Influence of tumour size on human prostate tumour metastasis in athymic nude mice

Prostate tumor RON receptor signaling mediates macrophage recruitment to drive androgen deprivation therapy resistance through Gas6-mediated Axl and RON signaling

BACKGROUND

Androgen deprivation therapy (ADT), or chemical castration, is the first-line therapy for prostate cancer; however, resistance leaves few treatment options. Prostatic tumor-associated macrophages (TAMs) have been shown to promote prostate cancer growth and are abundant in castration-resistant prostate cancer (CRPC), suggesting a role in promoting CRPC. We recently showed a tumor cell-intrinsic mechanism by which RON promotes CRPC. Given previous reports that RON alters prostate cancer cell chemokine production and RON-overexpressing tumors alter macrophage function, we hypothesized that a macrophage-dependent mechanism regulated by tumor cell intrinsic RON also promotes CRPC.

METHODS

Using RON-modulated genetically engineered mouse models (GEMMs) and GEMM-derived cell lines and co-cultures with bone marrow-derived macrophages, we show functional and molecular characteristics of signaling pathways in supporting CRPC. Further, we used an unbiased phosphokinase array to identify pathway interactions regulated by RON. Finally, using human prostate cancer cell lines and prostate cancer patient data sets, we show the relevance of our findings to human prostate cancer.

RESULTS

Studies herein show that macrophages recruited into the prostate tumor microenvironment (TME) serve as a source for Gas6 secretion which serves to further enhance RON and Axl receptor activation in prostate tumor cells thereby driving CRPC. Further, we show targeting RON and macrophages in a murine model promotes CRPC sensitization to ADT.

CONCLUSIONS

We discovered a novel role for the RON receptor in prostate cancer cells in promoting CRPC through the recruitment of macrophages into the prostate TME. Macrophage-targeting agents in combination with RON/Axl inhibition are likely to provide clinical benefits for patients with CRPC.

Xenografts on nude mouse diaphragm of human DU145 prostate carcinoma cells: mesothelium removal by outgrowths and angiogenesis

Human prostate carcinoma DU145 cells, androgen-independent malignant cells, implanted in the athymic nu/nu male mouse, developed numerous tumors on peritoneal and retro-peritoneal organs whose growth aspects and vascular supply have yet to be investigated with fine structure techniques. A series of necropsies from moribund implanted mice diaphragms were examined with light, scanning, and transmission electron microscopy. DU145 xenografts installations, far away from the implanted site, were described as the smallest installation to large diaphragm outgrowths in moribund mice. Carcinomas did not show extracellular matrix and, reaching more than 0.15 mm in thickness, they revealed new structures in these outgrowths. Voids to be gland-like structures with mediocre secretion and, unexpectedly, intercellular spaces connected with fascicles of elongated DU145 cells that merged with a vascular supply originated from either the tumor cells and/or some perimysium vessels. In the largest carcinomas, most important vascular invasions coincidently accompanied the mouse lethality, similarly to human cancers. This androgen-independent model would be useful to study tumor outgrowth's changes related to testing anticancer strategy, including anti-angiogenic therapies involving toxicity, simultaneously with those of other vital organs with combined biomolecular and fine structure techniques.

Efficient antitumor effects of a novel oncolytic adenovirus fully composed of species B adenovirus serotype 35

Oncolytic adenoviruses (OAds) are among the most promising oncolytic viruses. Almost all oncolytic adenoviruses are composed of human adenovirus serotype 5 (Ad5) (OAd5). However, expression of the primary infection receptor for Ad5, coxsackievirus-adenovirus receptor (CAR), often declines on malignant tumor cells, resulting in inefficient infection in CAR-negative tumor cells. In addition, at least 80% of adults have neutralizing antibodies against Ad5. In this study, we developed a novel OAd fully composed of OAd35. OAd35 recognizes CD46, which is ubiquitously expressed on almost all human cells and is often upregulated on malignant tumor cells, as an infection receptor. Moreover, 20% or fewer adults have neutralizing antibodies against Ad35. OAd35 mediated efficient cell lysis activities at levels similar to OAd5 in CAR-positive tumor cells, while OAd35 showed higher levels of cell lysis activities than OAd5 in CAR-negative tumor cells. Anti-Ad5 serum significantly inhibited in vitro tumor cell lysis activities of OAd5, whereas OAd35 exhibited comparable levels of in vitro tumor cell lysis activities in the presence of anti-Ad5 and naive serum. OAd35 significantly suppressed growth of the subcutaneous CAR-positive and CAR-negative tumors following intratumoral administration. These results indicated that OAd35 is a promising alternative oncolytic virus for OAd5.

Novel Cellularly Active Inhibitor Regresses DDAH1 Induced Prostate Tumor Growth by Restraining Tumor Angiogenesis through Targeting DDAH1/ADMA/NOS Pathway

Dimethylarginine dimethylaminohydrolase1 (DDAH1) inhibitors are important therapeutics by virtue of their ability to control nitric oxide (NO) production by elevating asymmetric dimethylarginine (ADMA) levels. In a screening campaign, we identified that DD1E5 (3-amino-6- tert-butyl-N-(1,3-thiazol-2-yl)-4-(trifluoromethyl)thieno[2,3- b]pyridine-2- carboxamide) inhibits the DDAH1 activity both in vitro and in cultured cells. Mechanistic studies found that DD1E5 is a competitive inhibitor (dissociation constant ( K_i) of 2.05 ± 0.15 μM). Enzyme kinetic assays showed time and concentration dependent inhibition of DDAH1 with DD1E5, which shows tight binding with an inactivation rate constant of 0.2756 ± 0.015 M^-1 S^-1. Treatment of cancer cells with DDAH1 inhibitors shows inhibition of cell proliferation and a subsequent decrease in NO production with ADMA accumulation. DD1E5 reversed the elevated VEGF, c-Myc, HIF-1α, and iNOS levels induced by exogenous DDAH1 overexpression in PCa cells. Moreover, DD1E5 significantly increased intracellular levels of ADMA and reduced NO production, suggesting its therapeutic potential for cancers in which DDAH1 is upregulated. In in vitro assays, DD1E5 abrogated the secretion of angiogenic factors (bFGF and IL-8) into conditional media, indicating its antiangiogenic potential. DD1E5 inhibited in vivo growth of xenograft tumors derived from PCa cells with DDAH1 overexpression, by reducing tumor endothelial content represented with low CD31 expression. VEGF, HIF-1α, and iNOS expression were reversed in DD1E5 treated tumors compared to respective control tumors. In this work, integrating multiple approaches shows DD1E5 is a promising tool for the study of methylarginine-mediated NO control and a potential therapeutic lead compound against pathological conditions with elevated NO production such as cancers and other diseases.

Tumor Cell Autonomous RON Receptor Expression Promotes Prostate Cancer Growth Under Conditions of Androgen Deprivation

Current treatment strategies provide minimal results for patients with castration-resistant prostate cancer (CRPC). Attempts to target the androgen receptor have shown promise, but resistance ultimately develops, often due to androgen receptor reactivation. Understanding mechanisms of resistance, including androgen receptor reactivation, is crucial for development of more efficacious CRPC therapies. Here, we report that the RON receptor tyrosine kinase is highly expressed in the majority of human hormone-refractory prostate cancers. Further, we show that exogenous expression of RON in human and murine prostate cancer cells circumvents sensitivity to androgen deprivation and promotes prostate cancer cell growth in both in vivo and in vitro settings. Conversely, RON loss induces sensitivity of CRPC cells to androgen deprivation. Mechanistically, we demonstrate that RON overexpression leads to activation of multiple oncogenic transcription factors (namely, β-catenin and NF-κB), which are sufficient to drive androgen receptor nuclear localization and activation of AR responsive genes under conditions of androgen deprivation and support castration-resistant growth. In total, this study demonstrates the functional significance of RON during prostate cancer progression and provides a strong rationale for targeting RON signaling in prostate cancer as a means to limit resistance to androgen deprivation therapy.

Antitumor Activity of Intratumoral Ethanol Injection in an Orthotopic Pancreatic Cancer Cell Mouse Xenograft Model

Purpose

Pancreatic cancer is a lethal disease and usually is diagnosed at advanced stages of disease. This study assessed the effects of intratumoral ethanol injection using an endoscopic ultrasound (EUS) probe on the control of pancreatic cancer in a mouse orthotopic xenograft model.

Materials and Methods

The subcutaneous and orthotopic human pancreatic cancer cell mouse xenograft models were established. Different concentrations of ethanol (0–95%) were injected into subcutaneous xenograft tumors. In the orthotopic tumor model, ethanol was injected into the tumor lesions under the guidance of a high-frequency EUS probe. Tumor volume, relative tumor volume (RTV), and histopathology were evaluated. The serum amylase level was analyzed at baseline and 24 h after treatment in the orthotopic tumor model.

Results

Injection of 40–95% ethanol induced tumor necrosis in the subcutaneous tumor model, while there was no statistical difference between the RTVs of the two groups (P = 0.81). In the orthotopic tumor model, the RTV of the 80% ethanol treatment group was less than that of the saline injection group (P < 0.01); and histologically, there was a large area of necrosis observed in the 80% ethanol group. The serum amylase level was slightly elevated at 24 h after injection and returned to the baseline level at 7 days.

Conclusion

Injection of 80% ethanol into xenograft tumor lesions of orthotopic pancreatic cancer resulted in tumor necrosis, and the procedure was safe and effective. Future studies will further confirm its antitumor activity as well as assess its safety and feasibility.

Overexpression of ETV4 is oncogenic in prostate cells through promotion of both cell proliferation and epithelial to mesenchymal transition

The discovery of translocations that involve one of the genes of the ETS family (ERG, ETV1, ETV4 and ETV5) has been a major advance in understanding the molecular basis of prostate cancer (PC). Each one of these translocations results in deregulated expression of one of the ETS proteins. Here, we focus on the mechanism whereby overexpression of the ETV4 gene mediates oncogenesis in the prostate. By siRNA technology, we show that ETV4 inhibition in the PC3 cancer cell line reduces not only cell mobility and anchorage-independent growth, but also cell proliferation, cell cycle progression and tumor growth in a xenograft model. Conversely, ETV4 overexpression in the nonmalignant human prostate cell line (RWPE) increases anchorage-independent growth, cell mobility and cell proliferation, which is probably mediated by downregulation of p21, producing accelerated progression through the cell cycle. ETV4 overexpression is associated with changes in the pattern of E-cadherin and N-cadherin expression; the cells also become spindle-shaped, and these changes are characteristic of the so-called epithelial to mesenchymal transition (EMT). In RWPE cells overexpressing ETV4 EMT results from a marked increase in EMT-specific transcription factors such as TWIST1, SLUG1, ZEB1 and ZEB2. Thus, whereas ETV4 shares with the other ETS proteins (ERG, ETV5 and ETV1) a major role in invasiveness and cell migration, it emerges as unique in that it increases at the same time also the rate of proliferation of PC cells. Considering the wide spectrum in the clinical course of patients with PC, it may be highly relevant that ETV4 is capable of inducing most and perhaps all of the features that make a tumor aggressive.

Thrombospondin-1, vascular endothelial growth factor and fibroblast growth factor-2 are key functional regulators of angiogenesis in the prostate

BACKGROUND

Prostate cells secrete many molecules capable of regulating angiogenesis; however, which of these actually function as essential regulators of neovascularization is not yet clear.

METHODS

Functional angiogenic mediators secreted by normal and diseased prostate cells were identified using an in vitro angiogenesis assay. These factors were quantified by immunoblot or ELISA and localized in tissue by immunohistochemistry.

RESULTS

Normal prostate epithelial cell secretions were anti-angiogenic due to inhibitory thrombospondin-1 (TSP-1) whereas this inhibitor was decreased in the pro-angiogenic secretions derived from benign prostatic hyperplasia (BPH) and cancer cells. This pro-angiogenic activity depended primarily on fibroblast growth factor-2 (FGF-2) and/or vascular endothelial growth factor (VEGF) whose secretion was increased. Immunolocalization studies confirmed that the changes detected in vitro also occurred in vivo.

CONCLUSIONS

During disease progression in the prostate, production of TSP-1, the major inhibitor, is down-regulated while that of stimulatory FGF-2 and/or VEGF rise, leading to the induction of the new vessels necessary to support tumor growth.

A microcomputer program for calculating cell population doubling time in vitro and in vivo

Determination of the doubling time for a population of cells can involve tedious calculations. We have developed computer software for MS-DOS microcomputers to expedite the analysis of tumor cell growth in vitro and in vivo. This program, DOUBLE-TIME, assists in the collection of cell numbers into a database and calculates the doubling time for a population of cells from the plot of cell growth over time. For experiments where tumor mass is measured in vivo, the software collects measurements of tumor size, calculates tumor volume (mass), generates growth curves for tumor volume change over time, and determines the doubling time of the tumor and the mean for multiple tumors. DOUBLE-TIME plots both total and viable cell numbers over time, calculates standard error of the doubling time, and the doubling time for a selected portion of a growth curve. This software also automates the cell counting process with a software-generated cell counter that allows cell counts to be tallied directly into the computer via a mouse.

Prostate cancer progression. Implications of histopathology

This review examines selected areas of contemporary prostate cancer research in terms of the impact of prostatic cellular and histopathological heterogeneity. Prostate tumor progression is accompanied by dysregulation of multiple growth factor networks as well as disruption of normal patterns of cell-cell interactions. Molecular and cytogenetic studies demonstrate that prostate cancer results from the accumulation of several different genetic defects. No single event predominates, but modifications in tumor suppressor genes or functional elimination of the suppressor gene product are more common than activation of known oncogenes. Intratumor heterogeneity is also detectable at the genetic level. This further complicates efforts to correlate modifications at specific loci with progression or outcome. The development of new in vitro and in vivo systems for the study of human prostate cancer should increase our understanding of this complex disease. In each approach, knowledge of the histopathology of the normal and neoplastic prostate is essential.

Growth factors and their receptors as determinants in the proliferation and metastasis of human prostate cancer

Prostate adenocarcinoma, the most common tumor occurring among North American men, preferentially metastasizes to bone, where it characteristically forms osteoblastic lesions. The following growth regulatory factors are expressed in some human prostate cancers and/or established cell lines: epidermal growth factor (EGF), transforming growth factor alpha, transforming growth factor beta, basic fibroblast growth factor (bFGF), and insulin-like growth factor. Some of these, especially EGF, bFGF, and TGF-beta, are also implicated in growth regulation in normal and benign hyperplastic prostates. Although evidence from in vitro study of the small number of prostate cell lines available demonstrates that these growth regulatory pathways are exploited by some of these cells, direct in vivo evidence is limited. The development of human prostate cancer cell lines which grow and metastasize in immune-deficient rodents is an advance which now permits experimental analysis of the role of these growth factors in prostatic metastasis, particularly to bone. The progression and metastasis of human prostate cancer results from the complex interactions of multiple growth factors, androgens, and cellular communication, which form a dynamic network. Continued progress in the study and treatment of this disease will require new conceptual frameworks as well as successful application of the techniques of molecular and cellular biology.

Growth patterns of pulmonary metastases and primary tumours from five murine fibrosarcoma cell clones

The growth patterns, including the size, shape and regional preferences, of lung metastases from five murine fibrosarcoma cell clones were studied. Spontaneous metastases developed from tumours formed by subcutaneous inoculation of the cell clones. Lung colonies (experimental metastases) were established by i.v. injection of cells. The numbers of both spontaneously and experimentally formed subpleural lung metastases were counted through a stereomicroscope. The fraction of colonies that was located subpleurally was determined in histological sections of lungs. The growth kinetics of clonally derived primary tumours, and the number of spontaneous and experimental lung metastases, differed greatly between certain cell clones. The number of spontaneous lung metastases was correlated with the maximum size of primary tumours. No close correlation was observed between the size of the primary tumours and the size of experimental metastases. There were differences between the cell clones in the shape and regional preferences of their lung deposits. The subpleural colonies were generally larger than the intrapulmonary ones. Thus, both the regional distribution and the growth pattern of lung deposits differed between the clones.

Isolation and characterization of transforming growth factor beta response variants from human prostatic tumor cell lines

In this study we examined the relation between the response to transforming growth factor beta (TGF beta 1) in vitro and the growth in vivo of 1-LN-PC3-1A (1-LN) human prostatic carcinoma cells. 1-LN cells resistant to the growth-inhibitory effects of TGF beta 1 were isolated after exposure to 2 ng/ml TGF beta 1 in an anchorage-independent growth assay. Cloning of TGF beta 1-resistant and -sensitive populations produced 2 clones (R2-6 and 1-LN clone 4), which maintained relatively stable resistance or sensitivity, respectively, in the absence of TGF beta 1 for up to 12 passages. Colony formation by the R2-6 cells in the presence of TGF beta 1 was 2-10 times greater than that of 1-LN clone 4, depending upon the TGF beta 1 concentration. Injection of 1 x 10(5) R2-6 cells into athymic nude mice produced tumors with a significantly shorter latency interval as compared with 1-LN clone 4 tumors (P < 0.0001). Western immunoblotting showed that higher levels of latent TGF beta 1 protein were secreted into the culture medium by 1-LN clone 4 cells. Acidified conditioned media from both clones inhibited mink lung epithelial cell DNA synthesis. Neutralizing monoclonal antibody to TGF beta 1 but not TGF beta 2 abrogated this inhibitory effect. Comparison of the different sensitive and resistant clones showed that in vitro sensitivity to TGF beta 1 and in vivo tumor latency interval were not invariably correlated. Thus, the TGF beta 1 response phenotype in vitro was not always predictive of growth delay in vivo.

Isolation and characterization of PC-3 human prostatic tumor sublines which preferentially metastasize to select organs in S.C.I.D. mice

We have developed and partially characterized a mouse model system for studying human prostate tumor cell metastases in vivo. To develop this model we have selected highly invasive (3 x I.) and non-invasive (3 x N.I.) PC-3 human prostatic tumor sublines based on enhanced and diminished capacities to migrate across a reconstituted basement membrane barrier (Matrigel) in Boyden chamber chemotactic assays. When the 3 x I. cells were injected intravenously (i.v.) in the tail vein of severe combined immune deficient (scid) mice, the cells initially metastasized to a wide variety of tissues as demonstrated by using [125I] IUdR labeled cells and histology. Four distinct sublines were eventually isolated which preferentially metastasized at approximately 80% efficiency to the lumbar vertebrae (PC-3 ML), the mandibular region of the right cheek (PC-3 MC), the rib cartilage (PC-3 MR), and the right front knee bone (PC-3 MK), respectively. Implantation experiments at different sites indicated that organ metastases may somehow be conferred on the tumor subclones by the host tissue.

The effect of radiation therapy and hyperthermia on a human prostatic carcinoma cell line grown in athymic nude mice

The effect of radiation and/or hyperthermia on a human prostatic carcinoma xenograft in athymic nude mice was investigated. A human prostate carcinoma subline (1-LN-PC-3-1A) was inoculated subcutaneously in the thigh of male athymic nude mice. When tumors reached a size of approximately 200 mm.3, they were treated with either radiation (X) or hyperthermia (H) alone, or in combination (X + H). In the combined treatment, hyperthermia was delivered immediately after radiation exposure. Comparison of the time required to reach twice the tumor volume observed at the time of treatment was used to define therapeutic impact on tumor growth. The combined treatment resulted in median tumor volume doubling time of 35.5 days, compared to 18 days and 25.5 days, respectively, for hyperthermia or radiation alone. Analysis of tumor doubling time using a proportional hazards regression indicates that under the conditions of this experiment, the effect of radiation and hyperthermia for 1-LN-PC-3-1A tumors is additive. The impact of this treatment regimen in the management of prostatic cancer requires further investigation.

Characterization of gelatin-degrading metalloproteinase activities of the Dunning rat prostate tumor grown in nude mice

Proteinase activities in the Dunning R-3327 prostatic tumor grown in nude mice and the dorsal lobe of the normal Copenhagen rat prostate were characterized using gelatin-containing SDS-polyacrylamide gel electrophoresis. Calcium-stimulated activities of approximately 33, 42, 64, 71, 76, 85, 98, 115, and 120 Kd as well as a 91 Kd calcium-independent proteinase were detected in the tumor, whereas the dorsal prostate showed calcium-dependent activities of approximately 62 and 80 Kd and a calcium-independent activity much greater than 120 Kd. The zymographic calcium-dependent proteinase patterns in the other rat prostatic lobes (a 62 Kd proteinase in the anterior lobe; 59, 62, and 67 Kd forms in the ventral lobe; and 52, 62, and 72 Kd activities in the lateral lobe) were distinctive from that of the tumor and of the dorsal lobe. The calcium-dependent and -independent proteinases of the tumor were active over a broad range of pH values with optimal activity near pH 8.0-8.4. The calcium-dependent activities were inhibited by EDTA and EGTA. Barium and strontium could partially substitute for calcium. The calcium-independent activities were not affected by these chelators nor by the proteinase inhibitors benzamidine, epsilon-aminocaproic acid, tranexamic acid, hydrocinnamic acid, or iodoacetate. Similarly, the metalloproteinase activities were not affected by the latter inhibitors. There was little change in the predominant molecular forms (64, 71, and 76 Kd) of proteinase following castration of tumor-bearing nude mice; however, the 98 Kd calcium-dependent activity decreased and the 91 Kd calcium-independent activity increased as a result of this treatment.

Determination of subcutaneous tumor size in athymic (nude) mice

The athymic (nude) mouse is a useful model for studying the biology and response to therapies of human tumors in vivo. A survey of recent literature revealed the use of 19 different formulas for determining the size of subcutaneous tumors grown as xenografts in nude mice (2 for determining tumor area, 3 for tumor diameter, and 14 for calculating tumor volume). We compared the volumes, areas, and diameters predicted by each of the 19 formulas with the actual weights of 50 tumors ranging from 0.46 to 22.0 g established in nude mice as xenografts from human cell lines. In addition to determining how well each formula predicted relative tumor size, we analyzed how well each formula estimated actual tumor mass. The ellipsoid volume formulas (pi/6 x L x W x H and 1/2 x L x W x H) were best for estimating tumor mass (r = 0.93), whereas measurements of diameter correlated poorly with tumor mass (r less than 0.66). Although determination of tumor area correlated well with tumor mass in small tumors (r = 0.89), correlations of area with tumor mass for large tumors were poor (r = 0.41). We conclude that determination of the ellipsoid volume from measurements of three axes consistently yields the most accurate estimations of both relative and actual tumor mass.

Effects of the immunomodulator PSK on growth of human prostate adenocarcinoma in immunodeficient mice

Tumor growth alterations were studied using an immunomodulator, PSK. Four human prostate tumor lines were grown in two types of immunodeficient mice. Two of the lines were selected because they are able to metastasize to lungs in host animals. Outbred NIH Swiss athymic mice having normal natural killer cells and athymic Beige mice deficient in natural killer cells were used as animal hosts. PSK treatment was given to tumor-bearing hosts to some animals soon after solid tumors were injected and to others after solid tumors were well-established. Low dose cyclophosphamide was given to some animals to decrease host natural killer cells and polyinosinic-polycytidylic acid (poly I:C) was given to other animals to increase natural killer cell activity. Measurement of tumor doubling times, host survival and metastatic capabilities showed that either poly I:C or PSK treatment in NIH Swiss animals soon after tumor cells were injected significantly increased tumor doubling times and host survival and decreased the incidence and number of metastatic lung lesions. Two of the tumor lines incapable of metastasizing in NIH Swiss mice were metastatic in the Beige athymic, natural killer-cell-deficient animals.

Patterns of metastasis by the human prostate cancer cell line PC-3 in athymic nude mice

Cells from the PC-3 human prostate cancer cell line were evaluated in athymic nude mice in order to determine the influence of size of the primary tumor and site inoculation on the incidence and pattern of metastasis. At autopsy, all organs, including the skeleton, were evaluated for metastasis. Subcutaneous injections resulted in metastases to the draining axillary lymph node and lungs (56% and 13%, respectively), and were correlated with size of the primary tumor. Tail vein injection resulted in a high incidence of lung metastasis, while injection into the peritoneal space, spleen, and seminal vesicles resulted in intraabdominal tumor growth, liver metastasis, and large tumors within the seminal vesicles, respectively. Skeletal metastases were not observed in any of the animals studied. We conclude that injection of PC-3 cells into various sites results in different patterns of metastasis, but may not constitute an entirely suitable animal model of human prostate cancer due to the lack of metastasis to the skeleton.

A new experimental metastasis model in athymic nude mice, the human malignant melanoma LOX

The human tumor line LOX was established as an s.c. xenograft in nude mice from a lymph-node metastasis of a patient with malignant melanoma. I.v. injection into adult nude mice of single-cell suspensions prepared from xenografts resulted in progressively growing lung tumor colonies that killed the animals. No difference in colony formation was seen between cells taken from lung colonies and s.c. xenografts. An in vitro cell line, LOX-L, was established from lung colonies, and the monolayer cells, detached with EDTA, retained the same ability to form experimental lung metastases. In a total of 14 experiments, 82 of 89 mice receiving 1 X 10(6) viable tumor cells died with a mean survival time of 34.1 +/- 4.8 days. Long-term passaging in vivo and in vitro did not result in any alteration of the lung-colonizing potential of the LOX cells, whereas trypsinization of the cells before i.v. injection reduced lung colony formation. The life span was inversely related to the number of LOX cells injected, permitting estimation of the cell kill caused by chemotherapy. Mice injected i.v. with the LOX cells showed the same relative response to cis-diamminedichloroplatinum (CDDP) and mitozolomide (MZA) as did animals carrying s.c. xenografts. The LOX cells have shown a remarkable stability and similarity to the cells of the patient's tumor with respect to morphology, karyotype and chemosensitivity. The LOX model may be useful for testing effects of therapy on lung micro- and macrometastases, and the activity of antimetastatic agents, as well as for studying mechanisms involved in the metastatic process.

Metastatic phenotype of human prostate tumor cells in athymic nude mice: alteration by exposure to ethyl methanesulfonate and "reversion" by 5-azacytidine

The human prostate tumor subline 1-LN-PC-3-1A (1-LN) is reproducibly metastatic in adult athymic nude mice. Cells surviving a brief in vitro exposure to ethyl methanesulfonate (EMS) exhibited a profound decrease in capacity for experimental lung metastasis in nude mice. Thirty days after EMS treatment, 1 X 10(6) uncloned EMS-treated 1-LN cells (1-LN-EMS-10) were injected IV into groups of 6 to 8-week-old male athymic nude mice (BALB/cAnBOM). A median of 8.5 colonies/lung was observed among 20 1-LN-EMS-10-injected mice, which was significantly different from the median of 51 colonies/lung produced among 14 1-LN-injected mice (P = 0.0002). This altered phenotype remained stable during 150 days of continuous culture. However, the 1-LN-EMS-10 cells were tumorigenic in 10/10 nude mice injected SC. Single lung tumor colonies recovered from 1-LN-EMS-10-injected mice and reinjected IV into nude mice produced medians of 32-63 colonies/lung. The altered metastatic phenotype resulting from treatment of 1-LN with EMS was reversed by exposure to a noncytotoxic dose of 5-azacytidine, but unaffected by a second exposure to EMS. Collectively these data demonstrate that the metastatic phenotype of these human tumor cells in athymic nude mice can be heritably altered by in vitro exposure to EMS and 5-azacytidine. Analysis of the mechanisms underlying these phenotypic changes may provide insight into parts of the complex process of tumor cell evolution.