We investigated the mechanism of toxicity and resistance development of small molecule tyrosine kinase inhibitor lapatinib in HCT 116 colon cancer cells. Lapatinib mediated cell death in HCT 116 cells was caspase independent and involved cytosolic release of apoptosis inducing factor. Treatment of HCT 116 cells with 10μM Lapatinib lead to the outgrowth of lapatinib resistant HCT 116 cells. Our studies show that alterations in the expression and activation of Bcl-2 family proteins allow lapatinib resistant HCT 116 cells to resist cytotoxic effects of lapatinib as well as of other commonly used chemotherapeutic agents.;In hepatoma and pancreatic cancer cells, the effects of combining multi-kinase inhibitor sorafenib with histone deacetylase inhibitors (HDACIs) namely, vorinostat and sodium valproate were investigated. It was found that sorafenib synergizes with HDACIs resulting in enhanced cell death compared to death induced by the drugs individually. The mechanism of action of sorafenib and vorinostat combination treatment as well as sorafenib and sodium valproate combined treatment was shown to involve activation of the CD95 death receptor pathway. Alterations in the CD95 pathway can render cancer cells resistant to chemotherapeutic agents. Hence, we combined sorafenib+sodium valproate with a BH-3 domain mimetic named obatoclax (GX-15-070) which resulted in enhanced toxicity to cancer cells. More importantly, knock-down of CD95 (to mimic non-functional CD95 pathway) reduced cell death induced by sorafenib+sodium valproate combined but failed to protect cells from cell death induced by sorafenib+sodium valproate+obatoclax combined. This suggests that combining sorafenib+HDACI with obatoclax may not only enhance toxicity to cancer cells but may also reduce chances of resistance development via alterations in the CD95 pathway. These studies enhance our knowledge of existing treatment strategies for cancer as well as throw light on how current approaches can be improved in order to better diagnose and treat cancer. Understanding mechanisms of drug action as well as resistance development will allow us to combine existing therapies effectively in order best target cancer cells as well as provide us with information that can help us design new cancer treatment strategies.
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