Brain accumulation of sunitinib is restricted by P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) and can be enhanced by oral elacridar and sunitinib coadministration

Predictive genomic biomarkers of therapeutic effects in renal cell carcinoma

BACKGROUND

In recent years, there have been great improvements in the therapy of renal cell carcinoma. Nevertheless, the therapeutic effect varies significantly from person to person. To discern the effective treatment for different populations, predictive molecular biomarkers in response to target, immunological, and combined therapies are widely studied.

CONCLUSION

This review summarized those studies from three perspectives (SNPs, mutation, and expression level) and listed the relationship between biomarkers and therapeutic effect, highlighting the great potential of predictive molecular biomarkers in metastatic RCC therapy. However, due to a series of reasons, most of these findings require further validation.

Constant-rate perfused array chip for high-throughput screening of drug permeability through brain endothelium

The development of an in vitro model for predicting drug permeability through the human blood-brain barrier (BBB) will greatly accelerate the development of neural therapy. Previously reported platforms for BBB model construction cannot meet the requirements of constant-rate and high-throughput flow, as well as compatibility with the commercial meter for real-time transendothelial electrical resistance (TEER) measurement. Herein, a constant-rate perfused array chip (cPAC) was developed to establish a brain endothelium model for screening drug permeability. The cPAC consisted of 24 units with four layers. Three reservoirs on the top had a 0.5 mm center-to-center spacing, enabling real-time detection of the TEER with the commercial volt-ohm meter. With the optimized chip design, the constant-rate and high-throughput flow by gravity was achieved. Compared with the static culture of the Transwell, the brain endothelium model on the cPAC exhibited superior performance in barrier function, efflux functionality of the transporters, and reversible osmotic opening of the brain endothelium. More importantly, the permeability of model drugs on the cPAC matched the in vivo results with the correlation coefficient reaching 0.994. Finally, the brain endothelium model was cocultured with 3D tumor cells for simultaneous evaluation of drug permeability and brain tumor therapy. The drug efficacy at the target cells on the coculture model was also consistent with clinical findings. These results demonstrated that this platform provides a promising tool for brain endothelium model establishment to predict drug permeability and brain therapy. We anticipate the cPAC to be widely accepted for establishing various barrier models.

Protective effects of NAMPT or MAPK inhibitors and NaR on Wallerian degeneration of mammalian axons

Wallerian degeneration (WD) is a conserved axonal self-destruction program implicated in several neurological diseases. WD is driven by the degradation of the NAD+ synthesizing enzyme NMNAT2, the buildup of its substrate NMN, and the activation of the NAD+ degrading SARM1, eventually leading to axonal fragmentation. The regulation and amenability of these events to therapeutic interventions remain unclear. Here we explored pharmacological strategies that modulate NMN and NAD+ metabolism, namely the inhibition of the NMN-synthesizing enzyme NAMPT, activation of the nicotinic acid riboside (NaR) salvage pathway and inhibition of the NMNAT2-degrading DLK MAPK pathway in an axotomy model in vitro. Results show that NAMPT and DLK inhibition cause a significant but time-dependent delay of WD. These time-dependent effects are related to NMNAT2 degradation and changes in NMN and NAD+ levels. Supplementation of NAMPT inhibition with NaR has an enhanced effect that does not depend on timing of intervention and leads to robust protection up to 4 days. Additional DLK inhibition extends this even further to 6 days. Metabolite analyses reveal complex effects indicating that NAMPT and MAPK inhibition act by reducing NMN levels, ameliorating NAD+ loss and suppressing SARM1 activity. Finally, the axonal NAD+/NMN ratio is highly predictive of cADPR levels, extending previous cell-free evidence on the allosteric regulation of SARM1. Our findings establish a window of axon protection extending several hours following injury. Moreover, we show prolonged protection by mixed treatments combining MAPK and NAMPT inhibition that proceed via complex effects on NAD+ metabolism and inhibition of SARM1.

Risk assessment and molecular mechanism study of drug-drug interactions between rivaroxaban and tyrosine kinase inhibitors mediated by CYP2J2/3A4 and BCRP/P-gp

Cancer patients generally has a high risk of thrombotic diseases. However, anticoagulant therapy always aggravates bleeding risks. Rivaroxaban is one of the most widely used direct oral anticoagulants, which is used as anticoagulant treatment or prophylaxis in clinical practice. The present study aimed to systemically estimate the combination safety of rivaroxaban with tyrosine kinase inhibitors (TKIs) based on human cytochrome P450 (CYPs) and efflux transporters and to explore the drug–drug interaction (DDI) mechanisms in vivo and in vitro. In vivo pharmacokinetic experiments and in vitro enzyme incubation assays and bidirectional transport studies were conducted. Imatinib significantly increased the rivaroxaban C_max value by 90.43% (p < 0.05) and the area under the curve value by 119.96% (p < 0.01) by inhibiting CYP2J2- and CYP3A4-mediated metabolism and breast cancer resistance protein (BCRP)- and P-glycoprotein (P-gp)-mediated efflux transportation in the absorption phase. In contrast, the combination of sunitinib with rivaroxaban reduced the exposure in vivo by 62.32% (p < 0.05) and the C_max value by 72.56% (p < 0.05). In addition, gefitinib potently inhibited CYP2J2- and CYP3A4-mediated rivaroxaban metabolism with K_i values of 2.99 μΜ and 4.91 μΜ, respectively; however, it almost did not affect the pharmacokinetics of rivaroxaban in vivo. Taken together, clinically significant DDIs were observed in the combinations of rivaroxaban with imatinib and sunitinib. Imatinib increased the bleeding risks of rivaroxaban, while sunitinib had a risk of reducing therapy efficiency. Therefore, more attention should be paid to aviod harmful DDIs in the combinations of rivaroxaban with TKIs.

Relevance of Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors in Routine Clinical Practice: A Pilot Study

INTRODUCTION

The main goal of treatment in cancer patients is to achieve the highest therapeutic effectiveness with the least iatrogenic toxicity. Tyrosine kinase inhibitors (TKIs) are anticancer oral agents, usually administered at fixed doses, which present high inter- and intra-individual variability due to their pharmacokinetic characteristics. Therapeutic drug monitoring (TDM) can be used to optimize the use of several types of medication.

OBJECTIVE

We evaluated the use of TDM of TKIs in routine clinical practice through studying the variability in exposure to erlotinib, imatinib, lapatinib, and sorafenib and dose adjustment.

MATERIALS AND METHODS

We conducted a retrospective analytical study involving patients who received treatment with TKIs, guided by TDM and with subsequent recommendation of dose adjustment. The quantification of the plasma levels of the different drugs was performed using high-performance liquid chromatography (HPLC). The Clinical Research Ethics Committee of the Hospital Quirónsalud Torrevieja approved this study.

RESULTS

The inter-individual variability in the first cycle and in the last monitored cycle was 46.2% and 44.0% for erlotinib, 48.9 and 50.8% for imatinib, 60.7% and 56.0% for lapatinib and 89.7% and 72.5% for sorafenib. Relationships between exposure and baseline characteristics for erlotinib, imatinib, lapatinib and sorafenib were not statistically significant for any of the variables evaluated (weight, height, body surface area (BSA), age and sex). Relationships between height (p = 0.021) and BSA (p = 0.022) were statistically significant for sorafenib. No significant relationships were observed between C_trough and progression-free survival (PFS) or overall survival (OS) for any drug, except in the case of sunitinib (correlation between C_trough and PFS p = 0.023) in the exposure-efficacy analysis.

CONCLUSIONS

Erlotinib, imatinib, lapatinib and sorafenib show large inter-individual variability in exposure. TDM entails a significant improvement in exposure and enables more effective and safe use of TKIs in routine clinical practice.

Role of the Efflux Transporters Abcb1 and Abcg2 in the Brain Distribution of Olaparib in Mice

Olaparib is a first-in-class poly (ADP-ribose) polymerase oral inhibitor used to treat various tumors. In this study, we clarified the roles of ABCB1/Abcb1 and ABCG2/Abcg2 transporters in restricting olaparib distribution to the brain. Olaparib was efficiently transported by human ABCG2, human ABCB1, and mouse Abcg2 in vitro. In the in vivo disposition study of olaparib using single or combination knockout mice, the systemic exposure of olaparib did not differ significantly between the strains over an 8-h period. However, the brain-to-plasma unbound concentration ratio of olaparib increased 5.6- and 8.1-fold in Abcb1a/1b and Abcb1a/1b;Abcg2 knockout mice, respectively, compared with wild-type mice. The Abcg2 single knockout mice exhibited a similar brain-to-plasma unbound concentration ratio to wild-type mice. Moreover, the brain distribution of olaparib could be modulated by the ABCB1/ABCG2 dual inhibitor elacridar to reach a similar degree of inhibition to Abcb1a/1b^-/-. These findings suggest that olaparib is actively transported by both human and mouse ABCB1/Abcb1 and ABCG2/Abcg2; while Abcb1a/1b is a major determinant of olaparib brain penetration in mice, Abcg2 is likely to be a minor contributor. Concomitant treatment with temozolomide slightly increased the brain distribution of olaparib in mouse, but the clinical impact of the interaction was expected to be limited.

The roles of the human ATP-binding cassette transporters P-glycoprotein and ABCG2 in multidrug resistance in cancer and at endogenous sites: future opportunities for structure-based drug design of inhibitors

The ATP-binding cassette (ABC) transporters P-glycoprotein (P-gp) and ABCG2 are multidrug transporters that confer drug resistance to numerous anti-cancer therapeutics in cell culture. These findings initially created great excitement in the medical oncology community, as inhibitors of these transporters held the promise of overcoming clinical multidrug resistance in cancer patients. However, clinical trials of P-gp and ABCG2 inhibitors in combination with cancer chemotherapeutics have not been successful due, in part, to flawed clinical trial designs resulting from an incomplete molecular understanding of the multifactorial basis of multidrug resistance (MDR) in the cancers examined. The field was also stymied by the lack of high-resolution structural information for P-gp and ABCG2 for use in the rational structure-based drug design of inhibitors. Recent advances in structural biology have led to numerous structures of both ABCG2 and P-gp that elucidated more clearly the mechanism of transport and the polyspecific nature of their substrate and inhibitor binding sites. These data should prove useful helpful for developing even more potent and specific inhibitors of both transporters. As such, although possible pharmacokinetic interactions would need to be evaluated, these inhibitors may show greater effectiveness in overcoming ABC-dependent multidrug resistance in combination with chemotherapeutics in carefully selected subsets of cancers. Another perhaps even more compelling use of these inhibitors may be in reversibly inhibiting endogenously expressed P-gp and ABCG2, which serve a protective role at various blood-tissue barriers. Inhibition of these transporters at sanctuary sites such as the brain and gut could lead to increased penetration by chemotherapeutics used to treat brain cancers or other brain disorders and increased oral bioavailability of these agents, respectively.

Untangling Absorption Mechanisms and Variability in Bioequivalence Studies Using Population Analysis

PURPOSE

Both inter-individual (IIV) and inter-occasion (IOV) variabilities are observed in bioequivalence studies. High IOV may be a cause of problems on the demonstration of bioequivalence, despite strict measures are taken to control it. The objective of this study is to investigate further means of controlling IIV by optimizing study design of crossover studies.

METHODS

Data from 18 bioequivalence studies were used to develop population pharmacokinetics (popPK) models to characterize the absorption and disposition processes of 14 drugs, to estimate IOV for each drug substance and to evaluate possible correlations with biopharmaceutical properties of drug substances, classified in accordance to the Biopharmaceutics Drug Disposition Classification System (BDDCS).

RESULTS

Plasma-pharmacokinetics profiles for the 14 drugs analyzed were successfully described using popPK. The pharmacokinetic parameters that showed greater variability were first-order rate constant of absorption, duration of the zero-order absorption process, relative bioavailability and time of latency. ISCV% estimated for C_max seems to correlate with the log-Dose-Number for Class 1, 2 and 3, despite no direct correlation was observed between popPK model residual variability (RUV) and ISCV%. Nevertheless, higher RUV estimates were observed for Class 2 drugs in comparison to Class 1 and 3.

CONCLUSION

Pharmacokinetic parameters related to drug absorption showed greater variability. Ingestion of the IMP along with 240 mL of water showed to standardize gastric emptying. Given the dependency between C_max variability and dose-solubility ratio, for classes 2 and 4, ad libitum water intake may increase C_max and AUC ISCV%. A water ingestion standardization until the expected T_max of the drug is suggested.

Investigation of the role and quantitative impact of breast cancer resistance protein on drug distribution into brain and CSF in rats

Breast cancer resistance protein (BCRP) expressed in the blood-brain barrier plays a major role in limiting drug distribution into the central nervous system (CNS). However, functional involvement of BCRP in drug distribution into the brain and cerebrospinal fluid (CSF) remains unclear. The aim of present study was to reveal the role and quantitative impact of BCRP on CNS distribution. The brain-to-plasma unbound concentration ratio (K_p,uu,brain) and CSF-to-plasma unbound concentration ratio (K_p,uu,CSF) values of BCRP-specific substrates were determined in rats. The K_p,uu,brain values decreased, as the in vitro BCRP corrected flux ratio (CFR) increased. The K_p,uu,CSF values of BCRP-specific substrates were greater than the K_p,uu,brain values. Increase in the K_p,uu,brain values induced by co-administration of BCRP inhibitor correlated with the in vitro BCRP CFR and were greater than the increase in K_p,uu,CSF values induced by BCRP inhibitor except nebicapone. The contribution of BCRP to the brain and CSF distribution of the dual P-glycoprotein/BCRP substrates, imatinib and prazosin, was similar to that of BCRP-specific substrates. Thus, we revealed that the impact of in vivo BCRP on CNS distribution is correlated with in vitro BCRP CFR, and that BCRP limits drug distribution into the brain more strongly than into the CSF.

Brain Metastasis Treatment: The Place of Tyrosine Kinase Inhibitors and How to Facilitate Their Diffusion across the Blood-Brain Barrier

The incidence of brain metastases has been increasing constantly for the last 20 years, because of better control of metastases outside the brain, and the failure of most drugs to cross the blood–brain barrier at relevant pharmacological concentrations. Recent advances in the molecular biology of cancer have led to the identification of numerous molecular alterations, some of them targetable with the development of specific targeted therapies, including tyrosine kinase inhibitors. In this narrative review, we set out to describe the state-of-the-art in the use of tyrosine kinase inhibitors for the treatment of melanoma, lung cancer, and breast cancer brain metastases. We also report preclinical and clinical pharmacological data on brain exposure to tyrosine kinase inhibitors after oral administration and describe the most recent advances liable to facilitate their penetration of the blood–brain barrier at relevant concentrations and limit their physiological efflux.

Branebrutinib (BMS-986195), a Bruton's Tyrosine Kinase Inhibitor, Resensitizes P-Glycoprotein-Overexpressing Multidrug-Resistant Cancer Cells to Chemotherapeutic Agents

The overexpression of P-glycoprotein (P-gp/ABCB1), an ATP-binding cassette (ABC) drug transporter, often contributes to the development of multidrug resistance (MDR) in cancer cells. P-gp mediates the ATP hydrolysis-dependent efflux of a wide range of chemotherapeutic agents out of cancer cells, thereby reducing the intracellular drug accumulation and decreasing the chemosensitivity of these multidrug-resistant cancer cells. Studies with tyrosine kinase inhibitors (TKIs) in P-gp-overexpressing cells have shown that certain TKIs could reverse MDR mediated by P-gp, while some TKIs are transported by P-gp. In the present work, we explored the prospect of repositioning branebrutinib (BMS-986195), a highly selective inhibitor of Bruton’s tyrosine kinase (BTK), to resensitize P-gp-overexpressing multidrug-resistant cancer cells to chemotherapeutic agents. Our results demonstrated that branebrutinib is capable of reversing P-gp-mediated MDR at sub-toxic concentrations, most likely by directly inhibiting the drug transport function of P-gp. Our findings were supported by the result of branebrutinib stimulating the ATPase activity of P-gp in a concentration-dependent manner and the in silico study of branebrutinib binding to the substrate-binding pocket of P-gp. In addition, we found that branebrutinib is equally cytotoxic to drug-sensitive parental cell lines and the respective P-gp-overexpressing multidrug-resistant variants, suggesting that it is unlikely that the overexpression of P-gp in cancer cells plays a significant role in reduced susceptibility or resistance to branebrutinib. In summary, we discovered an additional pharmacological action of branebrutinib against the activity of P-gp, which should be investigated further in future drug combination studies.

Therapeutic Drug Monitoring of Sunitinib in Gastrointestinal Stromal Tumors and Metastatic Renal Cell Carcinoma in Adults-A Review

BACKGROUND

Sunitinib is an inhibitor of multiple receptor tyrosine kinases and is a standard-of-care treatment for advanced and metastatic renal cell carcinoma and a second-line treatment in locally advanced inoperable and metastatic gastrointestinal stromal tumors. A fixed dose of the drug, however, does not produce a uniform therapeutic outcome in all patients, and many face adverse effects and/or toxicity. One of the possible causes of the interindividual variability in the efficacy and toxicity response is the highly variable systemic exposure to sunitinib and its active metabolite. This review aims to summarize all available clinical evidence of the treatment of adult patients using sunitinib in approved indications, addressing the necessity to introduce proper and robust therapeutic drug monitoring (TDM) of sunitinib and its major metabolite, N-desethylsunitinib.

METHODS

The authors performed a systematic search of the available scientific literature using the PubMed online database. The search terms were "sunitinib" AND "therapeutic drug monitoring" OR "TDM" OR "plasma levels" OR "concentration" OR "exposure." The search yielded 520 journal articles. In total, 447 publications were excluded because they lacked sufficient relevance to the reviewed topic. The remaining 73 articles were, together with currently valid guidelines, thoroughly reviewed.

RESULTS

There is sufficient evidence confirming the concentration-efficacy and concentration-toxicity relationship in the indications of gastrointestinal stromal tumors and metastatic renal clear-cell carcinoma. For optimal therapeutic response, total (sunitinib + N-desethylsunitinib) trough levels of 50-100 ng/mL serve as a reasonable target therapeutic range. To avoid toxicity, the total trough levels should not exceed 100 ng/mL.

CONCLUSIONS

According to the current evidence presented in this review, a TDM-guided dose modification of sunitinib in selected groups of patients could provide a better treatment outcome while simultaneously preventing sunitinib toxicity.

Guanabenz Sensitizes Glioblastoma Cells to Sunitinib by Inhibiting GADD34-Mediated Autophagic Signaling

Limited therapeutic efficacy of temozolomide (TMZ) against glioblastomas highlights the importance of exploring new drugs for clinical therapy. Sunitinib, a multitargeted receptor tyrosine kinase inhibitor, is currently being tested as therapy for glioblastomas. Unfortunately, sunitinib still has insufficient activity to cure glioblastomas. Our aim was to determine the molecular mechanisms counteracting sunitinib drug sensitivity and find potential adjuvant drugs for glioblastoma therapy. Through in vitro experiments, transcriptome screening by RNA sequencing, and in silico analyses, we found that sunitinib induced glioma apoptotic death, and downregulated genes were enriched in oncogenic genes of glioblastoma. Meanwhile, sunitinib-upregulated genes were highly associated with the protective autophagy process. Blockade of autophagy significantly enhanced sunitinib's cytotoxicity. Growth arrest and DNA damage-inducible protein (GADD) 34 was identified as a candidate involved in sunitinib-promoted autophagy through activating p38-mitogen-activated protein kinase (MAPK) signaling. Higher GADD34 levels predicted poor survival of glioblastoma patients and induced autophagy formation in desensitizing sunitinib cytotoxicity. Guanabenz, an alpha2-selective adrenergic agonist and GADD34 functional inhibitor, was identified to enhance the efficacy of sunitinib by targeting GADD34-induced protective autophagy in glioblastoma cells, TMZ-resistant cells, hypoxic cultured cells, sphere-forming cells, and colony formation abilities. A better combined treatment effect with sunitinib and guanabenz was also observed by using xenograft mice. Taken together, the sunitinib therapy combined with guanabenz in the inhibition of GADD34-enhanced protective autophagy may provide a new therapeutic strategy for glioblastoma.

Role of ATP-Binding Cassette Transporter Proteins in CNS Tumors: Resistance- Based Perspectives and Clinical Updates

Despite gigantic advances in medical research and development, chemotherapeutic resistance remains a major challenge in complete remission of CNS tumors. The failure of complete eradication of CNS tumors has been correlated with the existence of several factors including overexpression of transporter proteins. To date, 49 ABC-transporter proteins (ABC-TPs) have been reported in humans, and the evidence of their strong association with chemotherapeutics' influx, dissemination, and efflux in CNS tumors, is growing. Research studies on CNS tumors are implicating ABC-TPs as diagnostic, prognostic and therapeutic biomarkers that may be utilised in preclinical and clinical studies. With the current advancements in cell biology, molecular analysis of genomic and transcriptomic interplay, and protein homology-based drug-transporters interaction, our research approaches are streamlining the roles of ABC-TPs in cancer and multidrug resistance. Potential inhibitors of ABC-TP for better clinical outcomes in CNS tumors have emerged. Elacridar has shown to enhance the chemo-sensitivity of Dasatanib and Imatinib in various glioma models. Tariquidar has improved the effectiveness of Temozolomide's in CNS tumors. Although these inhibitors have been effective in preclinical settings, their clinical outcomes have not been as significant in clinical trials. Thus, to have a better understanding of the molecular evaluations of ABC-TPs, as well as drug-interactions, further research is being pursued in research labs. Our lab aims to better comprehend the biological mechanisms involved in drug resistance and to explore novel strategies to increase the clinical effectiveness of anticancer chemotherapeutics, which will ultimately improve clinical outcomes.

Efficacy of BRAF Inhibitors in Combination With Stereotactic Radiosurgery for the Treatment of Melanoma Brain Metastases: A Systematic Review and Meta-Analysis

Background

BRAF inhibitors have improved the outcome for patients with BRAF mutant metastatic melanoma and have shown intracranial responses in melanoma brain metastases. Stereotactic radiosurgery (SRS) is being used as a local treatment for melanoma brain metastasis (MBM) with better local control and survival. We searched for studies comparing the combination of two treatments with SRS alone to detect any clinical evidence of synergism.

Materials and Methods

PubMed, EMBASE, Medline, and Cochrane library were searched until May 2020 for studies with desired comparative outcomes. Outcomes of interest that were obtained for meta-analysis included survival as the primary, and local control as the secondary outcome.

Results

A total of eight studies involving 976 patients with MBM were selected. Survival was significantly improved for patients receiving BRAF inhibitor plus SRS in comparison to SRS alone as assessed from the time of SRS induction (SRS survival: hazard ratio [HR] 0.67 [0.58–0.79], p <0.00001), from the time of brain metastasis diagnosis (BM survival: HR 0.65 [0.54, 0.78], p < 0.00001), or from the time of primary diagnosis (PD survival: HR 0.74 [0.57–0.95], p = 0.02). Dual therapy was also associated with improved local control, indicating an additive effect of the two treatments (HR 0.53 [0.31–0.93], p=0.03). Intracranial hemorrhage was higher in patients receiving BRAF inhibitors plus SRS than in those receiving SRS alone (OR, 3.16 [1.43–6.96], p = 0.004).

Conclusions

BRAF inhibitors in conjunction with SRS as local treatment appear to be efficacious. Local brain control and survival improved in patients with MBM receiving dual therapy. Safety assessment would need to be elucidated further as the incidence of intracranial hemorrhage was increased.

The Pharmacology of Xenobiotics after Intracerebro Spinal Fluid Administration: Implications for the Treatment of Brain Tumors

The incidence of brain metastasis has been increasing for 10 years, with poor prognosis, unlike the improvement in survival for extracranial tumor localizations. Since recent advances in molecular biology and the development of specific molecular targets, knowledge of the brain distribution of drugs has become a pharmaceutical challenge. Most anticancer drugs fail to cross the blood–brain barrier. In order to get around this problem and penetrate the brain parenchyma, the use of intrathecal administration has been developed, but the mechanisms governing drug distribution from the cerebrospinal fluid to the brain parenchyma are poorly understood. Thus, in this review we discuss the pharmacokinetics of drugs after intrathecal administration, their penetration of the brain parenchyma and the different systems causing their efflux from the brain to the blood.

Lapatinib Plus Local Radiation Therapy for Brain Metastases From HER-2 Positive Breast Cancer Patients and Role of Trastuzumab: A Systematic Review and Meta-Analysis

Background

Intracranial activity of lapatinib has been demonstrated in several studies in patients with human epidermal growth factor receptor-2 positive breast cancers (HER-2+ BC). Stereotactic radiosurgery (SRS) has been increasingly used as the local therapy for brain metastases in breast cancer patients. Increased objective response rate was observed for lapatinib plus whole brain radiotherapy (WBRT) is such patients with high toxicity.

Objective

We seek to obtain clinical evidence of synergistic efficacy of lapatinib in combination with radiation therapy, in particular, SRS.

Materials and methods

We carried out a comprehensive research using the following databases: PubMed; Medline; EMBASE; Cochrane library. These databases were searched until 10 June 2020. PRISMA guidelines were followed step by step for carrying out this systematic review and meta-analysis. Review Manager v 5.4 software was used for statistical evaluation of data.

Results

Overall 6 studies with 843 HER-2 positive breast cancer patients (442 HER-2 amplified disease, 399 luminal B disease) were included in this systematic review and meta-analysis. A total 279 patients had received lapatinib in addition to HER-2 antibody (trastuzumab) plus/minus chemoradiotherapy, while 610 patients had received trastuzumab-based management or only chemoradiotherapy. Lapatinib-based management of BM was associated with significant increase in overall survival (HR 0.63 [0.52, 0.77], p < 0.00001). Combination of the two (trastuzumab plus lapatinib) was associated with increased survival advantage compared to each agent alone (0.55 [0.32, 0.92], p = 0.02). SRS in combination with lapatinib was associated with increased local control (HR 0.47 [0.33, 0.66], p = 0.0001). Ever use of lapatinib with SRS was associated an increased survival as reported in two studies (Shireen et al.: 27.3 vs. 19.5 months, p = 0.03; Kim et al.: 33.3 vs. 23.6 months, p = 0.009). Kim et al. also revealed significant increase in intracranial activity with concurrent lapatinib reporting 57% complete response compared to 38% (p < 0.001) and lower progressive disease rate of 11 vs. 19% (p < 0.001). Risk of radiation necrosis was decreased with lapatinib use.

Conclusions

Lapatinib has shown intracranial activity and yielded better survival for HER-2+ BC patients with BMs. SRS in combination with ever use of lapatinib had better local control and were associated with better survival. Radiation necrosis risk was reduced with the use of lapatinib.

Repurposing of Kinase Inhibitors for Treatment of COVID-19

The outbreak of COVID-19, the pandemic disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spurred an intense search for treatments by the scientific community. In the absence of a vaccine, the goal is to target the viral life cycle and alleviate the lung-damaging symptoms of infection, which can be life-threatening. There are numerous protein kinases associated with these processes that can be inhibited by FDA-approved drugs, the repurposing of which presents an alluring option as they have been thoroughly vetted for safety and are more readily available for treatment of patients and testing in clinical trials. Here, we characterize more than 30 approved kinase inhibitors in terms of their antiviral potential, due to their measured potency against key kinases required for viral entry, metabolism, or reproduction. We also highlight inhibitors with potential to reverse pulmonary insufficiency because of their anti-inflammatory activity, cytokine suppression, or antifibrotic activity. Certain agents are projected to be dual-purpose drugs in terms of antiviral activity and alleviation of disease symptoms, however drug combination is also an option for inhibitors with optimal pharmacokinetic properties that allow safe and efficacious co-administration with other drugs, such as antiviral agents, IL-6 blocking agents, or other kinase inhibitors.

Impact of Tyrosine Kinase Inhibitors (TKIs) Combined With Radiation Therapy for the Management of Brain Metastases From Renal Cell Carcinoma

Background: Targeted therapy has transformed the outcome for patients with metastatic renal cell carcinoma. Their efficacy and safety have also been demonstrated in brain metastatic RCC. Preclinical evidence suggests synergism of radiation and tyrosine kinase inhibitors. Consequently, several studies have compared their efficacy in the treatment of RCC brain metastases to the era of brain management with surgery/radiation only.

Objectives: We seek to systematically review and meta-analyze the results of those studies that involved comparative intervention groups of brain management; TKIs, and never used TKIs.

Methods and Materials: Online databases (PubMed, EMBASE, Cochrane library, and ClinicalTrials.gov) were searched for comparative studies. Overall survival as the primary outcome of interest, and local brain control, distant control, and adverse events as secondary outcomes of interest were recorded for meta-analysis. Hazard ratios were pooled together using Review Manager 5.3. Fixed effects or random effects model were adopted according to the level of heterogeneity. Subgroup analysis included studies that involved SRS as the local treatment of management.

Results: Overall 7 studies (n = 897) were included for meta-analysis. TKI use was associated with better survival (HR 0.60 [0.52, 0.69], p < 0.00001) and local brain control (HR 0.34 [0.11, 0.98], p = 0.05). SRS subgroup also revealed significantly better survival (HR 0.61 [0.44, 0.83], p = 0.002) and local brain control (HR 0.19 [0.08, 0.45], p = 0.0002). Distant brain control (HR 0.95 [0.67, 1.35], p = 0.79) and brain progression free survival were unaffected (HR 0.94 [0.56, 1.56], p = 0.80). Only one study (n = 376) reported significantly greater 12-months cumulative incidence of radiation necrosis with TKI use within 30 days of SRS (10.9 vs. 6.4%, p = 0.04).

Conclusions: TKIs use in combination with SRS is safe and effective for treating RCC brain metastases. Larger randomized controlled trials are warranted to validate the results.

Brain accumulation of tivozanib is restricted by ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein) in mice

Tivozanib is a potent and selective inhibitor of VEGFR1-3, recently approved by the EMA for first-line treatment of renal cell carcinoma. We used wild-type, knockout, and transgenic mouse strains to study the effects of the drug transporters ABCB1, ABCG2, and OATP1A/1B, and of the CYP3A enzymes on the oral availability and tissue distribution of tivozanib. Tivozanib was transported by human ABCB1 and mouse Abcg2 in polarized MDCK-II cells. Upon oral administration, tivozanib showed rapid absorption and the plasma concentration-time curves showed secondary peaks in all mouse strains, suggesting enterohepatic recirculation. The brain-to-plasma ratios were significantly increased in Abcb1a/1b^-/- (2.2-fold) and Abcb1a/1b;Abcg2^-/- (2.6-fold) mice compared to wild-type mice, indicating a modest protective role of these transporters in the blood-brain barrier. Slco1a/1b^-/- mice showed a 1.2-fold lower liver-to-plasma ratio than wild-type mice, suggesting a minor role of mOatp1a/1b in tivozanib liver distribution. Oral plasma pharmacokinetics of tivozanib was not significantly altered in these mouse strains, nor in Cyp3a knockout and CYP3A4-humanized mice. The modest effect of ABC transporters on tivozanib brain accumulation, if also true in humans, might mean that this drug is not strongly limited in its therapeutic efficacy against malignant lesions situated partly or completely behind the blood-brain barrier.

Abcg2 transporter affects plasma, milk and tissue levels of meloxicam

ATP-binding cassette (ABCG2) is an efflux transporter that extrudes xenotoxins from cells in liver, intestine, mammary gland, brain and other organs, affecting the pharmacokinetics, brain accumulation and secretion into milk of several compounds, including antitumoral, antimicrobial and anti-inflammatory drugs. The aim of this study was to investigate whether the widely used anti-inflammatory drug meloxicam is an Abcg2 sustrate, and how this transporter affects its systemic distribution. Using polarized ABCG2-transduced cell lines, we found that meloxicam is efficiently transported by murine Abcg2 and human ABCG2. After oral administration of meloxicam, the area under the plasma concentration-time curve in Abcg2^-/- mice was 2-fold higher than in wild type mice (146.06 ± 10.57 µg·h/ml versus 73.80 ± 10.00 µg·h/ml). Differences in meloxicam distribution were reported for several tissues after oral and intravenous administration, with a 20-fold higher concentration in the brain of Abcg2^-/- after oral administration. Meloxicam secretion into milk was also affected by the transporter, with a 2-fold higher milk-to-plasma ratio in wild-type compared with Abcg2^-/- lactating female mice after oral and intravenous administration. We conclude that Abcg2 is an important determinant of the plasma and brain distribution of meloxicam and is clearly involved in its secretion into milk.

Association between clinically relevant toxicities of pazopanib and sunitinib and the use of weak CYP3A4 and P-gp inhibitors

PURPOSE

Sunitinib and pazopanib, two tyrosine kinase inhibitors (TKI), may be targets of potential pharmacokinetic drug-drug interactions (P-PK-DDIs). While strong cytochrome P4503A (CYP3A4) inhibitors or inducers should cause a clinically relevant modification in plasma TKI concentrations, the effect of weak inhibitors is unknown. The objective of this study was to evaluate the association between weak P-PK-DDI and clinically relevant toxicity in real life.

PATIENTS AND METHODS

This was a single-center retrospective study including patients treated with sunitinib or pazopanib for any malignancies, for whom a PK-DDI analysis was performed before starting TKI. The primary endpoint was the correlation between P-PK-DDIs and a dose decrease after 1 month of treatment. The secondary endpoint was the correlation between PK-DDIs and drug withdrawal due to toxicity.

RESULTS

Seventy-six patients were assessed. A P-PK-DDI with weak CYP3A4 or P-gp inhibition was found in 14 patients. In patients with P-PK-DDI or without, the dose was reduced during the first month in 57.1% and 17.7% (p = 0.003) and the drug withdrawn in 42.8% and 11.3% (p = 0.011), respectively. In multivariate analysis, a significant correlation was found between P-PK-DDI (CYP3A4 and P-gp inhibitors) and dose reduction, and between drug withdrawal and PK-DDI (CYP3A4 inhibitors).

CONCLUSION

P-PK-DDI was correlated with dose reduction and drug withdrawal due to toxicity. The causality of this relationship warrants to be assessed; therefore, therapeutic drug monitoring is necessary in patients treated with TKI.

Targeted disruption of dual leucine zipper kinase and leucine zipper kinase promotes neuronal survival in a model of diffuse traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a major cause of CNS neurodegeneration and has no disease-altering therapies. It is commonly associated with a specific type of biomechanical disruption of the axon called traumatic axonal injury (TAI), which often leads to axonal and sometimes perikaryal degeneration of CNS neurons. We have previously used genome-scale, arrayed RNA interference-based screens in primary mouse retinal ganglion cells (RGCs) to identify a pair of related kinases, dual leucine zipper kinase (DLK) and leucine zipper kinase (LZK) that are key mediators of cell death in response to simple axotomy. Moreover, we showed that DLK and LZK are the major upstream triggers for JUN N-terminal kinase (JNK) signaling following total axonal transection. However, the degree to which DLK/LZK are involved in TAI/TBI is unknown.

METHODS

Here we used the impact acceleration (IA) model of diffuse TBI, which produces TAI in the visual system, and complementary genetic and pharmacologic approaches to disrupt DLK and LZK, and explored whether DLK and LZK play a role in RGC perikaryal and axonal degeneration in response to TAI.

RESULTS

Our findings show that the IA model activates DLK/JNK/JUN signaling but, in contrast to axotomy, many RGCs are able to recover from the injury and terminate the activation of the pathway. Moreover, while DLK disruption is sufficient to suppress JUN phosphorylation, combined DLK and LZK inhibition is required to prevent RGC cell death. Finally, we show that the FDA-approved protein kinase inhibitor, sunitinib, which has activity against DLK and LZK, is able to produce similar increases in RGC survival.

CONCLUSION

The mitogen-activated kinase kinase kinases (MAP3Ks), DLK and LZK, participate in cell death signaling of CNS neurons in response to TBI. Moreover, sustained pharmacologic inhibition of DLK is neuroprotective, an effect creating an opportunity to potentially translate these findings to patients with TBI.

Botryllamide G is an ABCG2 inhibitor that improves lapatinib delivery in mouse brain

Introduction: Transporters comprising the blood-brain barrier complicate delivery of many therapeutics to the central nervous system. The present study ascertained whether the natural product botryllamide G is viable for in vivo inhibition of ABCG2 using lapatinib as a probe for ABCB1 and ABCG2-mediated efflux from the brain. Methods: Wild-type and Mdr1a/Mdr1b (-/-) mice were treated with botryllamide G and lapatinib ("doublet therapy"), and while a separate cohort of wild-type mice was treated with botryllamide, tariquidar and lapatinib ("triplet therapy"). Results: Botryllamide G demonstrates biphasic elimination with a rapid distribution, decreasing below the in vitro IC50 of 6.9 µM within minutes, yet with a relatively slower terminal half-life (4.6 h). In Mdr1a/Mdr1b (-/-) mice, doublet therapy resulted in a significant increase in brain lapatinib AUC at 8 h (2058 h*ng/mL vs 4007 h*ng/mL; P = .031), but not plasma exposure (P = .15). No significant differences were observed after 24 h. Lapatinib brain exposure was greater through 1 h when wild-type mice were administered triplet therapy (298 h*pg/mg vs 120 h*pg/mg; P < .001), but the triplet decreased brain AUC through 24 h vs. mice administered lapatinib alone (2878 h*pg/mg vs 4461hr*ng/mL; P < .001) and did not alter the brain:plasma ratio. Conclusions: In summary, the ABCG2 inhibitor, botryllamide G, increases brain exposure to lapatinib in mice lacking Abcb1, although the combination of botryllamide G and tariquidar increases brain exposure in wild-type mice only briefly (1 h). Additional research is needed to find analogs of this compound that have better pharmacokinetics and pharmacodynamic effects on ABCG2 inhibition.

Development of MAP4 Kinase Inhibitors as Motor Neuron-Protecting Agents

Disease-causing mutations in many neurodegenerative disorders lead to proteinopathies that trigger endoplasmic reticulum (ER) stress. However, few therapeutic options exist for patients with these diseases. Using an in vitro screening platform to identify compounds that protect human motor neurons from ER stress-mediated degeneration, we discovered that compounds targeting the mitogen-activated protein kinase kinase kinase kinase (MAP4K) family are neuroprotective. The kinase inhibitor URMC-099 (compound 1) stood out as a promising lead compound for further optimization. We coupled structure-based compound design with functional activity testing in neurons subjected to ER stress to develop a series of analogs with improved MAP4K inhibition and concomitant increases in potency and efficacy. Further structural modifications were performed to enhance the pharmacokinetic profiles of the compound 1 derivatives. Prostetin/12k emerged as an exceptionally potent, metabolically stable, and blood-brain barrier-penetrant compound that is well suited for future testing in animal models of neurodegeneration.

Extracellular Vesicles: A Possible Link between HIV and Alzheimer's Disease-Like Pathology in HIV Subjects?

The longevity of people with HIV/AIDS has been prolonged with the use of antiretroviral therapy (ART). The age-related complications, especially cognitive deficits, rise as HIV patients live longer. Deposition of beta-amyloid (Aβ), a hallmark of Alzheimer's disease (AD), has been observed in subjects with HIV-associated neurocognitive disorders (HAND). Various mechanisms such as neuroinflammation induced by HIV proteins (e.g., Tat, gp120, Nef), excitotoxicity, oxidative stress, and the use of ART contribute to the deposition of Aβ, leading to dementia. However, progressive dementia in older subjects with HIV might be due to HAND, AD, or both. Recently, extracellular vesicles (EVs)/exosomes, have gained recognition for their importance in understanding the pathology of both HAND and AD. EVs can serve as a possible link between HIV and AD, due to their ability to package and transport the toxic proteins implicated in both AD and HIV (Aβ/tau and gp120/tat, respectively). Given that Aß is also elevated in neuron-derived exosomes isolated from the plasma of HIV patients, it is reasonable to suggest that neuron-to-neuron exosomal transport of Aβ and tau also contributes to AD-like pathology in HIV-infected subjects. Therefore, exploring exosomal contents is likely to help distinguish HAND from AD. However, future prospective clinical studies need to be conducted to compare the exosomal contents in the plasma of HIV subjects with and without HAND as well as those with and without AD. This would help to find new markers and develop new treatment strategies to treat AD in HIV-positive subjects. This review presents comprehensive literatures on the mechanisms contributing to Aβ deposition in HIV-infected cells, the role of EVs in the propagation of Aβ in AD, the possible role of EVs in HIV-induced AD-like pathology, and finally, possible therapeutic targets or molecules to treat HIV subjects with AD.

Brain accumulation of osimertinib and its active metabolite AZ5104 is restricted by ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein)

Osimertinib is an irreversible EGFR inhibitor registered for advanced NSCLC patients whose tumors harbor recurrent somatic activating mutations in EGFR (EGFRm⁺) or the frequently occurring EGFR-T790M resistance mutation. Using in vitro transport assays and appropriate knockout and transgenic mouse models, we investigated whether the multidrug efflux transporters ABCB1 and ABCG2 transport osimertinib and whether they influence the oral availability and brain accumulation of osimertinib and its most active metabolite, AZ5104. In vitro, human ABCB1 and mouse Abcg2 modestly transported osimertinib. In mice, Abcb1a/1b, with a minor contribution of Abcg2, markedly limited the brain accumulation of osimertinib and AZ5104. However, no effect of the ABC transporters was seen on osimertinib oral availability. In spite of up to 6-fold higher brain accumulation, we observed no acute toxicity signs of oral osimertinib in Abcb1a/1b;Abcg2 knockout mice. Interestingly, even in wild-type mice the intrinsic brain penetration of osimertinib was already relatively high, which may help to explain the documented partial efficacy of this drug against brain metastases. No substantial effects of mouse Cyp3a knockout or transgenic human CYP3A4 overexpression on oral osimertinib pharmacokinetics were observed, presumably due to a dominant role of mouse Cyp2d enzymes in osimertinib metabolism. Our results suggest that pharmacological inhibition of ABCB1 and ABCG2 during osimertinib therapy might potentially be considered to further benefit patients with brain (micro-)metastases positioned behind an intact blood-brain barrier, or with substantial expression of these transporters in the tumor cells, without invoking a high toxicity risk.

Coexpression of ABCB1 and ABCG2 in a Cell Line Model Reveals Both Independent and Additive Transporter Function

Although overexpression of multiple ATP-binding cassette transporters has been reported in clinical samples, few studies have examined how coexpression of multiple transporters affected resistance to chemotherapeutic drugs. We therefore examined how coexpression of ABCB1 (P-glycoprotein) and ABCG2 contributes to drug resistance in a cell line model. HEK293 cells were transfected with vector-encoding full-length ABCB1, ABCG2, or a bicistronic vector containing both genes, each under the control of a separate promoter. Cells transfected with both transporters (B1/G2 cells) demonstrated high levels of both transporters, and uptake of both the ABCB1-specific substrate rhodamine 123 and the ABCG2-specific substrate pheophorbide a was reduced when examined by flow cytometry. B1/G2 cells were also cross-resistant to the ABCB1 substrate doxorubicin, the ABCG2 substrate topotecan, as well as mitoxantrone and the cell cycle checkpoint kinase 1 inhibitor prexasertib, both of which were found to be substrates of both ABCB1 and ABCG2. When B1/G2 cells were incubated with both rhodamine 123 and pheophorbide a, transport of both compounds was observed, suggesting that ABCB1 and ABCG2, when coexpressed, can function independently to transport substrates. ABCB1 and ABCG2 also functioned additively to transport the common fluorescent substrates mitoxantrone and BODIPY-prazosin, as it was necessary to inhibit both transporters to prevent efflux from B1/G2 cells. ABCG2 expression was also found to decrease the efficacy of the ABCB1 inhibitor tariquidar in B1/G2 cells. Thus, ABCB1 and ABCG2 can independently and additively confer resistance to substrates, underscoring the need to inhibit multiple transporters when they are coexpressed.

Tumor-induced neoangiogenesis and receptor tyrosine kinases - Mechanisms and strategies for acquired resistance

BACKGROUND

Angiogenesis is essential for tumor growth, proliferation and metastasis. Tumor-related angiogenesis is complex and involves multiple signaling pathways. Controlling angiogenesis is a promising strategy for limiting cancer progression.

SCOPE OF REVIEW

Several receptor tyrosine kinases influence the angiogenic response via multiple signaling molecules and pathways. Understanding the functional interaction of kinases in the angiogenic process and development of resistance to kinase inhibition is essential for future successful therapeutic strategies.

MAJOR CONCLUSIONS

Strategies that target receptor tyrosine kinases and other tumor microenvironment factors simultaneously, or sequentially, are required for achieving an efficient and robust anti-angiogenic response.

GENERAL SIGNIFICANCE

Understanding the molecular mechanism of angiogenesis has improved, and has led, to the clinical development and approval of anti-angiogenic drugs. While many patients have benefited from these agents, their limited efficacy and the development of resistance remains a challenge. This review highlights current therapies and challenges associated with targeting angiogenesis in cancer.

Inhibition of ABCB1 and ABCG2 at the Mouse Blood-Brain Barrier with Marketed Drugs To Improve Brain Delivery of the Model ABCB1/ABCG2 Substrate [11C]erlotinib

P-Glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) are two efflux transporters at the blood-brain barrier (BBB), which effectively restrict brain distribution of diverse drugs, such as tyrosine kinase inhibitors. There is a crucial need for pharmacological ABCB1 and ABCG2 inhibition protocols for a more effective treatment of brain diseases. In the present study, seven marketed drugs (osimertinib, erlotinib, nilotinib, imatinib, lapatinib, pazopanib, and cyclosporine A) and one nonmarketed drug (tariquidar), with known in vitro ABCB1/ABCG2 inhibitory properties, were screened for their inhibitory potency at the BBB in vivo. Positron emission tomography (PET) using the model ABCB1/ABCG2 substrate [¹¹C]erlotinib was performed in mice. Tested inhibitors were administered as i.v. bolus injections at 30 min before the start of the PET scan, followed by a continuous i.v. infusion for the duration of the PET scan. Five of the tested drugs increased total distribution volume of [¹¹C]erlotinib in the brain ( V_T,brain) compared to vehicle-treated animals (tariquidar, + 69%; erlotinib, + 19% and +23% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 22%; lapatinib, + 25%; and cyclosporine A, + 49%). For all drugs, increases in [¹¹C]erlotinib brain distribution were lower than in Abcb1a/b^(-/-)Abcg2^(-/-) mice (+149%), which suggested that only partial ABCB1/ABCG2 inhibition was reached at the mouse BBB. The plasma concentrations of the tested drugs at the time of the PET scan were higher than clinically achievable plasma concentrations. Some of the tested drugs led to significant increases in blood radioactivity concentrations measured at the end of the PET scan (erlotinib, + 103% and +113% for the 21.5 mg/kg and the 43 mg/kg dose, respectively; imatinib, + 125%; and cyclosporine A, + 101%), which was most likely caused by decreased hepatobiliary excretion of radioactivity. Taken together, our data suggest that some marketed tyrosine kinase inhibitors may be repurposed to inhibit ABCB1 and ABCG2 at the BBB. From a clinical perspective, moderate increases in brain delivery despite the administration of high i.v. doses as well as peripheral drug-drug interactions due to transporter inhibition in clearance organs question the translatability of this concept.

Oral coadministration of elacridar and ritonavir enhances brain accumulation and oral availability of the novel ALK/ROS1 inhibitor lorlatinib

Lorlatinib, a novel generation oral anaplastic lymphoma kinase (ALK) and ROS1 inhibitor with high membrane and blood-brain barrier permeability, recently received accelerated approval for treatment of ALK-rearranged non-small-cell lung cancer (NSCLC), and its further clinical development is ongoing. We previously found that the efflux transporter P-glycoprotein (MDR1/ABCB1) restricts lorlatinib brain accumulation and that the drug-metabolizing enzyme cytochrome P450-3A (CYP3A) limits its oral availability. Using genetically modified mouse models, we investigated the impact of targeted pharmacological inhibitors on lorlatinib pharmacokinetics and bioavailability. Upon oral administration of lorlatinib, the plasma AUC_0-8h in CYP3A4-humanized mice was ∼1.8-fold lower than in wild-type and Cyp3a^-/- mice. Oral coadministration of the CYP3A inhibitor ritonavir caused reversion to the AUC_0-8h levels seen in wild-type and Cyp3a^-/- mice, without altering the relative tissue distribution of lorlatinib. Moreover, simultaneous pharmacological inhibition of P-glycoprotein and CYP3A4 with oral elacridar and ritonavir in CYP3A4-humanized mice profoundly increased lorlatinib brain concentrations, but not its oral availability or other relative tissue distribution. Oral lorlatinib pharmacokinetics was not significantly affected by absence of the multispecific Oatp1a/1b drug uptake transporters. The absolute oral bioavailability of lorlatinib over 8 h in wild-type, Cyp3a^-/-, and CYP3A4-humanized mice was 81.6%, 72.9%, and 58.5%, respectively. Lorlatinib thus has good oral bioavailability, which is markedly restricted by human CYP3A4 but not by mouse Cyp3a. Pharmacological inhibition of CYP3A4 reversed these effects, and simultaneous P-gp inhibition with elacridar boosted absolute brain levels of lorlatinib by 16-fold without obvious toxicity. These insights may help to optimize the clinical application of lorlatinib.

P-glycoprotein (MDR1/ABCB1) and Breast Cancer Resistance Protein (BCRP/ABCG2) limit brain accumulation of the FLT3 inhibitor quizartinib in mice

Quizartinib, a second-generation FLT3 inhibitor, is in clinical development for the treatment of acute myeloid leukemia. We studied its pharmacokinetic interactions with the multidrug efflux transporters ABCB1 and ABCG2 and the multidrug metabolizing enzyme CYP3A, using in vitro transport assays and knockout and transgenic mouse models. Quizartinib was transported by human ABCB1 in vitro, and by mouse (m)Abcb1 and mAbcg2 in vivo. Upon oral administration, the brain accumulation of quizartinib was 6-fold decreased by mAbcb1 and 2-fold by mAbcg2 (together: 12-fold). Unexpectedly, the absence of mAbcb1 resulted in a ∼2-fold lower plasma exposure in Abcb1a/1b^-/- and Abcb1a/1b;Abcg2^-/- mice, suggesting that loss of mAbcb1 causes compensatory alterations in alternative quizartinib elimination or uptake systems. mAbcb1 and mAbcg2 themselves did not appear to restrict quizartinib oral availability. Oral and intravenous pharmacokinetics of quizartinib were not substantially altered between wild-type, Cyp3a knockout and CYP3A4-humanized mice. All three strains showed relatively high (33-51%) oral bioavailability. If this also applies in humans, this would suggest a limited risk of CYP3A-related inter-individual variation in exposure for this drug. Our results provide a possible rationale for using pharmacological ABCB1/ABCG2 inhibitors together with quizartinib when treating malignant lesions situated in part or in whole behind the blood-brain barrier.

WINDOW consortium: A path towards increased therapy efficacy against glioblastoma

Glioblastoma is the most common and malignant form of brain cancer, for which the standard treatment is maximal surgical resection, radiotherapy and chemotherapy. Despite these interventions, mean overall survival remains less than 15 months, during which extensive tumor infiltration throughout the brain occurs. The resulting metastasized cells in the brain are characterized by chemotherapy resistance and extensive intratumoral heterogeneity. An orthogonal approach attacking both intracellular resistance mechanisms as well as intercellular heterogeneity is necessary to halt tumor progression. For this reason, we established the WINDOW Consortium (Window for Improvement for Newly Diagnosed patients by Overcoming disease Worsening), in which we are establishing a strategy for rational selection and development of effective therapies against glioblastoma. Here, we overview the many challenges posed in treating glioblastoma, including selection of drug combinations that prevent therapy resistance, the need for drugs that have improved blood brain barrier penetration and strategies to counter heterogeneous cell populations within patients. Together, this forms the backbone of our strategy to attack glioblastoma.

Novel therapeutic compound acridine-retrotuftsin action on biological forms of melanoma and neuroblastoma

PURPOSE

As a continuation of our search for anticancer agents, we have synthesized a new acridine-retrotuftsin analog HClx9-[Arg(NO₂)-Pro-Lys-Thr-OCH₃]-1-nitroacridine (named ART) and have evaluated its activity against melanoma and neuroblastoma lines. Both tumors develop from cells (melanocytes, neurons) of neuroectodermal origin, and both are tumors with high heterogeneity and unsatisfactory susceptibility to chemotherapies. Thus, we analyzed the action of ART on pairs of biological forms of melanoma (amelanotic and melanotic) and neuroblastoma (dopaminergic and cholinergic) with regard to proliferation, mechanism of cell death, and effect on the activity of tricarboxylic acid cycle (TAC) enzymes.

METHODS

The cytotoxicity of ART was evaluated by XTT and trypan blue tests. Cell death was estimated by plasma membrane structure changes (phosphatidylserine and calreticulin externalization), caspase activation, presence of ROS (reactive oxygen species), activity of tricarboxylic acid cycle enzymes (pyruvate dehydrogenase complex, aconitase, and isocitrate dehydrogenase), NAD level, and ATP level.

RESULTS

ART influences the biological forms of melanoma and neuroblastoma in different ways. Amelanotic (Ab) melanoma (with the inhibited melanogenesis, higher malignancy) and SHSY5Y neuroblastoma (with cholinergic DC cells) were especially sensitive to ART action. The Ab melanoma cells died through apoptosis, while, with SH-SY5Y-DC neuroblastoma, the number of cells decreased but not as a result of apoptosis. With Ab melanoma and SH-SY5Y-DC cells, a diminished activity of TAC enzymes was noticed, along with ATP/NAD depletion.

CONCLUSION

Our data show that the biological forms of certain tumors responded in different ways to the action of ART. As a combination of retrotuftsin and acridine, the compound can be an inducer of apoptotic cell death of melanoma, especially the amelanotic form. Although the mechanism of the interrelationships between energy metabolism and cell death is not fully understood, interference of ART with TAC enzymes could encourage the further investigation of its anticancer action.

Revisiting the role of ABC transporters in multidrug-resistant cancer

Most patients who die of cancer have disseminated disease that has become resistant to multiple therapeutic modalities. Ample evidence suggests that the expression of ATP-binding cassette (ABC) transporters, especially the multidrug resistance protein 1 (MDR1, also known as P-glycoprotein or P-gp), which is encoded by ABC subfamily B member 1 (ABCB1), can confer resistance to cytotoxic and targeted chemotherapy. However, the development of MDR1 as a therapeutic target has been unsuccessful. At the time of its discovery, appropriate tools for the characterization and clinical development of MDR1 as a therapeutic target were lacking. Thirty years after the initial cloning and characterization of MDR1 and the implication of two additional ABC transporters, the multidrug resistance-associated protein 1 (MRP1; encoded by ABCC1)), and ABCG2, in multidrug resistance, interest in investigating these transporters as therapeutic targets has waned. However, with the emergence of new data and advanced techniques, we propose to re-evaluate whether these transporters play a clinical role in multidrug resistance. With this Opinion article, we present recent evidence indicating that it is time to revisit the investigation into the role of ABC transporters in efficient drug delivery in various cancer types and at the blood-brain barrier.

Therapeutic Potential and Utility of Elacridar with Respect to P-glycoprotein Inhibition: An Insight from the Published In Vitro, Preclinical and Clinical Studies

The occurrence of efflux mechanisms via Permeability-glycoprotein (P-gp) recognized as an important physiological process impedes drug entry or transport across membranes into tissues. In some instances, either low oral bioavailability or lack of brain penetration has been attributed to P-gp mediated efflux activity. Therefore, the objective of development of P-gp inhibitors was to facilitate the attainment of higher drug exposures in tissues. Many third-generation P-gp inhibitors such as elacridar, tariquidar, zosuquidar, etc. have entered clinical development to fulfil the promise. The body of evidence from in vitro and in vivo preclinical and clinical data reviewed in this paper provides the basis for an effective blockade of P-gp efflux mechanism by elacridar. However, clinical translation of the promise has been elusive not just for elacridar but also for other P-gp inhibitors in this class. The review provides introspection and perspectives on the lack of clinical translation of this class of drugs and a broad framework of strategies and considerations in the potential application of elacridar and other P-gp inhibitors in oncology therapeutics.

Obstacles to Brain Tumor Therapy: Key ABC Transporters

The delivery of cancer chemotherapy to treat brain tumors remains a challenge, in part, because of the inherent biological barrier, the blood-brain barrier. While its presence and role as a protector of the normal brain parenchyma has been acknowledged for decades, it is only recently that the important transporter components, expressed in the tightly knit capillary endothelial cells, have been deciphered. These transporters are ATP-binding cassette (ABC) transporters and, so far, the major clinically important ones that functionally contribute to the blood-brain barrier are ABCG2 and ABCB1. A further limitation to cancer therapy of brain tumors or brain metastases is the blood-tumor barrier, where tumors erect a barrier of transporters that further impede drug entry. The expression and regulation of these two transporters at these barriers, as well as tumor derived alteration in expression and/or mutation, are likely obstacles to effective therapy.

BCRP/ABCG2 and high-alert medications: Biochemical, pharmacokinetic, pharmacogenetic, and clinical implications

The human breast cancer resistance protein (BCRP/ABCG2) is an ATP-binding cassette efflux transporter that uses ATP hydrolysis to expel xenobiotics from cells, including anti-cancer medications. It is expressed in the gastrointestinal tract, liver, kidney, and brain endothelium. Thus, ABCG2 functions as a tissue barrier to drug transport that strongly influences the pharmacokinetics of substrate medications. Genetic polymorphisms of ABCG2 are closely related to inter-individual variations in therapeutic performance. The common single nucleotide polymorphism c.421C>A, p.Q141K reduces cell surface expression of ABCG2 protein, resulting in lower efflux of substrates. Consequently, a higher plasma concentration of substrate is observed in patients carrying an ABCG2 c.421C>A allele. Detailed pharmacokinetic analyses have revealed that altered intestinal absorption is responsible for the distinct pharmacokinetics of ABCG2 substrates in genetic carriers of the ABCG2 c.421C>A polymorphism. Recent studies have focused on the high-alert medications among ABCG2 substrates (defined as those with high risk of adverse events), such as tyrosine kinase inhibitors (TKIs) and direct oral anti-coagulants (DOACs). For these high-alert medications, inter-individual variation may be closely related to the severity of side effects. In addition, ethnic differences in the frequency of ABCG2 c.421C>A have been reported, with markedly higher frequency in East Asian (∼30-60%) than Caucasian and African-American populations (∼5-10%). Therefore, ABCG2 polymorphisms must be considered not only in the drug development phase, but also in clinical practice. In the present review, we provide an update of basic and clinical knowledge on genetic polymorphisms of ABCG2.

Overexpression of ATP-Binding Cassette Subfamily G Member 2 Confers Resistance to Phosphatidylinositol 3-Kinase Inhibitor PF-4989216 in Cancer Cells

Deregulated activation of phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is frequently found in human cancers, which plays a key role in promoting cancer proliferation and resistance to anticancer therapies. Therefore, developing inhibitors targeting key components of the PI3K/Akt/mTOR signaling pathway has great clinical significance. PF-4989216 is a novel, orally available small-molecule drug that was developed to selectively inhibit the PI3K/Akt/mTOR signaling pathway and subsequent cancer cell proliferation. PF-4989216 exhibited potent and selective inhibition against PI3K kinase activity in preclinical small-cell lung cancer (SCLC) models, and was especially effective against the proliferation of SCLCs harboring PIK3CA mutation. Unfortunately, in addition to innate resistance mechanisms, drug extrusion by the efflux pumps may also contribute to the development of acquired resistance to PI3K inhibitors in cancer cells. The overexpression of ATP-binding cassette (ABC) drug transporters ABCB1 and ABCG2 is one of the most common mechanisms for reducing intracellular drug concentration and developing multidrug resistance, which remains a substantial challenge to the effective treatment of cancer. In this study, we report the discovery of ABCG2 overexpression as a mechanism of resistance to PI3K inhibitor PF-4989216 in human cancer cells. We demonstrated that the inhibition of Akt and downstream S6RP phosphorylation by PF-4989216 were significantly reduced in ABCG2-overexpressing human cancer cells. Moreover, overexpression of ABCG2 in various cancer cell lines confers significant resistance to PF-4989216, which can be reversed by an inhibitor or competitive substrate of ABCG2, indicating that ABCG2-mediated transport alone can sufficiently reduce the intracellular concentration of PF-4989216.

Breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp/ABCB1) transport afatinib and restrict its oral availability and brain accumulation

Afatinib is a highly selective, irreversible inhibitor of EGFR and HER-2. It is orally administered for the treatment of patients with EGFR mutation-positive types of metastatic NSCLC. We investigated whether afatinib is a substrate for the multidrug efflux transporters ABCB1 and ABCG2 and whether these transporters influence oral availability and brain and other tissue accumulation of afatinib. We used in vitro transport assays to assess human (h)ABCB1-, hABCG2- or murine (m)Abcg2-mediated transport of afatinib. To study the single and combined roles of Abcg2 and Abcb1a/1b in oral afatinib disposition, we used appropriate knockout mouse strains. Afatinib was transported well by hABCB1, hABCG2 and mAbcg2 in vitro. Upon oral administration of afatinib, Abcg2^-/-, Abcb1a/1b^-/- and Abcb1a/1b^-/-;Abcg2^-/- mice displayed a 4.2-, 2.4- and 7-fold increased afatinib plasma AUC_0-24 compared with wild-type mice. Abcg2-deficient strains also displayed decreased afatinib plasma clearance. At 2h, relative brain accumulation of afatinib was not significantly altered in the single knockout strains, but 23.8-fold increased in Abcb1a/1b^-/-;Abcg2^-/- mice compared to wild-type mice. Abcg2 and Abcb1a/1b restrict oral availability and brain accumulation of afatinib. Inhibition of these transporters may therefore be of clinical importance for patients with brain (micro)metastases positioned behind an intact blood-brain barrier.

ABCG2/BCRP: Specific and Nonspecific Modulators

Multidrug resistance (MDR) in cancer cells is the development of resistance to a variety of structurally and functionally nonrelated anticancer drugs. This phenomenon has become a major obstacle to cancer chemotherapy seriously affecting the clinical outcome. MDR is associated with increased drug efflux from cells mediated by an energy-dependent mechanism involving the ATP-binding cassette (ABC) transporters, mainly P-glycoprotein (ABCB1), the MDR-associated protein-1 (ABCC1), and the breast cancer resistance protein (ABCG2). The first two transporters have been widely studied already and reviews summarized the results. The ABCG2 protein has been a subject of intense study since its discovery as its overexpression has been detected in resistant cell lines in numerous types of human cancers. To date, a long list of modulators of ABCG2 exists and continues to increase. However, little is known about the clinical consequences of ABCG2 modulation. This makes the design of novel, potent, and nontoxic inhibitors of this efflux protein a major challenge to reverse MDR and thereby increase the success of chemotherapy. The aim of the present review is to describe and highlight specific and nonspecific modulators of ABCG2 reported to date based on the selectivity of the compounds, as many of them are effective against one or more ABC transport proteins.

Blood-brain barrier transport machineries and targeted therapy of brain diseases

Introduction: Desired clinical outcome of pharmacotherapy of brain diseases largely depends upon the safe drug delivery into the brain parenchyma. However, due to the robust blockade function of the blood-brain barrier (BBB), drug transport into the brain is selectively controlled by the BBB formed by brain capillary endothelial cells and supported by astrocytes and pericytes.

Methods: In the current study, we have reviewed the most recent literature on the subject to provide an insight upon the role and impacts of BBB on brain drug delivery and targeting.

Results: All drugs, either small molecules or macromolecules, designated to treat brain diseases must adequately cross the BBB to provide their therapeutic properties on biological targets within the central nervous system (CNS). However, most of these pharmaceuticals do not sufficiently penetrate into CNS, failing to meet the intended therapeutic outcomes. Most lipophilic drugs capable of penetrating BBB are prone to the efflux functionality of BBB. In contrast, all hydrophilic drugs are facing severe infiltration blockage imposed by the tight cellular junctions of the BBB. Hence, a number of strategies have been devised to improve the efficiency of brain drug delivery and targeted therapy of CNS disorders using multimodal nanosystems (NSs).

Conclusions: In order to improve the therapeutic outcomes of CNS drug transfer and targeted delivery, the discriminatory permeability of BBB needs to be taken under control. The carrier-mediated transport machineries of brain capillary endothelial cells (BCECs) can be exploited for the discovery, development and delivery of small molecules into the brain. Further, the receptor-mediated transport systems can be recruited for the delivery of macromolecular biologics and multimodal NSs into the brain.

Impact of Membrane Drug Transporters on Resistance to Small-Molecule Tyrosine Kinase Inhibitors

Small-molecule inhibitors of tyrosine kinases (TKIs) are the mainstay of treatment for many malignancies and represent novel treatment options for other diseases such as idiopathic pulmonary fibrosis. Twenty-five TKIs are currently FDA-approved and >130 are being evaluated in clinical trials. Increasing evidence suggests that drug exposure of TKIs may significantly contribute to drug resistance, independently from somatic variation of TKI target genes. Membrane transport proteins may limit the amount of TKI reaching the target cells. This review highlights current knowledge on the basic and clinical pharmacology of membrane transporters involved in TKI disposition and their contribution to drug efficacy and adverse drug effects. In addition to non-genetic and epigenetic factors, genetic variants, particularly rare ones, in transporter genes are promising novel factors to explain interindividual variability in the response to TKI therapy.