Silicon amphiphilic compounds and the use thereof

Details Silicon amphiphilic compounds and the use thereof Silicon amphiphilic compounds and the use thereof

1996-09-03

2002-07-02

Shaver, Paul F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carbohydrates or derivatives

C556S428000, C556S437000, C556S427000, C556S436000, C556S404000, C556S405000, C556S425000

Reexamination Certificate

active

06414139

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to novel amphiphilic compounds and the use thereof. More particularly, the present invention relates to novel silicon amphiphilic compounds and their use in diagnostic, therapeutic, and other applications.
BACKGROUND OF THE INVENTION
Ultrasound is a valuable diagnostic imaging technique for studying various areas of the body, for example, the vasculature, including tissue microvasculature. Ultrasound provides certain advantages. over other diagnostic techniques. For example, diagnostic techniques involving nuclear medicine and X-rays generally results in exposure of the patient to ionizing electron radiation. Such radiation can cause damage to subcellular material, including deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and proteins. Ultrasound does not involve such potentially damaging radiation. In addition, ultrasound is relatively inexpensive relative to other diagnostic techniques, including computed tomography (CT) and magnetic resonance imaging (MRI), which require elaborate and expensive equipment.
Ultrasound involves the exposure of a patient to sound waves. Generally, the sound waves dissipate due to absorption by body tissue, penetrate through the tissue or reflect off of the tissue. The reflection of sound waves off of tissue, generally referred to as backscatter or reflectivity, forms the basis for developing an ultrasound image. In this connection, sound waves reflect differentially from different body tissues. This differential reflection is due to various factors, including the constituents and the density of the particular tissue being observed. Ultrasound involves the detection of the differentially reflected waves, generally with a transducer that. can detect sound waves having a frequency of 1 megahertz (MHZ) to 10 MHZ. The detected waves can be integrated into an image which is quantitated and the quantitated waves converted into an image of the tissue being studied.
Ultrasound imaging techniques generally also involve the use of contrast agents. Contrast agents are used to improve the quality and usefulness of images which are obtained via ultrasound. Exemplary contrast agents include, for example, suspensions of solid particles, emulsified liquid droplets, and gas-filled bubbles. See, e.g., Hilmann et al., U.S. Pat. No. 4,466,442, and published International Patent Applications WO 92/17212 and WO 92/21382.
The quality of images produced from ultrasound has improved significantly. Nevertheless, further improvement is needed, particularly with respect to images involving vasculature in tissues that are perfused with a vascular blood supply. Accordingly, there is a need for improved ultrasound techniques, including improved contrast agents which are capable of providing medically useful images of the vasculature and vascular-related organs.
The reflection of sound from a liquid-gas interface is extremely efficient. Accordingly, bubbles, including gas-filled bubbles, are useful as contrast agents. The term “bubbles”, as used herein, refers to vesicles which are generally characterized by the presence of one or more membranes or walls surrounding an internal void that is filled with a gas or precursor thereto. Exemplary bubbles include, for example, vesicles which are surrounded by monolayers and/or bilayers to form, for example, unilamellar, oligolamellar and/or multilamellar vesicles, such as liposomes, micelles and the like. As discussed more fully hereinafter, the effectiveness of bubbles as contrast agents depends upon various factors, including, for example, the size and/or elasticity of the bubble.
With respect to the effect of bubble size, the following discussion is provided. As known to the skilled artisan, the signal which is reflected off of a bubble is a function of the radius (r
6
) of the bubble (Rayleigh Scatterer). Thus, a bubble having a diameter of 4 micrometer (&mgr;m) possesses about 64 times the scattering ability of a bubble having a diameter of 2 &mgr;m. Thus, generally speaking, the larger the bubble, the greater the reflected signal.
However, bubble size is limited by the diameter of capillaries through which the bubbles must pass. Generally, contrast agents which comprise bubbles having a diameter of greater than 10 &mgr;m can be dangerous since microvessels may be occluded. Accordingly, it is preferred that greater than about 90% of the bubbles in a contrast agent have a diameter of less than about 10 &mgr;m, with greater than about 95% being more preferred, and greater than about 98% being even more preferred. Mean bubble diameter is important also, and should be greater than 1 &mgr;m, with greater than 2 &mgr;m being preferred. The volume weighted mean diameter of the bubbles should be about 7 to 10 micrometer.
As noted above, the elasticity of bubbles is also important. This is because highly elastic bubbles can deform, as necessary, to “squeeze” through capillaries. This decreases the likelihood of occlusion. The effectiveness of a contrast agent which comprises bubbles is also dependent on the bubble concentration. Generally, the higher the bubble concentration, the greater the reflectivity of the contrast agent.
Another important characteristic which is related to the effectiveness of bubbles as contrast agents is bubble stability. As used herein, particularly with reference to gas-filled bubbles, “bubble stability” refers to the ability of bubbles to retain gas entrapped therein after exposure to a pressure greater than atmospheric pressure. To be effective as contrast agents, bubbles generally need to retain greater than 50% of entrapped gas after exposure to pressure of 300 millimeters (mm) of mercury (Hg) for about one minute. Particularly effective bubbles retain 75% of the entrapped gas after being exposed for one minute to a pressure of 300 mm Hg, with an entrapped gas content of 90% providing especially effective contrast agents. It is also highly desirable that, after release of the pressure, the bubbles return to their original size. This is referred to generally as “bubble resilience.”
Bubbles which lack desirable stability provide poor contrast agents. If, for example, bubbles release the gas entrapped therein in vivo, reflectivity is diminished. Similarly, the size of bubbles which possess poor resilience will be decreased in vivo, also resulting in diminished reflectivity.
The stability of bubbles disclosed in the prior art is generally inadequate for use as contrast agents. For example, the prior art discloses bubbles, including gas-filled liposomes, which comprise lipoidal walls or membranes. See, e.g., Ryan et al., U.S. Pat. Nos. 4,900,540 and 4,544,545; Tickner et al., U.S. Pat. No. 4,276,885; Klaveness et al., WO 93/13809 and Schneider et al., EPO 0 554 213 and WO 91/15244. The stability of the bubbles disclosed in the aforementioned references is poor in that as the solutions in which the bubbles are suspended become diluted, for example, in vivo, the walls or membranes of the bubbles are thinned. This results in a greater likelihood of rupture.
Various studies have been conducted in an attempt to improve bubble stability. Such studies have included, for example, the preparation of bubbles in which the membranes or walls thereof comprise materials that are apparently strengthened via crosslinking. See, e.g., Klaveness et al., WO 92/17212, in which there are disclosed bubbles which comprise proteins crosslinked with biodegradable crosslinking agents. Alternatively, bubble membranes can comprise compounds which are not proteins but which are crosslinked also with biocompatible compounds. See, e.g., Klaveness et al., WO 92/17436, WO 93/17718 and WO 92/21382.
Prior art techniques for stabilizing bubbles, including crosslinking, suffer from various drawbacks. For example, the crosslinking described above generally involves the use of new materials, including crosslinked proteins or other compounds, for which the metabolic fate is unknown. In addition, crosslinking requires additional chemical process steps, including isolation and purification of the c

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