Strategies for molecular imaging of epidermal growth factor receptor tyrosine kinase in cancer

The Development of a Smart Magnetic Resonance Imaging and Chemical Exchange Saturation Transfer Contrast Agent for the Imaging of Sulfatase Activity

The molecular imaging of biomarkers plays an increasing role in medical diagnostics. In particular, the imaging of enzyme activity is a promising approach, as it enables the use of its inherent catalytic activity for the amplification of an imaging signal. The increased activity of a sulfatase enzyme has been observed in several types of cancers. We describe the development and in vitro evaluation of molecular imaging agents that allow for the detection of sulfatase activity using the whole-body, non-invasive MRI and CEST imaging methods. This approach relies on a responsive ligand that features a sulfate ester moiety, which upon sulfatase-catalyzed hydrolysis undergoes an elimination process that changes the functional group, coordinating with the metal ion. When Gd3+ is used as the metal, the complex can be used for MRI, showing a 25% decrease at 0.23T and a 42% decrease at 4.7T in magnetic relaxivity after enzymatic conversion, thus providing a "switch-off" contrast agent. Conversely, the use of Yb3+ as the metal leads to a "switch-on" effect in the CEST imaging of sulfatase activity. Altogether, the results presented here provide a molecular basis and a proof-of-principle for the magnetic imaging of the activity of a key cancer biomarker.

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.

Radiolabeled Peptide Probes for Liver Cancer Imaging

Liver cancer/Hepatocellular Carcinoma (HCC) is a leading cause of cancer death and represents an important cause of mortality worldwide. Several biomarkers are overexpressed in liver cancer, such as Glypican 3 (GPC3) and Epidermal Growth Factor Receptor (EGFR). These biomarkers play important roles in the progression of tumors and could serve as imaging and therapeutic targets for this disease. Peptides with adequate stability, receptor binding properties, and biokinetic behavior have been intensively studied for liver cancer imaging. A great variety of them have been radiolabeled with clinically relevant radionuclides for liver cancer diagnosis, and many are promising imaging and therapeutic candidates for clinical translation. Herein, we summarize the advancement of radiolabeled peptides for the targeted imaging of liver cancer.

Synthesis and evaluation of [18F]FP-Lys-GE11 as a new radiolabeled peptide probe for epidermal growth factor receptor (EGFR) imaging

INTRODUCTION

The epidermal growth factor receptor (EGFR) has emerged as an attractive target in the treatment of various cancers. Radiolabeled small molecules, antibodies, and peptides that specifically target EGFR are promising probes for tumor imaging to guide personalized treatment with EGFR-targeted drugs. This study aimed to radiolabel GE11 (an EGFR-specific targeting peptide) with 18-fluorine to develop a new EGFR-targeting positron emission tomography (PET) probe, [18F]FP-Lys-GE11, for imaging tumors overexpressing EGFR.

METHODS

[18F]FP-Lys-GE11 was produced by radiolabeling a GE11 peptide with the prosthetic group 4-nitrophenyl-2-[18F]fluoropropionate ([18F]NFP). Stability in PBS and mice serum, affinity for A431 cell line, U87 and PC-3 cells uptake and blocking studies, and biodistribution of [18F]FP-Lys-GE11 were determined. 2 h dynamic and static PET scans of probe for tumor-bearing mice normal and inhibition uptake were performed.

RESULTS

[18F]FP-Lys-GE11 was stable in PBS and mice serum. The Kd and Bmax values of probe for A431 were 42.43 ± 3.75 nM and 3383 ± 81.73 CPM, respectively. In cell uptake and blocking experiments, a significant reduction in radioactivity accumulation (over 4-fold) was observed by blocking U87 and PC-3 cells with unlabeled peptide. PET imaging of U87 and PC-3 tumor-bearing mice revealed clear tumor imaging (tumor radioactivity accumulation was 3.48 ± 0.44 and 3.68 ± 0.76%ID/g respectively, tumor-to-muscle ratio was 3.45 ± 0.43 and 3.64 ± 0.76 respectively). Blocking imaging revealed that the U87 tumor uptake was significantly inhibited (2.21 ± 0.41%ID/g). The biodistribution and dynamic PET imaging showed that [18F]FP-Lys-GE11 was mainly excreted by the kidneys and the rest was excreted through the bile and intestines.

CONCLUSION

The current results showed that [18F]FP-Lys-GE11was a good radiolabeled peptide probe for EGFR overexpression tumor's imaging.

Imaging of Tumor Spheroids, Dual-Isotope SPECT, and Autoradiographic Analysis to Assess the Tumor Uptake and Distribution of Different Nanobodies

PURPOSE

Recent studies have shown rapid accumulation of nanobodies (NBs) in tumors and fast clearance of the unbound fraction, making NBs exceptional tracers for cancer imaging. In this study, we investigate the combination of in vitro imaging of tumor spheroids, in vivo dual-isotope single-photon emission computed tomography (SPECT), and ex vivo autoradiographic analysis of tumors to efficiently, and with few mice, assess the tumor uptake and distribution of different NBs.

PROCEDURES

The irrelevant NB R2 (16 kDa) and the EGFR-targeted NBs 7D12 (16 kDa) and 7D12-R2 (32 kDa) were investigated. Confocal microscopy was used to study the penetration of the NBs into A431 tumor spheroids over time, using the anti-EGFR monoclonal antibody (mAb) cetuximab (150 kDa) as a reference. Dual-isotope [¹¹¹In]DOTA-NB/[¹⁷⁷Lu]DOTA-NB SPECT was used for longitudinal imaging of multiple tracers in the same animal bearing A431 tumor xenografts. Tumor sections were analyzed using autoradiography.

RESULTS

No binding of the irrelevant NB was observed in spheroids, whereas for the specific tracers an increase in the spheroid's covered area was observed over time. The NB 7D12 saturated the spheroid earlier than the larger, 7D12-R2. Even slower penetration was observed for the large mAb. In vivo, the tumor uptake of 7D12 was 19-fold higher than R2 after co-injection in the same animal, and 2.5-fold higher than 7D12-R2 when co-injected. 7D12-R2 was mainly localized at the rim of tumors, while 7D12 was found to be more evenly distributed.

CONCLUSIONS

This study demonstrates that the combination of imaging of tumor spheroids, dual-isotope SPECT, and autoradiography of tumors is effective in comparing tumor uptake and distribution of different NBs. Results were in agreement with published data, highlighting the value of monomeric NBs for tumor imaging, and re-enforcing the value of these techniques to accurately assess the most optimal format for tumor imaging. This combination of techniques requires a lower number of animals to obtain significant data and can accelerate the design of novel tracers.

Tumor-specific delivery of therapeutic siRNAs by anti-EGFR immunonanoparticles

Background

Efficient target-specific siRNA delivery has always been a primary concern in the field of siRNA clinical application.

Purpose

In this study, four different types of anti-epidermal growth factor receptor (EGFR) antibody-conjugated immunonanoparticles were prepared and tested for cancer cell-targeted therapeutic siRNA delivery.

Materials and methods

The prepared nanoparticles encapsulating siRNAs were character-ized by gel retardation and particle analysis using a Zetasizer. In vitro transfection and reduction of target genes, vimentin and JAK3, were determined using quantitative reverse transcription polymerase chain reaction. In vivo tumor targeting and antitumoral efficacies of the nanoparticles were evaluated in mice carrying tumors.

Results

Among these immunonanoparticles, anti-EGFR immunolipoplexes and immunoviroplexes exhibited remarkable cell binding and siRNA delivery to EGFR-expressing tumor cells compared to immunoliposomes and immunovirosomes. Especially, the anti-EGFR immunoviroplexes exhibited the most efficient siRNA transfection to target tumor cells. Therefore, antitumoral vimentin and Janus kinase-3 siRNAs were loaded in the anti-EGFR immunolipoplexes and immunoviroplexes, which were tested in mice carrying SK-OV-3 tumor xenografts. In fact, the therapeutic siRNAs were efficiently delivered to the tumor tissues by both delivery vehicles, resulting in significant inhibition of tumor growth. Moreover, administration of doxorubicin in combination with anti-EGFR immunoviroplexes resulted in remarkable and synergistic tumor growth inhibition.

Conclusion

This study provides experimental proof that cancer cell-targeted immunoviroplexes are an efficient siRNA delivery system for cancer therapy. Moreover, this study also suggests that a combination of conventional chemotherapy and tumor-directed anticancer siRNA therapy would be a better modality for cancer treatment.

[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。

Nanobody-Based Delivery Systems for Diagnosis and Targeted Tumor Therapy

The development of innovative targeted therapeutic approaches are expected to surpass the efficacy of current forms of treatments and cause less damage to healthy cells surrounding the tumor site. Since the first development of targeting agents from hybridoma’s, monoclonal antibodies (mAbs) have been employed to inhibit tumor growth and proliferation directly or to deliver effector molecules to tumor cells. However, the full potential of such a delivery strategy is hampered by the size of mAbs, which will obstruct the targeted delivery system to access the tumor tissue. By serendipity, a new kind of functional homodimeric antibody format was discovered in camelidae, known as heavy-chain antibodies (HCAbs). The cloning of the variable domain of HCAbs produces an attractive minimal-sized alternative for mAbs, referred to as VHH or nanobodies (Nbs). Apart from their dimensions in the single digit nanometer range, the unique characteristics of Nbs combine a high stability and solubility, low immunogenicity and excellent affinity and specificity against all possible targets including tumor markers. This stimulated the development of tumor-targeted therapeutic strategies. Some autonomous Nbs have been shown to act as antagonistic drugs, but more importantly, the targeting capacity of Nbs has been exploited to create drug delivery systems. Obviously, Nb-based targeted cancer therapy is mainly focused toward extracellular tumor markers, since the membrane barrier prevents antibodies to reach the most promising intracellular tumor markers. Potential strategies, such as lentiviral vectors and bacterial type 3 secretion system, are proposed to deliver target-specific Nbs into tumor cells and to block tumor markers intracellularly. Simultaneously, Nbs have also been employed for in vivo molecular imaging to diagnose diseased tissues and to monitor the treatment effects. Here, we review the state of the art and focus on recent developments with Nbs as targeting moieties for drug delivery systems in cancer therapy and cancer imaging.

Harnessing Preclinical Molecular Imaging to Inform Advances in Personalized Cancer Medicine

Comprehensive molecular analysis of individual tumors provides great potential for personalized cancer therapy. However, the presence of a particular genetic alteration is often insufficient to predict therapeutic efficacy. Drugs with distinct mechanisms of action can affect the biology of tumors in specific and unique ways. Therefore, assays that can measure drug-induced perturbations of defined functional tumor properties can be highly complementary to genomic analysis. PET provides the capacity to noninvasively measure the dynamics of various tumor biologic processes in vivo. Here, we review the underlying biochemical and biologic basis for a variety of PET tracers and how they may be used to better optimize cancer therapy.

Preparation and biological evaluation of 99mTc-HYNIC-(Ser)3-D4 peptide for targeting and imaging of non-small-cell lung cancer

Aim: In this study, radiolabeled D4 peptide conjugate was studied as a radiotracer for imaging of non-small-cell lung cancer with overexpression of EGFR. Methods: HYNIC-(Ser)3-D4 peptide was labeled with 99mTc using tricine as a co-ligand. Cellular specific binding and internalization as well as in vivo tumor targeting were assessed. Results: The in vitro experiments showed good cellular specific binding. Tumor uptake values as %ID/g were 7.55 and 6.82% at 1 and 4 h after injection, respectively. The presaturation of EGFR in xenografted nude mice reduced 36% tumor uptake of radioactivity at 1 h after injection that confirmed in vivo specificity. Conclusion: Findings showed this radiolabeled peptide is a promising candidate for tumor targeting and molecular imaging of non-small-cell lung cancer.

Predictive efficacy of (11)C-PD153035 PET imaging for EGFR-tyrosine kinase inhibitor sensitivity in non-small cell lung cancer patients

To determine the correlation of (11)C-PD153035 uptake with epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) sensitivity and phosphorylated EGFR (pEGFR) expression in non-small cell lung cancer (NSCLC) cell lines with different EGFR-TKI sensitivities and in their corresponding xenografts. Four human NSCLC cell lines (HCC827, PC9, A549, and H1975) in the logarithmic phase were co-incubated with (11)C-PD153035 to analyze the correlation of (11)C-PD153035 uptake with EGFR-TKI sensitivity, and EGFR/pEGFR expression. Nude mice xenograft models bearing the four NSCLCs were prepared. (11)C-PD153035 positron-emission tomography (PET)-computed tomography (CT) was used to image the xenografts and observe radioactive uptakes. Correlation of the in vivo uptakes with EGFR-TKI sensitivity, and EGFR/pEGFR expression was analyzed. HCC827 and PC9 cells, which were highly sensitive to EGFR-TKIs, exhibited higher (11)C-PD153035 uptakes than the other cells. A549 cells, which were moderately sensitive to EGFR-TKIs, showed higher uptake than the EGFR-TKI-resistant H1975 cells, which showed little or no uptake. Radioactive uptakes were positively correlated with pEGFR expression in all cells. PET-CT showed that radioactivity was highest in HCC827 xenografts. The radioactivity in PC9 xenografts was higher than that in A549 and H1975 xenografts. Tumor vs. non-tumor tissue ratio values were positively correlated with pEGFR expression in HCC827 and PC9 xenografts, but not in A549 and H1975 xenografts. In conclusion, (11)C-PD153035 can serve as an EGFR imaging agent in vitro and in vivo, and predicts sensitivity to EGFR-TKIs. This will provide an experimental basis for clinical applications of (11)C-PD153035 and individualized NSCLC therapy.

Identifying erlotinib-sensitive non-small cell lung carcinoma tumors in mice using [(11)C]erlotinib PET

Background

Non-small cell lung carcinoma (NSCLC) represents approximately 80% of lung cancer cases, and over 60% of these tumors express the epidermal growth factor receptor (EGFR). Activating mutations in the tyrosine kinase (TK) domain of the EGFR are detected in 10% to 30% of NSCLC patients, and evidence of their presence is a prerequisite for initiation of first-line therapy with selective TK inhibitors (TKIs), such as gefitinib and erlotinib. To date, the selection of candidate patients for first-line treatment with EGFR TKIs requires an invasive tumor biopsy to affirm the mutational status of the receptor. This study was designed to evaluate whether positron emission tomography (PET) of NSCLC tumor-bearing mice using [¹¹C]erlotinib could distinguish erlotinib-sensitive from erlotinib-insensitive or erlotinib-resistant tumors.

Methods

Four human NSCLC cell lines were employed, expressing either of the following forms of the EGFR: (i) the wild-type receptor (QG56 cells), (ii) a mutant with an exon 19 in-frame deletion (HCC827 cells), (iii) a mutant with the exon 21 L858R point mutation (NCI-H3255 cells), and (iv) a double mutant harboring the L858R and T790M mutations (NCI-H1975 cells). Sensitivity of each cell line to the anti-proliferative effect of erlotinib was determined in vitro. In vivo PET imaging studies following i.v. injection of [¹¹C]erlotinib were carried out in nude mice bearing subcutaneous (s.c.) xenografts of the four cell lines.

Results

Cells harboring activating mutations in the EGFR TK domain (HCC827 and NCI-H3255) were approximately 1,000- and 100-fold more sensitive to erlotinib treatment in vitro, respectively, compared to the other two cell lines. [¹¹C]Erlotinib PET scans could differentiate erlotinib-sensitive tumors from insensitive (QG56) or resistant (NCI-H1975) tumors already at 12 min after injection. Nonetheless, the uptake in HCC827 tumors was significantly higher than that in NCI-H3255, possibly reflecting differences in ATP and erlotinib affinities between the EGFR mutants.

Conclusions

[¹¹C]Erlotinib imaging in mice differentiates erlotinib-sensitive NSCLC tumors from erlotinib-insensitive or erlotinib-resistant ones.

Interactions of ABCG2 (BCRP) with epidermal growth factor receptor kinase inhibitors developed for molecular imaging

The objective of this study was to investigate in vitro the interactions between novel epidermal growth factor receptor kinase inhibitors (EGFRIs) developed for positron emission tomography (PET) imaging and the major efflux transporter breast cancer resistance protein (BCRP/ABCG2). Seven compounds were evaluated, using the ATPase activity assays and Madin-Darbey canine kidney (MDCK) cells overexpressing BCRP. Five of the tested compounds activated BCRP ATPase to various extent. Overexpression of BCRP conferred resistance to ML04, ML06, methoxy-Br-ML03, and PEG6-ML05 (IC₅₀ values for inhibition of control cell proliferation 2.1 ± 0.6, 2.2 ± 0.7, 1.8 ± 1.2, and 2.8 ± 3.1 μM, respectively, compared to >50 μM in MDCK-BCRP cells). At submicromolar concentrations, none of the EGFRIs significantly inhibited BCRP. Immunoblotting studies indicated that BCRP expression is evident in cell lines utilized for in vivo tumor grafting in small animal PET imaging studies. Thus, the intensity of EGFRIs radioactivity signals previously observed in tumor xenografts reflects an interplay between transporter-mediated distribution of the probe into tumor cells and target binding. Concomitant use of efflux transporter inhibitors may help distinguish between the contribution of efflux transport and EGFR binding to the tissue signal.

Perspectives in molecular imaging through translational research, human medicine, and veterinary medicine

The concept of molecular imaging has taken off over the past 15 years to the point of the renaming of the Society of Nuclear Medicine (Society of Nuclear Medicine and Molecular Imaging) and Journals (European Journal of Nuclear Medicine and Molecular Imaging) and offering of medical fellowships specific to this area of study. Molecular imaging has always been at the core of functional imaging related to nuclear medicine. Even before the phrase molecular imaging came into vogue, radionuclides and radiopharmaceuticals were developed that targeted select physiological processes, proteins, receptor analogs, antibody-antigen interactions, metabolites and specific metabolic pathways. In addition, with the advent of genomic imaging, targeted genomic therapy, and theranostics, a number of novel radiopharmaceuticals for the detection and therapy of specific tumor types based on unique biological and cellular properties of the tumor itself have been realized. However, molecular imaging and therapeutics as well as the concept of theranostics are yet to be fully realized. The purpose of this review article is to present an overview of the translational approaches to targeted molecular imaging with application to some naturally occurring animal models of human disease.

Rational development of radiopharmaceuticals for HIV-1

The global battle against HIV-1 would benefit from a sensitive and specific radiopharmaceutical to localize HIV-infected cells. Ideally, this probe would be able to identify latently infected host cells containing replication competent HIV sequences. Clinical and research applications would include assessment of reservoirs, informing clinical management by facilitating assessment of burden of infection in different compartments, monitoring disease progression and monitoring response to therapy. A "rational" development approach could facilitate efficient identification of an appropriate targeted radiopharmaceutical. Rational development starts with understanding characteristics of the disease that can be effectively targeted and then engineering radiopharmaceuticals to hone in on an appropriate target, which in the case of HIV-1 (HIV) might be an HIV-specific product on or in the host cell, a differentially expressed gene product, an integrated DNA sequence specific enzymatic activity, part of the inflammatory response, or a combination of these. This is different from the current approach that starts with a radiopharmaceutical for a target associated with a disease, mostly from autopsy studies, without a strong rationale for the potential to impact patient care. At present, no targeted therapies are available for HIV latency, although a number of approaches are under study. Here we discuss requirements for a radiopharmaceutical useful in strategies targeting persistently infected cells. The radiopharmaceutical for HIV should be developed based on HIV biology, studied in an animal model and then in humans, and ultimately used in clinical and research settings.

Molecular imaging of nonsmall cell lung carcinomas expressing active mutant EGFR kinase using PET with [(124)i]-morpholino-IPQA

Mutations in the kinase domain of epidermal growth factor receptor (EGFR) have high levels of basal receptor phosphorylation and are associated with clinical responsiveness to Iressa in patients with nonsmall cell lung cancer (NSCLC). This study aimed to assess the feasibility of morpholino-[(124)I]IPQA derivative as an in vivo PET imaging tool for the expression of different EGFR mutants in NSCLC. In vitro radiotracer accumulation and washout studies demonstrated a rapid accumulation and progressive retention after washout of morpholino-[(131)I]IPQA derivative in high EGFR-expressing H1299 NSCLC derivative cell lines (L858R and E746-A750 del cell lines), but not in EGFR-transfected H1299 cell line and vector-transfected H1299 cell line. Using the morpholino-[(124)I]IPQA derivative, we obtained noninvasive microPET images of EGFR activity in L858R and E746-A750 del subcutaneous tumor xenografts, but not in subcutaneous tumor xenografts grown form control cell line. Different EGFR mutant (activity) tumors have a different morpholino-[ (∗) I]IPQA derivative uptake. However, it still needs to modify the structure of IPQA to increase its water solubility and reduce hepatobiliary clearance. Morpholino-[(124)I]IPQA derivative may be a potential probe for selection of the candidate patients suffering from NSCLC for the small molecule tyrosine kinase inhibitor therapy (e.g., Iressa) in the future.

Bio-imaging of colorectal cancer models using near infrared labeled epidermal growth factor

Novel strategies that target the epidermal growth factor receptor (EGFR) have led to the clinical development of monoclonal antibodies, which treat metastatic colorectal cancer (mCRC) but only subgroups of patients with increased wild type KRAS and EGFR gene copy, respond to these agents. Furthermore, resistance to EGFR blockade inevitably occurred, making future therapy difficult. Novel bio-imaging (BOI) methods may assist in quantization of EGFR in mCRC tissue thus complementing the immunohistochemistry methodology, in guiding the future treatment of these patients. The aim of the present study was to explore the usefulness of near infrared-labeled EGF (EGF-NIR) for bio-imaging of CRC using in vitro and in vivo orthotopic tumor CRC models and ex vivo human CRC tissues. We describe the preparation and characterization of EGF-NIR and investigate binding, using BOI of a panel of CRC cell culture models resembling heterogeneity of human CRC tissues. EGF-NIR was specifically and selectively bound by EGFR expressing CRC cells, the intensity of EGF-NIR signal to background ratio (SBR) reflected EGFR levels, dose-response and time course imaging experiments provided optimal conditions for quantization of EGFR levels by BOI. EGF-NIR imaging of mice with HT-29 orthotopic CRC tumor indicated that EGF-NIR is more slowly cleared from the tumor and the highest SBR between tumor and normal adjacent tissue was achieved two days post-injection. Furthermore, images of dissected tissues demonstrated accumulation of EGF-NIR in the tumor and liver. EGF-NIR specifically and strongly labeled EGFR positive human CRC tissues while adjacent CRC tissue and EGFR negative tissues expressed weak NIR signals. This study emphasizes the use of EGF-NIR for preclinical studies. Combined with other methods, EGF-NIR could provide an additional bio-imaging specific tool in the standardization of measurements of EGFR expression in CRC tissues.

EGFR mutations are associated with favorable intracranial response and progression-free survival following brain irradiation in non-small cell lung cancer patients with brain metastases

BACKGROUND

The presence of epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) is associated with increased radiosensitivity in vitro. However, the results from clinical studies regarding the radiosensitivity in NSCLC with mutant EGFR are inconclusive. We retrospectively analyzed our NSCLC patients who had been regularly followed up by imaging studies after irradiation for brain metastases, and investigated the impact of EGFR mutations on radiotherapy (RT).

METHODS

Forty-three patients with brain metastases treated with RT, together with EGFR mutation status, demographics, smoking history, performance status, recursive partitioning analysis (RPA) class, tumor characteristics, and treatment modalities, were included. Radiological images were taken at 1 to 3 months after RT, and 3 to 6 months thereafter. Radiographic response was evaluated by RECIST criteria version 1.1 according to the intracranial images before and after RT. Log-rank test and Cox regression model were used to correlate EGFR mutation status and other clinical features with intracranial radiological progression-free survival (RPFS) and overall survival (OS).

RESULTS

The median follow-up duration was 15 months. Patients with mutant EGFR had higher response rates to brain RT than those with wild-type EGFR (80% vs. 46%; p = 0.037). Logistic regression analysis showed that EGFR mutation status is the only predictor for treatment response (p = 0.032). The median intracranial RPFS was 18 months (95% CI = 8.33-27.68 months). In Cox regression analysis, mutant EGFR (p = 0.025) and lower RPA class (p = 0.026) were associated with longer intracranial RPFS. EGFR mutation status (p = 0.061) and performance status (p = 0.076) had a trend to predict OS.

CONCLUSIONS

Mutant EGFR in NSCLC patients is an independent prognostic factor for better treatment response and longer intracranial RPFS following RT for brain metastases.

PET imaging with small-molecule tyrosine kinase inhibitors: TKI-PET

The discovery and increased understanding of tumor targets has led to the development and approval of 12 small molecule tyrosine kinase inhibitors (TKIs). Despite tremendous efforts in TKI development, treatment efficacies with these therapeutics are still too low and improvements require a personalized medicine approach. Positron emission tomography (PET) with radiolabeled TKIs (TKI-PET) is a tracking, quantification and imaging method, which provides a unique understanding of the behavior of these drugs in vivo and of the interaction with their target(s). In this article we provide an overview of tracer synthesis and development because each TKI requires a tailor made approach. Moreover, we describe current preclinical work and the first proof-of-principle clinical studies on the application of TKI-PET, illustrating the potential of this approach for improving therapy efficacy and personalized cancer treatment.

Nanoprobes for hybrid SPECT/MR molecular imaging

Hybrid imaging techniques provide enhanced visualization of biological targets by synergistically combining multiple imaging modalities, thereby providing information on specific aspects of structure and function, which is difficult to obtain by a single imaging modality. Advances in the field of hybrid imaging have resulted in the recent approval of PET/magnetic resonance (MR) imaging by the US FDA for clinical use in the USA and Europe. Single-photon emission computed tomography (SPECT)/MR imaging is another evolving hybrid imaging modality with distinct advantages. Recently reported progress in the development of a SPECT/MR imaging hybrid scanner provides a cue towards the need for multimodal SPECT/MR imaging nanoprobes to take full advantage of a scanner’s simultaneous imaging capability. In this review, we present some of the latest developments in the domain of SPECT/MR hybrid imaging, particularly focusing on multimodal nanoprobes.

Radioiodinated sunitinib as a potential radiotracer for imaging angiogenesis-radiosynthesis and first radiopharmacological evaluation of 5-[125I]Iodo-sunitinib

Sunitinib® (SU11248) is a highly potent tyrosine kinase inhibitor targeting vascular endothelial growth factor receptor (VEGFR). Radiolabeled inhibitors of RTKs might be useful tools for monitoring RTKs levels in tumour tissue giving valuable information for anti-angiogenic therapy. We report here the synthesis of a (125)I-labeled derivative of sunitinib® and its first radiopharmaceutical characterization. The non-radioactive reference compound 5-iodo-sunitinib 4 was prepared by Knoevenagel condensation of 5-iodo-oxindole with the corresponding substituted 5-formyl-1H-pyrrole. In a competition binding assay against VEGFR-2 a binding constant (K(d)) of 16 nM for 4 was found. The ability of 4 to inhibit tyrosine kinase activity was demonstrated on RTK expressing cells suggesting this radiotracer as a useful tool for monitoring VEGFR expression. 5-[(125)I]lodo-sunitinib, [(125)I]-4 was obtained via destannylation of the corresponding tributylstannyl precursor with [(125)I]NaI in the presence of H(2)O(2) in high radiochemical yield (>95%) and radiochemical purity (<98%) after HPLC purification. Determination of human plasma protein binding at time intervals of 0; 1; 2; 4 and 24h suggested a low non-specific binding of 5-10%. Preliminary biodistribution studies of [(125)I]-4 in healthy CD-1 mice showed a relatively high uptake in VEGFR-2 rich tissues like kidney and lung followed by rapid washout (9.6 and 9.7; 4.5 and 3.8% ID/g of kidney and lung at 1 and 4h, respectively).

Radiosynthesis and initial in vitro evaluation of [18F]F-PEG6-IPQA--a novel PET radiotracer for imaging EGFR expression-activity in lung carcinomas

INTRODUCTION

Epidermal growth factor receptor (EGFR)-targeted therapies with antibodies and small molecular EGFR kinase inhibitors have shown poor efficacy in unselected populations of patients with advanced non-small cell lung carcinomas (NSCLC). In contrast, patients with overexpression of EGFR and activating mutations in EGFR kinase domain demonstrated improved responses to EGFR kinase inhibitors. Therefore, we have developed a novel radiotracer, [(18)F]F-PEG(6)-IPQA for PET imaging of EGFR expression-activity in NSCLC, and have described its radiosynthesis and in vitro evaluation in two NSCLC cell lines with wild-type and L858R active mutant EGFR.

METHODS

A mesylate precursor was synthesized in multiple steps and radiofluorinated using K(18)F/Kryptofix. The fluorinated intermediate compound was reduced to an amino derivative then treated with acryloyl isobutyl carbonate, followed by purification by HPLC to obtain the desired product.

RESULTS

Decay-corrected radiochemical yields of [(18)F]F-PEG(6)-IPQA were 3.9-17.6%, with an average of 9.0% (n = 11). Radiochemical purity was >97% with specific activity of 34 GBq/μmol (mean value, n = 10) at the end of synthesis. The accumulation of [(18)F]F-PEG(6)-IPQA in H3255 cells was ten-fold higher than in H441 cells, despite a two-fold lower level of activated phospho-EGFR expression in H3255 cells compared with H441 cells. The accumulation of [(18)F]F-PEG(6)-IPQA in both cell lines was significantly decreased in the presence of a small molecular EGFR kinase inhibitor, Iressa, at 100 μM concentration in culture medium.

CONCLUSION

We have synthesized [(18)F]F-PEG(6)-IPQA and demonstrated its highly selective accumulation in active mutant L858R EGFR-expressing NSCLC cells in vitro. Further in vivo studies are warranted to assess the ability of PET imaging with [(18)F]F-PEG(6)-IPQA to discriminate the active mutant L858R EGFR-expressing NSCLC that are sensitive to therapy with EGFR kinase inhibitors vs NSCLC that express wild-type EGFR.

Metabolic stability of 6,7-dialkoxy-4-(2-, 3- and 4-[18F]fluoroanilino)quinazolines, potential EGFR imaging probes

Epidermal growth factor receptors (EGFR), upregulated in many tumor types, have been a target for therapeutic development and molecular imaging. The objective of this study was to evaluate the distribution and metabolic characteristics of fluorine-18 labeled anilinoquinazolines as potential imaging agents for EGFR tyrosine kinase expression. Fluorine-18 labeled fluoronitrobenzenes were prepared by reaction of potassium cryptand [(18)F]fluoride with 1,2- and 1,4-dinitrobenzenes, and 3-nitro-N,N,N-trimethylanilinium triflate in 5min. Decay-corrected radiochemical yields of [(18)F]fluoride incorporation into the nitro-aromatic compounds were 81±2%, 44±4% and 77±5% (n=3-5) for the 2-, 3- and 4-fluoro isomers, respectively. Sodium borohydride reduction to the corresponding [(18)F]fluoroanilines was achieved with greater than 80% conversion in 5min. Coupling of [(18)F]fluoroaniline-hydrochlorides to 6,7-dimethoxy-4-chloro-quinazoline gave the corresponding 6,7-dimethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 31±5%, 17±2% and 55±2% radiochemical yield, respectively, while coupling to the 6,7-diethoxy-4-chloro-quinazoline produced 6,7-diethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 19±6%, 9±3% and 36±6% radiochemical yield, respectively, in 90min to end of synthesis from [(18)F]fluoride. Biodistribution of 2- and 4-[(18)F]fluoroanilinoquinazolines was conducted in tumor-bearing mice (MDA-MB-435 and MDA-MB-468 xenografts). Low tumor uptake (<1% injected dose per gram (ID/g) of tissue up to 3h postinjection of the radiotracers) was observed. High bone uptake (5-15% ID/g) was noted with the 4-[(18)F]fluoroanilinoquinazolines. The metabolic stabilities of radiolabeled quinazolines were further evaluated by incubation with human female cryopreserved isolated hepatocytes. Rapid degeneration of the 4-fluoro-substituted compounds to baseline polar metabolites was observed by radio-TLC, whereas, the 2- and 3-[(18)F]fluoroaniline derivatives were significantly more stable, up to 2h, corroborating the in vivo biodistribution studies. para-Substituted [(18)F]fluoroanilines, a common structural motif in radiopharmaceuticals, are highly susceptible to metabolic degradation.

Affibody-functionalized gold-silica nanoparticles for Raman molecular imaging of the epidermal growth factor receptor

The affibody functionalization of fluorescent surface-enhanced Raman scattering gold-silica nanoparticles as multimodal contrast agents for molecular imaging specific to epidermal growth factor receptor (EGFR) is reported. This nanoparticle bioconjugate reports EGFR-positive A431 tumors with a signal nearly 35-fold higher than EGFR-negative MDA-435S tumors. The low-level EGFR expression in adjacent healthy tissue is 7-fold lower than in the positive tumors. Validation via competitive inhibition reduces the signal by a factor of six, and independent measurement of EGFR via flow cytometry correlates at R(2) = 0.92.

Molecular imaging of active mutant L858R EGF receptor (EGFR) kinase-expressing nonsmall cell lung carcinomas using PET/CT

The importance of the EGF receptor (EGFR) signaling pathway in the development and progression of nonsmall cell lung carcinomas (NSCLC) is widely recognized. Gene sequencing studies revealed that a majority of tumors responding to EGFR kinase inhibitors harbor activating mutations in the EGFR kinase domain. This underscores the need for novel biomarkers and diagnostic imaging approaches to identify patients who may benefit from particular therapeutic agents and approaches with improved efficacy and safety profiles. To this goal, we developed 4-[(3-iodophenyl)amino]-7-{2-[2-{2-(2-[2-{2-([(18)F]fluoroethoxy)-ethoxy}-ethoxy]-ethoxy)-ethoxy}-ethoxy]-quinazoline-6-yl-acrylamide ([(18)F]F-PEG6-IPQA), a radiotracer with increased selectivity and irreversible binding to the active mutant L858R EGFR kinase. We show that PET with [(18)F]F-PEG6-IPQA in tumor-bearing mice discriminates H3255 NSCLC xenografts expressing L858R mutant EGFR from H441 and PC14 xenografts expressing EGFR or H1975 xenografts with L858R/T790M dual mutation in EGFR kinase domain, which confers resistance to EGFR inhibitors (i.e., gefitinib). The T790M mutation precludes the [(18)F]F-PEG6-IPQA from irreversible binding to EGFR. These results suggest that PET with [(18)F]F-PEG6-IPQA could be used for the selection of NSCLC patients for individualized therapy with small molecular inhibitors of EGFR kinase that are currently used in the clinic and have a similar structure (i.e., iressa, gefitinib, and erlotinib).

Molecular imaging: current status and emerging strategies

In vivo molecular imaging has a great potential to impact medicine by detecting diseases in early stages (screening), identifying extent of disease, selecting disease- and patient-specific treatment (personalized medicine), applying a directed or targeted therapy, and measuring molecular-specific effects of treatment. Current clinical molecular imaging approaches primarily use positron-emission tomography (PET) or single photon-emission computed tomography (SPECT)-based techniques. In ongoing preclinical research, novel molecular targets of different diseases are identified and, sophisticated and multifunctional contrast agents for imaging these molecular targets are developed along with new technologies and instrumentation for multi-modality molecular imaging. Contrast-enhanced molecular ultrasound (US) with molecularly-targeted contrast microbubbles is explored as a clinically translatable molecular imaging strategy for screening, diagnosing, and monitoring diseases at the molecular level. Optical imaging with fluorescent molecular probes and US imaging with molecularly-targeted microbubbles are attractive strategies as they provide real-time imaging, are relatively inexpensive, produce images with high spatial resolution, and do not involve exposure to ionizing irradiation. Raman spectroscopy/microscopy has emerged as a molecular optical imaging strategy for ultrasensitive detection of multiple biomolecules/biochemicals with both in vivo and ex vivo versatility. Photoacoustic imaging is a hybrid of optical and US techniques involving optically-excitable molecularly-targeted contrast agents and quantitative detection of resulting oscillatory contrast agent movement with US. Current preclinical findings and advances in instrumentation, such as endoscopes and microcatheters, suggest that these molecular imaging methods have numerous potential clinical applications and will be translated into clinical use in the near future.

Radiolabeled small molecule protein kinase inhibitors for imaging with PET or SPECT

Imaging protein kinase expression with radiolabeled small molecule inhibitors has been actively pursued to monitor the clinical potential of targeted therapeutics and treatments as well as to determine kinase receptor density changes related to disease progression. The goal of the present review is to provide an overview of the breadth of radiolabeled small molecules that have been synthesized to target intracellular protein kinases, not only for imaging in oncology, but also for other areas of interest, particularly the central nervous system. Considerable radiotracer development has focused on imaging receptor tyrosine kinases of growth factors, protein kinases A, B and C, and glycogen synthase kinase-3ß. Design considerations, structural attributes and relevant biological results are summarized.

Optimizing tumor targeting of the lipophilic EGFR-binding radiotracer SKI 243 using a liposomal nanoparticle delivery system

Positron emission tomography (PET) of epidermal growth factor receptor (EGFR) kinase-specific radiolabeled tracers could provide a means for non-invasively characterizing EGFR expression and signaling activity in patients' tumors before, during, and after therapy with EGFR inhibitors. Towards this goal, our group has developed PET tracers which irreversibly bind to EGFR. However, tumor uptake is relatively low because of both the lipophilicity of such tracers (e.g. the morpholino-[124I]-IPQA [SKI 212243]), with octanol-to-water partition coefficients of up to 4, and a short dwell time in the blood and significant hepatobiliary clearance and intestinal reuptake. Liposomal nanoparticle delivery systems may favorably alter the pharmacokinetic profile and improve tumor targeting of highly lipophilic but otherwise promising cancer imaging tracers, such as the EGFR inhibitor SKI 243. SKI 243 is therefore an interesting model molecule for incorporation into lipid-based nanoparticles, as it would not only improve their solubility but also increase the circulation time, availability and, potentially, targeting of tumors. In the current study, we compared the pharmacokinetics and tumor targeting of the bare EGFR kinase-targeting radiotracer SKI 212243 (SKI 243) with that of the same tracer embedded in liposomes. SKI 243 and liposomal SKI 243 are both taken up by tumor xenografts but liposomal SKI 243 remained in the blood longer and consequently exhibited a 3- to 6-fold increase in uptake in the tumor among several other organs.

PET imaging of HER1-expressing xenografts in mice with 86Y-CHX-A''-DTPA-cetuximab

PURPOSE

Cetuximab is a recombinant, human/mouse chimeric IgG(1) monoclonal antibody that binds to the epidermal growth factor receptor (EGFR/HER1). Cetuximab is approved for the treatment of patients with HER1-expressing metastatic colorectal cancer. Limitations in currently reported radiolabeled cetuximab for PET applications prompted the development of (86)Y-CHX-A''-DTPA-cetuximab as an alternative for imaging HER1-expressing cancer. (86)Y-CHX-A''-DTPA-cetuximab can also serve as a surrogate marker for (90)Y therapy.

METHODS

Bifunctional chelate, CHX-A''-DTPA was conjugated to cetuximab and radiolabeled with (86)Y. In vitro immunoreactivity was assessed in HER1-expressing A431 cells. In vivo biodistribution, PET imaging and noncompartmental pharmacokinetics were performed in mice bearing HER1-expressing human colorectal (LS-174T and HT29), prostate (PC-3 and DU145), ovarian (SKOV3) and pancreatic (SHAW) tumor xenografts. Receptor blockage was demonstrated by coinjection of either 0.1 or 0.2 mg cetuximab.

RESULTS

(86)Y-CHX-A''-DTPA-cetuximab was routinely prepared with a specific activity of 1.5-2 GBq/mg and in vitro cell-binding in the range 65-75%. Biodistribution and PET imaging studies demonstrated high HER1-specific tumor uptake of the radiotracer and clearance from nonspecific organs. In LS-174T tumor-bearing mice injected with (86)Y-CHX-A''-DTPA-cetuximab alone, (86)Y-CHX-A''-DTPA-cetuximab plus 0.1 mg cetuximab or 0.2 mg cetuximab, the tumor uptake values at 3 days were 29.3 +/- 4.2, 10.4 +/- 0.5 and 6.4 +/- 0.3%ID/g, respectively, demonstrating dose-dependent blockage of the target. Tumors were clearly visualized 1 day after injecting 3.8-4.0 MBq (86)Y-CHX-A''-DTPA-cetuximab. Quantitative PET revealed the highest tumor uptake in LS-174T (29.55 +/- 2.67%ID/cm(3)) and the lowest tumor uptake in PC-3 (15.92 +/- 1.55%ID/cm(3)) xenografts at 3 days after injection. Tumor uptake values quantified by PET were closely correlated (r (2) = 0.9, n = 18) with values determined by biodistribution studies.

CONCLUSION

This study demonstrated the feasibility of preparation of high specific activity (86)Y-CHX-A''-DTPA-cetuximab and its application for quantitative noninvasive PET imaging of HER1-expressing tumors. (86)Y-CHX-A''-DTPA-cetuximab offers an attractive alternative to previously labeled cetuximab for PET and further investigation for clinical translation is warranted.