Search

Concomitant tumor resistance (CR) is a phenomenon in which a tumor-bearing host is resistant to the growth of secondary tumor implants and metastasis. Although previous studies indicated that T-cell-dependent processes mediate CR in hosts bearing immunogenic small tumors, manifestations of CR induced by immunogenic and nonimmunogenic large tumors have been associated with an elusive serum factor. In a recently published study, we identified this factor as meta-tyrosine and ortho-tyrosine, 2 isomers of tyrosine that would not be present in normal proteins. In 3 different murine models of cancer that generate CR, both meta- and orthotyrosine inhibited tumor growth. Additionally, we showed that both isoforms of tyrosine blocked metastasis in a fourth model that does not generate CR but is sensitive to CR induced by other tumors. Mechanistic studies showed that the antitumor effects of the tyrosine isomers were mediated in part by early inhibition of the MAP/ERK pathway and inactivation of STAT3, potentially driving tumor cells into a state of dormancy in G 0-phase. Other mechanisms, putatively involving the activation of an intra-S-phase checkpoint, would also inhibit tumor proliferation by accumulating cells in S-phase. By revealing a molecular basis for the classical phenomenon of CR, our findings may stimulate new generalized approaches to limit the development of metastases that arise after resection of primary tumors or after other stressors that may promote the escape of metastases from dormancy, an issue that is of pivotal importance to oncologists and their patients. ©2012 AACR. Fil: Ruggiero, Raul Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Bruzzo Iraola, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Chiarella, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Bustuoabad, Oscar David. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Medicina Experimental. Academia Nacional de Medicina de Buenos Aires. Instituto de Medicina Experimental; Argentina Fil: Meiss, Roberto P.. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Pasqualini, Christiane D.. Academia Nacional de Medicina de Buenos Aires; Argentina

Concomitant tumor resistance (CR) is a phenomenon originally described in 1906 in which a tumor-bearing host is resistant to the growth of secondary tumor implants and metastasis. Although recent studies have indicated that T-cell-dependent processes mediate CR in hosts bearing immunogenic small tumors, manifestations of CR induced by immunogenic and nonimmunogenic large tumors have been associated with an elusive serum factor. In this study, we identify this serum factor as tyrosine in its meta and ortho isoforms. In three different murine models of cancer that generate CR, both meta-tyrosine and ortho-tyrosine inhibited tumor growth. In addition, we showed that both isoforms of tyrosine blocked metastasis in a fourth model that does not generate CR but is sensitive to CR induced by other tumors. Mechanistic studies showed that the antitumor effects of the tyrosine isoforms were mediated, in part, by early inhibition of mitogen-activated protein/extracellular signal-regulated kinase pathway and inactivation of STAT3, potentially driving tumor cells into a state of dormancy. By revealing a molecular basis for the classical phenomenon of CR, our findings may stimulate new generalized approaches to limit the development of metastases that arise after resection of primary tumors, an issue of pivotal importance to oncologists and their patients. ©2011 AACR. Fil: Ruggiero, Raul Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Bruzzo Iraola, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Chiarella, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Di Gianni, Pedro. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Isturiz, Martín Amadeo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Linskens, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina Fil: Speziale, Norma. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina Fil: Meiss, Roberto P.. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Bustuoabad, Oscar David. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Academia Nacional de Medicina de Buenos Aires; Argentina Fil: Pasqualini, Christiane D.. Academia Nacional de Medicina de Buenos Aires; Argentina

Resistance of tumour-bearing mice to a second tumour challenge, that is concomitant resistance, was evaluated in euthymic and nude mice using nine tumours with widely different degrees of immunogenicity. Two temporally separate peaks of concomitant resistance were detected during tumour development. The first one was exhibited only by small immunogenic tumours; it was tumour specific and mediated by classical immunological T-cell-dependent mechanisms. The second peak was shared by both immunogenic and non-immunogenic large tumours; it was non-specific, thymus independent and correlated with the activity of a serum factor (neither antibody nor complement) that inhibited the in vitro proliferation of tumour cells. This factor was eluted from a Sephadex G-15 column at fractions corresponding to a molecular weight of approximately 1000 Da and it was recovered from a high-performance liquid chromatography column in one peak presenting maximum absorption at 215 and 266 nm. The data presented in this paper suggest for the first time, to our knowledge, that in spite of the differences between immunogenic and non-immunogenic tumours, a common serum-mediated mechanism seems to underlie the concomitant resistance induced by both types of tumours at late stages of tumour development.

The development of solid tumors is dependent on angiogenesis in such a way that a restriction in neovascularization would cause secondary tumor implants to remain in dormant state, establishing an apparent paradox. In this study an attempt has been made to demonstrate that in the tumor-host relationship a variable threshold of angiogenic response is generated which can be normal, enhanced or diminished depending on the intensity of the stimulus. The latter was determined by the number of PEM, semiallogeneic lynphocytes or irradiated tumor cells which were intradermally injected to induce the host angiogenic response. As compared to the normal controls, in tumor-bearing mice, capillary neoformation i) induced by a low angiogenic stimulus was progressively inhibited by tumor growth; ii) when induced by higher stimuli, in 9 day tumor-bearing mice the response was enhanced while in those of 12 days it was normal being completely inhibited in 15 day tumor-bearing mice; iii) when in a specific day of tumor growth (9, 12 or 15) progressively higher angiogenic stimuli were applied, the response was higher in tumor-bearing mice than in the corresponding controls. Similar results were obtained with PEM induced granulomas, suggesting the participation of a phenomenon of counter-inflammation. It can be concluded that there is an angiogenic threshold that increases as a function of tumor growth so that the response will depend on whether the stimulus attains or surpasses the threshold.

Estrogen compounds were used to treat mice bearing syngeneic transplants of medroxyprogesterone acetate(MPA)-induced BALB/c mammary adenocarcinomas. Both MPA-dependent and MPA-independent tumor lines were used. These lines expressed estrogen (ER) and progesterone receptors (PR). We demonstrate that different doses of estradiol benzoate (EB) and 17-beta-estradiol (E2) inhibit tumor growth and induce tumor regression in both MPA-independent and -dependent tumors, even in the presence of MPA or progesterone (P). EB was unable to induce regression of (ER-) hormone-independent tumor lines. A few MPA-dependent tumors became resistant to the estrogenic treatment; in subsequent passages some of these tumors retained their MPA-responsiveness, although estrogen sensitivity was not recovered.

MPA induces mammary tumors in virgin BALB/c mice with an average latency of 52 weeks. In order to determine whether the simultaneous administration of a chemical carcinogen, N-methyl-N-nitrosourea (MNU), shortened the latency of MPA-induced tumors, a total of 60 virgin female BALB/c mice were treated with either MNU + MPA or MNU or MPA. The experiment lasted 7 months. The incidence and latency of mammary tumors were significantly different between the 3 groups: 15/19 (79%) in MNU + MPA-treated mice with a latency of 154 +/- 19 days; 3/20 (15%) in MNU-treated mice with a latency of 179 +/- 7 days; 0/20 (tumors only start appearing after 10 months) in MPA-treated mice. Histologically, MNU + MPA-induced tumors were similar to the few tumors observed in MNU-treated mice: most of them were type B adenocarcinomas with a high degree of necrosis and calcification. Only one of the MNU + MPA-induced tumors expressed high levels of ER and PR and proved to be MPA-responsive in further passages. All the other tumors showed low or non-detectable levels of ER and PR together with an independent pattern of tumor growth. In MNU-treated mice the only tumor that was transplanted proved to be hormone independent and had low levels of PR and ER. In both MNU and MNU + MPA treated mice lung adenocarcinomas were detected. Cystic uterine glandular hyperplasias were observed in all animals. It can be concluded that MPA and MNU potentiate their carcinogenic effect in mammary gland.

The administration of MPA to virgin female BALB/c mice led to the development of mammary adenocarcinomas, which in further in vivo transplants gave rise to both MPA-dependent and MPA-independent lines. In this paper we chose one of the MPA-dependent lines with high contents of estrogen (ER) and progesterone (PR) receptors, and were able to demonstrate that a) the growth of these tumors could be manipulated by the administration or the withdrawal of the hormonal supply; b) PR were down-regulated in MPA-treated mice; c) progesterone had the same stimulatory effect as MPA on tumor growth; d) tumors did not grow in estrogen-treated mice; e) tumor growth was much lower in males than in females; f) the presence of the ovaries had a positive influence on tumor growth, even in the presence of MPA; g) the withdrawal of progestin pellets in ovariectomized mice usually led to complete remissions followed by regrowth of the tumors after several weeks; and h) the regrowing tumors maintained their steroid receptor pattern and (in 3 out of 4 cases) their hormone-dependent behavior in further passages.

Splenocytes from adult F1 mice were assayed for their capacity to induce popliteal lymph node enlargement (PLNE) when inoculated in the footpad of identical or reciprocal F1 hosts. The results obtained showed that: (i) T Lyt 1 + splenocytes from adult F1 hybrids were able to induce a significant PLNE when inoculated in reciprocal but not in identical F1 hosts. (ii) Foster-nursing of F1 hybrids on mothers from the paternal strain was able to induce permanent alterations in the ability of their T splenocytes to induce PLNE: Lyt 1 + splenocytes were able to induce significant PLNE in identical but not in reciprocal F1 hosts. Thus, the ability of T splenocytes from foster-nursed F1 hybrids to induce PLNE resembled that observed in reciprocal F1 hybrids nursed by their own mothers, (iii) PLNE was accompanied by cell proliferation involving host B and T lymphocytes. (iv) This PLNE could be detected using F1 hybrids from parental strains differing or not at H-2 antigens but involving a parental strain expressing the stimulatory Mls a allele and a parental strain bearing the nonstimulatory Mls b allele while it was not observed in F1 hybrids from parental strains sharing Mls a antigens.

The T-cell repertoire is shaped by the positive and negative selection of immature CD4(+) CD8(+) double positive (DP) thymocytes. Positive selection of DP T cells to the CD4(+) CD8(-) and CD4(-) CD8(+) simple positive (SP) lineages is a multistep process which involves cellular interactions between thymocytes and stromal cells. Mutant nackt (nkt/nkt) mice have been shown to have a deficiency in the CD4(+) CD8(-) T-cell subset both in the thymus and in the periphery. The present report suggests that nkt/nkt mice present alterations in early steps of positive selection because they show decreases in the percentages of CD69(+) and CD5(+) cells within the DP subset. Experiments involving bone marrow transfer and thymic chimeras demonstrate that the thymic epithelium of nkt/nkt mice is involved in the alterations registered during positive selection and dictates the ultimate fate of CD4(+) SP cells.

Concomitant resistance (CR) is the phenomenon according to which a tumor-bearing host inhibits the growth of a secondary implant of the same tumor at a distant site. Confirming and extending previous results of our laboratory, histological studies have revealed that two temporally separate peaks of CR can be detected throughout tumor evolution. The first peak induced by immunogenic small tumors, in euthymic but not in nude mice, is associated with extensive necrosis of the secondary tumor implant and a profuse infiltration of polymorphonuclear granulocytes and mononuclear cells resulting in its final destruction; these features correspond to a typical immunological rejection. The second peak of CR induced by both immunogenic and non-immunogenic large tumors, in euthymic as well as in nude mice, is characterized by a dormant tumor stage with scarce or null mononuclear infiltration, associated with a significant reduction of tumor mitotic index and of the number of PCNA+ cells along with an increase in apoptosis and an arrest in S phase. In previous reports we suggested that a 1000 D serum fraction from mice bearing large tumors could be responsible for the induction of this dormant tumor stage. In this study tumor cells incubated in vitro with that serum factor mimicked the inhibition and cellular alterations observed in vivo in the secondary tumor inhibited by the second peak of CR. Moreover, the passive transfer of this factor by the intra-peritoneal (i.p.) route induced an in vivo inhibition of an i.p. tumor reproducing the image characteristic of the second peak of CR. This represents a direct proof that this serum factor can restrain tumor growth in vivo and that it is, most probably, the effector of the second peak of CR.

Murine lung metatases growing undisturbed by the primary tumor were significantly inhibited by the concomitant resistance induced by a secondary subcutaneous implant of two unrelated tumors. Such inhibition was T-independent since it was also observed in nude mice; its full expression was dependent on the presence of the secondary tumor implant and it was exerted on both macroscopic and microscopic established metastases and not on the process of tumor cell dissemination from the primary tumor. Direct and indirect mechanisms seemed to be involved, the former affecting the metastatic cells per se by causing a decrease in proliferation and an increase in apoptosis while the latter affected neo-vascularization. These antitumor and antiangiogenic effects could be attributed to a serum factor induced by the unrelated tumors generating concomitant resistance. This factor proved to be heat, acid and alkaline resistant and dialysable; it was recovered in an HPLC column with maximum absorption at 215 and 266 nm; it was anionic at neutral pH, exhibiting free carboxil groups and one or more molecules of tyrosine, with a molecular weight between 870 and 1300 Dalton. Intravenous administration of this factor significantly inhibited lung metastases, decreasing mitosis and increasing apoptosis similar to that observed in the presence of the unrelated tumors.

A spontaneous recessive mutation named nackt (symbol: nkt) affecting hair growth and T-cell development was discovered in a moderately inbred stock of mice. Skin lesions were characterized by sparse rough coat, bare patches around the eyes and neck, and a scratching behavior throughout life. Fluorescence-activated cell sorter analysis indicated a deficiency in the CD4(+) 8(-) T-cell subset in the thymus and a marked decrease in CD4(+) T cells in peripheral lymphoid organs. Linkage analysis using a set of molecular markers and an F2 intersubspecific cross indicated that the mutation maps to the central region of mouse chromosome 13, in a region homologous to human chromosome 5q22-q35.

Several years ago, we demonstrated that medroxyprogesterone acetate (MPA)- induced mammary adenocarcinomas in female BALB/c mice with an incidence close to 80% and a mean latency of around 13 months (1). These tumors were mostly ductal, progestin-dependent (PD) adenocarcinomas with high levels of estrogen and progesterone receptors (ER and PR) (2). We later found that progesterone (P) also induced mammary carcinomas, but this time the tumors were mostly lobular, progestin-independent (PI) adenocarcinomas with lower levels of ER and PR (3). There was a constant correlation between progestin dependence and morphology, that is, lobular carcinomas were always PI and ductal carcinomas PD (3). To extend this study further, we designed a model of co-carcinogenesis using medroxyprogesterone (MPA) with N-methyl N-nitrosourea (MNU) in BALB/c mice. We obtained a high incidence of mammary adenocarcinomas similar to the hormone-induced lobular tumors, and showed that MPA can act as a potent promoter.

The effect of progesterone (Pg), medroxyprogesterone acetate (MPA), estradiol (E2), dihydrotestosterone (DHT) and dexamethasone (DEXA) was studied on the in vitro growth rate of a progestin-dependent (PD), estrogen-sensitive mammary tumor line originated in an MPA-treated BALB/c mouse (C4-HD), and on its estrogen-resistant variant (C4-HDR). The specificity of hormone action was further investigated using the anti-hormones RU-486 and hydroxyflutamide (FLU). Cell growth was evaluated in epithelial and fibroblast-enriched cultures using 3H-thymidine and/or autoradiography and immunocytochemistry. The results indicate that cell growth is directly stimulated by MPA and Pg at concentrations ranging from 10(-11) to 10(-7) M. RU486 prevented MPA-induced stimulation in concentrations 10 to 100 fold lower than those of MPA. When used alone, it inhibited cell proliferation only in concentrations higher than 10(-11) M. At nM concentrations, neither DEXA nor DHT stimulated 3H-thymidine uptake except DEXA at 100 nM. MPA-induced stimulation was not reverted by micromolar concentrations of FLU. As for E2 (10(-7)-10(-9) M) it prevented MPA stimulation only in cultures of estrogen-sensitive tumors. Progesterone receptors (PR) (475 +/- 115 fmoles/10(5) cells, n = 5) and estrogen receptors (ER) (ND-115 fmoles/10(5) cells, n = 5) were detected only in epithelial-enriched cultures. Serum from 7 day-MPA-treated mice induced a significant increase of 3H-thymidine uptake; an increase was also obtained with serum from untreated ovariectomized animals to which 1 nM-100 nM concentrations of MPA had been added. The stimulatory effect of the exogenous MPA was much lower than that of the serum obtained from MPA-treated animals. It is concluded that MPA stimulates cell growth of primary cultures of MPA-induced PD tumors via PR. The results provide support for a direct effect of MPA which may be mediated or potentiated by serum factors.

We have demonstrated that medroxyprogesterone acetate (MPA), when administered in high doses, induces mammary carcinomas in virgin female BALB/c mice. Since one of the possible explanations for this effect was its progestagenic effects, we decided to investigate whether progesterone (Pg) alone could also induce mammary adenocarcinomas in our model and if MPA at doses lower than those used to establish the model was also carcinogenic. A total of 136 mice were subdivided into 3 groups: Group 1, 44 mice were implanted s.c. with 40 mg Pg silastic pellets at the beginning of the experiment, and 6 months later with a 20 mg Pg pellet; Group 2, 45 mice were similarly treated with MPA pellets; Group 3, 47 mice were inoculated s.c. with 40 mg MPA every three months. At the end of 20 months, 9 animals had developed mammary tumors in Group 1, 18 in Group 2 and 34 in Group 3 (actuarial incidence = 28%, 58%, and 98%, respectively); tumor latency was similar in all groups: 46.2 +/- 13.1, 51.3 +/- 9.9, and 50.1 +/- 2.1 weeks, respectively. Seven (Group 1), 14 (Group 2), and 25 (Group 3) tumors were transplanted into syngeneic mice to determine progestin dependence. All tumors, except one from Group 1, were histologically characterized. In Group 1 (Pg 60 mg), 4 tumors (67%) were infiltrating lobular carcinomas and 2 were ductal carcinomas (33%). In Group 2 (MPA 60 mg), 2 tumors (14%) were lobular and 12 were ductal adenocarcinomas (86%) (Group 1 vs Group 2: p0.05), whereas in Group 3 (MPA 160 mg), 8 were lobular carcinomas (32%) and 17 were ductal carcinomas (68%). In syngeneic passages all lobular tumors behaved as progestin independent (PI) and ductal tumors as progestin dependent (PD). All ductal tumors, except one, expressed estrogen receptors (ER) and progesterone receptors (PR), whereas receptor expression was variable in lobular carcinomas. It can be concluded that Pg induces mostly lobular, PI mammary tumors in BALB/c female mice. The fact that most MPA-induced tumors are ductal and PD suggests that the two hormones use different carcinogenic pathways.

Cellular proliferation involves different regulatory molecules that include hormones and growth factors. Interestingly, progestins can stimulate as well as inhibit the growth of tumors depending on the experimental design (1). In mammary cancer, polypeptide growth factors, such as EGF, TGFα, TGFβ, and IGF-I, IGF-II, may play either an autocrine or a paracrine role. The present study investigates the presence of these factors and their receptors in mammary adenocarcinomas induced by medroxyprogesterone acetate (MPA).

The ability of neonatal murine F1 cells to regulate parental graft vs. host (GvH) reactions was investigated. Neonatal F1 splenocytes were able to decrease significantly the deleterious effects of systemic GvH reactions induced either with maternal or paternal splenocytes in a third party strain. Both neonatal F1 splenocytes or thymocytes were able to decrease local GvH reactions induced with maternal splenocytes towards paternal histocompatibility antigens. In the same experimental conditions, however, neonatal F1 cells were unable to decrease local GvH reactions induced with paternal splenocytes towards maternal histocompatibility antigens; using different numbers of neonatal F1 cells not only was no suppressive effect detected but even, a significant increase in GvH was registered. Similar results were obtained when mortality assays were carried out. It can be concluded that neonatal F1 mice differ in their capacity for regulating parental alloreactive T reactions against self histocompatibility antigens either of maternal or paternal origin.

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.

In a previous paper we reported early immunoregulatory mechanisms involving not only the appearance of progressive suppression but also significant increases in alloreactive T levels in paraaortic lymph nodes (PALN) and spleen, not only in allogeneic but also in syngeneic pregnancies. Taking into account the hypothesis of the superposition of the alloreactive and the anti-self plus conventional antigens T sets of cells, we investigated whether immunization with conventional antigens was able to alter alloreactive T levels. Weekly i.p. doses of rabbit red bloods cells (RRBC) in BALB/c mice resulted in a dose-dependent increase in spleen alloreactivity as determined by graft-versus-host (GvH) assays in strain combinations differing at H-2 level but not in those sharing the same H-2 with BALB/c. The increases could be significantly decreased by an anti-idiotype anti-RRBC serum. Pretreatment with i.p. weekly doses of sheep red blood cells (SRBC) before mating was able to induce dose-dependent fetal damage when the parents differed at the H-2 level. SRBC immunization in one of the uterine horns induced increases in PALN weight which were much higher in progesterone-pseudopregnant than in virgin mice; T alloreactivity was significantly increased in the draining PALN only in pseudopregnant females. These results favour the postulation of the superposition between the alloreactive and the anti-self plus conventional antigens T sets of cells and suggest a possible role for conventional fetal antigens (non H-2) in triggering immunoregulatory mechanisms operating in pregnancy.