Members of the family of cyclin dependent kinases (CDKs) have been recognized as pivotal regulators of cell cycle progression for more than 20 years. Concordant to their central role in the control of cell division they have been in the focus of research of proliferation associated diseases ever since, most prominently amongst these cancer. Although initial results obtained from first and second generation, low specificity CDK inhibitors (e.g. Flavopyridol, Roscovitine, Dinaciclib, AT7519, R547) have been sobering the recent approval of the first CDK-inhibitor Palbociclib for the treatment of certain forms of breast cancer clearly demonstrates the suitability of cell cycle CDKs as targets in oncology. Furthermore, in addition to cell cycle CDKs a second group of CDKs have been shown to have important roles in the regulation of gene transcription, and several of the “transcriptional” CDKs have become interesting targets in oncology. Recent results underline the notion that for being effective in the treatment of cancer, CDK inhibition requires very high specificity towards the respective target CDK(s). For example CDK1 knockdown or CDK9 inhibition have been shown to be synthetically lethal in combination with MYC overexpression. Selectivity of compounds within the family of CDKs could so far only be tested using a quite limited number of CDK-Cyclin complexes expressed in human cells. To date there are 20 CDK genes and at least 17 different Cyclin genes described, many of which give rise to different variants, e.g. there are 3 D-type cyclins, two A- and E-type cyclins etc.. Experimental data indicates that at least 50-60 different, biologically relevant CDK-Cyclin complexes may exist, but only a limited number of these are available for biochemical testing of drug candidates so far. We have recombinantly expressed and purified 28 different CDK-Cyclin complexes, covering a significant part of the CDK family, and established in-vitro kinase-activity assays for these recombinant enzymes. The resulting CDK panel represents the most comprehensive array for biochemical testing of this enzyme group currently available. We characterized the specificity of several CDK inhibitors that have been or are currently in preclinical or clinical development with this CDK collection. Results will be presented showing the specificity of these inhibitors not only for CDKs but also for CDKs complexed to different Cyclins. In several cases we could detect signifcant differences in the inhibition of the same CDK complexed to different Cyclins, e.g. a 10fold difference was seen for CDK6 complexes with Cyclin D1-3. A >100 fold difference was detected for CDK3 complexed to either Cyclin E1 or Cyclin C. This screening panel allows generating data on compound selectivity early in development, diminishing the risk of designing a compound with suboptimal target specificity. Citation Format: Daniel Mueller, Frank Totzke, Thomas Weber, Christian Beisenherz-Huss, Diane Kraemer, Carolin Heidemann-Dinger, Constance Ketterer, Chris Eckert, Michael H.G. Kubbutat. Characterization of CDK inhibitors in a biochemical assay using a comprehensive panel of human CDK-cyclin complexes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2821.

The present study was designed to assess the validity of the Torque Test as a measure of functional lateral dominance in children. One hundred forty-nine children were administered the Torque Test and The Harris Test of Lateral Dominance. A low but statistically significant correlation was found between torque and total lateral dominance.

Cyclin dependent kinases (CDK) form a family of 20 different CDKs with an additional 6 CDK-like proteins. Members of this family have been shown to be involved in the regulation of many critical cellular processes, including the regulation of cell cycle progression, gene transcription and neuronal function. Deregulated CDK activity has been observed frequently in human cancer and other diseases. Enzymatic kinase activity of CDKs has been found to depend on the formation of complexes with regulatory proteins of the Cyclin family and requires in some cases the presence of additional complex partners, like MAT1 for CDK7/Cyclin H. To date, at least 15 different Cyclins have been described. For some CDKs it has been shown that they can also be activated by binding to proteins distinct from classical Cyclins. However, even while the 20 canonical CDKs share significant structural homology, they regulate very different functions of cell growth and development, partially due to their inherent substrate specificity but also regulated by their respective Cyclin partners. During the past 30 years several CDKs have been subject to extensive study resulting in a multitude of publications. This includes specifically CDK1, CDK2 and CDK4/6 and to a lesser extend CDK7 and CDK9. Other CDKs have been studied much less extensively and consequently the accumulated knowledge about their biological function and regulation is very limited. CDK15 (also known as PFTK2 or ALS2CR7) is one of these understudied members of the CDK family, with less than 20 publications in PubMed and the search term "CDK15" in contrast to more than 8600 hits for "CDK2". Its biological function is largely obscure even while evidence was presented that CDK15 is involved in the regulation of breast and colorectal cancer. Comparable to all other members of the CDK family, recombinantly overexpressed purified CDK15 does not exhibit detectable in-vitro activity and to date no Cyclin or other activating complex partner for CDK15 has been published. Since CDK inhibitors have been in the focus of interest at least since the approval of the first candidate (Palbociclib) for the treatment of ER+/HER+ breast cancer, testing the selectivity of other drug candidates within the complete group of CDKs is critically important to avoid unwanted off-target effects and toxicity. In order to enable in-vitro activity studies with CDK15 we evaluated different CDK15 constructs in combination with a comprehensive panel of different Cyclins using the baculo virus expression system. CDK15 and the respective Cyclins were co-expressed in insect cells, purified by affinity chromatography and tested for in-vitro activity using a panel of generic, broad-spectrum protein kinase substrates. We will present data on the identification of CDK15 activating Cyclins and the biochemical characterization of the in-vitro kinase activity of such CDK15/Cyclin complexes including a panel of kinase inhibitors. Citation Format: Daniel Mueller, Constance Ketterer, Diane Kraemer, Carolin Heidemann-Dinger, Lena Pilgermayer, Thomas Weber, Andreas Gericke, Frank Totzke, Michael H. Kubbutat. Identification of CDK15 activating cyclins by a recombinant co-expression approach [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5980.

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