂ (OH)₂₂ is bound to the Tf tetramer, thus disturbing iron transport. This study well explains the inhibition mechanism of Gd@C₈₂ (OH)₂₂ and C₆₀ (OH)₂₂ on the iron uptake and the proliferation of A549 tumor cells and highlights the specific interactions of a nanomedicine with the target biomolecules in cancer therapy.

Molecular, structural, and functional comparison of N lobe and C lobe of the transferrin from rock bream, Oplegnathus fasciatus, with respect to its immune response

The iron-withholding strategy of innate immunity is an effective antimicrobial defense mechanism that combats microbial infection by depriving microorganisms of Fe³⁺, which is important for their growth and propagation. Transferrins (Tfs) are a group of iron-binding proteins that exert their antimicrobial function through Fe³⁺ sequestration. The current study describes both structural and functional characteristics of a transferrin ortholog from rock bream Oplegnathus fasciatus (RbTf). The RbTf cDNA possesses an open reading frame (ORF) of 2079 bp encoding 693 amino acids. It has a molecular mass of approximately 74 kDa and an isoelectric point of 5.4. In silico analysis revealed that RbTf has two conserved domains: N-terminal domain and C-terminal domain. Pairwise homology analysis and phylogenetic analysis revealed that RbTf shared the highest identity (82.6%) with Dicentrarchus labrax Tf. According to the genomic analysis, RbTf possesses 17 exons and 16 introns, similar to the other orthologs. Here, we cloned the N terminal and C terminal domains of RbTf to evaluate their distinct functional features. Results obtained through the CAS (chrome azurol S) assay confirmed the iron-binding ability of the RbTf, and it was further determined that the iron-binding ability of rRbTfN was higher than that of rRbTfC. The antimicrobial functions of the rRbTfN and the rRbTfC were confirmed via the iron-dependent bacterial growth inhibition assay. Tissue distribution profiling revealed a ubiquitous expression with intense expression in the liver. Temporal assessment revealed that RbTf increased after stimulation of LPS, Edwardsiella tarda, and Streptococcus iniae post injection (p.i.). These findings demonstrated that RbTf is an important antimicrobial protein that can combat bacterial pathogens.

In vitro and in vivo model systems used in prostate cancer research

New incidence of prostate cancer is a major public health issue in the Western world, and has been rising in other areas of the globe in recent years. In an effort to understanding the molecular pathogenesis of this disease, numerous cell models have been developed, arising mostly from patient biopsies. The introduction of the genetically engineered mouse in biomedical research has allowed the development of murine models that allow for the investigation of tumorigenic and metastatic processes. Current challenges to the field include lack of an animal model that faithfully recapitulates bone metastasis of prostate cancer.

Nanodelivery of MRI contrast agent enhances sensitivity of detection of lung cancer metastases

RATIONALE AND OBJECTIVES

Early detection of lung cancer can be problematic. Although current imaging methods can identify lung cancers, they are limited in the size of detectable nodules. There is also lack of evidence that these methods can correctly classify nodules <7 mm as malignant because lung cancer can be mimicked in appearance by benign lesions that lower specificity. Therefore, there is a need for enhanced sensitivity/specificity of detection for small lung cancers.

MATERIALS AND METHODS

We have developed a nanosized ( approximately 100 nm) immunoliposome complex for delivery of molecular medicines to tumors. In this complex, an anti-transferrin receptor single-chain antibody fragment (TfRscFv) decorates the surface of a cationic liposome encapsulating the payload. We have previously shown that this systemically administered complex (scL) selectively targets, and efficiently delivers its payload into, tumor cells. We have also encapsulated the magnetic resonance imaging (MRI) contrast agent gadopentetate dimeglumine ("gad-d") within this complex, resulting in increased resolution and image intensity in a mouse model of primary cancer. Here we examine the ability of the scL-gad-d complex to increase the sensitivity of detection of lung metastases.

RESULTS

These MRI studies show that the scL-gad-d nanocomplex is able to improve detection, and increase enhancement of, small lung cancers (400 microm and as small as 100 microm) compared to that of uncomplexed gad-d.

CONCLUSIONS

Because of its tumor targeting specificity, deliver of an MRI contrast agent via this nanocomplex has potential for use as an agent that can identify small lung cancers, thus improving early detection and possibly increasing survival.

Human prostate cancer: a direct role for oestrogens

We have studied the response to oestrogen and expression of oestrogen receptors in responsive LNCaP and androgen non-responsive PC3 human prostate cancer cell lines. Growth of LNCaP cells is significantly stimulated by physiological concentrations of oestradiol; this growth increase appears to be comparable to that induced by either testosterone or dihydrotestosterone. In contrast, oestradiol significantly inhibits the proliferation of PC3 cells. We also present novel evidence for functional oestrogen binding in LNCaP cells. This evidence was first obtained by means of radioligand binding assays and was further corroborated using: (a) immunocytochemical analysis of oestrogen and progesterone receptors; (b) reverse transcriptase polymerase chain reaction of oestrogen receptor mRNAs; and (c) immunofluorescence of the 27 kDa heat shock protein (Hsp27), which has been reported to be a marker of functional oestrogen receptors. There appeared to be significantly and consistently lower levels of oestrogen receptor expressed in PC3 cells than in LNCaP cells. The observation that oestradiol-induced growth of LNCaP cells is completely reversed by the pure anti-oestrogen ICI 182,780 clearly implies that the biological response of these cells to oestradiol is mediated mainly via its own receptor. On the other hand, use of a neutralizing antibody against transforming growth factor (TGF)-beta 1 results in a remarkable increase in the growth of PC3 cells; this effect is almost completely abolished after the addition of oestradiol. This suggests that the oestradiol-induced growth inhibition may be mediated by TGF-beta 1. These results suggest that the current model for hormone-dependence of human prostatic carcinoma should be revised. This is of special concern, because recent data indicate that prostate cancer has become the most prevalent cancer and the second principal cause of cancer death in western countries.

The “Emigration, Migration, and Immigration” of Prostate Cancer

In the vast majority of cases, cancer continues to be an incurable disease when it has spread beyond the primary organ. Most cancer research and therapy design to date has focused on chemotherapy directed at killing the replicating tumor cells. Little attention has been placed on targeting the microenvironments of the primary tumor site, the circulating tumor cells, or the metastatic or secondary (target) tumor site and how cancer cells move among them. To develop these targets, a better understanding of metastasis and the mechanisms underlying the spread of tumors is required. This review describes the steps of metastasis using a paradigm of emigration to migration to immigration, with prostate cancer as a model system.

Modulation of iron on mitochondrial aconitase expression in human prostatic carcinoma cells

The mitochondrial aconitase (mACON) containing a [4Fe-4S] cluster is regarded as the key enzyme for citrate oxidation in the epithelial cells of human prostate. In vitro studies using the human prostatic carcinoma cells, PC-3 cells, found that both hemin and ferric ammonium citrate (FAC) significantly increased mACON enzymatic activity and gene expression. The effect of FAC on mACON was enhanced 2-fold by co-treating with ascorbic acid but blocked by co-treating with iron chelator, deferoxamine mesylate. Hemin treatments blocked 30% of citrate secretion from PC-3 cells but upregualted 2-fold of intracellular ATP biosynthesis. Results from reporter assay by using a cytomegalovirus enhance/promoter driven luciferase mRNA ligated to the iron response element (IRE) of mACON as a reporter construct demonstrated that modulation of FAC on gene translation of mACON gene is dependent on the IRE. Transient gene expression assays indicated that upregulation of mACON gene transcription by FAC may through the putative antioxidant response element (ARE) signal pathway. This study provides the first evidence of the biologic mechanism of human mACON gene translation/transcription and suggests a regulatory link between the energy utilization and the iron metabolism in human prostatic carcinoma cells.

Transferrin and the innate immune response of fish: identification of a novel mechanism of macrophage activation

We have previously demonstrated that a non-cytokine serum protein called transferrin was a primary activating molecule of the goldfish (Carassius auratus) macrophage antimicrobial response. The ability of the enzymatically cleaved forms of this protein to modulate fish macrophage function is novel and may represent a primitive and evolutionary conserved mechanism for the induction of NO response of macrophages. In the present study we confirm our earlier findings using immunoaffinity purified goldfish transferrin from mitogen-stimulated leukocyte supernatants. In addition we demonstrate that: (1). products released by necrotic/damaged cells contain transferrin-cleaving activity; (2). the cleavage site is located within the bridge peptide connecting the two lobes of the transferrin molecule; (3). transferrin is expressed by activated goldfish macrophages but not mitogen-stimulated kidney leukocytes; and (4). addition of transferrin significantly enhanced the killing response of goldfish macrophages exposed to different pathogens or pathogen products (e.g. lipopolysaccharide, Mycobacterium chelonei, Trypanosoma danilewskyi, Aeromonas salmonicida, and Leishmania major). We propose a model of fish macrophage activation that is mediated by a non-cytokine host protein (i.e. transferrin) in combination with highly conserved innate immunity recognition receptors that are almost certain to exist in teleost.

Toward a high-throughput approach to quantitative proteomic analysis: expression-dependent protein identification by mass spectrometry

The isotope-coded affinity tag (ICAT) technology enables the concurrent identification and comparative quantitative analysis of proteins present in biological samples such as cell and tissue extracts and biological fluids by mass spectrometry. The initial implementation of this technology was based on microcapillary chromatography coupled on-line with electrospray ionization tandem mass spectrometry. This implementation lacked the ability to select proteins for identification based on their relative abundance and therefore to focus on differentially expressed proteins. In order to improve the sample throughput of this technology, we have developed a two-step approach that is focused on those proteins for which the abundance changes between samples: First, a new software program for the automated quantification of ICAT reagent labeled peptides analyzed by microcapillary electrospray ionization time-of-flight mass spectrometry determines those peptides that differ in their abundance and second, these peptides are identified by tandem mass spectrometry using an electrospray quadrupole time-of flight mass spectrometer and sequence database searching. Results from the application of this approach to the analysis of differentially expressed proteins secreted from nontumorigenic human prostate epithelial cells and metastatic cancerous human prostate epithelial cells are shown.

Transferrin is an insulin-like growth factor-binding protein-3 binding protein

Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) possesses both growth-inhibitory and -potentiating effects on cells that are independent of IGF action and are mediated through specific IGFBP-3 binding proteins/receptors located at the cell membrane, cytosol, or nuclear compartments and in the extracellular matrix. We have here characterized transferrin (Tf) as one of these IGFBP-3 binding proteins. Human serum was fractionated over an IGFBP-3 affinity column, and a 70-kDa protein was eluted, sequenced, and identified (through database searching and Western immunoblot) as human Tf. Tf bound IGFBP-3 but had negligible affinity to the other five IGFBPs, and iron-saturated holo-Tf bound IGFBP-3 more avidly than unsaturated Tf. Biosensor interaction analysis confirmed that this interaction is specific and sensitive, with a high association rate similar to IGF-I, and suggested that binding occurs in the vicinity of the IGFBP-3 nuclear localization site. As an independent confirmation of this interaction, using a yeast two-hybrid system, we cloned Tf from a human liver complementary DNA library as an IGFBP-3 protein partner. Tf treatment blocked IGFBP-3-induced cell proliferation in bladder smooth muscle cells, and IGFBP-3-induced apoptosis in prostate cancer cells. In summary, we have employed a combination of techniques to demonstrate that Tf specifically binds IGFBP-3, and we showed that this interaction has important physiological effects on cellular events.

Biological properties associated with the enhanced lung-colonizing potential in a B16 murine melanoma line grown in a medium conditioned by syngeneic Corynebacterium parvum-elicited macrophages

A previous study by our laboratory showed that the peritoneal murine Corynebacterium parnum-elicited macrophages released into their growth medium an activity which enhanced the ability of B16-F10 melanoma cells to form experimental metastases in the lung of syngeneic mice. In the present study, we used a clone of B16-F10 line (F10-M3 cells) to investigate whether the increase in lung-colonizing potential due to the pro-clonogenic activity released by C. parvum-elicited macrophages was associated with biological properties characteristic of a metastatic phenotype. We have found that the pulmonary retention, growth rate in lung parenchyma, invasiveness through Matrigel, adhesiveness to IL-1-activated endothelium and MHC class I expression were increased in F10-M3 cells stimulated by the macrophage pro-clonogenic activity. By using an in vitro experimental protocol, the enhancement of lung-colonizing potential in the stimulated melanoma cells turned out to be a transient phenomenon as was the increase of invasiveness through Matrigel and the higher expression of MHC class I antigens. In conclusion, the melanoma cells stimulated by the pro-clonogenic activity released by C. parvum-elicited macrophages showed changes in biological parameters which are relevant to metastatic diffusion. These changes appeared as a temporary phenomenon which sustains the view that the metastatic phenotype represents a transient biological character influenced by host factors.

Transferrin-liposome-mediated systemic p53 gene therapy in combination with radiation results in regression of human head and neck cancer xenografts

The use of cationic liposomes as nonviral vehicles for the delivery of therapeutic molecules is becoming increasingly prevalent in the field of gene therapy. We have previously demonstrated that the use of the transferrin ligand (Tf) to target a cationic liposome delivery system resulted in a significant increase in the transfection efficiency of the complex [Xu, L., Pirollo, K.F., and Chang, E.H. (1997). Hum. Gene Ther. 8, 467-475]. Delivery of wild-type (wt) p53 to a radiation-resistant squamous cell carcinoma of the head and neck (SCCHN) cell line via this ligand-targeted, liposome complex was also able to revert the radiation resistant phenotype of these cells in vitro. Here we optimized the Tf/liposome/DNA ratio of the complex (LipT) for maximum tumor cell targeting, even in the presence of serum. The efficient reestablishment of wtp53 function in these SCCHN tumor cells in vitro, via the LipT complex, restored the apoptotic pathway, resulting in a significant increase in radiation-induced apoptosis that was directly proportional to the level of exogenous wtp53 in the tumor cells. More significantly, intravenous administration of LipT-p53 markedly sensitized established SCCHN nude mouse xenograft tumors to radiotherapy. The combination of systemic LipT-p53 gene therapy and radiation resulted in complete tumor regression and inhibition of their recurrence even 6 months after the end of all treatment. These results indicate that this tumor-specific, ligand-liposome delivery system for p53 gene therapy, when used in concert with conventional radiotherapy, can provide a new and more effective means of cancer treatment.

Tyrosine kinases expressed in vivo by human prostate cancer bone marrow metastases and loss of the type 1 insulin-like growth factor receptor

An important biological feature of prostate cancer (PCa) is its marked preference for bone marrow as a metastatic site. To identify factors that may support the growth of PCa in bone marrow, expression of receptor and nonreceptor tyrosine kinases by androgen-independent PCa bone marrow metastases was assessed. Bone marrow biopsies largely replaced by PCa were analyzed using reverse transcriptase-polymerase chain reaction amplification with degenerate primers that amplified the conserved kinase domain. Sequence analyses of the cloned products demonstrated expression of multiple kinases. Expression of the receptor and nonreceptor tyrosine kinases, alpha platelet-derived growth factor receptor and Jak 1, respectively, was confirmed by immunohistochemistry. In contrast, the type 1 insulin-like growth factor receptor, thought to play a role in PCa development, was lost in metastatic PCa. These results implicate several specific growth factors and signaling pathways in metastatic androgen-independent PCa and indicate that loss of the type 1 insulin-like growth factor receptor contributes to PCa progression.

Transferrin receptor overexpression enhances transferrin responsiveness and the metastatic growth of a rat mammary adenocarcinoma cell line

We previously found that breast cancer cell transferrin receptor expression and proliferative response to transferrin often correlated with metastatic capability. To further explore this, we transfected mammary tumor cells with a cDNA coding for the transferrin receptor and examined the effects of its overexpression on various cellular properties. A human transferrin receptor expression plasmid was made by excising the cDNA for the receptor from pcDTR1 and ligating it into the multiple cloning site of pcDNAINeo. The resulting construct was transfected into the poorly metastatic rat MTLn2 line that expresses low endogenous levels of rat transferrin receptor, and transfection-induced receptor expression was ascertained using antibodies specific for the human protein. Approximately 50% of the initial geneticin-resistant transfected MTLn2 cells overexpressed human transferrin receptor protein. High expressors were further isolated by four sequential FACS sorts. The final cell population expressed approximately 3-7 times more cell surface transferrin receptor than did vector transfected controls. Both lines proliferated at the same rate in normal (medium plus 5% FBS) culture conditions. However, in serum-free conditions, the transferrin receptor overexpressor cells displayed a pronounced proliferative response to transferrin whereas the control line did not. When injected into the mammary fat pads of female nude mice, cells from both lines formed micrometastases to the lung that were specifically visualized by immunohistochemical staining of rat cytokeratin 17. This revealed that the transferrin receptor transfected line formed larger lesions of this nature than did cells from the vector transfected controls. When injected into the tail vein of female nude mice, the transferrin receptor overexpressors likewise formed gross lung metastases of remarkably greater size than did the vector only transfectants. Overexpression of cell surface human transferrin receptor on MTLn2 cells appeared to affect their in vitro growth response to transferrin and their ability to grow at a secondary site in vivo.

Osteoblast-derived survival factors protect PC-3 human prostate cancer cells from adriamycin apoptosis

OBJECTIVES

Hormone-independent and cytotoxic drug-resistant tumor growth in osteoblastic metastases defines poor survival in patients with advanced prostate cancer. Therefore, we analyzed the ability of human osteoblast-like cells (MG-63 cells) and MG-63 conditioned media (MG-63 CM) to protect PC-3 human prostate cancer cells from adriamycin cytotoxicity in vitro.

METHODS

Adriamycin cytotoxicity was assessed in MG-63 osteoblast-like and PC-3 prostate cancer monolayer and three-dimensional collagen coculture systems using the DNA content and trypan blue exclusion assays, analysis of indexes of cell cycle by flow cytometry, determination of DNA fragmentation on simple agarose gel and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay, and immunocytochemistry.

RESULTS

Adriamycin (100 nM) arrested both the PC-3 and MG-63 cells at the G2/M phase in the cell cycle but induced apoptosis only in PC-3 cells, as assessed by flow cytometry, trypan blue exclusion, and agarose gel. Optimal doses of MG-63 CM (50 microg/mL), insulin-like growth factor I (50 ng/mL), and transforming growth factor-beta-1 (25 ng/mL), as determined by DNA content assay, partially neutralized the adriamycin cytotoxicity of PC-3 cells detected by flow cytometry and trypan blue exclusion. In addition, MG-63 cells rescued PC-3 cells from adriamycin apoptosis in the three-dimensional type I collagen gel coculture system, as analyzed by TUNEL assay.

CONCLUSIONS

These data suggest that osteoblast-like cells and osteoblast-derived growth factors can optimize survival of metastatic prostate cancer cells, thereby helping to develop cytotoxic drug-resistant growth in vitro.

Osteopontin stimulates a subpopulation of quiescent human prostate epithelial cells with high proliferative potential to divide in vitro

BACKGROUND

Osteopontin (OPN) is a secreted extracellular matrix (ECM) protein found in bone, as well as associated with epithelial cells. The main objective of these studies was to test in vitro the hypothesis that interaction with OPN stimulates proliferation of a quiescent subpopulation of prostate epithelial cells with high proliferative potential.

METHODS

To simulate conditions that restrict proliferation and inhibit terminal differentiation of basal cells in vivo, control cultures grew on substrate coated with collagen (CO) or fibronectin (FN), in medium containing low levels of growth factors.

RESULTS

Under growth-restricting conditions, most prostate epithelial cells with high proliferative potential, seeded in control secondary cultures, were quiescent within the time frame of the studies, as indicated by the small number of large colonies in these cultures. Growing prostate epithelial cells (PR) under the same growth-restricting conditions, but on substrate coated with OPN instead of CO or FN, stimulated proliferation of a subpopulation of single cells with high proliferative ability as indicated by: 1) dose-dependent increase in the percentage of single cells incorporating bromodeoxyuridine, i.e., proliferating PR; and 2) subsequent dose-dependent increase in the percentage of large colonies. The OPN effect was not merely due to preferential attachment to OPN, because PR attachment to OPN, CO, or FN was identical. PR attachment to OPN was inhibited in the presence of GRGDTP or an antibody against the integrin subunit alphav, but not in the presence of an RGES peptide or a nonspecific IgG.

CONCLUSIONS

Integrin-mediated OPN/PR interaction stimulates proliferation of a quiescent subpopulation of prostate epithelial cells with high proliferative potential, possibly stem cells.

Selection of highly metastatic rat MTLn2 mammary adenocarcinoma cell variants using in vitro growth response to transferrin

We previously found that the proliferative response to transferrin and the expression of transferrin receptors (TfR) on the cell surface of various rat 13762NF mammary adenocarcinoma cell sublines correlated with their spontaneous metastatic capability. To further assess the involvement of transferrin and TfR in metastasis, transferrin-responsive cells were selected from the poorly-metastatic, low-transfferin responsive 13762NF MTLn2 subline. When maintained in low serum (0.3%) conditions, MTLn2 cells failed to survive. However, if like medium was supplemented with 0.5 microgram/ml rat transferrin, some colonies emerged, presumably due to their ability to proliferate in response to the added transferrin. The surviving cells were expanded and exposed to ten or 20 similar cycles of transferrin growth selection to obtain the sublines MTLn2-Tf10 and MTLn2-Tf20, respectively. The MTLn2-Tf20 cells proliferated in response to transferrin at a rate similar to that of the high metastatic 13762NF sublines. Using immunofluorescent staining, Scatchard analysis, and affinity isolation of TfR, we discovered that the MTLn2-Tf20 cells had 5 to 6 times more TfR than did the parental MTLn2 line. When injected into the mammary fat pads of rats, the MTLn2-Tf20 line metastasized to the axillary lymph node in seven out of ten animals and to the lungs in six out of ten (median number = 13). No metastases were seen in the MTLn2 parental line. The MTLn2-Tf10 cells showed intermediate properties compared with the MTLn2 and MTLn2-Tf20 cells. The results indicate that variant cells with a high response to transferrin may be more metastatic than the bulk cells in a poorly metastatic population. The selection of cells with high levels of TfR and a higher proliferative response to transferrin results in sublines with greater potentials for spontaneous metastasis.

Prostate-specific membrane antigen

BACKGROUND

In an effort to discover new prostate-specific antigens (PSAs) to enhance our understanding of the functions and behavior of the prostate and the complex processes involved in prostate tumor progression, the structure and function of the PSM antigen has been elucidated.

METHODS

The PSM antigen was recognized using the 7E11-C5.3 monoclonal antibody, generated against the LNCaP human prostate adenocarcinoma cell line. The PSM cDNA was isolated by PCR, using tryptic peptides of immunoprecipitated PSM to design degenerate primers.

RESULTS

The prostate specific membrane antigen (PSM) is a 100 KD glycoprotein which appears to be a type II integral membrane protein. The protein and cDNA have been extensively characterized and the findings reviewed in the report.

CONCLUSIONS

PSM, a new prostate antigen is valuable as a marker for hematogenous micro-metastatic tumor dissemination as detected in RT-PCR assays of peripheral blood. PSM has many properties that may be potentially useful as a molecular target in monoclonal antibody directed strategies of tumor imaging and therapy.

Prostate-specific membrane antigen and other prostatic tumor markers on the horizon

The PSM antigen is an exciting new molecule with many potentially valuable applications. Further research with PSM may help us to elucidate the complex process of prostatic neoplasia better. Current avenues of research with PSM include the generation of new and improved monoclonal antibodies targeting different portions of PSM and PSM', which may improve the results of imaging and targeting prostate cancer. Gene therapy using the PSM promoter to drive prostate-specific expression of various cytokines and other factors is another exciting potential application deserving of attention, and refinement of serum PSM assays may greatly add to the present array of diagnostic modalities offered to patients with suspected prostate cancer. Thus, PSM is a potentially valuable addition to our armamentarium of prostate markers. Additionally, a host of other potential markers to increase our understanding of the complex biology of the normal and malignant prostate are on the horizon. Just how far away that horizon is awaits further basic and clinical investigations.

Suramin in non-small cell lung cancer and advanced breast cancer. Two parallel phase II studies

Suramin inhibits the growth of non-small cell lung cancer (NSCLC) and breast cancer in vitro by blocking the action of most known growth factors. The clinical efficacy of suramin was evaluated in patients with unresectable or relapsed NSCLC (n = 16) and advanced breast cancer (ABC) resistant to conventional therapies (n = 12). A plasma level > or = 200 micrograms/ml was maintained by three times weekly administrations using adaptive control with feedback. Treatment was continued until documented progression of disease or unacceptable toxicity. No clinical responses were observed in any patient. Median overall survival was 4.5 months in NSCLC and 9 months in ABC patients. Mean treatment duration was 6.6 weeks in NSCLC patients and 15.9 weeks in ABC patients. Treatment was discontinued due to disease progression in 14 patients, unacceptable adverse effects in 11 patients, while three patients refused to continue therapy. We cannot recommend this drug for further clinical trials in NSCLC and ABC.

Immortalized and tumorigenic adult human prostatic epithelial cell lines: characteristics and applications Part 2. Tumorigenic cell lines

This is Part 2 of a three-part review and deals with tumorigenic cell lines. Several immortalized and malignant adult human prostatic epithelial cell lines have been recently developed. The three most widely used carcinoma cell lines-DU-145, PC-3, and LNCaP-developed between 1977 and 1980, have greatly contributed to our current understanding of prostate cancer. Before a cell line can be accepted as having prostatic epithelial origin, some basic characteristics must be established. Expression of specific cytokeratins but absence of desmin and factor VIII should be first determined to establish epithelial origin. Responsiveness to androgens and expression of androgen receptor and prostate-specific antigen should be examined under stringent culture conditions to establish prostatic epithelial origin. Response to growth factors and expression of their receptors facilitates further characterization of cell behavior. Cell lines immortalized by human papillomaviruses (HPVs) are of special interest because HPVs are involved in a variety of anogenital cancers and may also play a role in prostate carcinogenesis. Malignant transformation of HPV-18 immortalized cells with the ras oncogene provides cell systems for investigating the multistep process of carcinogenesis. Each cell line has some unique characteristics, whether it arose directly from a carcinoma or resulted from immortalization with Simian virus 40 (SV40) or HPV, or was transformed in vitro by oncogenes. Comparisons of these characteristics should facilitate elucidation of the mechanisms involved in the initiation, promotion, and progression of prostate cancer. These cell lines will further serve as useful models for investigating tumor progression, invasion, metastasis, new therapeutic strategies, drug resistance, and its reversal and chemoprevention. The nontumorigenic cell lines were discussed in Part 1 [1]. This review summarizes the characteristics of several currently available tumorigenic, adult human prostatic epithelial cell lines.

A phase II trial of deferoxamine in patients with hormone-refractory metastatic prostate cancer

The management of hormone-refractory metastatic prostate cancer remains a therapeutic dilemma. We report the results of a phase II trial with deferoxamine administrated at a dose of 50 mg/kg (maximum dose 5 g) administered intravenously over 8 hr daily, repeated for 5 days at 4-week intervals for 2 courses. Fourteen patients with advanced hormone-refractory prostate cancer were treated and 28 courses were delivered. Essentially no toxicity was observed. Using combined clinical and prostate-specific antigen (PSA) criteria. 13 of 14 patients had disease progression. However, 9 of 14 patients had stable measurable or evaluable disease and progressed solely based on PSA criteria. Deferoxamine in this dose and schedule has no activity in hormone-refractory prostate cancer. Further investigation of the effect of deferoxamine on PSA production/expression is warranted.

Expression of heme oxygenase-1 (HSP32) in human prostate: normal, hyperplastic, and tumor tissue distribution

OBJECTIVES

Heme oxygenase isozymes, HO-1 and HO-2, are members of the stress/heat shock (HSP) family of proteins, with the known function of cleaving the heme molecule to biliverdin, iron, and carbon monoxide. The aim of this study was to examine the pattern of tissue expression of HO-1 in the human prostate under different states of proliferation and differentiation and to investigate whether the pattern differs between these states.

METHODS

Presently, we have determined the pattern of tissue expression of the stress-inducible isozyme, HO-1 (HSP32), in human prostate under normal and pathologic conditions, by immunohistochemistry, using polyclonal antibodies, and have measured HO-1 and HO-2 mRNA levels in normal prostate and benign prostatic hyperplasia (BPH) by Northern blotting. The activity of prostate to catalyze heme degradation was also assessed.

RESULTS

In normal and BPH tissue, columnar epithelial cells of acini and ducts and cells in stroma displayed HO-1 immunoreactivity; in all cells, perinuclear staining was prominent. In BPH tissue, however, a more intense staining of the epithelial cells occurred, with notable staining of the basal cells. In undifferentiated malignant tumors, intense HO-1 staining was manifest in nearly all tumor cells, and also in the epithelial lining of blood vessels. HO-1 in the prostate tissue was found catalytically active and oxidatively cleaved the heme molecule (Fe-protoporphyrin IX) to biliverdin. Northern blot analysis shows that two forms of HO are present in the human prostate. Compared with normal tissue, predominantly hyperplastic tissue demonstrates a pronounced increase in the approximately 1.8 kb mRNA that hybridizes to the rat HO-1 probe. The levels of two transcripts, approximately 1.3 and approximately 1.7 kb, that hybridize to the rat HO-2 probe are not increased in BPH tissue.

CONCLUSIONS

The finding that HO-1 expression is increased in BPH and malignant prostate tissue is consistent with a role for this stress protein in the pathogenesis of BPH and prostate cancer; in the context of iron metabolism, an argument is made in support of this possibility.

Elevated expression of ferritin H-chain mRNA in metastatic ovarian tumor

To identify genes associated with tumor metastasis, we prepared 5 cDNA libraries using mRNA from normal ovaries, paired primary and metastatic ovarian tumors, as well as paired cultured ovarian tumor cells. By differential screening, we identified 12 clones, which can be divided into 3 classes based on hybridization to various probes. Class 1 clones showed no reaction with the normal probe, slight or no reaction with the primary probe, but high reaction with the metastatic probe. Class 2 clones showed some reaction with normal and primary probes, but showed stronger reaction with the metastatic probe. Class 3 clones showed strong hybridization to the normal probe, slight or no reaction with the primary probe, and did not hybridize with the metastatic clone. These clones were further analyzed by determination of DNA sequence. One of the class 1 clones (clone 1) was identified as ferritin heavy chain. Northern blot analysis showed higher expression of ferritin H-chain in metastatic samples compared to primary tumor in 16/23 pairs of samples analyzed so far.

Stimulation of human prostate cancer cell lines by factors present in human osteoblast-like cells but not in bone marrow

Secondary deposits of prostate tumours are frequently found in the skeleton where they produce osteoblastic lesions. In this study both osteoblast-like cells and bone marrow from the proximal femur have been cultured to determine whether or not they can release factors which could support the growth of secondary prostate tumours. Media conditioned by both osteoblast-like cells (OBCM) and bone marrow were examined for their potential to stimulate prostate carcinoma cell lines. Whilst the results obtained demonstrated that OBCM could enhance the growth of both the hormone sensitive (LNCaP) and hormone unresponsive (PC-3 and DU-145) prostate carcinoma cell lines, no proliferative effect could be shown on cell lines derived from cancers of the breast, bladder, and liver. Significantly, media conditioned by either bone marrow or human skin fibroblasts also had no effect on the growth of prostate carcinoma cell lines. This study supports the possibility that the proliferation of prostate cancer cells at secondary skeletal sites, in vivo, may be due to osteoblast derived factors.

Identification of an endogenous inhibitor of prostatic carcinoma cell growth

The rate of expansion of primary prostatic carcinoma is comparatively slow, with tumours frequently taking years or decades to reach clinically relevant size. We now report the presence of an endogenous inhibitor, derived from aqueous extracts of human prostate tissue, which blocks prostatic carcinoma cell proliferation in vitro and prevents subcutaneous tumour expansion in vivo. Purification and characterization revealed the inhibitor to be spermine, a polyamine known to be locally abundant in the prostate. These results suggest that endogenous polyamine can negatively regulate the growth of prostatic carcinoma cells at their primary site in vivo and may explain the slow rate of primary tumour expansion in the prostate.

Prostate-specific membrane antigen: evidence for the existence of a second related human gene

Prostate-specific membrane antigen (PSM) is a glycoprotein recognised by the prostate-specific monoclonal antibody 7E11-C5, which was raised against the human prostatic carcinoma cell line LNCaP. A cDNA clone for PSM has been described. PSM is of clinical importance for a number of reasons. Radiolabelled antibody is being evaluated both as an imaging agent and as an immunotherapeutic in prostate cancer. Use of the PSM promoter has been advocated for gene therapy applications to drive prostate-specific gene expression. Although PSM is expressed in normal prostate as well as in primary and secondary prostatic carcinoma, different splice variants in malignant tissue afford the prospect of developing reverse transcription-polymerase chain reaction (RT-PCR)-based diagnostic screens for the presence of prostatic carcinoma cells in the circulation. We have undertaken characterisation of the gene for PSM in view of the protein's interesting characteristics. Unexpectedly, we have found that there are other sequences apparently related to PSM in the human genome and that PSM genomic clones map to two separate and distinct loci on human chromosome 11. Investigation of the function of putative PSM-related genes will be necessary to enable us to define fully the role of PSM itself in the development of prostatic carcinoma and in the clinical management of this malignancy.

Organ culture of benign, aging, and hyperplastic human prostate

Organ culture of the human prostate began in the 1970s and was modeled after the work of Lasnitzki and her collaborators in the mouse two decades earlier. In organ culture of human prostates, one sees a rapid increase in epithelial cells and decrease in stromal cells during the first 3-5 days of culture. While modulation of many phenotypic properties occurs, these cultures provide a simple and rapid way to achieve large numbers of human prostatic epithelial cells in cultured tissues that are markedly depleted of stromal cells. There is some evidence that organ cultures are maintained in slightly better functional states in the presence of androgens; however, most of this evidence is less than quantitative. Most organ culture of prostates has been accomplished with tissues from unspecified locations within the prostate; interpretation of cultures carried out in this fashion has been less complete than would have been possible if they had been carried out from specific anatomic locations within the prostate. Careful pathological characterization of locations contiguous to the cultured tissue is mandatory if cultures are to be interpreted meaningfully.

Inhibition of tumor growth by elimination of granulocytes

As observed for many types of cancers, heritable variants of ultraviolet light-induced tumors often grow more aggressively than the parental tumors. The aggressive growth of some variants is due to the loss of a T cell-recognized tumor-specific antigen; however, other variants retain such antigens. We have analyzed an antigen retention variant and found that the variant tumor cells grow at the same rate as the parental tumor cells in vitro, but grew more rapidly than the parental cells in the T cell-deficient host. The growth of the variant cells was stimulated in vitro by factors released from tumor-induced leukocytes and by several defined growth factors. In addition, the variant cancer cells actually attracted more leukocytes in vitro than the parental cells. Furthermore, elimination of granulocytes in vivo in nude mice by a specific antigranulocyte antibody inhibited the growth of the variant cancer, indicating that this tumor requires granulocytes for rapid growth.

Inhibition of tumor growth by elimination of granulocytes

As observed for many types of cancers, heritable variants of ultraviolet light-induced tumors often grow more aggressively than the parental tumors. The aggressive growth of some variants is due to the loss of a T cell-recognized tumor-specific antigen; however, other variants retain such antigens. We have analyzed an antigen retention variant and found that the variant tumor cells grow at the same rate as the parental tumor cells in vitro, but grew more rapidly than the parental cells in the T cell-deficient host. The growth of the variant cells was stimulated in vitro by factors released from tumor-induced leukocytes and by several defined growth factors. In addition, the variant cancer cells actually attracted more leukocytes in vitro than the parental cells. Furthermore, elimination of granulocytes in vivo in nude mice by a specific antigranulocyte antibody inhibited the growth of the variant cancer, indicating that this tumor requires granulocytes for rapid growth.

Tumor metastasis: current biologic concepts and their implications for control of residual disease

Metastatic disease presents an important obstacle to curative cancer therapy. This article reviews cancer biology concepts relevant to the pathogenesis of tumor metastasis and their implications for the surgical oncologist seeking to control or eradicate metastatic disease.

Production and response of human prostate cancer cell lines to granulocyte macrophage-colony stimulating factor

Prostate cancer selectively metastasises to skeletal sites, where it normally produces osteoblastic lesions. This study investigated whether haematopoietic growth factors known to be present in the bone environment could be involved in the survival and proliferation of prostate skeletal metastases. To evaluate this hypothesis we investigated the effects of recombinant granulocyte/macrophage colony-stimulating factor (rGM-CSF), recombinant granulocyte colony-stimulating factor (rG-CSF), recombinant erythropoietin (rEPO) and recombinant interleukin-3 (rIL-3) on the growth of 3 human prostate cancer cell lines. Two hormone-insensitive cell lines, PC-3 and DU145, were significantly stimulated by rGM-CSF and rEPO in serum-free medium but their growth was unaffected by incubation with rIL-3 or rG-CSF. A hormone-sensitive cell line, LNCaP, was stimulated only by rGM-CSF. To investigate further the involvement of GM-CSF in prostate cancer, the presence of GM-CSF protein in the 3 prostate cancer cell lines was examined by immunohistochemistry, and analysis of cell line conditioned media was carried out by ELISA and Western blotting. These techniques demonstrated that GM-CSF-like material was produced by both DU145 and PC-3 cells but not by LNCaP. The results from ELISA found that media conditioned by DU145 and PC-3 cells contained 1.7 and 2.5 pg GM-CSF/micrograms protein, respectively, whereas no GM-CSF was detectable in the LNCaP conditioned media. Our results were also confirmed by Western blot analysis demonstrating one single band for DU145 and PC-3 conditioned media which co-migrated along with the standard rGM-CSF band. No bands were associated with the LNCaP conditioned media. The presence of GM-CSF gene transcripts in DU145 and PC-3 cells was established by reverse transcription and polymerase chain reaction of total RNA.

Derivation of androgen-independent human LNCaP prostatic cancer cell sublines: role of bone stromal cells

A model of human prostate cancer was established to study cellular interaction between prostate cancer and bone stroma in vivo. In this model, subcutaneous co-injection of 2 non-tumorigenic human cell lines--LNCaP, a prostate cancer cell line, and MS, a bone stromal cell-line--into intact adult male mice resulted in formation of carcinomas that secreted prostate-specific antigen (PSA), a clinically useful human serum prostate cancer marker. In castrated hosts, upon cellular interaction with bone fibroblasts, we observed the progression of these tumors from an androgen-dependent (AD) to an androgen-independent state (AI). We derived 4 LNCaP cell sublines from the chimeric LNCaP/MS tumors: the M subline from intact hosts and the C4, C4-2 and C5 sublines from castrated hosts. The LNCaP sublines had chromosomal markers similar to those of the parental LNCaP cells and distinctly different from those of the MS bone stromal cell line. Although the parental and derived cell lines expressed similar steady-state levels of ornithine decarboxylase transcript, the sublines expressed 5- to 10-fold higher basal steady-state levels of PSA transcript than did the parental LNCaP cell line. The LNCaP sublines formed 13- to 26-fold more soft-agar colonies than the parental LNCaP cell line. The sublines became tumorigenic, yielding an incidence of tumors in intact athymic mice of 7-75%. The LNCaP sublines C4 and C5 (but not the parental and M cell line) formed tumors in castrated hosts when co-injected with bone fibroblasts. A second-generation LNCaP subline, C4-2, was derived from a chimeric tumor induced by co-inoculating castrated mouse with C4 cells and MS cells. We found that C4-2 subline was tumorigenic when inoculated into castrated hosts in the absence of inductive fibroblasts. Moreover, C4-2 was the only subline capable of forming soft-agar colonies when cultured in serum-free medium. In comparison with the parental LNCaP cells, the C4-2 subline expressed lower steady-state levels of androgen receptor (AR) protein and mRNA transcript and lost its androgen responsiveness in vitro. Our results suggest that certain genetic traits of prostate cancer cells may be selected or altered through an "adaptive" mechanism that involves cellular interaction with the bone stromal cells.

Most free-radical injury is iron-related: it is promoted by iron, hemin, holoferritin and vitamin C, and inhibited by desferoxamine and apoferritin

Iron is a double-edged sword. In moderate quantities and leashed to protein, it is an essential element in all cell metabolism and growth, but it is toxic when unleashed. Because of its ability to switch back and forth between ferrous and ferric oxidation states, iron is both a strong biological oxidant and reductant. The human diet contains a multitude of natural chemicals which are carcinogens and anticarcinogens, many of which act by generating oxygen radicals, which initiate degenerative processes related to cancer, heart disease and aging (the "oxygen radical hypothesis of aging"). Among these many dietary chemicals are many redox agents, including vitamin C and beta carotene. Free radical damage is produced primarily by the hydroxyl radical (.OH). Most of the .OH generated in vivo comes from iron-dependent reduction of H2O2. Supporting too much iron as a free radical-generating culprit in the risk of cancer, NHANES I data indicated that high body iron stores, manifested by increased transferrin saturation, are associated with an increased cancer risk. Other data shows an increased heart attack risk.

Paracrine and autocrine growth mechanisms in tumor metastasis to specific sites with particular emphasis on brain and lung metastasis

Once metastatic cells successfully seed at distant sites, their clinical detection and danger to the host are dependent on growth to form gross metastases. Metastatic tumor cells proliferate in response to local paracrine growth factors and inhibitors, and their growth also depends on production and responses to autocrine growth factors. A major organ-derived (paracrine) growth factor from lung tissue-conditioned medium has been isolated that differentially stimulates the growth of cells metastatic to brain or lung. Characterization of this mitogen demonstrated that it is a transferrin or a transferrin-like glycoprotein. Furthermore, antibodies to transferrin can remove significant growth activity from lung tissue-conditioned medium. Cells that are metastatic to brain or lung express greater numbers of transferrin receptors on their surfaces than cells that are poorly metastatic or metastatic to liver. Growth responses of metastatic cells and organ preferences of colonization appear to change during progression to more malignant states. At early stages of metastatic progression there is a tendency for many common malignancies to metastasize and grow preferentially at particular sites, suggesting that paracrine growth mechanisms may dominate the growth signals at this stage of progression. In contrast, at later stages of metastatic progression widespread dissemination to various tissues and organs occurs, and autocrine growth mechanisms may dominate the growth responses of metastatic cells. Ultimately, the progression of malignant cells to completely autonomous (acrine) states can occur, and at this stage of metastatic progression cell growth may be completely independent of autocrine and paracrine growth factors or inhibitors.

Differences in transferrin response and numbers of transferrin receptors in rat and human mammary carcinoma lines of different metastatic potentials

We previously found that transferrin (Tf) differentially stimulated the growth of highly metastatic variant lines of murine melanoma and that these highly metastatic cells also had greater numbers of Tf receptors on their cell surfaces. In the present study we found that highly metastatic rat mammary adenocarcinoma cell lines also responded differentially to Tf in proliferation assays, and cell monolayers bound Tf in relation to their metastatic potential (MTPaB10 > MTPaB5 > MTLn3 > MTLn2 > MTC > MTF7 > MTPa). The brain-colonizing lines PaB10 and PaB5 were the most responsive to Tf and had the highest numbers of Tf receptors. Different human breast cancer cell lines also responded differentially to Tf in proliferation assays and bound different amounts of Tf to their cell surface Tf receptors. Transferrin binding, but not growth response, correlated with metastatic and invasive properties of lines selected from the human MCF-7 series (MCF7/LCC2 > MCF7/LCC1 > MCF7). In examining the transferrin binding and growth response of lines from the human MDA series, the Tf binding and growth response was MDA231 > MDA435 > MDA468. The lines MDA435 and MDA231 were metastatic in nude mouse assays, whereas the line MDA468 was not. Scatchard analysis indicated the presence of a single class of receptor for Tf on the rat and human mammary cell lines. The results suggest that neoplastic cells displaying various metastatic properties may express differing numbers of Tf receptors and respond differently to growth factors such as Tf.