Novel bisnaphthalimidopropyl polyamine derivatives: their mode of action in a breast cancer cell system.
Barron, Gemma A.
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The synthesis and characterisation of novel bisnaphthalimidopropyl polyamine (BNIPP) derivatives, has gained pace over the last couple of years, as they have enhanced aqueous solubility, without loss of biological activity, in contrast to parent bisnaphthalimide derivatives. Recent work has shown that bisnaphthalimidopropyl spermidine (BNIPSpd) bis-intercalates to DNA, induces oxidative DNA damage, depletes polyamine levels and causes cell death, by apoptosis, in human colon cancer CaCO-2 and HT-29 cells. The aim of this thesis was to synthesise new BNIPP derivatives to highlight the important structural features required for biological activity, particularly, bisnaphthalimidopropyl functionality, and investigate their subsequent modes of action in breast cancer MDA-MB-231 and breast epithelial MCF-10A cells. Initially, work focused on determining the DNA binding affinities and biological activity of BNIPP derivatives. All BNIPP derivatives, except bisphthalimidopropyl diaminodecane (BPHPDadec) and mononaphthalimidopropylamine (NPA) (Δ Tm values of 15.8 and 10.2 °C, respectively, C50 values of > 10 μM, IC50 values of > 40 μM), exhibited strong DNA binding affinities and cytotoxic properties in both cell lines. Results indicate that BNIPP derivatives interact with DNA by bis-intercalation suggesting, therefore, that BNIPP derivatives target DNA. For the first time, an investigation into the mechanism of cellular entry, via the polyamine transport (PAT) system, was studied. However, none of the BNIPP derivatives utilised the MGBG-specific PAT system, suggesting that BNIPP derivatives utilise other modes of cellular entry. Two BNIPP derivatives, BNIPSpd and BNIPDaCHM, were further investigated, and results show that these derivatives significantly induced a dose dependent increase in DNA strand breaks from ≥ 0.1 μM, after 4 hours. BNIPSpd and BNIPDaCHM (at non toxic concentrations) also inhibited the repair of oxidative (H2O2) and methylative (MMS)-induced DNA strand breaks. Based on phosphatidylserine exposure and membrane integrity analyses, early apoptotic cell death was determined as a mode of cell death utilised by both BNIPSpd and BNIPDaCHM (5 μM), after only 0.5 hours treatment in MDA-MB-231 cells. Interestingly, BNIPDaCHM was identified, using HDAC assay kits, as a potent and selective SIRT2 enzyme inhibitor, thus, identifying, a novel structural backbone for the selective inhibition of HDAC enzymes.