Applications of Positron Emission Tomography in the Development of Molecular Targeted Cancer Therapeutics

Preclinical Characterisation of PSMA/GRPR-Targeting Heterodimer [68Ga]Ga-BQ7812 for PET Diagnostic Imaging of Prostate Cancer: A Step towards Clinical Translation

The development of radioligands targeting prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR) has shown promising results for the imaging and therapy of prostate cancer. However, studies have shown that tumors and metastases can express such targets heterogeneously. To overcome this issue and to improve protein binding, radioligands with the ability to bind both PSMA and GRPR have been developed. Herein, we present the preclinical characterization of [68Ga]Ga-BQ7812; a PSMA/GRPR-targeting radioligand for the diagnostic PET imaging of prostate cancer. This study aimed to evaluate [68Ga]Ga-BQ7812 to promote the translation of such imaging probes into the clinic. [68Ga]Ga-BQ7812 demonstrated rapid and specific binding to both targets in a PSMA/GRPR-expressing PC3-pip cell line. Results from the biodistribution study in PC3-pip xenografted mice showed specific binding to both targets, with the highest activity uptake at 1 h pi in tumor (PSMA+/GRPR+, 10.4 ± 1.0% IA/g), kidneys (PSMA+, 45 ± 16% IA/g), and pancreas (GRPR+, 5.6 ± 0.7% IA/g). At 3h pi, increased tumour-to-organ ratios could be seen due to higher retention in the tumor compared with other PSMA or GRPR-expressing organs. These results, together with low toxicity and an acceptable estimated dosimetry profile (total effective dose = 0.0083 mSv/MBq), support the clinical translation of [68Ga]Ga-BQ7812 and represent a step towards its first clinical trial.

Strategies for the discovery and development of therapies for metastatic breast cancer

Nearly all deaths caused by solid cancers occur as a result of metastasis--the formation of secondary tumours in distant organs such as the lungs, liver, brain and bone. A major obstruction to the development of drugs with anti-metastatic efficacy is our fragmented understanding of how tumours 'evolve' and metastasize, at both the biological and genetic levels. Furthermore, although there is significant overlap in the metastatic process among different types of cancer, there are also marked differences in the propensity to metastasize, the extent of metastasis, the sites to which the tumour metastasizes, the kinetics of the process and the mechanisms involved. Here, we consider the case of breast cancer, which has some marked distinguishing features compared with other types of cancer. Considerable progress has been made in the development of preclinical models and in the identification of relevant signalling pathways and genetic regulators of metastatic breast cancer, and we discuss how these might facilitate the development of novel targeted anti-metastatic drugs.

Delivering affordable cancer care in high-income countries

The burden of cancer is growing, and the disease is becoming a major economic expenditure for all developed countries. In 2008, the worldwide cost of cancer due to premature death and disability (not including direct medical costs) was estimated to be US$895 billion. This is not simply due to an increase in absolute numbers, but also the rate of increase of expenditure on cancer. What are the drivers and solutions to the so-called cancer-cost curve in developed countries? How are we going to afford to deliver high quality and equitable care? Here, expert opinion from health-care professionals, policy makers, and cancer survivors has been gathered to address the barriers and solutions to delivering affordable cancer care. Although many of the drivers and themes are specific to a particular field-eg, the huge development costs for cancer medicines-there is strong concordance running through each contribution. Several drivers of cost, such as over-use, rapid expansion, and shortening life cycles of cancer technologies (such as medicines and imaging modalities), and the lack of suitable clinical research and integrated health economic studies, have converged with more defensive medical practice, a less informed regulatory system, a lack of evidence-based sociopolitical debate, and a declining degree of fairness for all patients with cancer. Urgent solutions range from re-engineering of the macroeconomic basis of cancer costs (eg, value-based approaches to bend the cost curve and allow cost-saving technologies), greater education of policy makers, and an informed and transparent regulatory system. A radical shift in cancer policy is also required. Political toleration of unfairness in access to affordable cancer treatment is unacceptable. The cancer profession and industry should take responsibility and not accept a substandard evidence base and an ethos of very small benefit at whatever cost; rather, we need delivery of fair prices and real value from new technologies.

Cancer-Induced, Immune-Mediated Ocular Degenerations

The means whereby vision can be lost from a disease located distant from the eye include autoimmunity, with sensitization resulting from extraocular stimuli, a process illustrated here by the immunologic confusion caused by cancers. The uncontrolled proliferation of malignancies commonly involves the expression of components of the central nervous system, but a damaging loss of tolerance is rare. When autoimmunity does develop, organ-specific antigens are more often involved than the more generalized and widely disseminated common neuronal components. A focus upon a single antigen is typical of the immune-mediated paraneoplasia, a collection of syndromes identified by unusual antibody reactions. This review provides an outline of the immunologic trail that led to the recognition of autoimmunity in paraneoplastic ocular degenerations, how specific antibody reactions aid in diagnosis, and the possibility of including antibodies in modes for sight-saving intervention. 'Those who do not know history are destined to repeat it'.

Évaluation de la radiosensibilité tumorale par l'imagerie fonctionnelle et métabolique : de la recherche à l'application clinique. Revue de la littérature

During the last half of century considerable research on radiosensitivity biomarkers has been published. However, to date there is no non-invasive marker of cellular radiosensitivity identified for clinical routinely use. In this review, the main functional and metabolic imaging isotopic techniques for tumor radiosensitivity that have been explored over the last years are being described. This indirect evaluation fall into 3 topics associated with tumor proliferation rate or apoptosis, tumor hypoxic fraction, neoangiogenesis and the intrinsic radiosensitivity of clonogenic tumor cells. The final objective of the radiosensitivity monitoring during radiotherapy would be to adapt treatment strategy for overcoming the identified radioresistance mechanism such as hypoxia by the addition of radiosensitisers for example. This would allow better tumor control rather than continue inefficient and costly treatment delivery, which in addition could compromise outcome.

Multi-tracer small animal PET imaging of the tumour response to the novel pan-Erb-B inhibitor CI-1033

PURPOSE

This study was designed as "proof of concept" for a drug development model utilising multi-tracer serial small animal PET imaging to characterise tumour responses to molecularly targeted therapy.

METHODS

Mice bearing subcutaneous A431 human squamous carcinoma xenografts (n=6-8) were treated with the pan-Erb-B inhibitor CI-1033 or vehicle and imaged serially (days 0, 3 and 6 or 7) with [(18)F]fluorodeoxyglucose, [(18)F]fluoro-L: -thymidine, [(18)F]fluoro-azoazomycinarabinoside or [(18)F]fluoromisonidazole. Separate cohorts (n=3) were treated identically and tumours were assessed ex vivo for markers of glucose metabolism, proliferation and hypoxia.

RESULTS

During the study period, mean uptake of all PET tracers generally increased for control tumours compared to baseline. In contrast, tracer uptake into CI-1033-treated tumours decreased by 20-60% during treatment. Expression of the glucose transporter Glut-1 and cell cycle markers was unchanged or increased in control tumours and generally decreased with CI-1033 treatment, compared to baseline. Thymidine kinase activity was reduced in all tumours compared to baseline at day 3 but was sevenfold higher in control versus CI-1033-treated tumours by day 6 of treatment. Uptake of the hypoxia marker pimonidazole was stable in control tumours but was severely reduced following 7 days of CI-1033 treatment.

CONCLUSION

CI-1033 treatment significantly affects tumour metabolism, proliferation and hypoxia as determined by PET. The PET findings correlated well with ex vivo biomarkers for each of the cellular processes studied. These results confirm the utility of small animal PET for evaluation of the effectiveness of molecularly targeted therapies and simultaneously definition of specific cellular processes involved in the therapeutic response.

Imaging hypoxia and angiogenesis in tumors

There is a clear need in cancer treatment for a noninvasive imaging assay that evaluates the oxygenation status and heterogeneity of hypoxia and angiogenesis in individual patients. Such an assay could be used to select alternative treatments and to monitor the effects of treatment. Of the several methods available, each imaging procedure has at least one disadvantage. The limited quantitative potential of single-photon emission CT and MR imaging always limits tracer imaging based on these detection systems. PET imaging with FMISO and Cu-ATSM is ready for coordinated multicenter trials, however, that should move aggressively forward to resolve the debate over the importance of hypoxia in limiting response to cancer therapy. Advances in radiation treatment planning, such as intensity-modulated radiotherapy, provide the ability to customize radiation delivery based on physical conformity. With incorporation of regional biologic information, such as hypoxia and proliferating vascular density in treatment planning, imaging can create a biologic profile of the tumor to direct radiation therapy. Presence of widespread hypoxia in the tumor benefits from a systemic hypoxic cell cytotoxin. Angiogenesis is also an important therapeutic target. Imaging hypoxia and angiogenesis complements the efforts in development of antiangiogenesis and hypoxia-targeted drugs. The complementary use of hypoxia and angiogenesis imaging methods should provide the impetus for development and clinical evaluation of novel drugs targeted at angiogenesis and hypoxia. Hypoxia imaging brings in information different from that of FDG-PET but it will play an important niche role in oncologic imaging in the near future. FMISO, radioiodinated azamycin arabinosides, and Cu-ATSM are all being evaluated in patients. The Cu-ATSM images show the best contrast early after injection but these images are confounded by blood flow and their mechanism of localization is one step removed from the intracellular O2 concentration. FMISO has been criticized as inadequate because of its clearance characteristics, but its uptake after 2 hours is probably the most purely reflective of regional PO2 at the time the radiopharmaceutical is used. The FMISO images show less contrast than those of Cu-ATSM because of the lipophilicity and slower clearance of FMISO but attempts to increase the rate of clearance led to tracers whose distribution is contaminated by blood flow effects. For single-photon emission CT the only option is radioiodinated azamycin arabinosides, because the technetium agents are not yet ready for clinical evaluation. Rather than develop new and improved hypoxia agents, or even quibbling about the pros and cons of alternative agents, the nuclear medicine community needs to convince the oncology community that imaging hypoxia is an important procedure that can lead to improved treatment outcome.

The role of positron emission tomography in the discovery and development of new drugs; As studied in laboratory animals

Drug discovery and development is time consuming and a costly procedure. The challenges for the pharmaceutical industry range from the evaluation of potential new drug candidates, the determination of drug pharmacokinetics/pharmacodynamics, the measurement of receptor occupancy as a determinant of drug efficacy, and the pharmacological characterisation of mechanisms of action. Positron emission tomography (PET) is a powerful quantitative imaging technique for looking at biochemical pathways, molecular interactions, drug pharmacokinetics and pharmacodynamics. Recent advances in emission tomography, particularly the development of small animal PET scanners, image reconstruction and animal models of disease have led to the development of extremely sensitive and specific tools for imaging biochemical processes in vivo, therefore representing a new means of providing information for drug development and evaluation. Many human genes have a related mouse gene, allowing mice to be used as a platform for mimicking human disease, using knock-out and knock-in gene technology. Consequently PET imaging of rodents is emerging as a cost effective means of screening new pharmaceuticals and decreasing the time required for new drug development.