Inhibition of MEK1 by NVP-MEK162 induces apoptosis and cell cycle arrest of Chronic Lymphocytic Leukemia (CLL) cells under <em>ex vivo</em> conditions that recapitulate the activity of the Erk1/2 pathway observed in freshly isolated CLL cells. — The Association Specialists
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  3. Inhibition of MEK1 by NVP-MEK162 induces apoptosis and cell cycle arrest of Chronic Lymphocytic Leukemia (CLL) cells under ex vivo conditions that recapitulate the activity of the Erk1/2 pathway observed in freshly isolated CLL cells.

Inhibition of MEK1 by NVP-MEK162 induces apoptosis and cell cycle arrest of Chronic Lymphocytic Leukemia (CLL) cells under ex vivo conditions that recapitulate the activity of the Erk1/2 pathway observed in freshly isolated CLL cells. (411)

Kyle Crassini 1 2 , Giles Best 1 2 3 , Stevenson William 1 2 , Mulligan Stephen 1 2 3
  1. Royal North Shore Hospital, St. Leonards
  2. Northern Blood Research Centre, Kolling Institute, St. Leonards
  3. CLL Australian Research Consortium, Sydney

There is growing evidence that CLL is a two compartmentalized disease; cells in the peripheral circulation are predominantly quiescent whereas cells in the lymph nodes, bone marrow and spleen congregate to form proliferation centres1 2 . Since the efficacy of any therapeutic strategy in CLL depends on targeting the proliferating tumour cells, studies of novel therapeutic agents must consider and model the microenvironment.

The mitogen-activated-protein kinase (MAPK) signaling pathway is known to play a role in the survival of CLL cells3 . We have observed the activity of the MAPK-Erk1/2 pathway is attenuated in CLL cells following ex-vivo culture. We hypothesized that although the MEK1 inhibitor, NVP-MEK162, has some activity against CLL cells in media, an accurate assessment of its effects would require recapitulation of Erk1/2 pathway activity.

We have shown that treatment of frozen/thawed fractions from CLL patients with PMA, CpG-ODN/IL2, CXCR4 stimulation or CD40 ligation, which support CLL cell survival, stimulate signaling via Erk1/2. Treatment with PMA or CpG-ODN/IL2 induced a significant increase in the proportion of viable cells and resistance to fludarabine. CpG-ODN/IL2 treatment had a marked effect cell cycling which was abrogated by simultaneous exposure to NVP-MEK162. MEK162 also significantly reduced PMA-stimulated cell survival in a dose dependent manner and restored sensitivity to fludarabine following either PMA or CpG-ODN/IL2 stimulation.

Our work suggests that the MAPK-Erk1/2 signaling pathway is active in CLL cells in-vivo but that a portion of this activity is lost ex-vivo.  We believe that activation of this pathway mimics one aspect of the support offered by the CLL tumor microenvironment. We show that an inhibitor of this pathway, NVP-MEK162, is effective at inducing apoptosis and restricts cell cycling. This highlights the importance of considering the influence of signals derived from the microenvironment in any studies of novel agents for this disease. 

  1. Burger, J.A., et al., The microenvironment in mature B-cell malignancies: a target for new treatment strategies, in Blood2009. p. 3367-75.
  2. Messmer, B.T., et al., In vivo measurements document the dynamic cellular kinetics of chronic lymphocytic leukemia B cells. J Clin Invest, 2005. 115(3): p. 755-64.
  3. Steelman, L.S., et al., Roles of the Ras/Raf/MEK/ERK pathway in leukemia therapy, in Leukemia2011. p. 1080-94.