Abstract 1993: Biomarker analyses from the Phase I clinical trial of the first-in-class SIRPa immune checkpoint inhibitor BI765063 in patients with advanced solid tumors

Background: BI 765063 (OSE-172) is a humanised IgG4 monoclonal antibody which binds selectively to the V1 allele of Signal Regulatory Protein α [SIRPα] blocking the SIRPα/CD47 “don't eat me” pathway. Preclinical studies showed that SIRPα blockage led to macrophage and T-cell recruitment into tumor xenografts, and induced upregulation of chemokines, cytokines and adaptive immune function genes in human tumor explants (Gauttier et al., 2020). The goal of the biomarker analyses was to characterize the BI 765063 impact on peripheral blood immune cells (PBMCs) and the tumor microenvironment (TME).

Methods: Fifty patients (26 V1/V1, 24 V1/V2) received BI 765063 IV from 0.02 mg/kg to 36 mg/kg every 3 weeks. Paired tumor biopsies were collected before and 2 weeks after first BI 765063 infusion. PBMCs were collected before, then 4 h, 1, 14, and 21 days after first infusion. BI 765063 receptor occupancy (RO) was determined on peripheral CD14+ monocytes. Immunophenotyping of PBMCs was performed by flow-cytometry. TME was analysed with a Brightplex® IHC panel including CD8+ T-cells, CD68+ macrophages, SIRPα, CD47, and PD-L1. Tumor gene expression profiling was performed using the Pan Cancer Immune gene set.

Results: BI 765063 full RO saturation was achieved at trough levels (C2D1, pre-dose) in V1/V1 patients treated with doses of 6 mg/kg and higher, while V1/V2 patients showed a more heterogeneous RO ranging from 40-80%, reaching an apparent saturation at ≥ 12 mg/kg. An increase of activated CD80+/CD14+ and CD40+/CD14+ monocytes in PBMCs was observed at 24 h post-treatment in both, V1/V1 and V1/V2 patients. In paired tumor biopsies, IFNγ, MHCII antigen presentation gene pathways, and CCL7 transcripts appeared to be upregulated at C1D15 in patients with a systemic exposure of ≥ 100 µg/ml. One patient with hepatocellular carcinoma (HCC) and liver and lung metastases treated with BI 765063 monotherapy at 24 mg/kg achieved partial response (Champiat et al., ASCO, 2021). Baseline tumor biopsy of that patient showed that 66% of HCC tumor cells were CD47+ and 87% of CD68+ macrophages were SIRPα+. Furthermore, high levels of CD8+ T-cells were observed at baseline. At C1D15 increased CD68+ macrophage infiltration, sustained CD8 T-cell tumor accumulation and higher PD-L1 CPS (48% at baseline vs 75% at C1D15) were observed. Analysis of paired tumor biopsies in other patients showed that often, increased levels of tumor CD68+ macrophages were accompanied by CD8+ T-cell infiltration.

Conclusion: This early biomarker analysis in patients with a wide range of solid tumors and treated with the first-in-class SIRPa inhibitor BI 765063 show encouraging signs of potentially mode-of-action related changes, both in peripheral blood and the TME. These early signals will be further evaluated in similar samples from the ongoing expansion cohorts in more homogeneous patient populations.

Citation Format: Stephane Champiat, Philippe A. Cassier, Nuria Kotecki, Carlos Gomez-Roca, Aurélien Marabelle, Armelle Vinceneux, Christiane Jungels, Mabrouk Elgadi, Ralph Graeser, Thomas Vandewalle, Isabelle Girault, Nina Salabert-Le Guen, Nicolas Poirier, Bérangère Vasseur, Dominique Costantini, Claudia Fromond, Jean-Pierre Delord. Biomarker analyses from the Phase I clinical trial of the first-in-class SIRPa immune checkpoint inhibitor BI765063 in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1993.

Abiraterone switches castration-resistant prostate cancer dependency from adrenal androgens towards androgen receptor variants and glucocorticoid receptor signalling

INTRODUCTION

Castration-resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signalling, which is largely driven by conversion of adrenal androgen precursors lasting after castration. Abiraterone, an inhibitor of the steroidogenic enzyme CYP17A1, has been demonstrated to reduce adrenal androgen synthesis and prolong CRPC patient survival. To study mechanisms of resistance to castration and abiraterone, we created coculture models using human prostate and adrenal tumours.

MATERIALS AND METHODS

Castration-naïve and CRPC clones of VCaP were incubated with steroid substrates or cocultured with human adrenal cells (H295R) and treated with abiraterone or the antiandrogen enzalutamide. Male mice bearing VCaP xenografts with and without concurrent H295R xenografts were castrated and treated with placebo or abiraterone. Response was assessed by tumour growth and PSA release. Plasma and tumour steroid levels were assessed by LC/MS-MS. Quantitative polymerase chain reaction determined steroidogenic enzyme, nuclear receptor and AR target gene expression.

RESULTS

In vitro, adrenal androgens induced castration-naïve and CRPC cell growth, while precursors steroids for de novo synthesis did not. In a coculture system, abiraterone blocked H295R-induced growth of VCaP cells. In vivo, H295R promoted castration-resistant VCaP growth. Abiraterone only inhibited VCaP growth or PSA production in the presence of H295R. Plasma steroid levels demonstrated CYP17A1 inhibition by abiraterone, whilst CRPC tumour tissue steroid levels showed no evidence of de novo intratumoural androgen production. Castration-resistant and abiraterone-resistant VCaP tumours had increased levels of AR, AR variants and glucocorticoid receptor (GR) resulting in equal AR target gene expression levels compared to noncastrate tumours.

CONCLUSIONS

In our model, ligand-dependent AR-regulated regrowth of CRPC was predominantly supported via adrenal androgen precursor production while there was no evidence for intratumoural androgen synthesis. Abiraterone-resistant tumours relied on AR overexpression, expression of ligand-independent AR variants and GR signalling.

Abstract C027: A Phase I, dose finding study of BI 754111, an anti-LAG-3 antibody, in combination with BI 754091, an anti-PD-1 antibody, in patients with advanced solid tumors: preliminary results from the microsatellite stable (MSS) metastatic colorectal cancer (mCRC) cohort

Background: Inhibition of the PD-1 pathway is an effective immunotherapeutic approach in a subset of patients with various solid tumors and hematologic malignancies. Blockade of the PD-1 pathway leads to overexpression of other checkpoint receptors, including LAG3, potentially providing an escape pathway for tumor cells. LAG-3 signaling contributes to immune cell exhaustion, preventing T-cell proliferation. Dual blockade of PD-1 and LAG-3 has the potential to synergistically restore T-cell functionality and therefore enhance antitumor immune responses. This Phase I trial is evaluating the combination of BI 754111, an anti-LAG-3 monoclonal antibody (mAb), and BI 754091, an anti-PD-1 mAb, in patients with advanced solid tumors. Methods: This open-label, Phase I study is being conducted in two parts. Part 1 (dose-escalation) enrolled patients with advanced solid tumors; no dose limiting toxicities were reported and BI 754111 600 mg intravenous (iv) every 3 weeks (q3w) in combination with BI 754091 (240 mg iv q3w) was selected for further assessment in part 2 (dose expansion). In part 2, patients are being enrolled in 4 cohorts: 1) anti-PD-(L)1 pretreated non-small cell lung cancer (NSCLC) that progressed after having achieved benefit on previous PD-(L)1; 2) previously treated (anti-PD-[L]1 naïve) MSS mCRC; 3) anti-PD-(L)1 pretreated TMB >10 and/or MSI-h and/or dMMR solid tumors; 4) treatment-naive NSCLC with EGFR and ALK wild type tumors. Primary endpoint for the expansion cohorts is objective response. Safety and pharmacokinetics of the combination were secondary endpoints. The mCRC cohort is fully recruited; other cohorts are open to recruitment. This abstract presents data from the MSS CRC cohort. Results. 40 patients with MSS mCRC were enrolled (27 male [67.5%]; median age 56.5 years [range 25–85]; median of 3.0 prior regimens [range 1–10]) and received BI 754111 600 mg q3w in combination with BI 754091 240 mg q3w. Treatment-related AEs (TRAEs) were reported in 18 patients (45%); most commonly infusion-related reactions (10.0%), myalgia (10.0%), hypothyroidism (7.5%), diarrhea (7.5%) and arthralgia (7.5%). Grade 3/4 TRAEs occurred in 4 patients (grade 3 colitis, grade 3 maculo-papular rash, grade 4 diabetic ketoacidosis [n=2]). Treatment-emergent immune-related AEs occurred in 9 patients; of these, 4 had grade 3/4 events (colitis and maculo-papular rash [grade 3] and diabetic ketoacidosis [grade 4; n=2]). To date, 2 (5%) patients achieved a partial response, and 12 (30%) achieved stable disease. Updates will be presented. Conclusion. BI 754111 + BI 754091 was well-tolerated and showed preliminary activity in patients with previously treated MSS mCRC. Assessment of the combination in other cohorts is ongoing.

Citation Format: Johanna Bendell, Susanna V Ulahannan, Quincy Chu, Manish Patel, Ben George, Renee Landsberg, Mabrouk Elgadi, Christine Duffy, Ralph Graeser, Wenbo Tang, Michael Merger, Miaomiao Ge, Melissa Johnson. A Phase I, dose finding study of BI 754111, an anti-LAG-3 antibody, in combination with BI 754091, an anti-PD-1 antibody, in patients with advanced solid tumors: preliminary results from the microsatellite stable (MSS) metastatic colorectal cancer (mCRC) cohort [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C027. doi:10.1158/1535-7163.TARG-19-C027

PREDECT Protocols for Complex 2D/3D Cultures

PREDECT, a European IMI consortium, has assumed the task to generate robust 2D and 3D culture platforms. Protocols established for 2D and 3D monoculture and stromal coculture models of increasing complexity (spheroid, stirred-tank bioreactor, Matrigel- and collagen-embedded cultures) have been established between six laboratories within academia, biotech, and pharma. These models were tested using three tumor cell lines (MCF7, LNCaP, and NCI-H1437), covering three pathologies (breast, prostate, and lung), but should be readily transferable to other model systems. Fluorescent protein tagged cell lines were used for all platforms, allowing for online measurement of growth curves and drug responses to treatments. All methods, from culture setup to phenotypic characterization and gene expression profiling are described in this chapter.The adaptable methodologies and detailed protocols described here should help to include these models more readily to the drug discovery pipeline.

Abstract 3610: CANCER ID and the identification of circulating tumor cells (CTCs) in NSCLC

The IMI-funded CANCER-ID consortium (https://www.cancer-id.eu/) was created in order to facilitate the use of Circulating Tumor Cells (CTCs) and other liquid biopsies (ctDNA, miRNA, exosomes) in the monitoring and treatment of cancer, via establishing and validating protocols for their detection and characterization. CTCs are tumor cells that have passively or actively migrated from the bulk of the primary or metastatic tumor(s) into the peripheral blood stream. While some of these cells may establish new metastases and mediate outgrowth of the disease, they can also serve as diagnostic, prognostic or potentially predictive biomarkers, providing non-invasive access to tumor material and information on tumor evolution. However, a major challenge remains in the identification of these very rare cells (1:106-8 WBCs). In the past years, a plethora of methods have been developed to isolate CTCs, via antibody enrichment/depletion strategies, size exclusion and/or based on density and dielectric properties. Yet despite this progress, the detection rate of CTCs in NSCLC (non-small cell lung cancer) is still very low (only ca. 20-30% of metastatic NSCLC patients have detectable CTCs). In stark contrast, SCLC (small cell lung cancer) patients have usually hundreds of detectable CTCs. A potential reason for the lack of detection of NSCLC CTCs may be the choice of surface markers used to detect the CTCs. Using NSCLC cell lines spiked into healthy donor blood, novel antibody cocktails, including positive and negative selection markers, and also markers for cells undergoing epithelial-mesenchymal transition were tested for their sensitivity and specificity to detect tumor cells in blood. Blood samples from NSCLC and SCLC patients are currently being analyzed using the Cell Search system (an EpCAM-based, FDA approved device - the current ‘gold standard' for CTC detection and enumeration), in parallel with the Parsortix device (a micro-fluidic platform that isolates CTCs according to size and deformability). This direct comparison permits an understanding of whether the combination of the Parsortix device with downstream novel antibody cocktails for CTC identification improves sensitivity, over Cell Search, while still retaining good selectivity. Results from this ongoing study will be presented. The goal of this project is to generate and clinically validate a protocol that would enable the use of CTCs as a liquid biopsy for NSCLC patients. Such an approach would be of particular benefit to these patients, since tumor biopsies cannot always being readily attained and the use of invasive intervention carries some risk of bleeding and infection. This work is supported by IMI JU & EFPIA (grand no. 115749).

Citation Format: Linda Scarrott, Hanny Musa, Harriet Wikman, Sonja Loges, Juergen Braunger, Klaus Pantel, Ralph Graeser. CANCER ID and the identification of circulating tumor cells (CTCs) in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3610.

Phase I trial of the programmed death receptor 1 (PD-1) inhibitor, BI 754091, in patients (pts) with advanced solid tumors

212

Background: Tumors may achieve immune evasion by expressing PD ligand-1 (PDL-1) to bind to PD-1 expressed on activated T cells, initiating immunosuppressive signals within the tumor. Pro-inflammatory anti-tumor activity can be restored when this interaction is blocked by therapeutic PD-1 or PDL-1 inhibition. BI 754091 is a monoclonal IgG4Pro antibody directed against PD-1 that has demonstrated anti-tumor activity in vitro and in vivo. We present the results of the first in human study evaluating BI 754091 in patients with advanced solid tumors. Methods: Patients who had exhausted standard treatment (tx) options, including prior anti-PD-1 tx, were enrolled to receive BI 754091 IV every 3 weeks (Q3W) in one of 3 sequential dose escalation cohorts (80, 240 and 400 mg), 3 patients/cohort, to evaluate the safety and tolerability and establish the maximum-tolerated dose (MTD) or recommended Phase II Dose (RPIID). Additional anti-PD-1 naïve patients with select solid tumors are being enrolled in dose expansion to be treated with the selected RPIID. The objectives of the dose expansion cohort are to evaluate the safety, tolerability, PK and preliminary efficacy of the RPIID of BI 754091, in patients with advanced solid tumors. Results: 17 patients have enrolled to date, 9 patients in the dose escalation and 8 patients in the dose expansion cohorts. Both, safety and PK profile supported a RPIID of 240 mg. The most common all grade Treatment Related Adverse Events (TRAE) were fatigue 35% (6 patients), decreased appetite 18% (3 patients) and arthralgia 12% (2 patients). There were no dose-limiting toxicities, tx-related serious adverse events, or TRAEs ≥Grade 3 reported. To date, one patient (gastric cancer) has had a partial response, 8 had stable disease, and 8 patients continue on treatment. Additional efficacy data among patients in dose-expansion will be reported. Conclusions: BI 754091 is safe and well-tolerated across all dose levels tested for advanced solid tumors, with preliminary evidence of activity. A dose of 240 mg Q3W was selected for dose expansion and RPIID based upon the available safety and PK data. Clinical trial information: NCT02952248.

A phase I study of BI 811283, an Aurora B kinase inhibitor, in patients with advanced solid tumors

PURPOSE

This phase I study investigated the maximum tolerated dose (MTD), safety, pharmacokinetics, pharmacodynamics, and antitumor activity of the Aurora B kinase inhibitor BI 811283 in patients with advanced solid tumors.

METHODS

BI 811283 was administered via 24-h infusion on Days 1 and 15 of a 4-week cycle (schedule A) or Day 1 of a 3-week cycle (schedule B) in a modified 3 + 3 dose-escalation design. Pharmacodynamic assessments included immunohistochemistry for phosphorylated histone H3 (pHH3) on skin biopsies to determine Aurora B kinase inhibition and plasma concentrations of caspase-cleaved CK-18 (apoptosis marker).

RESULTS

A total of 121 patients were treated. The MTDs of BI 811283 were 125 mg (schedule A) and 230 mg (schedule B). Dose-limiting toxicities were primarily hematological (febrile neutropenia and grade 4 neutropenia); the most common drug-related adverse effects included neutropenia, fatigue, leukopenia, nausea, alopecia, diarrhea, and decreased appetite. A trend toward a decrease in pHH3 was observed, with increasing BI 811283 doses, indicating target engagement; there was no consistent trend regarding caspase-cleaved CK-18 levels. No objective response was observed although 19 patients in each schedule achieved clinical benefit (stable disease).

CONCLUSIONS

BI 811283 demonstrated a generally manageable safety profile and disease stabilization in some patients.

TRIAL REGISTRATION

EudraCT No: 2007-000191-17, ClinicalTrials.gov Identifier: NCT00701324.

Ellipsoid Segmentation Model for Analyzing Light-Attenuated 3D Confocal Image Stacks of Fluorescent Multi-Cellular Spheroids

In oncology, two-dimensional in-vitro culture models are the standard test beds for the discovery and development of cancer treatments, but in the last decades, evidence emerged that such models have low predictive value for clinical efficacy. Therefore they are increasingly complemented by more physiologically relevant 3D models, such as spheroid micro-tumor cultures. If suitable fluorescent labels are applied, confocal 3D image stacks can characterize the structure of such volumetric cultures and, for example, cell proliferation. However, several issues hamper accurate analysis. In particular, signal attenuation within the tissue of the spheroids prevents the acquisition of a complete image for spheroids over 100 micrometers in diameter. And quantitative analysis of large 3D image data sets is challenging, creating a need for methods which can be applied to large-scale experiments and account for impeding factors. We present a robust, computationally inexpensive 2.5D method for the segmentation of spheroid cultures and for counting proliferating cells within them. The spheroids are assumed to be approximately ellipsoid in shape. They are identified from information present in the Maximum Intensity Projection (MIP) and the corresponding height view, also known as Z-buffer. It alerts the user when potential bias-introducing factors cannot be compensated for and includes a compensation for signal attenuation.

Abstract C97: Beyond intratumoural steroidogenesis: abiraterone resistance mediated by AR variants and glucocorticoid receptor signalling

Introduction

Castration resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signalling, driven by adrenal precursors and potentially de novo steroid synthesis in other organ tissues including prostate. Abiraterone, an inhibitor of the steroidogenic enzyme CYP17A1 and the AR has been demonstrated to prolong survival of CRPC patients. In this study, we created a co-culture model using human prostate and adrenal tumours to study abiraterone resistance.

Materials and Methods

Human androgen-dependent PC (VCaP) and CPRC clones were cultured with substrates for de novo androgen synthesis or with adrenal androgens, or cultured with human adrenal cells (H295R) and treated with either the CYP17A1 inhibitor abiraterone or the antiandrogen MDV3100. Male mice bearing VCaP tumours and human adrenal H295R xenografts were castrated and treated with placebo or abiraterone. Tumour response was assessed by tumour growth, PSA release, steroid quantitation by (LC/MS-MS), immunohistochemistry and mRNA expression analysis of steroidogenic enzymes and nuclear receptors.

Results

In vitro, physiological levels of adrenal androgen precursors DHEA and androstenedione induced cell growth in parental and CRPC VCaP sub clones, whereas precursor steroids pregnenolone and progesterone for de novo synthesis did not. In a co-culture model, abiraterone blocked H295R-induced growth of VCaP cells. Likewise, in vivo, H295R tumours stimulated castration-resistant VCaP growth. This stimulative effect was inhibited by abiraterone, reducing - but not fully blocking - growth and PSA production. In the absence of H295R tissue, VCaP xenografts grew slow but became castration resistant nonetheless. In contrast to the observed effects on VCaP growing in castrate animals bearing H295R tumours, abiraterone was unable to inhibit the slow VCaP growth and low PSA production in castrate mice without H295R xenografts. LC/MS-MS analysis of plasma and tumour tissue could not confirm increased de novo production of androgens. Castrate and abiraterone-resistant VCaP tumours were characterised by increased levels of AR, AR variants and glucocorticoid receptor (GR) expression, resulting in equal AR target gene expression levels.

Conclusions

Our data indicate that AR ligand dependent regrowth of CRPC is predominantly supported via adrenal steroid production. Abiraterone resistant disease of VCaP relies on AR overexpression, expression of ligand independent AR variants and GR signalling.

Citation Format: Jan Matthijs Moll, Johannes Hofland, Wilma Teubel, Corrina M.A. de Ridder, Anne E. Taylor, Ralph Graeser, Wiebke Arlt, Guido W. Jenster, Wytske M. van Weerden. Beyond intratumoural steroidogenesis: abiraterone resistance mediated by AR variants and glucocorticoid receptor signalling. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C97.

Abstract 1698: Systems pathology for characterization of cancer model systems in a multicenter IMI-PREDECT project

Despite of our increased understanding of cancer biology, the majority of anti-cancer therapies fail at late-stage clinical trials. Thus, there is an urgent need to develop and validate novel preclinical models that could predict drug efficacy in humans. For this purpose, as a part of IMI-PREDECT public-private research consortium, this study describes methodology and infrastructure for characterization and comparison of preclinical models for drug target validation applying a systems pathology approach. Formalin-fixed paraffin-embedded (FFPE) samples from 1050 different in vitro and in vivo models of breast, prostate and lung cancers, as well as 364 clinical tumors from the same origin, were collected from 26 PREDECT collaborators across the EU. We established standard operating procedures for central processing of FFPE samples, including tissue microarray (TMA) construction and immunohistochemistry (IHC) with 15 different antibodies (CK8, Ki67, p-histone H3, ER, AR, p-AKT, p-ERK, p-p38, γH2AX, cleaved caspase 3, p-MET, HIF1α, p63, vimentin, E-cadherin). We constructed 50 TMA blocks, from which sections were cut and stained as well as digitized using whole slide imaging. Images were hosted on a WebMicroscope digital pathology platform and sample metadata on a PREDECT Metadata database (MBase). We developed image analysis methods for the detection and quantification of IHC biomarkers in the 48,800 stained TMA spots. As a proof-of-concept, we compared MCF-7 on several preclinical platforms including cell cultures, xenografts and xenograft tissue slices. Our results of the integrated biomarker phenotype suggest that of the various MCF-7 in vivo and ex vivo complex cell culture models, the xenograft tissue slice model was the most similar model platform to human clinical samples. In summary, we established a systems pathology approach to analyse and compare novel preclinical cancer models with IHC and digital imaging. The intention is that this large database will be made publicly available on the web as images and summary data that could be broadly useful to the community of cancer researchers and drug developers in comparing cancer model systems. The established infrastructure and workflow integrating molecular and digital pathology in a large-scale consortium setting could be applied to quantitative characterisation of consortium data in collaborations similar to PREDECT.

Citation Format: Sami Blom, Yinhai Wang, Tauno Metsalu, Tiina Vesterinen, Teijo Pellinen, Anne Grote, Nina Linder, Jenni Säilä, Katja Välimäki, Ruusu-Maria Kovanen, Outi Monni, Panu Kovanen, Emma Davies, Kristin Stock, Marta Estrada, Georgios Sflomos, Sylvia Grünewald, Catarina Brito, Julia Schüler, Ronald de Hoogt, Cathrin Brisken, Heiko van der Kuip, Wytske van Weerden, Simon Barry, Wolgang Sommergruber, Elizabeth Anderson, Matthias Nees, Juha Klefström, Jaak Vilo, Emmy Verschuren, Ralph Graeser, John Hickman, Johan Lundin, Olli Kallioniemi. Systems pathology for characterization of cancer model systems in a multicenter IMI-PREDECT project. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1698. doi:10.1158/1538-7445.AM2015-1698

Three-dimensional models of cancer for pharmacology and cancer cell biology: capturing tumor complexity in vitro/ex vivo

Cancers are complex and heterogeneous pathological "organs" in a dynamic interplay with their host. Models of human cancer in vitro, used in cancer biology and drug discovery, are generally highly reductionist. These cancer models do not incorporate complexity or heterogeneity. This raises the question as to whether the cancer models' biochemical circuitry (not their genome) represents, with sufficient fidelity, a tumor in situ. Around 95% of new anticancer drugs eventually fail in clinical trial, despite robust indications of activity in existing in vitro pre-clinical models. Innovative models are required that better capture tumor biology. An important feature of all tissues, and tumors, is that cells grow in three dimensions. Advances in generating and characterizing simple and complex (with added stromal components) three-dimensional in vitro models (3D models) are reviewed in this article. The application of stirred bioreactors to permit both scale-up/scale-down of these cancer models and, importantly, methods to permit controlled changes in environment (pH, nutrients, and oxygen) are also described. The challenges of generating thin tumor slices, their utility, and potential advantages and disadvantages are discussed. These in vitro/ex vivo models represent a distinct move to capture the realities of tumor biology in situ, but significant characterization work still remains to be done in order to show that their biochemical circuitry accurately reflects that of a tumor.

Abstract 2023: Complex in vitro and in vivo prostate cancer models for the PREDECT consortium

The failure of many drugs in the clinic - drugs proven to be active in pre-clinical assays - has raised question marks on the predictive power of these models, often based on cell line data. The divergence of these cell lines from the original tumors, and their rapid growth as simple monocultures on 2D plastic were highlighted as potentially causing these issues. Implantation of the cell lines into mice adds complexity to these models, but the crosstalk with mouse stroma also leads to confounding results (eg, HGF, IL-6).

PREDECT, a European consortium funded by the Innovative Medicines Initiative (IMI), has the goal to build and characterise more predictive Oncology model platforms for three pathologies (lung, breast and prostate). Signalling pathways and heterogeneity of these model platforms are compared to each other as well as to primary human tissue using a central TMA-based platform.

For prostate cancer, a 3D tumor growth assay system was established recently using RFP/FLuc-labelled LNCaP, PC346C, or VCaP human prostate cancer cells grown in a matrix of Matrigel, collagen, or a mix of the two, in the presence or absence of GFP/RLuc labelled human stromal cells (WPMY, or an immortalised cancer-associated fibroblast cell line, CAF). Cell densities, ratios, and matrix concentrations/volumes were optimised for cells cultured for 3 weeks. In an approach to improve tumor-stroma crosstalk in vivo, LNCaP cells pre-grown in 3D cultures with or without human stromal cells were implanted orthotopically into SCID mice. Growth of the tumor and stromal cells was monitored by in vivo bioluminescence, and the effect of the co-implantation on the primary tumor and metastasis was analysed via ex-vivo luciferase assays and IHC.

Whereas LNCaP and PC346C cells readily formed spheroids in 3D culture, VCaPs remained as single cells. Growth of VCaPs was facilitated by pre-forming spheroids in vitro, followed by matrix embedding. Addition of stromal cells stimulated growth of not only the tumor, but also the stromal cells in some conditions, as monitored using RFP and GFP live cell imaging. 3D, as well as stromal cell-mediated treatment resistance was observed. Using the fluorescent dyes Hoechst, EdU, and NucView, the proliferative status of individual cells within spheroids could be analysed in situ. Finally, paraffin-embedding of the 3D cultures allowed for TMA analysis and comparison to other models and patient samples.Results will also be shown on the orthotopic growth of LNCaP tumors and the effect of stromal cell co-implantation.

Introducing complexity to cell culture may help to generate more realistic, and thus also more predictive models - in a first step using even standard cell lines.

Citation Format: Suzana Vidic, Norbert Esser, Ronald de Hoogt, Ingrid Verberne, Ira Kogan-Sakin, Yan Stein, Varda Rotter, Michael Barbier, Yolanda Chong, Sabine De Breucker, Karine Smans, Malin Akerfelt, Matthias Nees, Peter King, Ian Hickson, Wytske van Weerden, Ralph Graeser. Complex in vitro and in vivo prostate cancer models for the PREDECT consortium. [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 2023. doi:10.1158/1538-7445.AM2014-2023

Abstract A143: A preclinical in vivo model to assess pharmacodynamic inhibition of ACK1

Introduction: Activated Cdc42-associated kinase (ACK1, TNK2) has been reported to be over-expressed in a range of tumor types including prostate and lung cancer, and has been suggested as a potential novel anticancer target. A number of kinase inhibitors currently in clinical development show inhibition of ACK1 biochemical activity in enzyme assays, yet their ability to inhibit ACK1 in vivo is unknown. This study describes the development of a pharmacodynamic model to evaluate ACK1 target coverage in vivo.

Methods: MDA-MB-231 cells were engineered to over-express ACK1 under the control of a doxycycline-inducible promoter (MDA-MB-231-ACK1). MDA-MB-231-ACK1 cells were grown as subcutaneous xenografts in MF-1 nude mice and ACK1 expression induced by dosing doxycycline by oral gavage. Saracatinib/AZD-0530 (100mg/kg qd) or ASP-3026 (50mg/kg bid) were dosed for four consecutive days to reach steady state exposures at approximately MTD. Pharmacodynamic inhibition of ACK1 autophosphorylation was assessed using an in-house MSD assay and confirmed by Western blotting, in order to evaluate target inhibition in vivo.

Results: ASP-3026 and saracatinib showed inhibition of cellular pACK1 of MDA-MB-231-ACK1 cells in vitro, with IC50s of 0.12 μM and 1.1 μM, respectively. Using the same cell line in vivo, expression of total and phosphorylated ACK1 was induced by daily oral dosing of doxycycline. We used this model to evaluate PK-PD correlations of ASP-3026 and saracatinib using pACK1 as a marker of target inhibition. Good plasma and tumor exposure of ASP-3026 was achieved at 50mg/kg bid and no drug-drug interactions were observed in combination with doxycycline. ASP-3026 showed 50-80% inhibition of pACK1 in vivo consistent with unbound plasma concentrations in excess of in vitro IC50 and in good agreement with predictions. Good exposure of saracatinib was observed at 100 mg/kg qd with total plasma Cmax of >4μM in excess of maximally tolerated clinical exposures (0.82μM). Tumor exposures of saracatinib were up to 10 x higher than plasma exposures (Cmax >40 μM), and in considerable excess of the cellular IC50, yet no ACK1 inhibition was observed in vivo.

Conclusions: A robust PD model was established to evaluate ACK1 inhibition in vivo. Up to 80% inhibition of ACK1 in vivo was observed with ASP-3026, falling to approximately 50% at Cmin, suggesting that this agent does not completely inhibit ACK1 in vivo at steady state. In contrast, saracatinib did not significantly inhibit ACK1 at any of the exposures achieved, suggesting that it has limited in vivo activity against this target. Unbound plasma exposures predicted in vivo PD responses very well, whereas tumor exposures of these agents were not predictive of target inhibition. This model can be incorporated into a screening cascade for prioritising in vivo active ACK1 inhibitors.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A143.

Citation Format: Mark Albertella, Shilina Roman, Mike Briggs, Aaron Cranston, Ralph Graeser, George Hynd, David Jones, Peter Lockey, Akbor Malik, Stephen Price, Susanna Stimpson, Patrizia Tisselli, Janine Arts, Simon Green. A preclinical in vivo model to assess pharmacodynamic inhibition of ACK1. [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 A143.

Abstract 4770: Dual activity of abiraterone: CYP17 mediated androgen ablation and direct AR inhibition

Androgen ablation is the primary therapy for metastatic prostate cancer (PC). However, within 3 years progression towards castration resistant PC (CRPC) will occur. Despite low serum levels of testosterone (T) in patients under hormonal therapy, the androgen receptor (AR) remains active, indicating its remaining role in CPRC growth regulation. Previously, we demonstrated that conversion of adrenal androgens (AA) into T, rather than intratumoral de novo steroidogenesis, is the major source for AR activation in CRPC patients. AA are synthesized from precursor hormones, progesterone (Prog) and pregnenolone (Preg) by the enzyme CYP17A1. The CYP17A1 inhibitor Abiraterone (Abi) has shown to increase survival in CRPC patients even post-docetaxel. Blocking CYP17A1, however, may lead to the accumulation of precursor hormones such as Preg and Prog that have the potential to activate (over expressed) AR. In this preclinical study, we tested if Abi is able to block growth of CRPC cell lines and whether resulting accumulation of Preg and Prog can sustain cell growth.

Methods. CRPC clones were generated by long term culture of VCaP and DuCaP cell lines in steroid-stripped medium (DCC), with or without anti-androgens. Experiments using a subset of AR-overexpressing CRPC clones were done in DCC with the addition of Preg, Prog, DHT and/or Abi. Cell proliferation was assessed by MTT-assay. mRNA levels of AR target genes (PSA, FKB5) were assessed by RT-PCR. To study AR translocation HEP3B cells with GFP-tagged AR were used.

Results. Prog (100 nM) but not Preg (100 nM) induced cell growth in VCaP and DuCaP CRPC clones, which could not be blocked by levels of Abi (0.1 μM) known to inhibit CYP17A1 activity. Higher levels of Abi (>5 μM) inhibited cell growth. This finding and the observation that DHT-induced growth was inhibited by high levels of Abi indicate that Abi also acts as an anti-androgen. Expression of AR regulated genes was induced by 100 nM Prog, although not to the extent of DHT, and gene expression was again inhibited by higher levels of Abi (>5 μM). Finally, high levels of Prog (100 nM) induced AR translocation in eGFP-AR-HEP3B cells, suggesting that these levels of Prog can drive AR-regulated growth of VCaP and DuCaP CRPC clones. High levels of Abi (5> μM) slowed down R1881-induced AR translocation in eGFP-AR-HEP3B cells, further validating its additional property as an anti-androgen.

Conclusion. These data show that Prog, at 100 nM can activate AR driven cell growth in AR overexpressing CRPC in vitro. However, the direct anti androgen activity of abi at exposures achieved in patients may counter the precursor hormone levels induced by its CYP17 inhibitory activity. Thus Abi may interfere with prostate cancer growth at two levels CYP17 inhibition as well as direct AR inhibition.

Citation Format: Matthijs J. Moll, Robert J. van Soest, Jinpei Kumagai, Ralph Graeser, Ian Hickson, Guido W. Jenster, Wytske M. van Weerden. Dual activity of abiraterone: CYP17 mediated androgen ablation and direct AR inhibition. [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 4770. doi:10.1158/1538-7445.AM2013-4770

Efficacy of sequential treatment with sunitinib-everolimus in an orthotopic mouse model of renal cell carcinoma

BACKGROUND/AIM

Sequential treatment with targeted agents is standard of care for patients with metastatic renal cell carcinoma (mRCC). However, clinical data directly comparing treatment outcomes with a mammalian target of rapamycin inhibitor or a vascular endothelial growth factor-targeted agent in the second-line setting are lacking. We evaluated sequential treatment in a syngeneic, orthotopic mouse model of mRCC.

MATERIALS AND METHODS

BALB/c mice were orthotopically implanted with murine RCC (RENCA) cells expressing luciferase and randomized to vehicle, sunitinib, sunitinib followed by sorafenib, or sunitinib followed by everolimus. Tumor growth and metastases were assessed by in vivo (whole body) and ex vivo (primary tumor, lung, liver) luciferase activity and necropsies, performed on day 20 or 46 for vehicle and treatment groups, respectively.

RESULTS

Sunitinib followed by everolimus was associated with reduced luciferase activity and primary tumor weight and volume compared with sunitinib, and sunitinib followed by sorafenib.

CONCLUSION

Sequential therapy with sunitinib followed by everolimus demonstrated significant antitumor and anti-metastatic effects.

Abstract A141: Analysis of cellular kinase activity of resistance-related MET mutants using transmembrane-domain (TMD) activated kinase variants

Kinases are important targets in oncology. However, the frequent emergence of resistance (gatekeeper) mutants in target kinases seriously limits the patient's response time to a given drug. Secondary drugs need to be developed that specifically target mutant enzymes. The discovery of such kinase inhibitors requires relevant assay systems. In order to efficiently analyze whether novel inhibitors target gatekeeper mutants of a given kinase in a cellular context we set out to establish a suitable cellular test system for the receptor tyrosine kinase MET. Our aim was to minimize variations such as cellular background and ligand dependent activation while putting the focus on the mutation of interest. In an approach to uncouple kinase activity from ligand activation, we screened a set of artificial transmembrane domains (TMD) to identify a TMD that induces constitutive MET autophosphorylation in transient transfections. Subsequently, Rat1 cells were transduced to express the tag-labelled intracellular wild-type (wt) MET domain harbouring the activating TMD while lacking the extracellular domain. Characterization of TMD-MET-wt in Rat1 cells showed constitutive MET expression and phosphorylation. ELISA studies to analyze the inhibition of MET phosphorylation by cognate MET inhibitors revealed comparable IC50 values to those obtained with wild-type MET naturally over expressed in MKN45 gastric carcinoma cells. Moreover, expression of TMD-MET-wt in Rat1 cells led to cell transformation as assessed by growth in soft agar as well as in vivo as a subcutaneous xenograft. Interestingly, the same artificial TMD induced constitutive activity of various gatekeeper mutants of MET when transduced into Rat1 cells. This observation allowed for the comparative analysis of various small molecule MET inhibitors on multiple MET mutants in an identical cellular background and without the need of ligand-induced kinase activation. Using a straight forward ELISA-based approach, we generated profiles of various MET inhibitors on cellular MET mutant phosphorylation and compared these with inhibition profiles obtained in biochemical MET activity assays.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A141.

Generation of a conditionally transformed murine embryonic fibroblast cell line using doxycycline-dependent IGF-1R overexpression

The insulin-like growth factor I receptor (IGF1-R) system has long been implicated in cancer and is a promising target for tumor therapy. Besides in vitro screening assays, the discovery of specific inhibitors against IGF-1R requires relevant cellular models, ideally applicable to both in vitro and in vivo studies. With this aim in mind, the authors generated an inducible cell line using the tetracycline-responsive gene expression system to mimic the effects of therapeutic inhibition of the IGF-1R both in vitro and on established tumors in vivo. Inducible overexpression of IGF-1R in murine embryonic fibroblasts was achieved and resulted in the transformation of the cells as verified by their ability to grow in soft agar and in nude mice. Continuous repression of exogenous IGF-1R expression completely prevented outgrowth of the tumors. Furthermore, induced repression of IGF-1R expression in established tumors resulted in regression of the tumors. Interestingly, however, IGF-1R-independent relapse of tumor growth was observed upon prolonged IGF-1R repression. The IGF-1R cell line generated using this approach was successfully employed to test reference small-molecule inhibitors in vitro and an IGF-1R-specific inhibitory antibody, EM164, in vivo. Besides efficacy as a read-out, phospho-AKT could be identified as a pharmacodynamic biomarker, establishing this cell line as a valuable tool for the preclinical development of IGF-1R inhibitors.

Abstract 1726: Overcoming multi-drug resistance with Paclitaxel-loaded polymer nanoparticles

Multi-drug resistance against chemotherapeutic agents is a major problem in the treatment of cancer. It is primarily mediated by over-expression of P-glycoprotein (P-gp) encoded by the MDR-1 gene by the tumor cells. Most of the promising anticancer drugs such as doxorubicin, docetaxel, paclitaxel, and mitoxantrone are P-gp substrates. Thus, various ways for overcoming the multi-drug resistance, e.g. combination of an anticancer drug and a P-gp inhibitor or the formulation of nanoparticles in conjunction with anticancer drugs as well as the P-gp inhibitor, have been studied. Anticancer drug-loaded nanoparticles, such as paclitaxel-loaded polymer nanoparticles, are excellent candidates to overcome multi-drug resistance due to their enhanced therapeutic efficacy induced by increased cellular accumulation and sustained intracellular drug delivery.

In this work, we developed an ampholytic copolymer that can encapsulate paclitaxel, and the resulting nanoparticles were found to have good water-solubility. In addition, in contrast to native paclitaxel, the paclitaxel-loaded nanoparticles were able to reverse multi-drug resistance in MCF7/ADR and MT-3/ADR cell lines, resulting in drug sensitivities comparable to the parental MCF7 and MT3 cell lines. P-gp expression was confirmed in both ADR cell lines by Western blotting, and its functionality was verified using a rhodamine accumulation and efflux assay. The nanoparticles were taken up by endocytosis in both cell lines and their enhanced therapeutic efficacy is probably due to the different mode of entry into the cell that may avoid the P-gp efflux pump. As a consequence higher concentrations of paclitaxel reach the nucleus and induce cell killing.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1726. doi:10.1158/1538-7445.AM2011-1726

Abstract 5322: Bioluminescence, fluorescence, and biomarker mediated monitoring of an orthotopic model of colon cancer treated with VX-680

With 10% of all newly diagnosed cases per year, colon cancer ranks within the top 5 cancer types within the USA, and, with a similar figure of people succumbing to the disease, is a major cause of tumor-related deaths. Primary tumors may often be removed via surgery, but metastatic spread poses considerable difficulties and chemotherapeutic treatments are rarely curative. Novel drugs, and predictive pre-clinical model systems to better mimic human disease are therefore urgently needed.

Although subcutaneously implanted tumor cells have been used for pre-clinical drug testing for decades now, the predictive value of these models has recently become the subject of controversy. Orthotopically implanted cells reflect the human disease much better in that organo-typical tumor stromal interactions are enabled, and tumor cells spread to other sites with distribution patterns reflecting the human disease.

Orthotopical implantation requires sensitive imaging modalities, similar to the patient situation. Bioluminescence imaging (BLI) is a well established modality for pre-clinical models, but is not translatable to the clinic. Recently, fluorescence molecular tomography (FTM) imaging has been shown to offer good sensitivity and tissue penetration, and sensitive probes – that may be used in the clinic – have been developed.

A pre-clinical experiment was performed to compare the growth behaviour of orthotopically implanted, luciferase marked HCT116 wild-type and p53 KO human colon cancer cells and test their sensitivity towards the aurora-inhibitor VX-680. Growth of the tumors, and treatment effects were followed in vivo using BLI, and a final imaging analysis with integrisense, using FMT. The in vivo imaging data were validated with necropsy data, including sensitive luciferase assays to detect metastases in organs.

In vivo BLI suggested that p53 KO tumors grew much more aggressive, giving rise to larger, more fragmented signals than their wild-type counterparts. Imaging using integrisense confirmed the presence of much larger tumor masses in the p53 KO than in the wild-type group. VX-680 slightly reduced the BLI signals from both groups. Necropsy results confirmed the tumor size differences between wild-type and p53 KO tumors, also the VX-680 effect against wild-type tumors (−50%, SD 70%). However, the drug appeared ineffective against p53 KO tumors (+120%, SD 70%). Luciferase assays from potential target organs detected an increased metastasation in p53 KO tumor bearing animals compared to those with wild-type tumors. Interestingly, metastasation of the p53 KO tumors to the spleen was sensitive to VX-680 treatment (−90%, SD 20%). The effect of the drug could also be demonstrated in skin biopsies taken from the mice as a surrogate tissue.

This study represents a ‘high content’, partially translatable mouse model applicable also for the testing of other targeted therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5322. doi:10.1158/1538-7445.AM2011-5322

Abstract 2569: Combination of the albumin-binding prodrug of doxorubicin (INNO-206) and doxorubicin produces complete remissions in an ovarian A2780 xenograft model

INNO-206, the (6-maleimidocaproyl)hydrazone of doxorubicin (DOXO-EMCH) is an albumin-binding prodrug of doxorubicin with acid-sensitive properties that has demonstrated superior antitumor efficacy in eight murine tumor models compared to doxorubicin. After intravenous administration, INNO-206 rapidly binds to the cysteine-34 position of circulating albumin and accumulates in solid tumors due to passive targeting. It has shown objective responses in a phase I study, and phase II studies are planned for 2011 at the recommended dose of 260 mg/m2 i.e. an approximate 4-fold increase over the standard dose for doxorubicin.

Interestingly, in contrast to free doxorubicin, which primarily locates in the nucleus, INNO-206, mainly accumulates in the cytoplasm. Furthermore, the binding of INNO-206 to albumin and the resulting EPR-mediated accumulation and distribution in the tumor will differ from the distribution of free doxorubicin which will be mediated by diffusion. There might thus be a rationale to combine the two drug formulations for obtaining an optimal antitumor effect. Indeed, in cell culture experiments using A2780 cells, a moderate synergy was found at a 5:1 ratio of free Doxo : INNO-206.

In a next step, we therefore tested whether a combination of suboptimal doses of INNO-206 with doxorubicin improved the therapeutic efficacy of INNO-206 or doxorubicin at their respective maximum tolerated doses (MTDs) in the mouse model. We treated nude mice with subcutaneously growing ovarian A2780 xenografts on a weekly schedule with 2 × 8 mg/kg doxorubicin (MTD), 3 × 24 mg/kg INNO-206 (doxorubicin equivalents) (MTD) and a combination of 3 × 12 mg/kg INNO-206 (doxorubicin equivalents) and 3 × 4 mg/kg doxorubicin. In the combination protocol, INNO-206 was administered 6 h prior to doxorubicin treatment. Doxorubicin showed a very moderate effect and a body weight loss of -21 %, whereas INNO-206 and also the combination produced complete remissions. The combination, however, was much better tolerated causing a body weight loss of -12 % compared to -31 % for INNO-206. The surprising result of this experiment is that the doses used in the combination regimen were able to induce complete remission and the best tolerability considering that when dosed individually at these doses, neither doxorubicin or INNO-206 would have produced such an impressive antitumor response. This work is an impetus for investigating further combinations of albumin-binding prodrugs with clinically established anticancer agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2569. doi:10.1158/1538-7445.AM2011-2569

Abstract 3502: Activity of combinations of anticancer agents in pancreatic carcinoma cell lines

Long term and successful treatment of pancreatic cancer remains a considerable challenge, and there is an urgent need to develop new therapeutic strategies that improve the response rate and overall survival of this disease that responds poorly to monotherapy with anticancer agents such as gemcitabine or 5-fluorouracil. Instead of combining drugs at their respective maximum tolerated doses, a number of recent studies have shown that the “more is better” paradigm may not be the optimal strategy for maximizing the clinical outcome for combination therapy and rather synergistic effects can be achieved if the drugs are dosed at a defined ratio. Such an approach is currently being investigated clinically with liposomal formulations which contain irinotecan and floxuridine at a 1:1 ratio or cytarabine and daunorubicin at a 5:1 ratio. We therefore tested a number of combinations of chemotherapeutic agents using defined ratios ranging from 10:1 to 1:10 for their efficacy against a luciferase transduced pancreatic cell line, MIAPaCa2 ELN, using a 72 h Luciferase proliferation assay. Using this assay, a combination of camptothecin with gemcitabine showed synergy at a ratio of 1:5 over a cell survival range of 10-80% with combination indexes (CIs) between 0.36 and 0.71.

In addition, a synergy was found at a 1:10 ratio for methotrexate with doxorubicin with CI values from 0.36 to 0.32 over a 20-90% cell survival range. A third synergistic combination was observed between cytarabine and gemcitabine at a 1:5 ratio with CIs from 0.16 to 0.21 over a 20-90% cell survival range. None of the other combinations tested, including campthotecin with methotrexate, camptotecin with doxorubicin, or cytarabine with daunorubicin showed synergistic effects at ratios from 5:1 to 1:5.

These in vitro results show that the ratio of the respective drug combination is a decisive factor for inducing additive, synergistic or even antagonistic effects.

We are currently testing the most promising combinations in additional pancreatic carcinoma cell lines in order to elucidate whether the synergistic effects of these combinations and specific ratios apply to pancreatic cancer cells in general.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3502. doi:10.1158/1538-7445.AM2011-3502

A direct ELISA assay for quantitative determination of the inhibitory potency of small molecules inhibitors for JNK3

The c-jun N-terminal kinase 3 (JNK3) is a promising drug target for the treatment of neurological disorders. Here we report a direct ELISA including the optimization of a nonradioactive immunosorbent JNK3 activity assay to determine inhibitory potency of small-molecule inhibitors. Based on our previous JNK3 assay and our recently optimized p38α mitogen activated protein kinase (MAPK) protocol for monitoring the phosphorylation of activating-transcription factor 2 (ATF-2), we present a rapid and straightforward alternative to conventional radioactive and indirect ELISA kinase assays. To validate the assay with the optimized assay conditions we used reference compounds and achieved well comparable IC(50) results to published data. The use of a linked monoclonal antibody increased the specificity and the sensitivity of the assay, reducing the required antibody concentration by approximately 100-fold. The novel protocol is an accurate, easy-to-handle and robust screening assay for JNK3 and the assay performance was reduced from 7.5 to 3h.

Non-invasive in vivo imaging of tumor-associated CD133/prominin

Background

Cancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance.

Methodology/Principal Findings

Here, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities. The CD133-specific monoclonal antibody AC133.1 was used for quantitative fluorescence-based optical imaging of mouse xenograft models based on isogenic pairs of CD133 positive and negative cell lines. A first set consisted of wild-type U251 glioblastoma cells, which do not express CD133, and lentivirally transduced CD133-overexpressing U251 cells. A second set made use of HCT116 colon carcinoma cells, which uniformly express CD133 at levels comparable to primary glioblastoma stem cells, and a CD133-negative HCT116 derivative. Not surprisingly, visualization and quantification of CD133 in overexpressing U251 xenografts was successful; more importantly, however, significant differences were also found in matched HCT116 xenograft pairs, despite the lower CD133 expression levels. The binding of i.v.-injected AC133.1 antibodies to CD133 positive, but not negative, tumor cells isolated from xenografts was confirmed by flow cytometry.

Conclusions/Significance

Taken together, our results show that non-invasive antibody-based in vivo imaging of tumor-associated CD133 is feasible and that CD133 antibody-based tumor targeting is efficient. This should facilitate developing clinically applicable cancer stem cell imaging methods and CD133 antibody-based therapeutics.

In vivo evaluation of a novel albumin-binding prodrug of doxorubicin in an orthotopic mouse model of prostate cancer (LNCaP)

PSA, which is overexpressed in prostate carcinoma, represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. In this study, we report on the in vivo antitumor efficacy of an efficacious albumin-binding prodrug of doxorubicin (PSA9) that incorporates p-aminobenzyloxycarbonyl (PABC) as a self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, which serves as a substrate for PSA. The prodrug is cleaved very efficiently by PSA releasing H-Ser-Leu-PABC-doxorubicin and subsequently doxorubicin in PSA-positive cell lysates and prostate tumor homogenates as the final cleavage product. PSA9 at 3 × 6 mg kg(-1) doxorubicin equivalents (intravenous) was compared with conventional doxorubicin at equitoxic doses (at 3 × 3 mg kg(-1); intravenous) in an orthotopic mouse model of prostate cancer using LNCaP lentiviral luciferase-neomycin cells transduced with luciferase. Whereas doxorubicin did not show any efficacy against the primary tumor or metastases, the prodrug reduced the primary tumor by 30-50% and circulating PSA levels, and in addition, showed a pronounced reduction in lung and bone metastases by ∼77% and ∼96%, respectively, and a positive trend regarding the activity against liver and lymph-node metastases compared with control and doxorubicin-treated animals. The incorporation of PABC as a self-immolative spacer together with a PSA substrate demonstrates superior antitumor effects over doxorubicin attributed to an efficient cleavage by PSA releasing doxorubicin as the final active agent in prostate tumor homogenates. Using this approach for developing effective prodrugs against prostate cancer, is worthy of further preclinical optimization.

Optimization of an albumin-binding prodrug of Doxorubicin that is cleaved by prostate-specific antigen

We have developed a novel albumin-binding prodrug of doxorubicin that incorporates p-aminobenzyloxycarbonyl (PABC) as a 1,6 self-immolative spacer in addition to the heptapeptide, Arg-Ser-Ser-Tyr-Tyr-Ser-Leu, as a substrate for the prostate-specific antigen (PSA) that is overexpressed in prostate carcinoma and represents a molecular target for selectively releasing an anticancer agent from a prodrug formulation. The prodrug exhibited good water solubility and was bound rapidly to the cysteine-34 position of human serum albumin. Incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P1' scissile bond, releasing H-Ser-Leu-PABC-DOXO, which was further degraded to release doxorubicin as a final cleavage product within a few hours in prostate tumor tissue homogenates as well as in PSA-positive LNCaP LN cell lysates. Moreover, our prodrug exhibited antiproliferative activity in a low micromolar range against a PSA-expressing prostate cancer cell line (LNCaP).

Abstract 4665: A combined IHC/Western method to measure phosphorylated histone H3 in skin biopsies as potential biomarker for anticancer drug action

In recent years there has been a rapid increase in targeted tumor therapy approaches. Hand in hand with these novel approaches, the need has arisen to monitor specific target inhibition by the drug. In contrast to classic chemotherapy, which non-specifically targets proliferating cells, these novel approaches attempt to specifically interfere with some process thought to be crucial for the tumor cell survival. Nevertheless, despite extensive validation, an immediate effect of target interference on tumor growth may not necessarily be expected. Thus, in order to demonstrate activity of anti-cancer drugs, a marker known to be modified upon inhibition of the target may serve as a surrogate to tumor inhibition. Ideally, tumor biopsies would be analysed for monitoring of drug-induced effects. However, taking in consideration the difficulties to perform sequential tumor biopsies, the use of surrogate tissues like blood or skin is being explored instead. Blood is relatively easily accessible, but unlike skin tissue, blood may not reflect the fact that drugs have to penetrate multiple layers of tissue in order to reach their target in the tumor. Also, to monitor the effects of anti-mitotic drugs, the investigated specimen must exhibit proliferating features, which is given only in a very poor manner blood samples, as peripheral blood cells have typically exited the cell cycle. However cells in the dermis still proliferate, albeit to a small percentage.

Therefore, considering these issues, we set out to develop a method to analyse drug effects in skin biopsies. Traditionally, most analyses of skin biopsies have relied on immunohistochemistry (IHC) studies. However, the quantification of such results is time-consuming and error-prone. Western Blot analyses are easier to quantify, but require a considerable amount of protein lysate of sufficient concentration. We developed a protocol that reproducibly allows the detection and quantification of phosphorylated histone H3 in Western Blots from a single half of a skin biopsy. For normalization, the total amount of histone H3 present in the lysate is determined. The other half of the skin biopsy may be used for IHC analysis of phosphorylated histone H3, allowing the comparison to other studies relying solely on IHC.

We will present data on the measurement of phosphorylated histone H3 via Western Blots and IHC from skin biopsies of healthy donors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4665.

Abstract LB-37: In vitro and in vivo studies of novel acid-sensitive prodrugs derived from dendritic polyglycerol

Research in the development of tumor-specific nanocarriers is currently one of the major sources of innovation for improved anticancer chemotherapy. Due to their low degree of molecular weight dispersity, their flexible design and their biocompatible nature, dendritic polyglycerols (PGs) have a broad range of potential applications in medicine and pharmacology. Recently, we demonstrated that drugs could be bound to the thiolated hyperbranched polymers incorporating enzymatically cleavable spacers that were efficiently released by the target enzyme cathepsin B. These initially developed dug carriers with PGs, however, did not have an optimal molecular weight for EPR-mediated tumor targeting and remaining amino groups on the surface of the dendritic scaffold showed acute toxicity properties.

As a consequence, we set out to improve the conjugation method and fine-tune the architecture of the polyglycerol drug conjugates for optimal tumor targeting. A logically consistent option was to mask remaining and potentially toxic amino groups with the polymer polyethylene glycol which would have the additional advantage of increasing the molecular weight of drug polyglycerol conjugate to > 40 kDa which is a pre-requisite for passive targeting. Thus, we developed a macromolecular prodrug derived from hyperbranched amino-bearing polyglycerol that in a first step was partially thiolated with iminothiolane followed by a Michael addition to the maleimide group of the acid-sensitive 6-maleimidocaproyl(hydrazone) derivative of doxorubicin, and in a second step the maleimide group of 2 and 5 kDa PEG chains were reacted with the remaining sulfhydryl groups. Thus, the drug was covalently attached to the hyperbranched polyglycerol core and surrounded by a “shell” of long, solubilizing PEG chains which radiate from the core. By varying the amount of iminothiolane, of doxorubicin prodrug and of PEG-maleimide, drug PG conjugates with different drug loading (1 to 10) were isolated. Analysis by dynamic light scattering measurements (DLS) and z-potential showed that average diameters were in the range of 12 to 16 nm and the conjugates showed a slightly negative surface charge. The in vitro release studies showed that the release of doxorubicin was minimal at pH 7.4 after 22 h (less than 10%), while at acidic pH half-lives were below 4 h. Although free doxorubicin was more active than the PG doxorubicin conjugates against A2780 ovarian carcinoma cells, in the respective xenograft model the pegylated PG doxorubicin conjugates with 5 to 10 bound molecules of doxorubicin showed a distinct increase in tolerability and antitumor efficacy in comparison to the parent drug producing excellent antitumor effects with complete and transient tumor remissions (at 24 mg/kg doxorubicin equivalents). Doxorubicin treated animals only showed a moderate antitumor effect at its optimal dose of 2 × 8 mg/kg.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-37.

Abstract LB-39: Development of a novel water-soluble prodrug of paclitaxel that is cleaved by prostate-specific antigen (PSA): In vitro and in vivo evaluation

In developed countries, prostate cancer is the second most frequently diagnosed cancer, and the third most common cause of death from cancer in men. Unfortunately, while accumulating clinical data have suggested that the taxanes may prolong the survival in a subset of men with prostate carcinoma, the dose and duration of administration of these drugs are limited by their significant systemic toxicities due to a lack of tumor selectivity. Besides prostate cancer, paclitaxel (Taxol®) is currently showing a promising antitumor activity against a variety of human tumors. In an attempt to improve both the water solubility and tumor targeting properties of paclitaxel, we set out to develop a water soluble paclitaxel prodrug that is activated specifically by prostate-specific antigen (PSA) which is solely expressed in prostate tissue and prostate carcinoma with high levels up to mg/g present in human prostate carcinoma. Using albumin as an efficient carrier for drug delivery, we describe a novel albumin-binding prodrug of paclitaxel, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-Paclitaxel [EMC: -maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl] that was synthesized by reacting EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-OH with H-Leu-PABC-Paclitaxel. This prodrug exhibited excellent water-solubility and was bound rapidly to the cysteine-34 position of endogenous and exogenous albumin. Moreover, incubation studies with PSA demonstrated that the albumin-bound form of the prodrug was cleaved rapidly at the P1-P‘1 scissile bond releasing the paclitaxel-dipeptide H-Ser-Leu-PABC-Paclitaxel. Above all, due to the incorporation of a PABC self-eliminating linker, this dipeptide was rapidly degraded to liberate paclitaxel as a final cleavage product within a few hours in prostate tumor tissue homogenates. Of note was that the albumin-bound form of the prodrug was approximately 4-fold more active in killing PSA-positive LNCaP cells than paclitaxel. In addition, orientating toxicity studies in mice showed that the maximum tolerated dose of the novel paclitaxel prodrug was twice that of conventional paclitaxel. Therefore, the in vivo efficacy of the prodrug (24 mg/kg paclitaxel equivalents) in comparison to free paclitaxel (12 mg/kg) is currently being evaluated in a mouse model of human prostate cancer using luciferase transduced LNCaP LN cells orthotopically implanted in SCID mice.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-39.

Abstract LB-38: Evaluation of a PSA cleavable doxorubicin prodrug in the in vitro and in vivo LNCaP LN model

The goal of this work was to investigate the biological activity of a doxorubicin prodrug that is efficiently cleaved by prostate specific antigen (PSA) rapidly liberating doxorubicin as the final cleavage product. For this purpose we have developed an albumin-binding prodrug of doxorubicin, EMC-Arg-Ser-Ser-Tyr-Tyr-Ser-Leu-PABC-DOXO [EMC: ε-maleimidocaproyl; PABC: p-aminobenzyloxycarbonyl; DOXO: doxorubicin]. The incorporation of the PABC self-eliminating linker between the peptide sequence and doxorubicin enhanced the enzymatic cleavage rate and improved the cleavage profile. PSA cleavage produced the metabolite H-Ser-Leu-PABC-DOXO which was further degraded to release doxorubicin as a final cleavage product within a few hours in prostate tumor tissue homogenates as well as in PSA-positive LNCaP LN cell lysates. In the cell culture experiments, our prodrug exhibited antiproliferative activity in the low micromolar range with an IC50 value of ∼1 μM against a PSA-expressing prostate cancer cell line with a stably integrated Luciferase-Neomycin (LN) resistance fusion gene cassette (LNCaP LN). Moreover, H-Ser-Leu-PABC-DOXO showed comparable in vitro activity to doxorubicin (∼0.2 μM). Orientating toxicity studies in mice showed that the maximum tolerated dose of our novel prodrug was twice that of conventional doxorubicin. Consequently, the in vivo efficacy of the prodrug (6 mg/kg doxorubicin equivalents) is currently being compared to free doxorubicin (3 mg/kg) in a mouse model of human prostate cancer using luciferase transduced LNCaP cells orthotopically implanted in SCID mice.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-38.

Abstract C187: Antitumoral efficacy of the novel thrombin inhibitor Revasc©/Desirudin in an orthotopic metastatic AsPC-1 pancreas tumor model

Background: Thrombo-embolism is one of the most common secondary diseases in cancer patients and is the second leading cause of death of these patients. In pancreatic cancer patients, thrombosis occurs more frequently than in other cancer patients. Thus anticoagulants are widely used in cancer therapies mainly to prevent the development of thrombo-embolisms. However there is increasing evidence that anticoagulants have also antitumoral and anti-angiogenic effects. The aim of this study was to evaluate the anti-tumoral, anti-metastatic and anti-angiogenic efficacy of the novel anticoagulant Revasc© a recombinant hirudin and direct thrombin inhibitor, in an orthotopic mouse model of pancreatic cancer.

Material and Methods: To evaluate the anti-tumoral, anti-metastatic and anti-angogenic efficacy of Revasc©, luciferase labeled pancreatic AsPC-1-tumor cells were orthotopically implanted into the pancreas of NMRI nude mice. After onset of tumor growth, mice were randomized into six groups. Group 1 received vehicle control (0.9% NaCl) twice daily, Group 2 received Gemcitabine (240 mg/kg) once weekly; Group 3 received Revasc at a concentration of 1 mg/kg twice daily, Group 4 received Revasc© at a concentration of 3 mg/kg twice daily, Group 5 received Revasc© at a concentration of 10 mg/kg daily and Group 6 received a combination therapy of twice daily 10 mg/kg Revasc© plus a weekly dose of 240 mg/kg Gemcitabine. At the end of the study, tumor weight and volume were determined and luciferase activity was monitored in the primary tumor and selected organs (spleen, liver, stomach, intestine, lung and inguinal lymph nodes). In addition, microvessel densities and vessel maturation was determined by immunohistochemisty.

Results: In general, Revasc© was very well tolerated. The primary tumor weight was significantly reduced in the groups receiving Revasc© at a concentration of 3 mg/kg and 10 mg/kg as well as in the control group treated with Gemcitabine. The combination of Gemcitabine and Revasc©, however, did not show any additive effect. No significant reduction of metastasis could be observed in the Revasc© Groups, whereas Gemcitabine efficiently inhibited metastasis into the lung. However, Revasc© showed a significant anti-angiogenic potential at the lowest concentration of 1mg/kg, corroborating findings of other groups showing that thrombin inhibition acts anti-angiogenic.

Conclusion: Taken together the study showed that Revasc© has an anti-tumoral and a mild anti-angiogenic effect. The data suggest that Revasc© has a potential to be used for the treatment of patients with pancreatic cancers; primarily to prevent thromboembolism but secondarly also to inhibit tumor growth. It remains to be shown if Revasc will lead to a solid anti-tumoral effect in patients and if the relatively short mean elimination half life of Revasc© (2–3 h) will allow to identify a convenient dosing scheme. Alternatively a pegylated hirudin derivative (PEG-hirudin) which has a longer half life and which has proven to have a very efficient antitumoral activity could be of high therapeutic interest.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C187.

Abstract C183: Antitumor efficacy of PEG-Hirudin (LU 87981), administered three times weekly, in an orthotopic AsPC-1 pancreas carcinoma model

Background: Since anticoagulants could be shown as promising novel therapeutics in oncology, direct thrombin inhibitors like recombinant Hirudin (Revasc©/desirudin) were assessed in a preclinical orthotopic AsPC-1 mouse model in vivo. The challenges of desirudin for the treatment of cancer are its complex pharmacodynamics and a short half life (mean elimination half-life of 2–3h), requiring at least twice daily subcutaneous administration of the drug. PEG-Hirudin, the conjugate of recombinant Hirudin with two molecules of polyethylene glycol (PEG)-5000 represents a potential alternative to Revasc© with a longer half-life and more stable plasma levels. In order to test this compound, the pancreatic cancer cell line, AsPC-1 was chosen, for which preliminary results with Revasc© were available. AsPC-1 cells implanted orthotopically into the mouse pancreas reflect hallmarks of the human disease such as early invasion of the surrounding pancreatic tissue and the formation of metastases in the spleen and liver as well as the peritoneum.

Material and Methods: Luciferase expressing AsPC-1 cells were orthotopically implanted into mouse pancrei. The growth of the tumors was followed via bioluminescence measurements (whole body imaging). 13 days after surgery, 12 animals each were randomized into 5 treatment groups according to their bioluminescence signal. Group 1 served as vehicle control receiving 100µl saline solution three times weekly s.c. from day 15 to day 38. The application scheme was comparable to treatment groups receiving 1mg/kg (group 3), 3 mg/kg (group 4) and 0.3mg/kg (group 5) PEG-Hirudin three times weekly s.c. starting at day 15. The animals of group 2 received Gemcitabin at 240mg/kg administered i.v. once weekly starting at day 15. At the end of the study tumor weight and volume were determined and luciferase activity was monitored in the primary tumor and selected organs (spleen, liver, stomach, intestine, lung and inguinal lymph nodes).

Results: PEG-Hirudin was well tolerated, no bleeding at the injection site or other side effects could be observed. Only one animal of group 4 was found dead during the study, all other animals reached the end of the study. Gemcitabin, did not affect tumor growth according to in vivo bioluminescence imaging, whereas PEG-Hirudin at 1 and 3 mg reduced the increase of the bioluminescence signal during the treatment period significantly. Once the animals were sacrificed and tumor sizes measured, treatment with PEG-Hirudin at 1 and 3 mg/kg showed significant reduction of the average primary tumor size (Group 3: *p= 0.0129, Group 4:**p=0.0015). The positive control, Gemcitabin showed as well a significant antitumor efficacy (***p=0.0002). The differing results of in vivo imaging and primary tumor sizes are reflecting the different efficacy of the test items on primary tumor and peritoneal metastases.

Conclusion: The results presented here suggest a promising anti-tumoral efficacy of the PEG-Hirudin compound. Due to its extended half-life and the resulting relaxation of the application scheme, PEG-Hirudin is a promising alternative to Revasc© (desirudin) in oncology.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C183.

Abstract A132: Development of efficient macromolecular prodrugs derived from dendritic polyglycerol

Introduction: Utilizing the Enhanced Permeation Retention Effect (EPR) for passive targeting is one of the novel approaches for tumor-selective drug delivery. Polymer-based nanocarriers, especially those of dendritic architecture, have gained increasing interest for encapsulating or coupling diagnostic or therapeutic agents. Chemical conjugation to a dendritic scaffold, thereby exploiting the high multivalency, allows for the covalent attachment of different kinds of bioactive molecules (imaging agents, drugs, targeting moieties, or biocompatible molecules) in a controlled ratio. (1) Hyperbranched polyglycerol is a potent alternative to perfect dendrimers for biomedical applications because of its ease of preparation, non-immunogenicity, tuneable molecular weight, high water-solubility and structural flexibility through end group modification. (2)

Here we present a comprehensive study for the development of macromolecular doxorubicin-polyglycerol prodrugs. The effects of the conjugation approach, the polymeric architecture, the cleavable linker and the drug loading over the final properties are analyzed.

Results and Discussion: Hyperbranched polyglycerols partially modified with azido, propargyl, amine or polyethylene glycol were prepared with overall yields higher than 60%. Different reactions, e.g click coupling and Michael addition, were evaluated for the conjugation of several doxorubicin derivates to the polyglycerol scaffolds. UV-Visible, 1H-NMR, GPC and HPLC were used to demonstrate the obtention of macromolecular prodrugs with several molecular weights, architectures and different cleavable linkers. The conjugates showed rapid and selective release of doxorubicin after being triggered by a change in pH or in presence of enzymes, accordingly to the nature of conjugated prodrugs.

The antiproliferative activity assessed against two human tumor cell lines AsPC1 LN (pancreatic carcinoma) and MDA-MB-231 LN (mamma carcinoma) showed less (2- to 10-fold) cytotoxicity than the corresponding free drugs. Cellular uptake was confirmed by fluorescence microscopy. In all cases, the conjugates showed to be active in the low micromolar range that is relevant for further preclinical studies of anticancer prodrugs.

The in vivo efficacy was tested in ovarian carcinoma A2780 xenograft model. With respect to antitumor efficacy, some of the conjugates manifested excellent antitumor effects with complete tumor remissions up to day 30. No significant changes in body weight were observed even after administration of 3-fold the maximal tolerated dose for free doxorubicin.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A132.

Anti-metastatic effects of liposomal gemcitabine in a human orthotopic LNCaP prostate cancer xenograft model

Fatal outcomes of prostate carcinoma (PCa) mostly result from metastatic spread rather than from primary tumor burden. Here, we monitored growth and metastatic spread of an orthotopic luciferase/GFP-expressing LNCaP PCa xenograft model in SCID mice by in vivo imaging and in vitro luciferase assay of tissues homogenates. Although the metastatic spread generally shows a significant correlation to primary tumor volumes, the susceptibility of various tissues to metastatic invasion was different in the number of affected animals as well as in absolute metastatic burden in the individual tissues. Using this xenograft model we showed that treatment with liposomal gemcitabine (GemLip) inhibited growth of the primary tumors (83.9 +/- 6.4%; P = 0.009) as well as metastatic burden in lymph nodes (95.6 +/- 24.0%; P = 0.047), lung (86.5 +/- 10.5%; P = 0.015), kidney (88.4 +/- 9.2%; P = 0.045) and stomach (79.5 +/- 6.6%; P = 0.036) already at very low efficient concentrations (8 mg/kg) as compared to conventional gemcitabine (360 mg/kg). Our data show that this orthotopic LNCaP xenograft PCa model seems to reflect the clinical situation characterized by the fact that at time of diagnosis, prostate neoplasms are biologically heterogeneous and thus, it is a useful model to investigate new anti-metastatic therapies.

Liposomal gemcitabine (GemLip)-efficient drug against hormone-refractory Du145 and PC-3 prostate cancer xenografts

BACKGROUND

Gemcitabine (Gemc) is an efficient chemotherapeutic drug in various cancer types (e.g., pancreas) but has only limited effects on hormone-refractory prostate cancer (HRPCa). Since HRPCa cells are highly sensitive to even low doses of Gemc in vitro, the lack of clinical effects might be due to rapid degradation of Gemc by deaminases combined with impaired accumulation in tumor tissue and PCa cells. Liposomal formulation (GemLip) is expected to protect the entrapped cytotoxic substance from enzymatic degradation and furthermore augment its accumulation within tumor tissues due to an enhanced permeability of the tumor vessels.

METHODS

Anti-tumoral and anti-metastatic activity of GemLip and Gemc were investigated in two luciferase-expressing, human hormone-refractory PC-3 and Du145 HRPCa xenograft models in immunodeficient mice. Tumor growth was monitored by in vivo luminescence imaging (orthotopic) or callipering (subcutaneous). Anti-metastatic effects of treatment were determined by in vitro luciferase assay of the tissues.

RESULTS

Tumor growth of subcutaneous Du145 xenografts was significantly inhibited only by GemLip (8 mg/kg: P = 0.014 and 6 mg/kg: P = 0.011) but not by conventional Gemc (360 mg/kg). In contrast, growth of orthotopic PC-3 xenografts was significantly inhibited by both, GemLip (P = 0.041) and Gemc (P = 0.002). The drugs furthermore strongly reduced spleen and liver metastases in this model.

CONCLUSIONS

As shown by the very low efficient concentration of GemLip, liposomal entrapment of Gemc greatly enhances its activity. GemLip has, even at very low doses, a significant anti-tumoral and anti-metastatic therapeutic effect in HRPCa xenografts in vivo and was beneficial even when the conventional Gemc failed.

INNO-206, the (6-maleimidocaproyl hydrazone derivative of doxorubicin), shows superior antitumor efficacy compared to doxorubicin in different tumor xenograft models and in an orthotopic pancreas carcinoma model

The (6-maleimidocaproyl)hydrazone derivative of doxorubicin (INNO-206) is an albumin-binding prodrug of doxorubicin with acid-sensitive properties that is being assessed clinically. The prodrug binds rapidly to circulating serum albumin and releases doxorubicin selectively at the tumor site. This novel mechanism may provide enhanced antitumor activity of doxorubicin while improving the overall toxicity profile. Preclinically, INNO-206 has shown superior activity over doxorubicin in a murine renal cell carcinoma model and in breast carcinoma xenograft models. In this work, we compared the antitumor activity of INNO-206 and doxorubicin at their respective maximum tolerated doses in three additional xenograft models (breast carcinoma 3366, ovarian carcinoma A2780, and small cell lung cancer H209) as well as in an orthotopic pancreas carcinoma model (AsPC-1). INNO-206 showed more potent antitumor efficacy than free doxorubicin in all tumor models and is thus a promising clinical candidate for treating a broad range of solid tumors.