Cancer stem cells: are they responsible for treatment failure?

AML chemoresistance: The role of mutant TP53 subclonal expansion and therapy strategy

Acute myeloid leukemia (AML) is a heterogeneous clonal disease characterized by the proliferation and accumulation of myeloid blast cells in the bone marrow, which eventually lead to hematopoietic failure. Chemoresistance presents as a major burden for therapy of AML patients. p53 is the most important tumor suppressor protein that regulates cellular response to various stress. It is also important for hematopoietic stem cell development and hematopoiesis. Mutation or deletion of TP53 has been found to be linked to cancer progression, therapy-related resistance, and poor prognosis. TP53 mutation occurs in less than 10% of AML patients; however, it represents a subset of AML with therapy resistance and poor outcome. In addition, there is a subgroup of patients with low-frequency TP53 mutations. The percentage ranges from 1% to 3% of all AML patients. These patients have outcomes comparable to those of the high-frequency TP53 mutation patients. TP53-mutated clones isolated from the parental cells exhibit a survival advantage under drug treatment compared with cells with wild-type TP53, and have a higher population of leukemia stem cell (LSC) marker-positive cells, a characteristic of chemo-resistant cells. Therefore, low-frequency TP53 mutation, which is currently underappreciated, is an important prognosis factor for AML patients. Epigenetic drugs, such as hypomethylating agent and histone deacetylase inhibitors, have been found effective in targeting TP53-mutated AML. Histone deacetylase inhibitors can preferentially target the TP53-mutated subpopulation by reactivating p53-targeted genes and by eradicating LSC marker-positive cells. Therefore, combined treatment with epigenetic drugs may represent a new therapeutic strategy for treatments of TP53-mutated AML.

Synergistic Anticancer Effects of Curcumin and Hinokitiol on Gefitinib Resistant Non-Small Cell Lung Cancer Cells

This study evaluated the synergistic effect of curcumin (diferuloylmethane) and hinokitiol (β-thujaplicin), natural product derived phytochemicals, on gefitinib (Iressa) resistant non-small cell lung cancer (NSCLC) cells. Gefitinib, a tyrosine kinase inhibitor targeting epidermal growth factor receptor (EGFR), is widely used for lung cancer treatment. However, gefitinib resistance is easily acquired by NSCLC and followed by the development of progressive disease. Curcumin and hinokitiol are well-known bioactive compounds demonstrating anti-inflammation, anti-bacteria and anticancer effects. However, the effects of co-treatment of curcumin and hinokitiol on cancer cells have not been reported. Here, we postulated, for the first time, the possibility of combination therapy with curcumin and hinokitiol for treatment of gefitinib resistant NSCLC via increment of apoptosis and lysosomal enlargement.

Histone deacetylase inhibitor targets CD123/CD47-positive cells and reverse chemoresistance phenotype in acute myeloid leukemia

Chemoresistance may be due to the survival of leukemia stem cells (LSCs) that are quiescent and not responsive to chemotherapy or lie on the intrinsic or acquired resistance of the specific pool of AML cells. Here, we found, among well-established LSC markers, only CD123 and CD47 are correlated with AML cell chemosensitivities across cell lines and patient samples. Further study reveals that percentages of CD123⁺CD47⁺ cells significantly increased in chemoresistant lines compared to parental cell lines. However, stemness signature genes are not significantly increased in resistant cells. Instead, gene changes are enriched in cell cycle and cell survival pathways. This suggests CD123 may serve as a biomarker for chemoresistance, but not stemness of AML cells. We further investigated the role of epigenetic factors in regulating the survival of chemoresistant leukemia cells. Epigenetic drugs, especially histone deacetylase inhibitors (HDACis), effectively induced apoptosis of chemoresistant cells. Furthermore, HDACi Romidepsin largely reversed gene expression profile of resistant cells and efficiently targeted and removed chemoresistant leukemia blasts in xenograft AML mouse model. More interestingly, Romidepsin preferentially targets CD123⁺ cells, while chemotherapy drug Ara-C mainly targeted fast-growing, CD123^- cells. Therefore, Romidepsin alone or in combination with Ara-C may be a potential treatment strategy for chemoresistant patients.

DNA Repair

Cellular chromosomal DNA is the principal target through which ionising radiation exerts it diverse biological effects. This chapter summarises the relevant DNA damage signalling and repair pathways used by normal and tumour cells in response to irradiation. Strategies for tumour radiosensitisation are reviewed which exploit tumour-specific DNA repair deficiencies or signalling pathway addictions, with a special focus on growth factor signalling, PARP, cancer stem cells, cell cycle checkpoints and DNA replication. This chapter concludes with a discussion of DNA repair-related candidate biomarkers of tumour response which are of crucial importance for implementing precision medicine in radiation oncology.

Guanylate cyclase C as a target for prevention, detection, and therapy in colorectal cancer

INTRODUCTION

Colorectal cancer remains the second leading cause of cancer death in the United States, and new strategies to prevent, detect, and treat the disease are needed. The receptor, guanylate cyclase C (GUCY2C), a tumor suppressor expressed by the intestinal epithelium, has emerged as a promising target. Areas covered: This review outlines the role of GUCY2C in tumorigenesis, and steps to translate GUCY2C-targeting schemes to the clinic. Endogenous GUCY2C-activating ligands disappear early in tumorigenesis, silencing its signaling axis and enabling transformation. Pre-clinical models support GUCY2C ligand supplementation as a novel disease prevention paradigm. With the recent FDA approval of the GUCY2C ligand, linaclotide, and two more synthetic ligands in the pipeline, this strategy can be tested in human trials. In addition to primary tumor prevention, we also review immunotherapies targeting GUCY2C expressed by metastatic lesions, and platforms using GUCY2C as a biomarker for detection and patient staging. Expert commentary: Results of the first GUCY2C targeting schemes in patients will become available in the coming years. The identification of GUCY2C ligand loss as a requirement for colorectal tumorigenesis has the potential to change the treatment paradigm from an irreversible disease of genetic mutation, to a treatable disease of ligand insufficiency.

The many faces of SRPK1

Serine–arginine protein kinase 1 (SRPK1) phosphorylates proteins involved in the regulation of several mRNA‐processing pathways, including alternative splicing. SRPK1 has been recently reported to be overexpressed in multiple cancers, including prostate cancer, breast cancer, lung cancer, and glioma. Several studies have shown that inhibition of SRPK1 has anti‐tumoural effects, and SRPK1 has therefore become a new candidate for targeted therapies. Interestingly, in terms of molecular mechanism, SRPK1 seems to act heterogeneously, and has been reported to affect several processes in different cancers, e.g. angiogenesis in prostate and colon cancer, apoptosis in breast and colon cancer, and migration in breast cancer. A recent report adds to this puzzle, showing that the main effect of SRPK1 overexpression in non‐small‐cell lung carcinoma is to stimulate a stem cell‐like phenotype. This pleiotropy might be related to preferential activation of different downstream signalling pathways by SRPK1 in various cancers. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Linked Article: Gong et al. J Pathol 2016; 240: 184‐196.

Predictive significance of DNA damage and repair biomarkers in triple-negative breast cancer patients treated with neoadjuvant chemotherapy: An exploratory analysis

Response of cancer cells to chemotherapy-induced DNA damage is regulated by the ATM-Chk2 and ATR-Chk1 pathways. We investigated the association between phosphorylated H2AX (γ-H2AX), a marker of DNA double-strand breaks that trigger the ATM-Chk2 cascade, and phosphorylated Chk1 (pChk1), with pathological complete response (pCR) in triple-negative breast cancer (TNBC) patients treated with neoadjuvant chemotherapy. γ-H2AX and pChk1 were retrospectively assessed by immunohistochemistry in a series of pretreatment biopsies related to 66 patients. In fifty-three tumors hormone receptor status was negative in both the diagnostic biopsies and residual cancers, whereas in 13 cases there was a slight hormone receptor expression that changed after chemotherapy. Internal validation was carried out. In the entire cohort elevated levels of γ-H2AX, but not pChk1, were associated with reduced pCR rate (p = 0.009). The association tested significant in both uni- and multivariate logistic regression models (OR 4.51, 95% CI: 1.39–14.66, p = 0.012, and OR 5.07, 95% CI: 1.28–20.09, p = 0.021, respectively). Internal validation supported the predictive value of the model. The predictive ability of γ-H2AX was further confirmed in the multivariate model after exclusion of tumors that underwent changes in hormone receptor status during chemotherapy (OR 7.07, 95% CI: 1.39–36.02, p = 0.018). Finally, in residual diseases a significant decrease of γ-H2AX levels was observed (p < 0.001). Overall, γ-H2AX showed ability to predict pCR in TNBC and deserves larger, prospective studies.

Serine-arginine protein kinase 1 promotes a cancer stem cell-like phenotype through activation of Wnt/β-catenin signalling in NSCLC

Cancer stem cells (CSCs) are commonly associated with cancer recurrence and metastasis that occurs in up to 30-55% of non-small-cell lung carcinoma (NSCLC) patients. Herein, we showed that serine-arginine protein kinase 1 (SRPK1) was highly expressed at both the mRNA and the protein levels in human NCSLC. SRPK1 was associated with the clinical features of human NSCLC, including clinical stage (p < 0.001) and T (p = 0.001), N (p = 0.007), and M (p = 0.001) classifications. Ectopic overexpression of SRPK1 promoted the acquisition of a stem cell-like phenotype in human NSCLC cell lines cultured in vitro. Overexpression of SRPK1 increased sphere formation and the proportion of side-population cells that exclude Hoechst dye. Conversely, SRPK1 silencing reduced the number of spheres and the proportion of side-population cells. Mouse studies indicated that SRPK1 promoted NSCLC cell line tumour growth and SRPK1 overexpression reduced the number of tumour cells required to initiate tumourigenesis in vivo. Mechanistically, gene set enrichment analysis showed that Wnt/β-catenin signalling correlated with SRPK1 mRNA levels and this signalling pathway was hyperactivated by ectopic SRPK1 expression in NSCLC cell lines. Immunofluorescence demonstrated that SRPK1 enhanced β-catenin accumulation in the nuclei of NSCLC cell lines, and inhibition of β-catenin signalling abrogated the SRPK1-induced stem cell-like phenotype. Together, our findings suggest that SRPK1 promotes a stem cell-like phenotype in NSCLC via Wnt/β-catenin signalling. Moreover, SRPK1 may represent a novel target for human NSCLC diagnosis and therapy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Endocytosis and serpentine filopodia drive blebbishield-mediated resurrection of apoptotic cancer stem cells

The blebbishield emergency program helps to resurrect apoptotic cancer stem cells (CSCs) themselves. Understanding the mechanisms behind this program is essential to block resurrection of CSCs during cancer therapy. Here we demonstrate that endocytosis drives serpentine filopodia to construct blebbishields from apoptotic bodies and that a VEGF-VEGFR2-endocytosis-p70S6K axis governs subsequent transformation. Disengagement of RalGDS from E-cadherin initiates endocytosis of RalGDS and its novel interaction partners cdc42, VEGFR2, cleaved β-catenin, and PKC-ζ as well as its known interaction partner K-Ras. We also report novel interactions of p45S6K (cleaved p70S6K) and PKM-ζ with PAK-1 filopodia-forming machinery specifically in blebbishields. Thus, a RalGDS-endocytosis-filopodia-VEGFR2-K-Ras-p70S6K axis drives the blebbishield emergency program, and therapeutic targeting of this axis might prevent resurrection of CSCs during cancer therapy.

Biomarkers and signaling pathways of colorectal cancer stem cells

The progression of colorectal cancer is commonly characterized by accumulation of genetic or epigenetic abnormalities, altering regulation of gene expression as well as normal protein structures and functions. Nonetheless, there are some questions that remain to be elucidated, such as the origin of cancer cells and populations of cells initiating and propagating tumor development. Currently, there are two rival theories describing the process of carcinogenesis. One is the stochastic model, arguing that any cell is capable of initiating and triggering the development of cancer. Meanwhile, the cancer stem cell model hypothesizes that only a small fraction of stem cells possesses cancer-promoting properties. Typically, colorectal cancer stem cells (CSCs) share the same molecular signaling profiles with normal stem cells or embryonic stem cells, such as Wnt, Notch, TGF-β, and Hedgehog. Nevertheless, CSCs differ from normal stem cells and the bulk of tumor cells in their tumorigenic potential and susceptibility to chemotherapeutic drugs. This may be a possible explanation of the high percentage of cancer recurrence in patients who underwent chemotherapeutic treatment and surgery. This review article focuses on the colorectal cancer stem cell biomarkers and the role of upregulated signaling pathways implicated in the initiation and progression of colorectal cancer.