Synthesis of [11C]BIIB104, an α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic-Acid-Positive Allosteric Modulator, and Evaluation of the Bio-Distribution in Non-Human Primate Brains Using Positron Emission Tomography

The aim of this study was to measure the brain penetrance and kinetics of BIIB104, a first-in-class AMPA receptor potentiator developed for cognitive impairment associated with schizophrenia. It was recently halted in phase 2 clinical development, and there are a lack of tools to directly measure AMPA receptor engagement. To achieve this, the drug candidate was radiolabeled with carbon-11, and its brain penetrance and kinetics were measured in non-human primates via dynamic PET scans. Radiolabeling was achieved through a three-step nucleophilic [11C]cyanation reaction in one pot, resulting in the high radioactivity and radiochemical purity (>99%) of [11C]BIIB104. The study found that [11C]BIIB104 entered the non-human primate brains at 4-5% ID at peak, with a homogeneous distribution. However, a mild regional heterogeneity was observed in the thalamus. The lack of conclusive evidence for a change in regional values after BIIB104 dosing suggests that any specific binding component of BIIB104 is negligible compared to the free and non-specific components in the living brain. Overall, the study demonstrated high brain uptake with minor variability in [11C]BIIB104 distribution across various brain regions, its kinetics were consistent with those of passive diffusion, and the dominating components were the free concentration and non-specific binding. This information is valuable for understanding the potential effects and mechanisms of BIIB104 in the brain.

Development of a Novel [11C]CO-Labeled Positron Emission Tomography Radioligand [11C]BIO-1819578 for the Detection of O-GlcNAcase Enzyme Activity

Imaging O-GlcNAcase OGA by positron emission tomography (PET) could provide information on the pathophysiological pathway of neurodegenerative diseases and important information on drug-target engagement and be helpful in dose selection of therapeutic drugs. Our aim was to develop an efficient synthetic method for labeling BIO-1819578 with carbon-11 using ¹¹CO for evaluation of its potential to measure levels of OGA enzyme in non-human primate (NHP) brain using PET. Radiolabeling was achieved in one-pot via a carbon-11 carbonylation reaction using [¹¹C]CO. The detailed regional brain distribution of [¹¹C]BIO-1819578 binding was evaluated using PET measurements in NHPs. Brain radioactivity was measured for 93 min using a high-resolution PET system, and radiometabolites were measured in monkey plasma using gradient radio HPLC. Radiolabeling of [¹¹C]BIO-1819578 was successfully accomplished, and the product was found to be stable at 1 h after formulation. [¹¹C]BIO-1819578 was characterized in the cynomolgus monkey brain where a high brain uptake was found (7 SUV at 4 min). A pronounced pretreatment effect was found, indicating specific binding to OGA enzyme. Radiolabeling of [¹¹C]BIO-1819578 with [¹¹C]CO was successfully accomplished. [¹¹C]BIO-1819578 binds specifically to OGA enzyme. The results suggest that [¹¹C]BIO-1819578 is a potential radioligand for imaging and for measuring target engagement of OGA in the human brain.

Non-invasive Imaging of Antisense Oligonucleotides in the Brain via In Vivo Click Chemistry

PURPOSE

The treatment of complex neurological diseases often requires the administration of large therapeutic drugs, such as antisense oligonucleotide (ASO), by lumbar puncture into the intrathecal space in order to bypass the blood-brain barrier. Despite the growing number of ASOs in clinical development, there are still uncertainties regarding their dosing, primarily around their distribution and kinetics in the brain following intrathecal injection. The challenge of taking measurements within the delicate structures of the central nervous system (CNS) necessitates the use of non-invasive nuclear imaging, such as positron emission tomography (PET). Herein, an emergent strategy known as "pretargeted imaging" is applied to image the distribution of an ASO in the brain by developing a novel PET tracer, [¹⁸F]F-537-Tz. This tracer is able to undergo an in vivo "click" reaction, covalently binding to a trans-cyclooctene conjugated ASO.

PROCEDURES

A novel small molecule tracer for pretargeted PET imaging of ASOs in the CNS is developed and tested in a series of in vitro and in vivo experiments, including biodistribution in rats and non-human primates.

RESULTS

In vitro data and extensive in vivo rat data demonstrated delivery of the tracer to the CNS, and its successful ligation to its ASO target in the brain. In an NHP study, the slow tracer kinetics did not allow for specific binding to be determined by PET.

CONCLUSION

A CNS-penetrant radioligand for pretargeted imaging was successfully demonstrated in a proof-of-concept study in rats, laying the groundwork for further optimization.

Discovery of Phospholipase D Inhibitors with Improved Drug-like Properties and Central Nervous System Penetrance

Phospholipase D (PLD) is a phospholipase enzyme responsible for hydrolyzing phosphatidylcholine into the lipid signaling molecule, phosphatidic acid, and choline. From a therapeutic perspective, PLD has been implicated in human cancer progression as well as a target for neurodegenerative diseases, including Alzheimer's. Moreover, knockdown of PLD rescues the ALS phenotype in multiple Drosophila models of ALS (amyotrophic lateral sclerosis) and displays modest motor benefits in an SOD1 ALS mouse model. To further validate whether inhibiting PLD is beneficial for the treatment of ALS, a brain penetrant small molecule inhibitor with suitable PK properties to test in an ALS animal model is needed. Using a combination of ligand-based drug discovery and structure-based design, a dual PLD1/PLD2 inhibitor was discovered that is single digit nanomolar in the Calu-1 cell assay and has suitable PK properties for in vivo studies. To capture the in vivo measurement of PLD inhibition, a transphosphatidylation pharmacodynamic LC-MS assay was developed, in which a dual PLD1/PLD2 inhibitor was found to reduce PLD activity by 15-20-fold.

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.

The HDAC6 inhibitor C1A modulates autophagy substrates in diverse cancer cells and induces cell death

BACKGROUND

Cytosolic deacetylase histone deacetylase 6 (HDAC6) is involved in the autophagy degradation pathway of malformed proteins, an important survival mechanism in cancer cells. We evaluated modulation of autophagy-related proteins and cell death by the HDAC6-selective inhibitor C1A.

METHODS

Autophagy substrates (light chain-3 (LC-3) and p62 proteins) and endoplasmic reticulum (ER) stress phenotype were determined. Caspase-3/7 activation and cellular proliferation assays were used to assess consequences of autophagy modulation.

RESULTS

C1A potently resolved autophagy substrates induced by 3-methyladenine and chloroquine. The mechanism of autophagy inhibition by HDAC6 genetic knockout or C1A treatment was consistent with abrogation of autophagosome-lysosome fusion, and decrease of Myc protein. C1A alone or combined with the proteasome inhibitor, bortezomib, enhanced cell death in malignant cells, demonstrating the complementary roles of the proteasome and autophagy pathways for clearing malformed proteins. Myc-positive neuroblastoma, KRAS-positive colorectal cancer and multiple myeloma cells showed marked cell growth inhibition in response to HDAC6 inhibitors. Finally, growth of neuroblastoma xenografts was arrested in vivo by single agent C1A, while combination with bortezomib slowed the growth of colorectal cancer xenografts.

CONCLUSIONS

C1A resolves autophagy substrates in malignant cells and induces cell death, warranting its use for in vivo pre-clinical autophagy research.

Targeting autophagy sensitises lung cancer cells to Src family kinase inhibitors

Lung cancer is the main cancer killer in both men and women, mostly due to the rapid development of drug resistant metastatic disease. Here, we evaluate the potential involvement of SRC family kinases (SFK) in lung cancer biology and assess the possible benefits of their inhibition as a therapeutic approach. We demonstrated that various SRC family members, including LYN and LCK, normally expressed solely in hematopoietic cells and neural tissues, are overexpressed and activated in a panel of SCLC and NSCLC cell lines. This was clinically relevant as LYN and FYN are also overexpressed in lung cancer clinical specimens. Moreover, LYN overexpression correlated with decreased patient survival on univariate and multivariate analysis. Dasatinib (BMS-354825), a SRC/ABL inhibitor, effectively blocked SFK activation at nanomolar concentrations which correlated with a significant decrease in cell numbers of multiple lung cancer cell lines. This effect was matched by a decrease in DNA synthesis, but only moderate induction of apoptosis. Indeed, dasatinib as well as PP2, another SFK inhibitor, strongly induced autophagy that likely prevented apoptosis. However, inhibition of this autophagic response induced robust apoptosis and sensitised lung cancer cells to dasatinib in vitro and in vivo. Our results provide an explanation for why dasatinib failed in NSCLC clinical trials. Furthermore, our data suggest that combining SFK inhibitors with autophagy inhibitors could provide a novel therapeutic approach in this disease.

AKT activation controls cell survival in response to HDAC6 inhibition

HDAC6 is emerging as an important therapeutic target for cancer. We investigated mechanisms responsible for survival of tumor cells treated with a HDAC6 inhibitor. Expression of the 20 000 genes examined did not change following HDAC6 treatment in vivo. We found that HDAC6 inhibition led to an increase of AKT activation (P-AKT) in vitro, and genetic knockdown of HDAC6 phenocopied drug-induced AKT activation. The activation of AKT was not observed in PTEN null cells; otherwise, PTEN/PIK3CA expression per se did not predict HDAC6 inhibitor sensitivity. Interestingly, HDAC6 inhibitor treatment led to inactivating phosphorylation of PTEN (P-PTEN Ser380), which likely led to the increased P-AKT in cells that express PTEN. Synergy was observed with phosphatidylinositol 3'-kinases (PI3K) inhibitor treatment in vitro, accompanied by increased caspase 3/7 activity. Furthermore, combination of HDAC6 inhibitor with a PI3K inhibitor caused substantial tumor growth inhibition in vivo compared with either treatment alone, also detectable by Ki-67 immunostaining and (18)F-FLT positron emission tomography (PET). In aggregate AKT activation appears to be a key survival mechanism for HDAC6 inhibitor treatment. Our findings indicate that dual inhibition of HDAC6 and P-AKT may be necessary to substantially inhibit growth of solid tumors.

The novel choline kinase inhibitor ICL-CCIC-0019 reprograms cellular metabolism and inhibits cancer cell growth

The glycerophospholipid phosphatidylcholine is the most abundant phospholipid species of eukaryotic membranes and essential for structural integrity and signaling function of cell membranes required for cancer cell growth. Inhibition of choline kinase alpha (CHKA), the first committed step to phosphatidylcholine synthesis, by the selective small-molecule ICL-CCIC-0019, potently suppressed growth of a panel of 60 cancer cell lines with median GI50 of 1.12 μM and inhibited tumor xenograft growth in mice. ICL-CCIC-0019 decreased phosphocholine levels and the fraction of labeled choline in lipids, and induced G1 arrest, endoplasmic reticulum stress and apoptosis. Changes in phosphocholine cellular levels following treatment could be detected non-invasively in tumor xenografts by [18F]-fluoromethyl-[1,2-2H4]-choline positron emission tomography. Herein, we reveal a previously unappreciated effect of choline metabolism on mitochondria function. Comparative metabolomics demonstrated that phosphatidylcholine pathway inhibition leads to a metabolically stressed phenotype analogous to mitochondria toxin treatment but without reactive oxygen species activation. Drug treatment decreased mitochondria function with associated reduction of citrate synthase expression and AMPK activation. Glucose and acetate uptake were increased in an attempt to overcome the metabolic stress. This study indicates that choline pathway pharmacological inhibition critically affects the metabolic function of the cell beyond reduced synthesis of phospholipids.

Design, synthesis and initial characterisation of a radiolabelled [(18)F]pyrimidoindolone probe for detecting activated caspase-3/7

Evasion of apoptosis is one of the six initially proposed hallmarks of cancer, and as such, a method to detect apoptosis in a tumour would be of considerable interest in both clinical trials of new cancer therapeutics, as well as for routine patient management. Activation of caspase-3/7 is a key biomarker of cellular apoptosis. Herein we describe the design, synthesis and initial characterisation of the first pyrimidoindolone compound for detection of caspase-3/7 activation using positron emission tomography.

Preclinical evaluation of 3-18F-fluoro-2,2-dimethylpropionic acid as an imaging agent for tumor detection

Deregulated cellular metabolism is a hallmark of many cancers. In addition to increased glycolytic flux, exploited for cancer imaging with (18)F-FDG, tumor cells display aberrant lipid metabolism. Pivalic acid is a short-chain, branched carboxylic acid used to increase oral bioavailability of prodrugs. After prodrug hydrolysis, pivalic acid undergoes intracellular metabolism via the fatty acid oxidation pathway. We have designed a new probe, 3-(18)F-fluoro-2,2-dimethylpropionic acid, also called (18)F-fluoro-pivalic acid ((18)F-FPIA), for the imaging of aberrant lipid metabolism and cancer detection.

METHODS

Cell intrinsic uptake of (18)F-FPIA was measured in murine EMT6 breast adenocarcinoma cells. In vivo dynamic imaging, time course biodistribution, and radiotracer stability testing were performed. (18)F-FPIA tumor retention was further compared in vivo to (18)F-FDG uptake in several xenograft models and inflammatory tissue.

RESULTS

(18)F-FPIA rapidly accumulated in EMT6 breast cancer cells, with retention of intracellular radioactivity predicted to occur via a putative (18)F-FPIA carnitine-ester. The radiotracer was metabolically stable to degradation in mice. In vivo imaging of implanted EMT6 murine and BT474 human breast adenocarcinoma cells by (18)F-FPIA PET showed rapid and extensive tumor localization, reaching 9.1% ± 0.5% and 7.6% ± 1.2% injected dose/g, respectively, at 60 min after injection. Substantial uptake in the cortex of the kidney was seen, with clearance primarily via urinary excretion. Regarding diagnostic utility, uptake of (18)F-FPIA was comparable to that of (18)F-FDG in EMT6 tumors but superior in the DU145 human prostate cancer model (54% higher uptake; P = 0.002). Furthermore, compared with (18)F-FDG, (18)F-FPIA had lower normal-brain uptake resulting in a superior tumor-to-brain ratio (2.5 vs. 1.3 in subcutaneously implanted U87 human glioma tumors; P = 0.001), predicting higher contrast for brain cancer imaging. Both radiotracers showed increased localization in inflammatory tissue.

CONCLUSION

(18)F-FPIA shows promise as an imaging agent for cancer detection and warrants further investigation.

Positron emission tomography imaging with 18F-labeled ZHER2:2891 affibody for detection of HER2 expression and pharmacodynamic response to HER2-modulating therapies

PURPOSE

Expression of HER2 has profound implications on treatment strategies in various types of cancer. We investigated the specificity of radiolabeled HER2-targeting ZHER2:2891 Affibody, [(18)F]GE-226, for positron emission tomography (PET) imaging.

EXPERIMENTAL DESIGN

Intrinsic cellular [(18)F]GE-226 uptake and tumor-specific tracer binding were assessed in cells and xenografts with and without drug treatment. Specificity was further determined by comparing tumor localization of a fluorescently labeled analogue with DAKO HercepTest.

RESULTS

[(18)F]GE-226 uptake was 11- to 67-fold higher in 10 HER2-positive versus HER2-negative cell lines in vitro independent of lineage. Uptake in HER2-positive xenografts was rapid with net irreversible binding kinetics making possible the distinction of HER2-negative [MCF7 and MCF7-p95HER2: NUV60 (%ID/mL) 6.1 ± 0.7; Ki (mL/cm(3)/min) 0.0069 ± 0.0014] from HER2-positive tumors (NUV60 and Ki: MCF7-HER2, 10.9 ± 1.5 and 0.015 ± 0.0035; MDA-MB-361, 18.2 ± 3.4 and 0.025 ± 0.0052; SKOV-3, 18.7 ± 2.4 and 0.036 ± 0.0065) within 1 hour. Tumor uptake correlated with HER2 expression determined by ELISA (r(2) = 0.78), and a fluorophore-labeled tracer analogue colocalized with HER2 expression. Tracer uptake was not influenced by short-term or continuous treatment with trastuzumab in keeping with differential epitope binding, but reflected HER2 degradation by short-term NVP-AUY922 treatment in SKOV-3 xenografts (NUV60: 13.5 ± 2.1 %ID/mL vs. 9.0 ± 0.9 %ID/mL for vehicle or drug, respectively).

CONCLUSIONS

[(18)F]GE-226 binds with high specificity to HER2 independent of cell lineage. The tracer has potential utility for HER2 detection, irrespective of prior trastuzumab treatment, and to discern HSP90 inhibitor-mediated HER2 degradation.

A bioorthogonal 68Ga-labelling strategy for rapid in vivo imaging

The in vivo imaging of EGFR is achieved using a ⁶⁸Ga-labelled tetrazine via a fast and bioorthogonal IeDDA reaction.

Abstract A15: HDAC6 inhibitor C1A abrogates the recruitment of the autophagic machinery and synergizes with proteasome, src kinase, and PI3K-mTOR inhibition

The histone deacetylase (HDAC) family of proteins plays a profound role in transcriptional silencing and intracellular protein function, and HDAC inhibitors have shown promise for the treatment of human malignancies. HDAC6 activity is altered in tumorigenesis and its selective inhibition is likely to cause less toxicity compared to broad spectrum inhibitors. An important function of HDAC6 is the processing of misfolded proteins within cells during autophagy and formation of aggresomes. Prosurvival autophagy may represent a major impediment to successful cancer therapy and more potent and specific inhibitors of autophagy are needed. This study evaluated whether targeting HDAC6 could be used to impair autophagy and restore chemosensitivity. Treatment of colon cancer HCT-116 cells and osteosarcoma U2OS-LC3-GFP cells with HDAC6 inhibitor C1A for 24 hours (or tubastatin A, another HDAC6 inhibitor) caused a dose dependent increase in expression of lipid associated LC3 II, suggesting autophagosome formation or blockage. Using a pH-sensitive, double tagged mCherry-GFP-LC3 reporter, we could further demonstrate impairment of autophagosome-lysosome fusion. We hypothesized that the effect of autophagy tool compounds will be modulated by C1A. Increased LC3 II/p62 expression induced by chloroquine, 3-MA, bortezomib or BEZ-235 were inhibited by C1A (also seen with tubastatin A). Combination of C1A with bortezomib or BEZ-235 induced a greater proportion of cells undergoing apoptosis as depicted by an increase of caspase 3/7 activity in HCT-116 cells. Treatment with C1A (or tubastatin A) also impaired the formation of LC3 II following treatment with src inhibitor, dasatinib (or PP2, another src inhibitor but not PP3, a negative control compound); synergy as assessed by caspase 3/7 activity was seen in lung cancer A549 cells. Based on combination index values, we demonstrated that C1A synergistically enhanced proteasome, src kinase and PI3K-mTOR growth inhibition. In vivo, the anti-tumor activity of C1A in combination with bortezomib or BEZ-235 was confirmed in HCT-116 tumor bearing mice. Tumor growth was significantly delayed in animals treated with combination therapy. A similar observation was seen in A549 tumor bearing mice treated with C1A in combination with dasatinib. The efficacy of the combination C1A and BEZ-235 was also predicted as early as 48 h with [18F]fluorothymidine positron emission tomography ([18F]FLT-PET) in HCT-116 tumor bearing mice. These results provide a rationale for combination therapy with HDAC6 inhibitors and chemotherapy associated with pro-survival autophagy in the treatment of solid tumors. Imaging of cell proliferation with [18F]FLT-PET detected the mechanistic validity of this combination treatment approach and, thus, warrants further investigation in pre-clinical models and patients.

This work was supported in part by Cancer Research U.K.-Engineering and Physical Sciences Research Council Grant C2536/A10337.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A15.

Citation Format: Maciej Kaliszczak, Olivier E. Pardo, Michael J. Seckl, Eric O. Aboagye. HDAC6 inhibitor C1A abrogates the recruitment of the autophagic machinery and synergizes with proteasome, src kinase, and PI3K-mTOR inhibition. [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 A15.

Abstract B140: Positron emission tomography imaging of HER2 expression and pharmacodynamic response to HSP90 inhibition with the next-generation ZHER2:2891 Affibody molecule [18F]GE-226

Accurate assessment of HER2 status remains a clinical challenge, with up to 20% of patients being potentially withdrawn from therapy or exposed to unnecessary toxicity. Non-invasive imaging is widely seen as a viable alternative to current methods, in particular in the setting of locoregional and distant recurrences not amenable to biopsy. A next-generation HER2-targeting Affibody-based radiotracer has been developed, [18F]GE-226, with enhanced pharmacokinetic characteristics and improved properties for large-scale and GMP grade synthesis. Kinetic modeling gave insights into Affibody-HER2 interactions.

Intrinsic affinity to HER2 (KD = 76 pM) resulted in 11 to 67-fold higher [18F]GE-226 uptake in ten HER2 positive versus negative cell lines in vitro independent of lineage. Uptake correlated with HER2 protein expression but was independent of presence of other targets like EGFR. Blocking with [19F]GE-226 and HER2 siRNA treatment reduced uptake by 96.8 ± 2.6% and 81.7 ± 9.2%, respectively. Uptake in HER2 positive xenografts was rapid with steady state net irreversible binding kinetics making possible the distinction of HER2 negative (MCF7 (n = 6) and MCF7-p95HER2 (n = 3): NUV60 (normalized uptake value at 60 min; %ID/mL) 6.1 ± 0.7; Ki (irreversible uptake rate; mL/cm3/min) 0.0069 ± 0.0014) from HER2 positive tumors (NUV60 and Ki: MCF7-HER2, 10.9 ± 1.5 and 0.015 ± 0.0035; MDA-MB-361, 18.2 ± 3.4 and 0.025 ± 0.0052; SKOV-3, 18.7 ± 2.4 and 0.036 ± 0.0065; all n = 6) within 1 h. Tumor uptake correlated with HER2 expression determined by ELISA (r2=0.78). Specificity was further determined by comparing tumor localization of a fluorescently labeled tracer analogue with DAKO HercepTest. Affibody signal co-localized with HER2 expression at the cellular level independent of spatial heterogeneity. Tracer binding was not influenced by short-term or continuous exposure to trastuzumab in SKOV-3 xenografts (n=6) in keeping with differential epitope binding. Inhibition of the chaperone HSP90– of which HER2 is a client protein– by the therapeutic development candidate NVP-AUY922 caused dose-dependent HER2 degradation and consequently reduced tracer uptake in SKOV-3 cells in vitro and xenografts in vivo (area under the curve, AUC0-60: 618.4±90.1 and 446.7±42.8 %ID/mL*min for vehicle (n=4) and drug (n=5), respectively; P=0.043).

In conclusion, [18F]GE-226 differentiates HER2 negative from HER2 expressing tumors. The tracer has potential utility for HER2 detection, irrespective of prior trastuzumab treatment and to monitor response to HSP90 inhibition. Lineage-independence of these results extends application beyond breast cancer. Due to the specific annotation to HER2, enhanced pharmacokinetic properties and completion of initial preclinical toxicology testing, [18F]GE-226 is now transitioning into clinical development.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B140.

Citation Format: Sebastian Trousil, Susan Hoppmann, Quang-Dé Nguyen, Maciej Kaliszczak, Giampaolo Tomasi, Peter Iveson, Duncan Hiscock, Eric O. Aboagye. Positron emission tomography imaging of HER2 expression and pharmacodynamic response to HSP90 inhibition with the next-generation ZHER2:2891 Affibody molecule [18F]GE-226. [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 B140.

Development of a cyclin-dependent kinase inhibitor devoid of ABC transporter-dependent drug resistance

Background:

Cyclin-dependent kinases (CDKs) control cell cycle progression, RNA transcription and apoptosis, making them attractive targets for anticancer drug development. Unfortunately, CDK inhibitors developed to date have demonstrated variable efficacy.

Methods:

We generated drug-resistant cells by continuous low-dose exposure to a model pyrazolo[1,5-a]pyrimidine CDK inhibitor and investigated potential structural alterations for optimal efficacy.

Results:

We identified induction of the ATP-binding cassette (ABC) transporters, ABCB1 and ABCG2, in resistant cells. Assessment of features involved in the ABC transporter substrate specificity from a compound library revealed high polar surface area (>100 Ų) as a key determinant of transporter interaction. We developed ICEC-0782 that preferentially inhibited CDK2, CDK7 and CDK9 in the nanomolar range. The compound inhibited phosphorylation of CDK substrates and downregulated the short-lived proteins, Mcl-1 and cyclin D1. ICEC-0782 induced G2/M arrest and apoptosis. The permeability and cytotoxicity of ICEC-0782 were unaffected by ABC transporter expression. Following daily oral dosing, the compound inhibited growth of human colon HCT-116 and human breast MCF7 tumour xenografts in vivo by 84% and 94%, respectively.

Conclusion:

We identified a promising pyrazolo[1,5-a]pyrimidine compound devoid of ABC transporter interaction, highly suitable for further preclinical and clinical evaluation for the treatment of cancer.

Design of symmetrical and nonsymmetrical N,N-dimethylaminopyridine derivatives as highly potent choline kinase alpha inhibitors

Choline kinase alpha is hyperactivated in many solid tumours and regulates malignant progression, making it a promising cancer drug target. The successful design and synthesis of novel inhibitors with high cellular activity are described.

Abstract 2608: HDAC-C1A: An irreversible HDAC inhibitor with significant anti-tumor activity

Histone deacetylase (HDAC) enzymes exert control over gene transcription and cell cycle progression and their inhibition has recently emerged as an efficacious strategy to treat cancer. However, current HDAC inhibitors have been linked to a shared undesirable toxicological profile that prompts the development of new entities. The present study evaluates the in vitro and in vivo PK/PD of a newly developed HDAC inhibitor, HDAC-C1A.

HDAC-C1A inhibited class I, II and sirtuins, with highest affinity for HDAC6 (IC50 = 63 ng/mL), an HDAC subtype thought to be associated with low toxicity; HDAC6 knockout does not lead to embryonic lethality. The drug irreversibly inhibited HDAC from HeLa cell extract; in HCT116 cells inhibition of enzyme activity as assessed by levels of acetyl-histone H3, H4 and acetyl-tubulin was maintained after washout demonstrating an irreversible mechanism. HDAC-C1A treatment was associated with a dose and time dependent increase of histone and non-histone targets that was maintained at 4 hours after washout; acetylation was lost by 4 h with clinically licensed HDAC inhibitor SAHA. HDAC-C1A inhibited the growth of a panel of 7 cancer cell lines with a mean GI50 of 1.6 ± 0.6 µg/mL. The drug was relatively stable after parenteral administration for 4 h. The Cmax and AUC0-4h following i.p. injection (160 mg/kg) were 20.4 µg/mL and 50 µg/mL*h, respectively.

Regarding efficacy, HDAC-C1A treatment was associated with a Tumor Growth Delay (TGD2x) of 5.7 ± 1.4 days and a Tumor Growth Inhibition (TGI) of 78% compared with vehicle when given i.p. at 20 mg/kg b.i.d. in a HCT116 human colon cancer xenograft model. This dose was non-toxic (no reduction in body weight). We also assessed the potential of [18F]fluorothymidine positron emission tomography ([18F]FLT-PET) to measure early response to HDAC-C1A treatment in HCT116 xenograft bearing mice. There was a 2-fold decrease in tumor [18F]FLT uptake compared to vehicle treated animals at 48 h post-treatment; the area under the normalized [18F]FLT time versus activity curve was 117 ± 6.9 at before treatment and decreased to 106 ± 5.5 (P = 0.02) at 24 hours and 54 ± 5 (P = 0.0001) at 48 h after initiating treatment.

In summary, HDAC-C1A combines irreversible HDAC inhibition with a favourable pharmacokinetic profile leading to significant anti-tumor activity in the HCT116 tumor model. Early response to the drug was detectable by [18F]FLT-PET. These preclinical data support further development of HDAC-C1A. This work was supported in part by Cancer Research U.K.-Engineering and Physical Sciences Research Council Grant C2536/A10337.

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 2608. doi:10.1158/1538-7445.AM2011-2608

Optimization of the antitumor activity of sequence-specific pyrrolobenzodiazepine derivatives based on their affinity for ABC transporters

Pyrrolobenzodiazepine (PBD) derivatives are highly potent sequence-specific DNA cross-linking agents. The present study aimed to identify key physicochemical properties influencing the interaction of a series of PBDs (four dimers and 12 monomers) with the three major human ATP-binding cassette (ABC) transporters (P-gp, ABCG2, and MRP1). Isogenic cell lines expressing P-gp and ABCG2, cell lines with acquired resistance to cytotoxic agents due to the high expression of ABC transporters, and specific inhibitors against P-gp, ABCG2, and MRP1 were used. P-gp and ABCG2 decreased the permeability of the PBD dimers across cell membranes and their interaction with DNA, reducing DNA damage and the overall cytotoxic effect. PBD monomer SG-2823 formed a conjugate with glutathione and interacted with MRP1, reducing its cytotoxic effect in A549 cells. Structure-activity relationship revealed that the interaction of PBDs with the transporters could be predicted considering the molecular weight, the lipophilicity, the number of (N + O) atoms and aromatic rings, the polar surface area, the hydrogen bonding energy, and electrophilic centers. A rational design of novel PBDs with increased potency and reduced interaction with the ABC transporters is proposed.

Development of a new epidermal growth factor receptor positron emission tomography imaging agent based on the 3-cyanoquinoline core: synthesis and biological evaluation

The epidermal growth factor receptor (EGFR/c-ErbB1/HER1) is overexpressed in many cancers including breast, ovarian, endometrial, and non-small cell lung cancer. An EGFR specific imaging agent could facilitate clinical evaluation of primary tumors and/or metastases. To achieve this goal we designed and synthesized a small array of fluorine containing compounds based on a 3-cyanoquinoline core. A lead compound, 16, incorporating 2'-fluoroethyl-1,2,3-triazole was selected for evaluation as a radioligand based on its high affinity for EGFR kinase (IC50=1.81+/-0.18 nM), good cellular potency (IC50=21.97+/-9.06 nM), low lipophilicity and good metabolic stability. 'Click' labeling afforded [18F]16 in 37.0+/-3.6% decay corrected radiochemical yield based on azide [18F]14 and 7% end of synthesis (EOS) yield from aqueous fluoride. Compound [18F]16 was obtained with >99% radiochemical purity in a total synthesis time of 3 h. The compound showed good stability in vivo and a fourfold higher uptake in high EGFR expressing A431 tumor xenografts compared to low EGFR expressing HCT116 tumor xenografts. Furthermore, the radiotracer could be visualized in A431 tumor bearing mice by small animal PET imaging. Compound [18F]16 therefore constitutes a promising radiotracer for further evaluation for imaging of EGFR status.