Antonia Reale

Therapeutic targeting of the mTOR-signalling pathway in cancer: benefits and limitations

The mammalian target of rapamycin (mTOR) plays an important role in the regulation of protein translation, cell growth and metabolism. The mTOR protein forms two distinct multi‐subunit complexes: mTORC1 and mTORC2. The mTORC1 complex is activated by diverse stimuli, such as growth factors, nutrients, energy and stress signals; and essential signalling pathways, such as PI3K and MAPK, in order to control cell growth, proliferation and survival. mTORC1 also activates S6K1 and 4EBP1, which are involved in mRNA translation. The mTORC2 complex is resistant to rapamycin inhibitory activity and is generally insensitive to nutrient‐ and energy‐dependent signals. It activates PKC‐α and Akt and regulates the actin cytoskeleton. Deregulation of the mTOR‐signalling pathway (PI3K amplification/mutation, PTEN loss of function, Akt overexpression, and S6K1, 4EBP1 and eIF4E overexpression) is common in cancer, and alterations in components of the mTOR pathway have a major role in tumour progression. Therefore, mTOR is an appealing therapeutic target in many tumours. Here we summarize the upstream regulators and downstream effectors of the mTORC1 and mTORC2 pathways, the role of mTOR in cancer, and the potential therapeutic values and issues related to the novel agents targeting the mTOR‐signalling pathway.

Evidence for Bone Marrow Adult Stem Cell Plasticity: Properties, Molecular Mechanisms, Negative Aspects, and Clinical Applications of Hematopoietic and Mesenchymal Stem Cells Transdifferentiation

In contrast to the pluripotent embryonic stem cells (ESCs) which are able to give rise to all cell types of the body, mammalian adult stem cells (ASCs) appeared to be more limited in their differentiation potential and to be committed to their tissue of origin. Recently, surprising new findings have contradicted central dogmas of commitment of ASCs by showing their plasticity to differentiate across tissue lineage boundaries, irrespective of classical germ layer designations. The present paper supports the plasticity of the bone marrow stem cells (BMSCs), bringing the most striking and the latest evidences of the transdifferentiation properties of the bone marrow hematopoietic and mesenchymal stem cells (BMHSCs, and BMMSCs), the two BM populations of ASCs better characterized. In addition, we report the possible mechanisms that may explain these events, outlining the clinical importance of these phenomena and the relative problems.

Angiogenesis and progression in human melanoma.

In tumor growth, angiogenesis, the process of new-formation of blood vessels from pre-existing ones, is uncontrolled and unlimited in time. The vascular phase is characterized by the new-formation of vascular channels that enhances tumor cell proliferation, local invasion and hematogenous metastasis. Human malignant melanoma is a highly metastatic tumor with poor prognosis, and high resistance to treatment. Parallel with progression, melanoma acquires a rich vascular network, whereas an increasing number of tumor cells express the laminin receptor, which enables their adhesion to the vascular wall, favouring tumor cell extravasation and metastases. Melanoma neovascularization has been correlated with poor prognosis, overall survival, ulceration and increased rate of relapse. Secretion of various angiogenic cytokines, i.e. VEGF-A, FGF-2, PGF-1 and -2, IL-8, and TGF-1 by melanoma cells promote the angiogenic switch and has been correlated to transition from the radial to the vertical growth phase, and to the metastatic phase. Moreover, melanoma cells overexpress αvβ3, αvβ5, α2β1 and α5β1 integrins and release, together with stromal cells, higher amount of metalloproteases that increasing their invasive potential and angiogenesis. Basing on these observations, different molecular targets of antiangiogenic molecules has be recognized and various antiangiogenic agents are currently in preclinical and clinical trials for melanoma.

Multiple Myeloma Macrophages: Pivotal Players in the Tumor Microenvironment

Tumor microenvironment is essential for multiple myeloma (MM) growth, progression, and drug resistance through provision of survival signals and secretion of growth and proangiogenic factors. This paper examines the importance of macrophages within MM bone marrow (BM) microenvironment, referred to as MM-associated macrophages, as a potential niche component that supports tumor plasma cells. These macrophages are derived from peripheral blood monocytes recruited into the tumor. Upon activation by MM plasma cells and mesenchymal stromal cells, macrophages can release growth factors, proteolytic enzymes, cytokines, and inflammatory mediators that promote plasma cell growth and survival. Macrophages promote tumor progression through several mechanisms including angiogenesis, growth, and drug resistance. Indeed, these macrophages are essential for the induction of an angiogenic response through vasculogenic mimicry, and this ability proceeds in step with progression of the plasma cell tumors. Data suggest that macrophages play an important role in the biology and survival of patients with MM, and they may be a target for the MM antivascular management.

Angiogenesis in Multiple Myeloma

Angiogenesis is a constant hallmark of multiple myeloma progression and has prognostic potential. Multiple myeloma cells interact with surrounding host cells and extracellular matrix, this crosstalk affecting the most important aspects of the malignant phenotype, both at primary and secondary tumor sites. The pathophysiology of multiple myeloma-induced angiogenesis involves both direct production of angiogenic cytokines by plasma cells and their induction within the bone marrow microenvironment cells. A direct involvement of bone marrow macrophages and mast cells in vasculogenic mimicry has been demonstrated, thus contributing together with circulating endothelial cells and endothelial precursor cells to the multiple myeloma neovascularization. The role of host cells or the niche microenvironment and extracellular matrix represents an intense area of research, finalized at a better understanding of the pathophysiological modifications of the complete tumor entity, i.e. malignant cells and microenvironment.

Novel agents and new therapeutic approaches for treatment of multiple myeloma

This review summarizes the therapeutic strategies and the drugs actually in development for the management of myeloma patients. Multiple myeloma is caused by the expansion of monoclonal plasma cells and secretion of M-protein (immunoglobulins, Bence Jones protein and free light chains). Multiple myeloma still remains an incurable disease with a high incidence rate in the elderly, despite the introduction of several new therapeutic agents (bortezomib, lenalidomide and thalidomide) which have changed its natural history. The high heterogeneity of this disease leads to large differences in clinical responses to treatments. Thus, the choice of the best treatment is a difficult issue. However, the introduction of new drugs has made it possible to achieve high response rates and good quality responses with long-term disease control. Interactions between tumor cells and their bone marrow microenvironment play a pivotal role in the development, maintenance, and progression of myeloma, inducing also drug resistance. These knowledges have improved treatment options, leading to the approval of new drugs which not only target the malignant cell itself, but also its microenvironment. These agents are in preclinical/early clinical evaluation and they appear to further improve disease control, but their use is still not approved outside of clinical trials.

High-dose thiotepa, etoposide and carboplatin as conditioning regimen for autologous stem cell transplantation in patients with high-risk Hodgkin’s lymphoma

Abstract Background: Autologous stem cell transplantation (ASCT) generally provides good results in Hodgkin’s lymphoma (HL). We studied a high-dose chemotherapy regimen based on thiotepa, etoposide and carboplatin (TECA). Methods: Fifty-eight patients with advanced HL were treated with thiotepa, etoposide and carboplatin for transplant induction. Results: The overall response rate was 79·3% (39 CR: 67·2%; and 7 PR: 12·1%); 12 patients (20·1%) were non-responders. The 5-year overall survival rate was 77·6%; five initially responder patients relapsed within the first 5 years of follow-up and underwent salvage therapy. Conclusion: The TECA conditioning regimen for ASCT in HL results in a good anti-HL effect, positive response to treatment and high 5-year overall survival rate. It was also well tolerated and did not induce excessive toxicity, suggesting that TECA may be a very useful conditioning regimen for HL.

Filgrastim, lenograstim and pegfilgrastim in the mobilization of peripheral blood progenitor cells in patients with lymphoproliferative malignancies.

Patients with lymphoproliferative disorders, candidate to autologous stem cell transplantation (ASCT), require mobilization with chemotherapy and granulocyte colony -stimulating factor (G-CSF). This study looked for differences in hematopoietic peripheral stem cells (HPSCs) mobilization in response to the three available G-CSFs, namely lenograstim, filgrastim, and pegfilgrastim. Between 2000 and 2012, 146 patients (66 M and 80 F) who underwent ASCT for multiple myeloma, non-Hodgkin’s lymphoma or Hodgkin’s lymphoma were studied. All patients received induction therapy and then a mobilization regimen with cyclophosphamide plus lenograstim, or filgrastim, or pegfilgrastim. From days 12 to 14, HPSCs were collected by two to three daily leukaphereses. Our results show that high-dose cyclophosphamide plus lenograstim achieved adequate mobilization and the collection target more quickly and with fewer leukaphereses as compared to filgrastim and pegfilgrastim. No differences between the three regimens were observed regarding toxicity and days to WBC and platelet recovery. Thus, lenograstim may represent the ideal G-CSF for PBSC mobilization in patients with lymphoproliferative diseases. Further studies are needed to confirm these results and better understand the biological bases of these differences.

Functional and biological role of endothelial precursor cells in tumour progression: A new potential therapeutic target in haematological malignancies

It was believed that vasculogenesis occurred only during embryo life and that postnatal formation of vessels arose from angiogenesis. Recent findings demonstrate the existence of Endothelial Precursor Cells (EPCs), which take partin postnatal vasculogenesis. EPCs are recruited from the bone marrow under the stimulation of growth factors and cytokines and reach the sites of neovascularization in both physiological and pathological conditions such as malignancies where they contribute to the “angiogenic switch” and tumor progression. An implementation of circulating EPCs in the bloodstream of patients with haematological malignancies has been demonstrated. This increase is strictly related to the bone marrow microvessel density and correlated with a poor prognosis. The EPCs characterization is a very complex process and still under investigation. This literature review aims to provide an overview of the functional and biological role of EPCs in haematological malignancies and to investigate their potential as a new cancer therapeutic target.

Pharmacological Activation of Protein Phosphatase 2 A (PP2A): A Novel Strategy to Fight Against Human Malignancies?

BACKGROUND The serine-threonine protein phosphatase 2A (PP2A) regulates multiple cell signaling cascades and its inactivation by viral oncoproteins, mutation of specific structural subunits or upregulation of the cellular endogenous inhibitors may contribute to malignant transformation by regulating specific phosphorylation events. Pharmacological modulation of PP2A activity is becoming an attractive strategy for cancer treatment. Some compounds targeting PP2A are able to induce PP2A reactivation and subsequent cell death in several types of cancer. METHODS We undertook a search of bibliographic databases for peer-reviewed articles focusing on the main item of the review. We selected articles published in indexed journals. The quality of retrieved papers was appraised using the standard bibliometric indicators. RESULTS One hundred and fourteen papers were included in the review. Twenty-seven papers gave an overview of structure and physiological role of PP2A. Twenty-five papers outlined the role of PP2A in tumor suppression. Forty papers analyzed the mechanism involved in PP2A reactivation by synthetic compounds, and twenty-two papers outlined the capability of natural compounds of restoring PP2A activity and how this could be beneficial. CONCLUSION Findings analyzed in this review underline the central role of PP2A as a regulator of cell growth and survival, hence its function as tumor suppressor. The discovery that some compounds, either synthetic or natural, are capable of reactivating PP2A opens up new perspectives for future strategies to fully exploit therapeutic potential in human cancer. Thus, this review could also be of particular interest to pharmaceutical or biotechnology companies for drug design and targeted delivery.