Design, Synthesis, and Biological Investigation of Novel Classes of 3-Carene-Derived Potent Inhibitors of TDP1

Abstract

Two novel structural types of tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors with hexahydroisobenzofuran 11 and 3-oxabicyclo [3.3.1]nonane 12 scaffolds were discovered. These monoterpene-derived compounds were synthesized through preliminary isomerization of (+)-3-carene to (+)-2-carene followed by reaction with heteroaromatic aldehydes. All the compounds inhibit the TDP1 enzyme at micro- and submicromolar levels, with the most potent compound having an IC50 value of 0.65 μM. TDP1 is an important DNA repair enzyme and a promising target for the development of new chemosensitizing agents. A panel of isogenic clones of the HEK293FT cell line knockout for the TDP1 gene was created using the CRISPR-Cas9 system. Cytotoxic effects of topotecan (Tpc) and non-cytotoxic compounds of the new structures were investigated separately and jointly in the TDP1 gene knockout cells. For two TDP1 inhibitors, 11h and 12k, a synergistic effect was observed with Tpc in the HEK293FT cells but was not found in TDP1 −/− cells. Thus, it is likely that the synergistic effect is caused by inhibition of TDP1. Synergy was also found for 11h in other cancer cell lines. Thus, sensitizing cancer cells using a non-cytotoxic drug can enhance the efficacy of currently used pharmaceuticals and, concomitantly, reduce toxic side effects.

Novel Tdp1 Inhibitors Based on Adamantane Connected with Monoterpene Moieties via Heterocyclic Fragments

“…e.g., the aniline derivative 1 with a myrtenal moiety has inhibitory activity at submicromolar concentrations ( Figure 1 ) [ 16 ]; coumarin-based (-)-myrtenal derivative 2 potentiated the cytotoxicity of camptothecin in cancer cells [ 17 ]; it has also been shown that 3, comprising diazaadamantane and citronellal residues, inhibits Tdp1 with IC 50 (half maximal inhibitory concentration) values of ~15 µM [ 18 ]; geranyl derivative 4 enhances the topotecan antitumor effect in in vitro and in vivo tumor models [ 19 ]; octahydro-2 H -chromene-derived compound 5 was found to be an effective Tdp1 inhibitor with an IC 50 value of 2 µM [ 20 ]. Finally, isobenzofuran 6 , containing a thiophene fragment, has a synergistic effect with topotecan in wild type cells, but not in Tdp1 knockout cells [ 21 ].…”

Discovery of Novel Sultone Fused Berberine Derivatives as Promising Tdp1 Inhibitors

“…As already mentioned, we have previously shown that various Tdp1 inhibitors enhanced the cytotoxic and antitumor effects of topotecan [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. In this work, we also tested the ability of the berberrubine sultones to sensitize cells to the action of topotecan.…”

“…Thus, Tdp1 is a promising therapeutic target, and its inhibitors are expected to significantly synergize the effects of current anti-tumor therapies, including topoisomerase poisons and other DNA damaging agents. Indeed, it was found that combined treatment of tumor cells with Tdp1 inhibitors and anticancer drugs camptothecin or topotecan greatly increased the activity of these pharmaceuticals in in vitro [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ] and in vivo [ 29 , 30 ] experiments. Nevertheless, to the best of our knowledge, no Tdp1 inhibitors have reached human clinical trials.…”

Validating TDP1 as an Inhibition Target for the Development of Chemosensitizers for Camptothecin-Based Chemotherapy Drugs

“…Our laboratories have a long-standing interest in the development and validation of sensitizers for camptothecin-based chemotherapy drugs [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Specifically, our recent work indicated that TDP1 inhibitors may potentiate topotecan both in vitro and in vivo [31].…”