Positron Emission Tomography (PET) Imaging with [11C]-Labeled Erlotinib: A Micro-PET Study on Mice with Lung Tumor Xenografts

Normalization of Snai1-mediated vessel dysfunction increases drug response in cancer

Blood vessels in tumors are often dysfunctional. This impairs the delivery of therapeutic agents to and distribution among the cancer cells. Subsequently, treatment efficacy is reduced, and dose escalation can increase adverse effects on non-malignant tissues. The dysfunctional vessel phenotypes are attributed to aberrant pro-angiogenic signaling, and anti-angiogenic agents can ameliorate traits of vessel dysfunctionality. However, they simultaneously reduce vessel density and thereby impede drug delivery and distribution. Exploring possibilities to improve vessel functionality without compromising vessel density in the tumor microenvironment, we evaluated transcription factors (TFs) involved in epithelial-mesenchymal transition (EMT) as potential targets. Based on similarities between EMT and angiogenic activation of endothelial cells, we hypothesized that these TFs, Snai1 in particular, might serve as key regulators of vessel dysfunctionality. In vitro, experiments demonstrated that Snai1 (similarly Slug and Twist1) regulates endothelial permeability, permissiveness for tumor cell transmigration, and tip/stalk cell formation. Endothelial-specific, heterozygous knock-down of Snai1 in mice improved vascular quality in implanted tumors. This resulted in better oxygenation and reduced metastasis. Notably, the tumors in Snai1KD mice responded significantly better to chemotherapeutics as drugs were transported into the tumors at strongly increased rates and more homogeneously distributed. Thus, we demonstrate that restoring vessel homeostasis without affecting vessel density is feasible in malignant tumors. Combining such vessel re-engineering with anti-cancer drugs allows for strategic treatment approaches that reduce treatment toxicity on non-malignant tissues.

A Novel Dual-labeled Peptide for Multimodal Imaging of EGFR with L858R Mutation

BACKGROUND

The development of molecular imaging agents targeting epidermal growth factor receptor (EGFR) with L858R mutation may help with the selection of non-small cell lung carcinoma (NSCLCL) patients who may benefit from EFGR tyrosine kinase inhibitor (TKI) therapy.

OBJECTIVE

In this study, we developed 99mTc STHHYYP-GHEG-ECGK-tetramethylrhodamine (STHHYYP-ECGK-TAMRA) to target EGFR with L858R mutation in NSCLC tumors and verified its probability as a molecular imaging agent.

METHODS

Fmoc solid-phase peptide synthesis was used to synthesize STHHYYP-ECGKTAMRA. 99mTc labelled STHHYYP-ECGK-TAMRA was prepared. Gamma imaging, fluorescent imaging and biodistribution were performed in murine models bearing NCI-H1975 and NCI-H1650 tumors.

RESULTS

The binding affinity value (Kd) of 99mTc STHHYYP-ECGK-TAMRA was estimated to be 130.6 ± 29.2 nM in NCI-H1975 cells. The gamma camera images showed a substantial uptake of 99mTc STHHYYP-ECGK-TAMRA in the NCI-H1975 tumor. The % injected dose/gram of the NCI-H1975 tumor tissue was 2.77 ± 0.70 and 3.48 ± 1.01 at 1 and 3 h, respectively.

CONCLUSION

Specific binding of 99mTc STHHYYP-ECGK-TAMRA to L858R-mutated EGFRpositive NCI-H1975 cells and tumors was demonstrated in in vivo and in vitro studies. The results suggest that 99mTc STHHYYP-ECGK-TAMRA is a good candidate agent for dualmodality imaging targeting EGFR with L858R mutation.

Pharmacokinetic analysis of 6-O-[18F]FEE for PET imaging of EGFR mutation

6-O-[¹⁸F]Fluoroethylerlotinib (6-O-[¹⁸F]FEE), with a suitable half-life for commercial distribution, may be a good replacement for [¹¹C]erlotinib to identify epidermal growth factor receptor (EGFR) positive tumors with activating mutations to tyrosine kinase inhibitors therapy. In this study, we explored the fully automated synthesis of 6-O-[¹⁸F]FEE and investigated its pharmacokinetics in tumor-bearing mice. 6-O-[¹⁸F]FEE with high specific activity (28-100 GBq/μmol) and radiochemistry purity (over 99 %) was obtained by two-step reaction and Radio-HPLC separation in PET-MF-2 V-IT-1 automated synthesizer. PET imaging of 6-O-[¹⁸F]FEE in HCC827, A431, and U87 tumor-bearing mice with different EGFR expression and mutation was performed. Uptake and blocking of PET imaging indicated that the probe specifically targeted exon 19 deleted EGFR (the quantitative analysis of tumor-to-mouse ratio for HCC827, HCC827 blocking, U87, A431 was 2.58 ± 0.24, 1.20 ± 0.15, 1.18 ± 0.19, and 1.05 ± 0.13 respectively). Dynamic imaging was used to study the pharmacokinetics of the probe in tumor-bearing mice. Logan plot graphical analysis demonstrated late linearity and a high fitting correlation coefficient (0.998), supporting reversible kinetics. According to the Akaike Information Criterion (AIC) rule, the 2-compartment reversible model was more consistent with the metabolic properties of 6-O-[¹⁸F]FEE. The automated radiosynthesis and pharmacokinetic analysis will promote clinically transformation of 6-O-[¹⁸F]FEE.

Zero-Background Small-Molecule Sensors for Near-IR Fluorescent Imaging of Biomacromolecular Targets in Cells

In this study, we report a general approach to the design of a new generation of small-molecule sensors that produce a zero background but are brightly fluorescent in the near-IR spectral range upon selective interaction with a biomolecular target. We developed a fluorescence turn-on/-off mechanism based on the aggregation/deaggregation of phthalocyanine chromophores. As a proof of concept, we designed, prepared, and characterized sensors for in-cell visualization of epidermal growth factor receptor (EGFR) tyrosine kinase. We established a structure/bioavailability correlation, determined conditions for the optimal sensor uptake and imaging, and demonstrated binding specificity and applications over a wide range of treatment options involving live and fixed cells. The new approach enables high-contrast imaging and requires no in-cell chemical assembly or postexposure manipulations (i.e., washes). The general design principles demonstrated in this work can be extended toward sensors and imaging agents for other biomolecular targets.

First-, Second-, and Third-Generation Radiolabeled Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Positron Emission Tomography: State of the Art, a Systematic Review

Introduction: Lung cancer (LC) is a leading cause of death among men and women, with non-small cell LC (NSCLC) accounting for a substantial portion of the histopathological spectrum and epidermal growth factor receptor (EGFR) mutations being correlated with its manifestation and evolution. Positron emission tomography (PET)/computed tomography has been the most widely used instrument to assess and monitor LC in a noninvasive way, including EGFR-mutated NSCLC, and its course during therapy, indicating to the referring physician the response to ongoing treatment or the lack of it. This systematic review aims to evaluate the feasibility and safety of radiolabeled EGFR tyrosine kinase inhibitors (TKis) in PET in clinical practice. Materials and Methods: From 1999 to April 2022 a Medline search was conducted on four different databases such as PubMed, Cochrane Library, Scopus, and Web of Sciences. Clinical studies were assessed by Quality Assessment of Diagnostic accuracy Studies-2 (QUADAS-2) and preclinical studies were also reported in this review. Results: Nine clinical studies were QUADAS-2 assessed and risk-of-bias assessment, and it turned out acceptable as two out of eight studies had low risk of bias in all four domains for risk-of-bias assessment, and the other four studies had three low-risk domains. The overall assessment for applicability risks was low. Conclusions: Radiolabeled EGFR-TKis in PET are a valid tool in identifying patients who may benefit from TKi therapy and who may not as a means to start an effective treatment. Although the number of clinical studies conducted so far is meager, these new PET tracers are already proving to be very useful in clinical settings as patient prognosis can be better assessed.

A Novel Dextran-Based Dual Drug Conjugate Targeted Tumors with High Biodistribution Ratio of Tumors to Normal Tissues

PURPOSE

Most chemotherapeutic agents possess poor water solubility and show more significant accumulations in normal tissues than in tumor tissues, resulting in serious side effects. To this end, a novel dextran-based dual drug delivery system with high biodistribution ratio of tumors to normal tissues was developed.

METHODS

A bi-functionalized dextran was developed, and several negatively charged dextran-based dual conjugates containing two different types of drugs, docetaxel and docosahexaenoic acid (DTX and DHA, respectively) were synthesized. The structures of these conjugates were characterized using nuclear magnetic resonance and liquid chromatography/mass spectrometry (¹H-NMR and LC/MS, respectively) analysis. Cell growth inhibition, apoptosis, cell cycle distribution, and cellular uptake were measured in vitro. Drug biodistribution and pharmacokinetics were investigated in mice bearing 4T1 tumors using LC/MS analysis. Drug biodistribution was also explored by in vivo imaging. The effects of these conjugates on tumor growth were evaluated in three mice models.

RESULTS

The dextran-docosahexaenoic acid (DHA)- docetaxel (DTX) conjugates caused a significant enhancement of DTX water solubility and improvement in pharmacokinetic characteristics. The optimized dextran-DHA-DTX conjugate A treatment produced a 2.1- to 15.5-fold increase in intra-tumoral DTX amounts for up to 96 h compared to parent DTX treatment. Meanwhile, the concentrations of DTX released from conjugate A in normal tissues were much lower than those of the parent DTX. This study demonstrated that DHA could lead to an improvement in the efficacy of the conjugates and that the conjugate with the shortest linker displayed more activity than conjugates with longer linkers. Moreover, conjugate A completely eradicated all MCF-7 xenograft tumors without causing any obvious side effects and totally outperformed both the conventional DTX formulation and Abraxane in mice.

CONCLUSION

These dextran-based dual drug conjugates may represent an innovative tumor targeting drug delivery system that can selectively deliver anticancer agents to tumors.

Positron emission tomography imaging of lung cancer: An overview of alternative positron emission tomography tracers beyond F18 fluorodeoxyglucose

Lung cancer has been the leading cause of cancer-related mortality in China in recent decades. Positron emission tomography-computer tomography (PET/CT) has been established in the diagnosis of lung cancer. ¹⁸F-FDG is the most widely used PET tracer in foci diagnosis, tumor staging, treatment planning, and prognosis assessment by monitoring abnormally exuberant glucose metabolism in tumors. However, with the increasing knowledge on tumor heterogeneity and biological characteristics in lung cancer, a variety of novel radiotracers beyond ¹⁸F-FDG for PET imaging have been developed. For example, PET tracers that target cellular proliferation, amino acid metabolism and transportation, tumor hypoxia, angiogenesis, pulmonary NETs and other targets, such as tyrosine kinases and cancer-associated fibroblasts, have been reported, evaluated in animal models or under clinical investigations in recent years and play increasing roles in lung cancer diagnosis. Thus, we perform a comprehensive literature review of the radiopharmaceuticals and recent progress in PET tracers for the study of lung cancer biological characteristics beyond glucose metabolism.

Preparation of radiolabeled erlotinib analogues and analysis of the effect of linkers

Erlotinib is a first generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) which was granted Food and Drug administration (FDA) approval for treatment of patients with locally advanced or metastatic NSCLC. The present study aimed at development of radiolabeled erlotinib variants as tyrosine kinase inhibitors. Three DOTA-erlotinib conjugates were prepared for radiolabeling with ¹⁷⁷Lu. The terminal alkyne group of erlotinib was modified by performing Cu-catalyzed click chemistry and three different linkers were introduced which were then conjugated to the chelator, DOTA. The DOTA-erlotinib conjugates were characterized by ¹H NMR and ESI-MS. ¹⁷⁷Lu-DOTA-erlotinib complexes were characterized using ^natLu-DOTA-erlotinib conjugates. The ¹⁷⁷Lu-complexes exhibited high in vitro stability in human serum up to 48 h. They were highly hydrophilic in nature as observed from their log P_o/w values (¹⁷⁷Lu-DOTA-propyl-Er: -2.5 ± 0.1; ¹⁷⁷Lu-DOTA-PEG₃-Er: -3.0 ± 0.1; ¹⁷⁷Lu-DOTA-PEG₆-Er: -3.3 ± 0.1). The MTT assay in A431 human epidermoid carcinoma cell lines indicates that the chemical modification at the terminal alkyne group of the erlotinib molecule does not have significant effect on its TKI property. Biodistribution studies in normal Swiss mice demonstrated fast clearance and excretion of ¹⁷⁷Lu-labeled erlotinib complexes. These studies indicate that erlotinib variants with hydrophobic pharmacokinetic modifiers/chelators may enhance the retention of ¹⁷⁷Lu-labeled complexes in blood thereby increasing the probability to reach EGFR-expressing tumor.

PET Imaging of Lung Cancers in Precision Medicine: Current Landscape and Future Perspective

Despite the recent advances in cancer treatment, lung cancer remains the leading cause of cancer mortality worldwide. Immunotherapies using immune checkpoint inhibitors (ICIs) achieved substantial efficacy in nonsmall cell lung cancer (NSCLC). Currently, most ICIs are still a monoclonal antibody (mAb). Using mAbs or antibody derivatives labeled with radionuclide as the tracers, immunopositron emission tomography (immunoPET) possesses multiple advantages over traditional ¹⁸F-FDG PET in imaging lung cancers. ImmunoPET presents excellent potential in detecting, diagnosing, staging, risk stratification, treatment guidance, and recurrence monitoring of lung cancers. By using radiolabeled mAbs, immunoPET can visualize the biodistribution and uptake of ICIs, providing a noninvasive modality for patient stratification and response evaluation. Some novel targets and associated tracers for immunoPET have been discovered and investigated. This Review introduces the value of immunoPET in imaging lung cancers by summarizing both preclinical and clinical evidence. We also emphasize the value of immunoPET in optimizing immunotherapy in NSCLC. Lastly, immunoPET probes developed for imaging small cell lung cancer (SCLC) will also be discussed. Although the major focus is to summarize the immunoPET tracers for lung cancers, we also highlighted several small-molecule PET tracers to give readers a balanced view of the development status.

EGFR signaling pathway as therapeutic target in human cancers

Epidermal Growth Factor Receptor (EGFR) enacts major roles in the maintenance of epithelial tissues. However, when EGFR signaling is altered, it becomes the grand orchestrator of epithelial transformation, and hence one of the most world-wide studied tyrosine kinase receptors involved in neoplasia, in several tissues. In the last decades, EGFR-targeted therapies shaped the new era of precision-oncology. Despite major advances, the dream of converting solid tumors into a chronic disease is still unfulfilled, and long-term remission eludes us. Studies investigating the function of this protein in solid malignancies have revealed numerous ways how tumor cells dysregulate EGFR function. Starting from preclinical models (cell lines, organoids, murine models) and validating in clinical specimens, EGFR-related oncogenic pathways, mechanisms of resistance, and novel avenues to inhibit tumor growth and metastatic spread enriching the therapeutic portfolios, were identified. Focusing on non-small cell lung cancer (NSCLC), where EGFR mutations are major players in the adenocarcinoma subtype, we will go over the most relevant discoveries that led us to understand EGFR and beyond, and highlight how they revolutionized cancer treatment by expanding the therapeutic arsenal at our disposal.

The Development of Positron Emission Tomography Tracers for In Vivo Targeting the Kinase Domain of the Epidermal Growth Factor Receptor

Multiple small molecule PET tracers have been developed for the imaging of the epidermal growth factor receptor (EGFR). These tracers target the tyrosine kinase (TK) domain of the receptor and have been used for both quantifying EGFR expression and to differentiate between EGFR mutational statuses. However, the approaches for in vivo evaluation of these tracers are diverse and have resulted in data that are hard to compare. In this review, we analyze the historical development of the in vivo evaluation approaches, starting from the first EGFR TK PET tracer [11C]PD153035 to tracers developed based on TK inhibitors used for the clinical treatment of mutated EGFR expressing non-small cell lung cancer like [11C]erlotinib and [18F]afatinib. The evaluation of each tracer has been compiled to allow for a comparison between studies and ultimately between tracers. The main challenges for each group of tracers are thereafter discussed. Finally, this review addresses the challenges that need to be overcome to be able to efficiently drive EGFR PET imaging forward.

A novel dual-labeled small peptide as a multimodal imaging agent for targeting wild-type EGFR in tumors

The epidermal growth factor receptor (EGFR) is over-expressed in various human cancer. The over-expression of EGFR in tumors is an excellent target for the development of cancer imaging agents. In the present study, we developed Tc-99m SYPIPDT-GHEG-ECG-K-tetramethylrhodamine (SYPIPDT-ECG-TAMRA) as a molecular imaging agent targeting wild-type EFGR (wtEGFR)-positive tumor cells, and verified its feasibility as molecular imaging agent. SYPIPDT-ECG-TAMRA was synthesized using Fmoc solid-phase peptide synthesis. The radiolabeling of SYPIPDT-ECG-TAMRA with Tc-99m was accomplished using ligand exchange via tartrate. Cellular uptake and binding affinity studies were performed. In vivo gamma camera imaging, ex vivo imaging and biodistribution studies were performed using NCI-H460 and SW620 tumor-bearing murine models. After radiolabeling procedures with Tc-99m, Tc-99m SYPIPDT-ECG-TAMRA complexes were prepared at high yield (> 95%). The binding affinity value (K_d) of Tc-99m SYPIPDT-ECG-TAMRA for NCI-H460 cells was estimated to be 76.5 ± 15.8 nM. In gamma camera imaging, the tumor to normal muscle uptake ratios of Tc-99m SYPIPDT-ECG-TAMRA increased with time (2.7 ± 0.6, 4.0 ± 0.9, and 6.2 ± 1.0 at 1, 2, and 3 h, respectively). The percentage injected dose per gram of wet tissue for the NCI-H460 tumor was 1.91 ± 0.11 and 1.70 ± 0.22 at 1 and 3 h, respectively. We developed Tc-99m SYPIPDT-ECG-TAMRA, which is dual-labeled with both radioisotope and fluorescence. In vivo and in vitro studies demonstrated specific uptake of Tc-99m SYPIPDT-ECG-TAMRA into wtEGFR-positive NCI-H460 cells and tumors. Thus, the results of the present study suggest that Tc-99m SYPIPDT-ECG-TAMRA is a potential dual-modality imaging agent targeting wtEGFR.

Optical spectra and conformation pool of tyrosine kinase inhibitor PD153035 using a robust quantum mechanical conformation search

The most potent drug configuration is not necessarily the lowest energy conformer. The optical spectral profile of a flexible TKI depends on the distribution of the conformers and therefore the conditions such as environment (solvent).

Synthesis and biological evaluation of novel PET tracers [18F]AG120 & [18F]AG135 for imaging mutant isocitrate dehydrogenase 1 expression

Mutations in isocitrate dehydrogenase 1 (IDH1) are commonly found in various human malignancies. Inhibitors of several mutant IDH1 enzymes have entered clinical trials as target therapeutic drugs for the treatment of patients with IDH1 mutations. Herein, we report the synthesis and evaluation of two 18F-labeled tracers, [18F]AG120 and [18F]AG135 for imaging expression of mutated IDH1 in positron emission tomography (PET). [18F]AG120 and [18F]AG135 were synthesized in decay-corrected radiochemical yield of 1 % and 3 %, respectively, high molar activity (52-66 MBq/nmol and 216-339 MBq/nmol, respectively) and high radiochemical purity (>99%). Both tracers showed good in vitro stability, selective uptake into mutated IDH1-expressing cells and good pharmacokinetic profiles with low uptake in most organs/tissues. Furthermore, [18F]AG120 micro-PET/CT imaging displayed significantly greater uptake in IDH1-mutant than in wild-type tumors, Relatively, uptake of [18F]AG135 was observed neither in IDH1-mutant tumor xenografts nor in wild-type tumors. This study suggests that [18F]AG120 is a promising radiotracer for PET imaging of IDH1 mutation, However, further optimization and investigation are necessary for [18F]AG135 due to the limited uptake in mutated IDH1-expressing tumors.

[18F]F-ET-OTSSP167 Targets Maternal Embryo Leucine Zipper Kinase for PET Imaging of Triple-Negative Breast Cancer

Maternal embryo leucine zipper kinase (MELK) is a serine/threonine kinase and is highly expressed in triple-negative breast cancer (TNBC). This study aimed to develop a ¹⁸F-radiolabeled tracer based on the structure of a small-molecule MELK inhibitor OTSSP167 and evaluate its application for PET imaging of MELK expression in TNBC. OTSSP167 was modified with ethylene glycol to adjust its pharmacokinetics and was then radiolabeled with ¹⁸F to obtain [¹⁸F]F-ET-OTSSP167 at a labeling yield of 7.14 ± 2.19% and a molar activity of 16.23 ± 1.13 MBq/nmol. In vitro binding assays showed differentiated binding affinities of [¹⁸F]F-ET-OTSSP167 in different breast cancer cell lines, with high uptake in MDA-MB-231 (mild MELK expression) and low uptake in MCF-7 (negative MELK expression). PET imaging revealed that MDA-MB-231 tumors could be clearly delineated in vivo, while low tracer uptake was observed in MCF-7 tumors. These findings were confirmed by ex vivo biodistribution studies and were consistent with the immunohistochemistry and tissue staining results. Tracer accumulation in MDA-MB-231 tumors was significantly inhibited by excess amounts of OTSSP167, indicating high specificity of the tracer. In summary, [¹⁸F]F-ET-OTSSP167, an easily-prepared probe, can be used to visualize MELK positive tumors, demonstrating its promising clinical potential in selecting patients for MELK inhibitor therapy.

A novel carbon-11 radiolabeled maternal embryonic leucine zipper kinase inhibitor for PET imaging of triple-negative breast cancer

Maternal embryonic leucine zipper kinase (MELK) plays an important role in the regulation of tumor cell growth. It is abundant in triple-negative breast cancers (TNBC), making it a promising target for molecular imaging and therapy. Based on the structure of a potent MELK inhibitor (OTSSP167) with high affinity, we developed a novel carbon-11 radiolabeled molecular probe ¹¹C-methoxy-OTSSP167, and evaluated its application in positron emission tomography (PET) imaging of TNBC. ¹¹C-methoxy-OTSSP167 was successfully synthesized and was identical to its non-radiolabeled compound methoxy-OTSSP167 in high-pressure liquid chromatography (HPLC) chromatogram. The obtained tracer had 10 ± 2% radiolabeling yield with a total synthesis time of 40 min. The radiochemical purity of the tracer was more than 95%. The maximum uptake (9.97 ± 0.70%) of ¹¹C-methoxy-OTSSP167 in MELK-overexpressing MDA-MB-231 cells was at 60 min in vitro. On PET, MDA-MB-231 tumors were clearly visible at 30, 60, and 90 min after injection of ¹¹C-methoxy-OTSSP167, while no obvious radioactivity accumulation was found in the low-MELK MCF-7 tumors. In vivo biodistribution data were consistent with the findings of the PET images. However, the radioactive tracer showed high uptake in normal organs such as liver and intestine, which may limit the application of the tracer. In addition, a markedly different MELK expression level in MDA-MBA-231 and MCF-7 tumors was verified via IHC staining. In conclusion, ¹¹C-methoxy-OTSSP167 was successfully developed and exhibited elevated uptake in MELK overexpressed tumor, indicating its potential for noninvasively imaging of MELK overexpressed TNBC.

Novel anilino quinazoline-based EGFR tyrosine kinase inhibitors for treatment of non-small cell lung cancer

The epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of non-small cell lung cancer (NSCLC). EGFR-TKI positron emission tomography (PET) probes based on the central quinazoline core show great potential for NSCLC diagnosis, and pre-clinical and clinical therapy monitoring. In our previous research, anilino quinazoline based PET probe, N-(3-chloro-4-fluorophenyl)-7-(2-(2-(2-(2-¹⁸F-fluoroethoxy) ethoxy) ethoxy) ethoxy)-6-methoxyquinazolin-4-amine (¹⁸F-MPG), have been developed, and it has been successfully demonstrated to be a powerful non-invasive imaging tool for differentiating EGFR mutation status and stratifying NSCLC patients for EGFR-TKI treatment in a clinical study (n = 75 patients). Moreover, it has been found that ¹⁸F-MPG shows excellent tumor targeting performance and good pharmacokinetic characteristics in NSCLC patients. These results motivate us to investigate the cancer treatment efficacy of non-radioactive F-MPG and its analogue N-(3-chloro-4-fluorophenyl)-7-(2-(2-(2-(2-hydroxyethoxy)ethoxy) ethoxy) ethoxy)-6-methoxyquinazolin-4-amine (OH-MPG) in vitro and in small animal models. Our studies revealed that both F-MPG and OH-MPG displayed high therapeutic effect to NSCLC cells (IC₅₀ = 5.3 nM and 2.0 nM to HCC827 cells for F-MPG and OH-MPG, respectively). More importantly, compared with a standard EGFR-TKI, 4-(3-bromoanilino)-6,7-dimethoxyquinazoline (PD153035), F-MPG and OH-MPG showed stronger tumor inhibition in preclinical models. Furthermore, the treatment efficacy of F-MPG or OH-MPG monitored by ¹⁸F-FDG-PET indicated that tumor uptake in treated groups was significantly decreased. Ex vivo experiments showed that the levels of serum biomarkers and pathological changes in the liver were significantly reduced in the F-MPG and OH-MPG group, compared to PD153035 treated group. In conclusion, EGFR targeted F-MPG and OH-MPG exhibit promising anti-tumor activity with limited liver damage, thus representing promising drug candidates for further investigation for combating the deadly NSCLC.

11C-Labeled Pictilisib (GDC-0941) as a Molecular Tracer Targeting Phosphatidylinositol 3-Kinase (PI3K) for Breast Cancer Imaging

Pictilisib (GDC-0941) is an inhibitor of phosphatidylinositol 3-kinase (PI3K), part of a signaling cascade involved in breast cancer development. The purpose of this study was to evaluate the pharmacokinetics of pictilisib noninvasively by radiolabeling it with ¹¹C and to assess the usability of the resulting [¹¹C]-pictilisib as a positron-emission tomography (PET) tracer to screen for pictilisib-sensitive tumors. In this study, pictilisib was radiolabeled with [¹¹C]-methyl iodide to obtain ¹¹C-methylated pictilisib ([¹¹C]-pictilisib) using an automated synthesis module with a high radiolabeling yield. Considerably higher uptake ratios were observed in MCF-7 (PIK3CA mutation, pictilisib-sensitive) cells than those in MDA-MB-231 (PIK3CA wild-type, pictilisib-insensitive) cells at all evaluated time points, indicating good in vitro binding of [¹¹C]-pictilisib. Dynamic micro-PET scans in mice and biodistribution results showed that [¹¹C]-pictilisib was mainly excreted via the hepatobiliary tract into the intestines. MCF-7 xenografts could be clearly visualized on the static micro-PET scans, while MDA-MB-231 tumors could not. Biodistribution results of two xenograft models showed significantly higher uptake and tumor-to-muscle ratios in the MCF-7 xenografts than those in MDA-MB-231 xenografts, exhibiting high in vivo targeting specificity. In conclusion, [¹¹C]-pictilisib was first successfully prepared, and it exhibited good potential to identify pictilisib-sensitive tumors noninvasively, which may have a great impact in the treatment of cancers with an overactive PI3K/Akt/mTOR signal pathway. However, the high activity in hepatobiliary system and intestines needs to be addressed.

Preclinical Imaging in Targeted Cancer Therapies

Preclinical imaging with radiolabeled probes can provide noninvasive tools to test the efficacy of targeted agents in tumors harboring specific genetic alterations and to identify imaging parameters that can be used as pharmacodynamics markers in cancer patients. The present review will primarily focus on preclinical imaging studies that can accelerate the clinical approval of targeted agents and promote the development of imaging biomarkers for clinical applications. Since only subgroups of patients may benefit from treatment with targeted anticancer agents, the identification of a patient population expressing the target is of primary importance for the success of clinical trials. Preclinical imaging studies tested the ability of new radiolabeled compounds to recognize mutant, amplified, or overexpressed targets and some of these tracers were transferred to the clinical setting. More common tracers such as ¹⁸F-Fluorothymidine and ¹⁸F-Fluorodeoxyglucose were employed in animal models to test the inhibition of the target and downstream pathways through the evaluation of early changes of proliferation and glucose metabolism allowing the identification of sensitive and resistant tumors. Furthermore, since the majority of patients treated with targeted anticancer agents will invariably develop resistance, preclinical imaging studies were performed to test the efficacy of reversal agents to overcome resistance. These studies provided consistent evidence that imaging with radiolabeled probes can monitor the reversal of drug resistance by newly designed alternative compounds. Finally, despite many difficulties and challenges, preclinical imaging studies targeting the expression of immune checkpoints proved the principle that it is feasible to select patients for immunotherapy based on imaging findings. In conclusion, preclinical imaging can be considered as an integral part of the complex translational process that moves a newly developed targeted agent from laboratory to clinical application intervening in all clinically relevant steps including patient selection, early monitoring of drug effects and reversal of drug resistance.

Accurate Classification of Non-small Cell Lung Cancer (NSCLC) Pathology and Mapping of EGFR Mutation Spatial Distribution by Ambient Mass Spectrometry Imaging

Objectives: Tumor pathology examination especially epidermal growth factor receptor (EGFR) mutations molecular testing has been integral part of lung cancer clinical practices. However, the EGFR mutations spatial distribution characteristics remains poorly investigated, which is critical to tumor heterogeneity analysis and precision diagnosis. Here, we conducted an exploratory study for label-free lung cancer pathology diagnosis and mapping of EGFR mutation spatial distribution using ambient mass spectrometry imaging (MSI).

Materials and Methods: MSI analysis were performed in 55 post-operative non-small cell lung cancer (NSCLC) tumor and paired normal tissues to distinguish tumor from normal and classify pathology. We then compared diagnostic sensitivity of MSI and ADx-amplification refractory mutation system (ARMS) for the detection of EGFR mutation in pathological confirmed lung adenocarcinoma (AC) and explored EGFR mutations associated biomarkers to depict EGFR spatial distribution base on ambient MSI.

Results: Of 55 pathological confirmed NSCLC, MSI achieved a diagnostic sensitivity of 85.2% (23/27) and 82.1% (23/28) for AC and squamous cell carcinoma (SCC), respectively. Among 27 AC, there were 17 EGFR-wild-type and 10 EGFR-mutated-positive samples detected by ARMS, and MSI achieved a diagnostic sensitivity of 82.3% (14/17) and 80% (8/10) for these two groups. Several phospholipids were specially enriched in AC compared with SCC tissues, with the higher ions intensity of phospholipids in EGFR-mutated-positive compared with EGFR-wild-type AC tissues. We also found EGFR mutations distribution was heterogeneous in different regions of same tumor by multi-regions ARMS detection, and only the regions with higher ions intensity of phospholipids were EGFR-mutated-positive.

Conclusion: MSI method could accurately distinguish tumor pathology and subtypes, and phospholipids were reliable EGFR mutations associated biomarkers, phospholipids imaging could intuitively visualize EGFR mutations spatial distribution, may facilitate our understanding of tumor heterogeneity.

Novel derivatives of anaplastic lymphoma kinase inhibitors: Synthesis, radiolabeling, and preliminary biological studies of fluoroethyl analogues of crizotinib, alectinib, and ceritinib

Anaplastic lymphoma kinase (ALK), an oncogenic receptor tyrosine kinase, is a therapeutic target in various cancers, including non-small cell lung cancer. Although several ALK inhibitors, including crizotinib, ceritinib, and alectinib, are approved for cancer treatment, their long-term benefit is often limited by the cancer's acquisition of resistance owing to secondary point mutations in ALK. Importantly, some ALK inhibitors cannot cross the blood-brain barrier (BBB) and thus have little or no efficacy against brain metastases. The introduction of a lipophilic moiety, such as a fluoroethyl group may improve the drug's BBB penetration. Herein, we report the synthesis of fluoroethyl analogues of crizotinib 1, alectinib 4, and ceritinib 9, and their radiolabeling with ¹⁸F for pharmacokinetic studies. The fluoroethyl derivatives and their radioactive analogues were obtained in good yields with high purity and good molar activity. A cytotoxicity screen in ALK-expressing H2228 lung cancer cells showed that the analogues had up to nanomolar potency and the addition of the fluorinated moiety had minimal impact overall on the potency of the original drugs. Positron emission tomography in healthy mice showed that the analogues had enhanced BBB penetration, suggesting that they have therapeutic potential against central nervous system metastases.

Chronic Obstructive Pulmonary Disease and Lung Cancer: Underlying Pathophysiology and New Therapeutic Modalities

Chronic obstructive pulmonary disease (COPD) and lung cancer are major lung diseases affecting millions worldwide. Both diseases have links to cigarette smoking and exert a considerable societal burden. People suffering from COPD are at higher risk of developing lung cancer than those without, and are more susceptible to poor outcomes after diagnosis and treatment. Lung cancer and COPD are closely associated, possibly sharing common traits such as an underlying genetic predisposition, epithelial and endothelial cell plasticity, dysfunctional inflammatory mechanisms including the deposition of excessive extracellular matrix, angiogenesis, susceptibility to DNA damage and cellular mutagenesis. In fact, COPD could be the driving factor for lung cancer, providing a conducive environment that propagates its evolution. In the early stages of smoking, body defences provide a combative immune/oxidative response and DNA repair mechanisms are likely to subdue these changes to a certain extent; however, in patients with COPD with lung cancer the consequences could be devastating, potentially contributing to slower postoperative recovery after lung resection and increased resistance to radiotherapy and chemotherapy. Vital to the development of new-targeted therapies is an in-depth understanding of various molecular mechanisms that are associated with both pathologies. In this comprehensive review, we provide a detailed overview of possible underlying factors that link COPD and lung cancer, and current therapeutic advances from both human and preclinical animal models that can effectively mitigate this unholy relationship.

Identifying nonsmall-cell lung tumours bearing the T790M EGFR TKI resistance mutation using PET imaging

Specific mutations significantly affect response to epidermal growth factor tyrosine kinase inhibitor (EGFR-TKI) treatment in lung cancer patients. Identifying patients with these mutations remains a major clinical challenge. EGFR T790M mutation, which conveys resistance to in the present study, [¹⁸ F]FEWZ was assessed in vitro to determine efficacy relative to the starting compound and in vivo to measure the biodistribution and specificity of binding to EGFR wild-type, L858R and T790M bearing tumours. [¹⁸ F]FEWZ is the first evidence of a radiolabeled third generation anilinopyrimidine-derived tyrosine kinase inhibitor targeting T790M mutation bearing tumours in vivo.

Inhibition of platelet GPVI induces intratumor hemorrhage and increases efficacy of chemotherapy in mice

Maintenance of tumor vasculature integrity is indispensable for tumor growth and thus affects tumor progression. Previous studies have identified platelets as major regulators of tumor vascular integrity, as their depletion selectively rendered tumor vessels highly permeable and caused massive intratumoral hemorrhage. While these results established platelets as potential targets for antitumor therapy, their depletion is not a treatment option due to their essential role in hemostasis. Thus, a detailed understanding of how platelets safeguard vascular integrity in tumors is urgently demanded. Here, we show for the first time that functional inhibition of glycoprotein VI (GPVI) on the platelet surface with an antibody (JAQ1) F(ab)₂ fragment rapidly induces tumor hemorrhage and diminishes tumor growth similar to complete platelet depletion while not inducing systemic bleeding complications. The intratumor bleeding and tumor growth arrest could be reverted by depletion of Ly6G⁺ cells, confirming them to be responsible for the induction of bleeding and necrosis within the tumor. In addition, JAQ1 F(ab)₂-mediated GPVI inhibition increased intratumoral accumulation of coadministered chemotherapeutic agents, such as Doxil and paclitaxel, thereby resulting in a profound antitumor effect. In summary, our findings identify platelet GPVI as a key regulator of vascular integrity specifically in growing tumors and could serve as a basis for the development of antitumor strategies based on the interference with platelet function.

Real-time molecular optical micro-imaging of EGFR mutations using a fluorescent erlotinib based tracer

BACKGROUND

EGFR mutations are routinely explored in lung adenocarcinoma by sequencing tumoral DNA. The aim of this study was to evaluate a fluorescent-labelled erlotinib based theranostic agent for the molecular imaging of mutated EGFR tumours in vitro and ex vivo using a mice xenograft model and fibred confocal fluorescence microscopy (FCFM).

METHODS

The fluorescent tracer was synthesized in our laboratory by addition of fluorescein to an erlotinib molecule. Three human adenocarcinoma cell lines with mutated EGFR (HCC827, H1975 and H1650) and one with wild-type EGFR (A549) were xenografted on 35 Nude mice. MTT viability assay was performed after exposure to our tracer. In vitro imaging was performed at 1 μM tracer solution, and ex vivo imaging was performed on fresh tumours excised from mice and exposed to a 1 μM tracer solution in PBS for 1 h. Real-time molecular imaging was performed using FCFM and median fluorescence intensity (MFI) was recorded for each experiment.

RESULTS

MTT viability assay confirmed that addition of fluorescein to erlotinib did not suppress the cytotoxic of erlotinib on tumoral cells. In vitro FCFM imaging showed that our tracer was able to distinguish cell lines with mutated EGFR from those lines with wild-type EGFR (p < 0.001). Ex vivo FCFM imaging of xenografts with mutated EGFR had a significantly higher MFI than wild-type (p < 0.001). At a cut-off value of 354 Arbitrary Units, MFI of our tracer had a sensitivity of 100% and a specificity of 96.3% for identifying mutated EGFR tumours.

CONCLUSION

Real time molecular imaging using fluorescent erlotinib is able to identify ex vivo tumours with EGFR mutations.

CD147-mediated glucose metabolic regulation contributes to the predictive role of 18 F-FDG PET/CT imaging for EGFR-TKI treatment sensitivity in NSCLC

The aim of this study is to investigate the role of CD147 in glucose metabolic regulation and its association with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) treatment sensitivity prediction using ¹⁸ F-fluorodeoxyglucose (¹⁸ F-FDG) PET/CT imaging in non-small cell lung cancer (NSCLC). In this study, four human NSCLC cell lines with different EGFR-TKI responses were used to detect p-EGFR/EGFR and CD147 expression via Western blotting and flow cytometric analyses. Radioactive uptake of ¹⁸ F-FDG by established stable NSCLC cell lines (HCC827, H1975) with different levels of CD147 expression and the corresponding xenografts was assessed through γ-radioimmunoassays in vitro and micro-PET/CT imaging in vivo to study the role of CD147 in glucose metabolic reprogramming. Correlation analyses were performed to investigate the association between CD147 expression and PD-L1 expression in stable NSCLC cell lines. Higher CD147 expression was found in EGFR-TKI-sensitive NSCLC cell lines than in relatively resistant NSCLC cell lines (HCC827>PC9>A549>H1975). CD147 could promote ¹⁸ F-FDG uptake by HCC827 and H1975 cells in vitro and in vivo through an EGFR-initiated Akt/mTOR-dependent signaling pathway. Programmed cell death-ligand 1 (PD-L1) expression was positively correlated with CD147 expression in human NSCLC cell lines. EGFR-TKI treatment sensitivity prediction in NSCLC using ¹⁸ F-FDG PET/CT imaging significantly correlated with CD147-mediated glucose metabolic regulation via the Akt/mTOR-dependent pathway. Moreover, PD-L1 expression in NSCLC cell lines could be regulated by CD147, suggesting a potential immunosuppression induced by the upregulation of tumor glucose metabolism.

Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors for Central Nervous System Metastases from Non-Small Cell Lung Cancer

Central nervous system (CNS) metastases are a common complication in patients with epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC), resulting in a poor prognosis and limited treatment options. Treatment of CNS metastases requires a multidisciplinary approach, and the optimal treatment options and sequence of therapies are yet to be established. Many systemic therapies have poor efficacy in the CNS due to the challenges of crossing the blood-brain barrier (BBB), creating a major unmet need for the development of agents with good BBB-penetrating biopharmaceutical properties. Although the CNS penetration of first- and second-generation EGFR tyrosine kinase inhibitors (TKIs) is generally low, EGFR-TKI treatment has been shown to delay time to CNS progression in patients with CNS metastases from EGFR-mutated disease. However, a major challenge with EGFR-TKI treatment for patients with NSCLC is the development of acquired resistance, which occurs in most patients treated with a first-line EGFR-TKI. Novel EGFR-TKIs, such as osimertinib, have been specifically designed to address the challenges of acquired resistance and poor BBB permeability and have demonstrated efficacy in the CNS. A rational, iterative drug development process to design agents that could penetrate the BBB could prevent morbidity and mortality associated with CNS disease progression. To ensure a consistent approach to evaluating CNS efficacy, special consideration also needs to be given to clinical trial endpoints.

IMPLICATIONS FOR PRACTICE

Historically, treatment options for patients who develop central nervous system (CNS) metastases have been limited and associated with poor outcomes. The development of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) has improved outcomes for patients with EGFR-mutated disease, and emerging data have demonstrated the ability of these drugs to cross the blood-brain barrier and elicit significant intracranial responses. Recent studies have indicated a role for next-generation EGFR-TKIs, such as osimertinib, in the treatment of CNS metastases. In the context of an evolving treatment paradigm, treatment should be individualized to the patient and requires a multidisciplinary approach.

Comparison of fully-automated radiosyntheses of [11C]erlotinib for preclinical and clinical use starting from in target produced [11C]CO2 or [11C]CH4

BACKGROUND

[11C]erlotinib has been proposed as a PET tracer to visualize the mutational status of the epidermal growth factor receptor (EGFR) in cancer patients. For clinical use, a stable, reproducible and high-yielding radiosynthesis method is a prerequisite. In this work, two production schemes for [11C]erlotinib applied in a set of preclinical and clinical studies, starting from either [11C]CH4 or [11C]CO2, are presented and compared in terms of radiochemical yields, molar activities and overall synthesis time. In addition, a time-efficient RP-HPLC method for quality control is presented, which requires not more than 1 min.

RESULTS

[11C]erlotinib was reliably produced applying both methods with decay-corrected radiochemical yields of 13.4 ± 6.2% and 16.1 ± 4.9% starting from in-target produced [11C]CO2 and [11C]CH4, respectively. Irradiation time for the production of [11C]CO2 was higher in order to afford final product amounts sufficient for patient application. Overall synthesis time was comparable, mostly attributable to adaptions in the semi-preparative HPLC protocol. Molar activities were 1.8-fold higher for the method starting from [11C]CH4 (157 ± 68 versus 88 ± 57 GBq/μmol at the end of synthesis).

CONCLUSIONS

This study compared two synthetic protocols for the production of [11C]erlotinib with in-target produced [11C]CO2 or [11C]CH4. Both methods reliably yielded sufficiently high product amounts for preclinical and clinical use.

Radioiodinated Small-Molecule Tyrosine Kinase Inhibitor for HER2-Selective SPECT Imaging

One of the most clinically relevant molecular aberrations in breast cancer is overexpression of human epidermal growth factor receptor type 2 (HER2). We aimed to develop a radiolabeled tyrosine kinase inhibitor for HER2-targeted breast cancer imaging. In this study, a radioiodinated analog (^125/131I-IBA-CP) of the HER2-selective inhibitor CP724,714 was prepared and evaluated in HER2-positive or -negative subcutaneous human breast cancer xenografts. Methods: The CP724,714 analog IBA-CP was synthesized and assayed for its inhibitory activities against HER2 and 6 other tyrosine kinases. ^125/131I-IBA-CP was prepared using a copper-mediated radioiodination method with enhanced labeling yield and molar activity. In vitro biologic activity, including specific and nonspecific binding of ¹³¹I-IBA-CP to its HER2 kinase target, was assessed in different cell lines. In vivo small-animal ¹²⁵I-IBA-CP SPECT imaging and biodistribution studies were conducted on mice bearing HER2-positive, HER2-negative, or epidermal growth factor receptor (EGFR)-positive tumors. Nonradioactive IBA-CP and the EGFR inhibitor erlotinib were used as blocking agents to investigate the binding specificity and selectivity of ^125/131I-IBA-CP toward HER2 in vitro and in vivo. Additionally, ^125/131I-ICP was prepared by direct radioiodination of CP724,714 for comparison with ^125/131I-IBA-CP. Results: IBA-CP displayed superior in vitro inhibitory activity (half-maximal inhibitory concentration, 16 nM) and selectivity for HER2 over 6 other cancer-related tyrosine kinases. ^125/131I-IBA-CP was prepared in a typical radiochemical yield of about 65% (decay-corrected), radiochemical purity of more than 98%, and molar activity of 42 GBq/μmol at the end of synthesis. SPECT imaging revealed significantly higher uptake of ¹²⁵I-IBA-CP than of ¹²⁵I-ICP in the HER2-positive MDA-MB-453 tumors. Uptake in the HER2-negative MCF-7 tumors was much lower. Binding of ¹²⁵I-IBA-CP in the MDA-MB-453 tumors was blocked by coinjection with an excess amount of IBA-CP, but not by erlotinib. Conclusion: The radiolabeled HER2-selective inhibitor ^125/131I-IBA-CP is a promising probe for in vivo detection of HER2-positive tumors.

Development of [11C]vemurafenib employing a carbon-11 carbonylative Stille coupling and preliminary evaluation in mice bearing melanoma tumor xenografts

Over the last decade kinase inhibitors have witnessed tremendous growth as anti-cancer drugs. Unfortunately, despite their promising clinical successes, a large portion of patients does not benefit from these targeted therapeutics. Vemurafenib is a serine/threonine kinase inhibitor approved for the treatment of melanomas specifically expressing the BRAF^V600E mutation. The aim of this study was to develop vemurafenib as PET tracer to determine its potential for identification of tumors sensitive to vemurafenib treatment. Therefore, vemurafenib was labeled with carbon-11 and analyzed for its tumor targeting potential in melanoma xenografts Colo829 (BRAF^V600E) and MeWo (BRAF^wt) using autoradiography on tissue sections, in vitro tumor cell uptake studies and biodistribution studies in xenografted athymic nu/nu mice. [¹¹C]vemurafenib was synthesized in 21 ± 4% yield (decay corrected, calculated from [¹¹C]CO) in > 99% radiochemical purity and a specific activity of 55 ± 18 GBq/μmol. Similar binding of [¹¹C]vemurafenib was shown during autoradiography and cellular uptake studies in both cell lines. Plasma metabolite analysis demonstrated > 95% intact [¹¹C]vemurafenib in vivo at 45 minutes after injection, indicating excellent stability. Biodistribution studies confirmed the in vitro results, showing similar tumor-to-background ratios in both xenografts models. These preliminary results suggest that identification of BRAF^V600E mutations in vivo using PET with [¹¹C]vemurafenib will be challenging.

Evaluation of affibody charge modification identified by synthetic consensus design in molecular PET imaging of epidermal growth factor receptor

Tumor overexpression of epidermal growth factor receptor (EGFR) correlates to therapeutic response in select patient populations. Thus, molecular positron emission tomography (PET) imaging of EGFR could stratify responders versus non-responders. We previously demonstrated effectiveness of a "synthetic consensus" design principle to identify six neutralizing mutations within a 58-amino acid EGFR-targeted affibody domain. Herein, we extend the approach to identify additional neutralized variants that vary net charge from -2 to either -4 or +4 while retaining high affinity (1.6 ± 1.2 nM and 2.5 ± 0.7 nM), specific binding to EGFR, secondary structure, and stability (T_m = 68 °C and 59 °C). We radiolabeled the resultant collection of five charge variants with ⁶⁴Cu and evaluated PET imaging performance in murine models with subcutaneously xenografted EGFR^high and EGFR^low tumors. All variants exhibited good EGFR^high tumor imaging as early as 1 h, with EA35S (+3/-5) achieving 7.7 ± 1.4 %ID/g tumor at 4 h with 1.5 ± 0.3%ID/g EGFR^low tumor, 34 ± 5 tumor:muscle and 12 ± 3 tumor:blood ratios. The positively charged EA62S mutant (+6/-2) exhibited 2.2-3.3-fold higher liver signal than the other variants (p<0.01). The EA68 variant with higher charge density was more stable to human and mouse serum than neutralized variants. In a comparison of radiometal chelators, 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) exhibited superior physiological specificity to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA). In total, these studies comparatively evaluated a set of EGFR-targeted affibodies varying in net charge and charge density, which revealed functional variations that are useful in engineering an ideal probe for translational studies.

[Current Status and Progress in Molecular Imaging of Non-small Cell Lung Cancer for Molecular Targeted EGFR-TKI Treatment Sensitivity and Treatment Tolerance Prediction]

肺癌80%以上为非小细胞肺癌（non-small cell lung cancer, NSCLC），表皮生长因子受体（epidermal growth factor receptor, EGFR）介导的信号通路与NSCLC发生发展密切相关。针对EGFR的小分子EGFR赖氨酸激酶抑制剂（EGFR-tyrosine kinase inhibitor, EGFR-TKI）被应用于NSCLC的临床治疗，正电子发射计算机断层显像（positron emission tomography/computed tomgraphy, PET/CT）能够无创地对NSCLC患者全身EGFR表达及突变状况进行连续动态监测。¹⁸F-FDG PET/CT显像对于EGFR活化突变、EGFR-TKI治疗疗效具有预测价值，并且能够在体直接观察到药物与全身肿瘤病灶EGFR靶向结合的具体情况，通过治疗前后的PET-CT显像，实现治疗前高敏人群筛选和治疗全过程的动态监测、治疗策略指导，对实现NSCLC的EGFR-TKI精准治疗至关重要。

Molecular Imaging of ABCB1 and ABCG2 Inhibition at the Human Blood-Brain Barrier Using Elacridar and 11C-Erlotinib PET

Transporters such as ABCB1 and ABCG2 limit the exposure of several anticancer drugs to the brain, leading to suboptimal treatment in the central nervous system. The purpose of this study was to investigate the effects of the ABCB1 and ABCG2 inhibitor elacridar on brain uptake using ¹¹C-erlotinib PET. Methods: Elacridar and cold erlotinib were administered orally to wild-type (WT) and Abcb1a/b;Abcg2 knockout mice. In addition, brain uptake was measured using ¹¹C-erlotinib imaging and ex vivo scintillation counting in knockout and WT mice. Six patients with advanced solid tumors underwent ¹¹C-erlotinib PET scans before and after a 1,000-mg dose of elacridar. ¹¹C-erlotinib brain uptake was quantified by pharmacokinetic modeling using volume of distribution (V_T) as the outcome parameter. In addition, ¹⁵O-H₂O scans to measure cerebral blood flow were acquired before each ¹¹C-erlotinib scan. Results: Brain uptake of ¹¹C-erlotinib was 2.6-fold higher in Abcb1a/b;Abcg2 knockout mice than in WT mice, measured as percentage injected dose per gram of tissue (P = 0.01). In WT mice, the addition of elacridar (at systemic plasma concentrations of ≥200 ng/mL) resulted in an increased brain concentration of erlotinib, without affecting erlotinib plasma concentration. In patients, the V_T of ¹¹C-erlotinib did not increase after intake of elacridar (0.213 ± 0.12 vs. 0.205 ± 0.07, P = 0.91). ¹⁵O-H₂O PET showed no significant changes in cerebral blood flow. Elacridar exposure in patients was 401 ± 154 ng/mL. No increase in V_T with increased elacridar plasma exposure was found over the 271-619 ng/mL range. Conclusion: When Abcb1 and Abcg2 were disrupted in mice, brain uptake of ¹¹C-erlotinib increased both at a tracer dose and at a pharmacologic dose. In patients, brain uptake of ¹¹C-erlotinib was not higher after administration of elacridar. The more pronounced role that ABCG2 appears to play at the human blood-brain barrier and the lower potency of elacridar to inhibit ABCG2 may be an explanation of these interspecies differences.

Genomic Characterization of Lung Cancer and Its Impact on the Use and Timing of PET in Therapeutic Response Assessment

Significant advances in understanding the genomic landscape of non-small cell lung cancer (NSCLC) together with the coupling discovery of key oncogenic drivers and the development of effective targeted and immunotherapeutic agents have revolutionized the management of this malignancy. Although these therapies have resulted in improved outcomes for a subgroup of patients, their benefit may not necessarily be reflected by conventional response assessment criteria, because these therapeutic agents differ in their mechanism of action and response time compared with cytotoxic chemotherapy. Here the authors review available therapies in NSCLC and the utility of PET in therapeutic response assessment.

Speed matters to raise molar radioactivity: Fast HPLC shortens the quality control of C-11 PET-tracers

INTRODUCTION

The decision whether an in-house produced short-lived radiopharmaceutical can be applied in-vivo is based on (1) the fulfilment of all quality criteria; (2) the availability of enough radioactivity for subsequent imaging; and (3) a molar activity (MA) above the set limits to guarantee safe administration without competing occupancy of the non-radioactive compound; and (4) an activity concentration, which is high enough for the application in certain preclinical studies. Hence, time reduction can be of major importance to increase final product yields, MA and activity concentrations. Usually, optimization in this respect only focuses on the radiotracer preparation steps but especially quality control (QC) is rarely even mentioned. Therefore, aim of this work is the establishment of optimized conditions for chromatographic analysis using HPLC within the QC to enable a significant time reduction, which then directly leads to an increase in available amount of radioactive product as well as MA at the time of application.

METHODS

An optimized set-up using ultra-performance liquid chromatography ((U)HPLC) was established and tested on 7 carbon-11 labelled radiotracers used within patient routine or clinical trials.

RESULTS

A drastic time reduction was achieved for all tracers. The optimized protocol lead to a gain of 5-7min (70-86% compared to the original set-up).

CONCLUSIONS

An accelerated (U)HPLC method for radiotracers labelled with short-lived radionuclides was successfully established and conditions were optimized for 7 clinically used radiotracers. The significant gain in QC time leads to a drastic increase in available radioactivity and specific activity at the time of tracer administration.

Non-Small-Cell Lung Cancer PET Imaging Beyond F18 Fluorodeoxyglucose

F18 Flurodeoxyglucose (FDG) is a nonspecific PET tracer representing tumor energy metabolism, with common false-positive and false-negative findings in clinical practice. Non-small cell lung cancer is highly heterogeneous histologically, biologically, and molecularly. Novel PET tracers designed to characterize a specific aspect of tumor biology or a pathway-specific molecular target have the potential to provide noninvasive key information in tumor heterogeneity for patient stratification and in the assessment of treatment response. Non-FDG PET tracers, including ⁶⁸Ga-somatostatin analogs, and some PET tracers targeting tumor proliferation, hypoxia, angiogenesis, and pathway-specific targets are briefly reviewed in this article.

Radiosynthesis and biological evaluation of 18F-labeled 4-anilinoquinazoline derivative (18F-FEA-Erlotinib) as a potential EGFR PET agent

Epidermal growth factor receptor (EGFR) has gained significant attention as a therapeutic target. Several EGFR targeting drugs (Gefitinib and Erlotinib) have been approved by US Food and Drug Administration (FDA) and have received high approval in clinical treatment. Nevertheless, the curative effect of these medicines varied in many solid tumors because of the different levels of expression and mutations of EGFR. Therefore, several PET radiotracers have been developed for the selective treatment of responsive patients who undergo PET/CT imaging for tyrosine kinase inhibitor (TKI) therapy. In this study, a novel fluorine-18 labeled 4-anilinoquinazoline based PET tracer, 1N-(3-(1-(2-¹⁸F-fluoroethyl)-1H-1,2,3-triazol-4-yl)phenyl)-6,7-bis(2-methoxyethoxy)quinazolin-4-amine (¹⁸F-FEA-Erlotinib), was synthesized and biological evaluation was performed in vitro and in vivo. ¹⁸F-FEA-Erlotinib was achieved within 50min with over 88% radiochemical yield (decay corrected RCY), an average specific activity over 50GBq/μmol, and over 99% radiochemical purity. In vitro stability study showed no decomposition of ¹⁸F-FEA-Erlotinib after incubated in PBS and FBS for 2h. Cellular uptake and efflux experiment results indicated the specific binding of ¹⁸F-FEA-Erlotinib to HCC827 cell line with EGFR exon 19 deletions. In vivo, Biodistribution studies revealed that ¹⁸F-FEA-Erlotinib exhibited rapid blood clearance both through hepatobiliary and renal excretion. The tumor uptake of ¹⁸F-FEA-Erlotinib in HepG2, HCC827, and A431 tumor xenografts, with different EGFR expression and mutations, was visualized in PET images. Our results demonstrate the feasibility of using ¹⁸F-FEA-Erlotinib as a PET tracer for screening EGFR TKIs sensitive patients.

Multiplexed imaging for diagnosis and therapy

Complex molecular and metabolic phenotypes depict cancers as a constellation of different diseases with common themes. Precision imaging of such phenotypes requires flexible and tunable modalities capable of identifying phenotypic fingerprints by using a restricted number of parameters while ensuring sensitivity to dynamic biological regulation. Common phenotypes can be detected by in vivo imaging technologies, and effectively define the emerging standards for disease classification and patient stratification in radiology. However, for the imaging data to accurately represent a complex fingerprint, the individual imaging parameters need to be measured and analysed in relation to their wider spatial and molecular context. In this respect, targeted palettes of molecular imaging probes facilitate the detection of heterogeneity in oncogene-driven alterations and their response to treatment, and lead to the expansion of rational-design elements for the combination of imaging experiments. In this Review, we evaluate criteria for conducting multiplexed imaging, and discuss its opportunities for improving patient diagnosis and the monitoring of therapy.

Facilitating in vivo tumor localization by principal component analysis based on dynamic fluorescence molecular imaging

Fluorescence molecular imaging has been used to target tumors in mice with xenograft tumors. However, tumor imaging is largely distorted by the aggregation of fluorescent probes in the liver. A principal component analysis (PCA)-based strategy was applied on the in vivo dynamic fluorescence imaging results of three mice with xenograft tumors to facilitate tumor imaging, with the help of a tumor-specific fluorescent probe. Tumor-relevant features were extracted from the original images by PCA and represented by the principal component (PC) maps. The second principal component (PC2) map represented the tumor-related features, and the first principal component (PC1) map retained the original pharmacokinetic profiles, especially of the liver. The distribution patterns of the PC2 map of the tumor-bearing mice were in good agreement with the actual tumor location. The tumor-to-liver ratio and contrast-to-noise ratio were significantly higher on the PC2 map than on the original images, thus distinguishing the tumor from its nearby fluorescence noise of liver. The results suggest that the PC2 map could serve as a bioimaging marker to facilitate in vivo tumor localization, and dynamic fluorescence molecular imaging with PCA could be a valuable tool for future studies of in vivo tumor metabolism and progression.

[Molecular Imaging in vivo Detection of EGFR Mutations in Non-small Cell Lung Cancer]

靶向药物表皮生长因子受体酪氨酸激酶抑制剂（epidermal growth factor receptor tyrosine kinase inhibitor, EGFR-TKI）改变了非小细胞肺癌的治疗格局，研究表明只有EGFR敏感突变人群能从中获益。EGFR突变检测的主流方法是针对EGFR的DNA序列进行分析，标本可以是手术或穿刺获取的肺癌组织、胸水肿瘤细胞、循环肿瘤细胞、外周血游离DNA，其最大的缺点是无法分析EGFR突变的异质性。针对EGFR在蛋白质水平进行突变检测分析的技术尚不成熟，但随着分子影像学的发展，基于正电子发射型计算机断层显像（positron emission computed tomography, PET）-计算机断层扫描（computed tomography, CT）的靶向EGFR分子探针的研发，使得在体检测肺癌组织的EGFR突变状态成为了可能，而且可以检测EGFR突变的异质性。本文综述了目前靶向EGFR突变的分子探针的研究结果及进展。

Harnessing Integrative Omics to Facilitate Molecular Imaging of the Human Epidermal Growth Factor Receptor Family for Precision Medicine

Cancer is a growing problem worldwide. The cause of death in cancer patients is often due to treatment-resistant metastatic disease. Many molecularly targeted anticancer drugs have been developed against 'oncogenic driver' pathways. However, these treatments are usually only effective in properly selected patients. Resistance to molecularly targeted drugs through selective pressure on acquired mutations or molecular rewiring can hinder their effectiveness. This review summarizes how molecular imaging techniques can potentially facilitate the optimal implementation of targeted agents. Using the human epidermal growth factor receptor (HER) family as a model in (pre)clinical studies, we illustrate how molecular imaging may be employed to characterize whole body target expression as well as monitor drug effectiveness and the emergence of tumor resistance. We further discuss how an integrative omics discovery platform could guide the selection of 'effect sensors' - new molecular imaging targets - which are dynamic markers that indicate treatment effectiveness or resistance.

[11C]Erlotinib PET cannot detect acquired erlotinib resistance in NSCLC tumor xenografts in mice

INTRODUCTION

[¹¹C]Erlotinib PET has shown promise to distinguish non-small cell lung cancer (NSCLC) tumors harboring the activating epidermal growth factor receptor (EGFR) mutation delE746-A750 from tumors with wild-type EGFR. To assess the suitability of [¹¹C]erlotinib PET to detect the emergence of acquired erlotinib resistance in initially erlotinib-responsive tumors, we performed in vitro binding and PET experiments in mice bearing tumor xenografts using a range of different cancer cells, which were erlotinib-sensitive or exhibited clinically relevant resistance mechanisms to erlotinib.

METHODS

The following cell lines were used for in vitro binding and PET experiments: the epidermoid carcinoma cell line A-431 (erlotinib-sensitive, wild-type EGFR) and the three NSCLC cell lines HCC827 (erlotinib-sensitive, delE746-A750), HCC827_EPR (erlotinib-resistant, delE746-A750 and T790M) and HCC827_ERLO (erlotinib-resistant, delE746-A750 and MET amplification). BALB/c nude mice with subcutaneous tumor xenografts underwent two consecutive [¹¹C]erlotinib PET scans, a baseline scan and a second scan in which unlabeled erlotinib (10mg/kg) was co-injected. Logan graphical analysis was used to estimate total distribution volume (V_T) of [¹¹C]erlotinib in tumors.

RESULTS

In vitro experiments revealed significantly higher uptake of [¹¹C]erlotinib (5.2-fold) in the three NSCLC cell lines as compared to A-431 cells. In all four cell lines co-incubation with unlabeled erlotinib (1μM) led to significant reductions in [¹¹C]erlotinib uptake (-19% to -66%). In both PET scans and for all four studied cell lines there were no significant differences in tumoral [¹¹C]erlotinib V_T values. For all three NSCLC cell lines, but not for the A-431 cell line, tumoral V_T was significantly reduced following co-injection of unlabeled erlotinib (-20% to -35%).

CONCLUSIONS

We found no significant differences in the in vitro and in vivo binding of [¹¹C]erlotinib between erlotinib-sensitive and erlotinib-resistant NSCLC cells. Our findings suggest that [¹¹C]erlotinib PET will not be suitable to distinguish erlotinib-sensitive NSCLC tumors from tumors with acquired resistance to erlotinib.