Pancreatic cancer is almost always fatal, in part because of its delayed diagnosis, poor prognosis, rapid progression and chemoresistance. Oncogenic
proteins are stabilized by the Hsp90, making it a potential therapeutic target. We investigated the oxidative stress-mediated dysfunction of Hsp90 and the hindrance of its chaperonic activity by a
carbazole alkaloid,
mahanine, as a strategic therapeutic in
pancreatic cancer.
Mahanine exhibited antiproliferative activity against several
pancreatic cancer cell lines through apoptosis. It induced early accumulation of
reactive oxygen species (ROS) leading to
thiol oxidation, aggregation and dysfunction of Hsp90 in MIAPaCa-2.
N-acetyl-L-cysteine prevented
mahanine-induced ROS accumulation, aggregation of Hsp90, degradation of client
proteins and cell death.
Mahanine disrupted Hsp90-Cdc37 complex in MIAPaCa-2 as a consequence of ROS generation. Client
proteins were restored by
MG132, suggesting a possible role of ubiquitinylated protein degradation pathway. Surface plasmon resonance study demonstrated that the rate of interaction of
mahanine with recombinant Hsp90 is in the range of seconds. Molecular dynamics simulation showed its weak interactions with Hsp90. However, no disruption of the Hsp90-Cdc37 complex was observed at an early time point, thus ruling out that
mahanine directly disrupts the complex. It did not impede the
ATP binding pocket of Hsp90.
Mahanine also reduced in vitro migration and tube formation in
cancer cells. Further, it inhibited orthotopic pancreatic
tumor growth in nude mice. Taken together, these results provide evidence for
mahanine-induced ROS-mediated destabilization of Hsp90 chaperone activity resulting in Hsp90-Cdc37 disruption leading to apoptosis, suggesting its potential as a specific target in
pancreatic cancer.