Strategies to improve delivery of anticancer drugs across the blood-brain barrier to treat glioblastoma

Glioblastoma (GBM) is a lethal and aggressive brain tumor that is resistant to conventional radiation and cytotoxic chemotherapies. Molecularly targeted agents hold great promise in treating these genetically heterogeneous tumors, yet have produced disappointing results. One reason for the clinical failure of these novel therapies can be the inability of the drugs to achieve effective concentrations in the invasive regions beyond the bulk tumor. In this review, we describe the influence of the blood-brain barrier on the distribution of anticancer drugs to both the tumor core and infiltrative regions of GBM. We further describe potential strategies to overcome these drug delivery limitations. Understanding the key factors that limit drug delivery into brain tumors will guide future development of approaches for enhanced delivery of effective drugs to GBM.

Improving drug delivery to primary and metastatic brain tumors: strategies to overcome the blood-brain barrier

Brain tumor diagnosis has an extremely poor prognosis, due in part to the blood-brain barrier (BBB) that prevents both early diagnosis and effective drug delivery. The infiltrative nature of primary brain tumors and the presence of micro-metastases lead to tumor cells that reside behind an intact BBB. Recent genomic technologies have identified many genetic mutations present in glioma and other central nervous system (CNS) tumors, and this information has been instrumental in guiding the development of molecularly targeted therapies. However, the majority of these agents are unable to penetrate an intact BBB, leading to one mechanism by which the invasive brain tumor cells effectively escape treatment. The diagnosis and treatment of a brain tumor remains a serious challenge and new therapeutic agents that either penetrate the BBB or disrupt mechanisms that limit brain penetration, such as endothelial efflux transporters or tight junctions, are required in order to improve patient outcomes in this devastating disease.

Psychotic syndromes in epilepsy

Claims have been made that epilepsy is associated with both brief psychotic episodes and persistent psychotic states. The existence of brief, nonconfusional psychotic episodes in epilepsy has received some formal support; these may be a function of temporal lobe subictal activity. Persistent psychosis is found in about 7% of patients with epilepsy; independent evidence indicates this to be a significant association. Temporal lobe seizure activity, again probably acting subictally, may be involved in the pathogenesis of these states, perhaps in interaction with other factors. Occurrence of psychotic syndromes in epilepsy may be relevant to kindling, atypical psychoses unrelated to epilepsy, and the psychotropic effect of carbamazepine.

Efflux transporters at the blood-brain barrier limit delivery and efficacy of cyclin-dependent kinase 4/6 inhibitor palbociclib (PD-0332991) in an orthotopic brain tumor model

6-Acetyl-8-cyclopentyl-5-methyl-2-([5-(piperazin-1-yl)pyridin-2-yl]amino)pyrido(2,3-d)pyrimidin-7(8H)-one [palbociclib (PD-0332991)] is a cyclin-dependent kinase 4/6 inhibitor approved for the treatment of metastatic breast cancer and is currently undergoing clinical trials for many solid tumors. Glioblastoma (GBM) is the most common primary brain tumor in adults and has limited treatment options. The cyclin-dependent kinase 4/6 pathway is commonly dysregulated in GBM and is a promising target in treating this devastating disease. The blood-brain barrier (BBB) limits the delivery of drugs to invasive regions of GBM, where the efflux transporters P-glycoprotein and breast cancer resistance protein can prevent treatments from reaching the tumor. The purpose of this study was to examine the mechanisms limiting the effectiveness of palbociclib therapy in an orthotopic xenograft model. The in vitro intracellular accumulation results demonstrated that palbociclib is a substrate for both P-glycoprotein and breast cancer resistance protein. In vivo studies in transgenic mice confirmed that efflux transport is responsible for the limited brain distribution of palbociclib. There was an ∼115-fold increase in brain exposure at steady state in the transporter deficient mice when compared with wild-type mice, and the efflux inhibitor elacridar significantly increased palbociclib brain distribution. Efficacy studies demonstrated that palbociclib is an effective therapy when GBM22 tumor cells are implanted in the flank, but ineffective in an orthotopic (intracranial) model. Moreover, doses designed to mimic brain exposure were ineffective in treating flank tumors. These results demonstrate that efflux transport in the BBB is involved in limiting the brain distribution of palbociclib and this has critical implications in determining effective dosing regimens of palbociclib therapy in the treatment of brain tumors.

Efficacy of PARP Inhibitor Rucaparib in Orthotopic Glioblastoma Xenografts Is Limited by Ineffective Drug Penetration into the Central Nervous System

PARP inhibition can enhance the efficacy of temozolomide and prolong survival in orthotopic glioblastoma (GBM) xenografts. The aim of this study was to evaluate the combination of the PARP inhibitor rucaparib with temozolomide and to correlate pharmacokinetic and pharmacodynamic studies with efficacy in patient-derived GBM xenograft models. The combination of rucaparib with temozolomide was highly effective in vitro in short-term explant cultures derived from GBM12, and, similarly, the combination of rucaparib and temozolomide (dosed for 5 days every 28 days for 3 cycles) significantly prolonged the time to tumor regrowth by 40% in heterotopic xenografts. In contrast, the addition of rucaparib had no impact on the efficacy of temozolomide in GBM12 or GBM39 orthotopic models. Using Madin-Darby canine kidney (MDCK) II cells stably expressing murine BCRP1 or human MDR1, cell accumulation studies demonstrated that rucaparib is transported by both transporters. Consistent with the influence of these efflux pumps on central nervous system drug distribution, Mdr1a/b(-/-)Bcrp1(-/-) knockout mice had a significantly higher brain to plasma ratio for rucaparib (1.61 ± 0.25) than wild-type mice (0.11 ± 0.08). A pharmacokinetic and pharmacodynamic evaluation after a single dose confirmed limited accumulation of rucaparib in the brain is associated with substantial residual PARP enzymatic activity. Similarly, matrix-assisted laser desorption/ionization mass spectrometric imaging demonstrated significantly enhanced accumulation of drug in flank tumor compared with normal brain or orthotopic tumors. Collectively, these results suggest that limited drug delivery into brain tumors may significantly limit the efficacy of rucaparib combined with temozolomide in GBM.

Restricted Delivery of Talazoparib Across the Blood-Brain Barrier Limits the Sensitizing Effects of PARP Inhibition on Temozolomide Therapy in Glioblastoma

Poly ADP-ribose polymerase (PARP) inhibitors, including talazoparib, potentiate temozolomide efficacy in multiple tumor types; however, talazoparib-mediated sensitization has not been evaluated in orthotopic glioblastoma (GBM) models. This study evaluates talazoparib ± temozolomide in clinically relevant GBM models. Talazoparib at 1-3 nmol/L sensitized T98G, U251, and GBM12 cells to temozolomide, and enhanced DNA damage signaling and G₂-M arrest in vitroIn vivo cyclical therapy with talazoparib (0.15 mg/kg twice daily) combined with low-dose temozolomide (5 mg/kg daily) was well tolerated. This talazoparib/temozolomide regimen prolonged tumor stasis more than temozolomide alone in heterotopic GBM12 xenografts [median time to endpoint: 76 days versus 50 days temozolomide (P = 0.005), 11 days placebo (P < 0.001)]. However, talazoparib/temozolomide did not accentuate survival beyond that of temozolomide alone in corresponding orthotopic xenografts [median survival 37 vs. 30 days with temozolomide (P = 0.93), 14 days with placebo, P < 0.001]. Average brain and plasma talazoparib concentrations at 2 hours after a single dose (0.15 mg/kg) were 0.49 ± 0.07 ng/g and 25.5±4.1 ng/mL, respectively. The brain/plasma distribution of talazoparib in Bcrp^-/- versus wild-type (WT) mice did not differ, whereas the brain/plasma ratio in Mdr1a/b^-/- mice was higher than WT mice (0.23 vs. 0.02, P < 0.001). Consistent with the in vivo brain distribution, overexpression of MDR1 decreased talazoparib accumulation in MDCKII cells. These results indicate that talazoparib has significant MDR1 efflux liability that may restrict delivery across the blood-brain barrier, and this may explain the loss of talazoparib-mediated temozolomide sensitization in orthotopic versus heterotopic GBM xenografts. Mol Cancer Ther; 16(12); 2735-46. ©2017 AACR.

Enhanced antitumor immunity by a novel small molecule HPK1 inhibitor

Background

Hematopoietic progenitor kinase 1 (HPK1 or MAP4K1) has been demonstrated as a negative intracellular immune checkpoint in mediating antitumor immunity in studies with HPK1 knockout and kinase dead mice. Pharmacological inhibition of HPK1 is desirable to investigate the role of HPK1 in human immune cells with therapeutic implications. However, a significant challenge remains to identify a small molecule inhibitor of HPK1 with sufficient potency, selectivity, and other drug-like properties suitable for proof-of-concept studies. In this report, we identified a novel, potent, and selective HPK1 small molecule kinase inhibitor, compound K (CompK). A series of studies were conducted to investigate the mechanism of action of CompK, aiming to understand its potential application in cancer immunotherapy.

Methods

Human primary T cells and dendritic cells (DCs) were investigated with CompK treatment under conditions relevant to tumor microenvironment (TME). Syngeneic tumor models were used to assess the in vivo pharmacology of CompK followed by human tumor interrogation ex vivo.

Results

CompK treatment demonstrated markedly enhanced human T-cell immune responses under immunosuppressive conditions relevant to the TME and an increased avidity of the T-cell receptor (TCR) to recognize viral and tumor-associated antigens (TAAs) in significant synergy with anti-PD1. Animal model studies, including 1956 sarcoma and MC38 syngeneic models, revealed improved immune responses and superb antitumor efficacy in combination of CompK with anti-PD-1. An elevated immune response induced by CompK was observed with fresh tumor samples from multiple patients with colorectal carcinoma, suggesting a mechanistic translation from mouse model to human disease.

Conclusion

CompK treatment significantly improved human T-cell functions, with enhanced TCR avidity to recognize TAAs and tumor cytolytic activity by CD8+ T cells. Additional benefits include DC maturation and priming facilitation in tumor draining lymph node. CompK represents a novel pharmacological agent to address cancer treatment resistance.

ABCG2 and ABCB1 Limit the Efficacy of Dasatinib in a PDGF-B-Driven Brainstem Glioma Model

Dasatinib is a multikinase inhibitor in clinical trials for glioma, and thus far has failed to demonstrate significant efficacy. We investigated whether the ABC efflux transporters ABCG2 and ABCB1 expressed in the blood-brain barrier (BBB), are limiting the efficacy of dasatinib in the treatment of glioma using genetic and pharmacologic approaches. We utilized a genetic brainstem glioma mouse model driven by platelet-derived growth factor-B and p53 loss using abcg2/abcb1 wild-type (ABC WT) or abcg2/abcb1 knockout mice (ABC KO). First, we observed that brainstem glioma tumor latency is significantly prolonged in ABC KO versus ABC WT mice (median survival of 47 vs. 34 days). Dasatinib treatment nearly doubles the survival of brainstem glioma-bearing ABC KO mice (44 vs. 80 days). Elacridar, an ABCG2 and ABCB1 inhibitor, significantly increases the efficacy of dasatinib in brainstem glioma-bearing ABC WT mice (42 vs. 59 days). Pharmacokinetic analysis demonstrates that dasatinib delivery into the normal brain, but not into the tumor core, is significantly increased in ABC KO mice compared with ABC WT mice. Surprisingly, elacridar did not significantly increase dasatinib delivery into the normal brain or the tumor core of ABC WT mice. Next, we demonstrate that the tight junctions of the BBB of this model are compromised as assessed by tissue permeability to Texas Red dextran. Finally, elacridar increases the cytotoxicity of dasatinib independent of ABCG2 and ABCB1 expression in vitro In conclusion, elacridar improves the efficacy of dasatinib in a brainstem glioma model without significantly increasing its delivery to the tumor core. Mol Cancer Ther; 15(5); 819-29. ©2016 AACR.

Alcoholics with eating disorders: prevalence and clinical course. A study from Japan

Investigation of the prevalence of eating disorders among a large sample of Japanese alcoholics admitted for hospital treatment revealed a strong association between eating disorders and alcohol abuse and alcohol dependence among young women. That association was not apparent in young men. The results of this study of the clinical courses of eating disorders and alcohol abuse and alcohol dependence suggest that women with eating disorders, especially bulimia nervosa, are at high risk of becoming alcoholic.

A comparison of multimedia and standard advanced cardiac life support learning

OBJECTIVES

To compare student performance after Multimedia ACLS Learning System (MM) education compared with that after standard (ST) ACLS education.

METHODS

Final-year medical students were divided into 2 groups based on convenience scheduling and given ACLS instruction either in a standard format or with the MM course. The sizes of the small groups and the times in small-group instruction were identical. All students were evaluated with the same 50-item multiple-choice written examination, a structured evaluation immediately after the management of a mock cardiac arrest, and a second structured evaluation of the same mock arrest (videotaped) by an instructor blinded to the education method. Students were assigned a mark from 1 to 5 in each of 4 domains: assessment, immediate priorities, continual assessment, and leadership.

RESULTS

75 students took the MM and 38 took the ST course. The mean +/- SD mark for the multiple-choice test was 89.3 +/- 4.9% (MM) vs 89.3 +/- 4.8% (ST); the on-site mock arrest evaluation mark (20 maximum) was 14.1 +/- 2.5 (MM) vs 14.1 +/- 2.0 (ST); and the blinded mock arrest evaluation was 13.1 +/- 2.9 (MM) vs 14.4 +/- 2.9 (ST) (p = 0.024). 1/75 (MM) vs 0/38 (ST) did not successfully complete the on-site mock arrest evaluation. More students in the MM group (46% vs 25%) required multiple attempts to successfully complete the mock arrest evaluation (p < 0.02).

CONCLUSION

In medical students with no previous ACLS training, structured access to the multimedia ACLS Learning System provides immediate educational outcomes similar to those of a standard ACLS course. Multimedia computer-interactive learning should be enhanced with a short period of hands-on practice.

Efficacy of the MDM2 Inhibitor SAR405838 in Glioblastoma Is Limited by Poor Distribution Across the Blood-Brain Barrier

Controversy exists surrounding whether heterogeneous disruption of the blood-brain barrier (BBB), as seen in glioblastoma (GBM), leads to adequate drug delivery sufficient for efficacy in GBM. This question is especially important when using potent, targeted agents that have a poor penetration across an intact BBB. Efficacy of the murine double minute-2 (MDM2) inhibitor SAR405838 was tested in patient-derived xenograft (PDX) models of GBM. In vitro efficacy of SAR405838 was evaluated in PDX models with varying MDM2 expression and those with high (GBM108) and low (GBM102) expression were evaluated for flank and orthotopic efficacy. BBB permeability, evaluated using TexasRed-3 kDa dextran, was significantly increased in GBM108 through VEGFA overexpression. Drug delivery, MRI, and orthotopic survival were compared between BBB-intact (GBM108-vector) and BBB-disrupted (GBM108-VEGFA) models. MDM2-amplified PDX lines with high MDM2 expression were sensitive to SAR405838 in comparison with MDM2 control lines in both in vitro and heterotopic models. In contrast with profound efficacy observed in flank xenografts, SAR405838 was ineffective in orthotopic tumors. Although both GBM108-vector and GBM108-VEGFA readily imaged on MRI following gadolinium contrast administration, GBM108-VEGFA tumors had a significantly enhanced drug and gadolinium accumulation, as determined by MALDI-MSI. Enhanced drug delivery in GBM108-VEGFA translated into a marked improvement in orthotopic efficacy. This study clearly shows that limited drug distribution across a partially intact BBB may limit the efficacy of targeted agents in GBM. Brain penetration of targeted agents is a critical consideration in any precision medicine strategy for GBM. Mol Cancer Ther; 17(9); 1893-901. ©2018 AACR.

Pharmacokinetic Assessment of Cooperative Efflux of the Multitargeted Kinase Inhibitor Ponatinib Across the Blood-Brain Barrier

A compartmental blood-brain barrier (BBB) model describing drug transport across the BBB was implemented to evaluate the influence of efflux transporters on the rate and extent of the multikinase inhibitor ponatinib penetration across the BBB. In vivo pharmacokinetic studies in wild-type and transporter knockout mice showed that two major BBB efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), cooperate to modulate the brain exposure of ponatinib. The total and unbound (free) brain-to-plasma ratios were approximately 15-fold higher in the triple knockout mice lacking both P-gp and Bcrp [Mdr1a/b(-/-)Bcrp1(-/-)] compared with the wild-type mice. The triple knockout mice had a greater than an additive increase in the brain exposure of ponatinib when compared with single knockout mice [Bcrp1(-/-) or Mdr1a/b(-/-)], suggesting functional compensation of transporter-mediated drug efflux. Based on the BBB model characterizing the observed brain and plasma concentration-time profiles, the brain exit rate constant and clearance out of the brain were approximately 15-fold higher in the wild-type compared with Mdr1a/b(-/-)Bcrp1(-/-) mice, resulting in a significant increase in the mean transit time (the average time spent by ponatinib in the brain in a single passage) in the absence of efflux transporters (P-gp and Bcrp). This study characterized transporter-mediated drug efflux from the brain, a process that reduces the duration and extent of ponatinib exposure in the brain and has critical implications for the use of targeted drug delivery for brain tumors.

Discovery of 4-Azaindole Inhibitors of TGFβRI as Immuno-oncology Agents

The multifunctional cytokine TGFβ plays a central role in regulating antitumor immunity. It has been postulated that inhibition of TGFβ signaling in concert with checkpoint blockade will provide improved and durable immune response against tumors. Herein, we describe a novel series of 4-azaindole TGFβ receptor kinase inhibitors with excellent selectivity for TGFβ receptor 1 kinase. The combination of compound 3f and an antimouse-PD-1 antibody demonstrated significantly improved antitumor efficacy compared to either treatment alone in a murine tumor model.

Heterogeneous Binding and Central Nervous System Distribution of the Multitargeted Kinase Inhibitor Ponatinib Restrict Orthotopic Efficacy in a Patient-Derived Xenograft Model of Glioblastoma

This study investigated how differences in drug distribution and free fraction at different tumor and tissue sites influence the efficacy of the multikinase inhibitor ponatinib in a patient-derived xenograft model of glioblastoma (GBM). Efficacy studies in GBM6 flank (heterotopic) and intracranial (orthotopic) models showed that ponatinib is effective in the flank but not in the intracranial model, despite a relatively high brain-to-plasma ratio. In vitro binding studies indicated that flank tumor had a higher free (unbound) drug fraction than normal brain. The total and free drug concentrations, along with the tissue-to-plasma ratio (Kp) and its unbound derivative (Kp,uu), were consistently higher in the flank tumor than the normal brain at 1 and 6 hours after a single dose in GBM6 flank xenografts. In the orthotopic xenografts, the intracranial tumor core displayed higher Kp and Kp,uu values compared with the brain-around-tumor (BAT). The free fractions and the total drug concentrations, hence free drug concentrations, were consistently higher in the core than in the BAT at 1 and 6 hours postdose. The delivery disadvantages in the brain and BAT were further evidenced by the low total drug concentrations in these areas that did not consistently exceed the in vitro cytotoxic concentration (IC50). Taken together, the regional differences in free drug exposure across the intracranial tumor may be responsible for compromising efficacy of ponatinib in orthotopic GBM6.

Discovery of Orally Active Isofuranones as Potent, Selective Inhibitors of Hematopoetic Progenitor Kinase 1

While the discovery of immune checkpoint inhibitors has led to robust, durable responses in a range of cancers, many patients do not respond to currently available therapeutics. Therefore, an urgent need exists to identify alternative mechanisms to augment the immune-mediated clearance of tumors. Hematopoetic progenitor kinase 1 (HPK1) is a serine-threonine kinase that acts as a negative regulator of T-cell receptor (TCR) signaling, to dampen the immune response. Herein we describe the structure-based discovery of isofuranones as inhibitors of HPK1. Optimization of the chemotype led to improvements in potency, selectivity, plasma protein binding, and metabolic stability, culminating in the identification of compound 24. Oral administration of 24, in combination with an anti-PD1 antibody, demonstrated robust enhancement of anti-PD1 efficacy in a syngeneic tumor model of colorectal cancer.

Discovery of BMS-986260, a Potent, Selective, and Orally Bioavailable TGFβR1 Inhibitor as an Immuno-oncology Agent

Novel imidazole-based TGFβR1 inhibitors were identified and optimized for potency, selectivity, and pharmacokinetic and physicochemical characteristics. Herein, we report the discovery, optimization, and evaluation of a potent, selective, and orally bioavailable TGFβR1 inhibitor, 10 (BMS-986260). This compound demonstrated functional activity in multiple TGFβ-dependent cellular assays, excellent kinome selectivity, favorable pharmacokinetic properties, and curative in vivo efficacy in combination with anti-PD-1 antibody in murine colorectal cancer (CRC) models. Since daily dosing of TGFβR1 inhibitors is known to cause class-based cardiovascular (CV) toxicities in preclinical species, a dosing holiday schedule in the anti-PD-1 combination efficacy studies was explored. An intermittent dosing regimen of 3 days on and 4 days off allowed mitigation of CV toxicities in one month dog and rat toxicology studies and also provided similar efficacy as once daily dosing.

Effect of active management of labor on the incidence of cesarean section for dystocia in nulliparas

The hypothesis that introduction of a defined policy of managing labor in nulliparas, active management of labor, would reduce the incidence of cesarean section (CS) for dystocia was examined by the introduction of active management at Hermann Hospital, the University of Texas affiliated hospital in Houston. The study was conducted over four consecutive 6-month periods. Observational data were accumulated for the year preceding introduction of active management, which served as the control period. The overall incidence of CS in nulliparas in the two control periods was 23 and 25%, and declined significantly to 20 and 17.7% in the intervention periods. The incidence of CS for dystocia fell significantly from 13 and 15% to 10 and 8.1%, whereas the incidence for other indications was unchanged. There were no significant differences in perinatal outcome judged by incidence of fetal death in labor, neonatal death associated with asphyxia, rate of admission to neonatal care with a diagnosis of asphyxia, or incidence of neonatal seizure. The data suggest that active management of labor reduces the incidence of cesarean section significantly and that these results can be achieved without detriment to mother or child.

Brain Distribution and Active Efflux of Three panRAF Inhibitors: Considerations in the Treatment of Melanoma Brain Metastases

Targeted inhibition of RAF and MEK by molecularly targeted agents has been employed as a strategy to block aberrant mitogen-activated protein kinase (MAPK) signaling in melanoma. While the use of BRAF and MEK inhibitors, either as a single agent or in combination, improved efficacy in BRAF-mutant melanoma, initial responses are often followed by relapse due to acquired resistance. Moreover, some BRAF inhibitors are associated with paradoxical activation of the MAPK pathway, causing the development of secondary malignancies. The use of panRAF inhibitors, i.e., those that target all isoforms of RAF, may overcome paradoxical activation and resistance. The purpose of this study was to perform a quantitative assessment and evaluation of the influence of efflux mechanisms at the blood-brain barrier (BBB), in particular, Abcb1/P-glycoprotein (P-gp) and Abcg2/breast cancer resistance protein (Bcrp), on the brain distribution of three panRAF inhibitors: CCT196969 [1-(3-(tert-butyl)-1-phenyl-1H-pyrazol-5-yl)-3-(2-fluoro-4-((3-oxo-3,4-dihydropyrido[2,3-b]pyrazin-8-yl)oxy)phenyl)urea], LY3009120 1-(3,3-Dimethylbutyl)-3-(2-fluoro-4-methyl-5-(7-methyl-2-(methylamino)pyrido(2,3-d)pyrimidin-6-yl)phenyl)urea, and MLN2480 [4-pyrimidinecarboxamide, 6-amino-5-chloro-N-[(1R)-1-[5-[[[5-chloro-4-(trifluoromethyl)-2-pyridinyl]amino]carbonyl]-2-thiazolyl]ethyl]-]. In vitro studies using transfected Madin-Darby canine kidney II cells indicate that only LY3009120 and MLN2480 are substrates of Bcrp, and none of the three inhibitors are substrates of P-gp. The three panRAF inhibitors show high nonspecific binding in brain and plasma. In vivo studies in mice show that the brain distribution of CCT196969, LY3009120, and MLN2480 is limited, and is enhanced in transgenic mice lacking P-gp and Bcrp. While MLN2480 has a higher brain distribution, LY3009120 exhibits superior in vitro efficacy in patient-derived melanoma cell lines. The delivery of a drug to the site of action residing behind a functionally intact BBB, along with drug potency against the target, collectively play a critical role in determining in vivo efficacy outcomes.

Factors Influencing the Central Nervous System Distribution of a Novel Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Inhibitor GSK2126458: Implications for Overcoming Resistance with Combination Therapy for Melanoma Brain Metastases

Small molecule inhibitors targeting the mitogen-activated protein kinase pathway (Braf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase) have had success in extending survival for patients with metastatic melanoma. Unfortunately, resistance may occur via cross-activation of alternate signaling pathways. One approach to overcome resistance is to simultaneously target the phosphoinositide 3-kinase/mammalian target of rapamycin signaling pathway. Recent reports have shown that GSK2126458 [2,4-difluoro-N-(2-methoxy-5-(4-(pyridazin-4-yl)quinolin-6-yl)pyridin-3-yl) benzenesulfonamide], a dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor, can overcome acquired resistance to Braf and mitogen-activated protein kinase kinase inhibitors in vitro. These resistance mechanisms may be especially important in melanoma brain metastases because of limited drug delivery across the blood-brain barrier. The purpose of this study was to investigate factors that influence the brain distribution of GSK2126458 and to examine the efficacy of GSK2126458 in a novel patient-derived melanoma xenograft (PDX) model. Both in vitro and in vivo studies indicate that GSK2126458 is a substrate for P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), two dominant active efflux transporters in the blood-brain barrier. The steady-state brain distribution of GSK2126458 was 8-fold higher in the P-gp/Bcrp knockout mice compared with the wild type. We also observed that when simultaneously infused to steady state, GSK212658, dabrafenib, and trametinib, a rational combination to overcome mitogen-activated protein kinase inhibitor resistance, all had limited brain distribution. Coadministration of elacridar, a P-gp/Bcrp inhibitor, increased the brain distribution of GSK2126458 by approximately 7-fold in wild-type mice. In the PDX model, GSK2126458 showed efficacy in flank tumors but was ineffective in intracranial melanoma. These results show that P-gp and Bcrp are involved in limiting the brain distribution of GSK2126458 and provide a rationale for the lack of efficacy of GSK2126458 in the orthotopic PDX model.

Challenges in the delivery of therapies to melanoma brain metastases

Brain metastases are a major cause of morbidity and mortality in patients with advanced melanoma. Recent approval of several molecularly-targeted agents and biologics has brought hope to patients with this previously untreatable disease. However, patients with symptomatic melanoma brain metastases have often been excluded from pivotal clinical trials. This may be in part attributed to the fact that several of the approved small molecule molecularly-targeted agents are substrates for active efflux at the blood-brain barrier, limiting their effective delivery to brain metastases. We believe that successful treatment of melanoma brain metastases will depend on the ability of these agents to traverse the blood-brain barrier and reach micrometastases that are often not clinically detectable. Moreover, overcoming the emergence of a unique pattern of resistance, possibly through adequate delivery of combination targeted therapies in brain metastases will be important in achieving a durable response. These concepts, and the current challenges in the delivery of new treatments to melanoma brain metastases, are discussed in this review.

Brain Distributional Kinetics of a Novel MDM2 Inhibitor SAR405838: Implications for Use in Brain Tumor Therapy

Achieving an effective drug concentration in the brain is as important as targeting the right pathway when developing targeted agents for brain tumors. SAR405838 is a novel molecularly targeted agent that is in clinical trials for various solid tumors. Its application for tumors in the brain has not yet been examined, even though the target, the MDM2-p53 interaction, is attractive for tumors that could occur in the brain, including glioblastoma and brain metastases. In vitro and in vivo studies indicate that SAR405838 is a substrate of P-glycoprotein (P-gp). P-gp mediated active efflux at the blood-brain barrier plays a dominant role in limiting SAR405838 brain distribution. Even though the absence of P-gp significantly increases the drug exposure in the brain, the systemic exposure, including absorption and clearance processes, were unaffected by P-gp deletion. Model-based parameters of SAR405838 distribution across the blood-brain barrier indicate the CLout of the brain was approximately 40-fold greater than the CLin The free fraction of SAR405838 in plasma and brain were found to be low, and subsequent Kpuu values were less than unity, even in P-gp/Bcrp knockout mice. These results indicate additional efflux transporters other than P-gp and Bcrp may be limiting distribution of SAR405838 to the brain. Concomitant administration of elacridar significantly increased brain exposure, also without affecting the systemic exposure. This study characterized the brain distributional kinetics of SAR405838, a novel MDM2 inhibitor, to evaluate its potential in the treatment of primary and metastatic brain tumors. SIGNIFICANCE STATEMENT: This paper examined the brain distributional kinetics of a novel MDM2-p53 targeted agent, SAR405838, to see its possible application for brain tumors by using in vitro, in vivo, and in silico approaches. SAR405838 is found to be a substrate of P-glycoprotein (P-gp), which limits its distribution to the brain. Based on the findings in the paper, manipulation of the function of P-gp can significantly increase the brain exposure of SAR405838, which may give an insight on its potential benefit as a treatment for primary and metastatic brain cancer.

Enhancing Brain Retention of a KIF11 Inhibitor Significantly Improves its Efficacy in a Mouse Model of Glioblastoma

Glioblastoma, the most lethal primary brain cancer, is extremely proliferative and invasive. Tumor cells at tumor/brain-interface often exist behind a functionally intact blood-brain barrier (BBB), and so are shielded from exposure to therapeutic drug concentrations. An ideal glioblastoma treatment needs to engage targets that drive proliferation as well as invasion, with brain penetrant therapies. One such target is the mitotic kinesin KIF11, which can be inhibited with ispinesib, a potent molecularly-targeted drug. Although, achieving durable brain exposures of ispinesib is critical for adequate tumor cell engagement during mitosis, when tumor cells are vulnerable, for efficacy. Our results demonstrate that the delivery of ispinesib is restricted by P-gp and Bcrp efflux at BBB. Thereby, ispinesib distribution is heterogeneous with concentrations substantially lower in invasive tumor rim (intact BBB) compared to glioblastoma core (disrupted BBB). We further find that elacridar—a P-gp and Bcrp inhibitor—improves brain accumulation of ispinesib, resulting in remarkably reduced tumor growth and extended survival in a rodent model of glioblastoma. Such observations show the benefits and feasibility of pairing a potentially ideal treatment with a compound that improves its brain accumulation, and supports use of this strategy in clinical exploration of cell cycle-targeting therapies in brain cancers.

In Vivo Efficacy of Tesevatinib in EGFR-Amplified Patient-Derived Xenograft Glioblastoma Models May Be Limited by Tissue Binding and Compensatory Signaling

Tesevatinib is a potent oral brain penetrant EGFR inhibitor currently being evaluated for glioblastoma therapy. Tesevatinib distribution was assessed in wild-type (WT) and Mdr1a/b^(-/-)Bcrp^(-/-) triple knockout (TKO) FVB mice after dosing orally or via osmotic minipump; drug-tissue binding was assessed by rapid equilibrium dialysis. Two hours after tesevatinib dosing, brain concentrations in WT and TKO mice were 0.72 and 10.03 μg/g, respectively. Brain-to-plasma ratios (Kp) were 0.53 and 5.73, respectively. With intraperitoneal infusion, brain concentrations were 1.46 and 30.6 μg/g (Kp 1.16 and 25.10), respectively. The brain-to-plasma unbound drug concentration ratios were substantially lower (WT mice, 0.03-0.08; TKO mice, 0.40-1.75). Unbound drug concentrations in brains of WT mice were 0.78 to 1.59 ng/g. In vitro cytotoxicity and EGFR pathway signaling were evaluated using EGFR-amplified patient-derived glioblastoma xenograft models (GBM12, GBM6). In vivo pharmacodynamics and efficacy were assessed using athymic nude mice bearing either intracranial or flank tumors treated by oral gavage. Tesevatinib potently reduced cell viability [IC₅₀ GBM12 = 11 nmol/L (5.5 ng/mL), GBM6 = 102 nmol/L] and suppressed EGFR signaling in vitro However, tesevatinib efficacy compared with vehicle in intracranial (GBM12, median survival: 23 vs. 18 days, P = 0.003) and flank models (GBM12, median time to outcome: 41 vs. 33 days, P = 0.007; GBM6, 44 vs. 33 days, P = 0.007) was modest and associated with partial inhibition of EGFR signaling. Overall, tesevatinib efficacy in EGFR-amplified PDX GBM models is robust in vitro but relatively modest in vivo, despite a high brain-to-plasma ratio. This discrepancy may be explained by drug-tissue binding and compensatory signaling.

StORQS: Washington's Statewide Obstetrical Review and Quality System: overview and provider evaluation

The Foundation for Health Care Quality (Washington) used three administrative public databases and indicators recommended by the Joint Commission and the American College of Obstetrics and Gynecology to build algorithms to measure quality of obstetric care in the state of Washington. Analyses demonstrated a high degree of variability across hospitals for major processes of care such as cesarean section, vaginal birth after cesarean section, and forceps deliveries. Eighty-five percent of the participating hospitals concluded that important aspects of care were being measured. Ninety-four percent found the information useful in describing their performance compared with other hospitals. Sixty-two percent believed the information was useful for initiating quality improvement projects. Of the 25 indicators tested in the project, indicators rated as most useful were the same 10 obstetric indicators chosen by the Joint Commission after alpha testing.