The rapidly growing interest in kinases as drug targets has prompted the development of many kinase assay technologies. These technologies can be grouped into three categories: radiometric assays, phospho-antibody-dependent fluorescence/luminescence assays, and phospho-antibody-independent fluorescence/luminescence assays. This article will review some of the major kinase assay technologies on the market, with particular emphasis on the newest systems. We will describe the physical principles, the practical advantages and drawbacks, and the potential applications of these technologies in kinase drug discovery. Most of these technologies are suitable for HTS, but only a few can be utilized for kinetic and mechanistic studies. Significant progress towards development of generic assays, free of radioisotopes and custom reagents such as phospho-specific antibodies, has been made in recent years. However, due to various limitations of each format, none of these generic assay technologies can yet claim to be truly universal. Several factors, including the intended applications, cost, timeline, expertise, familiarity, and comfort level, should be considered prior to pursuing a particular kinase assay technology.

The identities and precise roles of the DNA polymerase(s) involved in mammalian cell DNA replication are uncertain. Circumstantial evidence suggests that DNA polymerase alpha and at least one form of DNA polymerase delta, that which is stimulated by Proliferating Cell Nuclear Antigen, catalyze mammalian cell replicative DNA synthesis. Further, the in vitro properties of polymerases alpha and delta suggest a model for their coordinate action at the replication fork. The present paper summarizes the current status of DNA polymerases alpha and delta in DNA replication, and describes newly available approaches to the study of those enzymes.

Twenty-three pyrophosphate analogues were screened as inhibitors of proliferating cell nuclear antigen independent DNA polymerase delta (pol delta) derived from calf thymus. Carbonyldiphosphonate (COMDP), also known as alpha-oxomethylenediphosphonate, inhibited pol delta with a potency (Ki = 1.8 microM) 20 times greater than that displayed for DNA polymerase alpha (pol alpha) derived from the same tissue. Characterization of the mechanism of inhibition of pol delta indicated that COMDP competed with the dNTP specified by the template and was not competitive with the template-primer. In the case of pol alpha, COMDP did not compete with either the dNTP or the polynucleotide substrate. COMDP inhibited the 3'----5' exonuclease activity of pol delta weakly, displaying an IC50 greater than 1 mM.

This thesis is divided into three parts, united by the theme of the development of selective inhibitors of mammalian cell DNA polymerase delta (pol δ). The first part consists of an investigation of the cytotoxic mechanism(s) of certain 2-substituted adenine analogs, selected on the basis of their inhibitory properties towards DNA polymerase alpha (pol α) and mammalian cell DNA synthesis. The second is a direct search for inhibitors of isolated pol δ, and an investigation of inhibitory mechanisms. The third consists of measurement of the effects of a selective pol δ inhibitor on cellular DNA synthesis. Mechanism of Cytotoxicity of 2-substituted adenine analoqs. The mechanism of inhibition by 2-(p-n-butylanilino)-2'-deoxyadenosine (BuAdA), and related compounds, of Chinese hamster ovary (CHO) cell ([3H]thymidine [3H]TdR) incorporation, was investigated. The potency of the compound could largely be explained by its potency (IC50 = 23 μM) as an inhibitor of CHO cell [3H]TdR uptake. BuAdA inhibited incorporation by CHO cells of [32p]phosphate into DNA relatively weakly, displaying an IC50value of 80 μM. Differential inhibition of DNA polymerases alpha and delta. Known DNA polymerase inhibitors of a structurally wide range were screened for their ability to inhibit pol δ derived from calf thymus selectively with respect to pol α derived from the same tissue. Pyrophosphate (PPi) and difluoromethanediphosphonate each inhibited pol δ weakly, but with greater potency than pol α. Based on this lead, an expanded series of PPi analogs was screened. Carbonyldiphosphonate (COMDP) inhibited pol δ with a potency (Ki = 1.8 μM) twenty-two times greater than that displayed for pol α. Kinetic studies indicated that COMDP inhibited pol δ competitively with the dNTP specified by the template, but not competitively with the template:primer. Analogous experiments with pol α showed that the compound inhibited that enzyme uncompetitively with the dNTP, and not competitively with the template:primer. COMDP was a weak inhibitor of the 3' → 5' exonuclease activity of pol δ, displaying an IC50value greater than 1 mM. Inhibition of permeabilized cell DNA synthesis bv a selective pol δ inhibitor. The potency of COMDP as an inhibitor of permeabilized CHO cell DNA synthesis (IC50= 200 μM) did not clearly indicate the participation of pol δ in cellular DNA replication. Prospectus. The thesis concludes with a prospectus for the development of pol δ inhibitors with improved properties compared to COMDP.