Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-02-09
2002-11-12
Berch, Mark L. (Department: 1611)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Heterocyclic carbon compounds containing a hetero ring...
C514S261100, C514S266400, C544S118000, C544S277000
Reexamination Certificate
active
06479487
ABSTRACT:
The present invention relates to 6,9-disubstituted 2-[trans-(4-aminocyclohexyl)amino]-purines and methods of using the same for antineoplastic agents or for treatment for neuronal injury and degeneration.
BACKGROUND OF THE INVENTION
Cell division, in both normal and neoplastic cells, is a tightly controlled event which occurs by defined stages. Quiescent cells which are not actively dividing, are in the G
0
phase, as are those terminally differentiated or in a state of temporary arrest. The first phase is the first gap (G
1
) phase during which the cell prepares to synthesize DNA. In late G
1
phase at what is termed a restriction point or R point, the cell commits to entering S phase during which DNA synthesis occurs. Upon completion of S phase, the cell enters the second gap (G
2
) phase during which the cell prepares to divide, which is followed by mitosis, or M phase.
Initial experiments in cell cycle regulation revealed the existence of a protein called “Maturation Promoting Factor” (MPF), a heterodimer with kinase activity. Later, comparison of subsequently identified proteins and their underlying genes revealed a family of yeast genes known as cell division control (cdc) genes. Further experiments demonstrated that some of the cdc genes encode kinases, and were later called cyclin-dependent kinases (cdks). As the result of this reclassification, some cell cycle proteins have dual designations, such as cdk1 which is also known as cdc2. The kinase component of the MPF is now identified as p34
cdc2
and the regulatory subunit of MPF is now called cyclin B. Cyclins were first identified as proteins whose levels oscillated during the cell cycle and were specifically degraded at mitosis. To date, animal cyclins A-I and cdks 1-8 have been identified. To further complicate nomenclature, subtypes of cyclins and cdks have been identified, such as cyclins B1 and B2.
Subsequent research on cell regulation has demonstrated that the stages of cellular division are achieved in part by modulation cyclins and cyclin-dependent kinases (cdks). Cyclins sequentially regulate cdks and are characterized by a 100 amino acid homology region termed the “cyclin box” which is involved in binding a protein kinase partner. Cdks are closely related in sequence and size (35-40 kDa) and are defined as protein kinases activated by bound cyclin regulatory subunits. Cdks contain a conserved active-site cleft of approximately 300 amino acids that is characteristic of all eukaryotic protein kinases. Thus, both the cyclins and cdks appear to be highly conserved protein families.
Isolation of individual cyclins and cdks has enabled further identification of the roles and interactions of each component in cell cycle phase transitions. Excess levels of cdks persist throughout the cell cycle. Activation of cdks occurs upon cyclin synthesis and binding to the catalytic cdk subunit, the result of which is stimulation of the cdk serine/threonine kinase activity. Complete cdk activation requires phosphorylation on a conserved threonine residue located in the T-loop by a cyclin-dependent kinase activating kinase (CAK), which is itself a cdk/cyclin complex composed of cyclin H and cdk7, and a third protein of about 32 kDa.
Inactivation of the cdk-cyclin complex can result from the phosphorylation of a threonine and/or tyrosine residue in the ATP-binding site of the cdk or from binding of one of a number of endogenous inhibitor proteins.
In G
1
phase, D-type cyclins bind to several different cdks, including cdk2, cdk4, cdk5 and cdk6, but are most commonly associated with cdk4 and cdk6. D-type cyclins are thought to act as growth factor sensors, which link cell cycle progression to external cues. Cyclin E-cdk2 complexes appear in the mammalian cell cycle after the D-type cyclin-cdk complexes. Cyclin E synthesis is tightly regulated and occurs in late G
1
and early S phase. The cyclin E-cdk2 complex is essential for the cell to begin DNA replication.
The G
1
cyclins, cyclin D and cyclin E, are transiently produced proteins, with a half-life of about 20 minutes. The short half-life is thought to result from a PEST sequence in the C-terminal regions of these proteins, the degradation of which appears to be mediated by the ubiquitination pathway.
The G
2
cyclins, cyclin A and cyclin B, are stable throughout interphase and specifically destroyed at mitosis through an ubiquitination pathway. Both cyclin A and cyclin B2 appear to be degraded only when complexed with their cdk partner [cyclinA-cdk2 and cyclin A/B-cdk1(cdc2)]. However, cyclin B1 destruction is connected with the integrity of the mitotic apparatus at the end of metaphase. If the spindle is incorrectly assembled, or chromosomes incorrectly aligned, then cyclin B1 destruction is prevented.
Retinoblastoma protein (Rb), a 105 kDa nuclear phosphoprotein, is a substrate of cyclin-cdk complexes of cdks-2, 4 and 6 in G
1
phase and functions as one of the major checkpoint controls in the cell cycle via carefully orchestrated phosphorylation and dephosphorylation. In G
0
/G
1
, Rb exists in a hypophosphorylated state. As the cell progresses into late G
1
, Rb becomes hyperphosphorylated by D-cyclin complexes, which inactivates Rb and drives the cell into S phase resulting in cell cycle progression and cell division. This state of hyperphosphorylation of Rb remains in G
2
. During late M phase, Rb is dephosphorylated, thus returning to the hypophosphorylated state. Phosphorylation of the Rb protein alters its binding characteristics; in the hypophosphorylated state, Rb binds to and sequesters specific transcription factors, such as E2F, the binding of which prevents the exit from the G
1
phase. Once cdks hyperphosphorylate Rb, the transcription factors are released which can then activate transcription of genes necessary for S phase progression, for example, thymdine kinase, myc, myb, dihydrofolate reductase, and DNA polymerase-&agr;.
Localization of cyclin-CDK complexes is also very suggestive about the role each complex plays in the pathway. Nuclear cyclins A and E bind to p107 and p130, possibly because they are in the nucleus. Mammalian cyclin B1 accumulates in the cytoplasm in G
2
phase and translocates into the nucleus at the beginning of mitosis. Cyclin B associates with the spindle apparatus, in particular with the spindle caps, and it is thought that the cyclin B-cdc2 kinase may be involved in the formation of the spindle through phosphorylating components of the mitotic apparatus. In addition, cyclin B1 is part of a feedback mechanism ensuring correct assembly of the metaphase mitotic apparatus. Human cyclin B2 is almost exclusively associated with the membrane compartment, and in particular the Golgi apparatus. Cyclin B2-cdc2 is involved in the disassembly of the Golgi apparatus when cells enter mitosis.
Cdc2-cyclin B kinase is a key mitotic factor which appears to be highly conserved and is thought to be involved in cell cycle transitions in all eukaryotic cells. Histone H1 is a substrate for cdc2-cyclin B; histone H1 is selectively phosphorylated on specific sites in mitosis, which is thought to be important for chromatin condensation. The cdc2-cyclin B complex also phosphorylates lamin, which is responsible for nuclear lamina breakdown. The nuclear lamina is made up of a polymer of lamin subunits that are hyperphosphorylated at mitosis, and this phosphorylation is responsible for their disassembly. Lamins are part of the intermediate filament family of proteins, and cdc2-cyclin B phosphorylates a subset of the sites phosphorylated at mitosis on the cytoplasmic intermediate filament subunits, vimentin and desmin. Thus, the cdc2-cyclin B complex is involved in the reorganization of the cell architecture at mitosis.
In addition, cdc2-cyclin B is involved in the reorganization of microfilaments, through phosphorylation of non-muscle caldesmon, an 83 kDa protein that binds to actin and calmodulin, and inhibits actomyosin ATPase activity. At mitosis, caldesmon is phosphorylated by cdc2-cyclin B, which weakens its affinity for actin and c
Bitonti Alan J.
Borcherding David R.
Dumont Jennifer A.
Munson, Jr. H. Randall
Peet Norton P.
Aventis Pharmaceuticals Inc.
Berch Mark L.
Strupczewski Joseph
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