Cytotoxicity of curcumin derivatives in ALK positive non-small cell lung cancer

Non-small cell lung cancer with ALK rearrangements can be targeted effectively with ALK inhibitors such as crizotinib. However, cancer progression typically occurs within a year as drug resistance develops. One strategy to overcome this drug resistance is to determine if novel cytotoxic agents retain the ability to kill lung cancer cells that have developed ALK inhibitor resistance. We therefore examined curcumin, a drug with anticancer properties, and 2 s-generation curcumin derivatives (1-methyl-3,5-bis[(E)-4-pyridyl) methylidene]-4-piperidone (RL66) and 1-isopropyl-3,5-bis [(pyridine-3-yl) methylene]piperidin-4-one (RL118)) in lung cancer cell lines. The cytotoxicity of curcumin, RL66, and RL118 were tested in both ALK(+) lung cancer cells (H3122), crizotinib resistant ALK(+) cells (CR-H3122) and ALK(-) lung cancer cells (A549), both alone and in combination with crizotinib. ALK(+) cells were 2-3x more sensitive to RL66 and RL118 than ALK(-) cells, with the drugs' eliciting IC50, values in the range of 0.7-1 mu M in H3122 cells. Retained cytotoxic potency of the curcumin derivatives in crizotinib resistant cells indicated that mechanisms of resistance to the two drug types are independent, with resistance to ALK inhibitors not necessarily causing cross-resistance to curcumin derivatives. This was further corroborated by drug combination analysis where the effect of the drugs in combination was consistent with Bliss additivity, consistent with independent targets for crizotinib and curcumin derivatives. Results from Western blotting showed that RL118 (2 mu M) inhibited p-ALK/ALK by similar to 50%, which was not as potent as the 90% inhibition elicited by crizotinib (0.25 mu M). Since this is the primary mechanism of crizotinib cytotoxicity this provides further evidence of independent mechanisms of toxicity.