Indole-3-Carbinol Synergizes with and Restores Fludarabine Sensitivity in Chronic Lymphocytic Leukemia Cells Irrespective of p53 Activity and Treatment Resistances

Abstract

Purpose: Chronic lymphocytic leukemia (CLL) still is lacking a cure. Relapse and development of refractoriness to current treatments are common. New therapies are needed to improve patient prognosis and survival. Experimental design: Indole-3-carbinol (I3C) is a natural product with antitumor properties already clinically tested. The effect of I3C, F-ara-A, and combinations of both drugs on CLL cells from patients representing different Rai stages, IGHV mutation status, cytogenetic alterations, p53 functionality, and treatment resistances was tested, as well as the toxicity of these treatments in mice. Results: I3C induces cytotoxicity in CLL cells but not in normal lymphocytes. I3C strongly synergized with F-ara-A in all CLL cells tested, including those with p53 deficiency and/or F-ara-A resistance. The mechanism of cell death involved p53-dependent and -independent apoptosis. The combination of I3C + F-ara-A was equally effective in CLL cells irrespective of IGHV mutation stage and patient refractoriness. Moreover, CLL survival and treatment resistance induced by co-culturing CLL cells on stroma cells were overcome by the combinatory I3C + F-ara-A treatment. No toxicity was associated with the combined I3C + fludarabine treatment in mice. Conclusions: I3C in combination with F-ara-A is highly cytotoxic in CLL cells from refractory patients and those with p53 deficiency. The striking dose reduction index for F-ara-A in combination with I3C would reduce fludarabine toxicity while having a similar or better anti-CLL effectiveness. Moreover, the low toxicity of I3C, already clinically tested, supports its use as adjuvant and combinatory therapy in CLL, particularly for patients with relapsed or refractory disease. Clin Cancer Res; 22(1); 134–45. ©2015 AACR.

Targeting DNA repair with aphidicolin sensitizes primary chronic lymphocytic leukemia cells to purine analogs

“…Although the sample size was limited and p53 dysfunction might not be complete, these data suggest that increase of cell death induced by aphidicolin could occur by p53-dependent and -independent mechanisms. That DNA damage can induce signaling for apoptosis in a p53-independent manner has recently became increasingly evident from literature data in different types of cancer cells including the leukemic cell line HL-60 and primary CLL cells [35, 36, 43]. …”