Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 14, Issue 2, 2014

Poxvirus-based vaccines have a long record of efficacy as both anti-tumour agents and vectors for gene therapy in different human tumour models. Interestingly, several studies of these vaccines have now entered the clinical evaluation phase for safety and effectiveness. A desirable outcome of antigen specific cancer immunotherapy is the disruption of host self-tolerance against endogenous tumour-associated antigens (TAAs). Nonetheless, recent studies have found reductions in vaccine efficacy due to host anti-vaccine immune reactions. Thus, newer approaches bringing together poxvirus-based vaccination and immunostimulation are being developed, and new poxvirus strains are being examined in tumour therapy studies. Our review summarizes the current knowledge on the efficacy of poxvirus-based vaccination on human tumours, with a particular focus on approaches aimed at increasing innate and specific immune responses. Special attention will be devoted to the new poxvirus strains that are currently under consideration for tumour therapy; the current knowledge on clinical trials and outcomes will also be reviewed.

The prognosis of patients with metastatic cervical cancer is poor with a median survival of 8-13 months. Despite the potency of chemotherapeutic drugs, this treatment is rarely curative and should be considered palliative only. The last decades, targeted therapies such as immunotherapy have emerged as an attractive option for the treatment of these patients. Immunotherapy can consist of different modalities such as monoclonal antibodies, adoptive lymphocyte transfer and vaccines, which all are intended to augment the antitumor immune responses in cancer patients. The available evidence indicates that both active and adoptive immunotherapeutical strategies are quite effective against small tumor burdens, but are usually insufficient to eradicate the disease in patients with advanced stages of different kinds of cancer, despite strong induction of tumor-specific immune responses. Although chemotherapy and immunotherapy have not shown to be curative as single modalities, accumulating evidence suggests that combinations of these treatments hold potential for improved clinical outcomes in advanced stages of cancer. Therefore, the combination of chemotherapy and immunotherapy is no longer considered incompatible, because of the emerging insight that certain chemotherapy-based cancer treatments may activate the immune system against the tumor through several molecular and cellular mechanisms. Chemotherapeutic agents and immunotherapy may thus be synergistic and enhance the clinical response. In this review, we show the rationale for combined chemo-immunotherapeutic strategies, and summarize recent data from clinical trials performed in patients with different types of cancer. Challenges such as the selection of the optimal dose and treatment schedule, will be discussed as well as the identification of immune-specific biomarkers. Furthermore, we evaluated the long-term clinical outcomes of patients with advanced cervical cancer treated with HPV16 E6/E7 SLP vaccination with or without chemotherapy. Finally, the future of vaccination therapy in combination with chemotherapy for the treatment of cervical cancer is discussed.

Effective elicitation of endogenous immunity is associated with improved prognosis for cancer patients. Clinical evidence in hematological and solid cancers shows that intratumoral injection of immunostimulatory genes primes and augments endogenous T cell responses. The ability of pro-inflammatory chemokines/cytokines to facilitate migration/activation of antigen-presenting cells (APC) and lymphocytes prompted our modeling of intratumoral delivery of a chemokine/cytokine combination for breast cancer treatment. Here, we demonstrate that expression of chemokine ligand 21 (CCL21) and interferon gamma (IFNγ) in tumors improves tumor specific T cell recruitment to tumor and activation in the tumor milieu. IFNγ and CCL21 were delivered into tumor cells via plasmids, and transfected cells were seeded to form spheroids on three-dimensional (3D) chitosan-alginate (CA) scaffolds. Co-expression of CCL21 and IFNγ, as evidenced by qRT-PCR and ELISA, induced increased recruitment, binding, and infiltration of anti-neu (p98) peptide specific T cells into the breast tumors as determined by SEM and immunofluorescence assays. The co-expression promoted recruitment of only p98 T cells, but not naive T cells, demonstrating an antigen-restricted activation. Furthermore, the co-expression impacted T helper (Th) cell immunity, promoting an increase in secretion of pro-inflammatory Th-associated cytokine, tumor necrosis factor alpha (TNFα), and cytotoxic T lymphocyte (CTL)-associated protease, Granzyme B (GzB). Therefore, 3D CA scaffolds may be a useful breast cancer tumor microenvironment model to evaluate T cell function. Further characterization of CCL21-IFNγ mediated anti-tumor immunity will potentially benefit the development of chemokine/cytokine combination platforms as anti-cancer agents.

Adoptive immunotherapy is considered a promising strategy for the treatment of metastatic tumors and current research efforts are directed to define the optimal approach and facilitate the transferability from preclinical to clinical settings. Among several approaches it is possible to schematically distinguish strategies based on either MHC-restricted or MHC-unrestricted immune effectors. The first are mainly based on the infusion of tumor-specific T lymphocytes capable of recognizing determined MHC-restricted tumor associated antigens (TAA) through their T cell receptor. MHC-unrestricted approaches do not target specific tumor associated antigens and are mainly mediated by effectors of the innate immune system, like natural killer (NK) cells or NKT cells, first barrier against pathogens and tumorigenesis processes, or by ex vivo activated lymphocytes like cytokine-induced killer (CIK) cells. MHC-unrestricted effectors are usually more abundant than TAA-specific precursors and easier to expand. Furthermore their activity is not restricted to precise HLAhaplotypes, not limited to a single tumor histotype and could overcome downregulation of MHC molecules operated by tumor cells as immune escape mechanism. In this review we will discuss the main cancer immunotherapy strategies based on MHC-unrestricted immune effectors. The topic will be approached from the angle of ex vivo expansion protocols in clinical prospective, as well as potential approaches to favorably modulate their functions.

Tumor cells, including leukemic cells, remodel their bioenergetic system in favor of aerobic glycolysis. This process is called “the Warburg effect” and offers an attractive pharmacological target to preferentially eliminate malignant cells. In addition, recent results show that metabolic changes can be linked to tumor immune evasion. Mouse models demonstrate the importance of this metabolic remodeling in leukemogenesis. Some leukemias, although treatable, remain incurable and resistance to chemotherapy produces an elevated percentage of relapse in most leukemia cases. Several groups have targeted the specific metabolism of leukemia cells in preclinical and clinical studies to improve the prognosis of these patients, i.e. using L-asparaginase to treat pediatric acute lymphocytic leukemia (ALL). Additional metabolic drugs that are currently being used to treat other diseases or tumors could also be exploited for leukemia, based on preclinical studies. Finally, we discuss the potential use of several metabolic drugs in combination therapies, including immunomodulatory drugs (IMiDs) or immune cell-based therapies, to increase their efficacy and reduce side effects in the treatment of hematological cancers.

Garlic (Allium sativum) has been used for centuries as a prophylactic and therapeutic medicinal agent. Importantly, garlic has been suggested to have both cancer-preventive potential as well as significant enhancing effects on the immune system. While these observations are supported experimentally both in vitro and in vivo, the impact of garlic in assisting the immune system in the prevention of cancer still lacks experimental confirmation. Studies addressing the immunomodulatory effects of garlic reveal conflicting data as to pro- or anti-inflammatory responses depending on the particular experimental set-ups and the garlic preparation used (i.e. garlic extract versus chemically pure garlic compounds). Here we provide an overview of the chemistry of the major garlic organosulfur compounds, summarize the current understanding and propose a link between the immunomodulating activity of garlic and the prevention of cancer. We hypothesize that garlic rather elicits anti-inflammatory and anti-oxidative responses that aid in priming the organism towards eradication of an emerging tumor.

Cancer cells create a microenvironment that prevents tumor rejection by the host’s immune system. The activation of pattern recognition receptors (PRRs) can elicit an innate immune response and guide the adaptive immune response to overcome this. dsRNA analogs can trigger TLR3, RIG-I, MDA5, NLRP3 and several other PRRs to induce not only robust immune response against cancer but also programmed cell death. This review focuses on the signal pathways activated by dsRNA and examines examples of their clinical application in cancer treatment.

Traditional anti-cancer therapies (surgery, radiotherapy and chemotherapy) have limited effectiveness in curbing progression of advanced tumors. However, with advances in immunology and molecular biology in the last two decades, the prognosis of cancer immunotherapy has improved. An emerging therapy is the cancer vaccine as adjunctive therapy. The purpose of this paper is to review this therapeutic modality for non-small cell lung cancer.

Cervical cancer is the second most common malignancy among women worldwide. The prime causal factor of the disease is a persistent infection with human papillomavirus (HPV) with individuals failing to mount a sufficient immune response against the virus. Despite the current success of HPV16- and 18-specific prophylactic vaccination, established HPV infections and associated neoplasia require therapeutic vaccines with the induction of cellular immunity. The sustained expression of early proteins E6 and E7 from major oncogenic HPV genotypes in cervical lesions are ideal targets for the design of immunotherapeutic strategies. These strategies, particularly subunit vaccines, may require additional help from immunomodulators to enhance HPV-specific cellular responses. This review discusses recent studies, published since 2008, relating to immunotherapeutic strategies against HPV that include immunomodulators. These immunomodulators fall within the category of toll-like receptor adjuvants for innate immune activation, adjuvants directly contributing to adaptive immunity, such as cytokines and costimulatory molecules, and those that target tumor-induced immunosuppressive mechanisms. Using a combination of these strategies with delivery-based approaches may be most beneficial for the success of therapeutic vaccines against HPV-induced neoplasia in the clinic.

Re-programming of metabolic pathways is a hallmark of pathological changes in cancer cells. The expression of certain genes that directly control the rate of key metabolic pathways including glycolysis, lipogenesis and nucleotide synthesis is dysregulated for the adaptation and progression of tumor cells to become more aggressive phenotypes. The pentose phosphate pathway controlled by glucose- 6-phosphate dehydrogenase (G6PD) has been appreciated largely to its role as a provider of reducing power and ribose phosphate to the cell for maintenance of redox balance and biosynthesis of nucleotides and lipids. Recently, G6PD has been revealed to be involved in apoptosis, angiogenesis, and the efficacy to anti-cancer therapy, making it as a promising target in cancer therapy. This review summarizes the information about the latest progress relating the activity of the G6PD to cell proliferation, angiogenesis, and resistance to therapy in cancer cells, and discusses the possibility of G6PD as a diagnostic biomarker of cancer and the therapeutic potentials of G6PD inhibitors in cancer treatment. The available data show that G6PD plays a critical role in survival, proliferation, and metastasis of cancer cells. Development of potent and selective G6PD inhibitors would provide novel opportunity for cancer therapy.

Recent data have shown strong chemopreventive and possibly cancer chemotherapeutic effects of green tea polyphenols against cancer. Despite advances in breast cancer treatment, mortality from breast cancer is still high. Undoubtedly novel treatment strategies are needed for chemoprevention of high risk women and for the treatment of receptor negative breast cancer. Green tea catechins have been shown to inhibit proliferation of breast cancer cells and to block carcinogenesis. This review attempts a critical presentation of the mechanisms of action of green tea catechins in breast cancer. Several mechanisms of action of green tea catechins in breast cancer have been proposed including modulation of extracellular signalling, induction of apoptosis through redox regulation, or through modulation of epigenetic alterations. A number of molecular targets of green tea catechins have been suggested i.e molecular chaperones, telomerase, apoptotic cascade. Although the molecular links among the proposed mechanisms of action of green tea catechins are often missing, it must be emphasized that all the proposed mechanisms indicate that green tea catechins inhibit growth and /or promote apoptosis. It would be interesting if future experimental trials could take into account that green tea catechins are multi-target agents and attempt to link every novel proposed target with the other already proposed targets of green tea catechins.

The term “angiogenic switch” describes one of the earlier events of tumorigenesis, that occurs when the balance between proand anti-angiogenic factors shifts towards a pro-angiogenic outcome. This leads to the transition from a microscopic indolent lesion to a macroscopic and vascularised primary tumor, that may eventually metastasize and spread to distant sites. The molecular mechanisms underlying such a critical step in the carcinogenetic process have been extensively investigated. Both local endothelial cells (ECs) and endothelial progenitor cells (EPCs), recruited from bone marrow, have been implicated in the angiogenic switch, which is ultimately triggered by a plethora of growth factors released by cancer cells, pivotal among which is vascular endothelial growth factor (VEGF); indeed, VEGF both activates ECs nearby the growing tumor, and leads to EPC mobilization into the circulation. In kidney, in particular, the frequent mutation of the Von Hippel Lindau tumor suppressor gene leads to an overproduction of pro-angiogenic factors which makes this neoplasm quite sensitive to antiangiogenic drugs. However, it is now evident that the use of VEGF(Rs) inhibitors in everyday clinical practice is not as effective as observed in murine models. The investigation of alternative signaling pathways involved in the angiogenic switch is, therefore, imperative in order to induce tumor regression whereby preventing harmful drawback consequences. Ca2+ entry across the plasma membrane has long been known to stimulate mature ECs to undergo angiogenesis. Recent work from several groups worldwide has then outlined that members of the Transient Receptor Potential (TRP) super-family of cationic channels and Orai1 provide the pathway for such proangiogenic Ca2+ signal. In addition, Canonical TRP 1 (TRPC1) and Orai1 channels control proliferation and tubulogenesis in both normal EPCs and EPCs isolated from peripheral blood of tumor patients. As a consequence, TRP channels and Orai1 might serve as novel molecular targets to develop alternative and more effective strategies of angiogenesis inhibition.

As chemotherapy with temozolomide is far from providing satisfactory clinical outcomes for patients with glioblastoma, more efficient drugs and drug combinations are urgently needed. The anti-malarial artesunate was previously shown to exert a profound cytotoxic effect on various tumor cell lines including those derived from glioblastoma. In the current study, we sought to examine the antiproliferative effect of a combination of temozolomide and artesunate on two different established human glioblastoma cell lines. The IC50 and IC25 were determined for temozolomide and artesunate in U87MG and A172 glioblastoma cell lines after 144 h of continuous drug exposure. The antiproliferative effect of combining both agents at IC50/IC50 and IC25/IC25 was determined by a cell viability assay. Moreover, necrosis and apoptosis were analyzed by annexin V/PI staining and flow cytometric analysis. In addition, cytostatic effects were examined by carboxyfluorescein diacetate succinimidyl ester staining and subsequent flow cytometry. In both glioblastoma cell lines, artesunate was found to enhance the antiproliferative effect exerted by temozolomide. Moreover, artesunate acted in concert with temozolomide in terms of cytostatic and necrotizing effects. These observations suggest that a combination of artesunate and temozolomide might result in increased cytotoxicity in glioblastoma.

A new series of N-substituted diarylidenepiperidin-4-ones was synthesized and screened for their possible anticancer activity at the NCI Developmental Therapeutic Program. Almost all the synthesized compounds showed more potent antiproliferative activity than curcumin. The most active compound in this study was 3,5-bis(4-bromobenzylidene)-1-propanoylpiperidin-4-one (8a) with MGMID GI50, TGI, and LC50 values of 0.35, 1.62 and 9.12 μM, respectively. Compound 8a displayed broad spectrum antiproliferative activity with GI50 values below 1 μM in 81% of the tested cell lines and was found to be two folds more potent than EF-24. A detailed study of the structure activity relationship of the N-substitution was also described.

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) is an alkaloid that has been isolated from plants of an Apocynaceae family. It is one of the simplest naturally occurring alkaloids with a planar structure. Over the past decades, ellipticine became a very promising antitumor agent. Interaction with DNA is one of the most studied ellipticine effects on cell division. This phenomenon is not clearly explained so far. In our experiments we studied interaction of ellipticine with single-stranded and double-stranded oligonucleotides by electrochemical methods on mercury electrode. Differential pulse voltammetry was applied for ellipticine (Elli) and CA peak detection. Square wave voltammetry was applied for G peak detection. The effect of the interaction time and ellipticine concentrations on interactions of ellipticine with single- and double-stranded oligonucleotides was tested too.