Influence of hepatic and intestinal efflux transporters and their genetic variants on the pharmacokinetics and pharmacodynamics of raloxifene in osteoporosis treatment

Comparative Pharmacokinetic Profiles of a Novel Low-Dose Micronized Formulation of Raloxifene 45 mg (AD-101) and the Conventional Raloxifene 60 mg in Healthy Subjects

Raloxifene hydrochloride shows poor bioavailability (only 2%) when orally administered because of its poor aqueous solubility and its extensive first-pass metabolism. A new micronized formulation of raloxifene was developed to improve bioavailability via enhanced gastrointestinal absorption. The primary objective of this study was to evaluate the pharmacokinetic characteristics of a new micronized raloxifene formulation (AD-101) in comparison with the conventional raloxifene formulation. This study was designed as an open-label, randomized, 2-treatment-period, crossover study with a 2-week washout period. Two treatments consisted of micronized raloxifene 45 mg daily; and conventional raloxifene 60 mg daily administered in fasting conditions. Plasma raloxifene concentrations were determined by a validated method using ultra-fast liquid chromatography-tandem mass spectrometry, and pharmacokinetic parameters were calculated using a noncompartmental model. In total, 49 subjects completed the study. The geometric mean ratio (micronized/conventional) of the maximum concentration and the area under the plasma concentration-time curve from time zero to the last concentration values were 1.08 (90% CI, 0.95-1.24) and 0.97 (90% CI, 0.89-1.05), respectively. The adverse event profile did not differ between the 2 formulations. The results demonstrate that micronized formulation of raloxifene 45 mg is equivalent to conventional formulation of raloxifene 60 mg when administered at the single dose in the fasted state. After single oral dosing of AD-101, there were no serious or unexpected adverse events.

Co-consuming green tea with raloxifene decreases raloxifene systemic exposure in healthy adult participants

Green tea is a popular beverage worldwide. The abundant green tea catechin (-)-epigallocatechin gallate (EGCG) is a potent in vitro inhibitor of intestinal UDP-glucuronosyltransferase (UGT) activity (Ki  ~2 μM). Co-consuming green tea with intestinal UGT drug substrates, including raloxifene, could increase systemic drug exposure. The effects of a well-characterized green tea on the pharmacokinetics of raloxifene, raloxifene 4'-glucuronide, and raloxifene 6-glucuronide were evaluated in 16 healthy adults via a three-arm crossover, fixed-sequence study. Raloxifene (60 mg) was administered orally with water (baseline), with green tea for 1 day (acute), and on the fifth day after daily green tea administration for 4 days (chronic). Unexpectedly, green tea decreased the geometric mean green tea/baseline raloxifene AUC0-96h ratio to ~0.60 after both acute and chronic administration, which is below the predefined no-effect range (0.75-1.33). Lack of change in terminal half-life and glucuronide-to-raloxifene ratios indicated the predominant mechanism was not inhibition of intestinal UGT. One potential mechanism includes inhibition of intestinal transport. Using established transfected cell systems, a green tea extract normalized to EGCG inhibited 10 of 16 transporters tested (IC50 , 0.37-12 μM). Another potential mechanism, interruption by green tea of gut microbe-mediated raloxifene reabsorption, prompted a follow-up exploratory clinical study to evaluate the potential for a green tea-gut microbiota-drug interaction. No clear mechanisms were identified. Overall, results highlight that improvements in current models and methods used to predict UGT-mediated drug interactions are needed. Informing patients about the risk of co-consuming green tea with raloxifene may be considered.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Pharmacokinetic Drug Interaction Between Raloxifene and Cholecalciferol in Healthy Volunteers

Osteoporosis is a common skeletal disorder, often leading to fragility fracture. Combination therapy with raloxifene, a selective estrogen receptor modulator, and cholecalciferol (vitamin D₃) has been proposed to improve the overall efficacy and increase compliance of raloxifene therapy for postmenopausal osteoporosis. To our knowledge, there has been no report of any study on the pharmacokinetic interaction between raloxifene and cholecalciferol. This study aimed to evaluate the possible pharmacokinetic interactions between raloxifene and cholecalciferol in healthy adult male Korean volunteers. Twenty subjects completed this open‐label, randomized, single‐dose, 3‐period, 6‐sequence, crossover phase 1 study with a 14‐day washout period. Serial blood samples were collected from 20 hours before dosing to 96 hours after dosing. The plasma concentrations of raloxifene and cholecalciferol were determined using a validated method for high‐performance liquid chromatography with tandem mass spectrometry. The geometric mean ratios (90%CIs) for area under the plasma concentration–time curve from time 0 to the last quantifiable time point and maximum plasma concentration of raloxifene with or without cholecalciferol were 1.02 (0.87‐1.20) and 0.87 (0.70‐1.08), respectively. For baseline‐corrected cholecalciferol, geometric mean ratios (90%CIs) of area under the plasma concentration–time curve from time 0 to the last quantifiable time point and maximum plasma concentration with or without raloxifene were 1.01 (0.93‐1.09) and 0.99 (0.92‐1.06), respectively. Concurrent treatment with raloxifene and cholecalciferol was generally well tolerated. These results suggest that raloxifene and cholecalciferol have no clinically relevant pharmacokinetic drug‐drug interactions when administered concurrently. All treatments were well tolerated, with no serious adverse events.

Raloxifene has favorable effects on the lipid profile in women explaining its beneficial effect on cardiovascular risk: A meta-analysis of randomized controlled trials

There is robust evidence that the appropriate treatment of dyslipidaemia substantially reduces cardiovascular disease-related morbidity and mortality. Raloxifene is a selective oestrogen receptor modulator that also interferes with the lipid metabolism and may be of aid in the management of lipid abnormalities in females. Therefore, we conducted a systematic review and meta-analysis of the available randomized clinical trials (RCTs) exploring the effect of raloxifene on the lipid profile in women. The Scopus, Web of Science, PubMed/Medline and EMBASE databases were systematically and independently searched by two assessors from inception until 20 November 2020 without time and language restrictions. The overall findings were generated from 30 eligible RCTs. As compared to controls, raloxifene resulted in a significant elevation of the high-density lipoprotein-cholesterol (HDL-C) (WMD: 2.41 mg/dL, 95% CI: 0.84-3.97, P = 0.003) and a significant reduction of the total cholesterol (TC) (WMD:-14.84 mg/dL, 95% CI: -20.37 to -9.317, P = 0.000) and of the low-density lipoprotein-cholesterol (LDL-C) (WMD: -17 mg/dL, 95% CI: -25.77, -8.22, P = 0.000). In the stratified analysis, a significant decrease of serum triglycerides (TG) (WMD: -22.06 mg/dL) was achieved in the RCTs with a duration of ≤ 26 weeks (WMD -8.70 mg/dL) and with baseline TG concentrations of ≥ 130 mg/dL (WMD: -23.02 mg/dL). In conclusion, raloxifene treatment can increase HDL-C and lower LDL-C and TC. In terms of TG, a significant decrease can be observed if the administration of raloxifene lasts ≤ 26 weeks and if the baseline TG concentrations are ≥ 130 mg/dL.

Nanostructured lipid carrier potentiated oral delivery of raloxifene for breast cancer treatment

Nanotherapeutics in cancer treatment are dominating global science and research, and have been recognized as the pioneering medical care regimen. Raloxifene (RLN) has been used for its anti-proliferative action on mammary tissue, however, it suffers from poor oral bioavailability. This investigation gives an account of the design and development of RLN-loaded nanostructured lipid carriers (RLN-NLCs) using a simple and scalable ultrasonication method for improved oral efficacy and limited offsite toxicity using Compritol^® 888 ATO as a solid lipid and Transcutol^® HP as a liquid lipid. In addition, the optimized RLN-NLCs were in the nanometric range (121 nm) with high % entrapment efficiency (%EE) (81%) for RLN, and were further freeze-dried in the presence of mannitol to enhance the stability of RLN-NLCs in the dry state for long-term use. Morphological observation under a transmission electron microscope and scanning electron microscope revealed the spherical smooth surface nanometric size of RLN-NLCs. Powder x-ray diffraction confirmed the encapsulation of RLN into the RLN-NLC's matrix with reduced crystallinity of the drug. The in vitro release study showed a burst release for an initial 4 h, and sustained release for up to 24 h. Furthermore, the RLN-NLCs showed higher cytotoxicity towards MCF-7 cells in vitro in comparison to RLN suspension, and an ex vivo intestinal permeation study demonstrated improved intestinal permeability of RLN-NLCs. Moreover, the in vivo pharmacokinetic study in female Wistar rats showed a 4.79-fold increment in oral bioavailability of RLN from RLN-NLCs compared to RLN suspension. Taken together, our results pave the way for a new nanotherapeutic approach towards breast cancer treatment.

Self-assembled lecithin-chitosan nanoparticles improve the oral bioavailability and alter the pharmacokinetics of raloxifene

In this study, we report the development and evaluation of soy lecithin-chitosan hybrid nanoparticles to improve the oral bioavailability of raloxifene hydrochloride. The nanoparticles were formed by interaction of negatively charged soy lecithin with positively charged chitosan. The ratio of soy lecithin to chitosan was critical for the charge, and hence the size of the nanoparticles. The optimal soy lecithin to chitosan ratio was 20:1 to obtain nanoparticles with particle size of 208 ± 3 nm, a ζ-potential of 36 ± 2 mV and an entrapment efficiency of 73 ± 3%. The nanoparticles were also characterized by differential scanning calorimetry and FT-IR spectrophotometer. In-vitro drug release was assessed using dialysis bag method in pH 7.4 buffer. The drug loaded nanoparticles did not cause significant reduction in the cell viability at low doses. Pharmacokinetic studies in female Wistar rats showed significant improvement (~4.2 folds) in the oral bioavailability of the drug when loaded into nanoparticles. Further, the modified everted gut sac study showed that these nanoparticles are taken up by active endocytic processes in the intestine. The ex-vivo mucoadhesion studies proved that the nanoparticles get bound to the mucus layer of the intestine, which in turn correlates with reduced excretion of the drug in faeces. In conclusion, the proposed nanoparticles appear promising for effective oral delivery of poorly bioavailable drugs like raloxifene hydrochloride.

Oral Bioavailability Enhancement of Raloxifene with Nanostructured Lipid Carriers

Raloxifene hydrochloride (RLX) shows poor bioavailability (<2%), high inter-patient variability and extensive gut metabolism (>90%). The objective of this study was to develop nanostructured lipid carriers (NLCs) for RLX to enhance its bioavailability. The NLC formulations were produced with glyceryl tribehenate and oleic acid. The particle characteristics, entrapment efficiency (EE), differential scanning calorimetry (DSC), in vitro drug release, oral bioavailability (in rats) and stability studies were performed. The optimized nanoparticles were 120 ± 3 nm in size with positive zeta potential (14.4 ± 0.5 mV); % EE was over 90% with the drug loading of 5%. The RLX exists in an amorphous form in the lipid matrix. The optimized RLX-NLC formulation showed sustained release in vitro. The RLX-NLC significantly (p < 0.05) enhanced oral bioavailability 3.19-fold as compared to RLX-free suspension in female Wistar rats. The RLX-NLC can potentially enhance the oral bioavailability of RLX. It can also improve the storage stability.

Raloxifene/SBE-β-CD Inclusion Complexes Formulated into Nanoparticles with Chitosan to Overcome the Absorption Barrier for Bioavailability Enhancement

Raloxifene (RXF) is a hormone-like medication used for treating postmenopausal osteoporosis and estrogen-dependent breast cancer, yet associated with bad low bioavailability due to poor solubility. This study was intended to develop cyclodextrin/chitosan nanoparticles (ccNPs) for oral delivery of RXF in order to enhance the oral bioavailability. RXF-loaded ccNPs (RXF-ccNPs) were prepared by cyclodextrin inclusion followed by complexation with chitosan. RXF-ccNPs were fully characterized by particle size, morphology and in vitro drug release. The oral delivery efficacy and transepithelial transport potential were evaluated by pharmacokinetics, in situ single-pass intestinal perfusion, cellular uptake and ex vivo imaging. The resulting RXF-ccNPs were around 165 nm in particle size with a narrow distribution. The oral bioavailability of RXF was enhanced by 2.6 folds through ccNPs compared to RXF suspensions in rats. It was shown that RXF-ccNPs could improve the intestinal permeability of RXF, increase the cellular uptake of RXF and facilitate its transport across the absorptive epithelia. The results indicate that our developed ccNPs based on sulfobutylether-β-cyclodextrin and oligochitosan are a promising vehicle to orally deliver poorly water-soluble drugs over and above RXF.

Expression, regulation and function of intestinal drug transporters: an update

Although oral drug administration is currently the favorable route of administration, intestinal drug absorption is challenged by several highly variable and poorly predictable processes such as gastrointestinal motility, intestinal drug solubility and intestinal metabolism. One further determinant identified and characterized during the last two decades is the intestinal drug transport that is mediated by several transmembrane proteins such as P-gp, BCRP, PEPT1 and OATP2B1. It is well-established that intestinal transporters can affect oral absorption of many drugs in a significant manner either by facilitating their cellular uptake or by pumping them back to gut lumen, which limits their oral bioavailability. Their functional relevance becomes even more apparent in cases of unwanted drug-drug interactions when concomitantly given drugs that cause transporter induction or inhibition, which in turn leads to increased or decreased drug exposure. The longitudinal expression of several intestinal transporters is not homogeneous along the human intestine, which may have functional implications on the preferable site of intestinal drug absorption. Besides the knowledge about the expression of pharmacologically relevant transporters in human intestinal tissue, their exact localization on the apical or basolateral membrane of enterocytes is also of interest but in several cases debatable. Finally, there is obviously a coordinative interplay of intestinal transporters (apical-basolateral), intestinal enzymes and transporters as well as intestinal and hepatic transporters. This review aims to give an updated overview about the expression, localization, regulation and function of clinically relevant transporter proteins in the human intestine.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Raloxifene nanomicelles reduce the growth of castrate-resistant prostate cancer

BACKGROUND

Castrate-resistant prostate cancer (CRPC) patients are characterised by a 5-year relative survival rate of ∼25-33%. Recently, our laboratory encapsulated a selective oestrogen receptor modulator, raloxifene, into poly(styrene-co-maleic acid) (SMA-raloxifene), which demonstrated superior in vitro cytotoxicity compared with free drug against several CRPC cell lines.

PURPOSE

To validate SMA-raloxifene for the management of CRPC using a mouse xenograft model.

METHODS

The internalisation and retention of micellar and free raloxifene in vitro were measured by HPLC. A PC3-CRPC xenograft model was used to compare the biodistribution of both raloxifene formulations, as well as their effect on tumour progression where mice received free raloxifene (1 or 5 mg/kg, i.v.) or SMA-raloxifene (1 mg/kg, i.v.) weekly for 4 weeks.

RESULTS

SMA-raloxifene exhibited 75% higher intracellular content compared to free drug after 48 h in PC3 cells. Biodistribution of raloxifene was 69% higher in tumours following SMA-raloxifene compared with free raloxifene. Weekly administration of 1 mg/kg free raloxifene reduced tumour progression by 20% after 4 weeks, whereas 1 mg/kg SMA-raloxifene and 5 mg/kg free raloxifene reduced progression by 40%.

CONCLUSION

Encapsulation of raloxifene increased its therapeutic potential for the management of CRPC.

Milk Thistle Constituents Inhibit Raloxifene Intestinal Glucuronidation: A Potential Clinically Relevant Natural Product-Drug Interaction

Women at high risk of developing breast cancer are prescribed selective estrogen response modulators, including raloxifene, as chemoprevention. Patients often seek complementary and alternative treatment modalities, including herbal products, to supplement prescribed medications. Milk thistle preparations, including silibinin and silymarin, are top-selling herbal products that may be consumed by women taking raloxifene, which undergoes extensive first-pass glucuronidation in the intestine. Key constituents in milk thistle, flavonolignans, were previously shown to be potent inhibitors of intestinal UDP-glucuronosyl transferases (UGTs), with IC50s ≤ 10 μM. Taken together, milk thistle preparations may perpetrate unwanted interactions with raloxifene. The objective of this work was to evaluate the inhibitory effects of individual milk thistle constituents on the intestinal glucuronidation of raloxifene using human intestinal microsomes and human embryonic kidney cell lysates overexpressing UGT1A1, UGT1A8, and UGT1A10, isoforms highly expressed in the intestine that are critical to raloxifene clearance. The flavonolignans silybin A and silybin B were potent inhibitors of both raloxifene 4'- and 6-glucuronidation in all enzyme systems. The Kis (human intestinal microsomes, 27-66 µM; UGT1A1, 3.2-8.3 µM; UGT1A8, 19-73 µM; and UGT1A10, 65-120 µM) encompassed reported intestinal tissue concentrations (20-310 µM), prompting prediction of clinical interaction risk using a mechanistic static model. Silibinin and silymarin were predicted to increase raloxifene systemic exposure by 4- to 5-fold, indicating high interaction risk that merits further evaluation. This systematic investigation of the potential interaction between a widely used herbal product and chemopreventive agent underscores the importance of understanding natural product-drug interactions in the context of cancer prevention.

Efflux and uptake transporters involved in the disposition of bazedoxifene

Bazedoxifene, a novel selective estrogen receptor modulator, has complex pharmacokinetics with rapid absorption, high metabolic clearance, low oral bioavailability (6.25 %) and a slow elimination phase. Our hypothesis is that drug uptake and efflux transporters may play an important role in its disposition. To adequately cover all aspects of bazedoxifene transport, several approaches were undertaken: PAMPA assay, ATPase assay, membrane inside-out vesicles and Caco-2 and CHO cell lines. The results obtained from PAMPA experiments showed moderate passive permeability of bazedoxifene (P app ≈ 2 × 10(-6)cm/s), suggesting the existence of an active transport during the rapid absorption phase. The Caco-2 transport assay showed large and significant changes in the measured efflux ratios of bazedoxifene when selective transporter inhibitors were applied: verapamil (a Pgp inhibitor), MK571 (an MRP inhibitor), Ko143 (a BCRP inhibitor) and DIDS (an OATP inhibitor). Additionally, membrane preparation experiments demonstrated the interaction of bazedoxifene with P-gp, MRP2 and BCRP. CHO experiments did not show any interactions of bazedoxifene with OATP1B1 or OATP1B3; therefore, bazedoxifene may be a substrate of other OATP isoform(s). The comprehensive in vitro study indicates a strong involvement of Pgp, MRP, BCRP and OATP in bazedoxifene disposition.

Pharmacogenetics of osteoporosis

The challenge of personalized medicine is to move away from the traditional 'one-size-fits-all' pharmacology to genotype-based individualized therapies. As an individual's response to drugs is under the control of genes, personal genetic profiles could help clinicians to predict individual drug response and prescribe the right drug and dose, thereby optimising efficacy and avoiding risk of adverse effects. Currently, the concrete application of pharmacogenetics into clinical practice is limited to a few drugs, and the genetic prediction of drug response is far from clear for many of thve principal complex disorders. This is even more evident in the field of osteoporosis and metabolic bone disorders, for which few pharmacogenetic studies have been conducted, and no conclusive results are available. In this chapter, we review recent research on pharmacogenetics of osteoporosis, evaluate criticisms, and offer possible suggestions for improvements in this field and for possible future applications into clinical practice.

Inverse correlation of carotid intima-media thickness with raloxifene serum levels in osteoporosis

BACKGROUND

Raloxifene is a selective oestrogen receptor modulator with effects on bone and breast cancer and cardiovascular disease risk. The aim of this study was to examine the influence of raloxifene treatment on surrogate markers of atherosclerosis and the correlation of these markers with raloxifene serum concentrations.

METHODS

A prospective clinical trial on 53 postmenopausal osteoporotic women treated with raloxifene was performed. Surrogate markers of atherosclerosis (flow-mediated vasodilatation, glyceryltrinitrate-induced vasodilatation of the brachial artery, carotid intima-media thickness (c-IMT), inter-cell adhesion molecule-1, vascular-cell adhesion molecule-1 and E-selectin) were measured before and after 6 months of treatment. Serum concentrations of raloxifene and raloxifene metabolites were assessed after 12 months of treatment. The tested markers were correlated with measured serum concentrations of raloxifene species.

RESULTS

Among the tested surrogate markers of atherosclerosis c-IMT, E-selectin and ICAM changed significantly during treatment. A negative correlation of the non-metabolized raloxifene serum levels with the percentage change of c-IMT during treatment (r = - 0.315, p = 0.048) was found. Likewise, the sum of the levels of three raloxifene metabolites, raloxifene-6-b-glucuronide (M1), raloxifene-4'-b-glucuronide (M2) and raloxifene-6,4'-diglucuronide (M3) in serum showed a negative correlation with the percentage change of c-IMT during treatment (r = - 0.375, p = 0.017). For the other tested parameters, no correlation with raloxifene serum levels was found.

CONCLUSIONS

To the best of our knowledge, this is the first study correlating raloxifene species serum concentrations with changes in the surrogate markers of atherosclerosis. A greater decrease of c-IMT in patients with higher raloxifene concentrations could contribute to a lower risk of cardiovascular events in these patients.

The use of raloxifene in osteoporosis treatment

INTRODUCTION

Osteoporosis is a common disease characterized by the occurrence of fragility fractures. Major osteoporotic fractures are associated with decreased quality of life and high costs.

AREAS COVERED

This review summarizes clinical data on raloxifene (RLX), a second generation selective estrogen-receptor modulator (SERM), currently approved for the treatment of postmenopausal osteoporosis. RLX has estrogen effects on bone and lipid profile, whereas it has anti-estrogen effects on uterus and breast cells. Its main side effects are hot flushes and venous thromboembolism. Literature searches were conducted to retrieve articles reporting RLX clinical trial data. For comparison of safety and efficacy, post-marketing studies on RLX were included.

EXPERT OPINION

RLX is effective in reducing vertebral fracture risk in osteoporotic women, it is safe and its ability to prevent breast cancer has to be considered in the analyses of cost/effect and of the ideal candidate to this treatment. RLX has to be avoided in patients with previous history of venous thromboembolism.