Colorectal carcinoma is a complex
malignancy and current
therapies are hampered by systemic toxicity and
tumor resistance to treatment. In the field of
cancer therapy,
copper (Cu) compounds hold great promise, with some reaching clinical trials. However, the anticancer potential of Cu complexes has not yet been fully disclosed due to speciation in
biological systems, leading to inactivation and/or potential side effects. This is the case of the widely studied Cu(II) complexes featuring
phenanthroline ligands, with potent antiproliferative effects in vitro, but often failing in vivo. Aiming to overcome these limitations and maximize its anticancer effects in vivo, the Cu(II) complex (Cu(1,10-phenanthroline)Cl2) (Cuphen), displaying IC50 values <6 μM against different tumor cell lines, was loaded in long circulating
liposomes with pH-sensitive properties (F1,
DMPC:CHEMS:
DSPE-PEG; F2, DOPE:CHEMS:
DMPC:
DSPE-PEG). This enabled a pH-dependent Cuphen release, with F1 and F2 releasing 36/78% and 47/94% of Cuphen at pH 6/4.5, respectively. The so formed nanoformulations preserved Cuphen effects towards
cancer cell lines, with F2 presenting IC50 of 2.7 μM and 4.9 μM towards
colon cancer CT-26 and HCT-116 cells, respectively. Additional in vitro studies confirmed that Cuphen antiproliferative activity towards
colon cancer cells does not rely on cell cycle effect. Furthermore, in these cells, Cuphen reduced
glycerol permeation and impaired cell migration. At 24 h incubation,
wound closure was reduced by Cuphen, with migration values of 29% vs 54% (control) and 45% (1,10-phenanthroline) in CT-26 cells, and 33% vs ~44% (control and 1,10-
phenanthroline) in HCT-116 cells. These effects were probably due to inhibition of
aquaglyceroporins, membrane water and
glycerol channels that are often abnormally expressed in
tumors. In a syngeneic murine
colon cancer model, F2 significantly reduced
tumor progression, compared to the control group and to mice treated with free Cuphen or with the
ligand,
1,10-phenanthroline, without eliciting toxic side effects. F2 led to a
tumor volume reduction of ca. 50%. This was confirmed by RTV analysis, where F2 reached a value of 1.3 vs 4.4 (Control), 5.8 (Phen) and 3.8 (free Cuphen). These results clearly demonstrated the important role of the Cu(II) for the observed
biological activity that was maximized following the association to a
lipid-based nanosystem. Overall, this study represents a step forward in the development of pH-sensitive nanotherapeutic strategies of metallodrugs for
colon cancer management.