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Original Studies |
Department of Obstetrics, Gynecology, and Reproductive Biology (B.-S.L., R.A.N.), Harvard Medical School, and Brigham and Womens Hospital, Boston, Massachusetts 02115; and Marnac, Inc. (S.B.M.), Dallas, Texas 75225
Address all correspondence and requests for reprints to: Dr. Romana A. Nowak, Laboratory of Human Reproduction and Reproductive Biology, Brigham and Womens Hospital, 221 Longwood Avenue, Boston, Massachusetts 02115.
| Abstract |
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| Introduction |
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GnRH analogs, which reduce serum estradiol and progesterone concentrations to those seen in postmenopausal women, have been used for a number of years as a medical therapy for treatment of leiomyomas (9). However, these compounds are not suitable for long-term treatment, because of detrimental side effects such as increased loss in bone density (9). Thus, there is a need to explore new pharmaceutical agents for the treatment of uterine leiomyomas.
Pirfenidone is an antifibrotic agent that is being investigated for use
in patients with pulmonary fibrosis. It is an investigational drug
whose structure is 5-methyl-1-phenyl-2(1H)-pyridone (Fig. 1
). Pirfenidone has been shown to produce
antifibrotic effects in a variety of animal models (10, 11) and to
inhibit fibroblast proliferation in vitro in response to a
number of growth factors (12).
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| Subjects and Methods |
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Leiomyoma and myometrial tissue were obtained from 12 premenopausal women with symptomatic uterine fibroids at the time of hysterectomy and who were not receiving any type of hormonal or drug therapy. Collection of tissues was obtained under a consent for use of discarded human tissue, in accordance with the Brigham and Womens Hospital policy. The stage of the menstrual cycle for each patient was determined by the pathologist, using endometrial dating. Seven of the patients were in the secretory phase at the time of surgery, 3 were in the proliferative phase, and 2 in the menstrual phase.
Cell culture
Primary cultures of myometrial and leiomyoma SMCs were
established as described previously (13). Cultures were determined to
be pure SMC cultures (>98%) by immunostaining for desmin and smooth
muscle
-actin, which are markers for SMCs (13). Cells were used in
experiments at passages 1 or 2.
Experimental design
Exp 1. For tritiated thymidine incorporation assays, leiomyoma and myometrial SMCs were cultured in 96-well plates (15,000 cells/well) for 48 h in medium with 10% serum. Cells were then made quiescent by culturing in medium with 0.5% serum for 48 h. These quiescent cells were washed and then received medium with 10% serum plus the various doses of pirfenidone (0, 0.01, 0.1, 0.3, and 1.0 mg/mL). After 18 h, the cells received 0.2 uCi/well [3H]-thymidine (New England Nuclear, Boston, MA), and the incubation was continued for a further 6 h. Cells were then harvested and counted, to measure the rate of incorporated [3H]-thymidine. Four experiments, using cells from four different patients, were performed with 6 wells/treatment group/experiment.
Exp 2. In a second set of experiments, myometrial and leiomyoma SMCs were plated in 100-mm dishes in medium with 10% serum and cultured until they reached 8090% confluence. Cells were washed in serum-free medium and then placed in serum-free medium containing the various concentrations of pirfenidone for a period of 3 days. Medium was collected for assay of lactate dehydrogenase (LDH) levels, and cells were harvested and processed for Northern blotting analysis. The LDH assay was used to measure cell toxicity effects of the various doses of pirfenidone and was performed using a colorimetric determination kit from Sigma (St. Louis, MO). Four experiments, using cells from four different patients, were performed with 2 dishes/treatment group/experiment.
Exp 3. In the third set of experiments, leiomyoma and myometrial cells were plated in 100-mm dishes (100,000/dish) and allowed to attach overnight in medium with 10% serum. The following day, all cells received fresh medium with 10% serum containing various concentrations of pirfenidone (0, 0.01, 0.1, 0.3, and 1.0 mg/mL) for a period of 7 days. Medium was changed, with addition of fresh treatments, on days 3 and 5. On day 7, cells were harvested and counted and viability assessed using the trypan blue exclusion stain. Four experiments, using cells from four different patients, were performed with 2 dishes/treatment group/experiment.
Northern blotting analysis
Total RNA was extracted from culture wells and processed for
Northern blot analysis using methods described previously (14). Blots
were probed with a human collagen type I,
1 chain complementary DNA
(cDNA) (ATCC, Rockville, MD), a human collagen type III,
1 chain
cDNA (ATCC), and a human ribosomal phosphoprotein cDNA (gift of Dr.
Dale Goad, Harvard School of Public Health) using methods established
in earlier studies (14, 15). Filters were autoradiographed with an
intensifying screen for 12 days at -70 C. Differences in sample
loading were corrected by normalization to ribosomal phosphoprotein.
Autoradiographs were analyzed on a scanning densitometer (GS-700,
Biorad, Hercules, CA) to quantitate the levels of transcripts for each
sample.
Statistics
Statistical analysis was carried out using two-way ANOVA. We used contrasts to perform pair-wise comparison after the ANOVA procedure. P < 0.05 was considered statistically significant. No significant differences in response to pirfenidone were noted between cells obtained at different stages of the menstrual cycle.
| Results |
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| Discussion |
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The mechanism by which pirfenidone acts to inhibit DNA synthesis and cell proliferation is not clear, but it does not seem to involve toxic effects on the cells. The results of the LDH assay showed no increase in LDH secretion by cells treated with any of the concentrations of pirfenidone. In addition, trypan blue exclusion staining, performed on cells treated with the various concentrations of pirfenidone for 7 days, showed an increase in the percentage of dead cells only at the highest concentration of pirfenidone (1 mg/mL). The inhibitory effect of pirfenidone on cell proliferation was apparent at one tenth this concentration (0.1 mg/mL). The relative lack of toxicity of pirfenidone in vitro is supported by findings in vivo. In clinical studies involving treatment of human subjects with pirfenidone as a treatment for pulmonary fibrosis, the daily dosage was 2400 mg, given orally (16) (Dr. G. Raghu, personal communication). Relatively mild adverse effects, including occasional drowsiness, skin rash, or gastric discomfort, were noted (16).
The effects of pirfenidone on cell proliferation are most likely mediated via inhibitory effects on specific growth factors. Studies on human fibroblasts have shown that pirfenidone inhibits basic fibroblast growth factor, platelet-derived growth factor, and transforming growth factor ß (TGFB)-stimulated cell proliferation (12). Furthermore, these investigators showed that fibroblasts treated with pirfenidone were unable to exit the G1 phase of the cell cycle. These results suggest a postreceptor site of action for pirfenidone. It is possible that pirfenidone may act as an antiestrogen or an aromatase inhibitor in uterine SMCs due to its chemical structure. However, such a mechanism could only be proven through studies showing that pirfenidone interacts directly with the estrogen receptor.
The mitotic activity of myometrial and leiomyoma SMCs in vivo varies throughout the menstrual cycle, suggesting that cell proliferation is regulated by ovarian steroid hormones (17, 18). However, studies by a number of investigators have been unable to show consistently a direct stimulatory effect of estradiol or progesterone on proliferation of these cells in vitro (19). This is, in part, because of the fact that uterine SMCs do not maintain steroid hormone responsiveness for prolonged periods of time when placed in culture. The results of a number of recent studies have led to the hypothesis that the effects of the ovarian steroid hormones on cell proliferation may be mediated indirectly through the activation of autocrine and paracrine peptide growth factors, including epidermal growth factor and insulin-like growth factors I and II (19, 20, 21). Basic FGF, platelet-derived growth factor, and TGFB also may be important regulators of cell proliferation in myometrial and leiomyoma cells (22, 23, 24). The antiproliferative effect of pirfenidone may involve a common postreceptor site of action, as has been suggested from the data on fibroblasts, or may involve inhibition of synthesis of one or more growth factors required for cell proliferation.
Leiomyomas contain large amounts of extracelluar matrix consisting of collagen, proteoglycan, and fibronectin, and show increased expression of collagen type I and type III mRNAs (14, 25, 26). The results of the present study showed that pirfenidone significantly inhibited steady-state levels of the mRNAs for both collagen type I and type III in myometrial cells at all concentrations tested. Collagen type I mRNA levels also were significantly inhibited in leiomyoma cells. However, the mRNA level of collagen type III was significantly reduced only at the highest concentration (1 mg/mL) of pirfenidone tested. Thus, in leiomyomas, pirfenidone seems to selectively inhibit collagen type I production over that of collagen type III. Fujita et al. (27) reported that the ratio of type III to type I collagen protein was decreased in leiomyomas, compared with the corresponding myometrium, because of an increase in collagen type I content and a decrease in collagen type III content in leiomyoma tumors. This suggests an alteration in the normal regulation of collagen production in these tumor cells, which may account for the differential effect observed between myometrial and leiomyoma cells. Leiomyoma SMCs may be more resistant to inhibition by specific growth factors. The decrease in steady-state levels of mRNAs for the collagens may reflect an inhibitory effect on gene transcription or an increase in mRNA turnover. In vivo studies, using the hamster model of artificially induced lung fibrosis, have shown that pirfenidone causes a marked inhibition of proline hydroxylase levels (10). This finding suggests that pirfenidone may reduce the availability of the hydroxyproline required for collagen synthesis and, therefore, may inhibit collagen synthesis at the translational level, as well.
In summary, the results of the present studies show that pirfenidone inhibits proliferation of myometrial and leiomyoma SMCs and significantly suppresses steady-state mRNA levels of both collagen type I and collagen type III. Pirfenidone showed little toxic effect on either cell type, suggesting that this compound may prove to be an effective therapeutic agent for treatment of leiomyomas with minimal side effects. Studies are underway to investigate more thoroughly the mechanism of action of pirfenidone.
Received March 27, 1997.
Revised August 12, 1997.
Accepted September 25, 1997.
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