Stimulatory effects of dexamethasone and indomethacin on growth of androgen-dependent Shionogi carcinoma 115 in the mouse

Effect of social housing condition on heat shock protein (HSP) expression in the Shionogi mouse mammary carcinoma (SC115)

Our previous studies have shown that social housing conditions can significantly alter the growth rate of the Shionogi mouse mammary carcinoma (SC115). The present study extended our investigations to the molecular level by examining stressor effects on the expression of a group of stress-responsive proteins, the heat shock proteins (HSPs). We hypothesized that HSP expression in SC115 cells may be altered by (a) different social housing conditions in vivo and (b) steroid hormone and growth factor exposure in vitro. Mice were reared in groups (G) or as individuals (I). Immediately following tumor cell injection, mice were rehoused from group to individual (GI), from individual to group (IG), or they remained in groups (GG). Tumor tissue was resected at 0.8 g or 3.0 g, as evidence suggests that tumor size affects HSP expression, which in turn affects proliferation. The data demonstrate that expression of HSP25, 70, and 90 was increased in tumors from mice in the IG compared to GG and GI mice, at both tumor weights examined. In addition, in IG mice, HSP90 expression was greater in 0.8 g compared to 3.0 g tumors. Under controlled culture conditions, hormones known to stimulate SC115 growth both in vivo and in vitro altered HSP expression. Physiological levels of dihydrotestosterone (DHT) and pharmacological levels of hydrocortisone (HC) upregulated expression of HSP25, whereas physiological levels of beta-estradiol (E2) upregulated expression of HSP90. These data are the first to demonstrate that a psychosocial stressor, a change in social housing condition, can induce differential HSP expression. Further, these data show that hormones that regulate SC115 tumor growth, also alter HSP expression.

Psychosocial stressors and mammary tumor growth: an animal model

Stressful life events and the ability to cope with stress may play a role in the progression of breast cancer; however, the complex relationship between stressors and tumor growth is difficult to investigate in humans. Our studies have utilized the androgen-responsive Shionogi mouse mammary carcinoma (AR SC115) in male mice to investigate the effects of social housing condition on tumor growth rates and responses to chemotherapy. We demonstrate that, depending on social housing condition, mammary tumor growth and response to chemotherapy can both increase and decrease. We have examined the possible role(s) of 1) psychosocial variables, 2) testosterone and corticosterone, hormones altered by stress and known to stimulate SC115 cells in vivo and in vitro, 3) NK cells, one of the body's first lines of defense against tumor cells, 4) stress proteins, in mediating the differential tumor growth rates observed in our model. This review discusses the investigations we have undertaken to elucidate the mechanisms through which a psychosocial stressor, social housing condition, can alter tumor growth rate.

Corticosteroid administration does not affect viral oncolytic activity, but inhibits antitumor immunity in replication-competent herpes simplex virus tumor therapy

A multimutated, conditionally replicating herpes simplex virus type 1, G207, has been developed as an effective means of treating human malignant brain tumors. We have shown that intraneoplastic inoculation of G207 induces a specific and systemic antitumor immune response that plays an important role in the antitumor activity, in addition to the direct oncolytic action of G207. Since a large number of malignant brain tumor patients are treated with corticosteroids, it is important to evaluate whether the therapeutic efficacy of G207 is affected by corticosteroid-induced immunosuppression. For a tumor model, we used G207-permissive N18 murine neuroblastoma cells implanted subcutaneously in syngeneic A/J mice. Intraneoplastic inoculation of G207 (10(7) PFU) induced significant suppression of tumor growth whether or not dexamethasone (5 mg/kg) was given. When dexamethasone was given for an extensive time (16 days starting on day -2), all G207-treated mice showed tumor growth despite initial shrinkage, whereas in the saline group, four of eight of the G207-treated mice were cured. Dexamethasone administration significantly reduced serum neutralizing antibodies against G207 at 14 and 21 days after intraneoplastic G207 inoculation. However, there was no difference between the dexamethasone and saline groups in terms of the amount of infectious G207 isolated from tumors. Dexamethasone administration completely abolished G207-induced cytotoxic T lymphocyte activity against N18 cells. These results indicate that the oncolytic activity of G207 is retained under corticosteroid administration. However, intensive immunosuppression may diminish the long-term efficacy of G207 owing to suppression of tumor-specific cytotoxic T lymphocyte induction.

Two naturally-occurring isoforms and their expression of a glucocorticoid receptor gene from an androgen-dependent mouse tumor

We have isolated cDNAs encoding the glucocorticoid receptor from an androgen-dependent mouse tumor, Shionogi Carcinoma 115. The nucleotide sequence of the receptor revealed two different forms, designated as SC-GR I and SC-GR II. Both forms have a one-base substitution in the DNA binding domain of the wild-type mouse glucocorticoid receptor. Furthermore, SC-GR II has a three-base insertion in the interfinger region of this domain. By expressing the receptor cDNAs in cultured cells with MMTV-CAT reporter plasmid, SC-GR II was found to have about half of the activity of the wild-type mouse glucocorticoid receptor induced by either physiological or pharmacological doses of dexamethasone.

Alterations in splenic natural killer cell activity induced by the Shionogi mouse mammary tumor

We have previously demonstrated that differential housing conditions alter the growth rate of the Shionogi mouse mammary carcinoma (SC115). The present study was undertaken to determine if natural killer (NK) cells are involved in mediating the effects of differential housing on SC115 tumour growth rate. Splenic NK cell activity was assayed at 24 h, 3 days and 1 week post-injection in both tumour- and vehicle-injected animals. Significant stimulation of splenic NK cell activity occurred 3 days post-injection of SC115 cells. However, no correlation was observed between the level of splenic NK cell activity and tumour growth rate induced by housing condition. We conclude that either splenic NK cell activity does not accurately reflect NK cell activity at the tumour site or that NK cells are not a significant regulator of the differential tumour growth rates seen in this model.

Effects of psychosocial stressors on mouse mammary tumor growth

We describe a sensitive and replicable animal model which demonstrates that psychosocial variables both increase and decrease tumor growth rate. The effects of social housing condition and daily exposure to novel environments were investigated in mice bearing the transplantable androgen-responsive Shionogi mouse mammary carcinoma (SC115). Being reared individually housed and remaining individually housed or being reared in a sibling group and then singly housed following tumor cell injection markedly increased tumor growth compared to that in mice remaining in their standard sibling rearing groups (n = 2-3 per group), if animals were also exposed to acute daily novelty stress. In contrast, being reared individually and then moved to a larger social group (n = 4-5 nonsiblings per group) markedly reduced tumor growth, both in the presence and absence of acute daily novelty stress.

Interaction of different steroid hormones during progression of tumour cells to steroid autonomy

Progression to steroid insensitivity poses a major problem in therapy of breast cancer, but studies of the origin of steroid-insensitive cells have been few and have concentrated in any one system on the loss of response to only one steroid. Since both normal and tumour mammary cells have complex endocrine requirements, we wondered how different steroids might interact during loss of steroid sensitivity. Cloned cells from the androgen-responsive Shionogi 115 mouse mammary carcinoma respond in vitro to both androgens and glucocorticoids in terms of both cellular and molecular parameters but, following prolonged absence of any steroid, these cells become unresponsive. We show here that 2 steroids can interact to prevent the progression to steroid insensitivity since the S115 cells can be protected against any loss of response to either androgen or glucocorticoid with either steroid alone. Androgen protects against loss of glucocorticoid sensitivity and glucocorticoid protects against loss of androgen sensitivity. The clinical implications are discussed.

Evaluation of effect of host immunity on growth of androgen-dependent Shionogi carcinoma 115 in the mouse

Experiments were carried out to examine the role of the host defence mechanism in the proliferation of androgen-dependent Shionogi carcinoma 115 in the DS mouse. Stimulation of tumor growth by dexamethasone was synergistic with androgen action. Enhanced host immunity caused by bacterial infection resulted in remarkable inhibition of tumor growth. Not only androgen but also the host defence mechanism is one of the major factors that determine overall growth rate of the androgen-dependent tumor in this strain of mice.