Defining the spatial distribution of extracellular adenosine revealed a myeloid-dependent immunosuppressive microenvironment in pancreatic ductal adenocarcinoma

BACKGROUND

The prognosis for patients with pancreatic ductal adenocarcinoma (PDAC) remains extremely poor. It has been suggested that the adenosine pathway contributes to the ability of PDAC to evade the immune system and hence, its resistance to immuno-oncology therapies (IOT), by generating extracellular adenosine (eAdo).

METHODS

Using genetically engineered allograft models of PDAC in syngeneic mice with defined and different immune infiltration and response to IOT and autochthonous tumors in KPC mice we investigated the impact of the adenosine pathway on the PDAC tumor microenvironment (TME). Flow cytometry and imaging mass cytometry (IMC) were used to characterize the subpopulation frequency and spatial distribution of tumor-infiltrating immune cells. Mass spectrometry imaging (MSI) was used to visualize adenosine compartmentalization in the PDAC tumors. RNA sequencing was used to evaluate the influence of the adenosine pathway on the shaping of the immune milieu and correlate our findings to published data sets in human PDAC.

RESULTS

We demonstrated high expression of adenosine pathway components in tumor-infiltrating immune cells (particularly myeloid populations) in the murine models. MSI demonstrated that extracellular adenosine distribution is heterogeneous in tumors, with high concentrations in peri-necrotic, hypoxic regions, associated with rich myeloid infiltration, demonstrated using IMC. Protumorigenic M2 macrophages express high levels of the Adora2a receptor; particularly in the IOT resistant model. Blocking the in vivo formation and function of eAdo (Adoi), using a combination of anti-CD73 antibody and an Adora2a inhibitor slowed tumor growth and reduced metastatic burden. Additionally, blocking the adenosine pathway improved the efficacy of combinations of cytotoxic agents or immunotherapy. Adoi remodeled the TME, by reducing the infiltration of M2 macrophages and regulatory T cells. RNA sequencing analysis showed that genes related to immune modulation, hypoxia and tumor stroma were downregulated following Adoi and a specific adenosine signature derived from this is associated with a poorer prognosis in patients with PDAC.

CONCLUSIONS

The formation of eAdo promotes the development of the immunosuppressive TME in PDAC, contributing to its resistance to conventional and novel therapies. Therefore, inhibition of the adenosine pathway may represent a strategy to modulate the PDAC immune milieu and improve therapy response in patients with PDAC.

Suppression of Endothelial Cell FAK Expression Reduces Pancreatic Ductal Adenocarcinoma Metastasis after Gemcitabine Treatment

Despite substantial advances in the treatment of solid cancers, resistance to therapy remains a major obstacle to prolonged progression-free survival. Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers, with a high level of liver metastasis. Primary PDAC is highly hypoxic, and metastases are resistant to first-line treatment, including gemcitabine. Recent studies have indicated that endothelial cell (EC) focal adhesion kinase (FAK) regulates DNA-damaging therapy-induced angiocrine factors and chemosensitivity in primary tumor models. Here, we show that inducible loss of EC-FAK in both orthotopic and spontaneous mouse models of PDAC is not sufficient to affect primary tumor growth but reduces liver and lung metastasis load and improves survival rates in gemcitabine-treated, but not untreated, mice. EC-FAK loss did not affect primary tumor angiogenesis, tumor blood vessel leakage, or early events in metastasis, including the numbers of circulating tumor cells, tumor cell homing, or metastatic seeding. Phosphoproteomics analysis showed a downregulation of the MAPK, RAF, and PAK signaling pathways in gemcitabine-treated FAK-depleted ECs compared with gemcitabine-treated wild-type ECs. Moreover, low levels of EC-FAK correlated with increased survival and reduced relapse in gemcitabine-treated patients with PDAC, supporting the clinical relevance of these findings. Altogether, we have identified a new role of EC-FAK in regulating PDAC metastasis upon gemcitabine treatment that impacts outcome.

SIGNIFICANCE

These findings establish the potential utility of combinatorial endothelial cell FAK targeting together with gemcitabine in future clinical applications to control metastasis in patients with pancreatic ductal adenocarcinoma.

Size-tuneable and immunocompatible polymer nanocarriers for drug delivery in pancreatic cancer

Nanocarriers have emerged as one of the most promising approaches for drug delivery. Although several nanomaterials have been approved for clinical use, the translation from lab to clinic remains challenging. However, by implementing rational design strategies and using relevant models for their validation, these challenges are being addressed. This work describes the design of novel immunocompatible polymer nanocarriers made of melanin-mimetic polydopamine and Pluronic F127 units. The nanocarrier preparation was conducted under mild conditions, using a highly reproducible method that was tuned to provide a range of particle sizes (<100 nm) without changing the composition of the carrier. A set of in vitro studies were conducted to provide a comprehensive assessment of the effect of carrier size (40, 60 and 100 nm) on immunocompatibility, viability and uptake into different pancreatic cancer cells varying in morphological and phenotypic characteristics. Pancreatic cancer is characterised by poor treatment efficacy and no improvement in patient survival in the last 40 years due to the complex biology of the solid tumour. High intra- and inter-tumoral heterogeneity and a dense tumour microenvironment limit diffusion and therapeutic response. The Pluronic-polydopamine nanocarriers were employed for the delivery of irinotecan active metabolite SN38, which is used in the treatment of pancreatic cancer. Increased antiproliferative effect was observed in all tested cell lines after administration of the drug encapsulated within the carrier, indicating the system's potential as a therapeutic agent for this hard-to-treat cancer.

Method To Visualize the Intratumor Distribution and Impact of Gemcitabine in Pancreatic Ductal Adenocarcinoma by Multimodal Imaging

Gemcitabine (dFdC) is a common treatment for pancreatic cancer; however, it is thought that treatment may fail because tumor stroma prevents drug distribution to tumor cells. Gemcitabine is a pro-drug with active metabolites generated intracellularly; therefore, visualizing the distribution of parent drug as well as its metabolites is important. A multimodal imaging approach was developed using spatially coregistered mass spectrometry imaging (MSI), imaging mass cytometry (IMC), multiplex immunofluorescence microscopy (mIF), and hematoxylin and eosin (H&E) staining to assess the local distribution and metabolism of gemcitabine in tumors from a genetically engineered mouse model of pancreatic cancer (KPC) allowing for comparisons between effects in the tumor tissue and its microenvironment. Mass spectrometry imaging (MSI) enabled the visualization of the distribution of gemcitabine (100 mg/kg), its phosphorylated metabolites dFdCMP, dFdCDP and dFdCTP, and the inactive metabolite dFdU. Distribution was compared to small-molecule ATR inhibitor AZD6738 (25 mg/kg), which was codosed. Gemcitabine metabolites showed heterogeneous distribution within the tumor, which was different from the parent compound. The highest abundance of dFdCMP, dFdCDP, and dFdCTP correlated with distribution of endogenous AMP, ADP, and ATP in viable tumor cell regions, showing that gemcitabine active metabolites are reaching the tumor cell compartment, while AZD6738 was located to nonviable tumor regions. The method revealed that the generation of active, phosphorylated dFdC metabolites as well as treatment-induced DNA damage primarily correlated with sites of high proliferation in KPC PDAC tumor tissue, rather than sites of high parent drug abundance.

T Cell-Mediated Antitumor Immunity Cooperatively Induced By TGFβR1 Antagonism and Gemcitabine Counteracts Reformation of the Stromal Barrier in Pancreatic Cancer

The desmoplastic stroma of pancreatic cancers forms a physical barrier that impedes intratumoral drug delivery. Attempts to modulate the desmoplastic stroma to increase delivery of administered chemotherapy have not shown positive clinical results thus far, and preclinical reports in which chemotherapeutic drugs were coadministered with antistromal therapies did not universally demonstrate increased genotoxicity despite increased intratumoral drug levels. In this study, we tested whether TGFβ antagonism can break the stromal barrier, enhance perfusion and tumoral drug delivery, and interrogated cellular and molecular mechanisms by which the tumor prevents synergism with coadministered gemcitabine. TGFβ inhibition in genetically engineered murine models (GEMM) of pancreas cancer enhanced tumoral perfusion and increased intratumoral gemcitabine levels. However, tumors rapidly adapted to TGFβ-dependent stromal modulation, and intratumoral perfusion returned to pre-treatment levels upon extended TGFβ inhibition. Perfusion was governed by the phenotypic identity and distribution of cancer-associated fibroblasts (CAF) with the myelofibroblastic phenotype (myCAFs), and myCAFs which harbored unique genomic signatures rapidly escaped the restricting effects of TGFβ inhibition. Despite the reformation of the stromal barrier and reversal of initially increased intratumoral exposure levels, TGFβ inhibition in cooperation with gemcitabine effectively suppressed tumor growth via cooperative reprogramming of T regulatory cells and stimulation of CD8 T cell-mediated antitumor activity. The antitumor activity was further improved by the addition of anti-PD-L1 immune checkpoint blockade to offset adaptive PD-L1 upregulation induced by TGFβ inhibition. These findings support the development of combined antistroma anticancer therapies capable of impacting the tumor beyond the disruption of the desmoplastic stroma as a physical barrier to improve drug delivery.

Quantifying cell cycle-dependent drug sensitivities in cancer using a high throughput synchronisation and screening approach

BACKGROUND

Chemotherapy and targeted agent anti-cancer efficacy is largely dependent on the proliferative state of tumours, as exemplified by agents that target DNA synthesis/replication or mitosis. As a result, cell cycle specificities of a number of cancer drugs are well known. However, they are yet to be described in a quantifiable manner.

METHODS

A scalable cell synchronisation protocol used to screen a library of 235 anti-cancer compounds exposed over six hours in G1 or S/G2 accumulated AsPC-1 cells to generate a cell cycle specificity (CCS) score.

FINDINGS

The synchronisation method was associated with reduced method-related cytotoxicity compared to nocodazole, delivering sufficient cell cycle purity and cell numbers to run high-throughput drug library screens. Compounds were identified with G1 and S/G2-associated specificities that, overall, functionally matched with a compound's target/mechanism of action. This annotation was used to describe a synergistic schedule using the CDK4/6 inhibitor, palbociclib, prior to gemcitabine/AZD6738 as well as describe the correlation between the CCS score and published synergistic/antagonistic drug schedules.

INTERPRETATION

This is the first highly quantitative description of cell cycle-dependent drug sensitivities that utilised a tractable and tolerated method with potential uses outside the present study. Drug treatments such as those shown to be G1 or S/G2 associated may benefit from scheduling considerations such as after CDK4/6 inhibitors and being first in drug sequences respectively.

FUNDING

Cancer Research UK (CRUK) Institute core grants C14303/A17197 and C9545/A29580. The Li Ka Shing Centre where this work was performed was generously funded by CK Hutchison Holdings Limited, the University of Cambridge, CRUK, The Atlantic Philanthropies and others.

CXCR4 inhibition in human pancreatic and colorectal cancers induces an integrated immune response

Inhibition of the chemokine receptor CXCR4 in combination with blockade of the PD-1/PD-L1 T cell checkpoint induces T cell infiltration and anticancer responses in murine and human pancreatic cancer. Here we elucidate the mechanism by which CXCR4 inhibition affects the tumor immune microenvironment. In human immune cell-based chemotaxis assays, we find that CXCL12-stimulated CXCR4 inhibits the directed migration mediated by CXCR1, CXCR3, CXCR5, CXCR6, and CCR2, respectively, chemokine receptors expressed by all of the immune cell types that participate in an integrated immune response. Inhibiting CXCR4 in an experimental cancer medicine study by 1-wk continuous infusion of the small-molecule inhibitor AMD3100 (plerixafor) induces an integrated immune response that is detected by transcriptional analysis of paired biopsies of metastases from patients with microsatellite stable colorectal and pancreatic cancer. This integrated immune response occurs in three other examples of immune-mediated damage to noninfected tissues: Rejecting renal allografts, melanomas clinically responding to anti-PD1 antibody therapy, and microsatellite instable colorectal cancers. Thus, signaling by CXCR4 causes immune suppression in human pancreatic ductal adenocarcinoma and colorectal cancer by impairing the function of the chemokine receptors that mediate the intratumoral accumulation of immune cells.

Complete loss of ATM function augments replication catastrophe induced by ATR inhibition and gemcitabine in pancreatic cancer models

BACKGROUND

Personalised medicine strategies may improve outcomes in pancreatic ductal adenocarcinoma (PDAC), but validation of predictive biomarkers is required. Having developed a clinical trial to assess the ATR inhibitor, AZD6738, in combination with gemcitabine (ATRi/gem), we investigated ATM loss as a predictive biomarker of response to ATRi/gem in PDAC.

METHODS

Through kinase inhibition, siRNA depletion and CRISPR knockout of ATM, we assessed how ATM targeting affected the sensitivity of PDAC cells to ATRi/gem. Using flow cytometry, immunofluorescence and immunoblotting, we investigated how ATRi/gem synergise in ATM-proficient and ATM-deficient cells, before assessing the impact of ATM loss on ATRi/gem sensitivity in vivo.

RESULTS

Complete loss of ATM function (through pharmacological inhibition or CRISPR knockout), but not siRNA depletion, sensitised to ATRi/gem. In ATM-deficient cells, ATRi/gem-induced replication catastrophe was augmented, while phospho-Chk2-T68 and phospho-KAP1-S824 persisted via DNA-PK activity. ATRi/gem caused growth delay in ATM-WT xenografts in NSG mice and induced regression in ATM-KO xenografts.

CONCLUSIONS

ATM loss augments replication catastrophe-mediated cell death induced by ATRi/gem and may predict clinical responsiveness to this combination. ATM status should be carefully assessed in tumours from patients with PDAC, since distinction between ATM-low and ATM-null could be critical in maximising the success of clinical trials using ATM expression as a predictive biomarker.

Depletion of Macrophages Improves Therapeutic Response to Gemcitabine in Murine Pancreas Cancer

BACKGROUND

The tumor microenvironment (TME) is composed of fibro-inflammatory cells and extracellular matrix (ECM) components. However, the exact contribution of the various TME compartments towards therapeutic response is unknown. Here, we aim to dissect the specific contribution of tumor-associated macrophages (TAMs) towards drug delivery and response in pancreatic ductal adenocarcinoma (PDAC).

METHODS

The effect of gemcitabine was assessed in human and murine macrophages, human pancreatic stellate cells (hPSCs), and tumor cells (L3.6pl, BxPC3 and KPC) in vitro. The drug metabolism of gemcitabine was analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Preclinical studies were conducted using KrasG12D;p48-Cre and KrasG12D;p53172H;Pdx-Cre mice to investigate gemcitabine delivery at different stages of tumor progression and upon pharmacological TAM depletion.

RESULTS

Gemcitabine accumulation was significantly increased in murine PDAC tissue compared to pancreatic intraepithelial neoplasia (PanIN) lesions and healthy control pancreas tissue. In vitro, macrophages accumulated and rapidly metabolized gemcitabine resulting in a significant drug scavenging effect for gemcitabine. Finally, pharmacological TAM depletion enhanced therapeutic response to gemcitabine in tumor-bearing KPC mice.

CONCLUSION

Macrophages rapidly metabolize gemcitabine in vitro, and pharmacological depletion improves the therapeutic response to gemcitabine in vivo. Our study supports the notion that TAMs might be a promising therapeutic target in PDAC.

Targeting melanoma's MCL1 bias unleashes the apoptotic potential of BRAF and ERK1/2 pathway inhibitors

BRAF and MEK1/2 inhibitors are effective in melanoma but resistance inevitably develops. Despite increasing the abundance of pro-apoptotic BIM and BMF, ERK1/2 pathway inhibition is predominantly cytostatic, reflecting residual pro-survival BCL2 family activity. Here, we show that uniquely low BCL-XL expression in melanoma biases the pro-survival pool towards MCL1. Consequently, BRAF or MEK1/2 inhibitors are synthetic lethal with the MCL1 inhibitor AZD5991, driving profound tumour cell death that requires BAK/BAX, BIM and BMF, and inhibiting tumour growth in vivo. Combination of ERK1/2 pathway inhibitors with BCL2/BCL-w/BCL-XL inhibitors is stronger in CRC, correlating with a low MCL1:BCL-XL ratio; indeed the MCL1:BCL-XL ratio is predictive of ERK1/2 pathway inhibitor synergy with MCL1 or BCL2/BCL-w/BCL-XL inhibitors. Finally, AZD5991 delays acquired BRAFi/MEKi resistance and enhances the efficacy of an ERK1/2 inhibitor in a model of acquired BRAFi + MEKi resistance. Thus combining ERK1/2 pathway inhibitors with MCL1 antagonists in melanoma could improve therapeutic index and patient outcomes.

SPARC dependent collagen deposition and gemcitabine delivery in a genetically engineered mouse model of pancreas cancer

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is characterised by extensive matrix deposition that has been implicated in impaired drug delivery and therapeutic resistance. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that regulates collagen deposition and is highly upregulated in the activated stroma subtype with poor prognosis in PDAC patients.

METHODS

KrasG12D;p48-Cre;SPARC-/- (KC-SPARC-/-) and KrasG12D;p48-Cre;SPARCWT (KC-SPARCWT) were generated and analysed at different stages of carcinogenesis by histological grading, immunohistochemistry for epithelial and stromal markers, survival and preclinical analysis. Pharmacokinetic and pharmacodynamic studies were conducted by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunohistochemistry following gemcitabine treatment (100 mg/kg) in vivo.

FINDINGS

Global genetic ablation of SPARC in a KrasG12D driven mouse model resulted in significantly reduced overall and mature collagen deposition around early and advanced pancreatic intraepithelial neoplasia (PanIN) lesions and in invasive PDAC (p < .001). However, detailed pathological scoring and molecular analysis showed no effects on PanIN to PDAC progression, vessel density (CD31), tumour incidence, grading or metastatic frequency. Despite comparable tumour kinetics, ablation of SPARC resulted in a significantly shortened survival in KC-SPARC-/- mice (280 days versus 485 days, p < .03, log-rank-test). Using LC-MS/MS, we show that SPARC dependent collagen deposition does not affect intratumoural gemcitabine accumulation or immediate therapeutic response in tumour bearing KC-SPARCWT and KC-SPARC-/-mice.

INTERPRETATION

Global SPARC ablation reduces the collagen-rich microenvironment in murine PDAC. Moreover, global SPARC depletion did not affect tumour growth kinetics, grading or metastatic frequency. Notably, the dense-collagen matrix did not restrict access of gemcitabine to the tumour. These findings may have direct translational implications in clinical trial design.

Abstract 271: The role of ATM and DNA-PK in responding to AZD6738-induced damage in pancreatic ductal adenocarcinoma cells

Therapeutic targeting of the DNA damage response (DDR) has the potential to improve the poor survival outcomes of pancreatic ductal adenocarcinoma (PDAC). Many common genetic alterations in PDAC augment replication stress, which activates Ataxia-telangiectasia and Rad3-related kinase (ATR). We have demonstrated previously, efficacy of the ATR inhibitor (AZD6738) in PDAC models, particularly when combined with gemcitabine (gem) (Wallez et al, MCT, 2018). This combination strongly induces activation of Ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK), indicating the induction of double-strand breaks. It has been suggested that ATM-deficiency can sensitize cancer cells to ATR inhibitors. This study sought to assess the relevance of this finding to PDAC and to interrogate the distinct roles of ATM and DNA-PK in response to ATRi/gem in PDAC cell lines.

The ATM inhibitor, AZD0156, sensitized human pancreatic cancer cell lines (MIA PaCa-2, HPAF-II, AsPC-1) to AZD6738, as determined by SRB assays (e.g. MIA PaCa-2; AZD6738 GI50 = 3.8 µM, versus 1.3 µM in the presence of 30 nM AZD0156) and in longer term colony forming assays (surviving fraction (SF) (1 µM AZD6738); 78 +/- 0.9%, SF (1 µM AZD6738 + 30nM AZD0156); 11 +/- 4.2%). However, ATM knockdown with siRNA did not sensitize to AZD6738, nor to the combination of AZD6738/gem. This suggests that the presence of kinase-inhibited ATM at sites of DNA damage is more deleterious to PDAC cells than deficiency of ATM protein expression.

We established that AZD6738/gem could induce phosphorylation of the canonical targets of ATM (Chk2, KAP1) in MIA PaCa-2 when ATM was knocked down or inhibited. DNA-PK was also activated in response to exposure to ATRi/gem and we postulated that it was responsible for the Chk2/KAP1 activation. We then demonstrated that Chk2/KAP1 activation could be abrogated by DNA-PK inhibition with NU7441. Furthermore, in an ATM-null pancreatic cancer cell line, AZD6738/gem-induced KAP1 phosphorylation was also abrogated by inhibition of DNA-PK. Thus, DNA-PK appears to be responsible for the downstream activation of Chk2 and KAP1, induced by AZD6738/gem in PDAC cells.

Therefore, as well as revealing that inhibition of ATM using the novel inhibitor AZD0156 is highly deleterious to ATR inhibited PDAC cells, we have identified a compensatory mechanism via DNA-PK, which may be relevant for maximizing the therapeutic potential of DDR inhibitors in PDAC. Since DNA-PK clearly plays a dominant role in the DDR signaling pathways, we are now assessing whether DNA-PK inhibition synergizes with AZD6738+/- gem.

Citation Format: Charles R. Dunlop, Yann Wallez, Sandra Bernaldo de Quirós Fernández, Saadia A. Karim, Alan Lau, Frances M. Richards, Duncan I. Jodrell. The role of ATM and DNA-PK in responding to AZD6738-induced damage in pancreatic ductal adenocarcinoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 271.

Cytosolic 5'-nucleotidase 1A is overexpressed in pancreatic cancer and mediates gemcitabine resistance by reducing intracellular gemcitabine metabolites

BACKGROUND

Cytosolic 5'-nucleotidase 1A (NT5C1A) dephosphorylates non-cyclic nucleoside monophosphates to produce nucleosides and inorganic phosphates. Here, we investigate NT5C1A expression in pancreatic ductal adenocarcinoma (PDAC) and its impact on gemcitabine metabolism and therapeutic efficacy.

METHODS

NT5C1A expression was determined by semiquantitative immunohistochemistry using tissue microarrays. Gemcitabine metabolites and response were assessed in several human and murine PDAC cell lines using crystal violet assays, Western blot, viability assays, and liquid chromatography tandem mass-spectrometry (LC-MS/MS).

FINDINGS

NT5C1A was strongly expressed in tumor cells of a large subgroup of resected PDAC patients in two independent patient cohorts (44-56% score 2 and 8-26% score 3, n = 414). In contrast, NT5C1A was expressed at very low levels in the tumor stroma, and neither stromal nor tumoral expression was a prognostic marker for postoperative survival. In vitro, NT5C1A overexpression increased gemcitabine resistance by reducing apoptosis levels and significantly decreased intracellular amounts of cytotoxic dFdCTP in +NT5C1A tumor cells. Co-culture experiments with conditioned media from +NT5C1A PSCs improved gemcitabine efficacy in tumor cells. In vivo, therapeutic efficacy of gemcitabine was significantly decreased and serum levels of the inactive gemcitabine metabolite dFdU significantly increased in mice bearing NT5C1A overexpressing tumors.

INTERPRETATION

NT5C1A is robustly expressed in tumor cells of resected PDAC patients. Moreover, NT5C1A mediates gemcitabine resistance by decreasing the amount of intracellular dFdCTP, leading to reduced tumor cell apoptosis and larger pancreatic tumors in mice. Further studies should clarify the role of NT5C1A as novel predictor for gemcitabine treatment response in patients with PDAC.

The ATR Inhibitor AZD6738 Synergizes with Gemcitabine In Vitro and In Vivo to Induce Pancreatic Ductal Adenocarcinoma Regression

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest cancers, and overall survival rates have barely improved over the past five decades. The antimetabolite gemcitabine remains part of the standard of care but shows very limited antitumor efficacy. Ataxia telangiectasia and Rad3-related protein (ATR), the apical kinase of the intra-S-phase DNA damage response, plays a central role in safeguarding cells from replication stress and can therefore limit the efficacy of antimetabolite drug therapies. We investigated the ability of the ATR inhibitor, AZD6738, to prevent the gemcitabine-induced intra-S-phase checkpoint activation and evaluated the antitumor potential of this combination in vitro and in vivo In PDAC cell lines, AZD6738 inhibited gemcitabine-induced Chk1 activation, prevented cell-cycle arrest, and restrained RRM2 accumulation, leading to the strong induction of replication stress markers only with the combination. Moreover, synergistic growth inhibition was identified in a panel of 5 mouse and 7 human PDAC cell lines using both Bliss Independence and Loewe models. In clonogenic assays, the combination abrogated survival at concentrations for which single agents had minor effects. In vivo, AZD6738 in combination with gemcitabine was well tolerated and induced tumor regression in a subcutaneous allograft model of a KrasG12D; Trp53R172H; Pdx-Cre (KPC) mouse cancer cell line, significantly extending survival. Remarkably, the combination also induced regression of a subgroup of KPC autochthonous tumors, which generally do not respond well to conventional chemotherapy. Altogether, our data suggest that AZD6738 in combination with gemcitabine merits evaluation in a clinical trial in patients with PDAC. Mol Cancer Ther; 17(8); 1670-82. ©2018 AACR.

Mechanistic Distinctions between CHK1 and WEE1 Inhibition Guide the Scheduling of Triple Therapy with Gemcitabine

Combination of cytotoxic therapy with emerging DNA damage response inhibitors (DDRi) has been limited by tolerability issues. However, the goal of most combination trials has been to administer DDRi with standard-of-care doses of chemotherapy. We hypothesized that mechanism-guided treatment scheduling could reduce the incidence of dose-limiting toxicities and enable tolerable multitherapeutic regimens. Integrative analyses of mathematical modeling and single-cell assays distinguished the synergy kinetics of WEE1 inhibitor (WEE1i) from CHEK1 inhibitor (CHK1i) by potency, spatiotemporal perturbation, and mitotic effects when combined with gemcitabine. These divergent properties collectively supported a triple-agent strategy, whereby a pulse of gemcitabine and CHK1i followed by WEE1i durably suppressed tumor cell growth. In xenografts, CHK1i exaggerated replication stress without mitotic CDK hyperactivation, enriching a geminin-positive subpopulation and intratumoral gemcitabine metabolite. Without overt toxicity, addition of WEE1i to low-dose gemcitabine and CHK1i was most effective in tumor control compared with single and double agents. Overall, our work provides quantitative insights into the mechanisms of DDRi chemosensitization, leading to the rational development of a tolerable multitherapeutic regimen.Significance: Multiple lines of mechanistic insight regarding DNA damage response inhibitors rationally guide the preclinical development of a tolerable multitherapeutic regimen.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/11/3054/F1.large.jpg Cancer Res; 78(11); 3054-66. ©2018 AACR.

Fibroblast drug scavenging increases intratumoural gemcitabine accumulation in murine pancreas cancer

OBJECTIVE

Desmoplasia and hypovascularity are thought to impede drug delivery in pancreatic ductal adenocarcinoma (PDAC). However, stromal depletion approaches have failed to show clinical responses in patients. Here, we aimed to revisit the role of the tumour microenvironment as a physical barrier for gemcitabine delivery.

DESIGN

Gemcitabine metabolites were analysed in LSL-KrasG12D/+ ; LSL-Trp53R172H/+ ; Pdx-1-Cre (KPC) murine tumours and matched liver metastases, primary tumour cell lines, cancer-associated fibroblasts (CAFs) and pancreatic stellate cells (PSCs) by liquid chromatography-mass spectrometry/mass spectrometry. Functional and preclinical experiments, as well as expression analysis of stromal markers and gemcitabine metabolism pathways were performed in murine and human specimen to investigate the preclinical implications and the mechanism of gemcitabine accumulation.

RESULTS

Gemcitabine accumulation was significantly enhanced in fibroblast-rich tumours compared with liver metastases and normal liver. In vitro, significantly increased concentrations of activated 2',2'-difluorodeoxycytidine-5'-triphosphate (dFdCTP) and greatly reduced amounts of the inactive gemcitabine metabolite 2',2'-difluorodeoxyuridine were detected in PSCs and CAFs. Mechanistically, key metabolic enzymes involved in gemcitabine inactivation such as hydrolytic cytosolic 5'-nucleotidases (Nt5c1A, Nt5c3) were expressed at low levels in CAFs in vitro and in vivo, and recombinant expression of Nt5c1A resulted in decreased intracellular dFdCTP concentrations in vitro. Moreover, gemcitabine treatment in KPC mice reduced the number of liver metastases by >50%.

CONCLUSIONS

Our findings suggest that fibroblast drug scavenging may contribute to the clinical failure of gemcitabine in desmoplastic PDAC. Metabolic targeting of CAFs may thus be a promising strategy to enhance the antiproliferative effects of gemcitabine.

Development of In Vitro Co-Culture Model in Anti-Cancer Drug Development Cascade

BACKGROUND

Tumour microenvironment is recognized as a major determinant of intrinsic resistance to anticancer therapies. In solid tumour types, such as breast cancer, lung cancer and pancreatic cancer, stromal components provide a fibrotic niche, which promotes stemness, EMT, chemo- and radioresistance of tumour. However, this microenvironment is not recapitulated in the conventional cell monoculture or xenografts, hence these in vitro and in vivo preclinical models are unlikely to be predictive of clinical response; which might attribute to the poor predictively of these preclinical drug-screening models.

CONCLUSION

In this review, we summarized recently developed co-culture platforms in various tumour types that incorporate different stromal cell types and/or extracellular matrix (ECM), in the context of investigating potential mechanisms of stroma-mediated chemoresistance and evaluating novel agents and combinations. Some of these platforms will have great utility in the assessment of novel drug combinations and mechanistic understanding of the tumor-stroma interactions.

Abstract 3190: Using a genome-wide shRNA screen to investigate the mechanism of stroma-conferred gemcitabine resistance in pancreatic ductal adenocarcinoma

The purpose of this study is to identify mechanisms of resistance to gemcitabine in pancreatic ductal adenocarcinoma (PDAC) using an in vitro coculture system. The inherent resistance of PDAC to first line treatments such as gemcitabine has been attributed to the dense fibrotic stroma. Targeting stromal components, in particular cancer-associated fibroblasts (CAFs), the activated form of pancreatic stellate cells (PSCs), is a promising avenue for therapeutic intervention. We have demonstrated previously the induction of gemcitabine resistance when co-culturing KRAS G12D; p53 R172H; Pdx-cre (KPC) mouse PDAC-derived tumour cells with αSMA+ fibroblast-like cells from PDAC tumour (FLCs), in comparison to PDAC cells co-cultured with PSCs or in monoculture. This resistance-inducing effect is specific to cells of mesenchymal phenotype, is transient in nature and a product of cell-cell contact. To investigate the exact mechanism by which PDAC cells become resistant to gemcitabine in coculture, we undertook a genome-wide shRNA depletion viability screen, infecting KPC mouse PDAC cells with a pooled shERWOOD UltramiR shRNA library both in mono- and co-culture with FLCs, in the presence and absence of gemcitabine. Next-generation sequencing and differential expression analysis, using DESeq2, identified shRNAs depleted through 6 cycles of gemcitabine treatment in coculture, indicating they target genes driving the resistance effect. Pathway analysis of differential expression using MetaCore implicated DNA damage repair and protein modification pathways in the gemcitabine resistance effect. Depletion of p97, ATR, or Chk1 all sensitised PDAC cells to gemcitabine in coculture, corroborating findings with translational value in previous studies. Further evaluation is ongoing using validation shRNA dropout assays in combination with targeted literature reviews to collate a candidate list of targetable genes with translational value in preventing and combating chemotherapy resistance in patients with PDAC.

Citation Format: Graham D. Mills, Nicolas Erard, Frances M. Richards, Gregory J. Hannon, Duncan I. Jodrell. Using a genome-wide shRNA screen to investigate the mechanism of stroma-conferred gemcitabine resistance in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3190. doi:10.1158/1538-7445.AM2017-3190

Modelling of the cancer cell cycle as a tool for rational drug development: A systems pharmacology approach to cyclotherapy

The dynamic of cancer is intimately linked to a dysregulation of the cell cycle and signalling pathways. It has been argued that selectivity of treatments could exploit loss of checkpoint function in cancer cells, a concept termed "cyclotherapy". Quantitative approaches that describe these dysregulations can provide guidance in the design of novel or existing cancer therapies. We describe and illustrate this strategy via a mathematical model of the cell cycle that includes descriptions of the G1-S checkpoint and the spindle assembly checkpoint (SAC), the EGF signalling pathway and apoptosis. We incorporated sites of action of four drugs (palbociclib, gemcitabine, paclitaxel and actinomycin D) to illustrate potential applications of this approach. We show how drug effects on multiple cell populations can be simulated, facilitating simultaneous prediction of effects on normal and transformed cells. The consequences of aberrant signalling pathways or of altered expression of pro- or anti-apoptotic proteins can thus be compared. We suggest that this approach, particularly if used in conjunction with pharmacokinetic modelling, could be used to predict effects of specific oncogene expression patterns on drug response. The strategy could be used to search for synthetic lethality and optimise combination protocol designs.

Abstract B19: The ATR inhibitor, AZD6738, synergizes with other DNA damage response inhibitors and genotoxic drugs in pancreatic ductal adenocarcinoma cell lines: Opportunities for new therapeutic combinations

Mutations in oncogenes, tumor suppressor and DNA damage response (DDR) mediator genes drive or permit malignant transformation but also increase endogenous replication stress. The serine/threonine kinase ATR plays a critical role in safeguarding genome integrity from such replication stress and several studies have demonstrated the increased reliance of cancer cells on ATR function. We investigated the therapeutic opportunities for the ATR inhibitor, AZD6738, in combination with DNA damaging or DDR-targeted agents, in the context of pancreatic ductal adenocarcinoma (PDAC).

We evaluated four DNA-damaging agents (gemcitabine, 5-fluorouracil, oxaliplatin, SN38 (the active metabolite of irinotecan)) and three DDR-targeted agents (Wee1 inhibitor (AZD1775), Chk1 inhibitor (MK8776), PARP inhibitor (AZD2281)), each in combination with AZD6738 at multiple concentrations. Efficacy of these combinations was tested in growth inhibition assays in vitro, using a panel of cell lines in order to capture some of the genetic heterogeneity observed in PDAC: two human cell lines and four lines from the KrasG12D; Trp53R172H; Pdx-Cre (KPC) mouse. Synergistic growth inhibition was identified applying both Bliss Independence and Loewe models, using Combenefit software. All the KPC mouse cell lines were sensitive to AZD6738 as a single agent, with GI50 ranging from 346 to 566 nM. MIA PaCa-2 were sensitive to AZD6738, achieving &gt;90% growth inhibition, with GI50 of 2.2 μM. PANC-1 cells were less sensitive, with GI50 21 μM and achieving only ~60% GI, at the highest concentration tested. PANC-1 cells are also less sensitive to gemcitabine than the other cell lines. Synergy was detected in most of the cell lines, with each of the seven drug combinations tested. The combinations of AZD6738 with gemcitabine and with oxaliplatin showed synergy in all cell lines tested.

We next investigated scheduling of the gemcitabine/ATRi combination, at the specific GI50 concentrations for each cell line, using kinetic live-cell imaging assays. Concurrent treatment of gemcitabine/ATRi for 16h proved to be most effective, almost completely inhibiting cell growth for more than three days after washout. Sequential treatment (irrespective of the order) or shorter pulses (8h) were less effective. Maintaining ATRi after gemcitabine washout further enhanced growth inhibition for most cell lines. Mechanistically, ATRi impaired Chk1 activation (p-Ser345) and, in combination with gemcitabine, strongly potentiated DNA damage (gamma H2AX). Maintaining ATRi after gemcitabine washout helped to sustain the level of DNA damage. In vivo studies are underway to determine whether the gemcitabine/ATRi combination enhances efficacy compared to gemcitabine alone. The ATRi/oxaliplatin combination is also being investigated in vitro and in vivo using similar methods.

Several genes have been described in the literature to increase the reliance on ATR functions when altered. Mining two published datasets (TCGA, 186 samples and UTSW, Nat. Commun. 2015, 109 samples) we have investigated the frequencies at which 21 of these genes were altered in human PDAC. Overall ~95% of PDAC samples exhibit at least one (9% only one, 28% two and 57% three or more) genetic alteration likely to sensitize to ATRi, potentially improving the therapeutic index of combination approaches. Thus, combinations including ATRi merit further evaluation as they have the potential to be effective in the treatment of patients with PDAC.

Citation Format: Yann Wallez, Siang-Boon Koh, Venkata Sai Vivek Bhogadi, Alan Lau, Frances M. Richards, Duncan I. Jodrell. The ATR inhibitor, AZD6738, synergizes with other DNA damage response inhibitors and genotoxic drugs in pancreatic ductal adenocarcinoma cell lines: Opportunities for new therapeutic combinations [abstract]. In: Proceedings of the AACR Special Conference on DNA Repair: Tumor Development and Therapeutic Response; 2016 Nov 2-5; Montreal, QC, Canada. Philadelphia (PA): AACR; Mol Cancer Res 2017;15(4_Suppl):Abstract nr B19.

A quantitative FastFUCCI assay defines cell cycle dynamics at a single-cell level

The fluorescence ubiquitination-based cell cycle indicator (FUCCI) is a powerful tool for use in live cells but current FUCCI-based assays have limited throughput in terms of image processing and quantification. Here, we developed a lentiviral system that rapidly introduced FUCCI transgenes into cells by using an all-in-one expression cassette, FastFUCCI. The approach alleviated the need for sequential transduction and characterisation, improving labelling efficiency. We coupled the system to an automated imaging workflow capable of handling large datasets. The integrated assay enabled analyses of single-cell readouts at high spatiotemporal resolution. With the assay, we captured in detail the cell cycle alterations induced by antimitotic agents. We found that treated cells accumulated at G2 or M phase but eventually advanced through mitosis into the next interphase, where the majority of cell death occurred, irrespective of the preceding mitotic phenotype. Some cells appeared viable after mitotic slippage, and a fraction of them subsequently re-entered S phase. Accordingly, we found evidence that targeting the DNA replication origin activity sensitised cells to paclitaxel. In summary, we demonstrate the utility of the FastFUCCI assay for quantifying spatiotemporal dynamics and identify its potential in preclinical drug development.

Abstract B62: Evaluation of scheduling for triple therapy gemcitabine/CHEK1 inhibitor/WEE1 inhibitor in pancreatic cancer models

Sensitization of cancer cells to gemcitabine (Gem) has been shown with checkpoint kinase CHEK1 (CHK1) and WEE1 inhibitors. Our aim is to determine, using in vitro and in vivo models, the optimal regime for application of the triple combination in pancreatic cancer. First, we have investigated the dual combinations of Gem + either CHEK1 or WEE1 inhibitors in growth inhibition assays in vitro. Synergistic growth inhibition was identified using both Bliss Independence and Loewe models, in MIA PaCa-2 cells at 10 – 30 nM Gem + 300 – 1000 nM CHEK1 inhibitor MK8776; or 10 – 30 nM Gem + 30 – 100 nM WEE1 inhibitor MK1775. The synergistic concentrations were submaximal, i.e. below the single agent GI50 concentrations, which were 30 nM for Gem, 6 μM for MK8776, and 500 nM for MK1775. The Panc-1 cell line is more resistant to Gem as a single agent, but synergy was evident: in colony forming assays the dual combination of either 30 nM gem + 300 nM MK1775 or 30 nM Gem + 1 μM MK8776 inhibited colony formation by 97 +/- 1.6 % and 91 +/- 2% respectively. Single agent Gem inhibited colony formation by only 23 +/- 4 % and MK1775 or MK8776 did not inhibit colony formation at these concentrations.

Next, we investigated scheduling of the Gem/CHEK1i/Wee1i triple combination, at the synergistic concentrations, with kinetic live-cell imaging assays. MIA PaCa-2 cells treated continuously with 10 nM Gem plus 1 μM MK8776 showed durable growth inhibition over 72 hours. However, if both drugs were washed off after 24 hours the Gem + CHEK1i-treated cells recovered and began to proliferate within 24 hours. Different schedules of the trio were tested, and the most durable growth inhibition (&gt; 5 days) was obtained when Gem + MK8776 were washed off at 24 hours and replaced with 300 nM MK1775, whereas 300 nM MK1775 in the absence of Gem + MK8776 pretreatment did not significantly inhibit growth, compared to control. Different scheduling options were also tested in Panc-1 cells in colony forming assays, and again the most effective schedule was Gem + MK8776 for 24 hours, followed by MK1775.

MIA PaCa-2 xenograft studies are now underway, initially with the dual combination, to be followed with the drug trio of simultaneous Gem + MK8776, followed by MK1775. To reduce the likelihood of toxicity, Gem doses lower than the typical “full” dose (100 mg/kg IP twice per week) were tested. We found that 25 mg/kg Gem twice in a day (8h apart), twice per week was not well tolerated even as a single agent, but both 25 and 50 mg/kg Gem once in a day, twice per week was tolerated when co-dosed with 25 mg/kg MK8776, and when this combination was followed 8 hours later by 60 mg/kg MK1775 (OG). A pharmacokinetic study revealed that plasma Gem (dFdC) concentrations were not altered by co-dosing Gem with MK8776, but intratumor dFdCTP (the active intracellular metabolite of Gem) was elevated at 1 – 8 hours after the 25 mg/kg Gem + MK8776 dose (AUC0 –last 49 +/- 7.9 hr.pmoles/mg tissue) compared to mice with 25 mg/kg Gem alone (AUC0-last 21 +/- 2.6 hr.pmoles/mg tissue). CHEK1 target inhibition was demonstrated in vivo, with abrogation of Gem-induced CHEK1 S296 autophosphorylation for at least 4h post Gem + MK8776 dosing, using Western blot analyses of tumor lysate. There was also increased γH2AX and pRPA32 S4/8 at 4 - 8 hours post-dose with Gem + MK8776 compared to Gem alone, indicating enhanced DNA damage. Pharmacodynamic and efficacy studies with the triple combination, will determine whether enhanced efficacy can be observed, when compared to full dose, single agent gemcitabine (100 mg/kg IP twice per week).

Citation Format: Siang-Boon Koh, Frances M. Richards, Yann Wallez, Duncan I. Jodrell.{Authors}. Evaluation of scheduling for triple therapy gemcitabine/CHEK1 inhibitor/WEE1 inhibitor in pancreatic cancer models. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B62.

Abstract B40: Evaluation of the combination of AZD2014 and olaparib in pancreatic cancer cells

The PI3K/Akt/mTOR pathway is frequently activated in human pancreatic ductal adenocarcinoma (PDAC) and in mouse models of Kras-driven pancreatic cancer. In addition, 20-30% of pancreatic cancers may have “unstable” genomes, associated with somatic or germline BRCA mutations, mutations in genes involved in DNA maintenance (eg. PALB2, ATM) or genes not previously associated with DNA maintenance. We therefore evaluated the efficacy of the mTORC1/2 inhibitor AZD2014 and olaparib, as single agents and in combination in vitro in human (MIA PaCa-2 and Capan-1) and murine (K8484: KRASG12D; p53R172H; Pdx1-cre (KPC)) PDAC cell lines. We also assessed the effect of AZD2014 in combination with gemcitabine, and the triple agent combination.

Drug-induced cytotoxicity and cell proliferation were evaluated in 96-well plates, using the high-throughput sulforhodamine B (SRB) assay. The efficacy of 2-drug combinations was assessed by treating cells with serial dilutions of the compounds in an 8X8 grid format. Synergy was assessed using the Bliss Independence model, as implemented in Combenefit software (http://www.cruk.cam.ac.uk/research-groups/jodrell-group/combenefit). Western blotting showed that phosphorylation of Akt, NDRG1, S6 ribosomal protein and 4EBP1 were suppressed by AZD2014. AZD2014 inhibited the growth of all 3 cell lines, with GI50s in the nanomolar range. At the highest AZD2014 concentration, the growth of all 3 cell lines was inhibited at least 70%. Olaparib was ineffective as a single agent in K8484 and MIA PaCa-2 cells, but reassuringly inhibited the growth of Brca2 deficient Capan-1 cells. Synergy was observed in K8484 cells, and mild synergy in MIA PaCa-2 cells, when AZD2014 was combined with gemcitabine. No synergy was observed with the combination of AZD2014 and olaparib in any of the cell lines, although some additivity was observed in Capan-1 cells. When the 3 drugs were combined, higher olaparib concentrations increased cytotoxicity at lower concentrations of AZD2014, however this did not provide any additional benefit, compared to the combination of AZD2014 and gemcitabine at higher concentrations.

Although the combination of AZD2014 and olaparib did not exhibit synergistic activity, AZD2014 showed efficacy as a single agent, and with gemcitabine is a promising combination that warrants further investigation in patients with pancreatic cancer. Further work is required to understand the mechanism of action of this combination, which may also reveal other promising targets to combine with inhibition of mTORC1/2.

This study was funded by the Cancer Research UK New Agents Committee, with compounds supplied by AstraZeneca.

Citation Format: Aarthi Gopinathan, Frances M. Richards, Sabina Cosulich, Bristi Basu, Duncan I. Jodrell.{Authors}. Evaluation of the combination of AZD2014 and olaparib in pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B40.

Abstract B54: Genetically engineered mouse-derived allografts (GEDAs): an immunocompetent mouse model of PDAC for the evaluation of novel therapeutic strategies

Despite recent advances in the treatment of patients with pancreatic adenocarcinoma (PDAC), survival remains low. Pre-clinical models of human malignancies often fail to capture the complexity of tumors and as such lack clinical predictive power. Patient-derived tumor xenografts (PDXs) are an emerging pre-clinical platform, capable of retaining the molecular heterogeneity of their originating sample and able to predict the response to therapies in some cases. However, the lack of immune system of the mouse PDX host is a major drawback for a preclinical model, especially with the advent of promising cancer immunotherapies (e.g. anti-PD-1/PD-L1, CXCR4 antagonist). Genetically Engineered Mouse models (GEMMs) carry mutations in genes that are associated with the human disease and can thus mimic the genetic, phenotypic and physiological aspect of the human disease, in an immunocompetent background. The Lox-Stop-Lox (LSL)-Kras(G12D); LSL-Trp53(R172H); Pdx1-cre (KPC) mouse is a favoured model of PDA, recapitulating the desmoplastic tumor histology, immune profile and drug resistance of human PDAC. However, KPC tumor development speed is variable and tumor monitoring requires ultrasound imaging, so therapeutic studies are long, complex and expensive.

We describe here a new model, Genetically Engineered mouse-Derived Allograft (GEDA), that applies the methods developed for PDXs to KPC tumors. Pieces of KPC tumor were implanted subcutaneously in the flank of recipient LSL-Trp53 (R172H); Pdx1-cre (PC), immunocompetent mice. At primary passage, 10 mice were implanted from a single primary tumor, and the engraftment rate is 90%. Tumors are palpable 2 weeks after the tumor implantation and can be monitored by calliper measurement for up to 10 weeks, with a tumor doubling time of 14.4 ± 1.5 days. The incidence of metastases was similar to KPC mice, but organ distribution was different, with 57% of 45 recipient mice developing lung metastases, and 0% liver metastases. Histologically the GEDAs appeared more like primary KPC tumors than subcutaneous allograft of KPC cell lines, with intratumoral heterogeneity including desmoplastic regions identified by the presence of collagen fibres and αSMA-expressing cells. Implantation of GEDAs onto GFP-mice revealed that the original donor stroma disappeared within 2 weeks and was replaced by host stroma, but the stromal composition remained comparable even over 5 passages in vivo, with ±15% of variation in αSMA-expressing area between donor and recipients. Typically, around 20% of the GEDA cells were positive for Ki67, remaining stable over 5 passages, suggesting that aggressiveness of the tumor was stable. Qualitatively, by CD3 IHC, the T cell distribution is similar to that reported in KPC tumors (Feig et al, PNAS 2013) with T cell exclusion from tumor cell nests.

A therapeutic study was performed with gemcitabine. Tumor growth was not inhibited by gemcitabine (100 mg/kg IP, twice per week); tumor volume change at day 60 (%): 1544 ± 263 (treated) vs. 1350 ± 156 (control), n= 6 per group, p=0.25 ). Few KPC primary tumors show significant response to gemcitabine, so the PDA GEDA was more like KPC than subcutaneous allografts of KPC cell lines which tend to be gemcitabine sensitive. A biobank of KPC GEDAs is now being generated, which will be tested to determine the heterogeneity of therapeutic response to gemcitabine and other agents.In conclusion, we have generated PDAC GEDAs, which combine advantages of both GEMMs and PDXs, cost-effective generation of cohorts of mice for therapeutic studies. The stromal content and intact immune system should enable the evaluation of immunomodulatory therapies and also agents targeting the stromal components of PDAC.

Citation Format: Séverine Mollard, Kristopher K. Frese, Aarthi Gopinathan, Frances M. Richards, Duncan I. Jodrell.{Authors}. Genetically engineered mouse-derived allografts (GEDAs): an immunocompetent mouse model of PDAC for the evaluation of novel therapeutic strategies. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B54.

Combenefit: an interactive platform for the analysis and visualization of drug combinations

MOTIVATION

Many drug combinations are routinely assessed to identify synergistic interactions in the attempt to develop novel treatment strategies. Appropriate software is required to analyze the results of these studies.

RESULTS

We present Combenefit, new free software tool that enables the visualization, analysis and quantification of drug combination effects in terms of synergy and/or antagonism. Data from combinations assays can be processed using classical Synergy models (Loewe, Bliss, HSA), as single experiments or in batch for High Throughput Screens. This user-friendly tool provides laboratory scientists with an easy and systematic way to analyze their data. The companion package provides bioinformaticians with critical implementations of routines enabling the processing of combination data.

AVAILABILITY AND IMPLEMENTATION

Combenefit is provided as a Matlab package but also as standalone software for Windows (http://sourceforge.net/projects/combenefit/).

CONTACT

Giovanni.DiVeroli@cruk.cam.ac.uk

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Abstract 389: The dual mTOR inhibitor, AZD2014, and castration increase intra-tumoral immune cell infiltration and anti-tumour activity in a genetically engineered mouse model of prostate cancer

Background: Medical therapy for men with prostate cancer (PCa) is evolving, including recent evidence to support the use of chemotherapy for men with hormone sensitive disease. PI3K/AKT/mTOR pathway aberrations are common in patients with primary PCa and almost universal in metastatic tumours. The mTOR pathway acts as a central regulator of tumour cell metabolism, proliferation, cell cycle progression and immune regulation. The aim of this study was to investigate the effects of mTOR inhibitor AZD2014 on tumour growth and immune infiltration in a genetically engineered mouse model of PCa.

Methods: PtenL/L;PB-Cre4 mice, which developed invasive hormone-sensitive prostate tumours between 10-14 months of age, were enrolled (n = 13-15 per group) and treated with AZD2014 (15mg/Kg) or vehicle orally for 14 doses (QD 5/7) with or without castration. Tumour volumes were assessed by ultrasound imaging. Tumour samples were collected within 4 hours post 14th dose for histological and molecular analysis.

Results: AZD2014 was well tolerated, no overt toxicity was observed. Mean plasma concentrations of AZD2014 were 4.4±2.1μM at time of tumour sampling. AZD2014 alone or AZD2014+castration inhibited mTORC1 and mTORC2 activity as demonstrated by reduced p4EBP1(Thr37/46) 48%±27% (P&lt;0.001) and 37%±11% (P&lt;0.001), pS6(Ser235/236) 74%±43% (P&lt;0.001) and 44%±13% (P&lt;0.001), pAKT(Ser473) 36%±8% (P&lt;0.001) and 20%±3% (P&lt;0.01), respectively compared to vehicle-treated mice. Proliferation (Ki67+) was reduced in AZD2014-treated tumours by 70%±45% (P&lt;0.001) and AZD2014+castration by 42%±16% (P&lt;0.001). Apoptosis (CC3+) was increased in AZD2014 and AZD2014+castration groups by 3.3-fold (both, P&lt;0.001) or castration only group by 2-fold (P&lt;0.001). Tumour volumes were significantly reduced (54%, p&lt;0.05) in AZD2014+castration group. Castration induced increased infiltration of T cells (CD3+, 2-fold, P&lt;0.001) and macrophages (F4/80+, 1.6-fold, P&lt;0.001) in the tumour tissues. These effects were more pronounced when combined with AZD2014 (CD3+, 2.8-fold, P&lt;0.001; F4/80+, 2.3-fold, P&lt;0.001). Multi-channel flow cytometry has confirmed increased proliferation of CD45+, CD3+ and CD8+ cells in tumours from the AZD2014+castration group.

Conclusion: These data confirm the anti cancer effect of AZD2014 in this PCa model. Furthermore, AZD2014+castration was more effective than either treatment as a single agent. The increased intra-tumoral T cell infiltration observed may have contributed to the anti-tumour effect. Further studies are ongoing to maximise this therapeutic effect and will inform current clinical studies in men with hormone sensitive, high risk prostate cancer.

Citation Format: Chiranjeevi Sandi, Antonio Ramos-Montoya, Sergio L. Filisbino, Adina Hughes, Suzanne Mosely, Michelle Morrow, Robert W. Wilkinson, Sarah Jurmeister, Karan Wadhwa, Frances M. Richards, Duncan I. Jodrell, Sabina Cosulich, Barry R. Davies, Simon Pacey. The dual mTOR inhibitor, AZD2014, and castration increase intra-tumoral immune cell infiltration and anti-tumour activity in a genetically engineered mouse model of prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 389.

Anti-stromal treatment together with chemotherapy targets multiple signalling pathways in pancreatic adenocarcinoma

Stromal targeting for pancreatic ductal adenocarcinoma (PDAC) is rapidly becoming an attractive option, due to the lack of efficacy of standard chemotherapy and increased knowledge about PDAC stroma. We postulated that the addition of stromal therapy may enhance the anti-tumour efficacy of chemotherapy. Gemcitabine and all-trans retinoic acid (ATRA) were combined in a clinically applicable regimen, to target cancer cells and pancreatic stellate cells (PSCs) respectively, in 3D organotypic culture models and genetically engineered mice (LSL-Kras(G12D) (/+) ;LSL-Trp53(R172H) (/+) ;Pdx-1-Cre: KPC mice) representing the spectrum of PDAC. In two distinct sets of organotypic models as well as KPC mice, we demonstrate a reduction in cancer cell proliferation and invasion together with enhanced cancer cell apoptosis when ATRA is combined with gemcitabine, compared to vehicle or either agent alone. Simultaneously, PSC activity (as measured by deposition of extracellular matrix proteins such as collagen and fibronectin) and PSC invasive ability were both diminished in response to combination therapy. These effects were mediated through a range of signalling cascades (Wnt, hedgehog, retinoid, and FGF) in cancer as well as stellate cells, affecting epithelial cellular functions such as epithelial-mesenchymal transition, cellular polarity, and lumen formation. At the tissue level, this resulted in enhanced tumour necrosis, increased vascularity, and diminished hypoxia. Consequently, there was an overall reduction in tumour size. The enhanced effect of stromal co-targeting (ATRA) alongside chemotherapy (gemcitabine) appears to be mediated by dampening multiple signalling cascades in the tumour-stroma cross-talk, rather than ablating stroma or targeting a single pathway. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Understanding the Complexity of Porous Graphitic Carbon (PGC) Chromatography: Modulation of Mobile-Stationary Phase Interactions Overcomes Loss of Retention and Reduces Variability

Porous graphitic carbon (PGC) is an important tool in a chromatographer's armory that retains polar compounds with mass spectrometry (MS)-compatible solvents. However, its applicability is severely limited by an unpredictable loss of retention, which can be attributed to contamination. The solutions offered fail to restore the original retention and our observations of retention time shifts of gemcitabine/metabolites on PGC are not consistent with contamination. The mobile phase affects the ionization state of analytes and the polarizable PGC surface that influences the strength of dispersive forces governing retention on the stationary phase. We hypothesized that failure to maintain the same PGC surface before and after running a gradient is a cause of the observed retention loss/variability on PGC. Herein, we optimize the choice of mobile phase solvent in a gradient program with three parts: a preparatory phase, which allows binding of analytes to column; an elution phase, which gives the required separation/peak shape; and a maintenance phase, to preserve the required retention capacity. Via liquid chromatography/tandem mass spectrometry (LC-MS/MS) analysis of gemcitabine and its metabolites extracted from tumor tissue, we demonstrate reproducible chromatography on three PGC columns of different ages. This approach simplifies use of the PGC to the same level as that of a C-18 column, removes the need for column regeneration, and minimizes run times, thus allowing PGC columns to be used to their full potential.

Abstract A123: Preclinical evaluation of dual mTOR inhibitor, AZD2014, in prostate cancer

Background: An estimated 220,800 cases and 27,540 deaths from prostate cancer (PCa) will occur in the USA during 2015. Altered PI3K/AKT/mTOR signalling contributes to prostate cancer progression and transition to androgen-independent disease, for example one study reported 42% of primary and 100% of metastatic PCa tumours exhibited mutations, altered expression or copy number variations within this pathway. First generation mTOR inhibitors (preferentially inhibit mTORC1), have had limited anti-cancer effect in patients with PCa, possibly due to negative feedback activation of the AKT pathway via mTORC2. The dual mTORC1/2 inhibitor, AZD2014, may overcome this liability. Using a genetically engineered PTEN conditional mouse model (Ptenloxp/loxp;PB-Cre4), we have investigated the effects of AZD2014. The studies complement a clinical trial (NCT02064608) of AZD2014, given to men before radical prostatectomy and are timed for when invasive prostate carcinomas develop in the model around 10-14 months prior to onset of resistance to castration through AKT pathway activation. AZD2014, 15mg/kg daily, oral (with or without castration) or vehicle were administered for 14 days.

Results: AZD2014 was well tolerated with no overt toxicity observed. Pharmacokinetic (PK) analysis revealed mean concentrations of 4.4±2.1μM of AZD2014 in the plasma samples collected 4 hours after day 14 dose. AZD2014 alone or combined with castration inhibited mTORC1 and mTORC2 measured by reductions in p4EBP1(Thr37/46) by approximately 48%±27% (p&lt;0.001) and 37%±11% (p&lt;0.001); pS6(Ser235/236) by 74%±43% (p&lt;0.001) and 44%±13% (p&lt;0.001) and pAKT(Ser473) by 36%±8% (p&lt;0.001) and 20%±3% (p&lt;0.01) as compared to vehicle-treated mice. AZD2014 treatment was anti-proliferative; Ki67 was significantly reduced in AZD2014-treated mice (70%±45%, p&lt;0.001) or AZD2014 plus castration (42%±16%, p&lt;0.001). Apoptosis was detected with cleaved caspase 3 and increased by 3.3-fold (p&lt;0.001) in both AZD2014 or AZD2014 plus castration groups and 2-fold (p&lt;0.001) in the castration only group, respectively. In all cases, 10 mice were used in each group and 80-120 randomly chosen images were analysed using Aperio automatic quantitative algorithms. Tumour volumes (ultrasound imaging) were reduced by 51% (p&lt;0.05) comparing AZD2014 plus castration against control. HRMAS 1H NMR spectroscopy was used on tumour tissue to determine changes in metabolites following treatment and identified that the total choline to creatine ratio (t-Cho/Cr) was reduced by 40% in AZD2014-treated mice tumour samples (p&lt;0.05) as compared to control-treated mice.

Conclusions: Short term (14 days) treatment with AZD2014 with or without castration was associated with both pharmacodynamic and anti-tumour effects. The t-Cho/Cr ratio, previously reported as positively correlated with Gleason score in PCa patients, might be, in addition to our standard mTOR PD markers, utilised as a non-invasive biomarker of AZD2014 activity. The primary and phenotypic biomarker effects of monotherapy with AZD2014 in this relevant genetically engineered mouse model of prostate cancer will be compared with paired biopsies from the ongoing exploratory window study in the prostate cancer patients prior to prostatectomy, and may inform potential novel combination approaches that are translatable to the clinic.

Citation Format: Chiranjeevi Sandi, Antonio Ramos-Montoya, Sergio L. Felisbino, Sarah Jurmeister, Basetti Madhu, Karan Wadhwa, John R. Griffiths, Frances M. Richards, Duncan I. Jodrell, David E. Neal, Sabina Cosulich, Barry Davies, Simon Pacey. Preclinical evaluation of dual mTOR inhibitor, AZD2014, in prostate cancer. [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 A123.

An automated fitting procedure and software for dose-response curves with multiphasic features

In cancer pharmacology (and many other areas), most dose-response curves are satisfactorily described by a classical Hill equation (i.e. 4 parameters logistical). Nevertheless, there are instances where the marked presence of more than one point of inflection, or the presence of combined agonist and antagonist effects, prevents straight-forward modelling of the data via a standard Hill equation. Here we propose a modified model and automated fitting procedure to describe dose-response curves with multiphasic features. The resulting general model enables interpreting each phase of the dose-response as an independent dose-dependent process. We developed an algorithm which automatically generates and ranks dose-response models with varying degrees of multiphasic features. The algorithm was implemented in new freely available Dr Fit software (sourceforge.net/projects/drfit/). We show how our approach is successful in describing dose-response curves with multiphasic features. Additionally, we analysed a large cancer cell viability screen involving 11650 dose-response curves. Based on our algorithm, we found that 28% of cases were better described by a multiphasic model than by the Hill model. We thus provide a robust approach to fit dose-response curves with various degrees of complexity, which, together with the provided software implementation, should enable a wide audience to easily process their own data.

CHK1 Inhibition Synergizes with Gemcitabine Initially by Destabilizing the DNA Replication Apparatus

Combining cell-cycle checkpoint kinase inhibitors with the DNA-damaging chemotherapeutic agent gemcitabine offers clinical appeal, with a mechanistic rationale based chiefly on abrogation of gemcitabine-induced G2-M checkpoint activation. However, evidence supporting this mechanistic rationale from chemosensitization studies has not been consistent. Here we report a systematic definition of how pancreatic cancer cells harboring mutant p53 respond to this combination therapy, by combining mathematical models with large-scale quantitative biologic analyses of single cells and cell populations. Notably, we uncovered a dynamic range of mechanistic effects at different ratios of gemcitabine and CHK1 inhibitors. Remarkably, effective synergy was attained even where cells exhibited an apparently functional G2-M surveillance mechanism, as exemplified by a lack of both overt premature CDK1 activation and S-phase mitotic entry. Consistent with these findings, S-G2 duration was extended in treated cells, leading to a definable set of lineage-dependent catastrophic fates. At synergistic drug concentrations, global replication stress was a distinct indicator of chemosensitization as characterized molecularly by an accumulation of S-phase cells with high levels of hyperphosphorylated RPA-loaded single-stranded DNA. In a fraction of these cells, persistent genomic damage was observed, including chromosomal fragmentation with a loss of centromeric regions that prevented proper kinetochore-microtubule attachment. Together, our results suggested a "foot-in-the-door" mechanism for drug synergy where cells were destroyed not by frank G2-M phase abrogation but rather by initiating a cumulative genotoxicity that deregulated DNA synthesis.

Abstract 2540: A new mathematical model and software, to enable improved quantification and interpretation of combinatorial drug effects

Drug combinations are used commonly to treat patients with cancer. Combination studies are conducted in vitro, to support advancement to in vivo and/or clinical research. In order to interpret in vitro data, mathematical models and numerical methods are used to quantify degrees of drug synergism. Several traditional approaches exist but they have been questioned with regard to how resulting synergy or antagonism levels should be interpreted. Our aim was to develop a robust method to analyse in vitro drug combination data, avoiding the issues related to traditional models and methods. To facilitate its implementation, software to enable rigorous and systematic assessment of combinations in vitro was also developed. We have derived a new mathematical model to identify synergy distributions based on drug combination dose response surfaces. Our new model and the classical Bliss, Loewe and HSA models were incorporated into the newly developed Combenefit software. Combenefit enables systematic quantification of high-throughput screening data, incorporating statistical assessment, metrics to describe synergy distributions and advanced graphical visualisation. Using multiple simulations of combination data with expected outcomes, our approach showed that it always provided appropriate evaluation while classical models failed to do so. We showed how our new model is in principle better aligned with in vivo requirements of identifying combinations which provide improvements compared to single agents. We then proceeded to analyse a large high-throughput combination screen. We first demonstrated that dataset assessment is strongly model-sensitive. We then demonstrated that our new model identified the best combinations in terms of dose response, thus confirming our simulated cases. Therefore, we have developed a new mathematical model that solves fundamental issues of model relevance that are encountered with classical models in the context of drug combinations. The newly developed Combenefit software enables easily performing rigorous and systematic quantification of in vitro combinations based on this novel approach. (Combenefit is freely available on our institutional website http://www.cruk.cam.ac.uk/combenefit). The resulting procedure is robust and better aligned with our perception of in vivo requirements.

Citation Format: Giovanni Y. Di Veroli, Duncan I. Jodrell, Frances M. Richards, Ian Goldlust. A new mathematical model and software, to enable improved quantification and interpretation of combinatorial drug effects. [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 2540. doi:10.1158/1538-7445.AM2015-2540

Abstract 3497: Mechanism-based scheduling of triple therapy gemcitabine/CHK1i/WEE1i in pancreatic cancer at submaximal yet synergistic concentrations

Sensitization of cancer cells to gemcitabine has been shown with checkpoint kinase CHK1 and WEE1 inhibitors. To rationalize and optimize the concomitant use of these three agents, we first performed growth inhibition assays on MIA PaCa-2 pancreatic cancer cells using gemcitabine in combination with either CHIR-124 (CHK1 inhibitor) or MK-1775 (WEE1 inhibitor). In silico analysis with three mathematical models (Bliss Independence, Loewe and Highest Single Agent) identified synergistic growth inhibition at submaximal (i.e. &lt;GI50) concentrations of the single agents (10nM gemcitabine, 20nM CHIR-124, 300nM MK-1775) in MIA PaCa-2 cells. At these concentrations of gemcitabine+CHIR-124, quantitative image-based cytometry demonstrated S-phase redistribution, with 31% of &gt;8000 individual cells undergoing extensive fork collapse (compared to 0-1% with single agents) as evidenced by co-staining of yH2AX and hyper-phosphorylated RPA32. Conversely, submaximal gemcitabine+MK-1775 induced clear reduction of inhibitory CDK1 Y15 level compared to single agents. Consistent with this G2/M abrogation, in a Fucci-based CDT1/geminin-expressing MIA PaCa-2 stable cell line, gemcitabine+MK-1775 partially reversed the accumulation of the geminin-expressing (S/G2) population induced by gemcitabine alone. This was accompanied by an increase in the CDT1-expressing (G1) population, alongside aberrant mitotic cells with features of perturbed kinetochore-microtubule integrity. Based on these findings, we performed a series of long-term, kinetic live-cell imaging assays to determine the optimal scheduling for gemcitabine/CHK1i/WEE1i as a triplet at synergistic concentrations. In contrast to the widely proposed scheduling regimen, we found that delayed administration of CHK1i (at 24 hours), relative to gemcitabine, did not lead to synergy. However, concurrent administration yielded durable growth inhibition, even when the two agents were removed after 24 hours. This inhibition was further enhanced with the subsequent addition of WEE1i at 24 hours, but not continuation of a CHK1i. Together, our results illustrate differential mechanistic effects of CHK1 and WEE1 inhibitors with gemcitabine, when combined at sub-GI50 concentrations, and propose a novel triple agent schedule that will be evaluated in vivo.

Citation Format: Siang-Boon Koh, Frances M. Richards, Esther Rodriguez, Scott K. Lyons, Duncan I. Jodrell. Mechanism-based scheduling of triple therapy gemcitabine/CHK1i/WEE1i in pancreatic cancer at submaximal yet synergistic concentrations. [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 3497. doi:10.1158/1538-7445.AM2015-3497

The EGFR demonstrates linear signal transmission

Cells sense information encoded in extracellular ligand concentrations and process it using intracellular signalling cascades. Using mathematical modelling and high-throughput imaging of individual cells, we studied how a transient extracellular growth factor signal is sensed by the epidermal growth factor receptor system, processed by downstream signalling, and transmitted to the nucleus. We found that transient epidermal growth factor signals are linearly translated into an activated epidermal growth factor receptor integrated over time. This allows us to generate a simplified model of receptor signaling where the receptor acts as a perfect sensor of extracellular information, while the nonlinear input-output relationship of EGF-EGFR triggered signalling is a consequence of the downstream MAPK cascade alone.

Gemcitabine diphosphate choline is a major metabolite linked to the Kennedy pathway in pancreatic cancer models in vivo

BACKGROUND

The modest benefits of gemcitabine (dFdC) therapy in patients with pancreatic ductal adenocarcinoma (PDAC) are well documented, with drug delivery and metabolic lability cited as important contributing factors. We have used a mouse model of PDAC: KRAS(G12D); p53(R172H); pdx-Cre (KPC) that recapitulates the human disease to study dFdC intra-tumoural metabolism.

METHODS

LC-MS/MS and NMR were used to measure drug and physiological analytes. Cytotoxicity was assessed by the Sulphorhodamine B assay.

RESULTS

In KPC tumour tissue, we identified a new, Kennedy pathway-linked dFdC metabolite (gemcitabine diphosphate choline (GdPC)) present at equimolar amounts to its precursor, the accepted active metabolite gemcitabine triphosphate (dFdCTP). Utilising additional subcutaneous PDAC tumour models, we demonstrated an inverse correlation between GdPC/dFdCTP ratios and cytidine triphosphate (CTP). In tumour homogenates in vitro, CTP inhibited GdPC formation from dFdCTP, indicating competition between CTP and dFdCTP for CTP:phosphocholine cytidylyltransferase (CCT). As the structure of GdPC precludes entry into cells, potential cytotoxicity was assessed by stimulating CCT activity using linoleate in KPC cells in vitro, leading to increased GdPC concentration and synergistic growth inhibition after dFdC addition.

CONCLUSIONS

GdPC is an important element of the intra-tumoural dFdC metabolic pathway in vivo.

SPARC independent drug delivery and antitumour effects of nab-paclitaxel in genetically engineered mice

DESIGN

Pharmacokinetic and pharmacodynamic parameters of cremophor-paclitaxel, nab-paclitaxel (human-albumin-bound paclitaxel, Abraxane) and a novel mouse-albumin-bound paclitaxel (m-nab-paclitaxel) were evaluated in genetically engineered mouse models (GEMMs) by liquid chromatography-tandem mass spectrometry (LC-MS/MS), histological and biochemical analysis. Preclinical evaluation of m-nab-paclitaxel included assessment by three-dimensional high-resolution ultrasound and molecular analysis in a novel secreted protein acidic and rich in cysteine (SPARC)-deficient GEMM of pancreatic ductal adenocarcinoma (PDA).

RESULTS

nab-Paclitaxel exerted its antitumoural effects in a dose-dependent manner and was associated with less toxicity compared with cremophor-paclitaxel. SPARC nullizygosity in a GEMM of PDA, Kras(G12D);p53(flox/-);p48Cre (KPfC), resulted in desmoplastic ductal pancreas tumours with impaired collagen maturation. Paclitaxel concentrations were significantly decreased in SPARC null plasma samples and tissues when administered as low-dose m-nab-paclitaxel. At the maximally tolerated dose, SPARC deficiency did not affect the intratumoural paclitaxel concentration, stromal deposition and the immediate therapeutic response.

CONCLUSIONS

nab-Paclitaxel accumulates and acts in a dose-dependent manner. The interaction of plasma SPARC and albumin-bound drugs is observed at low doses of nab-paclitaxel but is saturated at therapeutic doses in murine tumours. Thus, this study provides important information for future preclinical and clinical trials in PDA using nab-paclitaxel in combination with novel experimental and targeted agents.

Abstract B96: Design, synthesis and biological evaluation of a novel allosteric inhibitor of HSET that damages cancer cells with supernumerary centrosomes

Almost a century ago Theodor Boveri suggested that tumor cells differ from normal cells in their high incidence of centrosome amplification. However, only recently have new therapeutic strategies been explored in an attempt to exploit these differences and the role of kinesins in mitosis. Intense interest in the field has led to development of KSP and CENP-E inhibitors that have been tested clinically as treatments for human cancer. Success has been limited because both motor proteins are essential to normal mitosis and inhibition leads to mitotic arrest and associated neutropenia toxicity in normal cells. In contrast HSET is essential for survival of cancer cells with centrosome amplification and has been shown to be dispensable in normal cells. Hence, HSET inhibition offers a unique opportunity to selectively damage malignant cells with supernumerary centrosomes without affecting normal cells. In keeping with these findings we report discovery of a novel allosteric inhibitor of HSET, CW069, that does not disrupt division in normal human fibroblast cells, or in MCF-7 cells with normal centrosome numbers. In fact, CW069 induces multipolar mitosis exclusively in cancer cells with extra centrosomes, causing apoptosis via catastrophic aneuploidy. The increased multipolar mitoses induced in N1E-115 cells by inhibitor CW069 recapitulates the phenotype described here, and by others, for siRNA depletion of HSET. The inhibitor also reduces cell growth and centrosome clustering in cancer cells with a lower incidence of centrosome amplification, including BT549 and MDA-MB-231 breast cancer cells. This is consistent with recent reports that depletion of HSET in DNA damage repair deficient cells may be lethal even to cancer cells with low-level centrosome amplification. Taken together, these data indicate that CW069 inhibition of HSET is not restricted to use in N1E-115 cells with high centrosome amplification, and could be broadly applicable to a range of human cancers. What is more, CW069 does not decrease the clonogenic capacity of primary adult human bone marrow cells, suggesting that it would not cause neutropenia toxicity in normal cells.

It is anticipated that HSET inhibition could have a greater therapeutic margin than KSP or CENP-E inhibition, and, to the best of our knowledge we have described the first allosteric inhibitor of HSET that reduces centrosome clustering but does not induce the mitotic phenotypes associated with inhibition of KSP or CENP-E. This selectivity for HSET is consistent with our computational model, which indicates that the HSET loop 5 displays dynamic conformational selection for CW069 that cannot be achieved by closely related KSP.

In summary, CW069 not only represents a substantial advance toward new cancer therapeutics, but also offers researchers a unique tool to unveil the full details of HSET function in mitosis.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B96.

Citation Format: Ciorsdaidh A. Watts, Frances M. Richards, Andreas Bender, Peter J. Bond, Oliver Korb, Oliver Kern, Michelle Riddick, Paul Owen, Rebecca M. Myers, Jordan Raff, Fanni Gergely, Duncan I. Jodrell, Steven V. Ley. Design, synthesis and biological evaluation of a novel allosteric inhibitor of HSET that damages cancer cells with supernumerary centrosomes. [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 B96.

Anti-tumour efficacy of capecitabine in a genetically engineered mouse model of pancreatic cancer

Capecitabine (CAP) is a 5-FU pro-drug approved for the treatment of several cancers and it is used in combination with gemcitabine (GEM) in the treatment of patients with pancreatic adenocarcinoma (PDAC). However, limited pre-clinical data of the effects of CAP in PDAC are available to support the use of the GEMCAP combination in clinic. Therefore, we investigated the pharmacokinetics and the efficacy of CAP as a single agent first and then in combination with GEM to assess the utility of the GEMCAP therapy in clinic. Using a model of spontaneous PDAC occurring in Kras(G12D); p53(R172H); Pdx1-Cre (KPC) mice and subcutaneous allografts of a KPC PDAC-derived cell line (K8484), we showed that CAP achieved tumour concentrations (∼25 µM) of 5-FU in both models, as a single agent, and induced survival similar to GEM in KPC mice, suggesting similar efficacy. In vitro studies performed in K8484 cells as well as in human pancreatic cell lines showed an additive effect of the GEMCAP combination however, it increased toxicity in vivo and no benefit of a tolerable GEMCAP combination was identified in the allograft model when compared to GEM alone. Our work provides pre-clinical evidence of 5-FU delivery to tumours and anti-tumour efficacy following oral CAP administration that was similar to effects of GEM. Nevertheless, the GEMCAP combination does not improve the therapeutic index compared to GEM alone. These data suggest that CAP could be considered as an alternative to GEM in future, rationally designed, combination treatment strategies for advanced pancreatic cancer.

Paclitaxel and CYC3, an aurora kinase A inhibitor, synergise in pancreatic cancer cells but not bone marrow precursor cells

BACKGROUND

Amplification of aurora kinase A (AK-A) overrides the mitotic spindle assembly checkpoint, inducing resistance to taxanes. RNA interference targeting AK-A in human pancreatic cancer cell lines enhanced taxane chemosensitivity. In this study, a novel AK-A inhibitor, CYC3, was investigated in pancreatic cancer cell lines, in combination with paclitaxel.

METHODS

Western blot, flow cytometry and immunostaining were used to investigate the specificity of CYC3. Sulforhodamine B staining, time-lapse microscopy and colony-formation assays were employed to evaluate the cytotoxic effect of CYC3 and paclitaxel. Human colony-forming unit of granulocyte and macrophage (CFU-GM) cells were used to compare the effect in tumour and normal tissue.

RESULTS

CYC3 was shown to be a specific AK-A inhibitor. Three nanomolar paclitaxel (growth inhibition 50% (GI(50)) 3 nM in PANC-1, 5.1 nM in MIA PaCa-2) in combination with 1 μM CYC3 (GI(50) 1.1 μM in MIA PaCa2 and 2 μM in PANC-1) was synergistic in inhibiting pancreatic cell growth and causing mitotic arrest, achieving similar effects to 10-fold higher concentrations of paclitaxel (30 nM). In CFU-GM cells, the effect of the combination was simply additive, displaying significantly less myelotoxicity compared with high concentrations of paclitaxel (30 nM; 60-70% vs 100% inhibition).

CONCLUSION

The combination of lower doses of paclitaxel and CYC3 merits further investigation with the potential for an improved therapeutic index in vivo.

Anti-tumour effects of a specific anti-ADAM17 antibody in an ovarian cancer model in vivo

ADAM 17 (TNF-α converting enzyme, TACE) is a potential target for cancer therapy, but the small molecule inhibitors reported to date are not specific to this ADAM family member. This membrane-bound metalloproteinase is responsible for ectodomain shedding of pathologically significant substrates including TNF-α and EGFR ligands. The aim of this study was to evaluate the pharmacokinetics, pharmacodynamics and anti-tumour efficacy of the first specific inhibitor, an anti-human ADAM17 IgG antibody, clone D1(A12). We used intraperitoneal xenografts of the human ovarian cancer cell line IGROV1-Luc in Balb/c nude mice, chosen because it was previously reported that growth of these xenografts is inhibited by knock-down of TNF-α. In vitro, 200 nM D1(A12) inhibited shedding of ADAM17 substrates TNF-α, TNFR1-α, TGF-α, amphiregulin (AREG), HB-EGF and IL-6Rα, from IGROV1-Luc cells, (4.7 nM IC(50) for TNF-α shedding). In IGROV1-Luc xenografts in vivo, D1(A12) IgG showed pharmacokinetic properties suitable for efficacy studies, with a single i.p. dose of 10 mg/kg D1(A12) sufficient to maintain IgG plasma and ascites fluid concentrations above 100 nM for more than 7 days. The plasma half life was 8.6 days. Next, an efficacy study was performed, dosing D1(A12) or anti-human TNF-α antibody infliximab at 10 mg/kg q7d, quantifying IGROV1-Luc tumour burden by bioluminescence. D1(A12) IgG showed a significant reduction in tumour growth (p = 0.005), 56% of vehicle control. Surprisingly, D1(A12) did not reduce the concentration of circulating human TNF-α, suggesting that another enzyme may compensate for inhibition of ADAM17 in vivo (but not in vitro). However, D1(A12) did show clear pharmacodynamic effects in the mice, with significant inhibition of shedding from tumour of ADAM17 substrates TNFR1-α, AREG, and TGF-α (4-15-fold reductions, p<0.0001 for all three). Thus, D1(A12) has anti-ADAM17 activity in vivo, inhibits shedding of EGFR ligands and has potential for use in EGF ligand-dependent tumours.

Abstract 2724: Activity of the specific anti-ADAM17 inhibitory IgG antibody (Ab), D1(A12) in an ovarian cancer model in vivo

ADAM17 (TNF-α converting enzyme, TACE) is a membrane-bound metalloproteinase responsible for ectodomain shedding of TNF-α, EGFR ligands and other pathologically significant proteins. ADAM17 overexpression is reported in many cancers, with roles in cancer cell proliferation, migration and drug resistance. Small molecule inhibitors of ADAM17 lack specificity, so we developed a specific human ADAM17 inhibitory IgG Ab, D1(A12), which inhibits the proteolysis of ADAM17 substrates (TNF-α, amphiregulin, etc.,) in cancer cells in vitro (C.J. Tape, et al., Proc Natl Acad Sci USA 108: 5578-83, 2011). We have now assessed the suitability of the D1(A12) Ab for therapeutic use, by investigating its pharmacokinetics (PK), pharmacodynamics (PD) and anti-tumour efficacy in mice. The IGROV1-Luc xenograft model of intraperitoneal (i.p.) disseminated ovarian carcinoma in nude mice was used, as IGROV1-Luc cells secrete TNF-α and other ADAM17 products and knockdown of TNF-α expression inhibits tumour growth (H. Kulbe, et al., Cancer Res., 67: 585- 592, 2007). We investigated the PK of D1(A12) Ab using a single 10 mg/kg dose i.p., first in non-tumour-bearing (NTB) mice and then in mice bearing IGROV1-Luc tumours, measuring the concentration of D1(A12) IgG in plasma and ascitic fluid by ELISA. In NTB mice, plasma Cmax was 512 nM, half life 8.6 days. The concentrations in tumour-bearing mice were expected to be lower due to a larger volume of distribution due to the ascitic fluid, and in tumour-bearing mice the Cmax was 425 nM in plasma and 391 nM in ascitic fluid. The PK data suggest that weekly dosing with 10 mg/kg D1(A12) maintains therapeutically active concentrations of the IgG, so this regimen was used for an efficacy study comparing D1(A12) with vehicle. D1(A12) showed clear PD effects: Ascitic fluid concentrations of 3 ADAM17 products were reduced when compared to vehicle: AREG (55 +/− 19 vs 302 +/− 37 pg/ml, p &lt; 0.001), soluble hTNFR1α (479 +/− 100 vs 2108 +/− 204 pg/ml, p &lt; 0.001) and TGF-β (0.35 +/− 0.67 vs 5.2 +/− 2.2 pg/ml, p = 0.002), indicative of inhibition of ADAM17 activity in vivo. However, D1(A12) did not significantly reduce the concentration of TNF-α in ascitic fluid (109 +/− 21 vs 134 +/−32 pg/ml, p = 0.06), suggesting that in this system ADAM17 is not the only metalloproteinase with TACE activity. Tumour burden was quantified using bioluminescence generated from the luciferase expressing cells, measured using an IVIS xenogen 200 imager. There was decreased tumour growth in the D1(A12)-treated group (compared to vehicle), although this did not reach statistical significance (p=0.09). In conclusion we have shown that the anti-ADAM17 antibody has PK properties suitable for therapeutic studies and that it can inhibit shedding of ADAM17-dependent growth factors in vivo.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2724. doi:1538-7445.AM2012-2724

Abstract 3771: Capecitabine pharmacokinetics and efficacy in spontaneous tumors occurring in a genetically engineered mouse model (GEMM) of pancreatic cancer

Capecitabine (CAP) is an oral fluoropyrimidine, converted sequentially and selectively to 5-FU at the tumour site. It is used in the treatment of a number of cancers as a single agent and in patients with pancreatic cancer, in combination with gemcitabine. However, pre-clinical data in pancreatic cancer models are limited. In this study, we investigated the pharmacokinetics (PK) and efficacy of CAP in a GEMM of spontaneous pancreatic adenocarcinoma (PDA) occurring in KrasG12D; p53R172H; Pdx1-Cre (KPC) mice, compared to an allograft model of a cell line isolated from a PDA arising in the KPC mice. In the PK study, tumour was collected 2 hours after CAP treatment (755 mg/kg by oral gavage), homogenates were analysed using an LC-MS/MS assay developed to simultaneously detect capecitabine and its 3 metabolites DFCR, DFUR and 5-FU (modified from S.M.Guichard, et al., J. Chrom. B. 2005). Data were compared to our previously reported studies in an allograft model (Proc. AACR 2011 a 5446). After a QDx7 treatment, 5-FU concentrations of 27 ± 13 μM were achieved (compared to 23.0 ± 8.1 μM and 22.7 ± 7.7 μM in allograft tumours after 1 and 5 consecutive doses respectively), confirming adequate drug delivery to the in situ tumour following oral administration of CAP. Therefore we proceeded to efficacy studies in this model. In the allograft model we had identified a significant reduction of the tumour doubling time with 755 mg/kg CAP (5 days/week, 3 weeks), compared to control (7.5 ± 3.0 vs 3.5 ± 0.5 days; P&lt;0.001). In in situ tumours, a short term study over 7 days showed a reduction in tumour growth in CAP-treated KPC PDA tumours compared to control (199% ± 22% vs 121% ± 10%; P&lt;0.01). In a survival study in KPC mice, CAP (755 mg/kg, 5 days/week) was compared to the standard treatment for advanced pancreatic cancer, gemcitabine (GEM, 100 mg/kg, Q3D), and there was no difference in the median survival of mice with spontaneous PDA tumours (P=0.61) suggesting a similar efficacy of CAP to GEM. There is conflicting evidence regarding the utility of the combination of GEM and CAP in this disease, so we also investigated the combination in mice bearing allograft PDA tumours. Full doses of both drugs were not tolerated, but the combination of GEM (75 mg/kg Q3D, 2 weeks) plus CAP (539 mg/kg, 5 days/week, 2 weeks) was feasible. This regimen was associated with significant growth inhibition, but this was not superior to GEM alone (75 mg/kg) at the same dose (tumour doubling time: 8.6 ± 10.8 vs 7.2 ± 2.8 days respectively). In summary, orally administered CAP achieves active concentrations of 5-FU in PDA tumours. Similar effects on survival compared to GEM are seen in PDA tumours. Growth inhibition data in allograft tumours did not show any additional benefit for the GEMCAP combination, when compared to GEM alone. CAP could be considered as an alternative to GEM in future, rationally designed, combination treatment strategies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3771. doi:1538-7445.AM2012-3771

A novel method for quantification of gemcitabine and its metabolites 2',2'-difluorodeoxyuridine and gemcitabine triphosphate in tumour tissue by LC-MS/MS: comparison with (19)F NMR spectroscopy

PURPOSE

To develop a sensitive analytical method to quantify gemcitabine (2',2'-difluorodeoxycytidine, dFdC) and its metabolites 2',2'-difluorodeoxyuridine (dFdU) and 2',2'-difluorodeoxycytidine-5'-triphosphate (dFdCTP) simultaneously from tumour tissue.

METHODS

Pancreatic ductal adenocarcinoma tumour tissue from genetically engineered mouse models of pancreatic cancer (KP ( FL/FL ) C and KP ( R172H/+) C) was collected after dosing the mice with gemcitabine. (19)F NMR spectroscopy and LC-MS/MS protocols were optimised to detect gemcitabine and its metabolites in homogenates of the tumour tissue.

RESULTS

A (19)F NMR protocol was developed, which was capable of distinguishing the three analytes in tumour homogenates. However, it required at least 100 mg of the tissue in question and a long acquisition time per sample, making it impractical for use in large PK/PD studies or clinical trials. The LC-MS/MS protocol was developed using porous graphitic carbon to separate the analytes, enabling simultaneous detection of all three analytes from as little as 10 mg of tissue, with a sensitivity for dFdCTP of 0.2 ng/mg tissue. Multiple pieces of tissue from single tumours were analysed, showing little intra-tumour variation in the concentrations of dFdC or dFdU (both intra- and extra-cellular). Intra-tumoural variation was observed in the concentration of dFdCTP, an intra-cellular metabolite, which may reflect regions of different cellularity within a tumour.

CONCLUSION

We have developed a sensitive LC-MS/MS method capable of quantifying gemcitabine, dFdU and dFdCTP in pancreatic tumour tissue. The requirement for only 10 mg of tissue enables this protocol to be used to analyse multiple areas from a single tumour and to spare tissue for additional pharmacodynamic assays.

Abstract 5446: The activity and pharmacokinetics of capecitabine in a mouse model (K8484) of pancreatic adenocarcinoma

The pharmacokinetics (PK) of the oral fluoropyrimidine capecitabine were investigated in a mouse model of pancreatic cancer. Allografts of a cell line (K8484) derived from a pancreatic adenocarcinoma which occurred in a KrasG12D; p53R172H; Pdx1-Cre (KPC) mouse (S. Hingorani, et al., Cancer Cell 2005) were grown subcutaneously in left and right flanks of syngeneic immunocompetent recipient mice. Mice were dosed with either a single dose or 5 daily doses of capecitabine at 755 mg/kg (2.1 mmol/kg/day) with tumour volumes of approximately 250 mm3. Plasma and tissue homogenates were analysed using an LC-MS/MS assay developed to simultaneously detect capecitabine and its 3 metabolites DFCR, DFUR and 5-FU (S.M.Guichard, et al., J. Chrom. B. 2005).

Forty minutes after a single dose the mean plasma concentrations (n=3) were 28 +/- 20 mg/ml capecitabine, 78 +/- 48 mg/ml DFCR, 41 +/- 17 mg/ml DFUR and 0.19 +/- 0.07 mg/ml (1.5 µM) 5-FU, with concentrations of all analytes falling at 2 and 4 hours. In the tumour tissue, mean concentrations at 40 mins were capecitabine: 37 +/- 19 ng/mg tissue, DFCR: 56 +/- 12 ng/mg; DFUR: 20 +/- 8 ng/mg and 5-FU: 3.3 +/- 0.7 ng/mg. At 2 and 4 hours the tumour 5-FU concentrations were 3.0 +/- 1.1 and 1.4 +/- 0.6 ng/mg respectively. In the liver, DFCR concentrations were higher than in the tumour from the same mice but DFUR concentrations were lower and 5-FU was below the limit of quantification (&lt;0.4 ng/mg) in most, consistent with the reported distribution of carboxylesterases, cytidine deaminase and thymidine phosphorylase in tissues (M. Miwa, et al., Eur. J. Cancer 1998). In animals dosed for 5 days, there was no evidence of accumulation of capecitabine or its metabolites in tumour tissue when compared to the single dose. The concentration of tumour 5-FU, ranging from 1.4 to 3.3 ng/mg, is estimated to be equivalent to 11 to 25 µM, more than 10-fold higher than the plasma concentration. The IC50 for 5-FU in K8484 cells, grown in vitro, was 1.4 +/- 0.8 µM suggesting that oral dosing with capecitabine delivers a therapeutically effective dose to the allograft. This was then confirmed in an efficacy study, treating tumour-bearing mice with oral capecitabine for 5 days per week for 3 weeks, which resulted in significant inhibition of tumour growth rate compared to the vehicle treated group, with mean tumour doubling time of 7.5 +/- 3.0 days for capecitabine compared to 3.5 +/- 0.5 days for the vehicle treated group (P &lt; 0.001).

Despite identical germline Kras and p53 genotypes, the KPC PDA and KPC allograft tumour types have previously shown differences in gemcitabine sensitivity in vivo, predicted to be due to differences in drug delivery (K. Olive, et al., Science 2009). Therefore, capecitabine PK and efficacy are now being investigated in the autochthonous tumours arising in the KPC model.

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 5446. doi:10.1158/1538-7445.AM2011-5446

Zebrafish based assays for the assessment of cardiac, visual and gut function--potential safety screens for early drug discovery

INTRODUCTION

Safety pharmacology is integral to the non-clinical safety assessment of new chemical entities prior to first administration to humans. The zebrafish is a well established model organism that has been shown to be relevant to the study of human diseases. The potential role of zebrafish in safety pharmacology was evaluated using reference compounds in three models assessing cardiac, visual and intestinal function.

METHODS

Compound toxicity was first established in zebrafish to determine the non toxic concentration of a blinded set of 16 compounds. In the cardiac assay, zebrafish larvae at 3 days post fertilisation (d.p.f.) were exposed to compounds for 3 h before measurement of the atrial and ventricular rates. To investigate visual function, the optomotor response was assessed in 8 d.p.f. larvae following a 5 day compound exposure. In the intestinal function assay, the number of gut contractions was measured in 7 d.p.f. larvae after a 1 h compound exposure. Finally, compound uptake was determined for 9 of the 16 compounds to measure the concentration of compound absorbed by the zebrafish larvae.

RESULTS

Seven compounds out of nine produced an expected effect that was statistically significant in the cardiac and visual functions assays. In the gut contraction assay, six out of ten compounds showed a statistically significant effect that was also the expected result whilst two displayed anticipated but non-significant effects. The compound uptake method was used to determine larval tissue concentrations and allowed the identification of false negatives when compound was poorly absorbed into the zebrafish.

DISCUSSION

Overall, results generated in three zebrafish larvae assays demonstrated a good correlation between the effects of compounds in zebrafish and the data available from other in vivo models or known clinical adverse effects. These results suggest that for the cardiac, intestinal and visual function, zebrafish assays have the potential to predict adverse drug effects and supports their possible role in early safety assessment of novel compounds.

Solvents, interfaces and protein structure

Mean packing densities in protein interiors are comparable to those of most organic solids but the variations between small regions may be substantial. Packing defects may be related to allowed structural fluctuations. Molecular surface areas can be correlated with free energies of transfer between different solvents. The proportionality factor will depend, in general, on the nature of the solute and both the solvents. The changes in solvent-protein interfacial area on chain folding are large and the implied changes in free energy from this solvent-squeezing effect are correspondingly large. The strong tendency to minimize surface area is reflected in the globular shape of most protein molecules or domains in larger structures. The formation of isolated units of secondary structure from an extended chain represents about one half of the eventual total area change. The tendencies of amino acids to form beta-sheets correlate well with the rank-ordered list based on non-polar area change for each residue type. The calculated area changes for helix and sheet formation are not identical in rank order. The rank-ordered list for alpha-helix formation correlates satisfactorily with the probability list prepared from actual structures if glutamic acid and tyrosine are removed. What special characteristics unrelated to surface area these two amino acids might have is not clear. Tertiary structure formation from preformed secondary structural units can be rank ordered on area change and possible nucleation sites can be identified. A prediction scheme for helix-helix interactions is proposed. The hydrophobic force begins to be felt when two helices are about 0.6 nm (6 A) from their final contact positions. Interfacial surface tension is a logical parameter to relate free energy and solvent contact area, but this macroscopic parameter must be used with great caution. It is suggested that water in the deep grooves, characteristic of the active sites of many enzymes, may have a substantially higher fugacity than bulk water as indicated, at least qualitatively, by the Kelvin equation based on surface curvature. Such water would be more easily displaced than its plane surface counterpart and could contribute significantly to ligand-binding energy. This factor would be in addition to the usual solvent entropic effects associated with surface area reduction on association.

GBR12909 Possesses Anticonvulsant Activity in Zebrafish and Rodent Models of Generalized Epilepsy but Cardiac Ion Channel Effects Limit Its Clinical Utility

BACKGROUND/AIMS

GBR12909 has been reported to possess anticonvulsant activity with focal brain perfusion to the hippocampus of pilocarpine, although an earlier publication suggested any anticonvulsant effects were only mild. Here we further explored the anticonvulsant potential of GBR12909 with a suite of anticonvulsant assays in both zebrafish and mammals and then explored whether it possessed any QT effects which might limit clinical utility.

METHODS

We assessed the anticonvulsant effects of GBR12909 in zebrafish pentylenetetrazole (PTZ), mammalian maximal electroshock and PTZ models of generalized epilepsy and a rodent hippocampal kindling model. Cardiac effects were assessed in zebrafish and man.

RESULTS

GBR12909 possesses anticonvulsant activity in zebrafish and rodent models of generalized epilepsy. However, phase 1 human data indicated potential QT effects. Subsequent testing in a zebrafish QT assay confirmed marked arrhythmogenic potential.

CONCLUSION

Further clinical development of GBR12909 in epilepsy was considered inappropriate because of insufficient window between the therapeutic effects and the cardiac arrhythmia problems identified in zebrafish assays. Any further development based on this mechanism of action should avoid the GBR12909 chemical scaffold, or involve structure-activity dissociation of its neurological and cardiac effects.

Identification of novel VHL targets that are associated with the development of renal cell carcinoma

von Hippel-Lindau (VHL) disease is a dominantly inherited family cancer syndrome characterized by the development of retinal and central nervous system haemangioblastomas, renal cell carcinoma (RCC) and phaeochromocytoma. Specific germline VHL mutations may predispose to haemangioblastomas, RCC and phaeochromocytoma to a varying extent. Although dysregulation of the hypoxia-inducible transcription factor-2 and JunB have been linked to the development of RCC and phaeochromocytoma, respectively, the precise basis for genotype-phenotype correlations in VHL disease have not been defined. To gain insights into the pathogenesis of RCC in VHL disease we compared gene expression microarray profiles in a RCC cell line expressing a Type 1 or Type 2B mutant pVHL (RCC-associated) to those of a Type 2A or 2C mutant (not associated with RCC). We identified 19 differentially expressed novel VHL target genes linked to RCC development. Eight targets were studied in detail by quantitative real-time polymerase chain reaction (three downregulated and five upregulated by wild-type VHL) and for six genes the effect of VHL inactivation was mimicked by hypoxia (but hypoxic-induction of smooth muscle alpha-actin 2 was specific for a RCC cell line). The potential role of four RCC-associated VHL target genes was assessed in vitro. NB thymosin beta (TMSNB) and proteinase-activated receptor 2 (PAR2) (both downregulated by wt pVHL) increased cell growth and motility in a RCC cell line, but aldehyde dehydrogenase (ALDH)1 and ALDH7 had no effect. These findings implicate TMSNB and PAR2 candidate oncogenes in the pathogenesis of VHL-associated RCC.