Progestins - a review of clinical application in gynecology

Among the array of therapeutic interventions, the utilization of progesterone compounds is a fundamental aspect, harnessing the physiological actions of progesterone naturally produced within the human body [ 1 ]. Within this realm, progestogens, also referred to as gestagens or gestogens in the literature, emerge as pivotal agents with diverse applications. These include primarily the most commonly known ones, i.e. hormonal contraception in the form of progestin-only contraception (POC) or combination with other substances such as combined hormonal contraception (CHC) [ 1–8 ]. The POC includes progestin-only pills (POP), intrauterine devices with levonorgestrel (LNG-IUD) and etonogestrel implants [ 9 ]. CHC consists of combined oral contraception (COC) and non-oral combinations [ 1 ]. Interestingly, some of the mentioned methods can be applied not exclusively in women but also in men [ 1 , 10 ]. However, it brings benefits not only due to the avoidance of undesirable fertilization but also due to the additional benefits of using POC or COC in women struggling with other conditions, such as abnormal uterine bleeding [ 11 ]. In addition to the contraceptive effect, it is also possible to use progestins as menopausal hormone therapy (MHT) in women [ 12 , 13 ]. In this case, progestins are used in addition to estrogens to counterbalance their results. Estrogens increase the thickness of the endometrium and thus contribute to the increased risk of endometrial cancer (EC). Progestogens counteract this process by decreasing the number of estrogen receptors in target tissues. Moreover, they reduce the level of luteinizing hormone (LH), which is responsible for stimulating the ovaries to produce estrogens [ 14 ]. Figure 1 illustrates the role of P4 in the endometrium and the hormonal changes during different parts of the menstrual cycle. Other known applications include therapy in endometriosis, secondary amenorrhea, infertility, endometrial hyperplasia (EH), and the prevention of premature deliveries [ 11 , 15 , 16 ]. The use of progestins in cancer therapy remains controversial [ 11 , 17–20 ]. The studies conducted on this subject are described in our work, as well as other noteworthy works using progestogens, which constitute the prospect of new treatment options. Progesterone-mediated endometrial transformation during the menstrual cycle. Progestogens range from natural to synthetic progesterone molecules, presenting a nuanced classification system. The detailed classification is presented in Table 1 . Notably, synthetic progestogens comprise a broad group known as progestins, characterized by their synthetic origin and varied pharmacological profiles [ 10 , 19 ]. Apart from this classification system, a traditional categorization divides progestins into old and new. These are divided into first, second, third and fourth generations. The first three generations are derivatives of testosterone (TE). They have an affinity for androgenic receptors (AR) and may cause undesirable androgenic effects. The fourth generation has activity similar to progesterone (P4) and therefore does not show androgenic effects like the first three generations. P4 is synthesized from cholesterol. Furthermore, P4 is a part of the TE biosynthesis pathway [ 21 ]. Figure 2 shows the conversion of cholesterol to P4 and TE. Table 2 contains full names and functions of the ensymes. Further classification based on structural properties, including mainly pregnanes, estranes, and gonanes, elucidates the intricate diversity within this pharmacotherapeutic domain [ 11 ]. A common feature of the progestogens’ chemical structure is the presence of a 3-keto group and a double bond between C4 and C5 in the A-ring, collectively referred to as the Δ4-3-keto group. If a given progestin lacks a Δ4-3-keto group, it is reached as a prodrug. It exclusively reaches its activity after oral administration, when it is transformed into the appropriate form. Therefore, depending on the position of the methyl group, progestins related to P4 are divided into pregnanes (methyl group at the C10 position) and norpregnanes (no methyl group at C10 or no C19). TE-related progestins can be divided based on the presence of an ethyl group at the C13 position. Based on the above, estranes (no ethyl group in C13) and gonanes (ethyl group in C13) are distinguished [ 21 ]. Figure 3 illustrates the chemical structure and structure-activity relationships (SARs) of progestins. Progestins share many common applications. However, despite their general classification, they exhibit varying levels of effectiveness in specific medical conditions [ 24 ]. Biosynthesis of testosterone from cholesterol via pregnenolone and progesterone. Key steroidogenic enzymes involved include CYP11A1, 3β-HSD, CYP17A1, and 17β-HSD. Comparative analysis of progestin classes and generations: Key structural features and activity profiles. The chemical structures for the described progestins are provided in the appropriate subsections. Classification of progestogens [ 21–23 ]. Due to their chemical origin, progestogens are divided into progesterone, retroprogesterone, progesterone derivative, spironolactone derivative and several larger groups such as pregnanes, nonpregnanes, estranes and gonanes. Individual agents were assigned to corresponding groups. N/A: not applicable; 1: first generation; 2: second generation; 3: third generation; 4: fourth generation. Enzymes involved in the enzymatic pathway of steroidogenesis leading to testosterone synthesis. The current study aims to undertake an exhaustive examination of existing literature pertaining to the utilization of progestogens in clinical practice. By synthesizing previous research findings and elucidating emerging perspectives, this review seeks to provide a comprehensive guide delineating the diverse applications and therapeutic considerations surrounding progestogens in contemporary medical practice.

Progesterone (P4) is an endogenous steroid hormone produced by the adrenal cortex, ovaries and testes. It is also produced by the ovarian corpus luteum during the first 10 weeks of pregnancy. After this time, it is secreted by the placenta. P4 has many functions in the human body, mainly in the reproductive system, maintains the endometrium during pregnancy by reducing uterine myometrial contractility and regulates uterine myometrial blood flow during ovulation [ 25–27 ]. P4 fulfils a role in maintaining pregnancy by regulating the immune response of the mother’s body, inhibiting inflammatory reactions, reducing uterine contraction and improving circulation in the uterine-placental area. Particularly in the early stages of pregnancy, progesterone has a key function in preparing the endometrium for embryo implantation and maintaining the gestational sac inside the uterus. It stimulates endometrial endothelial proliferation and increases the number of vessels, leading to increased blood flow [ 25 , 28 ]. Additionally, P4 has a crucial function in the menstrual cycle. During the luteal phase, it induces cell proliferation in the endometrium by leading to an enlargement in its thickness. This process causes the endometrium to become thicker, which in turn increases the surface area available for potential embryo implantation [ 25 ]. In addition to the above, P4 redounds to bone formation. It stimulates the growth of osteoblasts responsible for bone formation by the P4 receptor [ 25 ].

A literature review was conducted by PubMed, Google Scholar, Scopus and ClinicalTrials. The following search terms and their combinations were used when reviewing the aforementioned databases: (progestogen OR progestogens OR progestin OR progestins) AND (women OR woman OR men OR man OR adult). The analyzed publications about progestogens were dated from 2005 to 2024. The review process began in November 2023 and continued for 8 months until June 2024. Initially, the list of titles and abstracts from the available papers was examined. Full-text publications about progestogens were used in the study. Books and documents, clinical trials, meta-analyses, randomized controlled trials and systematic reviews were included. Abstracts from conferences, reviews, case reports and articles not written in English were excluded. The chemical structures of the compounds we described come from PubChem.

In our study, we presented progestins as an extremely broad group of substances used in numerous aspects. A significant number of clinical conditions in which progestins are used have already been thoroughly described in the literature. Further conditions involve the use of progestins in the oncology treatment of P4-sensitive cancers such as endometrial, renal or breast cancers [ 11 ]. However, the use of MA in the therapy of ovarian or prostate cancer is an off-label use, as is anorexia-cachexia syndrome [ 46 ]. Additionally, it was noticed that the antiangiogenic effect used in EC to inhibit tumor progression positively affects the treatment of deep endometriosis [ 174 ]. Fairly controversial research includes the use of MA in the treatment of hepatocellular carcinoma (HCC). According to some researchers, MA slows down tumor growth (only in PR-positive tumors) and thus improves the survival of palliative patients. Nevertheless, additional studies do not show a significant improvement in the quality of life of patients after using this P4 therapy. MA cannot be clearly defined as a therapeutic agent in the palliative therapy of HCC [ 129 , 176 ]. Moreover, it is suggested that MPA may have a positive influence on the treatment of liver tumors. Whereas, these must be PR-positive metastases of breast cancer because HCC is still a highly controversial subject due to the lack of clear evidence of the effectiveness of the therapy, as well as the lack of understanding of some processes taking place in the liver [ 176 ]. The use of progestins in breast cancer remains controversial. There are indications of the possible proliferative and antiproliferative effects of progestins [ 167 ]. Due to the above, in our study, we included breast cancer entities both as a probable indication and contraindication to their use [ 1 , 11 , 167 ]. The suggested effect of progestins has still not been confirmed, which complicates the treatment of patients. Therefore, clinical trials are being conducted on the possibility of using these substances in breast cancer [ 1 , 11 ]. A connection has been noted between the effect of PR agonists and the expression of the estrogen receptor (ER). This is supported by the favorable therapeutic results of patients. In this regard, the PIONEER study focuses on the combination of MA with letrozole. The study included postmenopausal women with newly diagnosed, untreated ER+, HER2-, invasive breast cancer with a size of at least 1 cm. It assumes that patients will be given a low (40 mg) or high (160 mg) dose of MA in combination with letrozole [ 18 ]. This is a promising preoperative therapy that reduces tumor mass and offers opportunities for new breast cancer treatment programs. Another current study suggests increased long-term survival of patients with operable breast cancer through the use of hydroxyprogesterone during surgery. The reports analyzed by the researchers show that performing surgery in the luteal phase of the menstrual cycle significantly improved women’s survival. Therefore, this study aims to create a luteal environment in patients by intramuscular injection of 500 mg of hydroxyprogesterone 5 to 15 days before surgery [ 19 ]. The use of hydroxyprogesterone appears to be a favorable prognostic factor for overall survival. P4 may counteract the harmful effects of estrogen during surgery [ 20 ]. Concurrently, authors S. Zaami et al. suggest the use of reproductive counselling before initiating breast cancer treatment. In their study, the relationship between diagnosis and the offer of fertility preservation in patients was examined. The study included 51 women aged 31 to 40 diagnosed with breast cancer. According to the collected data, only 21 of the 51 patients (40%) were offered the option of undergoing fertility preservation interventions. This indicates a lack of adequate training among medical personnel to provide reproductive counselling. However, subsequent data reviewed by the authors reveal an upward trend in information about fertility preservation options (an increase of up to 60%) [ 198 ]. According to one study, P4 has beneficial effects on ‘thin endometry’ syndrome. P4 therapy increases the thickness of the endometrium and, therefore, increases the implantation capacity. It constitutes a reasonable treatment path for patients with miscarriage. However, depending on the dose, P4 can both raise and lower INF-ץ levels [ 150 ]. At low doses, P4 increases IFN-ץ, while at high doses, it decreases IFN-ץ. Interestingly, progestin, which also increases the level of IFN-ץ in high doses, is MPA [ 152 ]. Thus, the anti-inflammatory effect of P4 can be modulated, depending on the dose. Nevertheless, P4 is a crucial factor in supporting the luteal phase, especially during IVF, when its endogenous production is impaired. Exogenous hCG supplementation is particularly indicated due to the high pregnancy loss rate (79%) in the mid-luteal phase, when P4 levels are lowest [ 199 ]. Therefore, progesterone administered intramuscularly or intravaginally is used as adjunctive therapy [ 200 , 201 ]. In addition to the progestins used in PCOS mentioned in our study, myo-inositol (MI), already well-known in research, may also have a supportive effect. Researchers D. Coldebella et al. report that, in addition to its insulin-sensitizing effects, MI may also participate in pathways responsible for fertility. This improves ovarian stimulation protocols in IVF. Another form, D-Chiro-Inositol (DCI), has anti-inflammatory effects by reducing IL-6 levels and, correspondingly, acts as an antioxidant. This is crucial in infertility associated with endometriosis caused by oxidative stress [ 202 ]. Appropriate supplementation, especially based on resveratrol, leads to the production of more mature follicles, as well as a higher number of fertilizations in ICSI [ 203 ]. Alpha-lipoic acid (ALA) may exert a supportive effect on MI. Due to its effect on glucose metabolism, ALA may alleviate symptoms associated with PCOS. However, it does not significantly affect hormonal levels. The association between ALA and MI should be further investigated [ 204 ]. Interestingly, MI has been shown to affect FSH levels in postmenopausal women. MI causes a decrease in FSH levels and therefore sensitizes cells to insulin [ 205 ]. Furthermore, a randomized, double-blind trial was conducted evaluating the combination of MI, boswellia, and betaine in the treatment of mammographic breast density. Highly dense breasts in women increase the risk of developing breast cancer 6-fold compared to low-density breasts. The study included 76 premenopausal women aged 22–51 years with high-density breasts. Patients were randomly assigned to the experimental group or the placebo group. After 6 months, a statistically significantly greater decrease in breast density was observed in the experimental group compared to the placebo group (60% vs. 9%). This indicates the noteworthy clinical importance of substance combination in preventing breast cancer development [ 206 ].

By the hydrophobic character of the P4 molecule, attempts are constantly being made to improve alternative routes of administration. A study conducted by P. Suryaamporn et al. discusses the development of lipid-based formulations for improved transdermal action with P4. Due to the above, it may be applied in Alzheimer’s disease prevention in the postmenopausal period. The transdermal system consisted of progesterone-loaded solid-lipid nanoparticles (SLNs) with progesterone-loaded solid-lipid nanoparticles (PG‑SLNs) with the support of the Design of Experiments (DoE) and Artificial Neural Networks (ANN). Ultrasound-assisted emulsification was used to prepare the nanoparticles. The optimal mixture of nanoparticles was determined, comprising 5% stearate, 1.76% medium-chain triglycerides (MCT), 0.30% Pluronic F-127, and 0.5% propylene glycol. Transdermal permeability tests were further conducted using Franz-type diffusion chambers. Three formulations were compared: progesterone suspension, PG-SLNs without enhancer, and PG-SLNs with 2% limonene as a permeability enhancer. The results showed that the formulation with limonene achieved significantly higher diffusion parameters. The lag time for the suspension was 5.33 h, for PG-SLNs without limonene, 2.33 h, and for the formulation with limonene, merely 0.53 h. The permeability coefficient (Kp) for the formulation with limonene reached 19.03 cm/h, which means almost 20 times higher permeation than for the classic progesterone suspension. The developed formulation of SLNs showed high stability, increased homogeneity, significant drug loading and efficiency in transdermal permeation after application of the limonene enhancer. The study confirmed that the combination of the DoE method and ANN could be an effective tool in optimizing advanced drug delivery systems to alleviate neurodegenerative disorders in postmenopausal women [ 196 ]. Moreover, N. S. Velasquez et al. decided to develop a vaginal thermosensitive gel with P4. It was decided to use chitosan as the base of the gel, into which an inclusion complex of P4 with methylated β-cyclodextrin was introduced. In this combination, it was achievable to significantly increase the solubility of P4. Particularly if there was a notable concern in vaginal medication forms. In the study, P4 complexes with natural and methylated β-cyclodextrin were prepared by freeze-drying and then introduced into a chitosan thermosensitive gel. The physicochemical properties of the resulting gel-including its macroscopic and microscopic appearance, temperature and time of transition from liquid to gel form (important for vaginal application), as well as the stability of the mixture using porcine vaginal mucosa, were evaluated. The results were compared with the commercially available Crinone ® , used to treat progesterone deficiency. After 24 h of incubation in artificial vaginal fluid, the new formulation retained its gel structure. Crinone ® disintegrated more rapidly. The conclusions of the study indicate the developed chitosan thermosensitive gel with a progesterone-methylated β-cyclodextrin complex as an effective and more stable alternative to the P4 vaginal formulations currently in use. The advantages of the substance include easy application, adequate release profile and good stability in the physiological environment [ 197 ].

It is possible to select the appropriate therapy due to the broad spectrum of usage forms and the ability to combine them with estrogen or testosterone. Many significant applications are undergoing clinical trials, which promise a positive effect on expanding the prospects of using progestogens. However, some of them may create a legal risk to medics by patients due to their off-label use, which increases the need to propose further guidelines. By using progestogens in the treatment of non-gynecological patients, it is worth considering the development of research on this group of substances also towards the therapy of diseases related to completely different sites in the human body.

P4 has anti-inflammatory and anti-angiogenic effects [ 59 , 150 , 151 ]. The anti-inflammatory effect of P4 is based on its influence on cellular and humoral immunity. P4 regulation is associated with mediators such as P4-induced blocking factor (PIBF) and leukaemia inhibitory factor (LIF) [ 152 ]. PIBF is a P4-regulated gene and can be secreted by immune cells and host cells possessing the P4 receptor [ 153 ]. The increased level of this factor leads to an increase in the synthesis of cytokines responsible for immunotolerance, as well as to the introduction of cytotoxic lymphocytes themselves into a state of immunotolerance. Interestingly, CD4+ and CD8+ T cells show a dose-dependent effect of P4 [ 152 ]. LIF belongs to the IL-6 family of cytokines [ 154 ]. P4 increases LIF levels by increasing IL-4. LIF has anti-inflammatory and analgesic effects by reducing the expression of IL-1β and nerve growth factor (NGF) [ 151 ]. Both PIBF and LIF directly influence the differentiation of T lymphocytes. Figure 17 shows the mechanisms of immunomodulatory action of PIBF and LIF dependent on P4. The above-mentioned cytokines have an inhibitory effect on Th1 and reduce the production of pro-inflammatory cytokines. Moreover, they increase the differentiation of regulatory T lymphocytes (Tregs), which further enhances immune tolerance [ 155 ]. In addition to their antagonistic effect on Th1, they activate Th2 and thus increase the production of appropriate anti-inflammatory cytokines. Furthermore, they reduce CD8+ T cytotoxicity [ 17 ]. Mechanisms of P4 anti-inflammatory action [ 17 , 152–155 ]. green arrow - stimulation; red arrow - inhibition.