Abstract
This thesis explores the potential of the Diptheria-toxin like ADP-ribosyltransferase member 8 (ARTD8) as a viable drug target for cancer treatment. It achieves this through a literature review, an investigation into the potential role of natural products in ARTD8 inhibition, and through the synthesis and in vitro evaluation of a series of compounds designed to inhibit ARTD8. Many of these stages have been supported by peer-reviewed publications.ARTD8 regulates key enzymes within the JAK/STAT, PGI/AMF, PI3K/Akt/mTOR and JNK1/JNK2 signalling pathways, thereby promoting the growth and survival of multiple forms of cancer. More recent studies revealed that ARTD8’s manipulation of these pathways could also affect allergic airway diseases and host-responses to viral infections. The consequences of ARTD8’s involvement in these inflammatory pathways appear to be tissue dependent. Therefore, although targeting ARTD8 is promising for cancer therapy, investigation is needed to ascertain whether an ARTD8 inhibitor would be beneficial for these other conditions (1).
In a natural products approach, preliminary evidence suggested that epigallocatechin gallate (EGCG) possessed an inhibitory effect on ARTD8. EGCG appeared to influence similar enzymes within the PI3K/Akt/mTOR pathway as desired by an ARTD8 inhibitor. Subsequent molecular modelling and in vitro assays revealed that EGCG completely inhibited ARTD8 activity at 10 μM, while having a lesser effect on ARTD1. The apparent preference towards ARTD8 inhibition was promising. However, as EGCG contained the pan assay interference compound motif, catechol, future studies should go beyond the assay to validate EGCG’s activity.
In a de novo approach, a small series of benzylaniline compounds were designed to inhibit ARTD8. These compounds contained a nicotinamide mimicking region and an elongated chain to selectively target ARTD8’s catalytic domain. Synthesis of compounds 26 – 31 was achieved via reductive amination with sodium borohydride. Compound 31 was identified as the lead benzylaniline due to is reduction in ARTD8 activity to 52% ± 12%, whilst also showing a lesser response against ARTD1. This library was compared to the previously synthesised 22 – 24 in which 24 showed the greatest activity towards ARTD8, reducing activity by 73% ± 2% and showing a preference towards ARTD8 inhibition. In a second de novo approach, the benzylaniline scaffold was modified and another 31 compounds were proposed. Only 32 and 56 could be effectively isolated, due to the rapid degradation of the other compounds. Along with the benzylanilines, 45, 47 and 48, these were screened in vitro for activity against ARTD1 and ARTD8, revealing 45 as the lead, however all five compounds assessed showed similar inhibitory patterns towards both ARTD1 and ARTD8.
In a final screening against ARTD1 – ARTD3, ARTD5, ARTD7, ARTD10 and ARTD14, 22 showed the greatest potential as a selective ARTD8 inhibitor. Compound 22 significantly reduced ARTD8 activity while showing little to no effect on the remaining ARTD enzymes. Similar to 23 and 24, 22 contained a terminal amide, in substitution of the carboxylic acid present on most other compounds, suggesting this group is important for ARTD8 binding. Chloro substitutions, such as that on 24 may increase ARTD8 activity, however, resulted in less selectivity.
Date of Award | 1 Dec 2022 |
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Original language | English |
Supervisor | Stephan Levonis (Supervisor), Stephanie Schweiker (Supervisor) & Kevin Ashton (Supervisor) |