The discovery and mechanism of action of letrozole

Elacestrant in the treatment landscape of ER-positive, HER2-negative, ESR1-mutated advanced breast cancer: a contemporary narrative review

Introduction

Estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer with ESR1 mutations presents a significant therapeutic challenge due to its adaptive resistance mechanisms to chemotherapy, especially endocrine treatment. Elacestrant, a novel oral selective estrogen receptor degrader (SERD), has emerged as a promising agent in this treatment-resistant era.

Method

A comprehensive search was conducted on pivotal clinical trials, including the RAD1901-005 Trial, EMERALD TRIAL, ELIPSE, and ELEVATE, focusing on their methodologies, patient populations, treatment regimens, and outcomes.

Discussion

This narrative review describes the available preclinical and clinical evidence on elacestrant, focusing on its pharmacodynamics, pharmacokinetics, efficacy, and safety within the existing literature. Elacestrant has demonstrated excellent activity against ESR1 mutations associated with resistance to first-line endocrine therapies. Clinical trials have shown improved progression-free survival in patients with advanced ER+/HER2-, ESR1-mutated breast cancer. Safety profiles indicate a tolerable side effect spectrum consistent with other agents. Its oral bioavailability offers a convenient alternative to injectable SERDs, with potential implications for patient adherence and quality of life. The review also discusses the comparative efficacy of elacestrant relative to existing endocrine therapies and its possible use in combination regimens.

Conclusion

Ongoing clinical trials assessing elacestrant and other SERDs will yield data that might aid clinicians in determining the optimal selection and order of endocrine treatment drugs for ER+ breast cancer. The integration of targeted and immunotherapeutic agents with traditional chemotherapy represents a pivotal shift in Breast Cancer treatment, moving towards more personalized and effective regimens.

Secondary Analysis of Human Bulk RNA-Seq Dataset Suggests Potential Mechanisms for Letrozole Resistance in Estrogen-Positive (ER+) Breast Cancer

Estrogen receptor-positive (ER+) breast cancer is common among postmenopausal women and is frequently treated with Letrozole, which inhibits aromatase from synthesizing estrogen from androgens. Decreased estrogen slows the growth of tumors and can be an effective treatment. The increase in Letrozole resistance poses a unique problem for patients. To better understand the underlying molecular mechanism(s) of Letrozole resistance, we reanalyzed transcriptomic data by comparing individuals who responded to Letrozole therapy (responders) to those who were resistant to treatment (non-responders). We identified SOX11 and S100A9 as two significant differentially expressed genes (DEGs) between these patient cohorts, with "PLK1 signaling events" being the most significant signaling pathway. We also identified PRDX4 and E2F8 gene products as being the top mechanistic transcriptional markers for ER+ treatment resistance. Many of the significant DEGs that we identified play a known role in ER+ breast cancer or other types of cancer, which partially validate our results. Several of the gene products we identified are novel in the context of ER+ breast cancer. Many of the genes that we identified warrant further research to elucidate the more specific molecular mechanisms of Letrozole resistance in this patient population and could potentially be used as prognostic markers with further wet lab validation. We anticipate that these findings could contribute to improved detection and therapeutic outcomes in aromatase-resistant ER+ breast cancer patients.

Aromatase inhibitors for the treatment of breast cancer: An overview (2019-2023)

Aromatase inhibition is considered a legitimate approach for the treatment of ER-positive (ER+) breast cancer as it accounts for more than 70% of breast cancer cases. Aromatase inhibitor therapy has been demonstrated to be highly effective in decreasing tumour size, increasing survival rates, and lowering the chance of cancer recurrence. The present review deliberates the pathophysiology and the role of aromatase in estrogen biosynthesis. Estrogen biosynthesis, various androgens, and their function in the human body have also been discussed. The salient aspects of the aromatase active site, its mode of action, and AIs, along with their intended interactions with presently FDA-approved inhibitors, have been briefly discussed. It has been detailed how different reported AIs were designed, their SAR investigations, in silico analysis, and biological evaluations. Various AIs from multiple origins, such as synthetic and semi-synthetic, have also been discussed.

Androgen receptor and estrogen receptor variants in prostate and breast cancers

The androgen receptor (AR) and estrogen receptor alpha (ERα) are steroid receptor transcription factors with critical roles in the development and progression of prostate and breast cancers. Advances in the understanding of mechanisms underlying the ligand-dependent activation of these transcription factors have contributed to the development of small molecule inhibitors that block AR and ERα actions. These inhibitors include competitive antagonists and degraders that directly bind the ligand binding domains of these receptors, luteinizing hormone releasing hormone (LHRH) analogs that suppress gonadal synthesis of testosterone or estrogen, and drugs that block specific enzymes required for biosynthesis of testosterone or estrogen. However, resistance to these therapies is frequent, and is often driven by selection for tumor cells with alterations in the AR or ESR1 genes and/or alternatively spliced AR or ESR1 mRNAs that encode variant forms AR or ERα. While most investigations involving AR have been within the context of prostate cancer, and the majority of investigations involving ERα have been within the context of breast cancer, important roles for AR have been elucidated in breast cancer, and important roles for ERα have been elucidated in prostate cancer. Here, we will discuss the roles of AR and ERα in breast and prostate cancers, outline the effects of gene- and mRNA-level alterations in AR and ESR1 on progression of these diseases, and identify strategies that are being developed to target these alterations therapeutically.

Steroidogenic cytochrome P450 enzymes as drug target

Human cytochrome P450 (CYP) enzymes are composed of 57 individual enzymes that perform monooxygenase activities. They have diverse physiological roles in metabolizing xenobiotics and producing important endogenous compounds, such as steroid hormones and vitamins. At least seven CYP enzymes are involved in steroid biosynthesis. Steroidogenesis primarily occurs in the adrenal glands and gonads, connecting each reaction to substrates and products. Steroids are essential for maintaining life and significantly contribute to sexual differentiation and reproductive functions within the body. Disorders in steroid biosynthesis can frequently cause serious health problems and lead to the development of diseases, such as prostate cancer, breast cancer, and Cushing's syndrome. In this review, we provide current updated knowledge on the major CYP enzymes involved in the biosynthetic process of steroids, with respect to their enzymatic mechanisms and clinical implications for the development of new drug candidates.

Evaluation of Anticholinesterase Activity of the Fungicides Mefentrifluconazole and Pyraclostrobin

Triazoles are compounds with various biological activities, including fungicidal action. They became popular through cholinesterase studies after the successful synthesis of the dual binding femtomolar triazole inhibitor of acetylcholinesterase (AChE, EC 3.1.1.7) by Sharpless et al. via in situ click chemistry. Here, we evaluate the anticholinesterase effect of the first isopropanol triazole fungicide mefentrifluconazole (Ravystar®), developed to overcome fungus resistance in plant disease management. Mefentrifluconazole is commercially available individually or in a binary fungicidal mixture, i.e., with pyraclostrobin (Ravycare®). Pyraclostrobin is a carbamate that contains a pyrazole ring. Carbamates are known inhibitors of cholinesterases and the carbamate rivastigmine is already in use for the treatment of Alzheimer's disease. We tested the type and potency of anticholinesterase activity of mefentrifluconazole and pyraclostrobin. Mefentrifluconazole reversibly inhibited human AChE and BChE with a seven-fold higher potency toward AChE (Ki = 101 ± 19 μM). Pyraclostrobin (50 μM) inhibited AChE and BChE progressively with rate constants of (t1/2 = 2.1 min; ki = 6.6 × 103 M-1 min-1) and (t1/2 = 1.5 min; ki = 9.2 × 103 M-1 min-1), respectively. A molecular docking study indicated key interactions between the tested fungicides and residues of the lipophilic active site of AChE and BChE. Additionally, the physicochemical properties of the tested fungicides were compared to values for CNS-active drugs to estimate the blood-brain barrier permeability. Our results can be applied in the design of new molecules with a lesser impact on humans and the environment.

Quantification of the aromatase inhibitor letrozole and its carbinol metabolite in mouse plasma by UHPLC-MS/MS

A liquid chromatography - electrospray ionization-mass spectrometry (LC-ESI-MS) method was developed for the quantification of letrozole, a third-generation aromatase inhibitor, and its main carbinol metabolite (CM) in support of murine pharmacokinetic studies. Using polarity switching, simultaneous ESI-MS measurement of letrozole and CM was achieved in positive and negative mode, respectively. The assay procedure involved a one-step protein precipitation and extraction of all analytes from mouse plasma requiring only 5 μL of sample. Separation was optimized on an Accucore aQ column with gradient elution at a flow rate of 0.4 mL/min in 5 min. Two calibration curves per day over four consecutive measurement days showed satisfactory linear responses (r2 > 0.99) over concentration ranges of 5-1000 ng/mL and 20-2000 ng/mL for letrozole and CM, respectively. No matrix effect was found, and the mean extraction recoveries were 103-108 % for letrozole and 99.8-107 % for CM. Precision and accuracy within a single run and over four consecutive measurement days were verified to be within acceptable limits. Application of the developed method to preclinical pharmacokinetic studies in mice receiving oral letrozole at a dose 1 or 10 mg/kg revealed that the systemic exposure to letrozole was dose-, formulation-, and strain-dependent. These findings may inform the future design of preclinical studies aimed at refining the pharmacological profile of this clinically important drug.

Design and Pharmacophore Study of Triazole Analogues as Aromatase Inhibitors

BACKGROUND

In current scenario breast cancer measured as one of the dangerous health issues. An effective therapeutic class of drug known as aromatase inhibitors (AIs) is dominant against estrogen receptorpositive breast cancer. However, there is an urgent need to create target-specific AIs with better anti-breast cancer profiles due to the increased toxicity and adverse effects related to currently existing anti-breast cancer drugs.

OBJECTIVES

In the present study, we have designed of 100 novel tiazole analogues as aromatase inhibitors their pharmacophoric features were explored.

METHOD

Molecular docking was applied to a series of 4-substituted-1, 2, 3-triazoles containing letrozole for their aromatase inhibitory effects. The aromatase inhibitory activity of the compound in a series varies in the range of (IC50 = 0.008-31.26 μM). A hydrogen atom positioned at R1 of the triazole ring in compound (01) was responsible for the most potent compound (IC50 = 0.008 μM) in the series of 28 compounds as compared to letrozole. The self-organizing molecular field study was used to assess the molecular characteristics and biological activities of the compounds. The four models were developed using PLS and MLR methods. The PLS method was good for statistical analysis. The letrozole scaffold-based 100 compounds were designed by selecting an effective pharmacophore responsible for aromatase inhibitory activity. The designed compound was placed on the previous model as a test set, and its IC50 values were calculated.

RESULT

Hydrogen bonds were established between the potent molecule (01) and the essential residues Met 374 and Arg 115, which were responsible for the aromatase-inhibiting action. Cross-validated q2 (0.6349) & noncross- validated r2 (0.7163) were discovered in the statistical findings as having reliable predictive power. Among 100 designed compounds, seven compounds showed good aromatase inhibitory activities.

CONCLUSION

The additional final SOMFA model created for the interactions between the aromatase and the triazole inhibitors may be helpful for future modification and enhancement of the inhibitors of this crucial enzyme.

Aromatase inhibitors: the journey from the state of the art to clinical open questions

Breast cancer is a major cause of death among females. Great advances have been made in treating this disease, and aromatase inhibitors (AIs) have been recognized as the cornerstone. They are characterized by high efficacy and low toxicity. The authors reviewed the available literature and defined state-of-the-art AI management. This study was designed to assist clinicians in addressing the need to equally weigh patients' needs and disease control rates in their everyday clinical practice. Today, AIs play a central role in the treatment of hormone receptor-positive breast cancer. In this study, an expert panel reviewed the literature on the use of AIs, discussing the evolution of their use in various aspects of breast cancer, from pre- and postmenopausal early breast cancer to metastatic breast cancer, along with their management regarding efficacy and toxicity. Given the brilliant results that have been achieved in improving survival in everyday clinical practice, clinicians need to address their concerns about therapy duration and the adverse effects they exert on bone health, the cardiovascular system, and metabolism. Currently, in addition to cancer treatment, patient engagement is crucial for improving adherence to therapy and supporting patients' quality of life, especially in a selected subset of patients, such as those receiving an extended adjuvant or combination with targeted therapies. A description of modern technologies that contribute to this important goal is provided.

A comparative study of green solid contact ion selective electrodes for the potentiometric determination of Letrozole in dosage form and human plasma

Analysis of drugs clinically and their identification in biological samples are of utmost importance in the process of therapeutic drug monitoring, also in pharmacokinetic investigations and tracking of illicit medications. These investigations are carried out using a variety of analytical methods, including potentiometric electrodes. Potentiometric electrodes are a wonderful solution for researchers because they outperform other methods in terms of sustainability, greenness, and cost effectiveness. In the current study, ion-selective potentiometric sensors were assembled for the aim of quantification of the anticancer drug Letrozole (LTZ). The first step was fabrication of a conventional sensor based on the formation of stable host-guest inclusion complex between the cationic drug and 4-tert-butylcalix-8-arene (TBCAX-8). Two additional sensors were prepared through membrane modification with graphene nanocomposite (GNC) and polyaniline (PANI) nanoparticles. Linear responses of 1.00 × 10-5-1.00 × 10-2, 1.00 × 10-6-1.00 × 10-2 and 1.00 × 10-8-1.00 × 10-3 with sub-Nernstian slopes of 19.90, 20.10 and 20.30 mV/decade were obtained for TBCAX-8, GNC, and PANI sensors; respectively. The developed sensors were successful in determining the drug LTZ in bulk powder and dosage form. PANI modified sensor was used to determine LTZ in human plasma with recoveries ranging from 88.00 to 96.30%. IUPAC recommendations were followed during the evaluation of the electrical performance of the developed sensors. Experimental conditions as temperature and pH were studied and optimized. Analytical Eco-scale and Analytical GREEness metric were adopted as the method greenness assessment tools.

Clomiphene citrate plus letrozole versus clomiphene citrate alone for ovulation induction in infertile women with ovulatory dysfunction: a randomized controlled trial

BACKGROUND

The aim of this study was to compare the efficacy of the combination of clomiphene citrate (CC) and letrozole to that of CC alone in inducing ovulation in infertile women with ovulatory dysfunction.

METHODS

A randomized controlled trial was conducted at a single academic medical center between November 2020 and December 2021. Anovulatory infertility females, aged 18 to 40, were evenly distributed by a computer-generated block of four into two treatment groups. A "combination group" received a daily dose of CC (50 mg) and letrozole (2.5 mg), while a "CC-alone group" received a daily dose of CC alone (50 mg). The study medications were administered on days 3 through 7 of menstrual cycle. The primary outcome was the ovulation rate, defined by serum progesterone levels exceeding 3 ng/mL at the mid-luteal phase. The secondary outcomes were ovulation induction cycle characteristics, endometrial thickness, conception rate, and adverse events.

RESULTS

One hundred women (50 per group) were enrolled in the study. The mean age was not significantly different in both groups: 31.8 years in the combination group and 32.4 years in the CC-alone groups (P = 0.54). The prevalence of polycystic ovary syndrome in the combination and CC-alone groups was 48% and 44%, respectively (P = 0.841). According to intention-to-treat analysis, the ovulation rates were 78% and 70% in the combination and CC-alone groups, respectively (P > 0.05). There was no significant difference in the mean endometrial thickness or the number of dominant follicles of the groups. No serious adverse events were observed in either group.

CONCLUSIONS

Our study found no significant difference between the combination of CC and letrozole and CC alone in inducing ovulation in infertile women with ovulatory dysfunction in one cycle. The small number of live births precluded any meaningful statistical analysis. Further studies are needed to validate and extend our findings beyond the scope of the current study.

TRIAL REGISTRATION

The study was registered at https://www.thaiclinicaltrials.org with the following number: TCTR20201108004 and was approved on 08/11/2020.

Mini review: Breast cancer care in individuals with differences of sexual development

Disorders or differences of sexual development encompasses an important group of conditions that affects up to 1 in 5,000 live births. Many individuals living in the female gender includes Turner syndrome, congenital adrenal hyperplasia and conditions with 46XY karyotype such as gonadal dysgenesis (Swyer syndrome). Individuals are commenced on high dose oestrogen to initiate and maintain development of secondary sexual characteristics such as breasts which is paramount in them identifying in the female gender. We highlight the first case of a patient with Swyer syndrome who was treated with long term oestrogen therapy and later developed breast cancer. In individuals with gonadal dysgenesis, testicular malignancy is a recognised risk and is screened for. Prolonged exposure to exogenous and endogenous hormones can increase the risk of breast cancer however how much this risk increases in those taking high dose hormones is not documented in the literature. We aim to highlight the importance of breast cancer treatment and surgical reconstruction in this group and whether they should be considered for early breast cancer screening. CONCLUSION: It is imperative that triple assessment is undertaken in every patient with a breast lump, regardless of gender identification. Clinicians must not delay investigations in this patient group due to a misunderstanding of their condition. Those on long term hormone supplementation should be entered into the breast screening program at an earlier age with Magnetic Resonance Imaging surveillance. Careful consideration of post treatment endocrine therapy is required and under the care of the multi-disciplinary team.

LC-MS/MS based quantification of steroidal biomarkers in polycystic ovary syndrome induced rats

Polycystic ovary syndrome (PCOS) is a common endocrine disorder that causes reproductive hormones imbalance, missed periods, infertility and distributed steroidogenesis. Reportedly, during PCOS, the endogenous levels of P4 (Progesterone), 17OHP4 (17-α hydroxy progesterone), and T4 (Testosterone) were significantly altered. Thus, quantification of steroid biomarkers involved in the steroidogenesis pathway of PCOS, such as P4, 17OHP4, and T4, holds significant importance. One important drawback of current methods is steroid metabolome traceability. Without adequate traceability, the findings of these techniques will be less reliable for identifying P4, 17OHP4, and T4. These methods also need a high sample size, especially for the most important biomarker that initiates steroidogenesis. To address these challenges, we require a new liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for steroid biomarker analysis. Herein the present work, using validated LC-MS/MS, PCOS biomarkers were measured and compared between normal control rats and PCOS-induced rats before and after analyte administration. The experiment utilized an isocratic separation method employing an analytical C18 column. The mobile phase consisted of acetonitrile (ACN) and aqueous 0.1% formic acid (FA) in a ratio of 90:10 (v/v). The plasma samples were processed with protein precipitation (PPT) followed by the liquid-liquid extraction (LLE) method. The lower limit of quantification (LLOQ) was 0.5 ng/mL in plasma. According to USFDA criteria, the method's systematic validation took into account linearity (r2 > 0.99), accuracy and precision of intra- and inter-batch measurements, stability, biomarker recovery (60-85%) and matrix effect (<± 15%), all of which were determined to be within range ( ± 15%). The pharmacokinetic data showed that, as compared to normal rats, PCOS-induced animals had significantly higher Cmax values for 17OHP4 and T4 (∼2 fold), while lower Cmax values for P4 (∼2 fold). The present work is novel and provides scientific information to explore systematic processes involved in steroidogenesis and boost clinical applicability for PCOS therapy.

A review of FDA approved drugs and their formulations for the treatment of breast cancer

Breast cancer is one of the most diagnosed solid cancers globally. Extensive research has been going on for decades to meet the challenges of treating solid tumors with selective compounds. This article aims to summarize the therapeutic agents which are either being used or are currently under approval for use in the treatment or mitigation of breast cancer by the US FDA, to date. A structured search of bibliographic databases for previously published peer-reviewed research papers on registered molecules was explored and data was sorted in terms of various categories of drugs used in first line/adjuvant therapy for different stages of breast cancer. We included more than 300 peer-reviewed papers, including both research and reviews articles, in order to provide readers an useful comprehensive information. A list of 39 drugs are discussed along with their current status, dose protocols, mechanism of action, pharmacokinetics, possible side effects, and marketed formulations. Another interesting aspect of the article included focusing on novel formulations of these drugs which are currently in clinical trials or in the process of approval. This exhaustive review thus shall be a one-stop solution for researchers who are working in the areas of formulation development for these drugs.

Research advances in drug therapy of endometriosis

Endometriosis is one of the most common benign gynecological disorders in reproductive-aged women. The major symptoms are chronic pelvic pain and infertility. Despite its profound impact on women's health and quality of life, its pathogenesis has not been fully elucidated, it cannot be cured and the long-term use of drugs yields severe side effects and hinders fertility. This review aims to present the advances in pathogenesis and the newly reported lead compounds and drugs managing endometriosis. This paper investigated Genetic changes, estrogen-dependent inflammation induction, progesterone resistance, imbalance in proliferation and apoptosis, angiogenesis, lymphangiogenesis and neurogenesis, and tissue remodeling in its pathogenesis; and explored the pharmacological mechanisms, constitutive relationships, and application prospects of each compound in the text. To date, Resveratrol, Bay1316957, and bardoxifene were effective against lesions and pain in controlled animal studies. In clinical trials, Quinagolide showed no statistical difference with the placebo group; the results of phase II clinical trial of the IL-33 antibody have not been announced yet; clinical trial stage III of vilaprisan was suspended due to drug toxicity. Elagolix was approved for the treatment of endometriosis-related pain, but clinical studies of Elagolix for the pretreatment of patients with endometriosis to before In vitro fertilization treatment have not been fulfilled. The results of a clinical study of Linzagolix in patients with moderate to severe endometriosis-related pain have not been disclosed yet. Letrozole improved the fertility of patients with mild endometriosis. For endometriosis patients with infertility, oral GnRH antagonists and aromatase inhibitors are promising drugs, especially Elagolix and Letrozole.

Transvaginal needle versus laparoscopic ovarian drilling in hormonal profile and pregnancy outcomes of polycystic ovary syndrome: a systematic review and meta-analysis

BACKGROUND

Polycystic ovary syndrome (PCOS) is a prevalent hormonal disorder distinguished by a persistent absence of ovulation. Ovarian drilling is a recognized therapeutic approach for PCOS patients who are unresponsive to medication and can be performed through invasive laparoscopic access or less-invasive transvaginal access. The aim of this systematic review and meta-analysis was to assess the efficacy of transvaginal ultrasound -guided ovarian needle drilling with conventional laparoscopic ovarian drilling (LOD) in patients with PCOS.

METHODS

PUBMED, Scopus, and Cochrane databases were systematically searched for eligible randomized controlled trials (RCTs) from articles published from inception to January 2023. We include RCTs of PCOS that compared transvaginal ovarian drilling and LOD and reported on ovulation and pregnancy rates as the main outcome variable. We evaluated study quality using the Cochrane Risk of bias 2 tool. A random-effects meta-analysis was performed and the certainty of the evidence was assessed according to the GRADE approach. We registered the protocol prospectively in PROSPERO (CRD42023397481).

RESULTS

Six RCTs including 899 women with PCOS met the inclusion criteria. LOD was found to significantly reduce anti-Mullerian hormone (AMH) (SMD: -0.22; 95% CI: -0.38, -0.05; I² = 39.85%) and antral follicle count (AFC) (SMD: -1.22; 95% CI: -2.26, -0.19; I² = 97.55%) compared to transvaginal ovarian drilling. Our findings also indicated that LOD significantly increased the ovulation rate by 25% compared to transvaginal ovarian drilling (RR: 1.25; 95% CI: 1.02, 1.54; I2 = 64.58%). However, we found no significant difference between the two groups in terms of follicle stimulating hormone (SMD: 0.04; 95% CI: -0.26, 0.33; I2 = 61.53%), luteinizing hormone (SMD: -0.07; 95% CI: -0.90, 0.77; I2 = 94.92%), and pregnancy rate (RR: 1.37; 95% CI: 0.94, 1.98; I2 = 50.49%).

CONCLUSION

LOD significantly lowers circulating AMH and AFC and significantly increases ovulation rate in PCOS patients compared to transvaginal ovarian drilling. As transvaginal ovarian drillingremains a less-invasive, more cost-effective, and simpler alternative, further studies are warranted to compare these two techniques in large cohorts, with a particular focus on ovarian reserve and pregnancy outcomes.

Development of an efficient insecticide substrate and inhibitor screening system of insect P450s using fission yeast

Metabolic resistance is one of the most frequent mechanisms of insecticide resistance, characterized by an increased expression of several important enzymes and transporters, especially cytochrome P450s (CYPs). Due to the large number of P450s in pests, determining the precise relationship between these enzymes and the insecticide substrates is a challenge. Herein, we developed a luminescence-based screening system for efficient identification of insecticide substrates and insect P450 inhibitors. We recombinantly expressed Bemisia tabaci CYP6CM1vQ (Bt CYP6CM1vQ) in the fission yeast Schizosaccharomyces pombe and subsequently permeabilized the yeast cells to convert them into "enzyme bags". We exploited these enzyme bags to screen the activity of twelve luciferin substrates and identified Luciferin-FEE as the optimal competing probe that was further used to characterize the metabolism of eight candidate commercial insecticides. Among them, Bt CYP6CM1vQ exhibited notable activity against pymetrozine and imidacloprid. Their binding modes were predicted by homology modeling and molecular docking, revealing the mechanisms of the metabolism. We also tested the inhibitory effect of eight known P450 inhibitors using our system and identified letrozole and 1-benzylimidazole as showing significant activity against Bt CYP6CM1vQ, with IC₅₀ values of 23.74 μM and 1.30 μM, respectively. Their potential to be developed as an insecticide synergist was further proven by an in vitro toxicity assay using imidacloprid-resistant Bemisia tabaci. Overall, our luciferin-based enzyme bag method is capable of providing a robust and efficient screening of insect P450 substrates and, more importantly, inhibitors to overcome the resistance.

Targeting mitochondria as a potential therapeutic strategy against chemoresistance in cancer

The importance of mitochondria is not only limited to energy generation but also in several physical and chemical processes critical for cell survival. Mitochondria play an essential role in cellular apoptosis, calcium ion transport and cellular metabolism. Mutation in the nuclear and mitochondrial genes, altered oncogenes/tumor suppressor genes, and deregulated signalling for cell viability are major reasons for cancer progression and chemoresistance. The development of drug resistance in cancer patients is a major challenge in cancer treatment as the resistant cells are often more aggressive. The drug resistant cells of numerous cancer types exhibit the deregulation of mitochondrial function. The increased biogenesis of mitochondria and its dynamic alteration contribute to developing resistance. Further, a small subpopulation of cancer stem cells in the heterogeneous tumor is primarily responsible for chemoresistance and has an attribute of mitochondrial dysfunction. This review highlights the critical role of mitochondrial dysfunction in chemoresistance in cancer cells through the processes of apoptosis, autophagy/mitophagy, and cancer stemness. Mitochondria-targeted therapeutic strategies might help reduce cancer progression and chemoresistance induced by various cancer drugs.

A phase I/II study of preoperative letrozole, everolimus, and carotuximab in stage 2 and 3 hormone receptor-positive and Her2-negative breast cancer

PURPOSE

In nonmetastatic hormone receptor-positive and Her2-negative breast cancer, preoperative endocrine therapies can yield outcomes similar with chemotherapy. We evaluated the tolerability and preliminary antitumor activity of preoperative letrozole, everolimus, and carotuximab, a monoclonal antibody targeting endoglin, in nonmetastatic breast cancer.

METHODS

Eligible patients had newly diagnosed, stage 2 or 3, hormone receptor-positive and Her2/neu-negative breast cancer. Patients received escalating doses of everolimus; the dose of letrozole and carotuximab were fixed at 2.5 mg PO daily and 15 mg/kg intravenously every 2 weeks, respectively. The primary objective was to determine the safety and tolerability of the combination. Secondary objectives included pharmacokinetic and pharmacodynamic studies and assessments of antitumor activity.

RESULTS

Fifteen patients enrolled. The recommended phase 2 dose of everolimus in combination with letrozole and carotuximab was 10 mg PO daily. The most frequent adverse events were headache (67%), fatigue (47%), facial flushing and swelling (47%), gingival hemorrhage (40%), epistaxis (33%), nausea and vomiting (27%). Headache constituted a dose-limiting toxicity. At least two signs of mucocutaneous telangiectasia developed in 92% of patients. Carotuximab accumulated in the extravascular space and accelerated the biodistribution and clearance of everolimus. All patients had residual disease. Gene expression analyses were consistent with downregulation of genes involved in proliferation and DNA repair. Among 6 patients with luminal B breast cancer, 5 converted to luminal A after one cycle of therapy.

CONCLUSION

Letrozole, everolimus, and carotuximab were tolerated in combination at their single-agent doses. Pharmacokinetic studies revealed an interaction between everolimus and carotuximab.

TRIAL REGISTRATION

This trial is registered with ClinicalTrials.gov (Identifier: NCT02520063), first posted on August 11, 2015, and is active, not recruiting.

Azolation of Benzylic C-H Bonds via Photoredox-Catalyzed Carbocation Generation

A visible-light photoredox-catalyzed method is reported that enables the coupling between benzylic C-H substrates and N-H azoles. Classically, medicinally relevant N-benzyl azoles are produced via harsh substitution conditions between the azole and a benzyl electrophile in the presence of strong bases at high temperatures. Use of C-H bonds as the alkylating partner streamlines the preparation of these important motifs. In this work, we report the use of N-alkoxypyridinium salts as a critically enabling reagent for the development of a general C(sp3)-H azolation. The platform enables the alkylation of electron-deficient, -neutral, and -rich azoles with a range of C-H bonds, most notably secondary and tertiary partners. Moreover, the protocol is mild enough to tolerate benzyl electrophiles, thus offering an orthogonal approach to existing SN2 and cross-coupling methods.

Cellular and molecular basis of therapeutic approaches to breast cancer

In recent decades, there has been a significant amount of research into breast cancer, with some important breakthroughs in the treatment of both primary and metastatic breast cancers. It's a well-known fact that treating breast cancer is still a challenging endeavour even though physicians have a fantastic toolset of the latest treatment options at their disposal. Due to limitations of current clinical treatment options, traditional chemotherapeutic drugs, and surgical options are still required to address this condition. In recent years, there have been several developments resulting in a wide range of treatment options. This review article discusses the cellular and molecular foundation of chemotherapeutic drugs, endocrine system-based treatments, biological therapies, gene therapy, and innovative techniques for treating breast cancer.

Identification of Non-steroidal Aromatase Inhibitors via In silico and In vitro Studies

INTRODUCTION

Breast cancer is the most common cancer affecting women worldwide, including Pakistan. More than half of breast cancer patients have hormone-dependent breast cancer, which is developed due to the over-production of estrogen (the main hormone in breast cancer).

METHOD

The biosynthesis of estrogen is catalyzed by the aromatase enzyme, which thus serves as a target for the treatment of breast cancer. During the current study, biochemical, computational, and STD-NMR methods were employed to identify new aromatase inhibitors. A series of phenyl-3- butene-2-one derivatives 1-9 were synthesized and evaluated for human placental aromatase inhibitory activity. Among them, four compounds 2, 3, 4, and 8 showed a moderate to weak inhibitory activity (IC50 = 22.6 - 47.9 µM), as compared to standard aromatase inhibitory drugs, letrozole (IC50 = 0.0147 ± 1.45 µM), anastrozole (IC50 = 0.0094 ± 0.91 µM), and exemestane (IC50 = 0.2 ± 0.032 µM). Kinetic studies on two moderate inhibitors, 4 and 8, revealed a competitive- and mixed-type of inhibition, respectively.

RESULT

Docking studies on all active compounds indicated their binding adjacent to the heme group and interaction with Met374, a critical residue of aromatase. STD-NMR further highlighted the interactions of these ligands with the aromatase enzyme.

CONCLUSION

STD-NMR-based epitope mapping indicated close proximity of the alkyl chain followed by an aromatic ring with the receptor (aromatase). These compounds were also found to be non-cytotoxic against human fibroblast cells (BJ cells). Thus, the current study has identified new aromatase inhibitors (compounds 4, and 8) for further pre-clinical and clinical research.

Letrozole treatment alters hippocampal gene expression in common marmosets (Callithrix jacchus)

Aromatase inhibitors (AIs) are a class of drugs commonly given to patients with estrogen receptor (ER)-dependent breast cancers to reduce estrogenic stimulation. However, AIs like Letrozole are associated with negative side effects such as cognitive deficits, sleep disturbances and hot flashes. We have previously shown that these negative effects can be recapitulated in common marmosets (Callithrix jacchus) treated with Letrozole (20 μg daily) for 4 weeks and that marmosets treated with Letrozole show increased levels of estradiol in the hippocampus (Gervais et al., 2019). In order to better understand the mechanisms through which AIs affect cognitive function and increase steroid levels in the hippocampus, we used bulk, paired-end RNA-sequencing to examine differentially expressed genes among Letrozole-treated (LET; n = 8) and vehicle-treated (VEH; n = 8) male and female animals. Gene ontology results show significant reduction across hundreds of categories, some of the most significant being inflammatory response, stress response, MHC Class II protein complex binding, T-cell activation, carbohydrate binding and signaling receptor binding in LET animals. GSEA results indicate that LET females, but not LET males, show enrichment for hormonal gene sets. Based on the transcriptional changes observed, we conclude that AIs may differentially affect the sexes in part due to processes mediated by the CYP-450 superfamily. Ongoing studies will further investigate the longitudinal effects of AIs on behavior and whether AIs increase the risk of stress-induced neurodegeneration.

Transcriptomic analysis reveals the molecular mechanisms underlying osteoclast differentiation in the estrogen-deficient pullets

Several previous reports have suggested that estrogen (E2) is a vital signal responsible for the regulation of skeletal homeostasis and bone remodeling in mammals. E2 could efficiently accelerate the growth of medullary bone in pullets during sexual maturity. Furthermore, the low E2 level can strengthen the mechanical bone functions in female hens. However, mechanistic studies to describe the effects of E2 on bone in pullets during the initiation of the puberty period are remaining elusive. Therefore, the aim of this study was to explore the effect of inhibiting E2 biosynthesis on the biomechanical properties and its molecular mechanism during sexual maturity of pullets. In this study, a total of 90 Hy-line Sonia pullets with comparable body weight at 13 wk of age were selected and categorized into 2 separate groups. Daily, 0.5 mg/4 mL of letrozole (LZ) was orally administered to the treatment (TRT) group and 4 mL of saline to the control (CON) group of pullets for 6 wk. Compared with the CON group, a lower plasma E2 level was observed in the TRT group. Furthermore, plasma P, Gla protein (BGP), and 1,25-dihydroxy vitamin D3 (1,25-(OH)₂D₃) levels were markedly suppressed, whereas the plasma alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) levels were significantly elevated. Moreover, the cortical bone thickness and breaking strength of the tibia and femur, the bone mineral density of the humerus, and the bone mineral content of the humerus as well as the femur were increased significantly. The expression levels of 340 differentially expressed genes (DEGs) differed significantly between the CON and TRT group in the tibia at 19 wk of age. Among them, 32 genes were up-regulated, whereas 308 were down-regulated in the TRT group. The variations in candidate genes associated with osteoclast differentiation and cell adhesion may indicate that LZ inhibits E2 biosynthesis, consequently, reduces osteoclast differentiation by suppressing inter-cellular communication and cells attaching to extracellular matrix components. Taken together, the present study demonstrated that inhibiting E2 synthesis during sexual maturity of pullets decreased osteoclast differentiation and considerably enhanced bone quality.

In vitro Development of Controlled-Release Nanoniosomes for Improved Delivery and Anticancer Activity of Letrozole for Breast Cancer Treatment

INTRODUCTION

Breast cancer is among the most prevalent mortal cancers in women worldwide. In the present study, an optimum formulation of letrozole, letrozole-loaded niosome, and empty niosome was developed, and the anticancer effect was assessed in in vitro MCF-7, MCF10A and MDA-MB-231 breast cancer cell lines.

MATERIALS AND METHODS

Various niosomal formulations of letrozole were fabricated through thin-film hydration method and characterized in terms of size, polydispersity index (PDI), morphology, entrapment efficiency (EE%), release kinetics, and stability. Optimized niosomal formulation of letrozole was achieved by response surface methodology (RSM). Antiproliferative activity and the mechanism were assessed by MTT assay, quantitative real-time PCR, and flow cytometry. Furthermore, cellular uptake of optimum formulation was evaluated by confocal electron microscopy.

RESULTS

The formulated letrozole had a spherical shape and showed a slow-release profile of the drug after 72 h. The size, PDI, and eEE% of nanoparticles showed higher stability at 4°C compared with 25°C. The drug release from niosomes was in accordance with Korsmeyer-Peppa's kinetic model. Confocal microscopy revealed the localization of drug-loaded niosomes in the cancer cells. MTT assay revealed that all samples exhibited dose-dependent cytotoxicity against breast cancer cells. The IC50 of mixed formulation of letrozole with letrozole-loaded niosome (L + L3) is the lowest value among all prepared formulations. L+L3 influenced the gene expression in the tested breast cancer cell lines by down-regulating the expression of Bcl 2 gene while up-regulating the expression of p53 and Bax genes. The flow cytometry results revealed that L + L3 enhanced the apoptosis rate in both MCF-7 and MDA-MB-231 cell lines compared with the letrozole (L), letrozole-loaded niosome (L3), and control sample.

CONCLUSION

Results indicated that niosomes could be a promising drug carrier for the delivery of letrozole to breast cancer cells.

A Review on the Use of Letrozole in Female and Male Infertility

Infertility in developing countries is a distinct and complex problem that disproportionately affects women. Though not a physically restraining disease, it causes a huge social burden on the emotional, financial, and psychosocial quotients of those who suffer from it. Assisted reproductive procedures are frequently used to treat infertility. Years ago, the emergence of ovulation induction represented a significant advancement in treating female infertility. Letrozole, an aromatase inhibitor, is a potential therapy for ovulation induction. Numerous clinical conditions, including anovulatory infertility, polycystic ovarian syndrome, unexplained infertility, and early stages of endometriosis-related infertility, as well as many with improved live birth rates, have been proven to benefit from letrozole treatment. Letrozole is a superior alternative to the widely utilized ovulation induction with clomiphene citrate. While clomiphene citrate has certain limitations, letrozole successfully overcomes these limitations because of its lack of prolonged anti-estrogenic activity, short half-life, and lack of estrogen receptor activation. In most cases, this results in mono-follicular development and excellent live birth rates. According to the most recent research, letrozole can be used as the first-line therapy to treat infertility caused by polycystic ovarian syndrome and other causes. Letrozole is also emerging as a possible treatment for male infertility of unknown cause, proving to be an effective way of influencing hormonal profiles and increasing various seminal parameters such as sperm motility and concentration, as it inhibits aromatization affecting the feedback mechanism to the hypothalamus. This review focuses on our current knowledge of the uses of letrozole for female and male infertility, its mechanisms, and its benefits.

Co-targeting CDK2 and CDK4/6 overcomes resistance to aromatase and CDK4/6 inhibitors in ER+ breast cancer

Resistance to aromatase inhibitor (AI) treatment and combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy (ET) are crucial clinical challenges in treating estrogen receptor-positive (ER+) breast cancer. Understanding the resistance mechanisms and identifying reliable predictive biomarkers and novel treatment combinations to overcome resistance are urgently needed. Herein, we show that upregulation of CDK6, p-CDK2, and/or cyclin E1 is associated with adaptation and resistance to AI-monotherapy and combined CDK4/6i and ET in ER+ advanced breast cancer. Importantly, co-targeting CDK2 and CDK4/6 with ET synergistically impairs cellular growth, induces cell cycle arrest and apoptosis, and delays progression in AI-resistant and combined CDK4/6i and fulvestrant-resistant cell models and in an AI-resistant autocrine breast tumor in a postmenopausal xenograft model. Analysis of CDK6, p-CDK2, and/or cyclin E1 expression as a combined biomarker in metastatic lesions of ER+ advanced breast cancer patients treated with AI-monotherapy or combined CDK4/6i and ET revealed a correlation between high biomarker expression and shorter progression-free survival (PFS), and the biomarker combination was an independent prognostic factor in both patients cohorts. Our study supports the clinical development of therapeutic strategies co-targeting ER, CDK4/6 and CDK2 following progression on AI-monotherapy or combined CDK4/6i and ET to improve survival of patients exhibiting high tumor levels of CDK6, p-CDK2, and/or cyclin E1.

Pamidronate, a promising repositioning drug to treat leishmaniasis, displays antileishmanial and immunomodulatory potential

Visceral leishmaniasis (VL) is an infectious disease caused by Leishmania infantum (L. infantum). Currently, there are no vaccines and/or prophylactic therapies against VL, and the recentpharmacological approaches come from the drug repositioning strategy. Here, we evaluated the anticancer drug pamidronate (PAM) to identify a new therapeutic option for the treatment of human VL. We assessed its in vitro antileishmanial activity against the promastigote and amastigote forms of L. infantum by evaluating cell cytotoxicity. The antileishmanial and immunomodulatory activities were assessed using human peripheral blood leukocytes ex vivo. PAM induced the formation of vacuoles in the cytoplasm of the promastigotes and alterations in the morphology of the kinetoplast and mitochondria in vitro, which indicates anti-promastigote activity. PAM also reduced the number of infected macrophages and intracellular amastigotes in a concentration-dependent manner, with cell viability above 70%. In ex vivo, PAM reduced the internalized forms of L. infantum in the classical monocyte subpopulation. Furthermore, it enhanced IL-12 and decreased IL-10 and TGF-β by monocytes and neutrophils. Increased IFN-γ and TNF levels for CD8^- and CD8⁺ T lymphocytes and B lymphocytes, respectively, were observed after the treatment with PAM, as well as a reduction in IL-10 by the lymphocyte subpopulations evaluated. Taken together, our results suggest that PAM may be eligible as a potential therapeutic alternative for drug repurposing to treat human visceral leishmaniasis.

Synthesis of New Pyrimidine-Triazole Derivatives and Investigation of Their Anticancer Activities

Aromatase inhibitors are the most used anticancer drug group in breast cancer cases. The development of resistance in cancer patients over time and the side effects of existing drugs make the need for new and effective agents permanent. In this study, 10 novel pyrimidine-triazole derivatives were synthesized and their anticancer activities were investigated. Compounds  5c  and  5g  showed inhibitor activity against MCF-7 cell line with IC 50 =1.573±0.020; 3.698±0.056 µM value, respectively.  As a result of  in vitro  aromatase enzyme inhibition test, compounds  5c  and  5g  were exhibited significant activity with IC 50 =0.082±0.007 µM and IC50=0.198±0.015 µM, respectively. Estimated physicochemical parameters were calculated using the online SwissADME program for all compounds. Interaction modes of the compounds  5c  and  5g  were investigated against aromatase enzyme by means of docking studies. As a result of the studies, the importance of the triazole ring for aromatase inhibition has been understood.

Induced mammary cancer in rat models: pathogenesis, genetics, and relevance to female breast cancer

Mammary cancer, or breast cancer in women, is a polygenic disease with a complex etiopathogenesis. While much remains elusive regarding its origin, it is well established that chemical carcinogens and endogenous estrogens contribute significantly to the initiation and progression of this disease. Rats have been useful models to study induced mammary cancer. They develop mammary tumors with comparable histopathology to humans and exhibit differences in resistance or susceptibility to mammary cancer depending on strain. While some rat strains (e.g., Sprague-Dawley) readily form mammary tumors following treatment with the chemical carcinogen, 7,12-dimethylbenz[a]-anthracene (DMBA), other strains (e.g., Copenhagen) are resistant to DMBA-induced mammary carcinogenesis. Genetic linkage in inbred strains has identified strain-specific quantitative trait loci (QTLs) affecting mammary tumors, via mechanisms that act together to promote or attenuate, and include 24 QTLs controlling the outcome of chemical induction, 10 QTLs controlling the outcome of estrogen induction, and 4 QTLs controlling the outcome of irradiation induction. Moreover, and based on shared factors affecting mammary cancer etiopathogenesis between rats and humans, including orthologous risk regions between both species, rats have served as useful models for identifying methods for breast cancer prediction and treatment. These studies in rats, combined with alternative animal models that more closely mimic advanced stages of breast cancer and/or human lifestyles, will further improve our understanding of this complex disease.

Simultaneous Quantification of Aromatase Inhibitors and Estrogens in Postmenopausal Breast Cancer Patients

CONTEXT

Currently there are no assays that can simultaneously quantify serum levels of the third-generation aromatase inhibitors (AIs): letrozole, anastrozole, and exemestane, and the ultra-low levels of estrogens in postmenopausal breast cancer patients on AI treatment. Such measurements may be pivotal for the determination of optimal and individualized treatment regimens. We aimed at developing a liquid chromatography-tandem mass spectrometry (MS/MS) method for simultaneous assessment of letrozole, anastrozole, exemestane, and 17-hydroxyexemestane as well as subpicomolar levels of estradiol and estrone.

METHODS

Internal standards, calibrators, serum samples, and quality controls were in fully automated steps transferred to a deep-well plate for a 2-step liquid-liquid extraction. The extracts were reconstituted and analytes were separated chromatographically using 2 serially coupled columns, then subject to MS/MS in electrospray ionization mode. The method was thoroughly validated and is traceable to 2 accredited estrogen methods.

RESULTS

The measurement range for estrone and estradiol was 0.2 to 12 000 pmol/L and 0.8 to 13 000 pmol/L, and covered the expected therapeutic range for the AIs. All analytes had a precision of less than or equal to 13%, and accuracies within 100 ± 8%. As proof of concept, AI and estrogen levels were determined in serum samples from postmenopausal breast cancer patients under treatment.

CONCLUSION

We present here an assay suitable for the simultaneous measurement of serum levels of all third-generation AIs and ultra-low levels of estrogens, providing a powerful new tool to study drug efficacy and compliance. The method is highly valuable for postmenopausal patients whose pretreatment estradiol levels are below the threshold of detection for most routine assays, but still require suppression.

Delayed Implantation Induced by Letrozole in Mice

Implantation timing is critical for a successful pregnancy. A short delay in embryo implantation caused by targeted gene ablation produced a cascading problem in the later stages of the pregnancy. Although several delayed implantation models have been established in wild mice, almost none of them is suitable for investigating the early delay's effects on the late events of pregnancy. Here, we report a new delayed implantation model established by the intraperitoneal administration of letrozole at 5 mg/kg body weight on day 3 of pregnancy. In these mice, initiation of implantation was induced at will by the injection of estradiol (E2). When the estradiol (3 ng) was injected on day 4 of pregnancy (i.e., without delay), the embryo implantation restarted, and the pregnancy continued normally. However, 25 ng estrogen caused compromised implantation. We also found that 67% of the female mice could be pregnant normally and finally gave birth when the estradiol injection (3 ng) was on day 5 of pregnancy (i.e., 1-day delay). Most failed pregnancies had impaired decidualization, decreased serum progesterone levels, and compromised angiogenesis. Progesterone supplementation could rescue decidualization failure in the mice. Collectively, we established a new model of delayed implantation by letrozole, which can be easily applied to study the effect and mechanisms of delay of embryo implantation on the progression of late pregnancy events.

Role of high-fat diet on letrozole-induced polycystic ovarian syndrome in rats

Polycystic ovary syndrome (PCOS) is one of the most prevalent hormonal disorders in women of reproductive age. Letrozole (LET)-induced PCOS is a good model but has drawbacks such as the absence of metabolic changes. Hence, in the present study, we aimed to develop a new animal model combining a high-fat diet (HFD) and LET. Female Wistar rats were divided into a control group, LET group, and LET + HFD (45% energy from fat) group. Compared with the control group, the LET and LET + HFD groups showed ovarian cysts and elevated testosterone levels, whereas oestradiol and progesterone levels were reduced. The LET + HFD group displayed significant changes in body weight, as well as in levels of triglycerides, fasting blood glucose, direct bilirubin, alanine aminotransferase, and uric acid; in terms of glucose intolerance and insulin resistance, the LET + HFD group showed better results than the LET group. Compared with the control group, elevated levels of tumour necrosis factor-α were detected in both the LET and LET + HFD groups. The addition of HFD to the LET model afforded good metabolic aberrations, along with ovarian cysts. In contrast, the LET-only model failed to demonstrate metabolic anomalies observed in the human PCOS condition.

Construction of CF3-Functionalized Fully Substituted Benzonitriles through Rauhut-Currier Reaction Initiated [3 + 3] Benzannulation

Though numerous cyanation reactions have been developed for the synthesis of benzonitriles, the construction of valuable fully substituted benzonitriles is still a challenging task. Herein, we reported a tertiary amine-catalyzed [3 + 3]-benzannulation for the green synthesis of CF₃-functionalized fully substituted benzonitriles. This strategy features exclusive chemoselectivity, high atom-economy, and good step-economy with environment-friendly reagents and mild conditions. Unique triphenyl-substituted dicyanobenzoate products could be rapidly constructed using this method. The practicality and reliability of this reaction were proved by the successful scale-up synthesis. A mechanistic study indicates that the [3 + 3]-benzannulation was initiated by an intermolecular Rauhut-Currier reaction.

The pharmacokinetics of letrozole and its effect on gonadotropins in anestrous ewes

The aim of this study was to determine the pharmacokinetics of letrozole and its effect on FSH and LH concentrations after single (IV, IM, SC) and repeated IV doses in anestrous ewes. This study was conducted in experiments 1 and 2 by randomly dividing 24 healthy Akkaraman ewes in anestrus into two equal groups. In experiment 1, the pharmacokinetics of letrozole following single IV, IM, and SC administration at 1 mg/kg dose and its effect of a single IV dose on plasma FSH and LH concentration were determined. In experiment 2, the effect of repeated IV doses of letrozole on FSH and LH concentrations was established. Plasma concentration of letrozole was measured using high-performance liquid chromatography, and pharmacokinetic parameters were calculated by non-compartmental analysis. FSH and LH concentrations were quantified using ELISA. The elimination half-life (t_1/2ʎz) for IV, IM, and SC routes were 9.94, 37.29, and 41.07 h, respectively. The IV route for letrozole had a total clearance of 0.11 L/h/kg and a volume of distribution at a steady state of 1.50 L/kg. The peak plasma concentration was 0.11 μg/mL for the IM route and 0.14 μg/mL for the SC routes. The bioavailability was 55.18% for the IM route and 75.34% for the SC route. Letrozole following single and repeated (every 24 h for 3 days) IV administrations at 1 mg/kg dose did not affect LH concentration in anestrous ewes but caused an increase in the FSH concentration. This increase in FSH concentration may create a potential for the use of letrozole in ovarian superstimulation protocols. Favorable pharmacokinetic properties (long t_1/2ʎz and good bioavailability) of letrozole for IM and SC routes require further investigation before use in estrus induction or estrus synchronization protocols in sheep.

Gum Acacia Functionalized Colloidal Gold Nanoparticles of Letrozole as Biocompatible Drug Delivery Carrier for Treatment of Breast Cancer

The most prevalent malignancy among postmenopausal women is breast cancer. It is one of the leading causes of cancer-related mortality among women. Letrozole (LTZ) is a clinically approved inhibitor for breast cancer in postmenopausal women. However, due to poor aqueous solubility, non-specific binding, unwanted toxicity, and poor blood circulation hampered its clinical applications. To maximize the pharmacological effects and minimize the side effects, inorganic nanoparticles are a good alternative. Due to excellent biocompatibility and minimum cytotoxicity, gold nanoparticles (AuNPs) offer distinct benefits over other metal nanoparticles. Emerging as attractive components, AuNPs and Gum acacia (GA) have been extensively studied as biologically safe nanomaterials for the treatment of cancers. This study reports the synthesis and characterization of GA stabilized gold nanoparticles (GA-AuNPs) of LTZ for breast cancer treatment. The observed particle size of optimized LTZ @ GA-AuNPs was 81.81 ± 4.24 nm in size, 0.286 ± 0.143 of polydispersity index (PDI) and -14.6 ± -0.73 mV zeta potential. The biologically synthesized LTZ @ GA-AuNPs also demonstrated dose-dependent cytotoxicity against the human breast cancer cell line MCF-7, with an inhibitory concentration (IC50) of 3.217 ± 0.247. We determined the hemolytic properties of the LTZ @ GA-AuNPs to evaluate the interaction between the nanoparticles and blood components. Results showed that there is no interaction between LTZ @ GA-AuNPs and blood. In conclusion, the findings indicate that LTZ @ GA-AuNPs has significant potential as a promising drug delivery carrier for treating breast cancer in postmenopausal women.

Recent Advancement in the One-Pot Synthesis of the Tri-Substituted Methanes (TRSMs) and Their Biological Applications

The history of tri-substituted methanes (TRSMs) in chemical industries is much older. Tri-substituted methanes were previously used as dyes in the chemical industries. Still, there is a significant surge in researchers' interest in them due to their wide range of bioactivities. Tri-substituted methane derivatives show a wide range of biological activities like anti-tumor, antimicrobial, antibiofilm, antioxidant, anti-inflammatory, anti-arthritic activities. Due to the wide range of medicinal applications shown by tri-substituted methanes, most of the methodologies reported in the literature for the synthesis of TRSMs are focused on the one-pot method. This review explored the recently reported one-pot processes for synthesizing tri-substituted methanes and their various medicinal applications. Based on the substitution attached to the -CH carbon, this review categorizes them into two major classes: (I) symmetrical and (II) unsymmetrical trisubstituted methanes. In addition, this review gives an insight into the growing opportunities for the construction of trisubstituted scaffolds via one-pot methodologies. To the best of our knowledge, no one has yet reported a review on the one-pot synthesis of TRSMs. Therefore, here we present a brief literature review of the synthesis of both symmetrical and unsymmetrical TRSMs covering various one-pot methodologies along with their medicinal applications.

The aromatase inhibitor letrozole restores FADS2 function in ER+ MCF7 human breast cancer cells

PURPOSE

Plasticity in fatty acid metabolism is increasingly recognized as a major feature influencing cancer progression and efficacy of treatments. Estrogen receptor positive MCF7 human breast cancer cells have long been known to have no FADS2-mediated Δ6-desaturase activity. Our objective was to examine the effect of estrogen and the "antiestrogen" aromatase inhibitor letrozole, on Δ5- and Δ6-desaturase synthesized fatty acids in vitro.

METHODS

Eicosa-11,14-dienoic acid (20:2n-6), a known substrate for both FADS1 and FADS2, was used as a sentinel of relative FADS2 and FADS1 activity. MCF7 cells and four additional estrogen responsive wild type cell lines (HepG2, SK-N-SH, Y79 and Caco2) were studied. FAME were quantified by GC-FID and structures identified by GCCACI-MS/MS.

RESULTS

In all five cell lines, estrogen caused a dose dependent decrease in sciadonic acid (5,11,14-20:3, ScA) via apparent inhibition of FADS1 activity, and had no effect on FADS2 catalyzed synthesis of dihomo-gamma linolenic acid (8,11,14-20:3; DGLA). In MCF7 cells, letrozole caused a dose dependent increase in FADS2-catalyzed DGLA synthesis, which plateaued in SK-N-SH cells.

CONCLUSION

Letrozole restores Δ6-desaturase mediated synthesis of the anti-inflammatory PGE1-precursor DGLA in vitro and is the first endocrine-active agent to have opposing effects on FADS1 and FADS2 catalyzed activities.

Prolonged use of letrozole causes morphological changes on gonads in Galea spixii

Letrozole is used as a therapeutic agent in reproductive disorders caused by high estrogen levels. Letrozole inhibits cytochrome P450 aromatase and reduces estrogen levels. However, the effects of long-term use on reproductive traits are unknown. The aim of this study was to evaluate the prolonged use of letrozole in the gonads of rodents (Spix's yellow-toothed cavy; Galea spixii). Forty-eight rodents (24 males and 24 females) were randomly divided into the treated and control groups. Letrozole administration started at 15 days of age and continued weekly until 30, 45, 90, and 120 days of age. The body, testis, and ovary weights were analyzed, as well as the morphological progression of spermatogenesis and folliculogenesis. Macroscopically, body weight gain and gonads weight were increased in the letrozole group. Microscopically, the ovaries of treated females showed stratified epithelium and a cellular disorder of the tunica albuginea. In the testes of treated males, the development of seminiferous tubules was delayed and sperm was absent. The collective findings indicate that the prolonged use of letrozole alters secondary sexual characteristics, and causes weight gain, reproductive changes, and male infertility.

A Fluorometric CYP19A1 (Aromatase) Activity Assay in Live Cells

Inhibition of estrogen synthesis is an integral component of the frontline pharmacologic therapy for the treatment of estrogen receptor positive cancers. However, there is currently no direct, high-throughput-ready assay for aromatase (also known as CYP19A1) that can be performed in live cells. Herein we present a cell-based assay that allows for multiplexed assessment of enzyme activity, protein half-life, cell viability, and identification of inhibitors with slow off-rates.

Transdermal Delivery of Chemotherapeutics: Strategies, Requirements, and Opportunities

Chemotherapeutic drugs are primarily administered to cancer patients via oral or parenteral routes. The use of transdermal drug delivery could potentially be a better alternative to decrease the dose frequency and severity of adverse or toxic effects associated with oral or parenteral administration of chemotherapeutic drugs. The transdermal delivery of drugs has shown to be advantageous for the treatment of highly localized tumors in certain types of breast and skin cancers. In addition, the transdermal route can be used to deliver low-dose chemotherapeutics in a sustained manner. The transdermal route can also be utilized for vaccine design in cancer management, for example, vaccines against cervical cancer. However, the design of transdermal formulations may be challenging in terms of the conjugation chemistry of the molecules and the sustained and reproducible delivery of therapeutically efficacious doses. In this review, we discuss the nano-carrier systems, such as nanoparticles, liposomes, etc., used in recent literature to deliver chemotherapeutic agents. The advantages of transdermal route over oral and parenteral routes for popular chemotherapeutic drugs are summarized. Furthermore, we also discuss a possible in silico approach, Formulating for Efficacy™, to design transdermal formulations that would probably be economical, robust, and more efficacious.

A new clinically-relevant rat model of letrozole-induced chronic nociceptive disorders

Among postmenopausal women with estrogen receptor-positive breast cancer, more than 80% receive hormone therapy including aromatase inhibitors (AIs). Half of them develop chronic arthralgia - characterized by symmetric articular pain, carpal tunnel syndrome, morning stiffness, myalgia and a decrease in grip strength - which is associated with treatment discontinuation. Only a few animal studies have linked AI treatment to nociception, and none to arthralgia. Thus, we developed a new chronic AI-induced nociceptive disorder model mimicking clinical symptoms induced by AIs, using subcutaneous letrozole pellets in ovariectomized (OVX) rats. Following plasma letrozole dosage at the end of the experiment (day 73), only rats with at least 90 ng/ml of letrozole were considered significantly exposed to letrozole (OVX + high LTZ group), whereas treated animals with less than 90 ng/ml were pooled in the OVX + low LTZ group. Chronic nociceptive disorder set in rapidly and was maintained for more than 70 days in the OVX + high LTZ group. Furthermore, OVX + high LTZ rats saw no alteration in locomotion, myalgia or experimental anxiety during this period. Bone parameters of the femora were significantly altered in all OVX rats compared to Sham+vehicle pellet. A mechanistic analysis focused on TRPA1, receptor suspected to mediate AI-evoked pain, and showed no modification in its expression in the DRG. This new long-lasting chronic rat model, efficiently reproduces the symptoms of AI-induced nociceptive disorder affecting patients' daily activities and quality-of-life. It should help to study the pathophysiology of this disorder and to promote the development of new therapeutic strategies.

A review on diverse heterocyclic compounds as the privileged scaffolds in non-steroidal aromatase inhibitors

Breast cancer, emerging malignancy is common among women due to overexpression of estrogen. Estrogens are biosynthesized from androgens by aromatase, a cytochrome P450 enzyme complex, and play a pivotal role in stimulating cell proliferation. Therefore, deprivation of estrogen by blocking aromatase is considered as the effective way for the inhibition and treatment of breast cancer. In recent years, various non-steroidal heterocyclic functionalities have been extensively developed and studied for their aromatase inhibition activity. This review provides information about the structural-activity relationship of heterocycles (Type II) towards aromatase. This aids the medicinal chemist around the significance of different heterocyclic moieties and helps to design potent aromatase inhibitors.

The risk of menopausal symptoms in premenopausal breast cancer patients and current pharmacological prevention strategies

Introduction: For young premenopausal breast cancer (BC) patients, adjuvant chemotherapy and other anti-cancer treatments can increase the risk of menopausal symptoms and may cause chemotherapy-related amenorrhea (CRA), infertility and premature ovarian insufficiency (POI).Areas covered: In this report, menopausal symptoms related to anti-cancer treatment are described. Menstrual disturbances associated with the use of adjuvant chemotherapy, endocrine therapy, and targeted therapy against human epidermal growth factor receptor 2 (HER2) in premenopausal women withBC are discussed. To prevent menopausal symptoms, CRA and POI, data on the efficacy of temporary ovarian suppression with gonadotropin-releasing hormone analogues (GnRHa) during chemotherapy are highlighted. Pooled analyses have confirmed that concurrent administration of GnRHa during chemotherapy could significantly reduce the risk of developing chemotherapy-induced POI in premenopausal women with early-stageBC. In addition, reports have suggested that embryo/oocyte cryopreservation may increase the chance of pregnancy after the diagnosis ofBC, although such data remain limited.Expert opinion: Commonly experienced by pre-menopausal women withBC, anti-cancer treatment could cause severe menopausal symptoms. Temporary ovarian suppression with GnRHa during chemotherapy provided asafe and efficient strategy to reduce the likelihood of chemotherapy-induced POI in premenopausal patients with early-stageBC undergoing (neo)-adjuvant chemotherapy.

Computing Metal-Binding Proteins for Therapeutic Benefit

Over one third of biomolecules rely on metal ions to exert their cellular functions. Metal ions can play a structural role by stabilizing the structure of biomolecules, a functional role by promoting a wide variety of biochemical reactions, and a regulatory role by acting as messengers upon binding to proteins regulating cellular metal-homeostasis. These diverse roles in biology ascribe critical implications to metal-binding proteins in the onset of many diseases. Hence, it is of utmost importance to exhaustively unlock the different mechanistic facets of metal-binding proteins and to harness this knowledge to rationally devise novel therapeutic strategies to prevent or cure pathological states associated with metal-dependent cellular dysfunctions. In this compendium, we illustrate how the use of a computational arsenal based on docking, classical, and quantum-classical molecular dynamics simulations can contribute to extricate the minutiae of the catalytic, transport, and inhibition mechanisms of metal-binding proteins at the atomic level. This knowledge represents a fertile ground and an essential prerequisite for selectively targeting metal-binding proteins with small-molecule inhibitors aiming to (i) abrogate deregulated metal-dependent (mis)functions or (ii) leverage metal-dyshomeostasis to selectively trigger harmful cells death.

Gender-based differences in brain and plasma pharmacokinetics of letrozole in sprague-dawley rats: Application of physiologically-based pharmacokinetic modeling to gain quantitative insights

Based on the discovery that the estrogen synthase aromatase (CYP19A1) is abundantly expressed in high- grade gliomas, the aromatase inhibitor, letrozole is being investigated in pre-clinical models as a novel agent against this malignancy. Here, we investigated the systemic and brain pharmacokinetics of letrozole following single and steady state dosing in both male and female Sprague-Dawley rats. Furthermore, we employed physiologically-based pharmacokinetic (PBPK) modeling to gain quantitative insights into the blood-brain barrier penetration of this drug. Letrozole (4 mg/kg) was administered intraperitoneally daily for 5 days (for males) and 11 days (for females) and intracerebral microdialysis was performed for brain extracellular fluid (ECF) collection simultaneously with venous blood sampling. Drug levels were measured using HPLC and non-compartmental analysis was conducted employing WinNonlin®. Simcyp animal simulator was used for conducting bottom-up PBPK approach incorporating the specified multi-compartment brain model. Overall, marked gender-specific differences in the systemic and brain pharmacokinetics of letrozole were observed. Letrozole clearance was much slower in female rats resulting in markedly higher plasma and brain drug concentrations. At steady state, the plasma AUC 0-24 was 103.0 and 24.8 μg*h/ml and brain ECF AUC 0-12 was 24.0 and 4.8 μg*h/ml in female and male rats, respectively. The PBPK model simulated brain concentration profiles were in close agreement with the observed profiles. While gender-specific differences in letrozole PK are not observed in the clinical setting, these findings will guide the dose optimization during pre-clinical investigations of this compound. The PBPK model will serve as an important clinical translational tool.

Synthesis and Biological Evaluation of 1-(Diarylmethyl)-1H-1,2,4-triazoles and 1-(Diarylmethyl)-1H-imidazoles as a Novel Class of Anti-Mitotic Agent for Activity in Breast Cancer

We report the synthesis and biochemical evaluation of compounds that are designed as hybrids of the microtubule targeting benzophenone phenstatin and the aromatase inhibitor letrozole. A preliminary screening in estrogen receptor (ER)-positive MCF-7 breast cancer cells identified 5-((2H-1,2,3-triazol-1-yl)(3,4,5-trimethoxyphenyl)methyl)-2-methoxyphenol 24 as a potent antiproliferative compound with an IC50 value of 52 nM in MCF-7 breast cancer cells (ER+/PR+) and 74 nM in triple-negative MDA-MB-231 breast cancer cells. The compounds demonstrated significant G2/M phase cell cycle arrest and induction of apoptosis in the MCF-7 cell line, inhibited tubulin polymerisation, and were selective for cancer cells when evaluated in non-tumorigenic MCF-10A breast cells. The immunofluorescence staining of MCF-7 cells confirmed that the compounds targeted tubulin and induced multinucleation, which is a recognised sign of mitotic catastrophe. Computational docking studies of compounds 19e, 21l, and 24 in the colchicine binding site of tubulin indicated potential binding conformations for the compounds. Compounds 19e and 21l were also shown to selectively inhibit aromatase. These compounds are promising candidates for development as antiproliferative, aromatase inhibitory, and microtubule-disrupting agents for breast cancer.

Regulation of aromatase in cancer

The regulation of aromatase, an enzyme involved in the biosynthesis of estrogen in normal and cancer cells, has been associated with growth factor signaling and immune response modulation. The tissue-specific regulatory roles of these factors are of particular importance as local aromatase expression is strongly linked to cancer development/progression and disease outcomes in patients. Therefore, aromatase has become a chemotherapeutic target and aromatase inhibitors (AIs) are used in the clinic for treating hormone-dependent cancers. Although AIs have shown promising results in the treatment of cancers, the emerging increase in AI-resistance necessitates the development of new and improved targeted therapies. This review discusses the role of tumor and stromal-derived growth factors and immune cell modulators in regulating aromatase. Current single-agent and combination therapies with or without AIs targeting growth factors and immune checkpoints are also discussed. This review highlights recent studies that show new connections between growth factors, mediators of immune response, and aromatase regulation.