Pancreatic cancer inhibitory potential of hydrazine ligands and their corresponding metal complexes

Abstract

Introduction: Pancreatic cancer remains one of the deadliest cancers in the world. According to GLOBOCAN, in 2022, Pancreatic ductal adenocarcinoma cancer (PDAC) was the third leading and soon to become the second leading cause of cancer deaths. Current drugs used to manage PDAC demonstrate adverse side effects. Metal complexes such as Cisplatin (Cis) are more effective when combined with the first-line drug, gemcitabine. Unfortunately, there are limitations with these and existing drugs such as the development of drug resistance. In a quest to find novel therapeutic drugs, a series of hydrazone ligands and metal complexes were synthesized and characterized for screening their antioxidant activity, cytotoxicity and potential modes of cell death in pancreatic cancer cells. Methodology: The nitrogen-sulfur Schiff base Ligands (L1-L3) were synthesized by the reaction of hexyl dithiocarbamate and 4-methylbenzaldehyde in a 2:1 molar ratio with various divalent metal ions to form the neutral complexes AgL1, RuL1, NiL2, AgL2, CuL2, NiL3, ZnL3, and CuL3. Established physicochemical and spectroscopic techniques were used to characterize each compound, in which geometrical variations that occur in the coordination of the ligand to the single crystal structures were studied. The cytotoxic effect of the compounds was assessed against a pancreatic cancer cell line, MIA PaCa-2, using the (3-(4, 5- dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide) MTT assay tested across a range of concentrations (0.78 – 100 μM). The antioxidant activity was evaluated using 2, 2-Diphenyl- 1-picrylhydrazyl (DPPH). Compounds that showed cytotoxic effects were further analyzed for the mode of cell death using the flow cytometric assays, Annexin V/propidium iodide (PI) for apoptosis and necrosis determination and PI for cell cycle analysis. Results: The metal complexes AgL1 and RuL1 derived from the free ligand L1, demonstrated potent cytotoxicity against MIA Paca-2 cells, with IC50 values of 1.55 ± 0.59 μM and 1.44 ± 0.61 μM respectively. L1 demonstrated the highest cytotoxicity value with IC50 of 0.45 ± 0.25 μM. Complex NiL2 exhibited a cytotoxic potency against MIA Paca-2 with an IC50 value of 1.25 ± 0.71 μM. The free drug L2 exhibited a cytotoxicity of 21.41 ± 14 μM. In comparison, gemcitabine demonstrated a stronger cytotoxicity on MIA Paca-2 with IC50 of 6.57 ± 0.632 μM, while its effect on Vero cells was 11.30 ± 0.04 μM. vi An analysis of the antioxidant activity indicated that L1 and its metal complex RuL1 demonstrated antioxidant activity with an IC50 of 5.11 ± 0.47 μM, in comparison to L-ascorbic acid (Vitamin C), which showed an IC50 of 6.42 ± 0.24 μM. CuL3 exhibited the highest activity with a value of (4.25 ± 0.56 μM) when compared to all other complexes, including the ZnL3 complex (with a concentration of 5.62 ± 0.28 μM). Apoptosis determination was statistically significant (p < 0.001) for both the metal complexes of L1 with each exhibiting a percentage of 7.75% for AgL1 and 14.33% for RuL1 in comparison to the L1 (1.3%) when tested at the IC50 concentration of 1.48 μM. Cell cycle assessment showed that MIA Paca-2 cells treated with L1 and its complex AgL1 caused the sub-G1 phase arrest at 28 ± 2.97% and 18 ± 1.01%, respectively. The cell population grew by 34.83% in the S phase for L1 and 52% for RuL1. AgL1 was statistically significant (p < 0.001) in the G1 phase and p < 0.01 in the S phase, while RuL1 was significant (p < 0.001) in both phases. NiL2 treatment caused a sub-G1 phase arrest from 6.44 ± 1.45% to 16.9 ± 2.1%. L2 treated cells showed a 36.4 ± 5.6% arrest of the S phase when compared to the complex NiL2 (27.3 ± 10.35%). Conclusion: This study has established that complexation of nitrogen-sulphur Schiff base hydrazone ligands with metal complexes such as RuL1 results in anticancer properties. The complexation enhances the complexes’ ability to induce apoptosis and cell arrest in pancreatic cancer cells. These preliminary findings suggest that more investigations are needed to further understand the anticancer mechanism such as pathway analysis studies.