Contents
Cdks Inhibitors
Guest Editor: Doriano Fabbro
Chemical and
Biological Profile of Dual Cdk1 and Cdk2 Inhibitors Pp. 1-14
Stephan Ruetz, Doriano
Fabbro, Juerg Zimmermann, Thomas Meyer and Nathanael Gray
X-Ray Crystallographic
Studies of CDK2, a Basis for Cyclin-Dependent Kinase Inhibitor Design in
Anti-Cancer Drug Research Pp. 15-23
Pascal Furet
Structure-Based Design
of Novel Anti-Cancer Agents Targeting Aurora Kinases Pp. 25-34
Potentiation of
DNA-Damage-Induced Cytotoxicity by G2 Checkpoint Abrogators Pp. 35-46
A. Tenzer and M.
Pruschy
Cyclin-Dependent
Kinase Modulators Studied at the NCI:
Pre-Clinical and Clinical Studies Pp. 47-56
Edward A. Sausville
Peptidomimetic Design
of CDK Inhibitors Targeting the Recruitment Site of the Cyclin Subunit Pp.
57-69
Campbell McInnes,
Martin J.I. Andrews, Daniella I. Zheleva,
David P. Lane and Peter M. Fischer
[Back
to top] Chemical and Biological Profile of Dual Cdk1
and Cdk2 Inhibitors
Stephan Ruetz, Doriano
Fabbro, Juerg Zimmermann, Thomas Meyer and Nathanael Gray
The importance of Cdks in cell cycle regulation, their interaction with oncogenes and tumor suppressors, and their frequent deregulation in human tumors, has encouraged an active search for agents capable of perturbing the function of Cdks. In our laboratories, a variety of selective and potent low molecular weight inhibitors directed against the ATP binding sites of the Cdk1, Cdk2 have been developed. Extensive biological profiling of two distinct classes of Cdk inhibitors – the phenylamino pyrimidines (PAPs) and trisubstituted purines has revealed distinct differences in their cellular effects in normal cells compared to tumor cells. Due to their intact G1/S checkpoints, normal cells are shown to be reversibly blocked by these Cdk inhibitors in either the G1/S-phase or at the G2/M boarder. In transformed cells these control points are either absent or defective and treatment with the compounds resulted in pronounced proliferation block at the G2/M transition. Furthermore, there is strong evidence that this G2/M arrest is less well tolerated by the cells and consequently, they undergo apoptotic cell death. Finally, these dual Cdk1/ Cdk2 inhibitors are also found to be significantly more active on proliferating cells compared to quiescent cells reflecting their specific activity. Despite these encouraging results demonstrating a distinct outcome after treatment with such dual Cdk inhibitors in normal compared to de-regulated tumor cells, it remains to be determined whether a comparable therapeutic window might be observed in vivo experiments. Furthermore the intracellular kinase selectivity of inhibitors which are putatively selective in vitro remains a complicating feature that is only recently begun to be addressed by affinity chromatography and phosphoproteomics techniques. Once efficacy can be demonstrated in animal models at well-tolerated doses, there will be strong evidence for the development of cell cycle antagonists for cancer therapy.
[Back
to top] X-Ray Crystallographic Studies of CDK2, a
Basis for Cyclin-Dependent Kinase Inhibitor Design in Anti-Cancer Drug Research
Pascal Furet
Inhibition of cyclin-dependent kinases is a theme of major interest in current anti-cancer agents research. Different classes of chemical inhibitors of these enzymes have been identified during the past decade and the structural basis of inhibition has been elucidated by X-ray crystallography studies of one member of the family, CDK2. In this article, we review the structural biology work that has led to a precise knowledge of the interactions between CDK2 and small organic molecules binding to its ATP pocket that are determinant for inhibitory activity. The use of this information to design or optimize CDK inhibitors by molecular modeling is also reviewed.
[Back
to top] Structure-Based Design of Novel Anti-Cancer
Agents Targeting Aurora Kinases
Daruka Mahadevan,
David J. Bearss and Hariprasad Vankayalapati
Aurora kinases are a family of mitotic serine-threonine kinases (S/T kinases), that functions as a class of novel oncogenes and are over-expressed in several solid tumors including breast, ovary, prostate, pancreas and colorectal cancer. To validate human ARK1 (Aurora2, STK15, HsAIRK1) as a drugable target in pancreatic cancer, we undertook a structure-based approach to design specific inhibitors utilizing homology modeling, affinity docking and an in vitro kinase assay in an iterative process. In this review, we discuss the biology, rationale for targeting and approaches taken to inhibit this family of protein kinases, implicated in dysregulated chromosome segregation and cytokinesis.
[Back
to top] Potentiation of DNA-Damage-Induced
Cytotoxicity by G2 Checkpoint Abrogators
A. Tenzer and M.
Pruschy
Cell
cycle checkpoints are activated in response to DNA-damage to ensure that
accurate copies of the cellular genome are passed on to the next generation and
to avoid replication and segregation of damaged DNA. These cellular control
systems can be overcome by combining conventional DNA-damaging agents with
compounds that target the cell cycle regulatory pathways, to enhance
cytotoxicity. Tumor cells often comprise a corrupted G1 cell cycle checkpoint
while the G2 cell cycle checkpoint is still intact. This review describes the
concept of G2 checkpoint abrogation with recognized (methylxanthines, UCN-01)
and novel G2 checkpoint abrogators to potentiate the cytotoxicity of
DNA-damaging drugs and ionizing radiation. It illustrates the potential of G2
checkpoint abrogators to preferentially sensitize p53-mutated, treatment
resistant tumor cells for genotoxic treatment. Identification of the targets of
caffeine and UCN-01 to be key-players of the G2 checkpoint (ATM/ATR and Chk1,
respectively) promoted the search for novel inhibitors of this checkpoint. Even
though a direct causal link between G2 checkpoint abrogation and
chemo-/radiosensitization is difficult to prove the multitude of these novel
compounds validate that inhibition of critical elements of the G2 checkpoint
(ATM/ATR-Chk1/Chk2-CDC25C-cascade) potentiates the cytotoxicity of DNA-damaging
agents.
[Back
to top] Cyclin-Dependent Kinase Modulators Studied at
the NCI: Pre-Clinical and Clinical
Studies
Edward A. Sausville
The
cyclin dependent kinases (CDKs) are key regulators of cell cycle progression.
Lead compounds (from empirical anti-proliferative screening approaches) have
been defined which modulate CDK function and have evidence of
anti-proliferative activity in tissue culture systems and in some cases
anti-tumor activity in vivo in conventional xenogaft models. Two of these,
flavopiridol and UCN-01, have entered initial clinical testing. Flavopiridol is
a “pan-CDK” inhibitor, with essentially equal potency in inhibiting all CDKs
tested. The recent elucidation that in addition to cell cycle regulatory
functions, CDK family members have been defined which regulate transcription,
neuronal, and secretory function has increased the need for definition of CDK
antagonists with greater selectivity. Novel purine, pyrimidine, and
benzazepinone derivatives have been characterized in part through the National
Cancer Institute’s drug screening systems. UCN-01, in contrast to flavopiridol,
modulates CDK activity participating in the DNA damage response, possibly
through potent inhibition of the chk1 checkpoint kinase, as well as affecting
CDK function indirectly through activity on other kinase targets. An unexpected
feature in its development has been avid binding to a1 acid glycoprotein.
Further progress in CDK modulator development will require the definition of
additional lead structures that address issues raised by these early molecules
entering into clinical development.
[Back
to top] Peptidomimetic Design of CDK Inhibitors
Targeting the Recruitment Site of the Cyclin Subunit
Campbell McInnes,
Martin J.I. Andrews, Daniella I. Zheleva,
David P. Lane and Peter M. Fischer
The recognition of cyclin-dependent kinase (CDK)/cyclin complexes by various cell-cycle regulatory proteins, including certain tumour suppressors and transcription factors, occurs at least in part through a protein-protein interaction with a binding groove on the cyclin subunit. Since CDK function is generally deregulated in tumour cells, blocking of this recruitment site prevents recognition and subsequent phosphorylation of CDK substrates and offers a therapeutic approach towards restoration of checkpoint control in transformed cells. Here we discuss the finding that peptides derived from such cyclin-interacting proteins, and rendered permeable through conjugation to cellular delivery vectors, can apparently induce tumour cells to undergo apoptosis selectively. We review the current status of 3D-structural information available on cyclin-peptide interactions and we summarise our extensive peptide structure-activity relationship studies in light of this information. We also show how a combination of molecular modelling and introduction into synthetic peptides of peptidomimetic elements, such as non-natural amino acid residues and conformational constraints, is being used hopefully to arrive at drug candidates capable of modulating CDK function in a selective mechanism-based approach rather than through ATP antagonism.