Background: Apo2-ligand/TRAIL, a member of the TNF cytokine superfamily capable of inducing apoptosis
on tumor cells while sparing normal cells, is a promising anti-tumor agent. However, about 50% of human cancer are
TRAIL resistant. Consequently, future TRAIL-based therapies will require the use of novel highly bioactive forms of
TRAIL and/or the addition of sensitizing agents to TRAIL-induced apoptosis. Recently, we demonstrated that artificial
lipid nanoparticles coated with bioactive TRAIL (LUV-TRAIL) greatly improved TRAIL activity and were able to induce
apoptosis in chemoresistant hematological tumor cells.
Objective: In this study, we have tested LUV-TRAIL-pro-apoptotic potential in human breast cancer.
Method: Comparative analysis of cytotoxicity induced by sTRAIL and LUV-TRAIL was performed using several human
breast tumor cell lines with different sensitivity to TRAIL. In vivo anti-tumor activity of LUV-TRAIL was also studied using
a xeno-graft tumor model.
Results: LUV-TRAIL improved not only sTRAIL in vitro cytotoxicity in all breast tumor cell lines tested but also showed
more anti-tumor activity than sTRAIL in an in vivo xeno-graft tumor model. On the other hand, the concomitant treatment
of LUV-TRAIL with the sensitizing agent flavopiridol (FVP) induced a higher level of cell death in TRAIL-resistant cell
lines. TRAIL-sensitization induced by FVP was mediated by DR5 up-regulation, and interestingly TRAIL-apoptotic signaling
was completely shifted towards DR5 upon FVP treatment. LUV-TRAIL could especially take advantage of this
DR5 up-regulation, while sTRAIL was not able.
Conclusion: To date, no special attention had been paid to this aspect of FVP-induced TRAIL-sensitization, may be because
sTRAIL used were not able to take advantage of this DR5 up-regulation. Hence, LUV-TRAIL could be a better
choice than sTRAIL to be used in combination with anti-tumor drugs inducing DR5 over-expression, since LUV-TRAIL
is especially effective activating this death-receptor.