RNA-seq RNAaccess identified as the preferred method for gene expression analysis of low quality FFPE samples

Clinical tumor tissues that are preserved as formalin-fixed paraffin-embedded (FFPE) samples result in extensive cross-linking, fragmentation, and chemical modification of RNA, posing significant challenges for RNA-seq-based gene expression profiling. This study sought to define an optimal RNA-seq protocol for FFPE samples. We employed a common RNA extraction method and then compared RNA-seq library preparation protocols including RNAaccess, RiboZero and PolyA in terms of sequencing quality and concordance of gene expression using FFPE and case-matched fresh-frozen (FF) triple-negative breast cancer (TNBC) tissues. We found that RNAaccess, a method based on exome capture, produced the most concordant results. Applying RNAaccess to FFPE gastric cancer tissues, we established a minimum RNA DV200 requirement of 10% and a RNA input amount of 10ng that generated highly reproducible gene expression data. Lastly, we demonstrated that RNAaccess and NanoString platforms produced highly concordant expression profiles from FFPE samples for shared genes; however, RNA-seq may be preferred for clinical biomarker discovery work because of the broader coverage of the transcriptome. Taken together, these results support the selection of RNA-seq RNAaccess method for gene expression profiling of FFPE samples. The minimum requirements for RNA quality and input established here may allow for inclusion of clinical FFPE samples of sub-optimal quality in gene expression analyses and ultimately increasing the statistical power of such analyses.

A first-in-human study of AO-176, a highly differentiated anti-CD47 antibody, in patients with advanced solid tumors

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Background: AO-176 is a humanized IgG2 antibody that specifically targets CD47. Expressed by multiple tumor types, CD47 binds to signal regulatory protein a (SIRPa) on phagocytes, including macrophages and dendritic cells. The CD47-SIRPa complex results in a “don’t eat me” signal that allows the tumor to escape removal by the innate immune system, disabling the generation of an adaptive immune response. The differentiated mechanisms of action of AO-176 include promotion of phagocytosis, direct tumor cell killing through programmed cell death type III and induction of damage associated molecular patterns/immunogenic cell death, preferentially binding to tumor cells vs. normal cells, and enhanced binding at an acidic pH as found in tumor microenvironments. AO-176 has negligible binding to RBCs. Methods: In a phase 1/2 first-in-human study (NCT03834948) of AO-176, pts with advanced solid tumors associated with high CD47 expression and an ECOG PS of 0-1 were enrolled into escalating dose cohorts of AO-176 given IV every 7 days. Objectives included evaluation of safety, dose-limiting toxicity (DLT) and recommended phase 2 dose (RP2D), antitumor activity, pharmacokinetic (PK) parameters and exploratory biomarkers. Results: As of 4 Jan 2021, 27 pts were enrolled (median age 64 years; 67% female; 67% ECOG PS 1; median [range] of 4 [1-7] prior therapies for metastatic disease). Dose levels of 1, 3, 10, 20 and 20 (using step-up dosing) mg/kg were evaluated in >250 infusions. Most common (>10%) treatment-related adverse events (TRAEs) of any grade were thrombocytopenia and infusion-related reaction (IRR) (33% each), anemia (22%) with no evidence of hemolysis, nausea (19%), and fatigue (15%). The only G3+ TRAE occurring in >10% of pts was asymptomatic, brief thrombocytopenia (22%). No platelet transfusions were given. DLTs included IRRs in 2 pts dosed at 20 mg/kg, and asymptomatic thrombocytopenia and a cerebrovascular accident in 1 pt each in the 20 mg/kg step-up cohort. The RP2D was 10 mg/kg. Implementation of additional pre-medication and a 6-hr infusion duration in cycle 1 eliminated subsequent IRRs. Dexamethasone tapering and shortening of the infusion duration to 2 hrs was successful in all pts after cycle 1. Interim PK analysis of AO-176 demonstrated consistent exposure with linear PK. The T1/2 was ̃5 days. One pt with endometrial carcinoma who had not responded to any of 4 prior systemic regimens had a confirmed PR and remains on study for >1 year. 7 pts had SD as a best response, with 2 pts (endometrial carcinoma, gastric cancer) on study for >6 mos. Conclusions: AO-176 is a well-tolerated, differentiated anti-CD47 therapeutic. Durable anti-tumor activity was observed. Evaluations of AO-176 in combination with paclitaxel in pts with select solid tumors (NCT03834948) and as a single-agent in pts with multiple myeloma (NCT04445701) are ongoing. Clinical trial information: NCT03834948.

Immune monitoring of blood in advanced gastroesophageal adenocarcinoma patients treated with an anti-MMP9 monoclonal antibody in combination with nivolumab

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Background: A phase 1b study was conducted in Japanese patients with >2nd line advanced gastroesophageal adenocarcinoma (GEA) to evaluate the safety, tolerability and explore efficacy and biomarkers, of andecaliximab (ADX), an anti-MMP9 monoclonal antibody, in combination with nivolumab (nivo). In this study, 5 of the 10 enrolled patients had a partial response and the remaining 5 had progressive disease. A larger parallel study in western patients showed no improvement in response or survival for the addition of ADX to nivo. A biomarker study is reported here which explored the hypothesis that baseline levels or early changes in the frequency of peripheral immune cells might identify responders to immunotherapy. Methods: Blood samples were collected at screen, C1D1, C1D8, C1D15, C2D1, C2D15 and then at CXD1 until end of treatment and processed to viably-frozen PBMCs. Immune cell analysis was conducted by flow cytometry (FCM), and included evaluation of T cells, B cells, myeloid derived suppressor cells, NK cells, monocytes, and dendritic cells (DCs). Baseline status and on treatment changes were explored. Results: FCM analysis of peripheral blood showed that the 5 responders had higher frequency of LAG3+CD8+ T cells and myeloid DCs, and lower frequency of plasmacytoid DC than non-responders at baseline. The number of CD8+ T cells decreased at C1D8 and then recovered in responders. In contrast, no CD8+ T cell changes were observed in non-responders. CTLA-4+ CD4+ T cells also increased after treatment in responders but not in non-responders. Changes in other evaluated cell populations were not observed. Conclusions: The observation that baseline levels of LAG3+CD8+ T cells and DCs were higher in responders is consistent with a prior anti-tumor immune response. Transient decreased peripheral CD8+ T cells might reflect T-cell trafficking into tumor in response to immunotherapy, and increased peripheral CTLA-4+ CD4+ T cells may also relate to tumor-localized response. Although in a very small number of patients, the observations are consistent with early changes in peripheral immune cells that may relate to response to immunotherapy. Clinical trial information: NCT02862535.

Exploratory longitudinal analysis of cfDNA to reveal potential biomarkers of CRC progression and treatment response

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Background: Blood-based tests can predict drug response and disease progression. Many tests rely on detecting tumor DNA, which represents only a fraction of all cell-free DNA (cfDNA). Here, we used a novel methodology to infer gene activation from cfDNA. This unique platform offers the ability to identify potential non-tumor derived biomarkers that may be associated with clinical outcomes in colorectal cancer (CRC). Methods: Longitudinal plasma samples from metastatic CRC patients enrolled in NCT01803282 (andecaliximab/chemotherapy/bevacizumab; 92 samples from 12 patients) were evaluated. Patients were classified as progressors (SD+PD) or responders (CR+PR) based on best objective response. Gene activation was inferred from cfDNA fragment length and counts around transcription start sites using whole-genome sequencing. Transcription factor activity was estimated by measuring binding site accessibility across the genome. Tumor fraction (TF) was estimated using ichorCNA. Results: Gene activation profiles inferred from cfDNA across the entire genome identified several genes differentially expressed in progressors or responders. Specifically, all patients with elevated KIR2DL1, an inhibitory NK cell receptor, progressed (p = 6.35e-14). Additionally, BMPR1A activation decreased in responders (p = 0.002) while the DNA- binding activity of SMAD1, which functions directly downstream of BMPR1A in the BMP2 pathway, increased in responders post-therapy (p = 0.03). These 3 genes (i.e., KIR2DL1, BMPR1A and SMAD1) are related to NK cell maturation, suggesting an immunological mechanism. Notably, pre-therapy TF did not predict response. Conclusions: In this pilot study, we demonstrated the ability of a unique cfDNA platform to interrogate multiple features to reveal genes associated with drug response and their underlying mechanism. We identified that KIR2DL1 is associated with progression, and BMPR1A and SMAD1 are associated with response. This work highlights the potential of cfDNA to provide biological insights beyond TF and that identification of non-tumor-derived signals may benefit biomarker discovery and drug target identification.

Identification of cancer hallmarks associated with benefit in advanced gastroesophageal adenocarcinoma patients treated with checkpoint blockade

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Background: The benefit of checkpoint blockade in advanced gastric cancer is limited and biomarkers related to response are needed. Novel gene expression analysis software was used to identify Hallmarks of Cancer associated with clinical benefit following nivolumab treatment in >2nd line advanced gastroesophageal adenocarcinoma (GEA). Methods: RNA-sequencing data from baseline GEA patient diagnostic tumor samples (103 from NCT02862535; 5 from NCT02862535) were analyzed using the claraT platform (V2.0.0, Almac Diagnostic Services). 62 gene signatures were quantified representing 6 key Hallmarks of Cancer (Avoiding Immune Destruction, Activating Invasion and Metastases, Sustaining Proliferative Signaling, Inducing Angiogenesis, Resisting Cell Death and Genome Instability and Mutation). Clinical benefit (CB) was defined as tumor response or overall survival (OS) > 1 year. HER2 status was from medical records. Survival analyses used cox proportional hazards models. Results: Gene expression signatures (GES) identified 5 molecular subgroups (C1-C5). Rate of CB in each molecular subtype are outlined in Table. C3 and C4 had significantly improved OS compared to C2, (HR = 0.45; p= 0.02 and HR = 0.42; p= 0.02). Greater proportions of HER2+ subjects were present in C4 and C3 vs. C2, with C3 statistically significant (60% vs. 14%; p= 0.012). Gene expression characterized by chromosomal instability (CIN) and homologous recombination repair deficiency (HRD) were associated with HER2(+) (wilcox p= < 0.05). Patients selected by only using CIN & HRD had significant improvement in OS (HR = 0.63; p= 0.03). Conclusions: Interferon-based GES did not predict benefit from immune checkpoint blockade. GES representing HRD and activation of HER2, EGFR and MAPK (each enriched in CIN) were associated with improved survival upon checkpoint blockade in advanced GEA patients. Clinical trial information: NCT02862535 . [Table: see text]

A phase II, open-label, randomized study to evaluate the efficacy and safety of andecaliximab combined with nivolumab versus nivolumab alone in subjects with unresectable or recurrent gastric or gastroesophageal junction adenocarcinoma

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Background: Andecaliximab (ADX) is a monoclonal antibody that inhibits matrix metalloproteinase 9 (MMP9). Preclinical studies suggest that MMP9 inhibition relieves immune suppression and promotes T-cell infiltration to potentiate checkpoint blockade. Methods: Phase 2, open-label, randomized study of the efficacy and safety of ADX + nivolumab (NIVO) vs. NIVO alone in patients with pre-treated metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma. Patients were randomized to either ADX 800 mg IV + NIVO 3 mg/kg IV, or NIVO 3 mg/kg IV alone, and stratified by tumor PD-L1 status. Treatment was administered every 2 weeks. Re-staging CT scans were performed every 8 weeks to evaluate response. Primary endpoint: objective response rate (ORR). Secondary endpoints: progression-free survival (PFS), overall survival (OS), and adverse events (AEs). Results: Of the 144 patients randomized, 141 were treated, 109 (76%) completed tumor assessment. 81% of patients were white, with 69% male and a mean (SD) age of 59 (12) years. ORR (95% CI) was 11.1% (4.9–20.7%) in patients receiving ADX + NIVO, and 6.9% (2.3–15.5%) in those receiving NIVO alone, p = 0.6. Kaplan-Meier estimated median (95% CI) PFS was 1.8 (1.8–2.0) months in patients receiving ADX + NIVO, and 1.9 (1.7–1.9) months in those receiving NIVO alone, p = 0.2. Kaplan-Meier estimated median (95% CI) OS was 7.2 (5.2–9.1) months in patients receiving ADX + NIVO, and 5.9 (3.5–8.6) months in those receiving NIVO alone, p = 0.4. AEs leading to treatment discontinuation occurred in 1 patient in the ADX + NIVO group, and in 1 patient in NIVO-only group. PD-L1 and mismatch repair deficient subgroup analyses will be presented. Exploratory biomarker analyses will be submitted separately. Conclusions: Addition of ADX to NIVO did not improve ORR, PFS, or OS compared with NIVO alone in patients with pre-treated metastatic gastric or GEJ adenocarcinoma. Combination of ADX with NIVO had a favorable safety and tolerability profile. Clinical trial information: NCT02864381.

Exploratory evaluation of baseline tumor biomarkers and their association with response and survival in patients with previously treated advanced gastric cancer treated with andecaliximab combined with nivolumab versus nivolumab

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Background: Andecaliximab (ADX) is a monoclonal antibody that inhibits matrix metalloproteinase 9 (MMP9). Preclinical studies suggest that MMP9 inhibition relieves immune suppression and promotes T cell infiltration to potentiate checkpoint blockade. In the phase 2 study combining ADX with nivolumab (N) versus N monotherapy (NCT02864381), addition of ADX to N did not improve objective response rate, progression-free survival (PFS), or overall survival (OS). Methods: Archival tumor samples were collected from all patients (n = 141). CD8 and PD-L1 (28-8 DAKO) were assessed by immunohistochemistry. CD8+ cell density was measured in the tumor area. PD-L1 was prospectively scored by a pathologist for tumor cell (TC) and associated immune cell (IC) positivity. IFNg, Teffector (Teff), and activated CD8+ T cell (ActT) gene signatures were assessed by RNA sequencing. Due to a small number of responders, treatment arms were combined to evaluate response. Cox proportional hazards models were used for survival analyses. Nominal p-values are reported. Results: Baseline biomarkers of T cell infiltration and activation did not differentiate responders from non-responders (IFNg, Teff, ActT, CD8+; p > .10). None of the evaluated biomarkers were associated with PFS or OS for all treated patients or per treatment arm (IFNg, Teff, ActT; p > .10), with the exception of CD8+ (PFS HR = .43, p = .02). The majority of baseline samples were positive for IC PD-L1 (< 1%, n = 36; 1-10%, n = 50; > 10-25%, n = 32; > 25%, n = 20) and negative for TC PD-L1 (H = 0, n = 88; H < 1, n = 27; H > 1; n = 27). Comparing ADX/N to N, there was a trend toward longer OS for the PD-L1+ (TC + IC ≥ 1%) population (n = 102, HR = .621, p = .098), the TC H < 1 group (HR = .464, p = .08) and the IC > 10-25% (HR = .466, p = .08). Conclusions: Neither CD8+ cell density nor IFNg, Teff or ActT gene signatures were associated with response or survival to checkpoint blockade. While TC was low, IC intermediate and TC + IC ≥ 1% PD-L1+ groups trended toward better survival for the ADX+N arm, consistent with the hypothesis that ADX potentiates N activity; this did not translate into better outcome. Clinical trial information: NCT02864381.

Evaluation of intratumoral T cells in biopsies from advanced gastric cancer patients treated with andecaliximab and nivolumab

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Background: Preclinical studies suggest that MMP9 inhibition relieves immune suppression and promotes T cell infiltration to potentiate checkpoint blockade. To test this hypothesis, patient tumor samples obtained in a phase 2, open-label, randomized study (NCT02864381) of previously treated advanced gastric cancer comparing the MMP9-specific inhibitor andecaliximab (ADX) plus nivolumab (N) vs N alone were evaluated for T cell biomarkers. Methods: CD8 and PD-L1 (28-8 DAKO) were assessed by immunohistochemistry. IFNg, Teffector (Teff), and activated CD8+ T cell (ActT) gene signatures (GS) were assessed by RNASeq in archival baseline (BL) and biopsies obtained between weeks 5 and 9 (on-treatment; OT). Results: For both N and ADX/N, intratumoral CD8+ cells were significantly increased in OT biopsies relative to BL. The CD8+ OT increase was significantly greater for the ADX/N treatment relative to N in the PD-L1+ subgroup. In the ADX/N group only, IFNg, Teff, and ActT GS were significantly higher in OT biopsies relative to BL. OT change from BL of ≥ 300% vs <300% in CD8+ cells was associated with longer PFS (HR = 0.50, p = 0.032). The percentage of patients with increased CD8+ cells in OT biopsies was higher in the ADX/N arm. Conclusions: In the PD-L1+ ADX/N group, there was a significantly greater magnitude of CD8+ cell density increase, which was associated with gene signatures of T cell activation. More ADX/N-treated patients had an increase in tumor-associated CD8+ cells. Longer PFS was observed for patients in which CD8+ cells increased by ≥ 300%. These results are consistent with the hypothesis that ADX potentiates checkpoint inhibition by favorably altering the tumor immune microenvironment. Clinical trial information: NCT02864381. [Table: see text]

Effect of andecaliximab (anti-MMP9) on proteolysis of IL-7 in vitro, TCR diversity in mice, and serum IL-7 in gastric cancer patients in combination with chemotherapy

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Background: Andecaliximab (andeca) is a monoclonal antibody that selectively inhibits matrix metalloproteinase 9 (MMP9). IL-7 selectively enhances the proliferation and survival of naïve, memory, and effector T-cells (but not regulatory T-cells) in the periphery. Previous clinical trials with systemic recombinant IL-7 therapy increased TCR diversity. In the disease setting, elevated circulating IL-7 may be due to a compensatory increase in IL-7 production as demonstrated in mice upon inhibition of IL-7 signaling. Methods: An in vitro screen, in which recombinant active human MMP9 was incubated with > 140 human recombinant folded proteins, identified IL-7 as the most efficient substrate of MMP9. Results: IL-7 proteolysis occurred between A128:L129. IL-7 proteolysis altered the global protein structure, evidenced by a loss of cooperative unfolding observed with intact IL-7 (intrinsic fluorescence, Tm = 59.3o C). Mouse MMP9 proteolyzed mouse IL-7 in vitro. In the orthotopic syngeneic NeuT mouse model, MMP9 inhibition reduced tumor growth (p = 0.0005). In a 7-day NeuT study, anti-MMP9 alone improved TCR diversity (decreased clonality) within tumor-infiltrating T-cells (Dunnett’s p = 0.0083). Further, anti-MMP9 and anti-PDL1 co-treatment promoted an increase in CD3+ cells (p = 0.01), CD4+ T cells (p = 0.006), and CD8+ T cells (p = 0.013) concomitant with a decrease in tumor-associated CD25+ FoxP3+ regulatory T cells (p = 0.04) in the tumor. In gastric cancer patient serum, pro-MMP9 (p < 0.0001), active MMP9 (p < 0.0001), and IL-7 (p < 0.0001) were higher than healthy controls. Serum IL-7 levels were normalized upon treatment with andeca plus mFOLFOX6 (N = 40; FDR-corrected p < 0.001) in a Phase I gastric cancer study. Conclusions: MMP9 proteolyzed IL-7 in vitro. Specific MMP9 inhibition in a mouse tumor model improved TCR diversity. Andeca +mFOLFOX6 therapy normalized serum IL-7 levels, which could be due to andeca, chemotherapy, or disease resolution. The functional implications of IL-7 proteolysis by MMP9 in gastric cancer are currently under investigation.

A randomized, controlled phase III trial of nab-Paclitaxel versus dacarbazine in chemotherapy-naïve patients with metastatic melanoma

BACKGROUND

The efficacy and safety of nab-paclitaxel versus dacarbazine in patients with metastatic melanoma was evaluated in a phase III randomized, controlled trial.

PATIENTS AND METHODS

Chemotherapy-naïve patients with stage IV melanoma received nab-paclitaxel 150 mg/m(2) on days 1, 8, and 15 every 4 weeks or dacarbazine 1000 mg/m(2) every 3 weeks. The primary end point was progression-free survival (PFS) by independent radiologic review; the secondary end point was overall survival (OS).

RESULTS

A total of 529 patients were randomized to nab-paclitaxel (n = 264) or dacarbazine (n = 265). Baseline characteristics were well balanced. The majority of patients were men (66%), had an Eastern Cooperative Oncology Group status of 0 (71%), and had M1c stage disease (65%). The median PFS (primary end point) was 4.8 months with nab-paclitaxel and 2.5 months with dacarbazine [hazard ratio (HR), 0.792; 95.1% confidence interval (CI) 0.631-0.992; P = 0.044]. The median OS was 12.6 months with nab-paclitaxel and 10.5 months with dacarbazine (HR, 0.897; 95.1% CI 0.738-1.089; P = 0.271). Independently assessed overall response rate was 15% versus 11% (P = 0.239), and disease control rate (DCR) was 39% versus 27% (P = 0.004) for nab-paclitaxel versus dacarbazine, respectively. The most common grade ≥3 treatment-related adverse events were neuropathy (nab-paclitaxel, 25% versus dacarbazine, 0%; P < 0.001), and neutropenia (nab-paclitaxel, 20% versus dacarbazine, 10%; P = 0.004). There was no correlation between secreted protein acidic and rich in cysteine (SPARC) status and PFS in either treatment arm.

CONCLUSIONS

nab-Paclitaxel significantly improved PFS and DCR compared with dacarbazine, with a manageable safety profile.

Albumin-bound nanoparticle (nab) paclitaxel exhibits enhanced paclitaxel tissue distribution and tumor penetration

PURPOSE

nab-paclitaxel demonstrates improved clinical efficacy compared with conventional Cremophor EL (CrEL)-paclitaxel in multiple tumor types. This study explored the distinctions in drug distribution between nab-paclitaxel and CrEL-paclitaxel and the underlying mechanisms.

METHODS

Uptake and transcytosis of paclitaxel were analyzed by vascular permeability assay across human endothelial cell monolayers. The tissue penetration of paclitaxel within tumors was evaluated by local injections into tumor xenografts and quantitative image analysis. The distribution profile of paclitaxel in solid-tumor patients was assessed using pharmacokinetic modeling and simulation.

RESULTS

Live imaging demonstrated that albumin and paclitaxel were present in punctae in endothelial cells and could be observed in very close proximity, suggesting cotransport. Uptake and transport of albumin, nab-paclitaxel and paclitaxel were inhibited by clinically relevant CrEL concentrations. Further, nab-paclitaxel causes greater mitotic arrest in wider area within xenografted tumors than CrEL- or dimethyl sulfoxide-paclitaxel following local microinjection, demonstrating enhanced paclitaxel penetration and uptake by albumin within tumors. Modeling of paclitaxel distribution in patients with solid tumors indicated that nab-paclitaxel is more dependent upon transporter-mediated pathways for drug distribution into tissues than CrEL-paclitaxel. The percent dose delivered to tissue via transporter-mediated pathways is predicted to be constant with nab-paclitaxel but decrease with increasing CrEL-paclitaxel dose.

CONCLUSIONS

Compared with CrEL-paclitaxel, nab-paclitaxel demonstrated more efficient transport across endothelial cells, greater penetration and cytotoxic induction in xenograft tumors, and enhanced extravascular distribution in patients that are attributed to carrier-mediated transport. These observations are consistent with the distinct clinical efficacy and toxicity profile of nab-paclitaxel.

Abstract 5666: Albumin and paclitaxel co-localize in endocytic vesicles in HUVEC cells, and uptake is blocked by Cremophor EL

Nab®-paclitaxel is an albumin-bound nanoparticle formulation of paclitaxel (ptx) that does not contain Cremophor EL (CrEL), and results in higher drug levels in xenografts and increased clinical activity in breast and lung cancers compared to ptx formulated with CrEL (Taxol®). Above the critical micellar concentration of 0.009%, CrEL forms long-lived micelles in circulation that can sequester ptx (peak plasma concentration in clinical use is 0.3%). Previous studies have shown CrEL reduces ptx binding to albumin, and Taxol® has reduced association with, and transport across endothelial cells compared to nab®-ptx (Desai, CCR 2006).

Endothelial cells take up albumin, which is trafficked into recycling or transcytosis pathways or into lysosomes for degradation. Here, we explore mechanisms of uptake and trafficking of albumin and ptx in endothelial cells and the effect of CrEL on these events. Using fluorescence microscopy, we visualized the uptake of rhodamine-albumin and fluorescent ptx (Flutax). Albumin was present in EEA1-positive early endosomes and LAMP1-positive lysosomes. Notably, ptx was also present in vesicular structures and was often co-localized with albumin. The uptake of albumin was blocked by increasing concentrations (0.003%-0.3%) of CrEL, and also by inhibitors of caveolin-mediated endocytosis including indomethacin (blocks internalization of caveolae) and methyl-β-cyclodextrin (prevents formation of lipid rafts).

The effect of CrEL on paclitaxel and albumin cellular uptake was confirmed by flow cytometry studies. 0.3% CrEL reduced the uptake of Flutax in DMSO, Flutax-modified nab®-ptx, and FITC-labeled albumin to close to background levels in both HUVEC and PC3 cells. Thus, in addition to its drug sequestration activity, CrEL directly affects endocytosis.

We further evaluated CrEL effects on Flutax and ptx transport across endothelial monolayers in transwell chambers using a fluorescence detection assay. Two-fold more ptx crossed monolayers exposed to Flutax-containing nab®-ptx as compared to Taxol®. The effects of 0.001% to 0.3% CrEL on ptx transport at varying timepoints were investigated by mass spectrometry. Dose-dependent inhibition was observed, with a 3-fold reduction in transported ptx at 24 hrs.

In summary, we have demonstrated that ptx co-localizes with albumin in endothelial cells, suggesting that the nab-ptx complex can remain intact within cells. Furthermore, CrEL interferes with albumin uptake at clinically relevant concentrations, thereby affecting paclitaxel cellular uptake and transport. These mechanistic studies further elucidate the basis of increased delivery of drug into the target cells by the nab®-ptx formulation as compared to Taxol®.

Citation Format: Xiping Liu, Carrie Brachmann, Sean Hong, Shijuan Wu, Zeen Tong, Tapas De, Willard Foss, Gondi Kumar, Sekhar Surapaneni, Rajesh Chopra, Daniel Pierce, Carla Heise. Albumin and paclitaxel co-localize in endocytic vesicles in HUVEC cells, and uptake is blocked by Cremophor EL. [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 5666. doi:10.1158/1538-7445.AM2013-5666

Coordinated expression of cell death genes regulates neuroblast apoptosis

Properly regulated apoptosis in the developing central nervous system is crucial for normal morphogenesis and homeostasis. In Drosophila, a subset of neural stem cells, or neuroblasts, undergo apoptosis during embryogenesis. Of the 30 neuroblasts initially present in each abdominal hemisegment of the embryonic ventral nerve cord, only three survive into larval life, and these undergo apoptosis in the larvae. Here, we use loss-of-function analysis to demonstrate that neuroblast apoptosis during embryogenesis requires the coordinated expression of the cell death genes grim and reaper, and possibly sickle. These genes are clustered in a 140 kb region of the third chromosome and show overlapping patterns of expression. We show that expression of grim, reaper and sickle in embryonic neuroblasts is controlled by a common regulatory region located between reaper and grim. In the absence of grim and reaper, many neuroblasts survive the embryonic period of cell death and the ventral nerve cord becomes massively hypertrophic. Deletion of grim alone blocks the death of neuroblasts in the larvae. The overlapping activity of these multiple cell death genes suggests that the coordinated regulation of their expression provides flexibility in this crucial developmental process.

The Drosophila homolog of the putative phosphatidylserine receptor functions to inhibit apoptosis

Exposure of phosphatidylserine is a conserved feature of apoptotic cells and is thought to act as a signal for engulfment of the cell corpse. A putative receptor for phosphatidylserine (PSR) was previously identified in mammalian systems. This receptor is proposed to function in engulfment of apoptotic cells, although gene ablation of PSR has resulted in a variety of phenotypes. We examined the role of the predicted Drosophila homolog of PSR (dPSR) in apoptotic cell engulfment and found no obvious role for dPSR in apoptotic cell engulfment by phagocytes in the embryo. In addition, dPSR is localized to the nucleus, inconsistent with a role in apoptotic cell recognition. However, we were surprised to find that overexpression of dPSR protects from apoptosis, while loss of dPSR enhances apoptosis in the developing eye. The increased apoptosis is mediated by the head involution defective (Wrinkled) gene product. In addition, our data suggest that dPSR acts through the c-Jun-NH(2) terminal kinase pathway to alter the sensitivity to cell death.