A multidisciplinary investigation into the design, synthesis and evaluation of a novel class of anti-glioblastoma drug fragments

Abstract

Cancer is the second biggest global killer,[1,2] with cancers of the brain and central nervous system accounting for a disproportionately high number of deaths.[3] The most prolific cancer of the central nervous system is glioblastoma, for which prognosis is still very poor. In this project, analogues of two lead compounds with known activity against glioblastoma cell lines (compounds 4 and 5, Figure 1) were produced in order to develop structure-activity relationships and discover compounds with superior activities against glioblastoma.

Figure 1 - The structures of the lead compounds 4 and 5
Analogues of compound 4 were the result of a rigorous similarity search of the ZINC database,[4,5] as well as using chemical intuition to identify potential analogues. A scaffold-hopping approach was undertaken, through which two new compound classes were identified as potentially superior lead compounds for future work (Figure 2).

Figure 2 - The structures of two analogues of compound 4 with different scaffolds and superior activity, compounds 168 and 214
Compound 4 is known to induce cell death through the induction of elevated levels of cellular reactive oxygen species (ROS),[6] which may be formed via the radical form of compound 4 and its analogues. The connection between the anticancer activity of 4 and its analogues with the propensity of these compounds to form radicals was also investigated. Enthalpic values relevant to radical formation (BDE, AIP, PDE, PA and ETE) were calculated using a density functional theory (DFT) approach. Although no strong correlation was found for the whole series of compounds, the data indicates that correlations may exist within certain structural classes.
The anticancer activity of compound 5, a prodrug, was compared against 11 analogues of both the prodrug and active form of the compound (Scheme 1). It was found that compound 9 has superior activity to that of the prodrug 5. Substitutions at the N-position of 5 were also found to have a significant effect on activity, with an N-tosyl analogue having significantly improved activity against glioblastoma cell lines and short term cultures. The results obtained suggest that future work on this series should therefore be based around compound 9, a subclass of indoles that have wide ranging anticancer activity, but have not yet been reported against glioblastoma.

Scheme 1 - The degradation of 5 into its suspected active form (9)
In conclusion, analogues were discovered within this project which improved upon the anticancer activity of both compounds 4 and 5. For compound 4, two alternative scaffolds were identified as superior and novel lead compounds against glioblastoma, and there is some indication that there may be a correlation between radical formation and anticancer activity within specific structural classes of this functional class of compounds. For prodrug 5, substituents at the N positon were found to have a significant effect on activity, and the activity of the active form (9) was found to be superior to the activity of the prodrug.