Combination of cationic dexamethasone derivative and STAT3 inhibitor (WP1066) for aggressive melanoma: a strategy for repurposing a phase I clinical trial drug.

Glucocorticoid, such as dexamethasone (Dex) is often used along with chemotherapy to antagonize side effects of chemotherapy. However, sustained use of Dex frequently develops drug resistance in patients. As a strategy to re-induce drug sensitivity, we planned to modify Dex by chemically conjugating it with twin ten carbon aliphatic chain containing cationic lipid. The resultant molecule, DX10, inhibited STAT3 activation through lowering the production of IL-6. To enhance the STAT3 inhibitory effect of DX10, we used WP (a commercially available STAT3 inhibitor) along with DX10. Combination treatment of both significantly inhibited STAT3 activation when compared to either of the individual treatment. The effect of DX10, either in combination or alone, was mediated through glucocorticoid receptor (GR), thereby repurposing the role of GR in the context of p-STAT3 inhibition-mediated cancer treatment. Cellular viability study proved the synergistic effect of WP and DX10. Further, combination treatment led to induction of early stage of apoptosis and cell cycle arrest. In vivo melanoma tumor regression study confirmed the enhanced anti-tumor activity of co-treatment over individual treatment of DX10 or WP. Thus, together our result demonstrates that DX10 may be used in combination therapy with STAT3 inhibitor like WP for combating cancer with constitutively active STAT3.