Absolute quantification of [(11)C]docetaxel kinetics in lung cancer patients using positron emission tomography

Copper-Mediated Late-stage Radiofluorination: Five Years of Impact on Pre-clinical and Clinical PET Imaging

PURPOSE

Copper-mediated radiofluorination (CMRF) is emerging as the method of choice for the formation of aromatic C-18F bonds. This minireview examines proof-of-concept, pre-clinical, and in-human imaging studies of new and established imaging agents containing aromatic C-18F bonds synthesized with CMRF. An exhaustive discussion of CMRF methods is not provided, although key developments that have enabled or improved upon the syntheses of fluorine-18 imaging agents are discussed.

METHODS

A comprehensive literature search from April 2014 onwards of the Web of Science and PubMed library databases was performed to find reports that utilize CMRF for the synthesis of fluorine-18 radiopharmaceuticals, and these represent the primary body of research discussed in this minireview. Select conference proceedings, previous reports describing alternative methods for the synthesis of imaging agents, and preceding fluorine-19 methodologies have also been included for discussion.

CONCLUSIONS

CMRF has significantly expanded the chemical space that is accessible to fluorine-18 radiolabeling with production methods that can meet the regulatory requirements for use in Nuclear Medicine. Furthermore, it has enabled novel and improved syntheses of radiopharmaceuticals and facilitated subsequent PET imaging studies. The rapid adoption of CMRF will undoubtedly continue to simplify the production of imaging agents and inspire the development of new radiofluorination methodologies.

In vitro and in vivo evaluation of radiolabeled methyl N-[5-(3'-halobenzoyl)-1H-benzimidazol-2-yl]carbamate for cancer radiotherapy

The role of theranostics in cancer management is growing so is the selection of vectors used to deliver these modalities to cancer cells. We describe biological evaluation of a novel theranostic agent targeted to microtubules. Methyl N-[5-(3'-[¹³¹ I]iodobenzoyl)-1H-benzimidazol-2-yl]carbamate (1) and methyl N-[5-(3'-[¹²⁵ I]iodobenzoyl)-1H-benzimidazol-2-yl]carbamate (2) were synthesized from a common precursor 3'-stannylated derivative (4). Antiproliferative effects and radiotoxicity of ¹³¹ I-labeled β-particle emitting 1 were examined in vitro in human neuroblastoma and glioblastoma cells lines. The therapeutic potential of 1 was also examined in a subcutaneous mouse model of human glioblastoma U-87 MG. Compound 1 at the extracellular radioactive concentration of 0.35 MBq/mL, easily achievable in vivo, kills >90% of neuroblastoma cells and >60% glioblastoma cells as measured in a clonogenic assay. D₁₀ doses established for 1 indicate that as few as 3,000 decays are sufficient to kill 90% of BE(2)-C cells. Even U-87 MG cells, the least sensitive of the tested cell lines, require <20,000 decays of intracellular ¹³¹ I to reduce number of clonogenic cells by 90%. Biodistribution studies of 2 delivered either intratumorally or intraperitoneally show a similar tissue distribution for both routes of the drug administration. The whole body clearance half-lives were on average 6 hr. Intratumor administration of 1 produces significant tumor growth delay. After a single dose of 8.4 ± 0.3 MBq of compound 1, the tumor doubling times were 3.2 ± 0.1 and 7.9 ± 0.6 days in control and treated mice, respectively. Methyl N-[5-(3'-radiohalobenzoyl)-1H-benzimidazol-2-yl]carbamates have properties compatible with a theranostic approach to cancer management.

Radiosynthesis of microtubule-targeted theranostic methyl N-[5-(3'-radiohalobenzoyl)-1H-benzimidazol-2-yl]carbamates

Microtubules are a target for a broad spectrum of drugs used as chemotherapeutics to treat hematological malignancies and solid tumors. Most of these drugs have significant dose-limiting toxicities including peripheral neuropathies that can be debilitating and permanent. In an ongoing effort to develop safer and more effective drugs, benzimidazole-based compounds are being developed as replacement for vincristine and similar agents. In this report, we describe radiosyntheses of novel microtubule-targeting methyl N-[5-(3'-radiohalobenzoyl)-1H-benzimidazol-2-yl]carbamates 4 that are intended as potential imaging agents and molecular radiotherapeutics. 125 I- and 131 I-radiolabeled derivatives were prepared either by direct radioiodination of methyl N-(6-benzoyl-1H-benzimidazol-2-yl)carbamate 1 or radioiododestannylation of the corresponding stannane precursor 3. The direct radioiodination was conducted in a solution of 1 in triflic acid and produced after ~1 hour at elevated temperatures and HPLC purification on average 62% of the no-carrier added products 125 I-4 and 131 I-4. Radioiododestannylation of 3'-trimethylstannane 3 proceeded with ease at room temperature in the presence of H2 O2 as the oxidant and produced no-carrier-added 125 I-4 and 131 I-4 in high isolated yields, on average 85%. The radiohalodestannylation protocol is universal and can be applied to other radiohalides including 124 I to produce 124 I-4, a positron emission tomography agent, and 211 At to produce 211 At-4, an α-particle emitting radiotherapeutic.

Clinical Applications of Small-molecule PET Radiotracers: Current Progress and Future Outlook

Radiotracers, or radiopharmaceuticals, are bioactive molecules tagged with a radionuclide used for diagnostic imaging or radiotherapy and, when a positron-emitting radionuclide is chosen, the radiotracers are used for PET imaging. The development of novel PET radiotracers in many ways parallels the development of new pharmaceuticals, and small molecules dominate research and development pipelines in both disciplines. The 4 decades since the introduction of [¹⁸F]FDG have seen the development of many small molecule PET radiotracers. Ten have been approved by the US Food and Drug Administration as of 2016, whereas hundreds more are being evaluated clinically. These radiotracers are being used in personalized medicine and to support drug discovery programs where they are greatly improving our understanding of and ability to treat diseases across many areas of medicine including neuroscience, cardiovascular medicine, and oncology.

Immunocytokines and bispecific antibodies: two complementary strategies for the selective activation of immune cells at the tumor site

The activation of the immune system for a selective removal of tumor cells represents an attractive strategy for the treatment of metastatic malignancies, which cannot be cured by existing methodologies. In this review, we examine the design and therapeutic potential of immunocytokines and bispecific antibodies, two classes of bifunctional products which can selectively activate the immune system at the tumor site. Certain protein engineering aspects, such as the choice of the antibody format, are common to both classes of therapeutic agents and can have a profound impact on tumor homing performance in vivo of individual products. However, immunocytokines and bispecific antibodies display different mechanisms of action. Future research activities will reveal whether an additive of even synergistic benefit can be obtained from the judicious combination of these two types of biopharmaceutical agents.

Positron emission tomography to assess hypoxia and perfusion in lung cancer

In lung cancer, tumor hypoxia is a characteristic feature, which is associated with a poor prognosis and resistance to both radiation therapy and chemotherapy. As the development of tumor hypoxia is associated with decreased perfusion, perfusion measurements provide more insight into the relation between hypoxia and perfusion in malignant tumors. Positron emission tomography (PET) is a highly sensitive nuclear imaging technique that is suited for non-invasive in vivo monitoring of dynamic processes including hypoxia and its associated parameter perfusion. The PET technique enables quantitative assessment of hypoxia and perfusion in tumors. To this end, consecutive PET scans can be performed in one scan session. Using different hypoxia tracers, PET imaging may provide insight into the prognostic significance of hypoxia and perfusion in lung cancer. In addition, PET studies may play an important role in various stages of personalized medicine, as these may help to select patients for specific treatments including radiation therapy, hypoxia modifying therapies, and antiangiogenic strategies. In addition, specific PET tracers can be applied for monitoring therapy. The present review provides an overview of the clinical applications of PET to measure hypoxia and perfusion in lung cancer. Available PET tracers and their characteristics as well as the applications of combined hypoxia and perfusion PET imaging are discussed.

State of the art: Response assessment in lung cancer in the era of genomic medicine

Tumor response assessment has been a foundation for advances in cancer therapy. Recent discoveries of effective targeted therapy for specific genomic abnormalities in lung cancer and their clinical application have brought revolutionary advances in lung cancer therapy and transformed the oncologist's approach to patients with lung cancer. Because imaging is a major method of response assessment in lung cancer both in clinical trials and practice, radiologists must understand the genomic alterations in lung cancer and the rapidly evolving therapeutic approaches to effectively communicate with oncology colleagues and maintain the key role in lung cancer care. This article describes the origin and importance of tumor response assessment, presents the recent genomic discoveries in lung cancer and therapies directed against these genomic changes, and describes how these discoveries affect the radiology community. The authors then summarize the conventional Response Evaluation Criteria in Solid Tumors and World Health Organization guidelines, which continue to be the major determinants of trial endpoints, and describe their limitations particularly in an era of genomic-based therapy. More advanced imaging techniques for lung cancer response assessment are presented, including computed tomography tumor volume and perfusion, dynamic contrast material-enhanced and diffusion-weighted magnetic resonance imaging, and positron emission tomography with fluorine 18 fluorodeoxyglucose and novel tracers. State-of-art knowledge of lung cancer biology, treatment, and imaging will help the radiology community to remain effective contributors to the personalized care of lung cancer patients.

Positron Emission Tomography as a Method for Measuring Drug Delivery to Tumors in vivo: The Example of [(11)C]docetaxel

Systemic anticancer treatments fail in a substantial number of patients. This may be caused by inadequate uptake and penetration of drugs in malignant tumors. Consequently, improvement of drug delivery to solid tumors may enhance its efficacy. Before evaluating strategies to enhance drug uptake in tumors, better understanding of drug delivery to human tumors is needed. Positron emission tomography (PET) is an imaging technique that can be used to monitor drug pharmacokinetics non-invasively in patients, based on radiolabeling these drugs with short-lived positron emitters. In this mini review, principles and potential applications of PET using radiolabeled anticancer drugs will be discussed with respect to personalized treatment planning in oncology. In particular, it will be discussed how these radiolabeled anticancer drugs could help to develop strategies for improved drug delivery to solid tumors. The development and clinical implementation of PET using radiolabeled anticancer drugs will be illustrated by validation studies of carbon-11 labeled docetaxel ([(11)C]docetaxel) in lung cancer patients.

Personalized medicine: through the looking glass of functional imaging

Imaging techniques afford the opportunity to personalize chemotherapy delivery by prospectively determining how much of an agent is delivered to which tumor site. Drug distribution can be prescribed by altering the properties of the drug (nontechnology) or the physiology of the host (induction of alterations of blood flow).

Toward prediction of efficacy of chemotherapy: a proof of concept study in lung cancer patients using [¹¹C]docetaxel and positron emission tomography

PURPOSE

Pharmacokinetics of docetaxel can be measured in vivo using positron emission tomography (PET) and a microdose of radiolabeled docetaxel ([(11)C]docetaxel). The objective of this study was to investigate whether a [(11)C]docetaxel PET microdosing study could predict tumor uptake of therapeutic doses of docetaxel.

EXPERIMENTAL DESIGN

Docetaxel-naïve lung cancer patients underwent 2 [(11)C]docetaxel PET scans; one after bolus injection of [(11)C]docetaxel and another during combined infusion of [(11)C]docetaxel and a therapeutic dose of docetaxel (75 mg·m(-2)). Compartmental and spectral analyses were used to quantify [(11)C]docetaxel tumor kinetics. [(11)C]docetaxel PET measurements were used to estimate the area under the curve (AUC) of docetaxel in tumors. Tumor response was evaluated using computed tomography scans.

RESULTS

Net rates of influx (Ki) of [(11)C]docetaxel in tumors were comparable during microdosing and therapeutic scans. [(11)C]docetaxel AUCTumor during the therapeutic scan could be predicted reliably using an impulse response function derived from the microdosing scan together with the plasma curve of [(11)C]docetaxel during the therapeutic scan. At 90 minutes, the accumulated amount of docetaxel in tumors was less than 1% of the total infused dose of docetaxel. [(11)C]docetaxel Ki derived from the microdosing scan correlated with AUCTumor of docetaxel (Spearman ρ = 0.715; P = 0.004) during the therapeutic scan and with tumor response to docetaxel therapy (Spearman ρ = -0.800; P = 0.010).

CONCLUSIONS

Microdosing data of [(11)C]docetaxel PET can be used to predict tumor uptake of docetaxel during chemotherapy. The present study provides a framework for investigating the PET microdosing concept for radiolabeled anticancer drugs in patients.

The Potential Benefit by Application of Kinetic Analysis of PET in the Clinical Oncology

PET is an appropriate method to display the functional activities in target tissue using many types of traces. The visual assessment of PET images plus the semiquantitative parameter (SUV) are the main diagnostic standards considered in identifying the malignant lesion. However, these standards lack occasionally the proper specificity and/or sensitivity. That emphasizes the importance of considering supplemental diagnostic criteria such as the kinetic parameter. The latter gives the way to image the ongoing metabolic processes within the target tissue as well as to identify the alterations occurring at the microscale level before they become observable in the conventional PET-imaging. The importance of kinetic analysis of PET imaging has increased with newly developed PET devices that offer images of good quality and high spatial resolution. In this paper, we highlighted the potential contribution of kinetic analysis in improving the diagnostic accuracy in intracranial tumour, lung tumour, liver tumour, colorectal tumour, bone and soft tissue tumours, and prostate cancer. Moreover, we showed that the appropriate therapy monitoring can be best achieved after considering the kinetic parameters. These promising results indicate that the kinetic analysis of PET imaging may become an essential part in preclinical and clinical molecular imaging as well.

Scheduling of anticancer drugs: timing may be everything

Many cancer patients are treated with a combination of anticancer drugs. Here, we discuss the importance of drug scheduling and the need for studies that investigate the optimal timing of the various anticancer drugs. Positron emission tomography (PET) using radiolabeled anticancer drugs could be an important tool for those studies.

Rapid decrease in delivery of chemotherapy to tumors after anti-VEGF therapy: implications for scheduling of anti-angiogenic drugs

Current strategies combining anti-angiogenic drugs with chemotherapy provide clinical benefit in cancer patients. It is assumed that anti-angiogenic drugs, such as bevacizumab, transiently normalize abnormal tumor vasculature and contribute to improved delivery of subsequent chemotherapy. To investigate this concept, a study was performed in non-small cell lung cancer (NSCLC) patients using positron emission tomography (PET) and radiolabeled docetaxel ([(11)C]docetaxel). In NSCLC, bevacizumab reduced both perfusion and net influx rate of [(11)C]docetaxel within 5 hr. These effects persisted after 4 days. The clinical relevance of these findings is notable, as there was no evidence for a substantial improvement in drug delivery to tumors. These findings highlight the importance of drug scheduling and advocate further studies to optimize scheduling of anti-angiogenic drugs.