The antitumor properties of a nontoxic, nitric oxide–modified version of saquinavir are independent of Akt

Danijela Maksimovic-Ivanic,Djordje Miljkovic,Ferdinando Nicoletti,Darrin Dabideen,Yousef Al-Abed,Massimo Libra,Ljubica Harhaji-Trajkovic,Katia Mangano,James A Mccubrey,Sanja Mijatovic,Gianni Garotta,Stanislava Stosic-Grujicic,Marija Mojic,Gordana Timotijevic,Kai Fan Cheng

doi:10.1158/1535-7163.mct-08-0998

Abstract

Application of the HIV protease inhibitor saquinavir (Saq) to cancer chemotherapy is limited by its numerous side effects. To overcome this toxicity, we modified the original compound by covalently attaching a nitric oxide (NO) group. We compared the efficacy of the parental and NO-modified drugs in vitro and in vivo. The novel compound saquinavir-NO (Saq-NO) significantly reduced the viability of a wide spectrum of human and rodent tumor cell lines at significantly lower concentration than the unmodified drug. In contrast to Saq, Saq-NO had no effect on the viability of primary cells and drastically reduced B16 melanoma growth in syngeneic C57BL/6 mice. In addition, at the equivalent of the 100% lethal dose of Saq, Saq-NO treatment caused no apparent signs of toxicity. Saq-NO blocked the proliferation of C6 and B16 cells, up-regulated p53 expression, and promoted the differentiation of these two cell types into oligodendrocytes or Schwann-like cells, respectively. Although it has been well documented that Saq decreases tumor cell viability by inhibiting Akt, the anticancer properties of Saq-NO were completely independent of the phosphatidylinositol 3-kinase/Akt signaling pathway. Moreover, Saq-NO transiently up-regulated Akt phosphorylation, delivering a protective signal that could be relevant for primary cell protection and the absence of drug toxicity in vivo. It was unlikely that released NO was independently responsible for these drug effects because Saq-NO treatment increased intracellular and secreted NO levels only slightly. Rather, the chemical modification seems to have produced a qualitatively new chemical entity, which may have a unique mode of action against cancer cells.

Highlights

HIV protease inhibitors (HIV-PI) are antiretroviral agents that have been approved for human use since 1993
We measured the effect of both drugs on the viability of transformed human (HeLa cervix adenocarcinoma, BT20 and HCC1419 breast carcinoma, and PC-3 prostate carcinoma) and rodent (C6 rat astrocytoma and B16 mouse melanoma) cell lines, as well as on primary astrocytes and fibroblasts
Saq-nitric oxide (NO) was more potent than Saq at significantly lower doses, with a clear plateau effect evident in all cell lines tested

Summary

Introduction

HIV protease inhibitors (HIV-PI) are antiretroviral agents that have been approved for human use since 1993. Recent evidence has indicated that the potent anticancer effects of HIV-PIs, both in vitro and in vivo, are mediated primarily through the induction of apoptotic cell death [6,7,8,9] Their mechanism of action against cancer cells is not completely understood, the potential targets of these drugs may include Akt, extracellular signal–regulated kinase, nuclear factor κB, signal transducers and activators of transcription 3, matrix metalloproteinase, basic fibroblast growth factor, and vascular endothelial growth factor [7, 10,11,12,13]. These drugs have been shown to sensitize tumor cells to radiation, enhance the anticancer effects of other cytostatic drugs, and to inhibit the growth and invasion of angiogenic tumor cells in nude mice [10, 11, 14]

Methods

Results

Conclusion