Gene therapy approaches to supply apolipoprotein A-I...

Details Gene therapy approaches to supply apolipoprotein A-I... Gene therapy approaches to supply apolipoprotein A-I...

1997-09-29

2003-02-11

Saidha, Tekchand (Department: 1652)

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

Organic compounds

Carbohydrates or derivatives

C435S069100, C435S069200, C435S252300, C435S320100, C530S324000, C530S325000, C530S326000

Reexamination Certificate

active

06518412

ABSTRACT:

1. INTRODUCTION
The invention relates to gene therapy approaches to supply nucleotide sequences encoding modified forms of the native forms of apolipoprotein A-I (ApoA-I) i.e., mature ApoA-I, preproApoA-I and proApoA-I; ApoA-I peptides; ApoA-I agonists and superagonists, peptides which mimic or exceed the activity of native ApoA-I; and the native ApoA-I gene for the treatment of disorders associated with dyslipoproteinemia, including cardiovascular disease, atherosclerosis, restenosis, hyperlipidemia, and other disorders such as septic shock.
2. BACKGROUND OF THE INVENTION
Circulating cholesterol is carried by plasma lipoproteins—particles of complex lipid and protein composition that transport lipids in the blood. Low density lipoproteins (LDL), and high density lipoproteins (HDL) are the major cholesterol carriers. LDL are believed to be responsible for the delivery of cholesterol from the liver (where it is synthesized or obtained from dietary sources) to extrahepatic tissues in the body. The term “reverse cholesterol transport” describes the transport of cholesterol from extrahepatic tissues to the liver where it is catabolized and eliminated. It is believed that plasma HDL particles play a major role in the reverse transport process, acting as scavengers of tissue cholesterol.
The evidence linking elevated serum cholesterol to coronary heart disease is overwhelming. For example, atherosclerosis is a slowly progressive disease characterized by the accumulation of cholesterol within the arterial wall. Compelling evidence supports the concept that lipids deposited in atherosclerotic lesions are derived primarily from plasma LDL; thus, LDLs have popularly become known as the “bad” cholesterol. In contrast, HDL serum levels correlate inversely with coronary heart disease—indeed, high serum levels of HDL are regarded as a negative risk factor. It is hypothesized that high levels of plasma HDL are not only protective against coronary artery disease, but may actually induce regression of atherosclerotic plaques (e.g., see Badimon et al., 1992, Circulation 86 (Suppl. III):86-94). Thus, HDL have popularly become known as the “good” cholesterol.
2.1. Cholesterol Transport
The fat-transport system can be divided into two pathways: an exogenous one for cholesterol and triglycerides absorbed from the intestine, and an endogenous one for cholesterol and triglycerides entering the bloodstream from the liver and other non-hepatic tissue.
In the exogenous pathway, dietary fats are packaged into lipoprotein particles called chylomicrons which enter the bloodstream and deliver their triglycerides to adipose tissue (for storage) and to muscle (for oxidation to supply energy). The remnant of the chylomicron, containing cholesteryl esters, is removed from the circulation by a specific receptor found only on liver cells. This cholesterol then becomes available again for cellular metabolism or for recycling to extrahepatic tissues as plasma lipoproteins.
In the endogenous pathway, the liver secretes a large, very-low-density lipoprotein particle (VLDL) into the bloodstream. The core of VLDLs consists mostly of triglycerides synthesized in the liver, with a smaller amount of cholesteryl esters (either synthesized in the liver or recycled from chylomicrons). Two predominant proteins are displayed on the surface of VLDLs, apoprotein B-100 and apoprotein E. When a VLDL reaches the capillaries of adipose tissue or of muscle, its triglycerides are extracted resulting in a new kind of particle, decreased in size and enriched in cholesteryl esters but retaining its two apoproteins, called intermediate-density lipoprotein (IDL).
In human beings, about half of the IDL particles are removed from the circulation quickly (within two to six hours of their formation), because they bind tightly to liver cells which extract their cholesterol to make new VLDL and bile acids. The IDL particles which are not taken up by the liver remain in the circulation longer. In time, the apoprotein E dissociates from the circulating particles, converting them to LDL having apoprotein B-100 as their sole protein.
Primarily, the liver takes up and degrades most of the cholesterol to bile acids, which are the end products of cholesterol metabolism. The uptake of cholesterol containing particles is mediated by LDL receptors, which are present in high concentrations on hepatocytes. The LDL receptor binds both apoprotein E and apoprotein B-100, and is responsible for binding and removing both IDLs and LDLs from the circulation. However, the affinity of apoprotein E for the LDL receptor is greater than that of apoprotein B-100. As a result, the LDL particles have a much longer circulating life span than IDL particles—LDLs circulate for an average of two and a half days before binding to the LDL receptors in the liver and other tissues. High serum levels of LDL (the “bad” cholesterol) are positively associated with coronary heart disease. For example, in atherosclerosis, cholesterol derived from circulating LDLs accumulates in the walls of arteries leading to the formation of bulky plaques that inhibit the flow of blood until a clot eventually forms, obstructing the artery causing a heart attack or stroke.
Ultimately, the amount of intracellular cholesterol liberated from the LDLs controls cellular cholesterol metabolism. The accumulation of cellular cholesterol derived from VLDLs and LDLs controls three processes: first, it reduces the cell's ability to make its own cholesterol by turning off the synthesis of HMGCOA reductase—a key enzyme in the cholesterol biosynthetic pathway. Second, the incoming LDL-derived cholesterol promotes storage of cholesterol by activating ACAT—the cellular enzyme which converts cholesterol into cholesteryl esters that are deposited in storage droplets. Third, the accumulation of cholesterol within the cell drives a feedback mechanism that inhibits cellular synthesis of new LDL receptors. Cells, therefore, adjust their complement of LDL receptors so that enough cholesterol is brought in to meet their metabolic needs, without overloading. (For a review, see Brown & Goldstein, In, The Pharmacological Basis Of Therapeutics, 8th Ed., Goodman & Gilman, Pergamon Press, NY, 1990, Ch. 36, pp. 874-896).
2.2. Reverse Cholesterol Transport
In sum, peripheral (non-hepatic) cells obtain their cholesterol from a combination of local synthesis and the uptake of preformed sterol from VLDLs and LDLs. In contrast, reverse cholesterol transport (RCT) is the pathway by which peripheral cell cholesterol can be returned to the liver for recycling to extrahepatic tissues, or excretion into the intestine in bile. The RCT pathway represents the only means of eliminating cholesterol from most extrahepatic tissues, and is crucial to maintenance of the structure and function of most cells in the body.
The RCT consists mainly of three steps: (a) cholesterol efflux, the initial removal of cholesterol from various pools of peripheral cells; (b) cholesterol esterification by the action of lecithin:cholesterol acyltransferase (LCAT), preventing a re-entry of effluxed cholesterol into cells; and (c) uptake/delivery of HDL cholesteryl ester to liver cells. The RCT pathway is mediated by HDLS. HDL is a generic term for lipoprotein particles which are characterized by their high density. The main lipidic constituents of HDL complexes are various phospholipids, cholesterol (ester) and triglycerides. The most prominent apolipoprotein components are A-I and A-II which determine the functional characteristics of HDL; furthermore minor amounts of apolipoproteins C-I, C-II, C-III, D, E, J, etc. have been observed. HDL can exist in a wide variety of different sizes and different mixtures of the above-mentioned constituents dependent on the status of remodeling during the metabolic RCT cascade.
The key enzyme involved in the RCT pathway is LCAT. LCAT is produced mainly in the liver and circulates in plasma associated with the HDL fraction. Cholesteryl ester transfer protein (CETP) and another lipid transfer protein, phospholipid transfer protei

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