Mammary carcinogenesis induced byN-methyl-N-nitrosourea (MNU) and medroxyprogesterone acetate (MPA) inBALB/c mice

Summary 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.Abbreviations MPA Medroxyprogesterone Acetate - MNU N-methyl-N-nitrosourea - ER Estrogen Receptors - PR Progesterone Receptors     

Induction of mammary adenocarcinomas by medroxyprogesterone acetate in BALB/c female mice

In a previous paper we reported that medroxyprogesterone acetate (MPA) decreased the incidence of foreign body tumorigenesis in BALB/c mice but that mammary adenocarcinomas appeared in some of the females. The experiment was repeated in 245 virgin females as follows: (1) 40 mice treated with 40 mg of MPA depot s.c. every 2 months during a whole year; (2) 117 mice bearing a foreign body (FB) and treated with MPA; (3) 46 mice bearing a FB; (4) 42 non-treated mice. Mammary adenocarcinomas developed in 16/40 in group 1 and 30/117 in group 2; no mammary tumors appeared in either control groups. The tumors were infiltrating adenocarcinomas often affecting more than one mammary gland; metastases were occasionally observed. Animals killed after 1 year of MPA treatment presented deciduomas. MPA also decreased the incidence of FB-induced sarcomas, confirming previous results.     

Idiopathic mammary tumors in BALB/c mice.

A colony of BALB/c mice consisting of two sublines with a high incidence of mammary tumors was examined for the presence of a mammary tumor virus (MuMTV). The mammary tumor incidences in the two sublines were 18% and 35% at average tumor age 19-20 months. Over a period of 8 years, their milk at third to tenth lactations were monitored for the presence of MuMTV antigen,and the milk and tumors were examined for the presence of B particles. Neither antigen nor B particles were found. Milk and tumor extracts from the higher mammary tumor lines were also assayed for MuMTV bioactivity by intraperitoneal inoculation of weanling C57BL, BALB/c, and RIIIf females. No response was obtained, except possible in RIIIf. Both the MuMTV antigen incidence and the tumor incidence in inoculated RIIIf mice were somewhat elevated over controls. The question remains unanswered as to whether there is an active MuMTV in our colony of tumor-bearing BALB/c mice and, if there is, whether it is associated with B particles.     

Combined therapies with medroxyprogesterone acetate (MPA) in DMBA-induced rat mammary cancer

Sixty-one female SD rats with 7, 12-dimethylbenz(a) anthracene (DMBA)-induced mammary cancer were divided into six groups according to the antitumor agent administered: MPA (20 mg/kg, Im), FT 207 (40 mg/kg, Ip), MPA (20 mg/kg, Im) + FT 207 (40 mg/kg, Ip), E2 priming (3 micrograms/body, Im, three days) + MPA (20 mg/kg, Im), E2 (3 mg/body, Im, three days) + MPA (20 mg/kg, Im) and control. The sizes of the tumors in all DMBA rats were measured at 1, 2, 3 and 4 weeks after the start of the administration, and the antitumor effects were compared among the groups. The antitumor effect of MPA + FT 207 was better than that when they were administered separately. It was shown that chemo-endocrine therapy with MPA was very effective. The antitumor effect was in the order of E2 priming + MPA, E2 + MPA and MPA among these three groups. E2 priming before MPA administration was thought to be very promising. The progesterone receptor (PgR) level tended to increase by E2 priming in DMBA tumors. Furthermore, in the E2 priming + MPA group, the tumors with high PgR levels before therapy tended to be more responsive than those with low PgR levels.     

Controlled release low dose medroxyprogesterone acetate (MPA) inhibits the development of mammary tumors induced by dimethyl-benz(a) anthracene in the rat

Summary Medroxyprogesterone acetate (MPA) is well recognized to have beneficial effects for the treatment of advanced breast cancer which are comparable to those achieved with other forms of endocrine therapy. Using mammary tumors induced in the rat by dimethylbenz(a)anthracene (DMBA) as a model, we have studied the possibility that low dose MPA could prevent the development of these tumors. Single subcutaneous injection of Depo-Provera (crystalline suspension of MPA) or MPA encapsulated in biodegradable microspheres of 50 : 50 poly[DL-lactide-co-glycolide] was given 7 days before oral DMBA. While 63% of intact animals developed palpable mammary tumors within 85 days after DMBA administration, tumor incidence decreased to 28% and 23% in animals who had received 30 mg and 100 mg of Depo-Provera, respectively. The same amounts of MPA delivered in microspheres caused a further decrease in tumor incidence to respective values of 7% and 6%. Average tumor area, on the other hand, decreased from 4.89 cm² in intact rats to about 0.75 (0.57–0.88) cm² and approximately 0.20 (0.14–0.22) cm² in the Depo-Provera and microsphere-treated groups, respectively. Using the 50 : 50 formulation of poly[DL-lactide-co-glycolide] designed to release MPA at a constant rate for a 4-month period, the serum MPA concentration at 3 months was measured at 4.99 ± 0.43 ng/ml. Such data suggest that administration of a low dose controlled-release formulation of MPA in 50 : 50 poly[DL-lactide-co-glycolide] microspheres could well be an efficient and well tolerated approach for the prevention of breast cancer in women.     

Protective role of medroxyprogesterone acetate on N-methyl-N-nitrosourea-induced lymphomas in BALB/c female mice

In a previous paper we reported the occurrence of a high incidence of lymphomas in N-methyl-N-nitrosourea (MNU)-treated mice, in the course of an experiment of combined chemical-hormonal carcinogenesis in mammary gland, in which we used medroxyprogesterone acetate (MPA) and MNU in different treatment protocols. In this report we have analyzed the action of MPA in the leukemogenic effects of MNU, by specifically selecting for the analysis experimental groups in which only few mammary carcinomas had developed. A high incidence of lymphomas (65%, median latency: 176 days) was registered in MNU-treated mice, and the administration of MPA was associated with a significant reduction in the incidence of lymphomas (P<0.001) in all protocols.     

Mouse mammary tumors induced by medroxyprogesterone acetate: immunohistochemistry and hormonal receptors

Mammary adenocarcinomas induced by medroxyprogesterone acetate (MPA) in female BALB/c mice were investigated as to their morphology and immunohistochemistry and their content of steroid, prolactin (PRL), and epidermal growth factor (EGF) receptors. Histologically, these tumors were mainly of ductal origin, since hyperplastic alveolar nodules were observed only in 3 cases. No viral particles were encountered in electron microscopic studies. Estrogen and/or progesterone, PRL, and EGF receptors were detected in MPA-induced tumors, as well as in the occasional spontaneous mammary tumors of multiparous females. EGF was detected, by a radioimmunoassay, in the cystic fluid of 12 mammary adenocarcinomas. MPA treatment was found to induce uterine secretory changes, glandular cystic hyperplasia, and eventually deciduomas that stained strongly for desmin and to a lesser degree for vimentin, suggesting a muscular differentiation. Consequently, MPA-induced adenocarcinomas can be considered as ductal tumors that possess estrogen and/or progesterone, PRL, and EGF receptors. Whether MPA induces tumor growth directly via progesterone receptors remains to be investigated.     

Experiences with doxo/epirubicin and medroxyprogesterone acetate (MPA) in prostatic cancer

Maximal androgen blockade (MAB) has been reported to prolong the time to progression and the duration of survival in metastatic prostatic cancer. The addition of epirubicin to MAB in such patients seems to improve the therapeutic results further. The beneficial effect of combining castration with epirubicin in metastatic cases appears questionable. In comparing the time to progession in patients treated with MAB±epirubicin versus castration ±epirubicin or estramustine, many studies reveal similar figures. Whether the results after treatment are actually improved remains controversial. In hormone-refractory cases, medroxyprogesterone acetate (MPA) alone seems superior to estramustine or prednisolone treatment. Combining MPA and epirubicin improves the results, but even if the improvement is of clinical value, it is nonetheless of limited magnitude.Paper presented at the 5th International Conference on Treatment of Urinary Tract Tumors with Adriamycin/Farmorubicin, 24–25 September 1993, Hakone, Japan     

Pharmacokinetic study of low- versus high-dose medroxyprogesterone acetate (MPA) in women

The present study was conducted to compare the pharmacokinetics (PK) of low-dose versus high-dose medroxyprogesterone (MPA) as a once-daily oral administration. Of 32 patients, all women, enrolled in this PK study, 18 received 600 mg MPA daily and 14 received 1200 mg daily. Detailed PK data were obtained on day 1 and after more than 4 weeks of MPA treatment. In addition, multiple data for the minimum steady-state concentration (Css min) were analyzed. The MPA serum concentrations were measured by high-performance liquid chromatography. Wide interpatient variability was found in the PK parameters obtained both on day 1 and after more than 4 weeks. There were no clear relationships between the oral dose and the MPA peak concentration (Cmax), area under the time versus concentration curve (AUC), or mean Css min. Weight gains of 10% or more were demonstrated more frequently in the high-dose group (P<0.01). Liver dysfunction (n=5) did not influence the PK of MPA. Five patients demonstrated extremely low AUC and Cmax (<10 ng/ml) values on day 1. Phenobarbital, dexamethasone and betamethasone were being taken concomitantly with the MPA each by one patient. The serum MPA concentrations were markedly increased after the discontinuation of phenobarbital in that patient, suggesting a drug interaction. At present we cannot recommend the high dose of MPA, except in clinical studies, from a PK or a pharmacodynamic points of view. Received: 2 May 1997 / Accepted: 13 October 1997     

Oral high-dose medroxyprogesterone acetate (MPA) treatment: cortisol/MPA serum profiles in relation to breast cancer regression

Medroxyprogesterone acetate (MPA), a potent synthetic progestin, has been widely used in the hormonal treatment of advanced breast cancer, but presently with varying dose schedules. The availability of a sensitive RIA-method for determination of serum MPA has stimulated the research on MPA serum levels in patients after repeated MPA administration. The aim of this study was to assay blood level profiles of MPA as well as of cortisol during repeated high-dose orally administered MPA. 34 patients with metastatic breast cancer were enrolled in this study. 12 patients died already within the first 4 weeks of MPA treatment due to multiple metastases. The dosage regimen based on the daily oral administration of 1,000 mg MPA suspension. During MPA treatment, a decrease of cortisol serum levels was observed in nearly all patients. Within the observation time of 8 months out of 22 evaluable cases 18.2% responded to the therapy (complete and partial response). No change was observed in 36.4% and progression in 45.5% of the patients. Within the remission (complete and partial) group, a good correlation between constant MPA serum levels above 150 ng/ml and remission was observed. But in the groups with no change and progression no such correlation could be observed.     

Mammary adenocarcinomas induced by medroxyprogesterone acetate: hormone dependence and EGF receptors of BALB/c in vivo sublines

Mammary adenocarcinomas were induced by medroxy-progesterone acetate (MPA) in female BALB/c mice. From 5 primary tumors, 9 different sublines were established by s.c. transplantation into syngeneic female mice; these developed after a long latent period (4-12 months). Each subline was transplanted both into 4 mice treated with 40mg of MPA depot (s.c. contralaterally to the tumor inoculum) and into 4 non-treated mice. Of the 9 sublines, 6 proved to be hormone-dependent (MPA-D) and 3 hormone-independent or autonomous (MPA-I). However, even the autonomous lines, when treated with MPA, showed a slight increase in growth. All MPA-D lines had a high content of ER (20-254 fmoles/mg of protein), PR (63-710), PRL-R (44-74) and low or non-detectable EGF-R. Of the 3 MPA-I sublines that were studied, 2 showed a high content of ER (16-125), PR (27-708), PRL-R (19-70) and EGF-R (29-65) while the other one had a low content of ER (0-36), PR (0-13), no EGF-R and moderate PRL-R (15-52). Spontaneous mammary tumors of BALB/c and C3H origin, which also showed an MPA-I pattern of tumor growth, had high levels of EGF-R. We postulate that MPA has a direct effect on mammary tumor cells in MPA-D lines and that the expression of EGF-R is correlated with an autonomous pattern of growth.     

Leukemoid reaction in BALB/c mice bearing primary tumors induced by 3-methylcholanthrene

During the growth of five of ten primary tumors that were induced by 3-methylcholanthrene in BALB/cMk and BALB/cMk X C57BL/6F1 mice, leukemoid reactions, characterized by increase in number of granulocytes in peripheral blood, and splenomegaly were observed. However, no such reactions occurred in five C57BL/6 mice bearing primary tumors induced by 3-methylcholanthrene. The results of leukemoid reactions in mice bearing 3-methylcholanthrene-induced primary tumors are compared with the reactions found in mice bearing transplanted tumors.     

Effect of medroxyprogesterone acetate (MPA) and serum factors on cell proliferation in primary cultures of an MPA-induced mammary adenocarcinoma

Summary The effect of progesterone (Pg), medroxyprogesterone acetate (MPA), estradiol (E₂), dihydrotestosterone (DHT) and dexamethasone (DEXA) was studied on thein 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 fibroblastenriched cultures using³H-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 stimulated³H-thyrnidine 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/10⁵ cells, n = 5) and estrogen receptors (ER) (ND-115 fmoles/10⁵ cells, n = 5) were detected only in epithelial-enriched cultures. Serum from 7 day-MPA-treated mice induced a significant increase of³H-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.     

Progesterone induction of mammary carcinomas in BALB/c female mice

Summary 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: p < 0.05), 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.     

A randomized comparison of megestrol acetate (MA) and medroxyprogesterone acetate (MPA) in patients with advanced breast cancer

The efficacy and side-effects of megestrol acetate and medroxyprogesterone acetate in postmenopausal patients with advanced breast cancer were compared in a prospectively randomized study. The dosage of MA was 2 × 80 mg p.o. or MPA 2 × 500 mg p.o. daily, given as a secondary hormonal treatment, mostly after previous treatment with tamoxifen.Ninety-eight patients entered the study and 92 were evaluable for effect, 48 patients on MA and 44 on MPA. Age, main tumor site and prior treatment were not different, but there was a preponderance of ER-negative tumors in the MA group. Responses appeared to be more frequent in the MPA-treated group (25% vs. 43%), predominantly in bone lesions, 12% for MA and 45% for MPA. Median progression-free survival was comparable, 15 vs. 10 months, and overall survival was not different (20 vs. 16 months).Toxicity was frequent, occurring in 83% vs. 74% of patients: increased appetite, nausea and dizziness in more than 20%, and a preponderance of pyrosis and breathlessness on MA and hot flashes, sweating and tremors on MPA. Cushingoid symptoms were present in about a quarter of the patients treated for more than 3 months. The occurrence of thrombo-embolic episodes and cardiovascular events was evenly distributed. Patients on MPA had more often increase in body weight, systolic blood pressure and serum creatinine than those treated with MA.It is concluded that MPA may be more effective for treatment of bone metastases, at the expense of more progestational side-effects. The occurrence of Cushingoid effects is frequent but similar in both arms, while the incidence of cardiovascular or thrombo-embolic events cannot be related to the use of either compound.     

High-dose medroxyprogesterone acetate (MPA) treatment in advanced breast cancer. A review.

Medroxyprogesterone acetate (MPA) when employed at high doses (greater than or equal to 500 greater than or equal to 1000 mg/day i.m.) can produce objective remission with improved survival in about 30% of postmenopausal women with advanced breast cancer resistant to cytotoxic drugs and endocrine therapies. When administered to women not previously treated with chemotherapy, the objective remission response rate reached 40%. From available evidence, high dose MPA can be considered a useful agent in the treatment of advanced breast cancer in postmenopausal women with soft tissue, pulmonary, pleural or osseous involvement even when patients have become refractory to prior hormone and cytotoxic therapies. Early results suggest that the response rate can be increased in patients with estrogen and/or progesterone-positive receptors. It is note worthy that in a study conducted on postmenopausal women resistant to cytotoxic and/or hormonal drugs, the median duration of survival was 13.5 months, while CRs plus PRs did not reach the median at 24 months after starting MPA treatment. High dose MPA is essentially devoid of major side effects. Relief of pain, increase in appetite and body weight, and sense of well being are characteristic features of the improved quality of life under MPA treatment. However, a gluteal abscess (from 2% to 20% dose related) is the most frequent side effect. A promising area for future studies is combined therapy using hormonal and cytotoxic agents or alternating sequential combinations. Well-designed studies are needed to develop means for increasing the complete response rate and therefore survival. Recent studies of combined chemo- and hormonal (MPA) therapy have yielded objective tumor regressions of 53 to 80% with an increased rate of complete remissions and duration of response.     

Growth inhibition of 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors by controlled-release low-dose medroxyprogesterone acetate

Summary Since our previous findings had indicated that the androgenic steroid medroxyprogesterone acetate (MPA) exerts potent inhibitory effects on 7,12-dimethylbenz(a)anthracene (DMBA)-induced tumor growth, we have studied the effect of low doses of MPA released from Depo-Provera and from 50:50 poly[DL-lactide-co-glycolide] microspheres in the same DMBA-induced tumor model. The present data show that single subcutaneous injection of a 4-month controlled-release formulation of biodegradable 50:50 poly[DL-lactide-co-glycolide] microspheres containing 10 mg of MPA giving serum levels of 3.14±0.32 ng/ml (8.12±0.83 nM) MPA causes a maximal or near-maximal 60% inhibition of tumor growth measured 56 days later. Such data suggest that controlled-release formulations giving constant and low blood levels of MPA could be used for the treatment of breast cancer in women. Such a low concentration of MPA should avoid the side effects observed with the high doses of the compound.     

The pharmacokinetics of high-dose medroxyprogesterone acetate (MPA) in the therapy of advanced breast cancer

Summary Oral MPA 1.5 g/day leads to plasma concentrations between 1 and 12 g/ml, with a broad intra-and interindividual variance. The plateau state is reached in between 4 and 16 days. Plasma concentrations in the plateau state are very sensitive to dose modifications. After cessation of administration, the decline in plasma levels seems to proceed in two phases, with half-times of about 20 h and 4 days. Extraction procedures reveal no benefit in discriminating between MPA and its metabolites.