ABSTRACT
E2F1-3a overexpression due to amplification or to mutation or loss of the retinoblastoma gene, induces genes involved in DNA synthesis and leads to abnormal cellular proliferation, tumor growth, and invasion. Therefore, inhibiting the overexpression of one or more of these activating E2Fs is a recognized target in cancer therapeutics. In previous studies we identified by phage display, a novel 7-mer peptide (PEP) that bound tightly to an immobilized consensus E2F1 promoter sequence, and when conjugated to penetratin to increase its uptake into cells, was cytotoxic to several malignant cell lines and human prostate and small cell lung cancer xenografts. Based on molecular simulation studies that showed that the D-Arg penetratin peptide (D-Arg PEP) secondary structure is more stable than the L-Arg PEP, the L-Arg in the peptide was substituted with D-Arg. In vitro studies confirmed that it was more stable than the L- form and was more cytotoxic as compared to the L-Arg PEP when tested against the human castrate resistant cell line, DU145 and the human lung cancer H196 cell line. When encapsulated in PEGylated liposomes, the D-Arg-PEP potently inhibited growth of the DU145 xenograft in mice. Our findings validate D- Arg PEP, an inhibitor of E2F1and 3a transcription, as an improved second generation drug candidate for targeted molecular therapy of cancers with elevated levels of activated E2F(s).
ABSTRACT
NAD+ kinase (NADK) catalyzes the phosphorylation of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide phosphate (NADP+) using ATP as the phosphate donor. NADP+ is then reduced to NADPH by dehydrogenases, in particular glucose-6-phosphate dehydrogenase and the malic enzymes. NADPH functions as an important cofactor in a variety of metabolic and biosynthetic pathways. The demand for NADPH is particularly high in proliferating cancer cells, where it acts as a cofactor for the synthesis of nucleotides, proteins, and fatty acids. Moreover, NADPH is essential for the neutralization of the dangerously high levels of reactive oxygen species (ROS) generated by increased metabolic activity. Given its key role in metabolism and regulation of ROS, it is not surprising that several recent studies, including in vitro and in vivo assays of tumor growth and querying of patient samples, have identified NADK as a potential therapeutic target for the treatment of cancer. In this review, we will discuss the experimental evidence justifying further exploration of NADK as a clinically relevant drug target and describe our studies with a lead compound, thionicotinamide, an NADK inhibitor prodrug. Clin Cancer Res; 22(21); 5189-95. ©2016 AACR.
