Abstract PD6-09: Herpet study- PET imaging of HER2 expression in breast cancer using the novel Affibody tracer [18F]GE-226, a first in patient study

Background 20% of breast cancers have over-expression of the human epidermal growth factor receptor-2 (HER2), which is an adverse prognostic factor and used to guide therapy selection. At present HER2 expression can only be determined using biopsy material which is then analysed using immunohistochemistry or fluorescence in situ hybridisation. GE-226 is a radiolabelled Affibody® tracer which binds to the HER2 receptor with high affinity at a different epitope than trastuzumab. Heterogeneous expression does exist but the impact this has on treatment response has not been well assessed. A non-invasive method for determining HER2 expression could have several advantages and help select appropriate therapy for patients.

Trial DesignPatients with locally advanced or metastatic breast cancer were recruited and scanned for 65 mins after iv injection of 200MBq (mean activity injected for each patient 198 MBq (range 164-219MBq), mean radiochemical purity 94.6%) of tracer, with one dynamic bed position, and then a half-body scan was performed. Blood sampling was used to measure metabolism of the tracer. Safety was recorded. HER2-extracellular domain (ECD) domain was measured in blood. The original accrual target was 16 patients. Tumoural uptake was quantified by semi-quantitative and fully quantitative parameters in HER2 positive and HER2 negative tumours.

ResultsThirteen patients were recruited. Scans were well tolerated. There were no serious adverse events. GE-226 was metabolised into a single metabolite in the liver. 96.8 % parent remained at 60 minutes post injection. There was a significant difference between HER2 positive and HER2 negative tumoural uptake of tracer as measured by SUVmean and SUVmax (p<0.05). Comparing HER2 positive to HER2 negative cases, there was also a significant difference between tumour to normal tissue uptake ratios (p<0.05). Heterogeneous uptake was observed in the same patient. Tumoural uptake increased over time. Uptake in salivary glands and the thyroid gland was noted. In one patient GE-226 was able to differentiate between lymphadenopathy due to sarcoidosis and cancer and was superior to FDG which had shown widespread uptake in the same patient.

Conclusions[18F]GE-226 imaging is well tolerated and shows promise for imaging of HER2 positive breast cancer. Further studies with this agent are now planned.

Citation Format: Laura M. Kenny, Gosala S. Gopalakrishnan, Tara D. Barwick, Vijay Vaja, S. Hope McDevitt, Robert Punjani, Neva H. Patel, Rathi Ramakrishnan, Naina R. Patel, Stephen Johnston, Janine Mansi, Gary J. Cook, Fiona J. Gilbert, Franklin I. Aigbirhio, Duncan Hiscock, Eric O. Aboagye. Herpet study- PET imaging of HER2 expression in breast cancer using the novel Affibody tracer [18F]GE-226, a first in patient study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD6-09.

FASTlab Radiosynthesis of the 18 F-labelled HER2-binding Affibody molecule [18 F]GE-226

An ¹⁸ F-labelled human epidermal growth factor receptor (HER2) receptor binding radiotracer is a potential tool to non-invasively identify HER2 positive tumour lesions in subjects with recurrent metastatic breast cancer. Having explored the manual radiochemistry to conjugate the Affibody molecule Z_HER2:2891 with [¹⁸ F]4-fluorobenzaldehyde, we have developed and optimised a full protocol for the automated GE FASTlab synthesiser. Our chemometric model predicted the best radiochemical purity for a short conjugation time (2.8 minutes), a low temperature (65°C), and a medium Affibody molecule precursor amount (5.5 mg). Under these optimised conditions, [¹⁸ F]GE-226 was produced after solid-phase extraction purification with activity yield of 30% ± 7 (n = 18) and a radiochemical purity of 94% ± 2 (n = 18). The synthesis and purification was complete after 43 minutes and provided apparent molar activities of 12 to 30 GBq/μmol (n = 12) at the end of synthesis.

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.

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.

[18F]-FLT positron emission tomography can be used to image the response of sensitive tumors to PI3-kinase inhibition with the novel agent GDC-0941

The phosphoinositide 3-kinase (PI3K) pathway is deregulated in a range of cancers, and several targeted inhibitors are entering the clinic. This study aimed to investigate whether the positron emission tomography tracer 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]-FLT) is suitable to mark the effect of the novel PI3K inhibitor GDC-0941, which has entered phase II clinical trial. CBA nude mice bearing U87 glioma and HCT116 colorectal xenografts were imaged at baseline with [(18)F]-FLT and at acute (18 hours) and chronic (186 hours) time points after twice-daily administration of GDC-0941 (50 mg/kg) or vehicle. Tumor uptake normalized to blood pool was calculated, and tissue was analyzed at sacrifice for PI3K pathway inhibition and thymidine kinase (TK1) expression. Uptake of [(18)F]-FLT was also assessed in tumors inducibly overexpressing a dominant-negative form of the PI3K p85 subunit p85α, as well as HCT116 liver metastases after GDC-0941 therapy. GDC-0941 treatment induced tumor stasis in U87 xenografts, whereas inhibition of HCT116 tumors was more variable. Tumor uptake of [(18)F]-FLT was significantly reduced following GDC-0941 dosing in responsive tumors at the acute time point and correlated with pharmacodynamic markers of PI3K signaling inhibition and significant reduction in TK1 expression in U87, but not HCT116, tumors. Reduction of PI3K signaling via expression of Δp85α significantly reduced tumor growth and [(18)F]-FLT uptake, as did treatment of HCT116 liver metastases with GDC-0941. These results indicate that [(18)F]-FLT is a strong candidate for the noninvasive measurement of GDC-0941 action.

Abstract 353: In vivo PET imaging of HER2 expression with GE226: An 18F-labelled affibody molecule

Background: The assessment of HER2 expression in biopsies from primary lesions of breast cancer patients is a standard procedure to select patients for HER2-targeted therapies. However, in metastatic disease in which HER2 status can change, determination of HER2 expression is not standard procedure, which complicates patient management. Herein we report evidence for GE226 ([18F]FBA-ZHER2:2891), a highly specific HER2 targeted imaging agent that can determine HER2 expression levels in preclinical tumour models. We propose that GE226 can be progressed to clinical development for non-invasive determination of the HER2 status in recurrent breast cancer patients to improve the clinical management and therapy selection. Methods: The highly selective HER2 targeted 18F-labelled Affibody molecule GE226 was characterized in a murine dual tumour breast cancer model bearing NCI-N87 (high HER2 status) and A431 (low HER2 status) xenografts in separate flanks. Tumour-bearing mice were injected with 3 to 10 MBq of GE226, followed by biodistribution or positron emission tomography (PET) imaging analysis. Results: Biodistribution analysis demonstrated good differentiation of GE226 retention between high and low HER2 expressing tumours (8.4% ID/g and 3.4% ID/g respectively, 30 min post injection). GE226 cleared quickly from background tissue, including kidneys, with excellent ratios for tumour-to-muscle (8.9 for high HER2 status tumours and 3.6 for low HER2 status tumours, 30 min post injection) and tumour-to-blood (2.5 for high HER2 status tumours and 1.0 for low HER2 status tumours, 30 min post injection). PET imaging of GE226 in the dual tumour mouse model showed a marked difference in signal intensity between the two tumour types. Conclusions: The highly selective HER2 targeted Affibody molecule GE226 can image different levels of HER2 expression in a dual-tumour preclinical model of breast cancer with good target-to-background ratios. These data compare favourably with previous patient SPECT and PET studies using the 111In- or 68Ga-labelled HER2-binding Affibody molecule ABY-002 (Baum et al., J Nucl Med. 2010;51(6):892-7) which supports the efficacy of this class of Affibody tracer for visualization of HER2 expressing metastases. We plan to progress GE226 further to assess HER2 status in metastatic breast cancer patients in clinical PET studies.

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 353. doi:1538-7445.AM2012-353

Viral Genome DataBase: storing and analyzing genes and proteins from complete viral genomes

SUMMARY

The Viral Genome DataBase (VGDB) contains detailed information of the genes and predicted protein sequences from 15 completely sequenced genomes of large (&100 kb) viruses (2847 genes). The data that is stored includes DNA sequence, protein sequence, GenBank and user-entered notes, molecular weight (MW), isoelectric point (pI), amino acid content, A + T%, nucleotide frequency, dinucleotide frequency and codon use. The VGDB is a mySQL database with a user-friendly JAVA GUI. Results of queries can be easily sorted by any of the individual parameters.

AVAILABILITY

The software and additional figures and information are available at http://athena.bioc.uvic.ca/genomes/index.html .