Citation
Yusoh, Nur Aininie
(2020)
Effect of combination therapy of ruthenium polypyridyl complex, [Ru(dppz)2(PIP)]2+ and parp inhibitors against several cancer cell lines.
Masters thesis, Universiti Putra Malaysia.
Abstract
Ruthenium polypyridyl complexes (RPCs) have been clinically studied as
promising anticancer agents in the last decades. The RPC, [Ru(dppz)2(PIP)]2+ or
RuPIP where dppz = dipyrido[3,2-a:2’,3’-c]phenazine and PIP = 2-(pheny)-
imidazo[4,5-f][1,10]phenantroline has demonstrated anticancer properties where
it was shown to stall DNA replication fork progression resulting in the initiation of
DNA damage response (DDR) signaling which further lead to the inhibition of
cell proliferation through G1/S-mediated cell cycle arrest. This has prompted us
to study the rational combination of RuPIP alongside DDR inhibitors, particularly
the inhibitors of poly (ADP-ribose) polymerase (PARP) to achieve synergistic
effect in cancer cells. This is to enhance the therapeutic response to RuPIP in
cancer cells while reducing the impact on normal cells. The cytotoxic effect of
RuPIP and PARP inhibitors as single agents on several cancer cell lines (A549,
MCF7, MDA-MB-231 and T24) were determined using MTT assay. RuPIP
showed time-dependent reduction in the IC50 values meanwhile, both PARP
inhibitors showed IC50 > 100 μM. All compounds showed IC50 > 100 μM on the
normal NHDF cells. Drug combination study was carried out based on Chou and
Talalay combination index (CI) method in which CI values were determined using
Calcusyn and Compusyn software. Synergy (CI < 1) was observed with majority
of RuPIP-olaparib combinations meanwhile, RuPIP-NU1025 resulted in a range
of combination indices, ranging from synergism to antagonism. Importantly, the
viability of normal cells observed for any combination tested was > 70%. Based
on the average CI values, the synergistic combination (CI = 0.87) of 25 μM RuPIP
alongside 25 μM NU1025 or 5 μM olaparib were chosen for further experiments.
Cells ability to survive post-treatment and form colonies was investigated using
clonogenic survival assay with single-agent treatments showed survival fractions
(S.F) > 75%. Interestingly, combination treatments reduced cell survival with
RuPIP-olaparib (S.F. < 2%) showed lower survival than RuPIP-NU1025 (S.F. <
57%). Besides, treatments with 25 μM RuPIP sensitize cells to olaparib where
60-fold reduction in IC50 value of olaparib was obtained for MCF7 (0.08 vs 4.75 μM) and 300-fold reduction was observed in MDA-MB-231 cells (0.06 vs 23.39
μM). Next, cell migration ability was investigated using cell scratch assay which
revealed that RuPIP-olaparib combination significantly (P < 0.001) reduced cell
migration with 40% reduction in wound closure was observed compared to
control. The flow cytometric analysis on cell cycle distribution revealed that the
combination treatment resulted in enhanced cell cycle arrest at G1/S phase in
A549 cells (17.1% increase compared to control). Whereas both MCF7 and
MDA-MB-231 cells were arrested at G2/M phase (19.7% and 20.4% increase
compared to control, respectively). Subsequently, Annexin V-FITC assay
showed that the combination treatment significantly (P < 0.001) increased the
percentage of apoptotic cells with 25%, 30% and 31% increase compared to
control in A549, MCF7 and MDA-MB-231 cells, respectively. These resultant cell
deaths are associated with significant (P < 0.001) increase in the accumulation
of double-strand breaks (DBSs) DNA damage with 45% increase in the
percentage of cells with γH2AX foci compared to control. These findings
established that RuPIP showed synergy with PARP inhibitors in several cancer
cell lines with reduced impact on normal cells.
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