Bystander effects, pharmacokinetics, and linker-payload stability of EGFR-targeting antibody-drug conjugates Losatuxizumab vedotin and Depatux-M in glioblastoma models

PURPOSE

Antibody-drug conjugates (ADCs) are targeted therapies with robust efficacy in solid cancers, and there is intense interest in using EGFR-specific ADCs to target EGFR-amplified glioblastoma (GBM). Given the molecular heterogeneity of GBM, bystander activity of ADCs may be important for determining treatment efficacy. In this study, the activity and toxicity of two EGFR-targeted ADCs, Losatuxizumab vedotin (ABBV-221) and Depatuxizumab mafodotin (Depatux-M), with similar auristatin toxins, were compared in GBM patient-derived xenografts (PDXs) and normal murine brain following direct infusion by convection enhanced delivery (CED).

METHODS

EGFRviii-amplified and non-amplified GBM PDXs were used to determine in vitro cytotoxicity, in vivo efficacy, and bystander activities of ABBV-221 and Depatux-M. Non-tumor bearing mice were used to evaluate pharmacokinetics and toxicity of ADCs using LC-MS/MS and immunohistochemistry.

RESULTS

CED improved intracranial efficacy of Depatux-M and ABBV-221 in three EGFRviii-amplified GBM PDX models (Median survival: 125 to >300 days vs 20-49 days with isotype-control AB095). Both ADCs had comparable in vitro and in vivo efficacy. However, neuronal toxicity and CD68+ microglia/macrophage infiltration were significantly higher in brains infused with ABBV-221, with the cell-permeable MMAE, as compared to Depatux-M, with the cell-impermeant MMAF. CED infusion of ABBV-221 into brain or incubation of ABBV-221 with normal brain homogenate resulted in significant release of MMAE, which is consistent with linker instability in the brain microenvironment.

CONCLUSION

EGFR-targeting ADCs are promising therapeutic options for GBM when delivered intra-tumorally by CED. However, the linker and payload for the ADC must be carefully considered to maximize the therapeutic window.

RBBP4-p300 axis modulates expression of genes essential for cell survival and is a potential target for therapy in glioblastoma

BACKGROUND

RBBP4 activates transcription by histone acetylation, but the partner histone acetyltransferases are unknown. Thus, we investigated the hypothesis that RBBP4 interacts with p300 in a complex in glioblastoma (GBM).

METHODS

shRNA silencing of RBBP4 or p300 and RNAseq was used to identify genes co-regulated by RBBP4 and p300 in GBM43 patient-derived xenograft (PDX). RBBP4/p300 complex was demonstrated using proximity ligation assay (PLA) and ChIPseq delineated histone H3 acetylation and RBBP4/p300 complex binding in promoters/enhancers. Temozolomide (TMZ)-induced DNA double strand breaks (DSBs) were evaluated by γ-H2AX and proliferation by CyQuant and live cell monitoring assays. In vivo efficacy was based on survival of mice with orthotopic tumors.

RESULTS

shRBBP4 and shp300 downregulated 4768 genes among which 1485 (31%) were commonly downregulated by both shRNAs, while upregulated genes were 2484, including 863 (35%) common genes. The pro-survival genes were the top-ranked among the downregulated genes, including C-MYC. RBBP4/p300 complex was demonstrated in the nucleus, and shRBBP4 or shp300 significantly sensitized GBM cells to TMZ compared to the control shNT in vitro (P < .05). Moreover, TMZ significantly prolonged the survival of mice bearing GBM22-shRBBP4 orthotopic tumors compared with control shNT tumors (median shNT survival 52 days vs. median shRBBP4 319 days; P = .001). CREB-binding protein (CBP)/p300 inhibitor CPI-1612 suppressed H3K27Ac and RBBP4/p300 complex target proteins, including C-MYC, and synergistically sensitized TMZ in vitro. Pharmacodynamic evaluation confirmed brain penetration by CPI-1612 supporting further investigation to evaluate efficacy to sensitize TMZ.

CONCLUSIONS

RBBP4/p300 complex is present in GBM cells and is a potential therapeutic target.

Heterogeneous delivery across the blood-brain barrier limits the efficacy of an EGFR-targeting antibody drug conjugate in glioblastoma

BACKGROUND

Antibody drug conjugates (ADCs) targeting the epidermal growth factor receptor (EGFR), such as depatuxizumab mafodotin (Depatux-M), is a promising therapeutic strategy for glioblastoma (GBM) but recent clinical trials did not demonstrate a survival benefit. Understanding the mechanisms of failure for this promising strategy is critically important.

METHODS

PDX models were employed to study efficacy of systemic vs intracranial delivery of Depatux-M. Immunofluorescence and MALDI-MSI were performed to detect drug levels in the brain. EGFR levels and compensatory pathways were studied using quantitative flow cytometry, Western blots, RNAseq, FISH, and phosphoproteomics.

RESULTS

Systemic delivery of Depatux-M was highly effective in nine of 10 EGFR-amplified heterotopic PDXs with survival extending beyond one year in eight PDXs. Acquired resistance in two PDXs (GBM12 and GBM46) was driven by suppression of EGFR expression or emergence of a novel short-variant of EGFR lacking the epitope for the Depatux-M antibody. In contrast to the profound benefit observed in heterotopic tumors, only two of seven intrinsically sensitive PDXs were responsive to Depatux-M as intracranial tumors. Poor efficacy in orthotopic PDXs was associated with limited and heterogeneous distribution of Depatux-M into tumor tissues, and artificial disruption of the BBB or bypass of the BBB by direct intracranial injection of Depatux-M into orthotopic tumors markedly enhanced the efficacy of drug treatment.

CONCLUSIONS

Despite profound intrinsic sensitivity to Depatux-M, limited drug delivery into brain tumor may have been a key contributor to lack of efficacy in recently failed clinical trials.

TMOD-15. EFFICACY OF THE MDM2 INHIBITOR KRT-232 IN GLIOBLASTOMA PATIENT-DERIVED XENOGRAFT MODELS

Non-genotoxic reactivation of p53 by MDM2 inhibitors represents a promising therapeutic strategy for tumors with wild-type TP53, particularly tumors harboring MDM2 amplification. MDM2 controls p53 levels by targeting it for degradation, while disruption of the MDM2-p53 interaction causes rapid accumulation of p53 and activation of the p53 pathway. We examined the efficacy of the small molecule MDM2 inhibitor KRT-232, alone and in combination with radiation therapy (RT), in MDM2-amplified and/or p53 wildtype patient-derived xenograft (PDX) models of glioblastoma in vitro and in vivo. In vitro, glioblastoma PDX explant cultures showed sensitivity to KRT-232, both tumors with MDM2 amplification (GBM108 and G148) and non-amplified but TP53-wildtype lines (GBM10, GBM14, and GBM39), with IC50s ranging from 300-800 nM in FBS culture conditions. A TP53 p.F270C mutant PDX (GBM43) was inherently resistant, with IC50 &gt;3000 nM. In the MDM2-amplified GBM108 line, KRT-232 led to a robust (5-6 fold) induction of p53-target genes p21, PUMA, and NOXA, with initiation of both apoptosis and senescence. Expression of p21 and PUMA was greater with KRT-232 in combination with RT (25-35 fold induction), while stable knock-down of p53 in GBM108 led to complete resistance to KRT-232. In contrast, GBM10 showed lower induction of p21 and PUMA (2-3 fold) and was more resistant to KRT-232. In an orthotopic GBM108 xenograft model, treatment with KRT-232 +/- RT for one week extended survival from 22 days (placebo) to 46 days (KRT-232 alone); combination KRT-232 + RT further extended survival (77 days) over RT alone (31 days). KRT-232 is an effective treatment in a subset of glioblastoma pre-clinical models alone and in combination with RT. Further studies are underway to understand the mechanisms conferring innate sensitivity or resistance to KRT-232.

ANGI-11. SEX DIFFERENCES IN IMAGING-BASED ASSESSMENT OF GLIOBLASTOMA INVASION

INTRODUCTION

Neuroimaging dogma for glioblastoma asserts that hyperintensity on T1Gd MRI reveals the bulk of the tumor, while T2/FLAIR signal indicates edema. However, it is unclear whether this edema results from immune response or increased tumor cells. Further, one significant driver of the known sex differences in glioblastoma may be differences in immune response, due to the X-linkage of many immune genes. Based on this, we hypothesized that assumptions regarding tumor cellularity in T2/FLAIR images should be tailored to the biological sex of the patient.

METHODS

Using a retrospective cohort of 18 primary glioblastoma patients receiving multiple image-localized biopsies (82 total) and standard MRI, we assessed: distance of biopsy from T1Gd and T2 areas; a pathologist’s score of percent tumor cell density; and an imaging-based invasion metric, D/ρ. This metric is derived from the biomathematical Proliferation-Invasion model of glioma growth, which features two parameters, net growth rate (ρ) and net invasion rate (D). Their ratio D/ρ is related to degree of invasion, and is estimated from volumetric measurements of MRI abnormalities. Additionally, 25 patient-derived xenograft models implanted in females were grown until moribund, at which point brains were excised and stained for DAPI (to show all cells) and Lamin (to highlight tumor cells). Image processing of lamin-stained sections defines contours of intensity correlating with cell density.

RESULTS

Outside both the T1Gd and T2 region, male patient biopsies had higher tumor cell densities than females. Males also tended to have higher invasion metrics. Although each set derived from different patients, preclinical metrics of invasion were positively correlated with clinical invasion in females but negatively correlated in males.

CONCLUSION

Our preliminary finding that cell distribution patterns correlate with imaging metrics differently between the sexes supports the hypothesis that the degree of tumor cell density represented on certain MRI sequences may be sex-specific.

Alisertib demonstrates significant antitumor activity in bevacizumab resistant, patient derived orthotopic models of glioblastoma

Aurora A kinase (AURKA), a member of the serine/threonine kinase family, plays a critical role in cell division, and it is widely overexpressed in a variety of tumors including glioblastoma (GBM). Alisertib (MLN8237) is an orally administered selective AURKA inhibitor with potent antiproliferative activity, currently undergoing clinical testing in different tumor types. In vitro evaluation of alisertib against the primary GBM lines, GBM6, GBM10, GBM12 and GBM39 showed significant antitumor activity with IC_50s ranging between 30 and 95 nM. Orthotopic xenografts of GBM10 and the bevacizumab resistant lines GBM6 and GBM39 were established by implantating 3 × 10⁵ cells in the caudate nucleus of nude mice; animals were randomized to treatment with either alisertib 30 mg/kg/day or vehicle. In all three models, treatment with alisertib resulted in a statistically significant prolongation of survival (p < 0.0001). In addition, alisertib administration in these mice decreased phosphorylated aurora-A, induced mitotic arrest and significantly decreased histone H3 phosphorylation in tumors. In conclusion, alisertib displays significant antitumor activity against primary GBM lines and xenografts, including patient derived GBM lines resistant to bevacizumab; these data support clinical translation in GBM.

Abstract B25: The critical importance of the blood-brain barrier in modulating the response to otherwise highly effective targeted therapies in patient-derived orthotopic glioblastoma xenografts

Clinical data indicate that certain regions within glioblastoma (GBM) have a relatively intact blood-brain barrier (BBB), but controversy surrounds whether associated heterogeneous delivery may limit efficacy for otherwise highly active drugs with poor brain distribution. In this study, the efficacy of molecularly targeted therapies was compared in relevant GBM patient-derived xenograft (PDX) models grown either as heterotopic or orthotopic tumors. The impact of further disrupting BBB integrity in non-responsive orthotopic tumors was evaluated by over-expressing vascular endothelial growth factor (VEGF) and measuring drug distribution by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). The brain:plasma ratio for five targeted agents was determined by LC-MSMS and treatment efficacy was evaluated in target-relevant GBM PDX lines: erlotinib (brain:plasma = 0.02 ± 0.02; efficacy tested in GBM6), palbociclib (brain:plasma = 0.06; efficacy tested in GBM22), AZD1775 (brain:plasma = 0.05; efficacy tested in GBM22), SAR405838 (brain:plasma = 0.01 ± 0.003; efficacy tested in GBM108), and AZD4547 (brain:plasma = 0.045 ± 0.02; efficacy tested in GBM150). Each of these drugs was effective in relevant GBM PDX flank tumor models with a 27% to 218% prolongation in the median time to exceed their pre-specified endpoint compared to placebo treatment (p≤0.02 for each drug). In contrast, none of these drugs were effective in prolonging survival in the same target-relevant orthotopic tumor models (-6% to 8% extension in median survival; p&gt;0.05 for each drug). Consistent with partial and heterogeneous disruption of the BBB, MALDI-MSI of erlotinib, AZD1775 or SAR405838 distribution within orthotopic tumors demonstrated highly heterogeneous drug levels with large regions within each tumor approaching the low drug levels observed within surrounding normal brain. To further evaluate whether heterogenous drug distribution in orthotopic tumors could account for poor treatment efficacy, GBM108 was transduced with lentiviral constructs encoding for VEGF or empty vector (EV). While both GBM108-sublines were readily detectable with gadolinium-enhanced magnetic resonance imaging (MRI), the GBM108-VEGF tumors had a significantly more disrupted BBB, as evidenced by a more uniform and intense distribution of a brain-impenetrant TexasRed-dextran vascular marker. Similarly, the distribution of SAR405838, measured by MALDI-MSI, was markedly higher and more uniform in the GBM108-VEGF tumors when compared to the GBM108-EV tumors. Enhanced delivery of SAR405838 into orthotopic GBM108-VEGF models translated into a marked enhancement in treatment efficacy in comparison to GBM108-EV with a median survival prolongation of 37 vs. 4 days, respectively (p=0.0055). Collectively, these data highlight the importance of testing novel therapeutic agents in orthotopic tumor models and suggest that limited brain penetration for many molecules may significantly limit their efficacy in brain tumors that have a partially intact BBB. In the face of continued failure to develop effective targeted agents for GBM, these in vivo results highlight the importance of re-evaluating the dogma in neuro-oncology that the BBB is fully disrupted in GBM and, therefore, drug delivery across the BBB is not a major factor limiting treatment efficacy.

Citation Format: Jann N. Sarkaria, David Calligaris, Daniel Ma, Karen Parrish, Ann C. Mladek, Janice Laramy, Minjee Kim, Shuangling Zhang, Mark Schroeder, Brett L. Carlson, Katrina Bakken, Aaron Johnson, Nathalie Agar, William Elmquist. The critical importance of the blood-brain barrier in modulating the response to otherwise highly effective targeted therapies in patient-derived orthotopic glioblastoma xenografts. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B25.

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.

Abstract 1799: Targeted murine double minute 2 (MDM2) inhibition results in dramatic tumor regression in an MDM2-amplified glioblastoma multiforme (GBM) xenograft model

Disruption of the MDM2/p53 pathway is an oncogenic driver alteration observed in the vast majority of GBM. This study evaluated the efficacy of the small molecule, human-specific, MDM2 inhibitor SAR405838 across a panel of GBM xenografts with distinct alterations within the MDM2/p53 pathway. Through screening a panel of 56 GBM xenografts with a combination of array CGH and MDM2-specific PCR amplification, five xenograft models were identified with high-level MDM2 amplification (GBM 5, 102, 108, 122, and 143). MDM2 transcript expression was elevated in all of these lines except GBM102, which had expression levels similar to non-amplified lines. The effects of SAR405838 were studied in 2 of the MDM2 amplified lines (GBM102, GBM108), and non-amplified lines with wild-type p53 (GBM10) or mutant p53 (GBM12). Using a combination of neurosphere and Cyquant assays to assess in vitro sensitivity, 100 nM SAR405838 completely inhibited growth of GBM108 (6% +/- 1% absorbance relative to control), partially inhibited GBM102 neurosphere formation (34 +/- 17% relative to control), and had nominal impact on relative neurosphere formation in GBM10 (51% +/- 4% relative to control) or GBM12 (96% +/- 4% relative to control). Twenty-four hours after treatment with 100 nM SAR405838, transcript expression of p53 target genes p21 and PUMA were elevated by 14 and 12 fold relative to control in GBM108, while more limited changes in expression were observed in GBM102 (4 and 2.5 fold increase, respectively). Similarly, analysis of apoptosis after 72h by Annexin-V staining demonstrated a 5-fold increase in apoptotic fraction from control in GBM108 compared to no increase in GBM102. A more striking difference in efficacy was observed in flank tumor xenograft studies where the time to reach a median tumor volume of 1000 mm3 was marginally extended in GBM102 (36 days for placebo vs. 44 days for SAR405838). In contrast, GBM108 placebo-treated mice grew to a median volume of 1000 mm3 in 53 days while treatment with SAR405838 resulted in complete tumor regression at 70 days. SAR405838 is a known substrate for the P-glycoprotein efflux pump that functions in the blood brain barrier to exclude xenobiotics from the central nervous system. Consistent with limited penetration of SAR405838 into the brain, a parallel study in an intracranial xenograft model for GBM108 demonstrated no significant survival benefit with SAR405838 treatment compared to placebo. Thus, although SAR405838 provides marked efficacy in vitro and in a flank tumor model of an MDM2 amplified tumor line, the lack of efficacy in an orthotopic model of this study suggests that more prudent investigation is needed before advancing the development of this specific drug in human tumors growing in the brain.

Citation Format: Ann C. Mladek, Isabelle Meaux, Katrina Bakken, Pascal Pannier, Cedric Barriere, James W. Watters, Laurent R.J. Debussche, Jann N. Sarkaria. Targeted murine double minute 2 (MDM2) inhibition results in dramatic tumor regression in an MDM2-amplified glioblastoma multiforme (GBM) xenograft model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1799. doi:10.1158/1538-7445.AM2014-1799

Abstract 2617: Preclinical efficacy of GNE-317, a dual PI3K/mTOR inhibitor, with or without bevacizumab in EGFR and/or PTEN-mutated glioblastoma multiforme

GNE-317 is a dual PI3K/mTOR inhibitor with excellent blood-brain barrier penetration. In this study, the efficacy of GNE-317 was evaluated in the Mayo panel of primary glioblastoma multiforme (GBM) xenografts. Based on the concept of oncogene addiction, we hypothesized that GNE-317 would be most efficacious in EGFR-hyper-activated and/or PTEN-deficient lines. In a CyQUANT cell proliferation assay, the inhibitory concentration of 50% cell number (IC50) for GBM6, 10, 22, and 84 were 0.59±0.50, 0.72±0.40, 0.26±0.14, and 3.49±1.64 microM, respectively. In these selected lines, there was a poor correlation between EGFR or PTEN status and in vitro response. The efficacy of GNE-317 also was evaluated in 10 lines in an orthotopic xenograft model. Mice with established tumors were randomized to daily dosing with GNE-317 (30 mg/kg) or placebo until moribund. Similar to in vitro data, there was a spectrum of response to GNE-317 (Table 1). The survival benefit ratio (ratio of median survival) did not correlate with EGFR amplification (P=0.78), EGFR mutation (P=0.25), or PTEN (P=0.55) status when analyzed singly. However, GNE-317 did extend survival in 4 of 5 lines in which either EGFR or PTEN were deregulated. To evaluate potentially clinically relevant combinations, the efficacy of GNE-317 combined with bevacizumab (BEV) was tested in the same orthotopic model in GBM8, 10, and 59. In GBM10, GNE-317/BEV provided a significant increase in survival compared to the most effective single agent (P&lt;0.0001). In GBM8, 10, and 59, the ratio of median survival for GNE-317/BEV vs. placebo were 1.47, 1.75, and 1.74, respectively (all P≤0.01). In conclusion, there may be a correlation between deregulation of the EGFR/PTEN signaling network and GNE-317 efficacy, and the efficacy of GNE-317 in some models can be extended when combined with bevacizumab.

Table 1:Molecular Characteristics and Efficacy of GNE-317 in Mayo Primary GBM XenograftsEGFR AmplifiedEGFR vIII MutatedPTEN MutatedGNE-317 Responder*Benefit Ratio** of GNE-317GBM6YesYesWTYes1.35GBM8YesNoYes, HDYes1.19GBM10NoNoYes, HDYes1.47GBM22NoNoWTNo0.85GBM59YesYesYes, HDYes1.27GBM84YesNoYes, del Exon 1No1.02GBM115NoNoTBDNo0.86GBM116NoNoTBDNo1.05GBM117NoNoTBDYes1.38GBM122YesNoTBDNo0.99Abbreviations: HD=homozygous deleted; del=deletion in; TBD=to be determined; WT=wild type.* If in vivo survival difference reached P&lt;0.05 by Log-rank Kaplan-Meier method between the GNE-317 treated and placebo groups, the GBM line was classified as a responder to GNE-317.** The benefit ratio equals to median survival of the GNE-317 treated group, divided by that of the placebo group.

Note: This abstract was not presented at the meeting.

Citation Format: Terence T. Sio, Jenny L. Pokorny, Ann C. Mladek, Brett L. Carlson, Mark A. Schroeder, Dennis O. Iyekegbe, Katrina Bakken, Laurent Salphati, Heidi Phillips, Jann N. Sarkaria. Preclinical efficacy of GNE-317, a dual PI3K/mTOR inhibitor, with or without bevacizumab in EGFR and/or PTEN-mutated glioblastoma multiforme. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2617. doi:10.1158/1538-7445.AM2014-2617

Abstract C81: BBB efflux pump activity limits brain penetration of palbociclib (PD0332991) in glioblastoma

Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and is associated with a poor prognosis. Progress in developing effective therapies for this disease is significantly limited by the blood-brain barrier (BBB), which limits the delivery of many anti-cancer agents to infiltrative tumor cells. In addition to physical barriers, such as tight junctions, the efflux proteins bcrp and P-gp in the BBB limit the brain distribution of numerous anti-cancer agents. Palbociclib (PD0332991) is a potent Cdk4/6 inhibitor which has shown remarkable efficacy in treating peripheral (non-brain) tumors. The Cdk4 pathway is dysregulated in approximately 75% of GBM; most commonly, the pathway is hyperactivated through the homozygous deletion of p16 (52%), amplification of Cdk4 (18%), or amplification of Cdk6 (1%). The purpose of this study is to define the role of the efflux transporters P-gp and bcrp in the brain distribution of palbociclib and to examine if an intact BBB limits efficacy.

Palbociclib brain distribution studies were performed in FVB wild-type, P-gp knockout (PKO; Mdr1a/b(-/-)), bcrp knockout (BKO; Bcrp1(-/-)), and triple knockout (TKO; Mdr1a/b(-/-)Bcrp1(-/-)) mice after an oral dose (10mg/kg). The concentrations of palbociclib from all distribution studies were determined by a sensitive and specific LC-MS/MS assay. Survival studies were conducted in patient-derived primary GBM xenograft models in athymic nu/nu mice.

The brain exposure of palbociclib (AUCbrain-to-AUCplasma ratio) was ∼ 33.5, 3.2, and 150-fold higher as compared to WT mice (WT: .044; PKO: 1.34; BKO: 0.13; TKO: 6.24). Further, the steady-state brain-to-plasma ratio (B/P) of palbociclib after a constant intra-peritoneal infusion of 10 µg/hr for 48hrs was ∼120-fold higher in the TKO mice than the WT mice [WT: (0.21 ± 0.07); PKO: (2.48 ± .13); BKO: (0.43 ± 0.12); TKO: (26.5 ± 5.4) p &lt; 0.0001]. Inhibition of P-gp and bcrp with elacridar (10 mg/kg IP) resulted in a marked increase in palbociclib brain distribution [control B/P (0.06 ± 0.02); elacridar treatment (2.0 ± 1.4)]. For survival studies, palbociclib was dosed at 150 mg/kg/day continuously. Consistent with limited brain penetration, palbociclib did not improve the median survival of an orthotopic GBM xenograft model. In contrast, treatment of GBM22 xenografts grown as flank tumors resulted in profound efficacy with a 70 day prolongation in the time for tumor volume to reach 1000mm3.

These data suggest the clinical paradigm of a potent anti-cancer agent (for instance, palbociclib) used in the treatment of peripheral disease is less effective in the treatment of brain tumors due to the BBB and active efflux by P-gp and bcrp.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C81.

Citation Format: Karen E. Parrish, Jenny L. Pokorny, Rajendar K. Mittapalli, Katrina Bakken, Jann N. Sarkaria, William F. Elmquist. BBB efflux pump activity limits brain penetration of palbociclib (PD0332991) in glioblastoma. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C81.

Abstract 3240: Pre-clinical investigation of the Wee1 inhibitor, MK1775, in glioblastoma multiforme

Wee1 is a key regulator of both G2/M transition and DNA replication fork stability. In this study, the efficacy of the Wee1 inhibitor MK1775 was evaluated in the Mayo primary glioblastoma multiforme (GBM) xenograft model. Based on western blot expression of Wee1, GBM22, GBM12 and GBM6 were selected for study based on low, intermediate and high-level expression, respectively. Wee1-mediated phosphorylation of Y15-Cdc2 was robustly suppressed in vitro in both GBM22 and GBM6 at 300 nM MK1775. At this concentration, MK1775 had marked anti-proliferative effects on GBM22 with 80±2.5% suppression of absorbance in a CyQUANT cell proliferation assay, while similar treatment of GBM6 had minimal effect on growth (26±21% suppression of absorbance). In a similar primary neurosphere formation assay, 300 nM completely inhibited neurosphere formation in GBM22 and GBM12, while having no effect on GBM6 neurosphere formation. Consistent with the cytotoxicity data, single agent treatment of GBM22 with MK1775 resulted in a marked S-phase arrest 24 hours after treatment (60% vs. 40% cells in S with MK1775 vs. control, respectively) and subsequent accumulation of cells in G2/M 48 hours after treatment (95% vs. 9.5%, respectively). In contrast, relatively minimal cell cycle perturbations were observed with MK1775 in GBM6 (24 hour S-phase accumulation 27% vs. 21%, respectively). Combination studies with MK1775 and temozolomide (TMZ) in a neurosphere formation assay demonstrated enhancement of treatment benefit only in GBM22 and GBM12 but not GBM6 (relative neurosphere numbers for TMZ, MK1775, or combined treatment compared to untreated were 34%, 16% and 7%, respectively for GBM22, 41%, 95% and 15%, respectively, for GBM12; while the same combination had no effect on GBM6 neurosphere formation). In anticipation of evaluating treatment efficacy in animal models, pharmacokinetic modeling of MK1775 brain delivery was performed in nude mice. Following a single MK1775 dose of 50 mg/kg, time to maximum blood concentration was 1.0 hours, AUC was 29.8 microM·h, and Cmax was 7.8 microM in whole blood and 0.24 microM in brain parenchyma. To evaluate whether limitations in brain delivery affected efficacy, parallel in vivo GBM12 heterotopic and orthotopic xenograft efficacy studies were performed with a 5 day dosing regimen of TMZ and MK1775 repeated every 28 days for 3 cycles. In the orthotopic model, MK1775 provided no survival benefit with median survival being 16, 15, 88 and 92 days for placebo, MK1775 alone, TMZ alone, or MK1775 + TMZ treatment, respectively. In contrast, there is some suggestion of MK1775 efficacy in the flank tumor model with median time to reach 1000 mm3 being 45, 56, 101 and 112 days, respectively. Collectively, these data suggest that despite promising in vitro activity for MK1775, limited drug delivery into the brain may reduce the efficacy of MK1775 therapy in an orthotopic GBM xenograft model.

Citation Format: Jenny Pokorny, Vincenzo Pucci, Stuart Shumway, Bennett Ma, Katrina Bakken, Mark Schroeder, Brett Carlson, Jann N. Sarkaria. Pre-clinical investigation of the Wee1 inhibitor, MK1775, in glioblastoma multiforme. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3240. doi:10.1158/1538-7445.AM2013-3240

Helicobacter pylori infection assessed by ELISA and by immunoblot and noncardia gastric cancer risk in a prospective study: the Eurgast-EPIC project

BACKGROUND

In epidemiological studies, Helicobacter pylori infection is usually detected by enzyme-linked immunosorbent assay (ELISA). However, infection can spontaneously clear from the mucosa during the progression of atrophy and could lead to substantial under-detection of infection and underestimation of its effect on gastric cancer (GC) risk. Antibodies detected by western blot are known to persist longer after the loss of the infection.

METHODS

In a nested case-control study from the Eurogast-EPIC cohort, including 88 noncardia GC cases and 338 controls, we assessed the association between noncardia GC and H. pylori infection comparing antibodies detected by western blot (HELICOBLOT2.1) to those detected by ELISA (Pyloriset EIA-GIII(®)).

RESULTS

By immunoblot, 82 cases (93.2%) were H. pylori positive, 10 of these cases (11.4%) were negative by ELISA and only 6 cases (6.8%) were negative by both ELISA and immunoblot. Multivariable odds ratio (OR) for noncardia GC comparing immunoglobulin G positive versus negative by ELISA was 6.8 [95% confidence interval (CI) 3.0-15.1], and by immunoblot, the OR was 21.4 (95% CI 7.1-64.4).

CONCLUSIONS

Using a western blot assay, nearly all noncardia GC were classified as H. pylori positive and the OR was more than threefold higher than the OR assessed by ELISA, supporting the hypothesis that H. pylori infection is a necessary condition for noncardia GC.

Oral contraceptives, reproductive history and risk of colorectal cancer in the European Prospective Investigation into Cancer and Nutrition

BACKGROUND

Oral contraceptive use and reproductive factors may initiate long-term changes to the hormonal milieu and thereby, possibly influence colorectal cancer risk.

METHODS

We examined the association of hormonal and reproductive factors with risk of colorectal cancer among 337,802 women in the European Prospective Investigation into Cancer and Nutrition, of whom 1878 developed colorectal cancer.

RESULTS

After stratification for center and age, and adjustment for body mass index, smoking, diabetes mellitus, physical activity and alcohol consumption, ever use of oral contraceptives was marginally inversely associated with colorectal cancer risk (hazard ratio (HR), 0.92; 95% confidence interval (CI), 0.83-1.02), although this association was stronger among post-menopausal women (HR, 0.84; 95% CI: 0.74-0.95). Duration of oral contraceptive use and reproductive factors, including age at menarche, age at menopause, type of menopause, ever having an abortion, parity, age at first full-term pregnancy and breastfeeding, were not associated with colorectal cancer risk.

CONCLUSION

Our findings provide limited support for a potential inverse association between oral contraceptives and colorectal cancer risk.

What characterizes substance abusers who commit suicide attempts? Factors related to Axis I disorders and patterns of substance use disorders. A study of treatment-seeking substance abusers in Norway

OBJECTIVE

The frequency of suicide attempts and clinical characteristics of attempters among poly-substance abusers and alcoholics were examined.

METHODS

A consecutive sample (n = 260) of in- and outpatients from two Norwegian counties were assessed by Composite International Diagnostic Interview (Axis I disorders), Millon's Clinical Multiaxial Inventory (Axis II disorders) and the Norwegian National Client Assessment Form. When analysing the association between suicide attempters and the range of predictor variables, logistic regression analysis was conducted.

RESULTS

Almost half (47%) of the sample reported lifetime suicide attempts; significantly more frequently in poly-substance abusers (58%) than alcoholics (38%). A substance use disorder with duration of >or=15 years and an early onset (<18 years of age) were independently associated with being a suicide attempter after controlling for Axis I disorders. In addition, eating disorders, agoraphobia and major depression were strongly and independently associated with being a suicide attempter.

CONCLUSION

Attempts at preventing suicidal behaviour should not ignore the suicide risk among poly-substance abusers. In addition, prevention of suicidal behaviour demands a treatment programme focusing concomitantly on both addictive behaviour and comorbid psychiatric disorders.

Substance-dependent patients with and without social anxiety disorder: occurrence and clinical differences. A study of a consecutive sample of alcohol-dependent and poly-substance-dependent patients treated in two counties in Norway

AIMS

(1) To identify clinically important differences between patients with and without social anxiety disorder (SAD) among alcohol-dependent and poly-substance-dependent patients. (2) To explore if primary SAD is a predictor of alcohol-dependency or poly-substance dependency when controlling for other Axes I and II disorders.

METHODS

A consecutive sample of in- and outpatient alcohol-dependent (N = 146) and poly-substance-dependent patients (N = 114) from public treatment programmes in two catchment areas was assessed by personal interview, the Composite International Diagnostic Interview and the Millon Clinical Multiaxial Inventory.

RESULTS

The frequency of current SAD was 42%; SAD was significantly more frequent among poly-substance-dependent patients (51%) than among alcohol-dependent patients (34%). Patients with SAD do not represent a distinct clinical subgroup, but the occurrence of SAD is combined with the occurrence of other anxiety disorders, affective disorders and personality disorders in both substance groups. The analysis showed a trend towards primary SAD as a predictor for developing poly-substance dependency.

CONCLUSIONS

Patients with SAD in both substance groups exhibited more comorbid Axis I and II disorders. They may need specific psychiatric treatment for such disorders in addition to treatment for SAD. Treatment of primary SAD could be a target for preventing poly-substance dependency in young populations.

Primary and secondary substance misusers: do they differ in substance-induced and substance-independent mental disorders?

AIMS

This study evaluated the primary/secondary distinction among substance misusers according to comorbid mental disorders.

METHODS

A consecutive sample (n = 287) of DSM-IV substance dependents from public treatment facilities in two counties in Norway were assessed by the Composite International Diagnostic Interview. According to the debut of the first independent mental disorder, patients were divided into primary substance use disorder (SUD) (17%), secondary SUD (76%) and SUD in the same year as the first mental disorder (7%).

RESULTS

A lifetime substance-independent mental disorder was found in 90%. Forty-two per cent had a combination of substance-independent and substance-induced mental disorders. Five per cent had substance-induced mental disorders only. Primary SUD patients comprised less women, and a lower number of substance-independent mental disorders. Secondary SUD patients had more major depression, phobic disorders and obsessive-compulsive disorder. There were no differences between primary SUD and secondary SUD regarding the number of substance-induced disorders or the pattern of substance misuse.

CONCLUSIONS

Clinical differences between primary and secondary SUD were small and do not support the distinction.

Gender differences in the prevalence of symptom disorders and personality disorders among poly-substance abusers and pure alcoholics. Substance abusers treated in two counties in Norway

OBJECTIVE

Gender differences in the prevalence of Axis I and II disorders in poly-substance abusers and pure alcoholics and between these two groups are explored.

METHOD

A consecutive sample (n = 260) of in- and out-patients from two Norwegian counties were assessed by CIDI (Axis I disorders) and MCMI-II (Axis II disorders).

RESULTS

Major depression, post-traumatic stress disorder (PTSD), and eating disorders were significantly more prevalent in women than in men. A significantly higher prevalence of antisocial, passive-aggressive, and borderline personality disorders (PD) was observed among poly-substance abusers, whereas pure alcoholics were found to have dependent PDs more often. Female poly-substance abusers differed significantly from all other substance abusers by suffering more often from major depression, simple phobia, PTSD and borderline PD. Male poly-substance abusers more often presented antisocial PD and less often Cluster C disorders than all other substance abusers. Female pure alcoholics more often had major depression and Cluster C disorders than all other substance abusers. Male pure alcoholics presented less often with Axis I disorders, major depression, and PTSD, but more often with Cluster A disorders, in particular schizoid PD, than all other substance abusers.

CONCLUSION

The pattern of comorbid disorders is clearly different between male and female poly-substance abusers and pure alcoholics. This implies that these four subgroups have important differences in their treatment needs.

Hormone replacement therapy in Norwegian women, 1996-1997

OBJECTIVES

To assess the prevalence of hormone replacement therapy (HRT) among Norwegian women and examine factors related to use.

MATERIALS AND METHODS

A random sample of 18,199 Norwegian women aged 45-64 years responded to a postal questionnaire in 1996-1997. The questionnaire included questions about menstruation status and fertility, oral contraceptives (OC) and HRT use, lifestyle, health and socio-economic status. The response rate was 60%.

RESULTS

Overall prevalence of ever using systemic or local HRT was 43.9%. Current use was reported by 31.9% of the women. The highest prevalence was in the age group of 55-59 years where 57.4% reported ever use, and 43.1% current use. Mean duration of use among current users was 4.6 years. More than 60% of the women were classified as postmenopausal, two-thirds of them naturally postmenopausal. The prevalence of ever using HRT was 51.8%. Prevalence of use was higher among earlier OC users, smokers, lean women and in households with high income. Among older women, users had a higher educational level than non-users, while this difference disappeared among the youngest of the women. Fixed combinations of estradiol and noretisteroneacetate either cyclic or continuous, are used by six out of ten users.

CONCLUSIONS

Our results confirm the increasing trend in sales of estrogens in Norway and suggest that user patterns are changing. More than four out of ten women aged 45-64 years reported ever use of HRT, and one out of three reported current use. Socio-economic differences between users and non-users seem to disappear among women under 55 years of age, but persist in the older age groups. Short time use still dominates.

[Local monitoring center for clozapine (Leponex) treatment]

A local centre for monitoring clozapine therapy has been in operation in the Pharmacy Department at Asgård Hospital in Tromsø since 1994. The centre utilizes an electronic reporting system and is available to clozapine-prescribers in the three northernmost countries in Norway: Nordland, Troms and Finnmark. The system fosters early detection of poor compliance with frequent blood tests and for signs of white blood cell suppression. This is a new concept in Norway and one way of assuring the quality of clozapine treatment. The purpose of the centre is to improve patient safety by facilitating early detection of potentially dangerous white blood cell suppression, thereby avoiding fatal consequences.