Tracing Nutrient Flux Following Monocarboxylate Transporter-1 Inhibition with AZD3965

The monocarboxylate transporter 1 (MCT1) is a key element in tumor cell metabolism and inhibition of MCT1 with AZD3965 is undergoing clinical trials. We aimed to investigate nutrient fluxes associated with MCT1 inhibition by AZD3965 to identify possible biomarkers of drug action. We synthesized an 18F-labeled lactate analogue, [18F]-S-fluorolactate ([18F]-S-FL), that was used alongside [18F]fluorodeoxyglucose ([18F]FDG), and 13C-labeled glucose and lactate, to investigate the modulation of metabolism with AZD3965 in diffuse large B-cell lymphoma models in NOD/SCID mice. Comparative analysis of glucose and lactate-based probes showed a preference for glycolytic metabolism in vitro, whereas in vivo, both glucose and lactate were used as metabolic fuel. While intratumoral L-[1-13C]lactate and [18F]-S-FL were unchanged or lower at early (5 or 30 min) timepoints, these variables were higher compared to vehicle controls at 4 h following treatment with AZD3965, which indicates that inhibition of MCT1-mediated lactate import is reversed over time. Nonetheless, AZD3965 treatment impaired DLBCL tumor growth in mice. This was hypothesized to be a consequence of metabolic strain, as AZD3965 treatment showed a reduction in glycolytic intermediates and inhibition of the TCA cycle likely due to downregulated PDH activity. Glucose ([18F]FDG and D-[13C6]glucose) and lactate-based probes ([18F]-S-FL and L-[1-13C]lactate) can be successfully used as biomarkers for AZD3965 treatment.

Development of Therapeutic Anti-JAGGED1 Antibodies for Cancer Therapy

The role of Notch signaling and its ligand JAGGED1 (JAG1) in tumor biology has been firmly established, making them appealing therapeutic targets for cancer treatment. Here, we report the development and characterization of human/rat-specific JAG1-neutralizing mAbs. Epitope mapping identified their binding to the Notch receptor interaction site within the JAG1 Delta/Serrate/Lag2 domain, where E228D substitution prevented effective binding to the murine Jag1 ortholog. These antibodies were able to specifically inhibit JAG1-Notch binding in vitro, downregulate Notch signaling in cancer cells, and block the heterotypic JAG1-mediated Notch signaling between endothelial and vascular smooth muscle cells. Functionally, in vitro treatment impaired three-dimensional growth of breast cancer cell spheroids, in association with a reduction in cancer stem cell number. In vivo testing showed variable effects on human xenograft growth when only tumor-expressed JAG1 was targeted (mouse models) but a more robust effect when stromal-expressed Jag1 was also targeted (rat MDA-MB-231 xenograft model). Importantly, treatment of established triple receptor-negative breast cancer brain metastasis in rats showed a significant reduction in neoplastic growth. MRI imaging demonstrated that this was associated with a substantial improvement in blood-brain barrier function and tumor perfusion. Lastly, JAG1-targeting antibody treatment did not cause any detectable toxicity, further supporting its clinical potential for cancer therapy.

Depicting Changes in Tumor Biology in Response to Cetuximab Monotherapy or Combination Therapy by Apoptosis and Proliferation Imaging Using 18F-ICMT-11 and 18F-FLT PET

Imaging biomarkers must demonstrate their value in monitoring treatment. Two PET tracers, the caspase-3/7-specific isatin-5-sulfonamide 18F-ICMT-11 (18F-(S)-1-((1-(2-fluoroethyl)-1H-[1,2,3]-triazol-4-yl)methyl)-5-(2(2,4-difluoro-phenoxymethyl)-pyrrolidine-1-sulfonyl)isatin) and 18F-FLT (3'-deoxy-3'-18F-fluorothymidine), were used to detect early treatment-induced changes in tumor biology and determine whether any of these changes indicate a response to cetuximab, administered as monotherapy or combination therapy with gemcitabine. Methods: In mice bearing cetuximab-sensitive H1975 tumors (non-small lung cancer), the effects of single or repeated doses of the antiepidermal growth factor receptor antibody cetuximab (10 mg/kg on day 1 only or on days 1 and 2) or a single dose of gemcitabine (125 mg/kg on day 2) were investigated by 18F-ICMT-11 or 18F-FLT on day 3. Imaging was also performed after 2 doses of cetuximab (days 1 and 2) in mice bearing cetuximab-insensitive HCT116 tumors (colorectal cancer). For imaging-histology comparison, tumors were evaluated for proliferation (Ki-67 and thymidine kinase 1 [TK1]), cell death (cleaved caspase-3 and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling [TUNEL]), and target engagement (epidermal growth factor receptor expression) by immunohistochemistry, immunofluorescence, and immunoblotting, respectively. Tumor and plasma were analyzed for thymidine and gemcitabine metabolites by liquid chromatography-mass spectrometry. Results: Retention of both tracers was sensitive to cetuximab in H1975 tumors. 18F-ICMT-11 uptake and ex vivo cleaved caspase-3 staining notably increased in tumors treated with repeated doses of cetuximab (75%) and combination treatment (46%). Although a single dose of cetuximab was insufficient to induce apoptosis, it did affect proliferation. Significant reductions in tumor 18F-FLT uptake (44%-50%; P < 0.001) induced by cetuximab monotherapy and combination therapy were paralleled by a clear decrease in proliferation (Ki-67 decrease, 72%-95%; P < 0.0001), followed by a marked tumor growth delay. TK1 expression and tumor thymidine concentrations were profoundly reduced. Neither imaging tracer depicted the gemcitabine-induced tumor changes. However, cleaved caspase-3 and Ki-67 staining did not significantly differ after gemcitabine treatment whereas TK1 expression and thymidine concentrations increased. No cetuximab-induced modulation of the imaging tracers or other response markers was detected in the insensitive model of HCT116. Conclusion:18F-ICMT-11 and 18F-FLT are valuable tools to assess cetuximab sensitivity depicting distinct and time-variant aspects of treatment response.

5T4 oncofoetal glycoprotein: an old target for a novel prostate cancer immunotherapy

The tumour-associated antigen 5T4 is an attractive target for cancer immunotherapy. However to date, reported 5T4-specific cellular immune responses induced by various immunisation platforms have been largely weak or non-existent. In the present study, we have evaluated a heterologous prime boost regime based on the simian adenovirus ChAdOx1 and modified vaccinia virus Ankara (MVA) expressing 5T4 for immunogenicity and tumour protective efficacy in a mouse cancer model. Vaccination-induced immune responses were strong, durable and attributable primarily to CD8+ T cells. By comparison, homologous MVA vaccination regimen did not induce detectable 5T4-specific T cell responses. ChAdOx1-MVA vaccinated mice were completely protected against subsequent B16 melanoma challenge, but in therapeutic settings this regime was only modestly effective in delaying tumour outgrowth. Concomitant delivery of the vaccine with monoclonal antibodies (mAbs) targeting immune checkpoint regulators LAG-3, PD-1 or PD-L1 demonstrated that the combination of vaccine with anti PD-1 mAb could significantly delay tumour growth and increase overall survival of tumour-bearing mice. Our findings support a translation of the combinatorial approach based on the heterologous ChAdOx1-MVA vaccination platform with immune checkpoint blockade into the clinic for the treatment of 5T4-positive tumours such as prostate, renal, colorectal, gastric, ovarian, lung cancer and mesothelioma.

Abstract C128: Development of therapeutic anti-Jagged1 monoclonal antibodies

Background: The Notch pathway is an evolutionarily conserved cell-signaling system that plays an important role in both physiologic and pathologic conditions such as embryonic development and cancer. In the latter, Notch signaling has been reported to promote tumor growth by regulating different aspects of tumor biology such as cell survival, proliferation, angiogenesis, and stemness. Because of its importance, targeting of this pathway has been attempted via both small molecules (γ-secretase inhibitors; GSIs) and neutralizing antibodies (against individual Notch receptors or DLL4 ligand) but limitations still hamper the clinical use of such therapeutics, generally due to pathway complexity and toxicities caused by complete pathway inhibition (GSIs). Targeting Notch ligands such as Jagged1 (JAG1), offers the opportunity to selectively block specific elements of the pathway important in tumor biology thus avoiding normal tissue toxicities.

Methods: Structural studies defined a region of JAG1 (DSL + EGF1-3) that bound Notch1, which was used as an immunogen. Using classical hybridoma technology we have generated and subsequently characterised a panel of monoclonal antibodies (mAbs) against the JAG1 ligand, both in vitro (cell signaling and cell biology assays) and in vivo (tumor xenografts in both mice and rats).

Results: Four functional blocking mAbs recognised a unique JAG1 epitope within its DSL domain binding interface with Notch1, effectively blocking ligand-receptor interaction in vitro. Importantly, our mAbs were cross-reactive with rat Jag1 but not the murine orthologue. These were able to inhibit endogenous JAG1-induced signaling in tumor and stromal cells (eg. vascular smooth muscle cells). JAG1 mAb treatment reduced in vitro breast cancer 3D growth, exhibiting reduced expression of important genes such as HES1, IL6 and decreased numbers of cancer stem cells. Treatment did not affect JAG2-induced growth, or signaling mediated by other Notch ligands (eg. DLL4), confirming mAb specificity. Importantly, JAG1 mAb treatment in vivo inhibited Notch signaling and tumor growth in cancer xenograft models in two different host animals. Host body weight, blood tests and histological analysis detected no toxicity.

Conclusions: We generated neutralizing mAbs able to inhibit JAG1-induced signaling both in vitro and in vivo. The ability of JAG1 blockade to impair tumor growth without toxicity indicates it has the potential to make a contribution to the current arsenal of cancer therapeutics. This mAb treatment will be subjected to further in vivo testing, both alone and in combination with other therapeutic approaches, to further expand our knowledge of its clinical potential and mechanism of action.

Funding and conflicts of interest

This work is supported by Cancer Research UK and the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre Programme. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.

We have filed a patent application, WO/2014/111704, claiming therapeutic use of the JAG1 antibodies.

Citation Format: Massimo Masiero, Demin Li, Pat Whiteman, Carol Bentley, Jenny Greig, Tasneem Hassanali, Sarah Watts, Stephen Stribbling, Jenna Yates, Ji-Liang Li, Susan Mary Lea, Penny Ann Handford, Adrian Llewellyn Harris, Alison Hilary Banham. Development of therapeutic anti-Jagged1 monoclonal antibodies. [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 C128.

Abstract B261: A novel small molecule inhibitor of protein kinase D blocks pancreatic cancer growth in vivo

Background: Protein kinase D (PKD) is a novel family of serine-threonine kinase with diverse biological functions including cell proliferation and growth. Pancreatic Cancer (PaCa) is a devastating disease with few therapeutic options. We showed earlier that PKD signaling pathways promote mitogenesis in multiple PaCa cell lines. However, nothing is known about targeting biological functions of PKD in PaCa. Our PKD inhibitor discovery program yielded CRT0066101 that specifically blocks PKD activation.

Aim: The aim of our study was to determine the effects of CRT0066101 in PaCa, both in vitro and in vivo.

Methods and Results: Our immunohistochemical analysis showed that activated PKD (pS916PKD1) is significantly upregulated in PaCa as compared to normal ducts (91% vs 22%; p&lt;0.001). Using Panc-1 as a model system, we demonstrated that CRT0066101 blocked proliferation and BrdU incorporation with an IC50 of 1 µM. We showed that CRT0066101 given orally (80 mg/kg/day) for 4 weeks significantly abrogated growth in a subcutaneous Panc-1 xenograft model (n=8; p&lt;0.01). The expression of activated PKD (pS916PKD1) in the treated tumor explants was significantly inhibited (p&lt;0.05) with peak concentration (12 M) of CRT0066101 achieved within 6 hours of oral administration. Further, we showed that CRT0066101 given orally (80 mg/kg/day) for 21 days in an orthotopic model potently blocked Panc-1 tumor growth (n=7; p&lt;0.01). CRT0066101 significantly reduced Ki-67+ proliferation index (p&lt; 0.01), increased apoptosis (measured by in situ TUNEL assay) of PaCa tumors (p&lt;0.05) and potently abrogated expression of multiple proliferative and pro-survival proteins including Cyclin D1, survivin, Bcl-2, Bcl-xL, activated PKD1 (pS916PKD1), and activated PKD2 (pS876PKD2).

Conclusion: Our results demonstrate for the first time that the PKD-specific small molecule inhibitor CRT0066101 blocks PaCa growth both in vitro and in vivo. Thus, PKD is a novel therapeutic target in PaCa.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B261.

The disposition of allyl isothiocyanate in the rat and mouse

The urine was the major route of excretion of radioactivity (50-80% of dose) following the oral administration (2.5 and 25 mg/kg body weight) of allyl[14C]isothiocyanate (AITC) to male and female Fischer 344 rats and B6C3F1 mice. Smaller amounts were found in the faeces (6-12%) and expired air (3-7%). The major difference between the two species was the greater retention of radioactivity after 4 days within rats (18-24% of dose) when compared with mice (2-5% of dose). Three radioactive components were found in the urine of mice and two in rats. The three components were inorganic thiocyanate, allylthiocarbamoylmercapturic acid and allylthiocarbamoylcysteine in mice, but no cysteine conjugate was found in rat urine. In the mouse, approximately 80% of the 14C was present in the urine as the thiocyanate ion whereas in the rat some 75% was as the mercapturate. This indicates that in the mouse, hydrolysis of AITC was the major metabolic pathway whereas in the rat glutathione conjugation was the major route. A species difference was seen in the amount of [14C]AITC-derived radioactivity present in the whole blood of rats and mice; measurable levels of radioactivity remained within rat blood for a longer time period (up to 240 hr) when compared with mice (96 hr). Examination of the urinary bladders of male and female rats following oral dosing with [14C]AITC showed a sex difference with greater amounts of [14C]AITC and/or its metabolites within the bladder tissue of male rats. This data is discussed in terms of the known species- and sex-specificity of the urinary bladder tumours, which occurred after long-term administration to male rats, but not to female rats or mice of either sex, in a carcinogenicity study conducted by the National Toxicology Program in the USA.