Recent advances in cancer stem/progenitor cell research: therapeutic implications for overcoming resistance to the most aggressive cancers

Cancer stem cell markers in common cancers - therapeutic implications

Rapid advances in the cancer stem cell (CSC) field have provided cause for optimism for the development of more reliable cancer therapies in the future. Strategies aimed at efficient targeting of CSCs are becoming important for monitoring the progress of cancer therapy and for evaluating new therapeutic approaches. Here, we characterize and compare the specific markers that have been found to be present on stem cells, cancer cells and CSCs in selected tissues (colon, breast, liver, pancreas and prostate). We then discuss future directions of this intriguing new research field in the context of new diagnostic and therapeutic opportunities.

Integrins in prostate cancer progression

Integrins, which are transmembrane receptors for extracellular matrix proteins, play a key role in cell survival, proliferation, migration, gene expression, and activation of growth factor receptors. Their functions and expression are deregulated in several types of cancer, including prostate cancer. In this article, we review the role of integrins in prostate cancer progression and their potential as therapeutic targets.

Stem cells, a two-edged sword: Risks and potentials of regenerative medicine

The recent advancements in stem cell (SC) biology have led to the concept of regenerative medicine, which is based on the potential of SC for therapies aimed to facilitate the repair of degenerating or injured tissues. Nonetheless, prior to large scale clinical applications, critical aspects need to be further addressed, including the long-term safety, tolerability, and efficacy of SC-based treatments. Most problematic among the risks of SC-based therapies, in addition to the possible rejection or loss of function of the infused cells, is their potential neoplastic transformation. Indeed, SCs may be used to cure devastating diseases, but their specific properties of self-renewal and clonogenicity may render them prone to generate cancers. In this respect, ‘Stemness’ might be seen as a two-edged sword, its bright side being represented by normal SCs, its dark side by cancer SCs. A better understanding of SC biology will help fulfill the promise of regenerative medicine aimed at curing human pathologies and fighting cancer from its roots.

Exploring the role of cancer stem cells in radioresistance

Radiobiological research over the past decades has provided evidence that cancer stem cell content and the intrinsic radiosensitivity of cancer stem cells varies between tumours, thereby affecting their radiocurability. Translation of this knowledge into predictive tests for the clinic has so far been hampered by the lack of methods to discriminate between stem cells and non-stem cells. New technologies allow isolation of cells expressing specific surface markers that are differentially expressed in tumour cell subpopulations that are enriched for cancer stem cells. Combining these techniques with functional radiobiological assays holds the potential to elucidate the role of cancer stem cells in radioresistance in individual tumours, and to use this knowledge for the development of predictive markers for optimization of radiotherapy.

Uveal vs. cutaneous melanoma. Origins and causes of the differences

Melanoma is a malignant tumour derived from melanocytes (dendritic cells originated from the neural crest and capable to produce melanin synthesis) that could be established on the skin or less frequently on the uvea. The cellular origin from both kind of melanoma seems to be the same but the melanocytes migrates to the epithelia for cutaneous melanoma, while for uveal melanoma, they migrate to mesodermic tissues. Despite the common origin, both melanomas show extreme differences in their metastatic potential, clinical response to treatments, immune response and genetic alterations. We will describe some of those differences in this review.

Stem cell-based therapy in gastroenterology and hepatology

Protagonists of a new scientific era, stem cells are promising tools on which regenerative medicine relies for the treatment of human pathologies. Stem cells can be obtained from various sources, including embryos, fetal tissues, umbilical cord blood, and also terminally differentiated organs. Once forced to expand and differentiate into functional progenies, stem cells may become suitable for cell replacement and tissue engineering. The manipulation and/or stimulation of adult stem cells seems to be particularly promising, as it could improve the endogenous regenerative potential without risks of rejection and overcome the ethical and political issues related to embryonic stem cell research. Stem cells are already leaving the bench and reaching the bedside, despite an incomplete knowledge of the genetic control program driving their fate and plasticity. In gastroenterology and hepatology, the first attempts to translate stem cell basic research into novel therapeutic strategies have been made for the treatment of several disorders, such as inflammatory bowel diseases, diabetes mellitus, celiachy and acute or chronic hepatopaties. Nonetheless, critical aspects need to be further addressed, including the long-term safety, tolerability and efficacy of cell-based treatments, as well as their carcinogenic potential. Aim of this review is to summarize the state-of-the-arts on gastrointestinal and hepatic stem cells and on stem cell-based therapies in gastroenterology and hepatology, highlighting both the benefits and the potential risks of these new tools for the treatment and prevention of human diseases.

Cancer stem cells in breast: current opinion and future challenges

There is increasing evidence for the cancer stem cell hypothesis, which holds that cancers are driven by a cellular subcomponent that has stem cell properties, that is, self-renewal, tumorigenicity and multilineage differentiation capacity. The cancer stem cell hypothesis modifies our conceptual approach of oncogenesis and shall have implications in breast cancer prevention, detection and treatment, especially in metastatic breast cancer for which no curative treatment exists. Given the specific stem cell features, novel therapeutic pathways can be targeted. Following this approach, new molecules are currently in development. Focusing on the cross-talk between stem cells and their microenvironment is also a promising way to explore how to better target cancer stem cells and be curative.

Functions of normal and malignant prostatic stem/progenitor cells in tissue regeneration and cancer progression and novel targeting therapies

This review summarizes the recent advancements that have improved our understanding of the functions of prostatic stem/progenitor cells in maintaining homeostasis of the prostate gland. We also describe the oncogenic events that may contribute to their malignant transformation into prostatic cancer stem/progenitor cells during cancer initiation and progression to metastatic disease stages. The molecular mechanisms that may contribute to the intrinsic or the acquisition of a resistant phenotype by the prostatic cancer stem/progenitor cells and their differentiated progenies with a luminal phenotype to the current therapies and disease relapse are also reviewed. The emphasis is on the critical functions of distinct tumorigenic signaling cascades induced through the epidermal growth factor system, hedgehog, Wnt/beta-catenin, and/or stromal cell-derived factor-1/CXC chemokine receptor-4 pathways as well as the deregulated apoptotic signaling elements and ATP-binding cassette multidrug transporter. Of particular therapeutic interest, we also discuss the potential beneficial effects associated with the targeting of these signaling elements to overcome the resistance to current treatments and prostate cancer recurrence. The combined targeted strategies toward distinct oncogenic signaling cascades in prostatic cancer stem/progenitor cells and their progenies as well as their local microenvironment, which could improve the efficacy of current clinical chemotherapeutic treatments against incurable, androgen-independent, and metastatic prostate cancers, are also described.

Targeting of cancer stem/progenitor cells plus stem cell-based therapies: the ultimate hope for treating and curing aggressive and recurrent cancers

The rapid progression from aggressive primary cancers into locally advanced and invasive and/or metastatic diseases remains a big obstacle for an early diagnosis and curative therapeutic intervention for cancer patients. The late-stage leukemias and disseminated and metastatic sarcomas, melanomas, brain tumors and epithelial cancers are the devastating diseases associated with a high rate of recurrence after treatment with the conventional clinical therapies including surgery, ionizing radiation, hormonal therapy and systemic chemotherapy, which generally lead to the death of patients. Therefore, the establishment of the molecular events underlying cancer initiation and progression into locally invasive and metastatic diseases is of major interest in basic cancer research as well as for the development of new effective clinical therapeutic options against the recurrent and lethal cancers. Recent advances have led to the identification of specific oncogenic products that are implicated in the malignant transformation of adult stem/progenitor cells into leukemic or tumorigenic and migrating cancer stem/progenitor cells during cancer progression. Of therapeutic interest, the molecular targeting of deregulated signaling elements in cancer stem/progenitor cells and their local microenvironment represents a new potential strategy for the development of more effective clinical treatments against aggressive cancers. Particularly, the combined use of chemotherapeutic drugs to eradicate cancer-initiating cells with hematopoietic stem cell or genetically-modified stem cell transplant is emerging as potential cancer treatments that hold great promise in the area of clinical cancer research. These targeting and stem cell-based therapies may offer the ultimate hope for treating and even curing the patients diagnosed with locally advanced cancers at high risk of recurrence, metastatic and/or relapsed cancers in the clinics.

PUMA expression in pancreatic cancer and its clinical significance

AIM: To investigate the role of PUMA in development of pancreatic cancer (PC) and its mechanism as well as its correlation with P53 up-regulate dmodulator of apoptosis (PUMA) expression and clinicopathologic parameters.

METHODS: Expression of PUMA, P53 and Bcl-2 in 60 PC tissue samples and 19 normal pancreatic tissue samples was assessed with immunohistochemical Envision method. Apoptosis index (AI) was detected with TUNEL method. Correlations between expressions of P53 up-regulated modulator of apoptosis (PUMA), P53, Bcl-2, AI and clinicopathologic parameters were analyzed.

RESULTS: The positive rate of PUMA expression was significantly lower in PC tissue samples than in normal pancreatic tissue samples (30% vs 52.6%, P < 0.05). The PUMA expression was correlated with tumor size, lymph node and distant metastasis (P < 0.05), but not with any other clinical or pathological parameters. The AI of positive and negative PUMA expression in PC tissue samples was 20.63% ± 6.27% and 17.44% ± 5.86%, respectively (P < 0.05). The positive rate of P53 and Bcl-2 expression in PC tissue samples was 46.7% (28/60) and 41.7% (25/60), respectively. Expression of PUMA was closely related with that of Bcl-2 and P53 in PC tissue samples (P < 0.05).

CONCLUSION: Absent PUMA expression in PC tissue is related with the development of PC and lymph node and distant metastasis. PUMA may be a new target for the treatment of PC.

Improvement of cytotoxic effects induced by mitoxantrone on hormone-refractory metastatic prostate cancer cells by co-targeting epidermal growth factor receptor and hedgehog signaling cascades

The results of the present study revealed for the first time the possibility to use a combination of mitoxantrone with gefitinib and cyclopamine for inhibiting the growth of epidermal growth factor (EGF), sonic hedgehog- (SHHNp), and serum-stimulated androgen-sensitive LNCaP-C33 and androgen-independent (AI) LNCaP-C81, DU145 and PC3 prostate cancer (PC) cells. The supra-additive anti-proliferative effects of drugs were mediated via a blockade of the PC3 cells in the G(1) and G(2)M phases of the cell cycle. Importantly, the combination of mitoxantrone plus gefitinib and/or cyclopamine also caused a higher rate of apoptotic death of PC cells including enriched fraction of CD44(high) PC3 cell subpopulation as compared to the individual agents or bi-combination of drugs. The cytotoxic effects induced by mitoxantrone, gefitinib and cyclopamine on PC3 cells appear to be at least partly mediated through the depolarization of the mitochondrial membrane, release of cytochrome c into the cytosol, hydrogen peroxide production and activation of caspase cascades. These findings indicate that the simultaneous blockade of EGF-EGFR and sonic hedgehog tumorigenic signaling cascades may represent a promising strategy for improving the efficacy of current mitoxantrone-based therapies against incurable AI and metastatic PCs in the clinics.