Role of the breast cancer resistance protein (BCRP/ABCG2) in drug transport--an update

Cancer stem cells: advances in knowledge and implications for cancer therapy

Cancer stem cells (CSCs), a small subset of cells in tumors that are characterized by self-renewal and continuous proliferation, lead to tumorigenesis, metastasis, and maintain tumor heterogeneity. Cancer continues to be a significant global disease burden. In the past, surgery, radiotherapy, and chemotherapy were the main cancer treatments. The technology of cancer treatments continues to develop and advance, and the emergence of targeted therapy, and immunotherapy provides more options for patients to a certain extent. However, the limitations of efficacy and treatment resistance are still inevitable. Our review begins with a brief introduction of the historical discoveries, original hypotheses, and pathways that regulate CSCs, such as WNT/β-Catenin, hedgehog, Notch, NF-κB, JAK/STAT, TGF-β, PI3K/AKT, PPAR pathway, and their crosstalk. We focus on the role of CSCs in various therapeutic outcomes and resistance, including how the treatments affect the content of CSCs and the alteration of related molecules, CSCs-mediated therapeutic resistance, and the clinical value of targeting CSCs in patients with refractory, progressed or advanced tumors. In summary, CSCs affect therapeutic efficacy, and the treatment method of targeting CSCs is still difficult to determine. Clarifying regulatory mechanisms and targeting biomarkers of CSCs is currently the mainstream idea.

Oncostatin M reverses ABCG2-mediated mitoxantrone resistance

Mitoxantrone resistant variant of SW620 line was developed, characterized and subsequently used as a model system to determine oncostatin M ability to modulate MDR phenomenon. The selection regimen allowed for overexpression of ABCG2 and ABCB1 both at the RNA and protein level, which was further confirmed by functional assays. Oncostatin M supplementation resulted in partial reversal of MDR phenotype by decreasing overexpression of ABCG2 demonstrating for the first time the ability of this cytokine for selective down-regulation of one of MDR proteins.

Synergistic anticancer effects of doxorubicin and metformin combination therapy: A systematic review

INTRODUCTION

Doxorubicin (DOX) a chemotherapy drug often leads to the development of resistance, in cancer cells after prolonged treatment. Recent studies have suggested that using metformin plus doxorubicin could result in synergic effects. This study focuses on exploring the co-treat treatment of doxorubicin and metformin for various cancers.

METHOD

Following the PRISMA guidelines we conducted a literature search using different databases such as Embase, Scopus, Web of Sciences, PubMed, Science Direct and Google Scholar until July 2023. We selected search terms based on the objectives of this study. After screening a total of 30 articles were included.

RESULTS

The combination of doxorubicin and metformin demonstrated robust anticancer effects, surpassing the outcomes of monotherapy drug treatment. In vitro experiments consistently demonstrated inhibition of cancer cell growth and increased rates of cell death. Animal studies confirmed substantial reductions in tumor growth and improved survival rates, emphasizing the synergistic impact of the combined therapy. The research' discoveries collectively emphasize the capability of the co-treat doxorubicin-metformin as a compelling approach in cancer treatment, highlighting its potential to address medicate resistance and upgrade generally helpful results.

CONCLUSION

The findings of this study show that the combined treatment regimen including doxorubicin and metformin has significant promise in fighting cancer. The observed synergistic effects suggest that this combination therapy could be valuable, in a setting. This study highlights the need for clinical research to validate and enhance the application of the doxorubicin metformin regimen.

Purpurogallin carboxylic acid exhibits synergistic effects with 5‑fluorouracil on liver cancer cells in vitro by targeting ABCG2

Purpurogallin carboxylic acid (PCA) is a natural phenol compound derived from Macleaya microcarpa (Maxim.) Fedde, which exerts particular antioxidant and anti-inflammatory capacities. However, the effects and mechanisms of PCA on liver cancer cells remain unknown. Therefore, network pharmacology and computer virtual docking were used to identify the target-proteins of PCA. In addition, surface plasmon resonance, protease activity and rhodamine excretion assays were carried out to evaluate the effects of PCA on the activity of ATP binding cassette subfamily G member 2 (ABCG2). The synergistic effects of PCA and 5-fluorouracil (5-FU) on liver cancer cell proliferation, cell cycle arrest, colony formation and spheroid formation abilities in vitro were determined by Cell Counting Kit-8 (CCK-8) assay, flow cytometry, western blot analysis, colony formation and spheroid formation assays, respectively. ABCG2 was identified as a potential target of PCA, with a high docking score. The equilibrium dissociation constant of PCA for ABCG2 protein was 1.84 µM, while the median inhibitory concentration of this protein was 3.09 µM. In addition, the results demonstrated that PCA could significantly reduce the drug efflux capacity of liver cancer cells. CCK-8 assays revealed that liver cancer cell treatment with 10 µM PCA and 10 µM 5-FU exhibited the most potent synergistic effects on liver cancer cell proliferation at 48 h. Additionally, cell co-treatment with PCA and 5-FU also significantly attenuated the colony and spheroid formation abilities of liver cancer cells in vitro, while it promoted their arrest at the G1 phase of the cell cycle. Furthermore, ABCG2 silencing in liver cancer cells notably abrogated the synergistic effects of PCA and 5-FU. In conclusion, the present study demonstrated that PCA exhibited synergistic effects with 5-FU on liver cancer cells in vitro via targeting ABCG2. Therefore, PCA combined with 5-FU may be a potential strategy for liver cancer therapy.

Enhancing PDT efficacy in NMIBC: Efflux inhibitor mediated improvement of PpIX levels and efficacy of the combination of PpIX-PDT and SO-cleavable prodrugs

Protoporphyrin IX (PpIX)-based photodynamic therapy (PDT) has shown limited efficacy in nonmuscle-invasive bladder cancer (NMIBC). To improve PDT efficacy, we developed singlet oxygen-cleavable prodrugs. These prodrugs, when combined with PpIX-PDT, induce cancer cell death through both PDT and drug release mechanisms. Inhibition of PpIX efflux was reported to be an effective strategy to improve PpIX-PDT in certain cancer cells. Our main goal was to investigate whether adding an efflux inhibitor to the combination of PpIX and prodrugs can improve the PpIX levels in bladder cancer cells and the release of active drugs, thus improving the overall efficacy of the treatment. We treated bladder cancer cell lines with lapatinib and evaluated intracellular PpIX fluorescence, finding significantly increased accumulation. Combining lapatinib with prodrugs led to significantly reduced cell viability compared to prodrugs or PpIX-PDT alone. The effect of lapatinib depended on the expression level of the efflux pump in bladder cancer cells. Interestingly, lapatinib increased paclitaxel (PTX) prodrug uptake by threefold compared to prodrug alone. Adding an efflux inhibitor (e.g., lapatinib) into bladder instillation solutions could be a straightforward and effective strategy for NMIBC treatment, particularly in tumors expressing efflux pumps, with the potential for clinical translation.

Cadmium transport by mammalian ATP-binding cassette transporters

Cellular responses to toxic metals depend on metal accessibility to intracellular targets, reaching interaction sites, and the intracellular metal concentration, which is mainly determined by uptake pathways, binding/sequestration and efflux pathways. ATP-binding cassette (ABC) transporters are ubiquitous in the human body-usually in epithelia-and are responsible for the transfer of indispensable physiological substrates (e.g. lipids and heme), protection against potentially toxic substances, maintenance of fluid composition, and excretion of metabolic waste products. Derailed regulation and gene variants of ABC transporters culminate in a wide array of pathophysiological disease states, such as oncogenic multidrug resistance or cystic fibrosis. Cadmium (Cd) has no known physiological role in mammalians and poses a health risk due to its release into the environment as a result of industrial activities, and eventually passes into the food chain. Epithelial cells, especially within the liver, lungs, gastrointestinal tract and kidneys, are particularly susceptible to the multifaceted effects of Cd because of the plethora of uptake pathways available. Pertinent to their broad substrate spectra, ABC transporters represent a major cellular efflux pathway for Cd and Cd complexes. In this review, we summarize current knowledge concerning transport of Cd and its complexes (mainly Cd bound to glutathione) by the ABC transporters ABCB1 (P-glycoprotein, MDR1), ABCB6, ABCC1 (multidrug resistance related protein 1, MRP1), ABCC7 (cystic fibrosis transmembrane regulator, CFTR), and ABCG2 (breast cancer related protein, BCRP). Potential detoxification strategies underlying ABC transporter-mediated efflux of Cd and Cd complexes are discussed.

Inhibition of human drug transporter activities by succinate dehydrogenase inhibitors

Succinate dehydrogenase inhibitors (SDHIs) are widely-used fungicides, to which humans are exposed and for which putative health risks are of concern. In order to identify human molecular targets for these environmental chemicals, the interactions of 15 SDHIs with activities of main human drug transporters implicated in pharmacokinetics were investigated in vitro. 5/15 SDHIs, i.e., benzovindiflupyr, bixafen, fluxapyroxad, pydiflumetofen and sedaxane, were found to strongly reduce activity of the renal organic anion transporter (OAT) 3, in a concentration-dependent manner (with IC50 values in the 1.0-3.9 μM range), without however being substrates for OAT3. Moreover, these 5/15 SDHIs decreased the membrane transport of estrone-3 sulfate, an endogenous substrate for OAT3, and sedaxane was predicted to inhibit in vivo OAT3 activity in response to exposure to the acceptable daily intake (ADI) dose. In addition, pydiflumetofen strongly inhibited the renal organic cation transporter (OCT) 2 (IC50 = 2.0 μM) and benzovindiflupyr the efflux pump breast cancer resistance protein (BCRP) (IC50 = 3.9 μM). Other human transporters, including organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 as well as multidrug and toxin extrusion protein (MATE) 1 and MATE2-K were moderately or weakly inhibited by SDHIs, whereas P-glycoprotein, multidrug resistance-associated protein (MRP), OCT1 and OAT1 activities were not or only marginally impacted. Then, some human drug transporters, especially OAT3, constitute molecular targets for SDHIs. This could have toxic consequences, notably with respect to levels of endogenous compounds and metabolites substrates for the considered transporters or to potential SDHI-drug interactions. This could therefore contribute to putative health risk of these fungicides.

Major Genetic Drivers of Statin Treatment Response in African Populations and Pharmacogenetics of Dyslipidemia Through a One Health Lens

A One Health lens is increasingly significant to address the intertwined challenges in planetary health concerned with the health of humans, nonhuman animals, plants, and ecosystems. A One Health approach can benefit the public health systems in Africa that are overburdened by noncommunicable, infectious, and environmental diseases. Notably, the COVID-19 pandemic revealed the previously overlooked two-fold importance of pharmacogenetics (PGx), for individually tailored treatment of noncommunicable diseases and environmental pathogens. For example, dyslipidemia, a common cardiometabolic risk factor, has been identified as an independent COVID-19 severity risk factor. Observational data suggest that patients with COVID-19 infection receiving lipid-lowering therapy may have better outcomes. However, among African patients, the response to these drugs varies from patient to patient, pointing to the possible contribution of genetic variation in important pharmacogenes. The PGx of lipid-lowering therapies may underlie differences in treatment responses observed among dyslipidemia patients as well as patients comorbid with COVID-19 and dyslipidemia. Genetic variations in APOE, ABCB1, CETP, CYP2C9, CYP3A4, CYP3A5, HMGCR, LDLR, NPC1L1, and SLCO1B1 genes affect the pharmacogenomics of statins, and they have individually been linked to differential responses to dyslipidemia and COVID-19 treatment. African populations are underrepresented in PGx research. This leads to poor accounting of additional diverse genetic variants that could be important in understanding interindividual and between-population variations in therapeutic responses to dyslipidemia and COVID-19. This expert review examines and synthesizes the salient and priority PGx variations, as seen through a One Health lens in Africa, to improve and inform personalized medicine in both dyslipidemia and COVID-19.

Recent strategies to overcome breast cancer resistance

Breast cancer is potentially a lethal disease and a leading cause of death in women. Chemotherapy and radiotherapy are the most frequently used treatment options. Drug resistance in advanced breast cancer limits the therapeutic output of treatment. The leading cause of resistance in breast cancer is endocrine and hormonal imbalance, particularly in triple negative and HER2 positive breast cancers. The efflux of drugs due to p-gp's activity is another leading cause of resistance. Breast cancer resistant protein also contributes significantly. Strategies used to combat resistance include the use of nanoparticles to target drug delivery by co-delivery of chemotherapeutic drugs and genes (siRNA and miRNA) that help to down-regulate genes causing resistance. The siRNA is specific and effectively silences p-gp and other proteins causing resistance. The use of chemosensitizers is also effective in overcoming resistance. Chemo-sensitizers sensitize cancer cells to the effects of chemotherapeutic drugs. Novel anti-neoplastic agents such as antibody-drug conjugates and mesenchymal stem cells are also effective tools used to improve the therapeutic response in breast cancer. Similarly, combination of photo/thermal ablation with chemotherapy can act to overcome breast cancer resistance. In this review, we focus on the mechanism of breast cancer resistance and the nanoparticle-based strategies used to combat resistance in breast cancer.

Successful Prediction of Fetal Exposure to Dual BCRP/P-gp Drug Substrates Using the Efflux Ratio-Relative Expression Factor Approach and PBPK M&S

To inform fetal drug safety, it is important to determine or predict fetal drug exposure throughout pregnancy. The former is not possible in the first or second trimester. In contrast, at the time of birth, fetal drug exposure, relative to maternal exposure, can be estimated as Kp,uu (unbound fetal umbilical venous (UV) plasma area under the curve (AUC)/unbound maternal plasma (MP) AUC), provided the observed UV/MP values, spanning the dosing interval, are available from multiple maternal-fetal dyads. However, this fetal Kp,uu cannot be extrapolated to other drugs. To overcome the above limitations, we have used an efflux ratio-relative expression factor (ER-REF) approach to successfully predict the fetal Kp,uu of P-gp substrates. Because many drugs taken by pregnant people are also BCRP substrates, here, we extend this approach to drugs that are effluxed by both placental BCRP and P-gp or P-gp alone. To verify our predictions, we chose drugs for which UV/MP data were available at term: glyburide and imatinib (both BCRP and P-gp substrates) and nelfinavir (only P-gp substrate). First, the ER of the drugs was determined using Transwells and MDCKII cells expressing either BCRP or P-gp. Then, the ER was scaled using the proteomics-informed REF value to predict the fetal Kp,uu of the drug at term. The ER-REF predicted fetal Kp,uu of glyburide (0.43), imatinib (0.42), and nelfinavir (0.40) fell within two-fold of the corresponding in vivo fetal Kp,uu (0.44, 0.37, and 0.46, respectively). These data confirm that the ER-REF approach can successfully predict fetal drug exposure to BCRP/P-gp and P-gp substrates, at term.

Clinical Evaluation of the Effect of Encorafenib on Bupropion, Rosuvastatin, and Coproporphyrin I and Considerations for Statin Coadministration

BACKGROUND AND OBJECTIVES

Encorafenib is a kinase inhibitor indicated for the treatment of patients with unresectable or metastatic melanoma or metastatic colorectal cancer, respectively, with selected BRAF V600 mutations. A clinical drug-drug interaction (DDI) study was designed to evaluate the effect of encorafenib on rosuvastatin, a sensitive substrate of OATP1B1/3 and breast cancer resistance protein (BCRP), and bupropion, a sensitive CYP2B6 substrate. Coproporphyrin I (CP-I), an endogenous substrate for OATP1B1, was measured in a separate study to deconvolute the mechanism of transporter DDI.

METHODS

DDI study participants received a single oral dose of rosuvastatin (10 mg) and bupropion (75 mg) on days - 7, 1, and 14 and continuous doses of encorafenib (450 mg QD) and binimetinib (45 mg BID) starting on day 1. The CP-I data were collected from participants in a phase 3 study who received encorafenib (300 mg QD) and cetuximab (400 mg/m2 initial dose, then 250 mg/m2 QW). Pharmacokinetic and pharmacodynamic analysis was performed using noncompartmental and compartmental methods.

RESULTS

Bupropion exposure was not increased, whereas rosuvastatin Cmax and area under the receiver operating characteristic curve (AUC) increased approximately 2.7 and 1.6-fold, respectively, following repeated doses of encorafenib and binimetinib. Increase in CP-I was minimal, suggesting that the primary effect of encorafenib on rosuvastatin is through BCRP. Categorization of statins on the basis of their metabolic and transporter profile suggests pravastatin would have the least potential for interaction when coadministered with encorafenib.

CONCLUSION

The results from these clinical studies suggest that encorafenib does not cause clinically relevant CYP2B6 induction or inhibition but is an inhibitor of BCRP and may also inhibit OATP1B1/3 to a lesser extent. Based on these results, it may be necessary to consider switching statins or reducing statin dosage accordingly for coadministration with encorafenib.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT03864042, registered 6 March 2019.

Impact of Hyperuricemia and Urate-Lowering Agents on Cardiovascular Diseases

The association between hyperuricemia and cardiovascular diseases has been studied for many years. Research has shown a link between high uric acid levels and increased risk of including coronary artery disease hypertension and other cardiovascular conditions. Urate-lowering therapy, particularly with xanthine oxidase inhibitors like allopurinol, has shown promising results in reducing blood pressure in individuals with hyperuricemia and hypertension. Clinical trials and studies have demonstrated significant reductions in both systolic and diastolic blood pressure with urate-lowering treatment. Urate-lowering treatment has shown a favorable effect on reducing systolic blood pressure and major adverse cardiovascular events in patients with previous cardiovascular disease. In terms of cardiovascular safety, clinical trials have indicated that xanthine oxidase inhibitors such as febuxostat are non-inferior to allopurinol and do not increase the risk of death or serious adverse events. Overall, these findings highlight the importance of managing hyperuricemia and utilizing urate-lowering therapy to mitigate the adverse cardiovascular effects associated with elevated uric acid levels.

Lycium barbarum polysaccharide reverses drug resistance in oxaliplatin-resistant colon cancer cells by inhibiting PI3K/AKT-dependent phosphomannose isomerase

Objective: Here, we aimed to explore the effect of LBP in combination with Oxaliplatin (OXA) on reversing drug resistance in colon cancer cells through in vitro and in vivo experiments. We also aimed to explore the possible mechanism underlying this effect. Finally, we aimed to determine potential targets of Lycium barbarum polysaccharide (LBP) in colon cancer (CC) through network pharmacology and molecular docking. Methods: The invasion ability of colon cancer cells was assessed using the invasion assay. The migration ability of these cells was assessed using the migration assay and wound healing assay. Cell cycle analysis was carried out using flow cytometry. The expression levels of phosphomannose isomerase (PMI) and ATP-binding cassette transport protein of G2 (ABCG2) proteins were determined using immunofluorescence and western blotting. The expression levels of phosphatidylinositol3-kinase (PI3K), protein kinase B (AKT), B-cell lymphoma 2 (Bcl-2), and BCL2-Associated X (Bax) were determined using western blotting. Forty BALB/c nude mice purchased from Weitong Lihua, Beijing, for the in vivo analyses. The mice were randomly divided into eight groups. They were administered HCT116 and HCT116-OXR cells to prepare colon cancer xenograft models and then treated with PBS, LBP (50 mg/kg), OXA (10 mg/kg), or LBP + OXA (50 mg/kg + 10 mg/kg). The tumor weight and volume of treated model mice were measured, and organ toxicity was evaluated using hematoxylin and eosin staining. The expression levels of PMI, ABCG2, PI3K, and AKT proteins were then assessed using immunohistochemistry. Moreover, PMI and ABCG2 expression levels were analyzed using immunofluorescence and western blotting. The active components and possible targets of LBP in colon cancer were explored using in silico analysis. GeneCards was used to identify CC targets, and an online Venn analysis tool was used to determine intersection targets between these and LBP active components. The PPI network for intersection target protein interactions and the PPI network for interactions between the intersection target proteins and PMI was built using STRING and Cytoscape. To obtain putative targets of LBP in CC, we performed GO function enrichment and KEGG pathway enrichment analyses. Results: Compared with the HCT116-OXR blank treatment group, both invasion and migration abilities of HCT116-OXR cells were inhibited in the LBP + OXA (2.5 mg/mL LBP, 10 μΜ OXA) group (p < 0.05). Cells in the LBP + OXA (2.5 mg/mL LBP, 10 μΜ OXA) group were found to arrest in the G1 phase of the cell cycle. Knockdown of PMI was found to downregulate PI3K, AKT, and Bcl-2 (p < 0.05), while it was found to upregulate Bax (p < 0.05). After treatment with L. barbarum polysaccharide, 40 colon cancer subcutaneous tumor models showed a decrease in tumor size. There was no difference in the liver index after LBP treatment (p > 0.05). However, the spleen index decreased in the OXA and LBP + OXA groups (p < 0.05), possibly as a side effect of oxaliplatin. Immunohistochemistry, immunofluorescence, and western blotting showed that LBP + OXA treatment decreased PMI and ABCG2 expression levels (p < 0.05). Moreover, immunohistochemistry showed that LBP + OXA treatment decreased the expression levels of PI3K and AKT (p < 0.05). Network pharmacology analysis revealed 45 active LBP components, including carotenoids, phenylpropanoids, quercetin, xanthophylls, and other polyphenols. It also revealed 146 therapeutic targets of LBP, including AKT, SRC, EGFR, HRAS, STAT3, and MAPK3. KEGG pathway enrichment analysis showed that the LBP target proteins were enriched in pathways, including cancer-related signaling pathways, PI3K/AKT signaling pathway, and IL-17 signaling pathways. Finally, molecular docking experiments revealed that the active LBP components bind well with ABCG2 and PMI. conclusion: Our in vitro experiments showed that PMI knockdown downregulated PI3K, AKT, and Bcl-2 and upregulated Bax. This finding confirms that PMI plays a role in drug resistance by regulating the PI3K/AKT pathway and lays a foundation to study the mechanism underlying the reversal of colon cancer cell drug resistance by the combination of LBP and OXA. Our in vivo experiments showed that LBP combined with oxaliplatin could inhibit tumor growth. LBP showed no hepatic or splenic toxicity. LBP combined with oxaliplatin could downregulate the expression levels of PMI, ABCG2, PI3K, and AKT; it may thus have positive significance for the treatment of advanced metastatic colon cancer. Our network pharmacology analysis revealed the core targets of LBP in the treatment of CC as well as the pathways they are enriched in. It further verified the results of our in vitro and in vivo experiments, showing the involvement of multi-component, multi-target, and multi-pathway synergism in the drug-reversing effect of LBP in CC. Overall, the findings of the present study provide new avenues for the future clinical treatment of CC.

Impact of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) on the expression and function of hepatobiliary transporters: A comprehensive mechanistic review

The liver plays a central role in the biotransformation and disposition of endogenous molecules and xenobiotics. In addition to drug-metabolizing enzymes, transporter proteins are key determinants of drug hepatic clearance. Hepatic transporters are transmembrane proteins that facilitate the movement of chemicals between sinusoidal blood and hepatocytes. Other drug transporters translocate molecules from hepatocytes into bile canaliculi for biliary excretion. The formers are known as basolateral, while the latter are known as canalicular transporters. Also, these transporters are classified into two super-families, the solute carrier transporter (SLC) and the adenosine triphosphate (ATP)-binding cassette (ABC) transporter. The expression and function of transporters involve complex regulatory mechanisms, which are contributing factors to interindividual variability in drug pharmacokinetics and disposition. A considerable number of liver diseases are known to alter the expression and function of drug transporters. Among them, non-alcoholic fatty liver disease (NAFLD) is a chronic condition with a rapidly increasing incidence worldwide. NAFLD, recently reclassified as metabolic dysfunction-associated steatotic liver disease (MASLD), is a disease continuum that includes steatosis with or without mild inflammation (NASH), and potentially neuroinflammatory pathology. NASH is additionally characterized by the presence of hepatocellular injury. During NAFLD and NASH, drug transporters exhibit altered expression and function, leading to altered drug pharmacokinetics and pharmacodynamics, thus increasing the risk of adverse drug reactions. The purpose of the present review is to provide comprehensive mechanistic information on the expression and function of hepatic transporters under fatty liver conditions and hence, the impact on the pharmacokinetic profiles of certain drugs from the available pre-clinical and clinical literature.

A time-resolved Förster resonance energy transfer assay to investigate drug and inhibitor binding to ABCG2

The human ATP-binding cassette (ABC) transporter, ABCG2, is responsible for multidrug resistance in some tumours. Detailed knowledge of its activity is crucial for understanding drug transport and resistance in cancer, and has implications for wider pharmacokinetics. The binding of substrates and inhibitors is a key stage in the transport cycle of ABCG2. Here, we describe a novel binding assay using a high affinity fluorescent inhibitor based on Ko143 and time-resolved Förster resonance energy transfer (TR-FRET) to measure saturation binding to ABCG2. This binding is displaced by Ko143 and other known ABCG2 ligands, and is sensitive to the addition of AMP-PNP, a non-hydrolysable ATP analogue. This assay complements the arsenal of methods for determining drug:ABCG2 interactions and has the possibility of being adaptable for other multidrug pumps.

Short-chain fatty acids (SCFA) in infants' plasma and corresponding mother's milk and plasma in relation to subsequent sensitisation and atopic disease

BACKGROUND

Short-chain fatty acids (SCFAs) in intestinal contents may influence immune function, while less is known about SCFAs in blood plasma. The aims were to investigate the relation between infants' and maternal plasma SCFAs, as well as SCFAs in mother's milk, and relate SCFA concentrations in infant plasma to subsequent sensitisation and atopic disease.

METHODS

Infant plasma (N = 148) and corresponding mother's milk and plasma were collected four months postpartum. Nine SCFA (formic, acetic, propionic, isobutyric, butyric, succinic, valeric, isovaleric, and caproic acid) were analysed by UPLC-MS. At 12 months of age, atopic disease was diagnosed by a pediatric allergologist, and sensitisation was measured by skin prick test. All families participated in the Swedish birth cohort NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment).

FINDINGS

Infants with sensitisation, atopic eczema, or food allergy had significantly lower concentrations of five, three, and two SCFAs, respectively, in plasma at four months. Logistic regressions models showed significant negative associations between formic, succinic, and caproic acid and sensitisation [ORadj (95% CI) per SD: 0.41 (0.19-0.91); 0.19 (0.05-0.75); 0.25 (0.09-0.66)], and between acetic acid and atopic eczema [0.42 (0.18-0.95)], after adjusting for maternal allergy. Infants' and maternal plasma SCFA concentrations correlated strongly, while milk SCFA concentrations were unrelated to both. Butyric and caproic acid concentrations were enriched around 100-fold, and iso-butyric and valeric acid around 3-5-fold in mother's milk, while other SCFAs were less prevalent in milk than in plasma.

INTERPRETATION

Butyric and caproic acid might be actively transported into breast milk to meet the needs of the infant, although mechanistic studies are needed to confirm this. The negative associations between certain SCFAs on sensitisation and atopic disease adds to prior evidence regarding their immunoregulatory potential.

FUNDING

Swedish Research Council (Nr. 2013-3145, 2019-0137 and 2023-02217 to A-S.S.), Swedish Research Council for Health, Working Life and Welfare FORTE, Nr 2018-00485 to A.W.), The Swedish Asthma and Allergy Association's Research Fund (2020-0020 to A.S.).

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

Screening Peptide-Binding Partners for GenX via Phage Display

Per- and poly-fluoroalkyl substances (PFAS), such as GenX, are a class of highly stable synthetic compounds that have recently become the focus of environmental remediation endeavors due to their toxicity. While considerable strides have been made in PFAS remediation, the diversity of these compounds, and the costs associated with approaches such as ion exchange resins and advanced oxidation technologies, remain challenging for widespread application. In addition, little is known about the potential binding and impacts of GenX on human proteins. To address these issues, we applied phage display and screened short peptides that bind specifically to GenX, with the ultimate goal of identifying human proteins that bind with GenX. In this study we identified the amino acids that contribute to the binding and measured the binding affinities of the two discovered peptides with NMR. A human protein, ankyrin-repeat-domain-containing protein 36B, with matching sequences of one of the peptides, was identified, and the binding positions were predicted by docking and molecular dynamics simulation. This study created a platform to screen peptides that bind with toxic chemical compounds, which ultimately helped us identify biologically relevant molecules that could be inhibited by the GenX, and also provided information that will contribute to future bioengineered GenX-binding device design.

Blood-brain barrier transporters: An overview of function, dysfunction in Alzheimer's disease and strategies for treatment

The blood-brain-barrier (BBB) has a major function in maintaining brain homeostasis by regulating the entry of molecules from the blood to the brain. Key players in BBB function are BBB transporters which are highly expressed in brain endothelial cells (BECs) and critical in mediating the exchange of nutrients and waste products. BBB transporters can also influence drug delivery into the brain by inhibiting or facilitating the entry of brain targeting therapeutics for the treatment of brain disorders, such as Alzheimer's disease (AD). Recent studies have shown that AD is associated with a disrupted BBB and transporter dysfunction, although their roles in the development in AD are not fully understand. Modulation of BBB transporter activity may pose a novel approach to enhance the delivery of drugs to the brain for enhanced treatment of AD. In this review, we will give an overview of key functions of BBB transporters and known changes in AD. In addition, we will discuss current strategies for transporter modulation for enhanced drug delivery into the brain.

Carboranes as Potent Phenyl Mimetics: A Comparative Study on the Reversal of ABCG2-Mediated Drug Resistance by Carboranylquinazolines and Their Organic Isosteres

Multidrug resistance is a major challenge in clinical cancer therapy. In particular, overexpression of certain ATP-binding cassette (ABC) transporter proteins, like the efflux transporter ABCG2, also known as breast cancer resistance protein (BCRP), has been associated with the development of resistance to applied chemotherapeutic agents in cancer therapies, and therefore targeted inhibition of BCRP-mediated transport might lead to reversal of this (multidrug) resistance (MDR). In a previous study, we have described the introduction of a boron-carbon cluster, namely closo-dicarbadodecaborane or carborane, as an inorganic pharmacophore into a polymethoxylated 2-phenylquinazolin-4-amine backbone. In this work, the scope was extended to the corresponding amide derivatives. As most of the amide derivatives suffered from poor solubility, only the amide derivative QCe and the two amine derivatives DMQCc and DMQCd were further investigated. Carboranes are often considered as sterically demanding phenyl mimetics or isosteres. Therefore, the organic phenyl and sterically demanding adamantyl analogues of the most promising carborane derivatives were also investigated. The studies showed that the previously described DMQCd, a penta-methoxylated N-carboranyl-2-phenylquinazolin-4-amine, was by far superior to its organic analogues in terms of cytotoxicity, inhibition of the human ABCG2 transporter, as well as the ability to reverse BCRP-mediated mitoxantrone resistance in MDCKII-hABCG2 and HT29 colon cancer cells. Our results indicate that DMQCd is a promising candidate for further in vitro as well as in vivo studies in combination therapy for ABCG2-overexpressing cancers.

Investigation of the Effect of Lasmiditan on the Pharmacokinetics of P-Glycoprotein and Breast Cancer Resistance Protein Substrates

Lasmiditan is an in vitro inhibitor of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) efflux transporters. We aimed to confirm predictions from physiologically based pharmacokinetic models of lasmiditan, and assess the safety and tolerability of rosuvastatin and dabigatran co-administered with lasmiditan. In this open-label, post-marketing drug-drug interaction, phase 1 clinical trial, eligible participants were adults aged 21-70 years with a body mass index of 18.5-35.0 kg/m2 . Part 1 (P-gp, 150 mg dabigatran etexilate with 200 mg lasmiditan) and part 2 (BCRP, 10 mg rosuvastatin with 200 mg lasmiditan) employed similar designs: a single dose of probe substrate administered on day -2 with pharmacokinetic evaluation; 1-week washout; lasmiditan administered on days 8 and 9 alone; lasmiditan co-administered with a single dose of probe substrate on day 10, with pharmacokinetic evaluation of probe substrate and lasmiditan. Sixty-six participants were included in part 1 and 30 participants were included in part 2. Following dabigatran co-administration with lasmiditan, versus dabigatran alone, 90% confidence intervals for geometric least-squares (LS) mean ratios of area under the plasma concentration-time curve from time 0 extrapolated to infinity (AUC0-∞ ) and maximum observed drug concentration (Cmax ) were not contained within the non-effect boundaries (0.80 to 1.25). Dabigatran AUC0-∞ increased by 25% and Cmax increased by 22%. The median time of maximum observed drug concentration (tmax ) for dabigatran was 2.0 to 3.0 hours. Following rosuvastatin co-administration with lasmiditan, versus rosuvastatin alone, 90%CIs for geometric LS mean ratios of AUC0-∞ and Cmax were contained within non-effect boundaries (0.80-1.25). Rosuvastatin AUC0-∞ increased by 15% and Cmax increased by 7%. The median tmax for rosuvastatin was 4.0 hours. Results suggest that lasmiditan has a weak effect on P-gp substrates and no clinically relevant effect on BCRP substrates.

Ningalins, Pyrrole-Bearing Metabolites Isolated from Didemnum spp. Synthesis and MDR-Reversion Activity in Cancer Therapy

Multi-Drug Resistance (MDR) is one of the most frequent problems observed in the course of cancer chemotherapy. Cells under treatment, tend to develop survival mechanisms to drug-action thus generating drug-resistance. One of the most important mechanism to get it is the over expression of P-gp glycoprotein, which acts as an efflux-pump releasing the drug outside of the cancer cell. A strategy for a succesfull treatment consists in the co-administration of one compound that acts against P-gp and another which acts against the cell during chemotherapy. Ningalins are pyrrole-containing naturally occurring compounds isolated mainly from the marine tunicate Didemnum spp and also they are some of the top reversing agents in MDR treatment acting on P-gp. Considering the relevance displayed for some of these isolated alkaloids or their core as a drug for co-administration in cancer therapy, all the total synthesis described to date for the members of ningalins family are reviewed herein.

[Mechanisms of cancer drug resistance]

Despite decades of research into the molecular mechanisms of cancer and the development of new treatments, drug resistance persists as a major problem. This is in part due to the heterogeneity of cancer, including the diversity of tumor cell lineage and cell plasticity, the spectrum of somatic mutations, the complexity of microenvironments, and immunosuppressive characteristic, then necessitating the use of many different therapeutic approaches. We summarize here the biological causes of resistance, thus offering new perspectives for tackle drug resistance.

Sniping Cancer Stem Cells with Nanomaterials

Cancer stem cells (CSCs) drive tumor initiation, progression, and therapeutic resistance due to their self-renewal and differentiation capabilities. Despite encouraging progress in cancer treatment, conventional approaches often fail to eliminate CSCs, necessitating the development of precise targeted strategies. Recent advances in materials science and nanotechnology have enabled promising CSC-targeted approaches, harnessing the power of tailoring nanomaterials in diverse therapeutic applications. This review provides an update on the current landscape of nanobased precision targeting approaches against CSCs. We elucidate the nuanced application of organic, inorganic, and bioinspired nanomaterials across a spectrum of therapeutic paradigms, encompassing targeted therapy, immunotherapy, and multimodal synergistic therapies. By examining the accomplishments and challenges in this potential field, we aim to inform future efforts to advance nanomaterial-based therapies toward more effective "sniping" of CSCs and tumor clearance.

GSK2606414 Sensitizes ABCG2-Overexpressing Multidrug-Resistant Colorectal Cancer Cells to Chemotherapeutic Drugs

Colorectal cancer is a common malignant tumor. A major factor in the high mortality rate of colorectal cancer is the emergence of multidrug resistance (MDR). Overexpression of the ABCG2 gene in cancer cells directly leads to MDR. Finding new inhibitors of ABCG2 may be an effective way to overcome drug resistance. We found that the compound GSK2606414 enhanced the sensitivity of the ABCG2 substrate to the chemotherapeutic drugs mitoxantrone and doxorubicin in ABCG2-overexpressing multidrug-resistant colorectal cancer cells by increasing their intracellular accumulation without affecting the protein expression of ABCG2. Molecular docking experiments predicted that GSK2606414 could stably bind in the drug-binding pocket of ABCG2. In conclusion, GSK2606414 can sensitize ABCG2-overexpressed multidrug-resistant colorectal cancer cells to chemotherapy drugs and can be used as a potential inhibitor of ABCG2.

Machine learning models based on residue interaction network for ABCG2 transportable compounds recognition

As the one of the most important protein of placental transport of environmental substances, the identification of ABCG2 transport molecules is the key step for assessing the risk of placental exposure to environmental chemicals. Here, residue interaction network (RIN) was used to explore the difference of ABCG2 binding conformations between transportable and non-transportable compounds. The RIN were treated as a kind of special quantitative data of protein conformation, which not only reflected the changes of single amino acid conformation in protein, but also indicated the changes of distance and action type between amino acids. Based on the quantitative RIN, four machine learning algorithms were applied to establish the classification and recognition model for 1100 compounds with transported by ABCG2 potential. The random forest (RF) models constructed with RIN presented the best and satisfied predictive ability with an accuracy of training set of 0.97 and the test set of 0.96 respectively. In conclusion, the construction of residue interaction network provided a new perspective for the quantitative characterization of protein conformation and the establishment of prediction models for transporter molecular recognition. The ABCG2 transport molecular recognition model based on residue interaction network provides a possible way for screening environmental chemistry transported through placenta.

Hollow MIL-125 Nanoparticles Loading Doxorubicin Prodrug and 3-Methyladenine for Reversal of Tumor Multidrug Resistance

Multidrug resistance (MDR) is a key factor in chemotherapy failure and tumor recurrence. The inhibition of drug efflux and autophagy play important roles in MDR therapy. Herein, a multifunctional delivery system (HA-MIL-125@DVMA) was prepared for synergistically reverse tumor MDR. Tumor-targeted hollow MIL-125-Ti nanoparticles were used to load the doxorubicin-vitamin E succinate (DV) prodrug and 3-methyladenine (3-MA) to enhance reverse MDR effects. The pH-sensitive DV can kill tumor cells and inhibit P-gp-mediated drug efflux, and 3-MA can inhibit autophagy. HA-MIL-125@DVMA had uniformly distributed particle size and high drug-load content. The nanoparticles could effectively release the drugs into tumor microenvironment due to the rapid hydrazone bond-breaking under low pH conditions, resulting in a high cumulative release rate. In in vitro cellular experiments, the accumulation of HA-MIL-125@DVMA and HA-MIL-125@DV in MCF-7/ADR cells was significantly higher than that in the control groups. Moreover, the nanoparticles significantly inhibited drug efflux in the cells, ensuring the accumulation of the drugs in cell cytoplasm and causing drug-resistant cells' death. Importantly, HA-MIL-125@DVMA effectively inhibited tumor growth without changes in body weight in tumor-bearing mice. In summary, the combination of the acid-sensitive prodrug DV and autophagy inhibitor 3-MA in a HA-MIL-125 nanocarrier can enhance the antitumor effect and reverse tumor MDR.

Recent advances in BCRP-induced breast cancer resistance treatment with marine-based natural products

Breast cancer is the prominent cause of cancer-related death in women globally in terms of incidence and mortality. Despite, recent advances in the management of breast cancer, there are still a lot of cases of resistance to medicines, which is currently one of the biggest problems faced by researchers across the globe. Out of several mechanisms, breast cancer resistance protein (BCRP) arbitrated drug resistance is a major concern. Hormonal, cytotoxic and immunotherapeutic drugs are used in the systemic therapy of breast cancer. It is vital to choose drugs based on the clinical and molecular attributes of the tumor to provide better treatment with greater efficacy and minimal harm. Given the aforementioned necessity, the use of marine flora in treating breast cancer cannot be neglected. The scientists also stressed the value of marine-derived goods in avoiding breast cancer resistance. Future research into the identification of anticancer drugs will heavily draw upon the marine environment's ample supply of marine-derived natural products (MNPs), which have a wide range of biological functions. Cell cycle arrest, induction of apoptosis and anti-angiogenic, anti-proliferative and anti-metastasis actions are all part of their processes. The overview of breast cancer, the mechanisms underlying its resistance, recent clinical trials based on marine-derived products in breast cancer and the use of marine products in the treatment of breast cancer are highlighted in this paper. Moreover, the authors also emphasised the importance of marine-derived products in preventing breast cancer resistance.

Effect of Daridorexant on the Pharmacokinetics of P-Glycoprotein Substrate Dabigatran Etexilate and Breast Cancer Resistance Protein Substrate Rosuvastatin in Healthy Subjects

BACKGROUND AND OBJECTIVE

The dual orexin receptor antagonist daridorexant was approved in 2022 for the treatment of insomnia at doses up to 50 mg once per night. This study aimed at investigating the effect of daridorexant 50 mg at steady state on the pharmacokinetics of dabigatran, the active moiety of dabigatran etexilate, and rosuvastatin, sensitive substrates of P-glycoprotein and breast cancer resistance protein, respectively.

METHODS

This single-center, open-label, fixed-sequence study enrolled 24 healthy male subjects who were dosed orally with dabigatran etexilate 75 mg on days 1 (Treatment A1) and 9 (Treatment C1) as well as rosuvastatin 10 mg on days 3 (Treatment A2) and 11 (Treatment C2). On days 7-14, daridorexant (50 mg once daily) was administered. Blood samples for the pharmacokinetics of both substrates and the pharmacodynamics of dabigatran, i.e., two coagulation tests, were collected and safety assessments performed. Noncompartmental pharmacokinetic parameters and pharmacodynamic variables were evaluated with geometric mean ratios and 90% confidence intervals of Treatment C1/C2 versus A1/A2.

RESULTS

Geometric mean ratios (90% confidence interval) of dabigatran maximum plasma concentration and area under the plasma concentration-time curve were 1.3 (1.0-1.7) and 1.4 (1.1-1.9), respectively, whereas the time to maximum plasma concentration and terminal half-life were comparable between treatments. Pharmacodynamic variables showed a similar pattern as dabigatran pharmacokinetics in both treatments. Rosuvastatin pharmacokinetics were unchanged upon concomitant daridorexant administration. All treatments were well tolerated.

CONCLUSIONS

A mild inhibition of P-glycoprotein was observed after administration of daridorexant (50 mg once daily) at steady state, whereas breast cancer resistance protein was not affected.

CLINICAL TRIAL REGISTRATION

NCT05480475; date of registration: 29 July, 2022.

Targeting ABCG2 transporter to enhance 5-aminolevulinic acid for tumor visualization and photodynamic therapy

5-Aminolevulinic acid (ALA) has been approved by the U. S. FDA for fluorescence-guided resection of high-grade glioma and photodynamic therapy (PDT) of superficial skin precancerous and cancerous lesions. As a prodrug, ALA administered orally or topically is metabolized in the heme biosynthesis pathway to produce protoporphyrin IX (PpIX), the active drug with red fluorescence and photosensitizing property. Preferential accumulation of PpIX in tumors after ALA administration enables the use of ALA for PpIX-mediated tumor fluorescence diagnosis and PDT, functioning as a photo-theranostic agent. Extensive research is currently underway to further enhance ALA-mediated PpIX tumor disposition for better tumor visualization and treatment. Particularly, the discovery of PpIX as a specific substrate of ATP binding cassette subfamily G member 2 (ABCG2) opens the door to therapeutic enhancement with ABCG2 inhibitors. Studies with human tumor cell lines and human tumor samples have demonstrated ABCG2 as an important biological determinant of reduced ALA-PpIX tumor accumulation, inhibition of which greatly enhances ALA-PpIX fluorescence and PDT response. These studies strongly support targeting ABCG2 as an effective therapeutic enhancement approach. In this review, we would like to summarize current research of ABCG2 as a drug efflux transporter in multidrug resistance, highlight previous works on targeting ABCG2 for therapeutic enhancement of ALA, and provide future perspectives on how to translate this ABCG2-targeted therapeutic enhancement strategy from bench to bedside.

Functional Evaluation of P-gp and Bcrp at the Murine Blood-Cerebrospinal Fluid Barrier

PURPOSE

The brain is protected from circulating metabolites and xenobiotics by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid (CSF) barrier. Previous studies report that P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) are expressed apically or subapically at the blood-CSF barrier (BCSFB), implying a paradoxical function to mediate blood-to-CSF transport of xenobiotics. As evidence of P-gp and Bcrp activity at the BCSFB is limited, the goal of this study is to investigate functional activity of P-gp and Bcrp at the murine BCSFB using a live tissue imaging approach.

METHODS

The choroid plexuses (CP) forming the BCSFB were freshly isolated from mouse brain ventricles and incubated with fluorescent probes calcein-AM and BODIPY FL-Prazosin. Using quantitative fluorescence microscopy, the functional contributions of Bcrp and P-gp were examined using inhibitors and mice with targeted deletion of the Abcb1a/b or Abcg2 gene.

RESULTS

Apical transport of calcein-AM in choroid plexus epithelial (CPE) cells is sensitive to inhibition by elacridar and Ko143 but is unaffected by P-gp deletion. In wild-type mice, elacridar increased CPE accumulation of BODIPY FL-Prazosin by 220% whereas deletion of Bcrp increased BODIPY FL-Prazosin accumulation by 43%. There was no change in Mdr1a/1b mRNA expression in CP tissues from the Bcrp-/- mice.

CONCLUSIONS

This study demonstrated functional activity of Bcrp at the BCSFB apical membrane and provided evidence supporting an additional contribution by P-gp. These findings contribute to the understanding of transport mechanisms that regulate CSF drug concentrations, which may benefit future predictions of CNS drug disposition, efficacy, and toxicity.

Transporter-Mediated Cellular Distribution of Tyrosine Kinase Inhibitors as a Potential Resistance Mechanism in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a hematologic neoplasm characterized by the expression of the BCR::ABL1 oncoprotein, a constitutively active tyrosine kinase, resulting in uncontrolled growth and proliferation of cells in the myeloid lineage. Targeted therapy using tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, dasatinib, bosutinib, ponatinib and asciminib has drastically improved the life expectancy of CML patients. However, treatment resistance occurs in 10-20% of CML patients, which is a multifactorial problem that is only partially clarified by the presence of TKI inactivating BCR::ABL1 mutations. It may also be a consequence of a reduction in cytosolic TKI concentrations in the target cells due to transporter-mediated cellular distribution. This review focuses on drug-transporting proteins in stem cells and progenitor cells involved in the distribution of TKIs approved for the treatment of CML. Special attention will be given to ATP-binding cassette transporters expressed in lysosomes, which may facilitate the extracytosolic sequestration of these compounds.

Doxorubicin and other anthracyclines in cancers: Activity, chemoresistance and its overcoming

Anthracyclines have been important and effective treatments against a number of cancers since their discovery. However, their use in therapy has been complicated by severe side effects and toxicity that occur during or after treatment, including cardiotoxicity. The mode of action of anthracyclines is complex, with several mechanisms proposed. It is possible that their high toxicity is due to the large set of processes involved in anthracycline action. The development of resistance is a major barrier to successful treatment when using anthracyclines. This resistance is based on a series of mechanisms that have been studied and addressed in recent years. This work provides an overview of the anthracyclines used in cancer therapy. It discusses their mechanisms of activity, toxicity, and chemoresistance, as well as the approaches used to improve their activity, decrease their toxicity, and overcome resistance.

PluriBAC: A Versatile Baculovirus-Based Modular System to Express Heterologous Genes in Different Biotechnological Platforms

Baculoviruses are insect-specific pathogens widely used in biotechnology. In particular, the Autographa californica nucleopolyhedrovirus (AcMNPV) has been exploited as a platform for bio-inputs production. This is why the improvement of the technologies used for the production of recombinant baculoviruses takes on particular relevance. To achieve this goal, we developed a highly versatile baculoviral transfer vector generation system called PluriBAC. The PluriBAC system consists of three insert entry levels using Golden Gate assembly technology. The wide availability of vectors and sticky ends allows enough versatility to combine more than four different promoters, genes of interest, and terminator sequences. Here, we report not only the rational design of the PluriBAC system but also its use for the generation of baculoviral reporter vectors applied to different fields of biotechnology. We demonstrated that recombinant AcMNPV baculoviruses generated with the PluriBAC system were capable of infecting Spodoptera frugiperda larvae. On the other hand, we found that the recombinant budded virions (BV) generated using our system were capable of transducing different types of tumor and normal cells both in vitro and in vivo. Our findings suggest that the PluriBAC system could constitute a versatile tool for the generation of insecticide and gene therapy vectors.

In vitro identification of decreased function phenotype ABCG2 variants

Reduced activity of efflux transporter ABCG2, caused e.g., by inhibition or decreased function genetic variants, can increase drug absorption and plasma levels. ABCG2 has one clinically significant single nucleotide variant Q141K (c.421C>A), which leads to decreased protein levels and transport activity. In addition to Q141K, ABCG2 has over 500 rare (<1% minor allele frequency) nonsynonymous variants, but their functionality remains unknown. We studied the transport activity and abundance of 30 rare ABCG2 variants. The variants were transiently expressed in HEK293 cells. Transport activity and protein abundance were measured from inside-out crude membrane vesicles. Results were normalised to the reference ABCG2, while Q141K was used to categorise variants into decreased and normal function phenotypes based on their apparent transport activity. Fourteen variants (G80E, D128V, T434M, Q437R, C438R, C438W, C438Y, L479S, P480L, S486N, T512N, S519P, G553D and K647E) had similar or lower apparent transport activity than Q141K and thus were categorised as having a decreased function phenotype. Protein abundance could not explain all of the observed changes in transport activity: Only six variants (D128V, Q437R, C438R, S519P, G553D, and K647E) had similar or lower abundance compared to Q141K. The decreased function variants may increase systemic drug exposure and therefore cause interindividual variability in pharmacokinetics. In the future, in vitro phenotype classification may help to design personalised drug treatments.

The response and resistance to drugs in ovarian cancer cell lines in 2D monolayers and 3D spheroids

Ovarian cancer is the most common type of gynecologic cancer. One of the leading causes of high mortality is chemoresistance, developed primarily or during treatment. Different mechanisms of drug resistance appear at the cellular and cancer tissue organization levels. We examined the differences in response to the cytotoxic drugs CIS, MTX, DOX, VIN, PAC, and TOP using 2D (two-dimensional) and 3D (three-dimensional) culture methods. We tested the drug-sensitive ovarian cancer cell line W1 and established resistant cell lines to appropriate cytotoxic drugs. The following qualitative and quantitative methods were used to assess: 1) morphology - inverted microscope and hematoxylin & eosin staining; 2) viability - MTT assay; 3) gene expression - a quantitative polymerase chain reaction; 4) identification of proteins - immunohistochemistry, and immunofluorescence. Our results indicate that the drug-sensitive and drug-resistant cells cultured in 3D conditions exhibit stronger resistance than the cells cultured in 2D conditions. A traditional 2D model shows that drug resistance of cancer cells is caused mainly by changes in the expression of genes encoding ATP-binding cassette transporter proteins, components of the extracellular matrix, "new" established genes related to drug resistance in ovarian cancer cell lines, and universal marker of cancer stem cells. Whereas in a 3D model, the drug resistance in spheroids can be related to other mechanisms such as the structure of the spheroid (dense or loose), the cell type (necrotic, quiescent, proliferating cells), drug concentrations or drug diffusion into the dense cellular/ECM structure.

The Dysregulated MAD in Mad: A Neuro-theranostic Approach Through the Induction of Autophagic Biomarkers LC3B-II and ATG

The word mad has historically been associated with the psyche, emotions, and abnormal behavior. Dementia is a common symptom among psychiatric disorders or mad (schizophrenia, depression, bipolar disorder) patients. Autophagy/mitophagy is a protective mechanism used by cells to get rid of dysfunctional cellular organelles or mitochondria. Autophagosome/mitophagosome abundance in autophagy depends on microtubule-associated protein light chain 3B (LC3B-II) and autophagy-triggering gene (ATG) which functions as an autophagic biomarker for phagophore production and quick mRNA disintegration. Defects in either LC3B-II or the ATG lead to dysregulated mitophagy-and-autophagy-linked dementia (MAD). The impaired MAD is closely associated with schizophrenia, depression, and bipolar disorder. The pathomechanism of psychosis is not entirely known, which is the severe limitation of today's antipsychotic drugs. However, the reviewed circuit identifies new insights that may be especially helpful in targeting biomarkers of dementia. Neuro-theranostics can also be achieved by manufacturing either bioengineered bacterial and mammalian cells or nanocarriers (liposomes, polymers, and nanogels) loaded with both imaging and therapeutic materials. The nanocarriers must cross the BBB and should release both diagnostic agents and therapeutic agents in a controlled manner to prove their effectiveness against psychiatric disorders. In this review, we highlighted the potential of microRNAs (miRs) as neuro-theranostics in the treatment of dementia by targeting autophagic biomarkers LC3B-II and ATG. Focus was also placed on the potential for neuro-theranostic nanocells/nanocarriers to traverse the BBB and induce action against psychiatric disorders. The neuro-theranostic approach can provide targeted treatment for mental disorders by creating theranostic nanocarriers.

Tumor-associated macrophages confer colorectal cancer 5-fluorouracil resistance by promoting MRP1 membrane translocation via an intercellular CXCL17/CXCL22-CCR4-ATF6-GRP78 axis

Chemotherapy represents a major type of clinical treatment against colorectal cancer (CRC). Aberrant drug efflux mediated by transporters acts as a key approach for tumor cells to acquire chemotherapy resistance. Increasing evidence implies that tumor-associated macrophages (TAMs) play a pivotal role in both tumorigenesis and drug resistance. Nevertheless, the specific mechanism through which TAMs regulate drug efflux remains elusive. Here, we discovered that TAMs endow CRC cells with resistance to 5-fluorouracil (5-FU) treatment via a cell-cell interaction-mediated MRP1-dependent drug efflux process. Mechanistically, TAM-secreted C-C motif chemokine ligand 17 (CCL17) and CCL22, via membrane receptor CCR4, activated the PI3K/AKT pathway in CRC tumor cells. Specifically, phosphorylation of AKT inactivated IP3R and induced calcium aggregation in the ER, resulting in the activation of ATF6 and upregulation of GRP78. Accordingly, excessive GRP78 can interact with MRP1 and promote its translocation to the cell membrane, causing TAM-induced 5-FU efflux. Taken together, our results demonstrated that TAMs promote CRC chemotherapy resistance via elevating the expression of GRP78 to promote the membrane translocation of MRP1 and drug efflux, providing direct proof for TAM-induced drug resistance.

Cancer chemoresistance and its mechanisms: Associated molecular factors and its regulatory role

Cancer therapy has advanced from tradition chemotherapy methods to targeted therapy, novel drug delivery mechanisms, combination therapies etc. Although several novel chemotherapy strategies have been introduced, chemoresistance still remains as one of the major barriers in cancer treatments. Chemoresistance can lead to relapse and hinder the development of improved clinical results for cancer patients, and this continues to be the major hurdle in cancer therapy. Anticancer drugs acquire chemoresistance through different mechanisms. Understanding these mechanisms is crucial to overcome and increase the efficiency of the cancer therapies that are employed. The potential molecular pathways behind chemoresistance include tumor heterogeneity, elevated drug efflux, multidrug resistance, interconnected signaling pathways, and other factors. To surpass this limitation, new clinical tactics are to be introduced. This review aims to compile the most recent information on the molecular pathways that regulate chemoresistance in cancers, which will aid in development of new therapeutic targets and strategies.

Long Noncoding RNAs in Taxane Resistance of Breast Cancer

Breast cancer is a common cancer in women and a leading cause of mortality. With the early diagnosis and development of therapeutic drugs, the prognosis of breast cancer has markedly improved. Chemotherapy is one of the predominant strategies for the treatment of breast cancer. Taxanes, including paclitaxel and docetaxel, are widely used in the treatment of breast cancer and remarkably decrease the risk of death and recurrence. However, taxane resistance caused by multiple factors significantly impacts the effect of the drug and leads to poor prognosis. Long noncoding RNAs (lncRNAs) have been shown to play a significant role in critical cellular processes, and a number of studies have illustrated that lncRNAs play vital roles in taxane resistance. In this review, we systematically summarize the mechanisms of taxane resistance in breast cancer and the functions of lncRNAs in taxane resistance in breast cancer. The findings provide insight into the role of lncRNAs in taxane resistance and suggest that lncRNAs may be used to develop therapeutic targets to prevent or reverse taxane resistance in patients with breast cancer.

Therapeutic Potential and Predictive Pharmaceutical Modeling of Stilbenes in Cannabis sativa

Cannabis sativa is a plant used for recreational and therapeutic purposes; however, many of the secondary metabolites in the plant have not been thoroughly investigated. Stilbenes are a class of compounds with demonstrated anti-inflammatory and antioxidant properties and are present in cannabis. Many stilbenes present in cannabis have been investigated for their therapeutic effects. Fourteen stilbenes have been identified to be present in cannabis, all of which are structurally dihydrostilbenoids, with half possessing a prenylated moiety. The stilbenes summarized in this analysis show varying degrees of therapeutic benefits ranging from anti-inflammatory, antiviral, and anti-cancer to antioxidant effects. Many of the identified stilbenes have been researched to a limited extent for potential health benefits. In addition, predictive in silico modeling was performed on the fourteen identified cannabis-derived stilbenes. This modeling provides prospective activity, pharmacokinetic, metabolism, and permeability data, setting the groundwork for further investigation into these poorly characterized compounds.

Landscape of NcRNAs involved in drug resistance of breast cancer

Breast cancer (BC) leads to the most amounts of deaths among women. Chemo-, endocrine-, and targeted therapies are the mainstay drug treatments for BC in the clinic. However, drug resistance is a major obstacle for BC patients, and it leads to poor prognosis. Accumulating evidences suggested that noncoding RNAs (ncRNAs) are intricately linked to a wide range of pathological processes, including drug resistance. Till date, the correlation between drug resistance and ncRNAs is not completely understood in BC. Herein, we comprehensively summarized a dysregulated ncRNAs landscape that promotes or inhibits drug resistance in chemo-, endocrine-, and targeted BC therapies. Our review will pave way for the effective management of drug resistance by targeting oncogenic ncRNAs, which, in turn will promote drug sensitivity of BC in the future.

Early in vitro evidence indicates that deacetylated sialic acids modulate multi-drug resistance in colon and lung cancers via breast cancer resistance protein

Cancers utilize sugar residues to engage in multidrug resistance. The underlying mechanism of action involving glycans, specifically the glycan sialic acid (Sia) and its various functional group alterations, has not been explored. ATP-binding cassette (ABC) transporter proteins, key proteins utilized by cancers to engage in multidrug resistant (MDR) pathways, contain Sias in their extracellular domains. The core structure of Sia can contain a variety of functional groups, including O-acetylation on the C6 tail. Modulating the expression of acetylated-Sias on Breast Cancer Resistance Protein (BCRP), a significant ABC transporter implicated in MDR, in lung and colon cancer cells directly impacted the ability of cancer cells to either retain or efflux chemotherapeutics. Via CRISPR-Cas-9 gene editing, acetylation was modulated by the removal of CAS1 Domain-containing protein (CASD1) and Sialate O-Acetyl esterase (SIAE) genes. Using western blot, immunofluorescence, gene expression, and drug sensitivity analysis, we confirmed that deacetylated Sias regulated a MDR pathway in colon and lung cancer in early in vitro models. When deacetylated Sias were expressed on BCRP, colon and lung cancer cells were able to export high levels of BCRP to the cell's surface, resulting in an increased BCRP efflux activity, reduced sensitivity to the anticancer drug Mitoxantrone, and high proliferation relative to control cells. These observations correlated with increased levels of cell survival proteins, BcL-2 and PARP1. Further studies also implicated the lysosomal pathway for the observed variation in BCRP levels among the cell variants. RNASeq data analysis of clinical samples revealed higher CASD1 expression as a favorable marker of survival in lung adenocarcinoma. Collectively, our findings indicate that deacetylated Sia is utilized by colon and lung cancers to engage in MDR via overexpression and efflux action of BCRP.

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

Interactions of human drug transporters with chemical additives present in plastics: Potential consequences for toxicokinetics and health

Human membrane drug transporters are recognized as major actors of pharmacokinetics; they also handle endogenous compounds, including hormones and metabolites. Chemical additives present in plastics interact with human drug transporters, which may have consequences for the toxicokinetics and toxicity of these widely-distributed environmental and/or dietary pollutants, to which humans are highly exposed. The present review summarizes key findings about this topic. In vitro assays have demonstrated that various plastic additives, including bisphenols, phthalates, brominated flame retardants, poly-alkyl phenols and per- and poly-fluoroalkyl substances, can inhibit the activities of solute carrier uptake transporters and/or ATP-binding cassette efflux pumps. Some are substrates for transporters or can regulate their expression. The relatively low human concentration of plastic additives from environmental or dietary exposure is a key parameter to consider to appreciate the in vivo relevance of plasticizer-transporter interactions and their consequences for human toxicokinetics and toxicity of plastic additives, although even low concentrations of pollutants (in the nM range) may have clinical effects. Existing data about interactions of plastic additives with drug transporters remain somewhat sparse and incomplete. A more systematic characterization of plasticizer-transporter relationships is needed. The potential effects of chemical additive mixtures towards transporter activities and the identification of transporter substrates among plasticizers, as well as their interactions with transporters of emerging relevance deserve particular attention. A better understanding of the human toxicokinetics of plastic additives may help to fully integrate the possible contribution of transporters to the absorption, distribution, metabolism and excretion of plastics-related chemicals, as well as to their deleterious effects towards human health.

Protective role of the placental efflux transporter BCRP/ABCG2 in the relationship between prenatal cadmium exposure, placenta weight, and size at birth

BACKGROUND AND AIM

Placental efflux transporter proteins, such as BCRP, reduce the placental and fetal toxicity of environmental contaminants but have received little attention in perinatal environmental epidemiology. Here, we evaluate the potential protective role of BCRP following prenatal exposure to cadmium, a metal that preferentially accumulates in the placenta and adversely impacts fetal growth. We hypothesized that individuals with a reduced function polymorphism in ABCG2, the gene encoding BCRP, would be most vulnerable to the adverse impacts of prenatal cadmium exposure, notably, smaller placental and fetal size.

METHODS

We measured cadmium in maternal urine samples at each trimester and in term placentas from UPSIDE-ECHO study participants (NY, USA; n = 269). We fit adjusted multivariable linear regression and generalized estimating equation models to examine log-transformed urinary and placental cadmium concentrations in relation to birthweight, birth length, placental weight, and fetoplacental weight ratio (FPR) and stratified models by ABCG2 Q141K (C421A) genotype.

RESULTS

Overall 17% of participants expressed the reduced-function ABCG2 C421A variant (AA or AC). Placental cadmium concentrations were inversely associated with placental weight (β = -19.55; 95%CI: -37.06, -2.04) and trended towards higher FPR (β = 0.25; 95%CI: -0.01, 0.52) with stronger associations in 421A variant infants. Notably, higher placental cadmium concentrations in 421A variant infants were associated with reduced placental weight (β = -49.42; 95%CI: 98.87, 0.03), and higher FPR (β = 0.85, 95%CI: 0.18, 1.52), while higher urinary cadmium concentration was associated with longer birth length (β = 0.98; 95%CI: 0.37, 1.59), lower ponderal index (β = -0.09; 95%CI: 0.15, -0.03), and higher FPR (β = 0.42; 95%CI: 0.14, 0.71).

CONCLUSIONS

Infants with reduced function ABCG2 polymorphisms may be particularly vulnerable to the developmental toxicity of cadmium as well as other xenobiotics that are BCRP substrates. Additional work examining the influence of placental transporters in environmental epidemiology cohorts is warranted.

Systematic screening identifies ABCG2 as critical factor underlying synergy of kinase inhibitors with transcriptional CDK inhibitors

BACKGROUND

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with limited treatment options and poor clinical prognosis. Inhibitors of transcriptional CDKs are currently under thorough investigation for application in the treatment of multiple cancer types, including breast cancer. These studies have raised interest in combining these inhibitors, including CDK12/13 inhibitor THZ531, with a variety of other anti-cancer agents. However, the full scope of these potential synergistic interactions of transcriptional CDK inhibitors with kinase inhibitors has not been systematically investigated. Moreover, the mechanisms behind these previously described synergistic interactions remain largely elusive.

METHODS

Kinase inhibitor combination screenings were performed to identify kinase inhibitors that synergize with CDK7 inhibitor THZ1 and CDK12/13 inhibitor THZ531 in TNBC cell lines. CRISPR-Cas9 knockout screening and transcriptomic evaluation of resistant versus sensitive cell lines were performed to identify genes critical for THZ531 resistance. RNA sequencing analysis after treatment with individual and combined synergistic treatments was performed to gain further insights into the mechanism of this synergy. Kinase inhibitor screening in combination with visualization of ABCG2-substrate pheophorbide A was used to identify kinase inhibitors that inhibit ABCG2. Multiple transcriptional CDK inhibitors were evaluated to extend the significance of the found mechanism to other transcriptional CDK inhibitors.

RESULTS

We show that a very high number of tyrosine kinase inhibitors synergize with the CDK12/13 inhibitor THZ531. Yet, we identified the multidrug transporter ABCG2 as key determinant of THZ531 resistance in TNBC cells. Mechanistically, we demonstrate that most synergistic kinase inhibitors block ABCG2 function, thereby sensitizing cells to transcriptional CDK inhibitors, including THZ531. Accordingly, these kinase inhibitors potentiate the effects of THZ531, disrupting gene expression and increasing intronic polyadenylation.

CONCLUSION

Overall, this study demonstrates the critical role of ABCG2 in limiting the efficacy of transcriptional CDK inhibitors and identifies multiple kinase inhibitors that disrupt ABCG2 transporter function and thereby synergize with these CDK inhibitors. These findings therefore further facilitate the development of new (combination) therapies targeting transcriptional CDKs and highlight the importance of evaluating the role of ABC transporters in synergistic drug-drug interactions in general.

An ATP-binding cassette transporter G2 (CgABCG2) regulates the haemocyte proliferation by modulating the G1/S phase transition of cell cycle in oyster Crassostrea gigas

ATP-binding cassette transporter G2 (ABCG2) is a half-transporter of the G subfamily in ATP-binding cassette transporters (ABC transporter), which is involved in the regulation of multidrug-resistant, cell cycle, and cell proliferation. In the present study, a homologue of ABCG2 (named as CgABCG2) with the conserved AAA domain and ABC2 membrane domain was identified from the Pacific oyster Crassostrea gigas. The open reading frame (ORF) of CgABCG2 was of 1956 bp encoding a predicted polypeptide of 652 amino acids, which shared 56.7%-65.7% sequence similarities with previously identified ABCG2s from other animals. The mRNA transcripts of CgABCG2 were detected in all the tested tissues with higher expression levels in gonad and haemocytes (19.31-fold and 11.23-fold of that in adductor muscle respectively, p < 0.05). CgABCG2 was mainly distributed on the cell membrane of the haemocytes with a partial distribution in the cytoplasm and nucleus. After Vibrio splendidus stimulation, the mRNA expression level of CgABCG2 in haemocytes was significantly up-regulated at 3 h and 6 h, which was 5.22-fold and 8.60-fold (p < 0.05) of that in control, respectively. After the expression of CgABCG2 was interfered by RNAi, the number of cells with EdU positive signals was reduced in both haemocytes and the potential hematopoietic sites. And the mRNA expression level of CgPCNA, CgGATA3, CgRunx, CgSCL and CgC-kit decreased significantly (p < 0.05), which were about 0.66-, 0.37-, 0.32-, 0.50-, and 0.50-fold of that in the negative control group, respectively. While the mRNA expression level of CgCDK2 increased significantly (1.84-fold to that in control, p < 0.05) and that of stem cell-related factor CgSOX2 did not change significantly in the si-CgABCG2 oysters. Moreover, the cell cycle of haemocytes was detected by flow cytometry, which was arrested at G0/G1 phase in the si-CgABCG2 oysters. All the results collectively suggested that CgABCG2 might involve the proliferation of haemocytes by regulating the expression of haematopoiesis related transcription factors and the G1/S phase transition of the cell cycle in oyster C. gigas.

5-Aminolevulinic Acid as a Theranostic Agent for Tumor Fluorescence Imaging and Photodynamic Therapy

5-Aminolevulinic acid (ALA) is a naturally occurring amino acid synthesized in all nucleated mammalian cells. As a porphyrin precursor, ALA is metabolized in the heme biosynthetic pathway to produce protoporphyrin IX (PpIX), a fluorophore and photosensitizing agent. ALA administered exogenously bypasses the rate-limit step in the pathway, resulting in PpIX accumulation in tumor tissues. Such tumor-selective PpIX disposition following ALA administration has been exploited for tumor fluorescence diagnosis and photodynamic therapy (PDT) with much success. Five ALA-based drugs have now received worldwide approval and are being used for managing very common human (pre)cancerous diseases such as actinic keratosis and basal cell carcinoma or guiding the surgery of bladder cancer and high-grade gliomas, making it the most successful drug discovery and development endeavor in PDT and photodiagnosis. The potential of ALA-induced PpIX as a fluorescent theranostic agent is, however, yet to be fully fulfilled. In this review, we would like to describe the heme biosynthesis pathway in which PpIX is produced from ALA and its derivatives, summarize current clinical applications of ALA-based drugs, and discuss strategies for enhancing ALA-induced PpIX fluorescence and PDT response. Our goal is two-fold: to highlight the successes of ALA-based drugs in clinical practice, and to stimulate the multidisciplinary collaboration that has brought the current success and will continue to usher in more landmark advances.

Cannabis Pharmacogenomics: A Path to Personalized Medicine

Cannabis and related compounds have created significant research interest as a promising therapy in many disorders. However, the individual therapeutic effects of cannabinoids and the incidence of side effects are still difficult to determine. Pharmacogenomics may provide the answers to many questions and concerns regarding the cannabis/cannabinoid treatment and help us to understand the variability in individual responses and associated risks. Pharmacogenomics research has made meaningful progress in identifying genetic variations that play a critical role in interpatient variability in response to cannabis. This review classifies the current knowledge of pharmacogenomics associated with medical marijuana and related compounds and can assist in improving the outcomes of cannabinoid therapy and to minimize the adverse effects of cannabis use. Specific examples of pharmacogenomics informing pharmacotherapy as a path to personalized medicine are discussed.