The NO-modified HIV protease inhibitor as a valuable drug for hematological malignancies: Role of p70S6K

Highlights

• Saq-NO exerts more potent anticancer effects on leukemia cell lines than Saq.

• Saq-NO exerts antiproliferative effects on Jurkat and Raji cells.

• Saq-NO promotes caspase-dependent apoptosis on HL-60 and K652 cells.

• Saq-NO is effective on primary acute lymphoblastic and acute myeloid leukemia cells.

• p70S6 kinase represents a possible intracellular target for Saq-NO.

Abstract

Covalent attachment of NO to the first approved HIV protease inhibitor Saquinavir (Saq-NO) expands the therapeutic potential of the original drug. Apart from retained antiviral activity, the modified drug exerts strong antitumor effects and lower toxicity. In the present study, we have evaluated the sensitivity of different hematological malignancies to Saq-NO. Saq-NO efficiently diminished the viability of Jurkat, Raji, HL-60 and K562 cells. While Jurkat and Raji cells (established from pediatric patients) displayed abrogated proliferative potential, HL-60 and K652 cells (originated from adults) exposed to Saq-NO treatment underwent caspase dependent apoptosis. In addition, similar sensitivity to Saq-NO was observed in mononuclear blood cells obtained from pediatric patients with acute lymphoblastic leukemia (ALL) and adult patients with acute myeloid leukemia (AML). Western blot analysis indicated p70S6 kinase as a possible intracellular target of Saq-NO action. Moreover, the addition of a NO moiety to Lopinavir resulted in improved antitumor potential as compared to the parental compound, suggesting that NO-derived HIV protease inhibitors are a potential new source of anticancer drugs with unique mode of action.

Introduction

Over the last few decades many discoveries have been achieved in the field of cancer therapy, and in particular in the area of small molecule inhibitors of oncogenic cell signaling pathways [1]. Unfortunately, therapy failure due to relapsed or primary resistant disease is still frequent and is associated to severe toxicity and side effects [2]. Thus, further studies are warranted to identify novel anticancer compounds with similar mode of action but with lower toxicity. Drugs used for the treatment of viral infection such as HIV protease inhibitors (HPIs) may represent a promising therapeutic option in the cancer setting [3]. Their anticancer properties were incidentally noticed when it was observed that patients exposed to HPIs, exhibited significantly lower rate of HIV associated cancers [3]. Independently of HIV protease inhibition, these drugs reduce angiogenesis, cell invasion and viability of malignant cell through induction of apoptosis/autophagy, accompanied with Akt inhibition [4], [5], [6], [7], [8], [9], [10], [11]. Beside their effectiveness on solid cancers, HPIs were found efficient in the treatment of blood cancers [12], [13], [14]. Ritonavir induced apoptosis and inhibited NF-kB activity in adult T cell leukemia. Ritonavir, Saquinavir (Saq) and Nelfinavir through their inactivation of STAT3 and ERK1/2 led to growth arrest and apoptosis of human multiple myeloma cells [15]. Nelfinavir was also found to induce mitochondria independent apoptosis of leukemia cell lines and impaired proteasome activity and proliferation of multiple myeloma cells in vitro and in vivo [16]. Importantly, Saq displayed antiproliferative activity even against imatinib-resistant chronic myelogenous leukemia cell lines [6]. Beside direct effects, HPIs are able to potentiate the effect of 1,25-dihydroxyvitamin D3 or ATR on myelioid leukemia cells [14], [17]. Recently, Kraus et al. [12] demonstrated that Nelfinavir augments proteasome inhibition by Bortezomib and overcomes Bortezomib and Carfilzomib resistance [12]. Limitations of the usage of HPIs are toxicity and development of resistance. Different chemical manipulation like packaging in nanostructured lipid carriers [18] has been examined to reduce toxicity. We focused our attention on a derivative of Saq obtained by the linkage of the NO moiety as NO-hybridization has found useful to increase the anticancer potential in the case of nonsteroidal anti-inflammatory drugs [19]. Saquinavir-NO (Saq-NO) was found to be significantly superior than Saq in diminishing the viability of a variety of adherent tumor cell lines in vitro and abrogating the growth of melanoma, prostate and colon cancer in syngeneic and xenograft models in vivo [20], [21], [22], [23], [24], [25]. Although in p53 deficient and iNOS positive cell lines, Saq-NO induced apoptotic cell death, its antitumor action was mostly executed through blockade of cellular proliferation of cancer cells and reversion to normal phenotype through process of differentiation or transdifferentiation [20], [21], [22]. Additional benefit of this drug is its potential to sensitize tumor cells to chemotherapeutics and antitumor immune responses [22], [25], [26], [27]. We also demonstrated that the mechanism of action of Saq-NO is partly based on the property to inhibit the activation of p70S6K protein that is important for many cellular processes, transcription, translation, protein and lipid synthesis, cell growth and metabolism [25].

In this paper, we have studied the effects of Saq-NO on different blood cancers. We found that Saq-NO efficiently suppressed the expansion of lymphoma and leukemia cell lines in vitro. Moreover, Saq-NO decreased the viability of malignant cells isolated from patients with acute lymphoblast leukemia and acute myeloid leukemia. To the best of our knowledge, this is the first evidence of efficacy of modified HIV protease inhibitors against blood cancers.