Recent advances in optical cancer imaging of EGF receptors

Molecular and functional imaging in cancer-targeted therapy: current applications and future directions

Targeted anticancer drugs block cancer cell growth by interfering with specific signaling pathways vital to carcinogenesis and tumor growth rather than harming all rapidly dividing cells as in cytotoxic chemotherapy. The Response Evaluation Criteria in Solid Tumor (RECIST) system has been used to assess tumor response to therapy via changes in the size of target lesions as measured by calipers, conventional anatomically based imaging modalities such as computed tomography (CT), and magnetic resonance imaging (MRI), and other imaging methods. However, RECIST is sometimes inaccurate in assessing the efficacy of targeted therapy drugs because of the poor correlation between tumor size and treatment-induced tumor necrosis or shrinkage. This approach might also result in delayed identification of response when the therapy does confer a reduction in tumor size. Innovative molecular imaging techniques have rapidly gained importance in the dawning era of targeted therapy as they can visualize, characterize, and quantify biological processes at the cellular, subcellular, or even molecular level rather than at the anatomical level. This review summarizes different targeted cell signaling pathways, various molecular imaging techniques, and developed probes. Moreover, the application of molecular imaging for evaluating treatment response and related clinical outcome is also systematically outlined. In the future, more attention should be paid to promoting the clinical translation of molecular imaging in evaluating the sensitivity to targeted therapy with biocompatible probes. In particular, multimodal imaging technologies incorporating advanced artificial intelligence should be developed to comprehensively and accurately assess cancer-targeted therapy, in addition to RECIST-based methods.

Expanded Application of a Photoaffinity Probe to Study Epidermal Growth Factor Receptor Tyrosine Kinase with Functional Activity

The abnormal activation of the epidermal growth factor receptor (EGFR) is strongly associated with cancer invasion and metastasis. Tools and methods are required to study and visualize EGFR activation under (patho)physiological conditions. Here, we report the development of a two-step photoaffinity probe (HX101) by incorporation of a diazirine as a photoreactive group and an alkyne as a ligation handle to quantitively study EGFR kinase activity in native cellular contexts and human tissue slices. HX101 is a multifunctional probe based on the pharmacophore of the EGFR tyrosine kinase inhibitor (EGFR-TKI) and can covalently target the EGFR upon photoactivation. The incorporated alkyne serves as a versatile ligation handle and enables HX101 to introduce distinct reporter groups (e.g., fluorophore and biotin) via click chemistry. With variable reporter tags, HX101 enables visualization and target engagement studies of the active EGFR in a panel of cancer cells using flow cytometry, confocal microscopy, and mass spectrometry. Furthermore, as a proof of concept study, we applied HX101 in stochastic optical reconstruction microscopy super-resolution imaging to study EGFR activation in live cells. Importantly, HX101 was also applied to visualize EGFR mutant activity in tumor tissues from lung cancer patients for prediction of EGFR-TKI sensitivity. Altogether, our results demonstrate the wide application of a selective photoaffinity probe in multi-modal assessment/visualization of EGFR activity in both live cells and tissue slices. We anticipate that these diverse applications can facilitate the translation of a strategically functionalized probe into medical use.

Potential applications of clickable probes in EGFR activity visualization and prediction of EGFR-TKI therapy response for NSCLC patients

The epithelial growth factor receptor (EGFR) is abnormally overexpressed on the cell surface of cancer cells and is strongly associated with cancer cell proliferation, migration, differentiation, apoptosis, and angiogenesis. Tools enabling the visualization of EGFR in a structure-function approach are highly desirable to predict EGFR mutations and guide EGFR tyrosine kinase inhibitor (TKI) treatment making. Here, we describe the design, synthesis, and application of new, potent and selective clickable probes 13 (HX03), 20 (HX04) and 24 (HX05) by introducing an alkyne ligation handle to visualize EGFR activity in living cancer cells and tissue slices. These clickable probes are versatile chemical tools based on the key pharmacophore (4-anilinoquinazoline) of EGFR-TKIs (e.g., canertinib, dacomitinib and afatinib) and are able to irreversibly target the kinase domain of EGFR. Among them, 13 exhibits the highest reactivity towards EGFR kinase, particularly to EGFR kinase with primary mutations. Using activity-based protein profiling strategy, 13 showed high sensitivity and selectivity in labeling of endogenous EGFR in a native cellular context. Moreover, 13 was applied to visualize EGFR mutant activity in tumour tissues from non-small-cell lung cancer (NSCLC) xenograft mouse models, and patients with NSCLC for the prediction of EGFR-TKI sensitivity. These results demonstrate that strategically designed EGFR-TKI-based probes allow discriminating EGFR mutations in human tissues and hold promise as useful diagnostic tools in predicting EGFR-TKI therapy response.

Molecular Targeting of Epidermal Growth Factor Receptor (EGFR) and Vascular Endothelial Growth Factor Receptor (VEGFR)

Epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) are two extensively studied membrane-bound receptor tyrosine kinase proteins that are frequently overexpressed in many cancers. As a result, these receptor families constitute attractive targets for imaging and therapeutic applications in the detection and treatment of cancer. This review explores the dynamic structure and structure-function relationships of these two growth factor receptors and their significance as it relates to theranostics of cancer, followed by some of the common inhibition modalities frequently employed to target EGFR and VEGFR, such as tyrosine kinase inhibitors (TKIs), antibodies, nanobodies, and peptides. A summary of the recent advances in molecular imaging techniques, including positron emission tomography (PET), single-photon emission computerized tomography (SPECT), computed tomography (CT), magnetic resonance imaging (MRI), and optical imaging (OI), and in particular, near-IR fluorescence imaging using tetrapyrrolic-based fluorophores, concludes this review.

The status of contemporary image-guided modalities in oncologic surgery

OBJECTIVE

To review the current trends in optical imaging to guide oncologic surgery.

BACKGROUND

Surgical resection remains the cornerstone of therapy for patients with early stage solid malignancies and more than half of all patients with cancer undergo surgery each year. The technical ability of the surgeon to obtain clear surgical margins at the initial resection remains crucial to improve overall survival and long-term morbidity. Current resection techniques are largely based on subjective and subtle changes associated with tissue distortion by invasive cancer. As a result, positive surgical margins occur in a significant portion of tumor resections, which is directly correlated with a poor outcome.

METHODS

A comprehensive review of studies evaluating optical imaging techniques is performed.

RESULTS

A variety of cancer imaging techniques have been adapted or developed for intraoperative surgical guidance that have been shown to improve functional and oncologic outcomes in randomized clinical trials. There are also a large number of novel, cancer-specific contrast agents that are in early stage clinical trials and preclinical development that demonstrate significant promise to improve real-time detection of subclinical cancer in the operative setting.

CONCLUSIONS

There has been an explosion of intraoperative imaging techniques that will become more widespread in the next decade.

New whole-body multimodality imaging of gastric cancer peritoneal metastasis combining fluorescence imaging with ICG-labeled antibody and MRI in mice

BACKGROUND

Peritoneal metastasis is the most frequent pattern of recurrence after curative surgery for gastric cancer. However, such a recurrence is difficult to detect by conventional computed tomography (CT) and magnetic resonance imaging (MRI) at an early stage. To improve the sensitivity and specificity of diagnostic imaging for peritoneal metastasis, we developed a new type of multimodality imaging combining fluorescence imaging with near-infrared fluorophore (NIR)-labeled antibodies and MRI.

METHODS

Dual optical imaging of peritoneal metastasis was carried out using luciferase-tagged gastric cancer cell lines and XenoLight CF750 or indocyanine green (ICG)-labeled anti-human epidermal growth factor receptor (EGFR) or CEA antibody as a probe in mice with Ivis in vivo imaging system.

RESULTS

This whole-body fluorescent imaging system sensitively detected metastatic foci <1 mm in diameter in the peritoneal cavity noninvasively. Fluorescence imaging proved to be specific because the fluorescence signal was abolished by blocking with excess unlabeled antibody. Although this fluorescence imaging had higher sensitivity for detection of small-sized peritoneal metastases than MRI, it proved difficult to accurately determine organ distribution of the metastasis. We thus developed a multimodality imaging system by the fusion of the three-dimensional fluorescence image with the MRI image and demonstrated its improved diagnostic accuracy over either method alone.

CONCLUSION

The present results suggest that multimodality imaging consisting of fluorescence imaging with NIR-labeled EGFR or CEA antibody and MRI allows sensitive, specific, and anatomically accurate detection of peritoneal metastasis noninvasively at an early stage.

Molecular imaging of EGFR/HER2 cancer biomarkers by protein MRI contrast agents

Epidermal growth factor receptor (EGFR) and HER2 are major prognosis biomarkers and drug targets overexpressed in various types of cancer cells. There is a pressing need to develop MRI contrast agents capable of enhancing the contrast between normal tissues and tumors with high relaxivity, capable of targeting tumors, and with high intratumoral distribution and minimal toxicity. In this review, we first discuss EGFR signaling and its role in tumor progression as a major drug target. We then report our progress in the development of protein contrast agents with significant improvement of both r1 and r2 relaxivities, pharmacokinetics, in vivo retention time, and in vivo dose efficiency. Finally, we report our effort in the development of EGFR-targeted protein contrast agents with the capability to cross the endothelial boundary and with good tissue distribution across the entire tumor mass. The noninvasive capability of MRI to visualize spatially and temporally the intratumoral distribution as well as quantify the levels of EGFR and HER2 would greatly improve our ability to track changes of the biomarkers during tumor progression, monitor treatment efficacy, aid in patient selection, and further develop novel targeted therapies for clinical application.