Multi-use multimodal imaging chelates

Abstract

Cyclen-based chelates can be used as contrast agents for multi-modal imaging of tissue cells. The cyclen-based chelates are preferably polyazamacrocyclic molecules formed from 1,4,7,10 tetraazacyclododecane (“cyclen”) having varying chelating ions, phosphoester chains, and light harvesting moieties. By changing the chelating ion, phosphoester chain length and / or the light harvesting moiety different imaging techniques, such as MRI, CT, fluorescence and absorption, x-ray and NIR, may be employed to image the tissue cells. Additionally, the cyclen-based chelates may be conjugated to provide for site-specific delivery of the cyclen-based chelate to the desired tissue cells. The cyclen-based chelates may also be delivered to the tissue cells by attaching the cyclen-based to a polymeric delivery vehicle. Although these cyclen-based chelates have a wide variety of application, the preferred use is for imaging of cancer cells, such as brain cancer, for improving resection of a cancerous tissue.

Description

CROSS REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit, under 35 U.S.C. 119(e), of U.S. Provisional Application Nos. 60 / 316,284 and 60 / 316,303 both filed Sep. 4, 2001, the contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates generally to the formation of contrast agents containing cyclen-based chelates in order to produce multimodal images of a sample of cells.[0004]2. Background Information[0005]The American Cancer Society estimates that 16,800 new intracranial tumors were diagnosed in 1999, more than double the number of diagnosed cases of Hodgkin's disease, and over half the number of cases of melanoma. Moreover, in the same year, primary cancer of the central nervous system was the cause of death in approximately 13,100 people. Despite aggressive treatment strategies including surgical resection, irradiation and chemotherapy, most patients die from the disease...

AI Technical Summary

Benefits of technology

The patent describes a new method for imaging and detecting diseases using cyclen-based chelates. These chelates can produce unique contrast agents that can be used in multiple modalities of imaging, such as MRI, fluorescence, and PET. The chelates can also be attached to targeting agents to create molecular imaging agents that can be used for brain cancer detection and therapy tracking. The cyclen-based chelates have long fluorescence life-times and can produce various spectroscopic signatures, making them ideal for molecular imaging. Overall, this patent introduces a new tool for molecular imaging that can improve cancer detection and therapy monitoring.

Problems solved by technology

Yet, it is impossible to over-emphasize the importance imaging and detection techniques play in influencing the success in treating a variety of cancers.

The degree to which a complete resection can be carried out in the brain is limited, however, by a number of factors unique to the central nervous system.

One variable that directly influences the extent of resection is the difficulty of visually detecting differences between normal brain tissue and malignant tissue.

Alternatively, patients may experience unexpected neurological morbidity if the resection is inadvertently carried into normal surrounding brain tissue.

Additionally, current tumor imaging methods are limited because they image the tumor indirectly.

Thus it is difficult to identify radiation necrosis and inflammatory changes, as well as to assess response to therapy or to provide the capability of following disease progression.

Furthermore, classical MRI contrast enhanced imaging fails to demarcate primary infiltrating glial tumors, with scans often indicating a discreet lesion border even though tumor cells typically extend several centimeters away.

Even with this dramatic improvement, MRI and CT scans cannot be used to identify the outermost border of the malignant brain tumor.

Current imaging methods do not adequately assess the extent of disease or differentiate between viable tumor infiltration, radiation necrosis, or inflammatory changes.

For these reasons, current imaging modalities are not ideal for following disease progression or assessing response to therapy.

Presently, in-vivo detection and surgical resection means are limited to either macroscopic gross visualization, white-light endoscopy or white-light microscopic visualization.

When the contrast for disease is low as it is for small foci of cancer cells, it makes surgical resection problematic.

These techniques tend to miss disease at its earliest stage because of low concentrations of the endogenous chromophores leading to contrast between normal tissue and disease.

Although MRI remains the hallmark imaging modality for examining many types of cancers, MRI does not provide a clinician with real-time intra-operative maps once surgery commences.

While there are numerous exogenous, topical or injectable agents being used to aid in the demarcating of normal tissue from disease tissue, including acetic acid, indocyanine green (ICG), methylene and toluidine blue, and 5-aminolevulinic acid (ALA), none of these agents can be used as an MRI agent.

These agents are also restricted in use due to tissue toxicity, low specificity, and / or long manifestation times, with contrast primarily based on differential permeability of the agent between normal and diseased tissue.

Generally they provide only modest diagnostic utility, primarily because of an inherent lack of specificity.

These techniques, while showing great promise, still suffer from relatively low S / N stemming from small changes in concentration of the solutes detected in early disease and the large background arising from other fluorophores, scattering, and reflected light.

While these types of markers have shown promise in a diagnostic setting, there are limitations.

Long delays for accumulation in tumors, prolonged photosensitization of skin, and phototoxicity of tissues being imaged are some examples of these limitations.

However, to date, their efficiency in intraoperative detection of tumor margins has been limited.

One drawback of this approach to cancer detection is that the chemistry required for conjugation can often be quite complicated or require great synthetic skill.

However, a major concern with using these pyclen-based lanthanide chelates is that the harvesting moiety, pyridine, requires high energy UV light (270 nm) to excite the lanthanide, which can be harmful to tissues.

Although PBRs are widely expressed throughout the body in all steroid-producing tissues, their density in the CNS is primarily limited to the ependymal cells and glia.

For various reasons, including non-ideal interstitial solute transport properties and complicated pharmokinetics, the approach of using high-affinity vector molecules as contrast agents has been limited by poor specificity when used in vivo.

However, these studies have not been fully explored nor demonstrate the potential use of PK-11195 as a vehicle for contrast enhancement in brain cancer imaging.

Furthermore, GFAP is inconsistently detectable in glioma cells.

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