Nicotinamide Blocks Proliferation and Induces Apoptosis of CLL Cells through Activation of the p53/miR-34a/SIRT1 Tumor Suppressor Network

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BlankNicotinamide Blocks Proliferation and Induces Apoptosis of Chronic

Lymphocytic Leukemia Cells through Activation of the p53/miR-34a/SIRT1 Tumor

Suppressor Network

1.. Valentina Audrito1,2,

2.. Tiziana Vaisitti1,2,

3.. e Rossi4,

4.. a Gottardi3,

5.. Giovanni D'Arena5,

6.. Luca ti6,

7.. Gianluca Gaidano4,

8.. Fabio Malavasi1, and

9.. Silvia Deaglio1,2

+ Author Affiliations

1.. Authors' Affiliations:1Laboratory of Immunogenetics, Department of

Genetics, Biology and Biochemistry, University of Turin; 2Human Genetics

Foundation (HuGeF); 3Division of Clinical Immunology and Hematology, Ospedale

Mauriziano Umberto I, Turin; 4Division of Hematology, Department of Clinical and

Experimental Medicine and BRMA, “Amedeo Avogadro” University of Eastern

Piedmont, Novara; 5IRCCS “Casa Sollievo della Sofferenza” Hospital, San Giovanni

Rotondo (FG); and 6Institute of Hematology, Catholic University of the Sacred

Heart, Rome, Italy

1.. Corresponding Authors:

Silvia Deaglio or Fabio Malavasi, Laboratory of Immunogenetics, Department of

Genetics, Biology and Biochemistry, University of Turin, via Santena 19, 10126

Turin, Italy. Phone: 39-011-670-9535; Fax: 39-011-670-9546; E-mails:

silvia.deaglio@... or fabio.malavasi@...

Abstract

Because of its relatively indolent clinical course, chronic lymphocytic leukemia

(CLL) offers a versatile model for testing novel therapeutic regimens and drug

combinations. Nicotinamide is the main NAD+ precursor and a direct inhibitor of

four classes of enzymes, including the sirtuins. SIRT1, the main member of the

sirtuin family, inactivates p53 by deacetylating a critical lysine residue. In

this study, we showed that CLL cells express high levels of functional SIRT1,

which is inhibited by exogenous nicotinamide. This agent blocks proliferation

and promotes apoptosis selectively in leukemic cells that express wild-type (wt)

p53. Nicotinamide modulates the p53-dependent genes p21, NOXA, BAX, and Mcl-1,

indicating an activation of the p53 pathway and of caspase-3. DNA-damaging

chemotherapeutics, such as etoposide, activate a functional loop linking SIRT1

and p53 through the induction of miR-34a. When leukemic cells are simultaneously

exposed to nicotinamide and etoposide, we observe a significant increase in

miR-34a levels with a concomitant inhibition of SIRT1. Furthermore, p53

acetylation levels are higher than with either agent used alone. Overall,

treatment with both nicotinamde and etoposide shows strongly synergistic effects

in the induction of apoptosis. We therefore concluded that nicotinamide has the

dual property of inhibiting SIRT1 through a noncompetitive enzymatic block (p53

independent) and at the same time through miR-34a induction (p53 dependent).

These observations suggested the therapeutic potential of nicotinamide, a novel,

safe, and inexpensive drug, to be used in addition to chemotherapy for CLL

patients with wt p53. Cancer Res; 71(13); 4473–83. ©2011 AACR.