Heteronemin, a marine natural product, sensitizes acute myeloid leukemia cells towards cytarabine chemotherapy by regulating farnesylation of Ras

// Minakshi Saikia 1, 3 , Archana P Retnakumari 1, * , Shabna Anwar 1, 3, * , Nikhil P Anto 1 , Rashmi Mittal 2 , Shabna Shah 1, 3 , Kavya S Pillai 1, 3 , Vinod S Balachandran 1 , Vidya Peter 1 , Reeba Thomas 1 and Ruby John Anto 1 1 Division of Cancer Research, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala, India 2 Department of Biotechnology, Maharishi Markandeshwar University, Haryana, India 3 Research Scholar, University of Kerala, India * These authors contributed equaly to this work Correspondence to: Ruby John Anto, email: rjanto@rgcb.res.in Keywords: acute myeloid leukemia; Ras; heteronemin; farnesyl transferase; chemosensitization Received: November 27, 2017      Accepted: February 23, 2018      Published: April 06, 2018 ABSTRACT Cytarabine is a conventionally used chemotherapeutic agent for treating acute myeloid leukemia (AML). However, chemoresistance, toxic side-effects and poor patient survival rates retard the efficacy of its performance. The current study deals with the chemosensitization of AML cells using heteronemin, a marine natural product towards cytarabine chemotherapy. Heteronemin could effectively sensitize HL-60 cells towards sub-toxic concentration of cytarabine resulting in synergistic toxicity as demonstrated by MTT assay and [ 3 H] thymidine incorporation studies, while being safe towards healthy blood cells. Flow cytometry for Annexin-V/PI and immunoblotting for caspase cleavage proved that the combination induces enhancement in apoptosis. Heteronemin being a farnesyl transferase inhibitor (FTI) suppressed cytarabine-induced, farnesyl transferase-mediated activation of Ras, as assessed by Ras pull-down assay. Upon pre-treating cells with a commercial FTI, L-744,832, the synergism was completely lost in the combination, confirming the farnesyl transferase inhibitory activity of heteronemin as assessed by thymidine incorporation assay. Heteronemin effectively down-regulated cytarabine-induced activation of MAPK, AP-1, NF-κB and c-myc, the down-stream targets of Ras signaling, which again validated the role of Ras in regulating the synergism. Hence we believe that the efficacy of cytarabine chemotherapy can be improved to a significant extent by combining sub-toxic concentrations of cytarabine and heteronemin.