Human polymerase α inhibitors for skin tumors. Part 2. Modeling, synthesis and influence on normal and transformed keratinocytes of new thymidine and purine derivatives

Abstract

Recently, the three-dimensional structure of the active site of human DNA polymerase α (pol α) was proposed based on the application of molecular modeling methods and molecular dynamic simulations. The modeled structure of the enzyme was used for docking selective inhibitors (nucleotide analogs and the non-nucleoside inhibitor aphidicolin) in its active site in order to design new drugs for actinic keratosis and squamous cell carcinoma (SCC). The resulting complexes explained the geometrical and physicochemical interactions of the inhibitors with the amino acid residues involved in binding to the catalytic site, and offered insight into the experimentally derived binding data. The proposed structures were synthesized and tested in vitro for their influence on human keratinocytes and relevant tumor cell lines. Effects were compared to aphidicolin which inhibits pol α in a non-competitive manner, as well as to diclofenac and 5-fluorouracil, both approved for therapy of actinic keratosis. Here we describe three new nucleoside analogs inhibiting keratinocyte proliferation by inhibiting DNA synthesis and inducing apoptosis and necrosis. Thus, the combination of modeling studies and in vitro tests should allow the derivation of new drug candidates for the therapy of skin tumors, given that the agents are not relevant substrates of nucleotide transporters expressed by skin cancer cells. Kinases for nucleoside activation were detected, too, corresponding with the observed effects of nucleoside analogs.

Keywords::

• Human DNA polymerase
• polymerase inhibitors
• keratinocytes
• molecular dynamic simulations
• nucleoside analogs
• kinases
• nucleoside transporters

Acknowledgements

The authors thank Novartis Pharma AG, Basel, Switzerland for supplying diclofenac and medac Gesellschaft für klinische Spezialpräparate mbH, Wedel, Germany for supplying doxorubicin.

Declaration of interest

Financial support of the German Ministry of Education and Research (13N9062 and 13N9061) is gratefully acknowledged. Two of the authors (H-D.H, M.S-K) are inventors of the respective patent applied for by RIEMSER Arzneimittel AG (Greifswald – Insel Riems), European Appl. No.: 07090098.0. Moreover, one of them (M.S.-K.) acts as a consultant for RIEMSER Arzneimittel AG (Greifswald – Insel Riems) with respect to the development of dermatics.