Advances in Cancer Drug Targets

Human neutrophil elastase (HNE), a main factor in the development of chronic obstructive pulmonary diseases, has been recently involved in non-small cell lung cancer progression. It can act at several levels (i) intracellularly, cleaving for instance the adaptor molecule insulin receptor substrate-1 (IRS-1) (ii) at the cell surface, hydrolyzing receptors as CD40 (iii) in the extracellular space, generating elastin fragments i.e. morphoelastokines which potently stimulate cancer cell invasiveness and angiogenesis.

Since decades, researchers identified natural compounds and/or synthesized agents which antagonize HNE activity that will be described in this review article. Some of these compounds might be of value as therapeutic agents in lung cancer.

However, it is now widely accepted that lung tumor invasion and metastasis involve proteolytic cascades. Accordingly, we will here mainly focus our attention to natural substances able to display a dual inhibitory capacity (i.e. lipids and derivatives, phenolics) towards HNE and matrix metalloproteinases (MMPs), particularly MMP-2. To that purpose, we had synthesized substances named “LipoGalardin” exhibiting such inhibitory bifunctionality. At last, we will propose an original synthetic scheme for designing a potent biheaded HNE/MMP-2 inhibitor.

The efficacy of cancer-immunotherapy with complement-activating monoclonal antibodies is limited by over-expression of one or more membrane-bound complement regulatory proteins (mCRPs: CD46, CD55, CD59) on the surface of neoplastic cells.

In this study we designed small interfering RNAs (siRNAs) for posttranscriptional gene knock down of CD46, CD55 and CD59 aiming to sensitize tumor cells to complement attack and thereby exploiting complement for tumor cell destruction. Tumor cell lines of different origin, such as Du145 (prostate), BT474 (breast) and K562 (erythroleukemia) were selected for the study. FACS-analysis demonstrated that siRNA anti-CD46 (301) reduced CD46 protein expression up to 80%, siRNA anti-CD55 (255) diminished CD55 protein expression up to 49%, and CD59 protein expression was inhibited up to 82% by siRNA anti-CD59 (1339). Time course experiments revealed a long-lasting silencing effect with >50% complement regulator inhibition up to day 13. Upon mCRP knock down, complement-dependent cytotoxicity (CDC) was augmented by 20-30% for CD46, by up to 24% for CD55 and by up to 55% for CD59. The combined inhibition of all three inhibitors further enhanced CDC by up to 66%. Dependent on the cell line, CD46 and CD55 downregulation increased significantly C3 opsonization, which is known to support cell-mediated defense mechanisms. mCRP blocking antibodies were only partly able to further augment the tumor cells’ susceptibility to complement lysis.

Thus, siRNA-induced inhibition of complement regulator expression clearly sensitizes malignant cells to complement attack and, if specifically targeted to the tumor, appears suited as adjuvant to improve antibody-based cancer immunotherapy.

Hepatocellular carcinoma (HCC) is the third most common cause related to cancer mortality worldwide. Due to frequently late diagnosis, overall prognosis of patients with liver cancer is poor. Unfortunately, there is no targeted therapeutics for the treatment of HCC except sorafenib, which has exhibited notable results in certain advanced HCC. Increasing evidences indicate that deregulation of Wnt/β-catenin signaling pathway plays a critical role in hepatic oncogenesis and mainly occurs at the early stage of hepatocarcinogenesis. In addition, aberrant activation of the Wnt/β- catenin signaling pathway has been linked with more aggressive HCCs. The major mechanism for aberrant activation of the signaling in HCC is caused by genetic mutations and/or altered expression of upstream components of the Wnt/β-catenin signaling. This leads to abnormal expression of the β-catenin/TCF-responsive target genes, which regulate cell growth, apoptosis, cell motility, and invasion. Thus, intervention of the Wnt/β-catenin signaling activity can be potential therapeutics for HCC. This review will discuss the identified potential molecular targets related to the Wnt/β-catenin signaling pathway and their potential therapeutic applications.

Overcoming intrinsic and acquired chemoresistance is the major challenge in treating ovarian cancer patients. Initially nearly 75% of ovarian cancer patients respond favorably to chemotherapy, but subsequently the majority gain acquired resistance resulting in recurrence, cancer dissemination and death. This chapter summarizes recent advances in our understanding of the cellular origin and the molecular mechanisms defining the basis of cancer initiation and malignant transformation with respect to epithelial-mesenchymal transition (EMT) of ovarian cancer cells. We discuss the critical role of EMT frequently encountered in different phases of ovarian cancer progression and its involvement in regulating cancer growth, survival, migration, invasion and drug resistance. Using model ovarian cancer cell lines we highlight the relationship between EMT and the ‘cancer stem cell (CSC)-like phenotype’ in response to drug treatment, and relate how these processes can impact on chemoresistance and ultimately recurrence. We propose the molecular targeting of distinct ‘EMT transformed CSC-like cells’ and suggest ways that may improve the efficacy of current chemotherapeutic regimens much needed for the management of this disease.

Oxaliplatin, is a platinum-based antineoplastic agent used in cancer chemotherapy and paclitaxel is one of several cytoskeletal drugs that target tubulin. Paclitaxel-treated cells have defects in mitotic spindle assembly, chromosome segregation, and cell division. Survivin is one of the key anti-apoptotic proteins which is over-expressed in most of the human cancers; and is associated with their biologically aggressive characteristics and drug resistance. Investigations presented deals with the evaluation of the efficacy of oxaliplatin and paclitaxel combination as a potential strategy in controlling HNSCC cell proliferation and the assessment of correlation between occurrence of apoptosis and changes in expression of survivin (IAP) by employing two HNSCC cell lines (Cal27 and NT8e) and one normal cell line (293) panel with differential level of survivin expression in accordance with chemosensitivity. The combined treatment of cells with paclitaxel and oxaliplatin resulted in a significantly higher cytotoxicity compared to individual single drug treatment. Cytotoxicity was prominent in paclitaxel to oxaliplatin (pacl-oxal) sequence treatment with an approximate two-fold increase in apoptosis compared to oxaliplatin to paclitaxel (oxal-pacl) sequence treatment.

Paclitaxel treatment also significantly increased survivin expression with reduced apoptosis at low concentration. Oxaliplatin, when combined with paclitaxel, decreased the survivin level with increased cell death. Study was further designed to explore the effect(s) of survivin-inhibition by a small interfering RNA (siRNA therapy) method on the apoptosis in HNSCC cells expressing increased sensitivity of the cancer cell lines to paclitaxel whereas over-expression of survivin in the transfected 293-cell line provided resistance. Survivin played a critical role in paclitaxel resistance through the suppression of apoptosis, and a significant induction of apoptosis was observed when oxaliplatin was combined with paclitaxel at least in part by the down-regulation of survivin. In conclusion, the interaction between drugs was synergistic and scheduledependent.

Melatonin has oncostatic effects on different neoplasias, particularly on estrogen-dependent breast cancer, by interacting with estrogen-responsive pathways, thus behaving as an antiestrogenic hormone. In MCF-7 (a human breast adenocarcinoma cell line), melatonin reduces both expression and activity of estrogen sulfatase, thus modulating the local estrogen biosynthesis. In order to investigate the in vivo sulfatase-inhibitory properties of melatonin, this indoleamine was given to ovariectomized rats bearing DMBA-induced mammary tumors also treated with estrone sulfate. In castrated animals, the growth of estrogen-sensitive mammary tumors depends on the local conversion of biologically inactive estrogens to bioactive unconjugated estrogens. Ovariectomy significantly reduced the size and the number of tumors while the administration of estrone sulfate to ovariectomized animals stimulated tumor growth, an effect otherwise abrogated by melatonin. The uterine weight of ovariectomized rats, which depends on the local synthesis of estrogens, was increased by estrone sulfate, being this effect abolished in those animals also treated with melatonin. The growth-stimulatory effects of estrone sulfate on the uterus and tumors depend exclusively on locally synthesized estrogens, since no changes in serum estradiol were observed in estrone sulfate-treated rats. Melatonin counteracted the stimulatory effects of estrone sulfate on sulfatase activity and expression and incubation with melatonin decreased the sulfatase activity of tumors from control animals.

Animals treated with melatonin had the same survival probability as the castrated animals and significantly higher than the uncastrated. We conclude that melatonin could exert its antitumoral effects on hormone-dependent mammary tumors by downregulating the sulfatase pathway of the tumoral tissue.

Tumor cell migration and invasion play fundamental roles in cancer metastasis. The mammalian target of rapamycin (mTOR), a highly conserved and ubiquitously expressed serine/threonine (Ser/Thr) kinase, is a central regulator of cell growth, proliferation, differentiation and survival. Recent studies have demonstrated that mTOR also plays a critical role in the regulation of tumor cell motility, invasion and cancer metastasis. Current knowledge indicates that mTOR functions as two distinct multiprotein complexes, mTORC1 and mTORC2. mTORC1 phosphorylates p70 S6 kinase (S6K1) and eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1), and regulates cell growth, proliferation, survival and motility. mTORC2 phosphorylates Akt, protein kinase C α (PKCα) and the focal adhesion proteins, and controls the activities of the small GTPases (RhoA, Cdc42 and Rac1), and regulates cell survival and the actin cytoskeleton. Here we briefly review current knowledge of mTOR complexes and the role of mTOR signaling in tumor cell migration and invasion. We also discuss recent findings about the mechanism by which rapamycin inhibits cell migration, invasion and cancer metastasis.

This paper reports on the synthesis of a panel of small molecules with arylamides and arylsulfonamides groups and their biological activity in inhibiting nucleotide exchange on human Ras. The design of these molecules was guided by structure-activity data previously collected on similar compounds. Aim of this work is the validation of the hypothesis that a phenyl hydroxylamine group linked to a second aromatic moiety generates a pharmacophore capable to interact with Ras and to inhibit its activation. In vitro experiments on purified human Ras clearly show that the presence of an aromatic hydroxylamine and a sulfonamide group in the same molecule is necessary to Ras binding and nucleotide exchange inhibition. The inhibitor potency is lower in molecules in which either the hydroxylamine has been replaced by other functional groups or the sulfonamide has been replaced by an amide. In this case both these moieties, the hydroxylamine and sulfonamide are absent, inactive compounds are obtained.