A novel function for platelet-derived growth factor D: induction of osteoclastic differentiation for intraosseous tumor growth

Although increasing evidence suggests a critical role for platelet-derived growth factor (PDGF) receptor β (β-PDGFR) signaling in prostate cancer (PCa) progression, the precise roles of β-PDGFR and PDGF isoform-specific cell signaling have not been delineated. Recently, we identified the PDGF-D isoform as a ligand for β-PDGFR in PCa and showed that PDGF-D is activated by serine protease-mediated proteolytic removal of the CUB domain in a two-step process, yielding first a hemidimer (HD) and then a growth factor domain dimer. Herein, we demonstrate that the expression of PDGF-D in human PCa LNCaP cells leads to enhanced bone tumor growth and bone responses in immunodeficient mice. Histopathological analyses of bone tumors generated by PDGF-D-expressing LNCaP cells (LNCaP-PDGF-D) revealed osteolytic and osteoblastic responses similar to those observed in human PCa bone metastases. Importantly, we discovered a novel function of PDGF-D in the regulation of osteoclast differentiation, independent of the RANKL/RANK signaling axis. Although both PDGF-B and -D were able to activate β-PDGFR, only PDGF-D was able to induce osteoclastic differentiation in vitro, and upregulate the expression and nuclear translocation of nuclear factor of activated T cells 1, a master transcription factor for osteoclastogenesis. Taken together, these results reveal a new function of PDGF-D as a regulator of osteoclastic differentiation, an activity critical for the establishment of skeletal metastatic deposit in PCa patients.

Are matrix metalloproteinases relevant therapeutic targets for prostate cancer bone metastasis?

After basal and squamous cell skin cancers, prostate cancer is the most frequent cancer in men in the United States, with 186,320 men estimated to be diagnosed with the disease and 28,660 expected to die from it in 2008 1. [...]

Inhibition of endothelial cell proliferation and tumor-induced angiogenesis by pentoxifylline

PURPOSE

In this study we investigated the effect of pentoxifylline (PTX) on tumor-induced neovascularization as well as on different steps involved in the angiogenic process.

METHODS

To assess angiogenesis inhibition. we injected intradermally (i.d.) 10 B16-F10 melanoma cells into C57BL/6J mice which were subsequently intraperitoneally (i.p.) inoculated with PTX or saline. On day 7 the number of blood vessels converging to the remnant of injected material was counted and the volumes of incipient tumors were calculated in each case. In vitro growth inhibition by PTX was evaluated in two different cell lines of endothelial origin and in human umbilical vein endothelial cells. Motility assays, as well as zymographic assays carried out to analyze gelatinolytic metalloproteinases and urokinase-type plasminogen activator, were performed in one of the endothelial cell lines.

RESULTS

A significant inhibition of tumor-induced angiogenesis was observed in C57B1/6 mice i.p. inoculated with PTX, that paralleled reduced incipient tumor volumes. The endothelial cells derived from different sources were inhibited in a dose-response manner by PTX in vitro. Non-cytotoxic PTX concentrations assayed in one of the endothelial cell lines did not inhibit its in vitro cell motility nor its gelatinase secretion, but its low molecular weight urokinase-type plasminogen activator expression.

CONCLUSIONS

Our findings suggest that the inhibitory effect of PTX on tumor angiogenesis is related to antiproliferative action on endothelial cells, as well as to down regulation of u-PA secreted by them.

Immunohistochemical analysis of Ki-67, p21waf1/cip1 and apoptosis in marker lesions from patients with superficial bladder tumours treated with vinorelbine intravesical therapy in a preliminary phase I trial

OBJECTIVE

To investigate Ki-67 and p21Waf1/Cip1 expression and apoptosis, before and after treatment, in tumour biopsies obtained from patients with superficial bladder cancer who underwent vinorelbine intravesical therapy.

PATIENTS AND METHODS

Twenty patients with high-risk superficial bladder cancer (including one or more of the following parameters: tumour diameter > 3 cm, histological grade 3, or multicentric tumours) were treated 1-6 times (weekly) with intravesical vinorelbine (50 mg/mL) instillations. Transurethral tumour marker biopsies were obtained one week before the first instillation of the drug and one week after the last. The biopsies were immunostained for Ki-67 and p21Waf1/Cip1 with monoclonal antibodies, on tissue sections derived from paraffin-embedded samples obtained before and after vinorelbine treatments. In addition, apoptosis was determined using a terminal deoxynucleotidyl transferase-mediated dUTP biotin nick-end labelling (TUNEL) technique.

RESULTS

There were no significant differences in the cell proliferation marker Ki-67 in biopsies taken before or after treatment. However, p21Waf1/Cip1 showed significantly higher expression in biopsies obtained after vinorelbine treatment, with median (range) values of 40 (20-90)% before and 70 (50-80)% after (P < 0.001, paired nonparametric Wilcoxon test). The apoptotic index was significantly higher after vinorelbine therapy, with median (range) values of 0.89 (0.06-3.8)% before and 2.25 (0.17-18.7)% after treatment (P < 0.001, paired nonparametric Wilcoxon test). Despite the brief treatment and few patients there was a clinical response in nine patients, together with low toxicity in all.

CONCLUSION

The intravesical treatment of tumours with vinorelbine affects p21Waf1/Cip1 expression without blocking cell proliferation, although increasing apoptosis. The preliminary results suggest that vinorelbine may be useful for treating superficial bladder tumours, and thus a phase II study is warranted.

Differential anthracycline sensitivity in two related human colon carcinoma cell lines expressing similar levels of P-glycoprotein

Chemosensitivity of the human colon carcinoma HCT-15 cell line to 4'-epidoxorubicin proved to be 100-fold higher than that of its variant HCT-15 EDR. Confocal scanning microscopy showed significant less drug accumulation in HCT-15 EDR. A 2-fold increase in hsp27 expression was found in HCT-15 EDR, with no alteration in hsp70. The expression of the drug exporter Pgp was similar in both cell lines, despite the lower drug accumulation shown by HCT-15 EDR in respect to HCT-15. Other molecules implicated in the acquisition of enhanced chemoresistance or a more active Pgp variant present in HCT-15 EDR, could explain the phenomenon.

CT-2584 (Cell Therapeutics)

CT-2584, an anticancer agent that inhibits phospholipid signaling, is under development by Cell Therapeutics Inc (CTI) as a potential treatment for various types of cancer. Phase II trials are underway for the treatment of prostate cancer and soft-tissue sarcoma [306617], [324290]. According to CIBC World Markets, completion of enrolment for these trials was expected in the fourth quarter of 2000. Furthermore, the initiation of phase II/III trials in combination with taxotere for the treatment of prostate cancer was anticipated in the second half of 2000, as were phase I/II trials in combination with cisplatin for the treatment of other cancers, including lung cancer [396582]. Results of a phase II study in patients with soft-tissue sarcomas evaluating pharmacokinetics, tolerance and therapeutic activity were presented at the 2000 American Society of Clinical Oncology (ASCO) meeting [367283]. Further data are expected to be presented at the ASCO meeting in May 2001 [396582]. Cell Therapeutics is seeking development and commercialization partners for CT-2584 [386398].

Modulation of the antimetastatic effect of a single low dose of cyclophosphamide on rat lymphoma

The aim of this paper was to identify the mechanism/s responsible of the antimetastatic effect of a single low dose of cyclophosphamide (Cy), previously demonstrated by us in the rat lymphoma LTACB. No direct cytotoxic antimetastatic activity of Cy could be proved. In vitro treatment of L-TACB cells with mafosfamide did not alter their invasiveness or their motility. The adoptive transfer of splenocytes from Cy-treated tumor-bearing rats, together with L-TACB cells inhibited their metastatic growth. The single low dose Cy treatment of T-immunodeficient nude mice did not show the antimetastatic effect on L-TACB observed in immunocompetent mice. An inhibition of the metastatic ability due to immunomodulation by Cy is proposed.

Mechanism of antimetastatic immunopotentiation by low-dose cyclophosphamide

We have previously reported the antimetastatic effect of a single low-dose of cyclophosphamide (Cy) on L-TACB rat lymphoma. The phenomenon could be adoptively transferred in immunocompetent rats and is abolished in nude mice, facts for which an immunomodulatory explanation was proposed. The aim of this paper was to identify the mechanism(s) by which spleen cells from Cy-treated tumour-bearing rats could exert this antimetastatic activity. Conditioned media obtained by incubation of spleen cells from Cy-treated and non-treated tumour-bearing rats, under specific or non-specific stimulation, were assayed to evaluate their effect on lymphocyte proliferation. The production of transforming growth factor beta (TGF-beta), interleukin-10 (IL-10) and nitric oxide (NO) by conditioned media was also studied. The restoration of spleen lymphoproliferative responses to normal levels when exposed to media conditioned by splenocytes from Cy-treated tumour-bearing rats, together with a decreased production of suppressive cytokines TGF-beta, IL-10 and NO, suggest an enhancement of host antimetastatic immunity triggered by single low-dose Cy treatment.

Studies on the mechanisms responsible for inhibition of experimental metastasis of B16-F10 murine melanoma by pentoxifylline

Pentoxifylline (PTX), a methylxanthine derivative widely used as a hemorheological agent in the treatment of peripheral vascular disease, was studied to unveil the mechanisms responsible for its inhibitory action on B16-F10 experimental metastasis. In vitro pretreatment of B16-F10 cells with noncytotoxic concentrations of PTX significantly inhibited their adhesion to reconstituted basement membrane Matrigel(R) and type IV collagen as well as the relative activity of secreted 92 kD metalloproteinase. However, PTX pretreatment of B16-F10 cells did not affect their in vitro invasiveness. Heterotypic organ adhesion assays carried out with B16-F10 cells and suspended organ tissues demonstrated that pretreatment with noncytotoxic concentrations of PTX of both, tumor cells or lung tissue, brought about a dose-dependent inhibition of melanoma cell adhesion to lung. Immunohistochemical studies using antibodies against CD31 adhesion molecule (PECAM-1) revealed that B16-F10 cells adhere to lung endothelial cells. Our results suggest that PTX may exert its inhibitory effect on tumor lodgment, and as a consequence of that on experimental metastases, through an inhibitory action on cell adhesion molecules.

Inhibitory effect of Lovastatin on spontaneous metastases derived from a rat lymphoma

The HMGCoA reductase inhibitor Lovastatin (LOV) has previously shown to abrogate p21ras farnesylation, which is associated with invasive and metastatic abilities in many tumor models. Considering the scarcity of therapeutic resources against metastasis, our objective was to study LOV as an antimetastatic agent on L-TACB rat lymphoma, which as a syngeneic tumor model resembles more closely the situation in human cancer. We also aimed to analyze the effect of LOV on chemoinvasion, motility, metalloproteases secretion, angiogenic capacity, and adhesion to the reconstituted basement membrane Matrigel. Our results showed that LOV caused no effect on cell motility, metalloprotease secretion and neovascularization. Conversely, LOV produced a significant inhibition of invasiveness, which could be a consequence of an impaired cell adhesion to the basement membrane observed. These effects could explain, at least in part, the inhibitory action of LOV on L-TACB rat lymphoma metastases.

Failure of wild-type p53 gene therapy in human cancer cells expressing a mutant p53 protein

The introduction of exogenous wild-type p53 into human cancer cells bearing p53 mutation does not necessarily result in inhibition of tumor growth. We have demonstrated this in MDA-MB468 breast cancer cells which are hemizygous for p53 mutation and also in KM12SM colorectal carcinoma cells which are heterozygous for p53 mutation. The wtp53 transfectants decreased three- to four-fold the number of colonies compared with controls. Most wtp53-expressing cells died by apoptosis at early passages, but some cells were able to form colonies and their proliferation rate was similar to control transfectants. This reversion was observed in three of the six MDA-MB-468 clones selected. When MDA-wtp53 transfectants were implanted orthotopically in nude mice only one clone showed prolonged tumor latency. No differences were found in either tumor proliferation or apoptosis in tumors. Integration and expression of exogenous wtp53 was assessed in early and late passages in vitro, and in tumors growing in vivo. Consistently, we found mutations in the exogenous wtp53 gene of MDA-MB468 transfectants. Excision of the exogenous gene was an alternative to abrogate the wtp53 function that was extremely efficient in KM12 cells, although they maintained resistance to geneticin. These results were corroborated by the functional assay in yeast. In conclusion, wtp53 is inactivated in these cancer cells by different mechanisms. The presence of mutated p53 may confer genome instability and mutator ability, which allows cells to escape the effects of the exogenous wtp53 and contributes to the failure of wtp53 gene therapy.

Antiangiogenesis and apoptosis as mediators of concomitant tumor resistance induced by Calu-6, a human lung carcinoma cell line, in nude mice

Concomitant resistance (CR), the phenomenon by which tumor-bearing hosts are able to inhibit secondary implants of the same tumor at distant sites of the body, has been previously observed by us and others in different murine tumor models. Here, we verified the generation of CR in nude mice by tumors induced by SC inoculation of Calu-6, a human lung carcinoma cell line. Histological analysis of secondary tumors subject to CR did not reveal macrophage infiltration nor cytotoxic signs. Although serum from tumor-bearing mice inhibited in vitro [3H]thymidine uptake by Calu-6 cells, no significant differences in [3H]thymidine labeling index of tumors implanted in the right flank of mice with and without a primary tumor in the left flank were detected. In our model, the presence of a primary tumor hindered remote tumor angiogenesis, as well as serum from tumor-bearing mice inhibited in vitro proliferation of an endothelial cell line derived from a murine hemangioendothelioma. Conversely, an enhancement of the apoptotic index was observed in secondary tumor implants carried out in tumor-bearing mice. The results reported herein show that human tumor cells are capable of inducing CR, and that this phenomenon would be a consequence of an impaired neovascularization as well as an increased programmed cell death at sites distant from the primary tumor.

Intravesical therapy with vinorelbine tartrate: antitumor activity in orthotopic murine cell carcinoma of the bladder

OBJECTIVES

To ascertain intravesical vinorelbine tartrate (VNR) antitumor activity against MB-49, a murine transitional cell carcinoma of the bladder (TCC), in an in vivo setting.

MATERIALS AND METHODS

C57B1/6J female mice were intravesically implanted with 5 x 10(4) MB-49 cells and treated locally with VNR. Tumor incidence and volume analyses, as well as survival studies were carried out.

RESULTS

Tumor incidence was significantly lower in VNR-treated mice (48%, n = 23) than in controls (84%, n = 19), as evaluated sixteen days after MB-49 orthotopic inoculation. Intravesical tumor volume was also significantly smaller in treated mice respect to controls (median [range]: 0.5 [0.4 to 61.8] mm.3 versus 47.7 [4.2 to 179.7] mm.3 respectively, p < 0.001 Kruskal-Wallis test). Median survival duration of the animals treated with VNR was 68 [21 to 68] days, and was significantly greater (p = 0.01, Kruskal-Wallis test) than that of untreated controls (18 [16 to 20] days).

CONCLUSION

Intravesical VNR treatment demonstrated an evident antitumor effect against the TCC model assayed. The results obtained suggest a potential use of VNR as intravesical treatment for superficial TCC following transurethral bladder tumor resection to prevent recurrence or retard tumor growth.

Exposure to vinorelbine inhibits in vitro proliferation and invasiveness of transitional cell bladder carcinoma

PURPOSE

To study the effect of vinorelbine (VNR) on in vitro cell proliferation, invasiveness, cell adhesion to substrate, cell motility and metalloproteinase secretion of MB-49, a murine transitional cell carcinoma of the bladder (TCC).

MATERIALS AND METHODS

The colorimetric MTS assay, which depends upon viable versus nonviable mitochondria, was used to evaluate the effect of graded concentrations of VNR on in vitro MB-49 cell growth. Chemoinvasion and cell motility were studied in TCC cells exposed for 24 hours to a noncytotoxic dose of VNR, through their ability to migrate across Matrigel-coated or Type IV collagen-coated 8-microns. pore filters. Zymographic studies in gelatin-embedded polyacrylamide gels were done to investigate gelatinolytic activity in conditioned media from treated and untreated MB-49 cells.

RESULTS

Vinorelbine inhibited MB-49 cell growth in a dose-dependent manner (IC(50)40 ng./ml.). In vitro cell invasive capacity of MB-49 cells pretreated for 24 hours with VNR at noncytotoxic doses (1 and 10 ng./ml.) was significantly lower than that of untreated cells. The decreased invasion of VNR-treated cells was not accompanied by a diminished adhesion to Matrigel or type IV collagen nor by a significant reduced secretion of gelatinolytic metalloproteinases. Instead, motility of MB-49 cells exposed to noncytotoxic concentrations of VNR was inhibited in a dose-response fashion similar to that of invasion.

CONCLUSION

Vinorelbine proved to be an effective drug to inhibit tumor cell growth and invasion in a transitional cell bladder carcinoma model. The results obtained would justify preclinical studies to evaluate the effectiveness of VNR as a potential treatment of TCC.

Secretion of gelatinases by human pancreatic cancer cell lines: lack of correlation with invasive ability

Twelve immortalized human cell lines derived from primary or metastatic lesions from pancreatic carcinomas were studied with respect to their in vitro invasiveness and motility. Various levels of invasive capacity and chemotactic responses were found. Zymograms of cells conditioned media were carried out to determine the role of metalloproteinases in pancreatic cancer invasion. No correlations were found, however, between invasive capacity of pancreatic carcinoma cell lines and gelatinase secretion. Putative reasons for these findings are discussed.

Stimulation of angiogenesis as an explanation of Matrigel-enhanced tumorigenicity

Matrigel, a reconstituted extract of basement membrane, enhances the growth of different human cancer cell lines when transplanted into nude mice. Here that stimulation was confirmed in the BALB/c murine mammary-tumor cell line M3MC, as well as in human colon (SW948) and mammary (MDA-MB-468) carcinoma cell lines transplanted in nude and SCID mice, respectively. Subcutaneous and intra-mammary fat-pad inoculations of Matrigel alone generated an angiogenic response which was macroscopically evident by day 9. Histological analysis of the local host reaction occurring at the site of injection revealed an early peripheral fibroblast response, followed by mononuclear cell infiltration, solid and hollow fibroblast cords projections from the edge to the center of the Matrigel plug, and finally capillary ingrowths. Conditioned media obtained from the gels generated in vivo, acted as very strong chemoattractants for mouse lung capillary endothelial cells, stimulating their motility between 38 and 82 times with respect to the control. Our results suggest an important role of host cells recruited by Matrigel, which could favor angiogenesis of the area and thus facilitate the growth of tumor cells co-inoculated with the basement membrane extract.

Expression of gelatinase/type IV collagenase in tumor necrosis correlates with cell detachment and tumor invasion

We have previously observed that acellular extracts from necrotic areas (NE) of the non-metastatic murine mammary adenocarcinoma M3, enhance in vitro cell detachment and spontaneous lung metastases. In the present study, using different proteinase inhibitors along with NE, only the calcium chelator EDTA could significantly abrogate the enhanced cell detachment from M3 produced by NE. The typical cleavage products of type IV collagenase were detected inside the tumor necrotic area, mainly in association with necrobiotic cells, as evaluated by Western blot analysis and immunohistochemical assays. Zymography revealed the presence of 72- and 92-kDa gelatinase/type IV collagenase in NE. Moreover, NE increased the in vitro invasive ability of cultured M3 cells. The use of specific antibodies against both 72- and 92-kDa type IV collagenases in the invasion assay showed that only the latter was able to revert the enhanced invasiveness to the baseline. It can be concluded that tumor necrosis is an important source of gelatinase/type IV collagenase, mainly in its 92 kDa form, and plays a major role in tumor invasion.

Correlation between seric antitumor activity and concomitant resistance in mice bearing nonimmunogenic tumors

Serum from mice bearing five weakly immunogenic or nonimmunogenic tumors inducing concomitant resistance exhibited a growth-inhibitory activity on in vitro proliferation of the tumor cells. This activity was proportional to the intensity of concomitant resistance and correlated with the capacity to restrain metastatic development. It was not attributable to cytotoxic antibodies, was relatively nonspecific, and operated through a cytostatic and reversible mechanism. All attempts to transfer antitumor resistance in vivo by serum inoculation have failed, but this could be attained by parabiosis. Physical and chemical serum treatments suggest that heat-, acid-, and alkali-resistant peptide(s) with molecular weights ranging from 1000 to 3000 could account for this inhibitory effect.

Enhancement of the invasive ability of a transformed human bronchial epithelial cell line by 12-O-tetradecanoyl-phorbol-13-acetate and diacylglycerol

The effect of the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was studied using an immortalized human bronchial epithelial cell line, BEAS-2B, both in vivo and in vitro. The in vivo model consisted of tracheas reconstituted with an epithelium of BEAS-2B cells xenotransplanted into athymic nude mice. Intraluminal TPA treatment caused increased BEAS-2B cell proliferation and downgrowth into the tracheal stroma. In an in vitro invasion assay, TPA enhanced the invasive capacity of BEAS-2B cells 20- to 25-fold. A similar result was observed with diacylglycerol (DAG), an endogenous activator of protein kinase C, and the effects of TPA and DAG were abolished by simultaneous treatment with H-7, a protein kinase C inhibitor. TPA induced type IV collagenolysis, and this effect also was prevented by H-7. These data are consistent with the hypothesis that TPA causes these cells to become invasive by inducing collagenase activity and that this effect is mediated via protein kinase C.

Multistage chemical carcinogenesis protocols produce spindle cell carcinomas of the mouse skin

Spindle cell carcinomas were identified using polyacrylamide gel electrophoresis and immunoblotting of proteins extracted from paraffin-embedded tissue sections. Immunohistochemistry using rabbit monospecific antisera against the mouse 55 kd keratin polypeptide also identified these tumors. A group of 53 SENCAR mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA) and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) yielded, after one year, four spindle cell carcinomas (0.07/mouse), whereas another group of 31 mice treated with a three-stage carcinogenesis protocol (initiation with DMBA and promotion for 10 weeks with TPA followed by 10 weeks of benzoyl peroxide) gave rise to six spindle cell carcinomas (0.19/mouse). The number of keratin-positive tumor cells and the intensity of the immunostain varied markedly, but all tumors expressed the 55 kd polypeptide. Although other carcinogens, mainly UV radiation, have been able to induce spindle cell tumors, the present data indicate that chemical carcinogenesis protocols are able to induce the formation of this highly malignant variant of skin carcinoma.

Expression of type IV collagenase and procollagen genes and its correlation with the tumorigenic, invasive, and metastatic abilities of oncogene-transformed human bronchial epithelial cells

In a series of immortalized human bronchial epithelial cell lines continuing various oncogenes, the transcriptional levels of the type IV collagenase and the type IV procollagen genes were compared with the properties of invasiveness in vitro and tumorigenicity and metastatic ability in athymic nude mice. v-Ha-ras greatly enhanced invasion and metastasis, whereas v-Ki-ras, c-myc, and c-raf had lesser effects on these malignant phenotypes. In addition, cell lines derived from tumors obtained by injecting the original immortalized human bronchial epithelial cell lines into nude mice exhibited enhanced invasive and metastatic abilities and increased level of type IV collagenase mRNA when compared with the original immortalized human bronchial epithelial cell lines. Invasiveness and metastatic capacity correlated positively with expression of the type IV collagenase gene and negatively with the expression of the type IV procollagen gene, suggesting that these phenotypes are associated both with decreased production and increased dissolution of extracellular matrix.

Benzoyl peroxide enhances the invasive ability of a mouse epidermal carcinoma cell line

The effect of the skin tumor promoter benzoyl peroxide on the invasive potential of a murine squamous carcinoma cell line was investigated using an in vitro assay based on the capacity of cells to migrate through a porous filter coated with matrigel. Pre-treatment of the murine squamous carcinoma cell line CH72 with benzoyl peroxide added to the tissue culture medium increased the invasive capacity of these cells 5-8 times. No effects were observed on cells from primary cultures of normal murine epidermis. The simultaneous treatment of CH72 cells with benzoyl peroxide and the free radical scavengers, superoxide dismutase or CuSO4, prevented the increase and the values did not differ significantly from the baseline invasive potential. This suggests that activated oxygen species participate in the benzoyl peroxide-induced enhancement of the invasive capacity of these carcinoma cells.

Invasive and metastatic potential of a v-Ha-ras-transformed human bronchial epithelial cell line

The in vivo growth behavior and invasive potential of normal and "immortalized" human bronchial epithelial cells were studied by xenotransplantation procedures, an in vitro assay of invasiveness, and determinations of type IV collagenase activity and mRNA expression. BEAS-2B cells, immortalized after hybrid virus infection (adenovirus 12-simian virus 40), reconstituted a columnar epithelium when xenotransplanted into de-epithelialized rat tracheas transplanted sc into athymic BALB/c mice. A few adenomatous growths could be seen 16 weeks after transplantation. BZR cells, obtained by transfer of the v-Ha-ras oncogene into BEAS-2B cells, were tumorigenic in this xenotransplantation model. BZR-T33 cells, obtained from a tumor produced after injection of BZR cells, were also tumorigenic; however, they exhibited a shorter latent period. When these same cell lines were injected sc and iv into athymic BALB/c mice, BEAS-2B cells were not tumorigenic, and the BZR-T33 cells were more tumorigenic than the BZR cells. The incidence of spontaneous metastases after sc inoculation was zero for BEAS-2B cells, 33% for BZR cells, and 100% for BZR-T33 cells. Similar increasing values that correlated well with the data on in vivo growth were noted in the in vitro invasion assay, the collagenolytic ability, and the mRNA expression of type IV collagenase. Normal human bronchial epithelial cells showed the lowest values in all the assays. These progressive changes occurring in cells derived from the same parental line indicate that the presence of the v-Ha-ras oncogene in immortalized bronchial cells is associated with a full-fledged malignant phenotype, which is further enhanced by in vivo passaging.

Effects of formaldehyde on normal xenotransplanted human tracheobronchial epithelium

Epithelial cells obtained from autopsies of full-term fetuses or infants less than 1 year old were isolated, amplified in primary cultures and inoculated in deepithelialized rat tracheas. These tracheas were then sealed and transplanted subcutaneously into irradiated athymic nude mice. Four weeks after transplantation the tracheal lumen was completely covered by epithelium, most of which was of mucociliary respiratory type. At this stage, tracheal transplants containing tracheobronchial epithelium from 20 different donors were exposed to silastic devices containing 0, 0.5, 1 and 2 mg paraformaldehyde. The tracheal transplants were examined histologically at 2, 4, 8, and 16 weeks after transplantation. Before sacrifice, all animals were injected with a single pulse of tritiated thymidine. Important epithelial alterations could be seen in the formaldehyde treated transplants with a maximum effect visible at 2 weeks after exposure. The highest dose of 2 mg produced, in most cases, numerous areas of epithelial erosion and inflammation whereas this effect was not as evident with the lower doses. All doses produced areas of hyperplastic epithelium alternating with areas of pleomorphic-atrophic epithelium. Although the differences in predominance of different types of epithelium was not clearly dose-dependent, the labeling index (LI) showed dose dependence between 2 and 4 weeks after initiation of exposure. The maximum mean LI was three to four times higher than normal, although in some focal hyperplastic-metaplastic lesions the LI was increased up to 20 times. These studies show that formaldehyde, although toxic at higher doses, is able to elicit at lower doses a proliferative response of the human respiratory epithelium that is not preceded by a massive toxic effect. This response is similar, although less intense than that of the rat respiratory epithelium in which formaldehyde proved to be a carcinogen.

Resistance to serum-induced terminal differentiation in normal human tracheobronchial epithelial cells after in vivo exposure to 7,12-dimethylbenz[a]anthracene

Normal human tracheobronchial epithelial cells (NHTBECs) from nine donors were used to repopulate de-epithelialized rat tracheas. After transplantation into nude mice and treatment with 7,12-dimethylbenz[a]anthracene (DMBA), the transplants were removed at 3, 4, 5 and 6 months. Epithelial cells from DMBA-treated tracheas were subculturable. Epithelial cells from most untreated tracheas were not subculturable. After treatment with 0.5, 1, 2, 4, 6 and 8% serum, cells exhibited increased subculturability after in vivo treatment with DMBA, did not terminally differentiate and were still proliferating even in medium containing 8% serum. Karyotypes from these cells showed considerable aneuploidy. Although these cells did not survive for more than 10 subcultures (42 weeks), this was considerably longer than the survival of control cells. Because of their longer survival, resistance to serum-induced terminal differentiation and chromosome alterations, they were considered to be phenotypically altered or partially transformed cells produced by in vivo treatment of human cells with a chemical carcinogen.

Role of concomitant resistance in the development of murine lung metastases

An attempt was made to explain the distinct lung metastatic patterns of 2 mammary adenocarcinomas with a common BALB/c origin: M3, which does not induce spontaneous metastases, and MM3 with an almost 100% incidence. No difference between the 2 tumors was detected with respect to host mononuclear cell content, degree of immunogenicity or lung-colony-forming ability. Conversely, there was a marked difference in the capacity to induce concomitant resistance: M3-bearing mice induced stronger and earlier resistance against i.v. challenge of both M3 and MM3 tumor cells than MM3-bearing mice; this resistance was expressed as lower number of lung metastases and lower tumor-cell proliferation in metastatic nodules. M3 was also able to control the development of spontaneous metastases: metastases developed in all M3-excised mice, compared with none in M3-bearing mice, while MM3-bearing mice also bearing a secondary M3 tumor developed fewer metastases than mice bearing MM3 only. This anti-metastatic effect does not appear to depend on classical immunological mechanisms since no difference could be detected between the 2 tumors in response to T cells, NK, macrophages or antibodies.

Tumor necrosis can facilitate the appearance of metastases

The non-metastatic murine mammary adenocarcinoma M3 and its metastatic variant MM3 were used to evaluate the role of intratumoral necrosis in cell detachment and metastasis. Accelular extracts from necrotic areas of both tumors increased in vitro cellular detachment from M3 but not from MM3 fragments. Furthermore, the in vivo inoculation of the necrotic extracts within non-metastatic M3 tumors gave rise to pulmonary metastases. Histological studies revealed in M3 a central necrosis limited by an uninterrupted peripheral ring of well preserved cells, while in MM3 necrotic and non-necrotic areas alternated. It is concluded that the distribution of necrosis within the primary tumor by facilitating cell detachment is, at least in part, responsible for the development of metastases.

Histologic aspects of concomitant resistance induced by nonimmunogenic murine tumors

Concomitant resistance to a second tumor implant was induced in both conventional and nude BALB/c mice by two nonimmunogenic syngeneic tumors of spontaneous origin, an epidermoid carcinoma and a lymphoid leukemia. In the secondary tumor, which was significantly inhibited by concomitant resistance, histologic examination revealed the presence of well-preserved tumor cells without any sign of necrosis and without any host cell infiltration, contrasting with classical immunologic rejection. Tumor cell proliferation as evaluated by the number of mitoses per high-power field was significantly inhibited in the secondary tumor as compared with the corresponding controls. No effect of concomitant resistance could be detected on primary tumor growth.