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The Role of Medical Imaging in Personalized Medicine

Writer & reporter: Dror Nir, PhD

The future of personalized medicine comprise quantifiable diagnosis and tailored treatments; i.e. delivering the right treatment at the right time. To achieve standardized definition of what “right” means, the designated treatment location and lesion size are important factors. This is unrelated to whether the treatment is focused to a location or general. The role of medical imaging is and will continue to be vital in that respect: Patients’ stratification based on imaging biomarkers can help identify individuals suited for preventive intervention and can improve disease staging. In vivo visualization of loco-regional physiological, biochemical and biological processes using molecular imaging can detect diseases in pre-symptomatic phases or facilitate individualized drug delivery. Furthermore, as mentioned in most of my previous posts, imaging is essential to patient-tailored therapy planning, therapy monitoring, quantification of response-to-treatment and follow-up disease progression. Especially with the rise of companion diagnostics/theranostics (therapeutics & diagnostics), imaging and treatment will have to be synchronized in real-time to achieve the best control/guidance of the treatment.

It is worthwhile noting that the new RECIST 1.1 criteria (used in oncological therapy monitoring) have been expanded to include the use of PET (in addition to lymph-node evaluation).

In previous posts I already discussed many examples concerning the use of medical imaging in personalized medicine: e.g. patients’ stratification; Imaging-biomarkers is Imaging-based tissue characterization, the future of imaging-biomarkers in diagnostic; Ultrasound-based Screening for Ovarian Cancer, imaging-based guided therapies; Minimally invasive image-guided therapy for inoperable hepatocellular carcinoma, treatment follow-up; the importance of spatially-localized and quantified image interpretation in cancer management, and imaging-based assessment of response to treatment; Causes and imaging features of false positives and false negatives on 18F-PET/CT in oncologic imaging

Browsing through our collaborative open-source initiative one can find many more articles and discussions on that matter; e.g. Tumor Imaging and Targeting: Predicting Tumor Response to Treatment: Where we stand?, In Search of Clarity on Prostate Cancer Screening, Post-Surgical Followup, and Prediction of Long Term Remission

In this post I would like to highlight the potential contribution of medical imaging to development of companion diagnostics. I do that through the story on co-development of Vintafolide (EC145) and etarfolatide (Endocyte/Merck). Etarfolatide is a folate-targeted molecular radiodiagnostic imaging agent that identifies tumors that overexpress the folate receptor. The folate receptor, a glycosylphosphatidylinositol anchored cell surface receptor, is overexpressed on the vast majority of cancer tissues, while its expression is limited in healthy tissues and organs. Folate receptors are highly expressed in epithelial, ovarian, cervical, breast, lung, kidney, colorectal, and brain tumors. When expressed in normal tissue, folate receptors are restricted to the lungs, kidneys, placenta, and choroid plexus. In these tissues, the receptors are limited to the apical surface of polarized epithelia. Folate, also known as pteroylglutamate, is a non-immunogenic water-soluble B vitamin that is critical to DNA synthesis, methylation, and repair (folate is used to synthesize thymine).

Vintafolide (EC145) delivers a very potent vinca chemotherapy directly to cancer cells by targeting the folate receptor expressed on cancer cells. Approximately 80-90 percent of ovarian and lung cancers express the receptor, as do many other types of cancer. Clinical data have shown that patients with metastases that are all positive for the folate receptor, identified by etarfolatide, benefited the most from the treatment with vintafolide, the corresponding folate-targeted small molecule drug conjugate.

Having both drug and imaging agent rely on folate receptors within the patients body Endocyte’s strategy was to develop the imaging agent and to use it to accelerate R&D and regulation. Endocyte and Merck entered into a partnership for vintafolide in April 2012. Under this partnership Merck was granted an exclusive license to develop, manufacture and commercialize vintafolide. Endocyte is responsible for conducting the PROCEED Phase 3 clinical study in women with platinum resistant ovarian cancer and the Phase 2b second line NSCLC (non-small cell lung cancer) study named TARGET. Merck is responsible for further clinical studies in additional indications. This Co-development of a diagnostic and therapeutic agent, was conducted according to the FDA guidance on personalized medicine and resulted with vintafolide gaining, already in 2012, status of orphan drug in EMA.

 The following is an extract from a post by Phillip H. Kuo, MD, PhD, associate professor of medical imaging, medicine, and biomedical engineering; section chief of nuclear medicine; and director of PET/CT at the University of Arizona Cancer Center.

Figure 1 — Targeted Radioimaging Diagnostic and Small Molecule Drug Conjugate

Etarfolatide is comprised of the targeting ligand folic acid (yellow), which has a high folate receptor binding affinity, and a Technetium-99m–based radioimaging agent (turquoise). Etarfolatide identifies metastases that express the folate receptor protein in real time (A). The folic acid-targeting ligand is identical to that found on vintafolide, the corresponding therapeutic small molecule drug conjugate, which also contains a linker system (blue) and a potent chemotherapeutic drug (red) (B).

Figure 2 — Whole-Body Scan With 111In-DTPA-Folate 

Diagnostic images of whole-body scans obtained following administration of the targeted radioimaging agent 111In-DTPA-folate, which is constructed with the same folic acid ligand as that engineered in etarfolatide. The healthy patient image on the left shows no folate receptor-positive abdominal tumor. Instead, only healthy kidneys (involved in excretion) are revealed. The patient on the right shows folate receptor-positive tumors in the abdomen and pelvis. Patients with metastases, identified with the companion imaging diagnostic etarfolatide as folate receptor-positive are most likely to respond to treatment with the corresponding small molecular drug conjugate vintafolide. Note: Vintafolide currently is being evaluated in a phase 3 clinical trial for platinum-resistant ovarian cancer and a phase 2 trial for non–small-cell lung cancer. Both studies also are using etarfolatide.

Figure 3 — Vintafolide’s Mechanism of Action

Folate is required for cell division, and rapidly dividing cancer cells often express folate receptors to capture enough folate to support rapid cell growth. Elevated expression of the folate receptor occurs in many human malignancies, especially when associated with aggressively growing cancers. The folate-targeted small molecule drug conjugate vintafolide binds to the folate receptor (A) and subsequently is internalized by a natural endocytosis process (B). Once inside the cell, vintafolide’s serum-stable linker selectively releases a potent vinca alkaloid compound (C) to arrest cell division and induce cell death.

Epilog

I think that those of you who reached this point in my post deserve a special bonus! So here it is: A medical-imaging initiative that is as ambitious and complex as the initiative to send humans into deep-space.

This is the The European Population Imaging Infrastructure initiative of the Dutch Federation of University Medical Centres (NFU) and the Erasmus University Medical Centre Rotterdam, Department of Radiology, chaired by Professor Gabriel P. Krestin. The NFU has made available initial funding for the development of this initiative.

The European Population Imaging Infrastructure closely cooperates with the European Biomedical Imaging Infrastructure Project EURO-BioImaging which is currently being developed.

The ultimate aim of the infrastructure is to help the development and implementation of strategies to prevent or effectively treat disease. It supports imaging in large, prospective epidemiological studies on the population level. Image specific markers of pre-symptomatic diseases can be used to investigate causes of pathological alterations and for the early identification of people at risk.

More information on this infrastructure and on the role of the European Population Imaging Infrastructure in this can be found in the Netherlands Roadmap for Large-Scale Research Facilities, the applicaton for funding of the Roadmap Large Scale Research Facilities Application form of the Roadmap EuroBioImaging, and on the Euro-BioImaging website.

Certainly, while making progress with this initiative, many lessons will be learned. I recommend to explore this site and Enjoy!