Targeting cancer stem cell propagation with palbociclib, a CDK4/6 inhibitor: Telomerase drives tumor cell heterogeneity

The crosstalk between glucose metabolism and telomerase regulation in cancer

Accumulated alterations in metabolic control provide energy and anabolic demands for enhanced cancer cell proliferation. Exemplified by the Warburg effect, changes in glucose metabolism during cancer progression are widely recognized as a characteristic of metabolic disorders. Since telomerases are a vital factor in maintaining DNA integrity and stability, any damage threatening telomerases could have a severe impact on DNA and, subsequently, whole-cell homeostasis. However, it remains unclear whether the regulation of glucose metabolism in cancer is connected to the regulation of telomerase. In this review, we present the latest insights into the crosstalk between telomerase function and glucose metabolism in cancer cells. However, at this moment this subject is not well investigated that the association is mostly indirectly regulations and few explicit regulating pathways were identified between telomerase and glucose metabolism. Therefore, the information presented in this review can provide a scientific basis for further research on the detail mechanism and the clinical application of cancer therapy, which could be valuable in improving the effectiveness of chemotherapy.

An Update on Stiripentol Mechanisms of Action: A Narrative Review

Stiripentol (Diacomit®) (STP) is an orally active antiseizure medication (ASM) indicated as adjunctive therapy, for the treatment of seizures associated with Dravet syndrome (DS), a severe form of childhood epilepsy, in conjunction with clobazam and, in some regions valproic acid. Since the discovery of STP, several mechanisms of action (MoA) have been described that may explain its specific effect on seizures associated with DS. STP is mainly considered as a potentiator of gamma-aminobutyric acid (GABA) neurotransmission: (i) via uptake blockade, (ii) inhibition of degradation, but also (iii) as a positive allosteric modulator of GABAA receptors, especially those containing α3 and δ subunits. Blockade of voltage-gated sodium and T-type calcium channels, which is classically associated with anticonvulsant and neuroprotective properties, has also been demonstrated for STP. Finally, several studies indicate that STP could regulate glucose energy metabolism and inhibit lactate dehydrogenase. STP is also an inhibitor of several cytochrome P450 enzymes involved in the metabolism of other ASMs, contributing to boost their anticonvulsant efficacy as add-on therapy. These different MoAs involved in treatment of DS and recent data suggest a potential for STP to treat other neurological or non-neurological diseases.

A cell cycle centric view of tumour dormancy

Tumour dormancy and recurrent metastatic cancer remain the greatest clinical challenge for cancer patients. Dormant tumour cells can evade treatment and detection, while retaining proliferative potential, often for years, before relapsing to tumour outgrowth. Cellular quiescence is one mechanism that promotes and maintains tumour dormancy due to its central role in reducing proliferation, elevating cyto-protective mechanisms, and retaining proliferative potential. Quiescence/proliferation decisions are dictated by intrinsic and extrinsic signals, which regulate the activity of cyclin-dependent kinases (CDKs) to modulate cell cycle gene expression. By clarifying the pathways regulating CDK activity and the signals which activate them, we can better understand how cancer cells enter, maintain, and escape from quiescence throughout the progression of dormancy and metastatic disease. Here we review how CDK activity is regulated to modulate cellular quiescence in the context of tumour dormancy and highlight the therapeutic challenges and opportunities it presents.

CDK7-YAP-LDHD axis promotes D-lactate elimination and ferroptosis defense to support cancer stem cell-like properties

Reprogrammed cellular metabolism is essential for maintaining cancer stem cells (CSCs) state. Here, we report that mitochondrial D-lactate catabolism is a necessary initiating oncogenic event during tumorigenesis of esophageal squamous cell carcinoma (ESCC). We discover that cyclin-dependent kinase 7 (CDK7) phosphorylates nuclear Yes-associated protein 1 (YAP) at S127 and S397 sites and enhances its transcription function, which promotes D-lactate dehydrogenase (LDHD) protein expression. Moreover, LDHD is enriched significantly in ESCC-CSCs rather than differentiated tumor cells and high LDHD status is connected with poor prognosis in ESCC patients. Mechanistically, the CDK7-YAP-LDHD axis helps ESCC-CSCs escape from ferroptosis induced by D-lactate and generates pyruvate to satisfy energetic demands for their elevated self-renewal potential. Hence, we conclude that esophageal CSCs adopt a D-lactate elimination and pyruvate accumulation mode dependent on CDK7-YAP-LDHD axis, which drives stemness-associated hallmarks of ESCC-CSCs. Reasonably, targeting metabolic checkpoints may serve as an effective strategy for ESCC therapy.

Fumagillin regulates stemness and malignancies in cancer stem-like cells derived from liver cancer via targeting to MetAP-2

BACKGROUND

Cancer relapse is associated with the presence of cancer stem-like cells (CSCs), which lead to multidirectional differentiation and unrestricted proliferative replication. Fumagillin, a myocotoxin produced by the saprophytic filamentous fungus Aspergillus fumigatus, has been reported to affect malignant characteristics in hepatocellular cancer cells. However, its exact role in CSCs is still unknown.

METHODS

CSCs were enriched by culturing cancer cells in serum-free medium. The effects of fumagillin on malignant cell characteristics and mitochondrial function were measured. The regulatory role of fumagillin on methionine aminopeptidase-2 (MetAP-2) was assessed.

RESULTS

When it was supplemented in medium, fumagillin treatment inhibited sphere formation and the maintenance of stemness of CSCs without disturbing cell growth. Fumagillin also decreased stemness-related markers and the aldehyde dehydrogenase 1 (ALDH1)-positive proportion, which demonstrated that fumagillin decreases stemness in CSCs. It was also found to inhibit malignant traits in CSCs, including cell proliferation, invasion, and tumor formation, and sensitize CSCs to chemoagents, including sorafenib and doxorubicin, by promoting chemoagent-induced apoptosis. Moreover, fumagillin treatment was found to disturb mitochondrial membrane homeostasis, ATP synthesis and mitochondrial transcriptional activity. In addition, we found that fumagillin decreased MetAP-2 protein levels and exerted anti-CSC effects potentially by regulating MetAP-2. We also found that fumagillin treatment activated p53 and its transcriptional activity and thus caused cell cycle blockade. Moreover, fumagillin treatment significantly decreased tumor formation in nude mice.

CONCLUSION

This work offers evidence for fumagillin as a specific inhibitor of liver cancer CSCs and proposes a novel strategy for cancer therapy.

Targeting Breast Cancer Stem Cells

The potential roles of breast cancer stem cells (BCSCs) in tumor initiation and recurrence have been recognized for many decades. Due to their strong capacity for self-renewal and differentiation, BCSCs are the major reasons for poor clinical outcomes and low therapeutic response. Several hypotheses on the origin of cancer stem cells have been proposed, including critical gene mutations in stem cells, dedifferentiation of somatic cells, and cell plasticity remodeling by epithelial-mesenchymal transition (EMT) and the tumor microenvironment. Moreover, the tumor microenvironment, including cellular components and cytokines, modulates the self-renewal and therapeutic resistance of BCSCs. Small molecules, antibodies, and chimeric antigen receptor (CAR)-T cells targeting BCSCs have been developed, and their applications in combination with conventional therapies are undergoing clinical trials. In this review, we focus on the features of BCSCs, emphasize the major factors and tumor environment that regulate the stemness of BCSCs, and discuss potential BCSC-targeting therapies.

Radiotherapeutic Strategies to Overcome Resistance of Breast Cancer Brain Metastases by Considering Immunogenic Aspects of Cancer Stem Cells

Breast cancer is the most diagnosed cancer in women, and symptomatic brain metastases (BCBMs) occur in 15-20% of metastatic breast cancer cases. Despite technological advances in radiation therapy (RT), the prognosis of patients is limited. This has been attributed to radioresistant breast cancer stem cells (BCSCs), among other factors. The aim of this review article is to summarize the evidence of cancer-stem-cell-mediated radioresistance in brain metastases of breast cancer from radiobiologic and radiation oncologic perspectives to allow for the better interpretability of preclinical and clinical evidence and to facilitate its translation into new therapeutic strategies. To this end, the etiology of brain metastasis in breast cancer, its radiotherapeutic treatment options, resistance mechanisms in BCSCs, and effects of molecularly targeted therapies in combination with radiotherapy involving immune checkpoint inhibitors are described and classified. This is considered in the context of the central nervous system (CNS) as a particular metastatic niche involving the blood-brain barrier and the CNS immune system. The compilation of this existing knowledge serves to identify possible synergistic effects between systemic molecularly targeted therapies and ionizing radiation (IR) by considering both BCSCs' relevant resistance mechanisms and effects on normal tissue of the CNS.

Targeting mitochondrial metabolism for metastatic cancer therapy

Primary tumors evolve metabolic mechanisms favoring glycolysis for adenosine triphosphate (ATP) generation and antioxidant defenses. In contrast, metastatic cells frequently depend on mitochondrial respiration and oxidative phosphorylation (OxPhos). This reliance of metastatic cells on OxPhos can be exploited using drugs that target mitochondrial metabolism. Therefore, therapeutic agents that act via diverse mechanisms, including the activation of signaling pathways that promote the production of reactive oxygen species (ROS) and/or a reduction in antioxidant defenses may elevate oxidative stress and inhibit tumor cell survival. In this review, we will provide (1) a mechanistic analysis of function-selective extracellular signal-regulated kinase-1/2 (ERK1/2) inhibitors that inhibit cancer cells through enhanced ROS, (2) a review of the role of mitochondrial ATP synthase in redox regulation and drug resistance, (3) a rationale for inhibiting ERK signaling and mitochondrial OxPhos toward the therapeutic goal of reducing tumor metastasis and treatment resistance. Recent reports from our laboratories using metastatic melanoma and breast cancer models have shown the preclinical efficacy of novel and rationally designed therapeutic agents that target ERK1/2 signaling and mitochondrial ATP synthase, which modulate ROS events that may prevent or treat metastatic cancer. These findings and those of others suggest that targeting a tumor's metabolic requirements and vulnerabilities may inhibit metastatic pathways and tumor growth. Approaches that exploit the ability of therapeutic agents to alter oxidative balance in tumor cells may be selective for cancer cells and may ultimately have an impact on clinical efficacy and safety. Elucidating the translational potential of metabolic targeting could lead to the discovery of new approaches for treatment of metastatic cancer.

The metabolic addiction of cancer stem cells

Cancer stem cells (CSC) are the minor population of cancer originating cells that have the capacity of self-renewal, differentiation, and tumorigenicity (when transplanted into an immunocompromised animal). These low-copy number cell populations are believed to be resistant to conventional chemo and radiotherapy. It was reported that metabolic adaptation of these elusive cell populations is to a large extent responsible for their survival and distant metastasis. Warburg effect is a hallmark of most cancer in which the cancer cells prefer to metabolize glucose anaerobically, even under normoxic conditions. Warburg's aerobic glycolysis produces ATP efficiently promoting cell proliferation by reprogramming metabolism to increase glucose uptake and stimulating lactate production. This metabolic adaptation also seems to contribute to chemoresistance and immune evasion, a prerequisite for cancer cell survival and proliferation. Though we know a lot about metabolic fine-tuning in cancer, what is still in shadow is the identity of upstream regulators that orchestrates this process. Epigenetic modification of key metabolic enzymes seems to play a decisive role in this. By altering the metabolic flux, cancer cells polarize the biochemical reactions to selectively generate "onco-metabolites" that provide an added advantage for cell proliferation and survival. In this review, we explored the metabolic-epigenetic circuity in relation to cancer growth and proliferation and establish the fact how cancer cells may be addicted to specific metabolic pathways to meet their needs. Interestingly, even the immune system is re-calibrated to adapt to this altered scenario. Knowing the details is crucial for selective targeting of cancer stem cells by choking the rate-limiting stems and crucial branch points, preventing the formation of onco-metabolites.

Metabostemness in cancer: Linking metaboloepigenetics and mitophagy in remodeling cancer stem cells

Cancer stem cells (CSCs) are rare populations of malignant cells with stem cell-like features of self-renewal, uninterrupted differentiation, tumorigenicity, and resistance to conventional therapeutic agents, and these cells have a decisive role in treatment failure and tumor relapse. The self-renewal potential of CSCs with atypical activation of developmental signaling pathways involves the maintenance of stemness to support cancer progression. The acquisition of stemness in CSCs has been accomplished through genetic and epigenetic rewiring following the metabolic switch. In this context, "metabostemness" denotes the metabolic parameters that essentially govern the epitranscriptional gene reprogramming mechanism to dedifferentiate tumor cells into CSCs. Several metabolites often referred to as oncometabolites can directly remodel chromatin structure and thereby influence the operation of epitranscriptional circuits. This integrated metaboloepigenetic dimension of CSCs favors the differentiated cells to move in dedifferentiated macrostates. Some metabolic events might perform as early drivers of epitranscriptional reprogramming; however, subsequent metabolic hits may govern the retention of stemness properties in the tumor mass. Interestingly, selective removal of mitochondria through autophagy can promote metabolic plasticity and alter metabolic states during differentiation and dedifferentiation. In this connection, novel metabostemness-specific drugs can be generated as potential cancer therapeutics to target the metaboloepigenetic circuitry to eliminate CSCs.

Lysosome Fe2+ release is responsible for etoposide- and cisplatin-induced stemness of small cell lung cancer cells

Iron metabolism has been shown to hand over cancer stem cell, which is regarded as the root of tumor progression, recurrence and chemoresistance. This study aims to explore whether iron metabolism is involved in etoposide- and cisplatin-induced stemness in small cell lung cancer (SCLC) cells. Here, analysis on tumor-sphere formation and stemness marker expression is performed to determine whether etoposide and cisplatin can induce SCLC cell stemness. Online dataset analysis is constructed to determine the correlation between iron transportation and the survival of lung cancer patients. Chromatin immunoprecipitation combined with rescuing experiments are carried out to reveal the underlying mechanisms. Additionally, the non-lethal doses of etoposide and cisplatin can induce SCLC cell stemness in a concentration-dependent manner and reduce the lysosome iron concentration dependent on Ferritin expression, which is positively regulated by HIF-1α/β. Moreover, HIF-1α/β can directly bind to Ferritin promoter region. This HIF/Ferritin axis is responsible for etoposide- and cisplatin-induced iron reduction in lysosomes and stemness of SCLC cells. This work demonstrates that iron in lysosomes is essential for etoposide and cisplatin-induced stemness of SCLC cells, which is regulated by the HIF/Ferritin axis.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

CDK4/6 inhibition promotes immune infiltration in ovarian cancer and synergizes with PD-1 blockade in a B cell-dependent manner

Great progress has been made in the field of tumor immunotherapy in the past decade. However, the therapeutic effects of immune checkpoint blockade (ICB) against ovarian cancer are still limited. Recently, an inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6i) has been reported to enhance antitumor immunity in preclinical models. The combined use of CDK4/6i and ICB may be beneficial, but the effects of CDK4/6is on the tumor immune microenvironment and whether they can synergize with ICB in treating ovarian cancer remain unknown.

Methods: In this study, we first assessed the antitumor efficacy of abemaciclib, an FDA-approved CDK4/6i, in a syngeneic murine ovarian cancer model. Then, immunohistochemistry, immunofluorescence and flow cytometry were performed to evaluate the number, proportion, and activity of tumor-infiltrating lymphocytes. Cytokine and chemokine production was detected both in vivo and in vitro by PCR array analysis and cytokine antibody arrays. The treatment efficacy of combined abemaciclib and anti-PD-1 therapy was evaluated in vivo, and CD8+ and CD4+ T cell activities were analyzed using flow cytometry. Lastly, the requirement for both CD8+ T cells and B cells in combination treatment was evaluated in vivo, and potential cellular mechanisms were further analyzed by flow cytometry.

Results: We observed that abemaciclib monotherapy could enhance immune infiltration, especially CD8+ T cell and B cell infiltration, in the ID8 murine ovarian cancer model. Immunophenotyping analysis showed that abemaciclib induced a proinflammatory immune response in the tumor microenvironment. PCR array analysis suggested the presence of a Th1-polarized cytokine profile in abemaciclib-treated ID8 tumors. In vitro studies showed that abemaciclib-treated ID8 cells secreted more CXCL10 and CXCL13, thus recruiting more lymphocytes than control groups. Combination treatment achieved better tumor control than monotherapy, and the activities of CD8+ and CD4+ T cells were further enhanced when compared with monotherapy. The synergistic antitumor effects of combined abemaciclib and anti-PD-1 therapy depended on both CD8+ T cells and B cells.

Conclusion: These findings suggest that combined treatment with CDK4/6i and anti-PD-1 antibody could improve the efficacy of anti-PD-1 therapy and hold great promise for the treatment of poorly immune-infiltrated ovarian cancer.

Transcriptional Factor Yin Yang 1 Promotes the Stemness of Breast Cancer Cells by Suppressing miR-873-5p Transcriptional Activity

Transcription factor Yin Yang 1 (YY1) is upregulated in multiple tumors and plays essential roles in tumor proliferation and metastasis. However, the function of YY1 in breast cancer stemness remains unclear. Herein, we found that YY1 expression was negatively correlated with the overall survival and relapse-free survival of breast cancer patients and positively correlated with the expression of stemness markers in breast cancer. Overexpression of YY1 increased the expression of stemness markers, elevated CD44⁺CD24⁻ cell sub-population, and enhanced the capacity of cell spheroid formation and tumor-initiation. In contrast, YY1 knockdown exhibited the opposite effects. Mechanistically, YY1 decreased microRNA-873-5p (miR-873-5p) level by recruiting histone deacetylase 4 (HDAC4) and HDAC9 to miR-873-5p promoter and thus increasing the deacetylation level of miR-873-5p promoter. Sequentially, YY1 activated the downstream PI3K/AKT and ERK1/2 pathways, which have been confirmed to be suppressed by miR-873-5p in our recent work. Moreover, the suppressed effect of YY1/miR-873-5p axis on the stemness of breast cancer cells was partially dependent on PI3K/AKT and ERK1/2 pathways. Finally, it was found that the YY1/miR-873-5p axis is involved in the chemoresistance of breast cancer cells. Our study defines a novel YY1/miR-873-5p axis responsible for the stemness of breast cancer cells.

Dynamic Transcriptional Responses to Injury of Regenerative and Non-regenerative Cardiomyocytes Revealed by Single-Nucleus RNA Sequencing

The adult mammalian heart is incapable of regeneration following injury. In contrast, the neonatal mouse heart can efficiently regenerate during the first week of life. The molecular mechanisms that mediate the regenerative response and its blockade in later life are not understood. Here, by single-nucleus RNA sequencing, we map the dynamic transcriptional landscape of five distinct cardiomyocyte populations in healthy, injured, and regenerating mouse hearts. We identify immature cardiomyocytes that enter the cell cycle following injury and disappear as the heart loses the ability to regenerate. These proliferative neonatal cardiomyocytes display a unique transcriptional program dependent on nuclear transcription factor Y subunit alpha (NFYa) and nuclear factor erythroid 2-like 1 (NFE2L1) transcription factors, which exert proliferative and protective functions, respectively. Cardiac overexpression of these two factors conferred protection against ischemic injury in mature mouse hearts that were otherwise non-regenerative. These findings advance our understanding of the cellular basis of neonatal heart regeneration and reveal a transcriptional landscape for heart repair following injury.

Grainyhead-like 2 as a double-edged sword in development and cancer

Grainyhead-like 2 (GRHL2), one of the three homologs of Drosophila grainyhead, contributes to epithelial morphogenesis and differentiation. Dysregulation of GRHL2 has been shown to be involved in hearing loss and neural tube defects during embryogenesis. Moreover, it is well-recognized that GRHL2 suppresses epithelial-to-mesenchymal transition (EMT) that is required for migration and invasion of carcinoma, implicating, GRHL2 in carcinogenesis. Diverse mechanisms, as well as the varied roles of GRHL2 in different tumor tissues, have been elucidated. However, the functions of GRHL2 appear to be more complicated than initially thought. GRHL2, acting as either a tumor enhancer or a tumor inhibitor, depends on the type of cancer. In this review, we summarize research progress about normal physiological functions of GRHL2 including epithelial morphogenesis, neural tube closure, and hearing loss. Moreover, the mechanisms of GRHL2 in tumorigenesis, containing EMT suppression, forming a negative feedback loop with ZEB1 and miR200 family, interactions with estrogen receptor (ER)-dependent signaling pathway, regulation of telomerase reverse transcriptase and relationships with TGF-beta signaling pathway are discussed in this review in an effort to better understand the roles of GRHL2 in a variety of cancers toward the goal of GRHL2-targeted treatment in the near future.

Anti-cell growth and anti-cancer stem cell activity of the CDK4/6 inhibitor palbociclib in breast cancer cells

BACKGROUND

A cyclin-dependent kinase (CDK) 4/6 inhibitor, palbociclib, has been used to treat patients with estrogen receptor (ER)-positive (+) and human epidermal growth factor receptor (HER) 2-negative (-) advanced breast cancer. To investigate the mechanisms underlying the antitumor activity of palbociclib, we conducted a preclinical study on the anti-cell growth and anti-cancer stem cell (CSC) activity of palbociclib in breast cancer cells.

METHODS

The effects of palbociclib on Rb phosphorylation, cell growth, cell cycle progression, apoptosis, cell senescence and the proportion of CSCs were investigated in five human breast cancer cell lines of different subtypes. To investigate the mechanisms of the anti-CSC activity of palbociclib, small-interfering RNAs for CDK4 and/or CDK6 were used. Palbociclib dose-dependently reduced Rb phosphorylation and cell growth in association with G1-S cell cycle blockade and the induction of cell senescence, but without increased apoptosis, in all breast cancer cell lines.

RESULTS

The anti-cell growth activity of palbociclib widely differed among the cell lines. Palbociclib also dose-dependently reduced the CSC proportion measured by three different assays in four of five cell lines. The inhibition of CDK4 expression, but not CDK6 expression, reduced the increased proportion of putative CSCs induced by estradiol in ER (+)/HER2 (-) cell lines.

CONCLUSIONS

These results suggest that palbociclib exhibits significant anti-cell growth and anti-CSC activity in not only ER (+) breast cancer cell lines but also ER (-) cell lines. CDK4 inhibition induced by palbociclib may be responsible for its anti-CSC activity.

Exploiting mitochondrial targeting signal(s), TPP and bis-TPP, for eradicating cancer stem cells (CSCs)

Tri-phenyl-phosphonium (TPP) is a non-toxic chemical moiety that functionally behaves as a mitochondrial targeting signal (MTS) in living cells. Here, we explored the hypothesis that TPP-related compounds could be utilized to inhibit mitochondria in cancer stem cells (CSCs). We randomly selected 9 TPP-related compounds for screening, using an ATP depletion assay. Based on this approach, five compounds were identified as “positive hits”; two had no detectable effect on ATP production. Remarkably, this represents a >50% hit rate. We validated that the five positive hit compounds all inhibited oxygen consumption rates (OCR), using the Seahorse XFe96 metabolic flux analyzer. Interestingly, these TPP-related compounds were non-toxic and had little or no effect on ATP production in normal human fibroblasts, but selectively targeted adherent “bulk” cancer cells. Finally, these positive hit compounds also inhibited the propagation of CSCs in suspension, as measured functionally using the 3D mammosphere assay. Therefore, these TPP-related compounds successfully inhibited anchorage-independent growth, which is normally associated with a metastatic phenotype. Interestingly, the most effective molecule that we identified contained two TPP moieties (i.e., bis-TPP). More specifically, 2-butene-1,4-bis-TPP potently and selectively inhibited CSC propagation, with an IC-50 < 500 nM. Thus, we conclude that the use of bis-TPP, a “dimeric” mitochondrial targeting signal, may be a promising new approach for the chemical eradication of CSCs. Future studies on the efficacy of 2-butene-1,4-bis-TPP and its derivatives are warranted. In summary, we show that TPP-related compounds provide a novel chemical strategy for effectively killing both i) “bulk” cancer cells and ii) CSCs, while specifically minimizing or avoiding off-target side-effects in normal cells. These results provide the necessary evidence that “normal” mitochondria and “malignant” mitochondria are truly biochemically distinct, removing a significant barrier to therapeutically targeting cancer metabolism.

Integrative analysis of gene expression and DNA methylation through one-class logistic regression machine learning identifies stemness features in medulloblastoma

Most human cancers develop from stem and progenitor cell populations through the sequential accumulation of various genetic and epigenetic alterations. Cancer stem cells have been identified from medulloblastoma (MB), but a comprehensive understanding of MB stemness, including the interactions between the tumor immune microenvironment and MB stemness, is lacking. Here, we employed a trained stemness index model based on an existent one‐class logistic regression (OCLR) machine‐learning method to score MB samples; we then obtained two stemness indices, a gene expression‐based stemness index (mRNAsi) and a DNA methylation‐based stemness index (mDNAsi), to perform an integrated analysis of MB stemness in a cohort of primary cancer samples (n = 763). We observed an inverse trend between mRNAsi and mDNAsi for MB subgroup and metastatic status. By applying the univariable Cox regression analysis, we found that mRNAsi significantly correlated with overall survival (OS) for all MB patients, whereas mDNAsi had no significant association with OS for all MB patients. In addition, by combining the Lasso‐penalized Cox regression machine‐learning approach with univariate and multivariate Cox regression analyses, we identified a stemness‐related gene expression signature that accurately predicted survival in patients with Sonic hedgehog (SHH) MB. Furthermore, positive correlations between mRNAsi and prognostic copy number aberrations in SHH MB, including MYCN amplifications and GLI2 amplifications, were detected. Analyses of the immune microenvironment revealed unanticipated correlations of MB stemness with infiltrating immune cells. Lastly, using the Connectivity Map, we identified potential drugs targeting the MB stemness signature. Our findings based on stemness indices might advance the development of objective diagnostic tools for quantitating MB stemness and lead to novel biomarkers that predict the survival of patients with MB or the efficacy of strategies targeting MB stem cells.

The Role of the Extracellular Matrix in Cancer Stemness

As our understanding of cancer cell biology progresses, it has become clear that tumors are a heterogenous mixture of different cell populations, some of which contain so called “cancer stem cells” (CSCs). Hallmarks of CSCs include self-renewing capability, tumor-initiating capacity and chemoresistance. The extracellular matrix (ECM), a major structural component of the tumor microenvironment, is a highly dynamic structure and increasing evidence suggests that ECM proteins establish a physical and biochemical niche for CSCs. In cancer, abnormal ECM dynamics occur due to disrupted balance between ECM synthesis and secretion and altered expression of matrix-remodeling enzymes. Tumor-derived ECM is biochemically distinct in its composition and is stiffer compared to normal ECM. In this review, we will provide a brief overview of how different components of the ECM modulate CSC properties then discuss how physical, mechanical, and biochemical cues from the ECM drive cancer stemness. Given the fact that current CSC targeting therapies face many challenges, a better understanding of CSC-ECM interactions will be crucial to identify more effective therapeutic strategies to eliminate CSCs.

Palbociclib, a selective CDK4/6 inhibitor, restricts cell survival and epithelial-mesenchymal transition in Panc-1 and MiaPaCa-2 pancreatic cancer cells

The mortality rate of pancreatic cancer has close parallels to its incidence rate because of limited therapeutics and lack of effective prognosis. Despite various novel chemotherapeutics combinations, the 5-year survival rate is still under 5%. In the current study, we aimed to modulate the aberrantly activated PI3K/AKT pathway and epithelial-mesenchymal transition (EMT) signaling with the treatment of CDK4/6 inhibitor PD-0332991 (palbociclib) in Panc-1 and MiaPaCa-2 pancreatic cancer cells. It was found that PD-0332991 effectively reduced cell viability and proliferation dose-dependently within 24 hours. In addition, PD-0332991 induced cell cycle arrest at the G1 phase by downregulation of aberrant expression of CDK4/6 through the dephosphorylation of Rb in each cell lines. Although PD-0332991 treatment increased epithelial markers and decreased mesenchymal markers, the nuclear translocation of β-catenin was not prevented by PD-0332991 treatment, especially in MiaPaCa-2 cells. Effects of PD-0332991 on the regulation of PI3K/AKT signaling and its downstream targets such as GSK-3 were cell type-dependent. Although the activity of AKT was inhibited in both cell lines, the phosphorylation of GSK-3β at Ser9 increased only in Panc-1. In conclusion, PD-0332991 induced cell cycle arrest and reduced the cell viability of Panc-1 and MiaPaCa-2 cells. However, PD-0332991 differentially affects the regulation of the PI3K/AKT pathway and EMT process in cells due to its distinct influence on Rb and GSK-3/β-catenin signaling. Understanding the effect of PD-0332991 on the aberrantly activated signaling axis may put forward a new therapeutic strategy to reduce the cell viability and metastatic process of pancreatic cancer.

Targeting flavin-containing enzymes eliminates cancer stem cells (CSCs), by inhibiting mitochondrial respiration: Vitamin B2 (Riboflavin) in cancer therapy

Here, we performed high-throughput drug-screening to identify new non-toxic mitochondrial inhibitors. This screening platform was specifically designed to detect compounds that selectively deplete cellular ATP levels, but have little or no toxic side effects on cell viability. Using this approach, we identified DPI (Diphenyleneiodonium chloride) as a new potential therapeutic agent. Mechanistically, DPI potently blocks mitochondrial respiration by inhibiting flavin-containing enzymes (FMN and FAD-dependent), which form part of Complex I and II. Interestingly, DPI induced a chemo-quiescence phenotype that potently inhibited the propagation of CSCs, with an IC-50 of 3.2 nano-molar. Virtually identical results were obtained using CSC markers, such as CD44 and CD24. We further validated the effects of DPI on cellular metabolism. At 10 nM, DPI inhibited oxidative mitochondrial metabolism (OXPHOS), reducing mitochondrial driven ATP production by >90%. This resulted in a purely glycolytic phenotype, with elevated L-lactate production. We show that this metabolic inflexibility could be rapidly-induced, after only 1 hour of DPI treatment. Remarkably, the mitochondrial inhibitory effects of DPI were reversible, and DPI did not induce ROS production. Cells maintained in DPI for 1 month showed little or no mitochondrial activity, but remained viable. Thus, it appears that DPI behaves as a new type of mitochondrial inhibitor, which maintains cells in a state of metabolic-quiescence or “suspended animation”. In conclusion, DPI treatment can be used to acutely confer a mitochondrial-deficient phenotype, which we show effectively depletes CSCs from the heterogeneous cancer cell population. These findings have significant therapeutic implications for potently targeting CSCs, while minimizing toxic side effects. We also discuss the possible implications of DPI for the aging process. Interestingly, previous studies in C. elegans have shown that DPI prevents the accumulation of lipofuscin (an aging-associated hallmark), during the response to oxidative stress. Our current results are consistent with data showing that flavins (FAD, FMN and/or Riboflavin) are auto-fluorescent markers of i) increased mitochondrial “power” (OXPHOS) and ii) elevated CSC activity. Finally, we believe that DPI is one of the most potent and highly selective CSC inhibitors discovered to date. Therefore, our current findings suggest a new impetus to create novel analogues of i) DPI (Diphenyleneiodonium chloride) and ii) DPI-related compounds (Diphenyliodonium chloride), using medicinal chemistry, to optimize this very promising and potent anti-CSC activity. We propose to call these new molecules “Mitoflavoscins”. For example, DPI is ∼30 times more potent than Palbociclib (IC-50 = 100 nM), which is an FDA-approved CDK4/6 inhibitor, that broadly targets proliferation in any cell type, including CSCs.

Transcriptional factor six2 promotes the competitive endogenous RNA network between CYP4Z1 and pseudogene CYP4Z2P responsible for maintaining the stemness of breast cancer cells

Background

The expression of CYP4Z1 and the pseudogene CYP4Z2P has been shown to be specifically increased in breast cancer by our group and others. Additionally, we previously revealed the roles of the competitive endogenous RNA (ceRNA) network mediated by these genes (ceRNET_CC) in breast cancer angiogenesis, apoptosis, and tamoxifen resistance. However, the roles of ceRNET_CC in regulating the stemness of breast cancer cells and the mechanisms through which ceRNET_CC is regulated remain unclear.

Methods

Transcriptional factor six2, CYP4Z1-3′UTR, and CYP4Z2P-3′UTR were stably overexpressed or knocked down in breast cancer cells via lentivirus infection. ChIP-sequencing and RNA-sequencing analysis were performed to reveal the mechanism through which ceRNET_CC is regulated and the transcriptome change mediated by ceRNET_CC. Clinical samples were used to validate the correlation between six2 and ceRNET_CC. Finally, the effects of the six2/ceRNET_CC axis on the stemness of breast cancer cells and chemotherapy sensitivity were evaluated by in vitro and in vivo experiments.

Results

We revealed that ceRNET_CC promoted the stemness of breast cancer cells. Mechanistically, six2 activated ceRNET_CC by directly binding to their promoters, thus activating the downstream PI3K/Akt and ERK1/2 pathways. Finally, we demonstrated that the six2/ceRNET_CC axis was involved in chemoresistance.

Conclusions

Our results uncover the mechanism through which ceRNET_CC is regulated, identify novel roles for the six2/ceRNET_CC axis in regulating the stemness of breast cancer cells, and propose the possibility of targeting the six2/ceRNET_CC axis to inhibit breast cancer stem cell (CSC) traits.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0697-6) contains supplementary material, which is available to authorized users.

ShRNA-mediated BMI-1 gene silencing inhibits gastrointestinal stromal tumor cell telomerase activity and enhances apoptosis

Gastrointestinal stromal tumors (GISTs) are the most frequently occurring mesenchymal tumors of the gastrointestinal tract. Telomerase activity is well acknowledged as a critical factor in oncogenesis. The objective of the present study is to evaluate the effect of BMI gene silencing on proliferation, apoptosis and telomerase activity in human GIST882 cells. GIST882 cells were transfected with a eukaryotic expression vector of an shRNA fragment. The silencing efficiency in the GIST882 cells was determined by RT-qPCR and a western blot analysis. After the shRNA-BMI-1 plasmid was transfected into the GIST882 cells and nude mice, a cell counting kit-8 (CCK-8) assay and flow cytometry were utilized to detect the GIST882 cell proliferation, the apoptosis rate and the cell cycle. Tumor growth was observed by tumor xenograft in nude mice. Telomerase activity and telomere length were detected by a Southern blot and a target region amplified polymorphism. The shRNA-BMI-1 recombinant plasmid was successfully constructed. The mRNA and protein expression of the BMI-1 gene in GIST882 cells was suppressed by the shRNA-BMI-1 recombinant plasmid. Meanwhile, BMI-1 gene silencing inhibited the cell proliferation, tumor growth, and cell cycle in the GIST882 cells. However, cell apoptosis was increased and telomerase activity was decreased with the silencing of the BMI-1 gene. Collectively, the results of this study suggest that silencing the BMI-1 gene may provide a new target for the treatment of GISTs.

CDK1 Interacts with Sox2 and Promotes Tumor Initiation in Human Melanoma

: Cancers are composed of heterogeneous subpopulations with various tumor-initiating capacities, yet key stem cell genes associated with enhanced tumor-initiating capacities and their regulatory mechanisms remain elusive. Here, we analyzed patient-derived xenografts from melanoma, colon, and pancreatic cancer tissues and identified enrichment of tumor-initiating cells in MHC class I-hi cells, where CDK1, a master regulator of the cell cycle, was upregulated. Overexpression of CDK1, but not its kinase-dead variant, in melanoma cells increased their spheroid forming ability, tumorigenic potential, and tumor-initiating capacity; inhibition of CDK1 with pharmacologic agents reduced these characteristics, which was unexplained by the role of CDK1 in regulating the cell cycle. Proteomic analysis revealed an interaction between CDK1 and the pluripotent stem cell transcription factor Sox2. Blockade or knockdown of CDK1 resulted in reduced phosphorylation, nuclear localization, and transcriptional activity of Sox2. Knockout of Sox2 in CDK1-overexpressing cells reduced CDK1-driven tumor-initiating capacity substantially. Furthermore, GSEA analysis of CDK1^hi tumor cells identified a pathway signature common in all three cancer types, including E2F, G2M, MYC, and spermatogenesis, confirming a stem-like nature of CDK1^hi tumor cells. These findings reveal a previously unrecognized role for CDK1 in regulating tumor-initiating capacity in melanoma and suggest a novel treatment strategy in cancer via interruption of CDK1 function and its protein-protein interactions. SIGNIFICANCE: These findings uncover CDK1 as a new regulator of Sox2 during tumor initiation and implicate the CDK1-Sox2 interaction as a potential therapeutic target in cancer.

A mitochondrial based oncology platform for targeting cancer stem cells (CSCs): MITO-ONC-RX

Here, we wish to propose a new systematic approach to cancer therapy, based on the targeting of mitochondrial metabolism, especially in cancer stem cells (CSCs). In the future, we envision that anti-mitochondrial therapy would ultimately be practiced as an add-on to more conventional therapy, largely for the prevention of tumor recurrence and cancer metastasis. This mitochondrial based oncology platform would require a panel of FDA-approved therapeutics (e.g. Doxycycline) that can safely be used to inhibit mitochondrial OXPHOS and/or biogenesis in CSCs. In addition, new therapeutics that target mitochondria could also be developed, to optimize their ability to eradicate CSCs. Finally, in this context, mitochondrial-based biomarkers (i.e. "Mito-signatures") could be utilized as companion diagnostics, to identify high-risk cancer patients at diagnosis, facilitating the early detection of tumor recurrence and the prevention of treatment failure. In summary, we suggest that new clinical trials are warranted to test and possibly implement this emerging treatment strategy, in a variety of human cancer types. This general approach, using FDA-approved antibiotics to target mitochondria, was effective in killing CSCs originating from many different cancer types, including DCIS, breast (ER(+) and ER(-)), prostate, ovarian, lung and pancreatic cancers, as well as melanoma and glioblastoma, among others. Thus, we propose the term MITO-ONC-RX, to describe this anti-mitochondrial platform for targeting CSCs. The use of re-purposed FDA-approved drugs will undoubtedly help to accelerate the clinical evaluation of this approach, as these drugs can move directly into Phase II clinical trials, saving considerable amounts of time (10-15 y) and billions in financial resources.

A new mutation-independent approach to cancer therapy: Inhibiting oncogenic RAS and MYC, by targeting mitochondrial biogenesis

Here, we used MCF7 cells as a model system to interrogate how MYC/RAS co-operativity contributes to metabolic flux and stemness in breast cancer cells. We compared the behavior of isogenic MCF7 cell lines transduced with c-Myc or H-Ras (G12V), either individually or in combination. Cancer stem cell (CSC) activity was measured using the mammosphere assay. c-Myc augmented both mammosphere formation and mitochondrial respiration, without any effects on glycolytic flux. In contrast, H-Ras (G12V) synergistically augmented both mammosphere formation and glycolysis, but only in combination with c-Myc, directly demonstrating MYC/RAS co-operativity. As c-Myc is known to exert its effects, in part, by stimulating mitochondrial biogenesis, we next examined the effects of another stimulus known to affect mitochondrial biogenesis, i.e. ROS production. To pharmacologically induce oxidative stress, we used Rotenone (a mitochondrial inhibitor) to target mitochondrial complex I. Treatment with Rotenone showed bi-phasic effects; low-dose Rotenone (1 to 2.5 nM) elevated mammosphere formation, while higher doses (10 to 100 nM) were inhibitory. Importantly, the stimulatory effects of Rotenone on CSC propagation were blocked using a mitochondrial-specific anti-oxidant, namely Mito-tempo. Thus, "mild" mitochondrial oxidative stress, originating at Complex I, was sufficient to pheno-copy the effects of c-Myc, effectively promoting CSC propagation. To validate the idea that mitochondrial biogenesis is required to stimulate CSC propagation, we employed Doxycycline, a well-established inhibitor of mitochondrial protein translation. Treatment with Doxycycline was indeed sufficient to block the stimulatory effects of H-Ras (G12V), c-Myc, and Rotenone on CSC propagation. As such, Doxycycline provides a strong rationale for designing new therapeutics to target mitochondrial biogenesis, suggesting a new "mutation-independent" approach to cancer therapy. In support of this notion, most currently successful anti-cancer agents therapeutically target "cell phenotypes", such as increased cell proliferation, rather than specific genetic mutations. Remarkably, we demonstrated that Doxycycline inhibits the effects of diverse oncogenic stimuli, of both i) genetic (MYC/RAS) and ii) environmental (Rotenone) origins. Finally, we discuss the advantages of our "Proteomics-to-Genomics (PTG)" approach for in silico validation of new biomarkers and novel drug targets. In this context, we developed a new Myc-based Mito-Signature consisting of 3 mitochondrial genes (HSPD1; COX5B; TIMM44) for effectively predicting tumor recurrence (HR=4.69; p=2.4e-08) and distant metastasis (HR=4.94; p=2.8e-07), in ER(+) in breast cancer patients. This gene signature could serve as a new companion diagnostic for the early prediction of treatment failure in patients receiving hormonal therapy.

Cancer stem cells (CSCs): metabolic strategies for their identification and eradication

Phenotypic and functional heterogeneity is one of the most relevant features of cancer cells within different tumor types and is responsible for treatment failure. Cancer stem cells (CSCs) are a population of cells with stem cell-like properties that are considered to be the root cause of tumor heterogeneity, because of their ability to generate the full repertoire of cancer cell types. Moreover, CSCs have been invoked as the main drivers of metastatic dissemination and therapeutic resistance. As such, targeting CSCs may be a useful strategy to improve the effectiveness of classical anticancer therapies. Recently, metabolism has been considered as a relevant player in CSC biology, and indeed, oncogenic alterations trigger the metabolite-driven dissemination of CSCs. More interestingly, the action of metabolic pathways in CSC maintenance might not be merely a consequence of genomic alterations. Indeed, certain metabotypic phenotypes may play a causative role in maintaining the stem traits, acting as an orchestrator of stemness. Here, we review the current studies on the metabolic features of CSCs, focusing on the biochemical energy pathways involved in CSC maintenance and propagation. We provide a detailed overview of the plastic metabolic behavior of CSCs in response to microenvironment changes, genetic aberrations, and pharmacological stressors. In addition, we describe the potential of comprehensive metabolic approaches to identify and selectively eradicate CSCs, together with the possibility to 'force' CSCs within certain metabolic dependences, in order to effectively target such metabolic biochemical inflexibilities. Finally, we focus on targeting mitochondria to halt CSC dissemination and effectively eradicate cancer.

Core signaling pathways in ovarian cancer stem cell revealed by integrative analysis of multi-marker genomics data

Tumor recurrence occurs in more than 70% of ovarian cancer patients, and the majority eventually becomes refractory to treatments. Ovarian Cancer Stem Cells (OCSCs) are believed to be responsible for the tumor relapse and drug resistance. Therefore, eliminating ovarian CSCs is important to improve the prognosis of ovarian cancer patients. However, there is a lack of effective drugs to eliminate OCSCs because the core signaling pathways regulating OCSCs remain unclear. Also it is often hard for biologists to identify a few testable targets and infer driver signaling pathways regulating CSCs from a large number of differentially expression genes in an unbiased manner. In this study, we propose a straightforward and integrative analysis to identify potential core signaling pathways of OCSCs by integrating transcriptome data of OCSCs isolated based on two distinctive markers, ALDH and side population, with regulatory network (Transcription Factor (TF) and Target Interactome) and signaling pathways. We first identify the common activated TFs in two OCSC populations integrating the gene expression and TF-target Interactome; and then uncover up-stream signaling cascades regulating the activated TFs. In specific, 22 activated TFs are identified. Through literature search validation, 15 of them have been reported in association with cancer stem cells. Additionally, 10 TFs are found in the KEGG signaling pathways, and their up-stream signaling cascades are extracted, which also provide potential treatment targets. Moreover, 40 FDA approved drugs are identified to target on the up-stream signaling cascades, and 15 of them have been reported in literatures in cancer stem cell treatment. In conclusion, the proposed approach can uncover the activated up-stream signaling, activated TFs and up-regulated target genes that constitute the potential core signaling pathways of ovarian CSC. Also drugs and drug combinations targeting on the core signaling pathways might be able to eliminate OCSCs. The proposed approach can also be applied for identifying potential activated signaling pathways of other types of cancers.

CDK4/6 inhibition as maintenance and combination therapy for high grade serous ovarian cancer

High grade serous ovarian cancer (HGSOC) is a disease with a high relapse rate and poor overall survival despite good initial responses to platinum-based therapy. Cell cycle inhibition with targeted CDK4/6 inhibitors is a new therapeutic approach showing promise as a maintenance therapy in cancer. As multiple genes in the CDK4/6 pathway are commonly mutated or dysregulated in ovarian cancer, we evaluated the efficacy of the CDK4/6 inhibitor Ribociclib alone, in combination with chemotherapy, and as maintenance therapy in several models of HGSOC. Ribociclib restricted cellular proliferation in multiple ovarian cancer cell lines. Restricted proliferation was associated with a pseudo-senescent cellular phenotype; Ribociclib-treated cells expressed markers of senescence, but could rapidly re-enter the cell cycle with discontinuation of therapy. Surprisingly, concurrent Ribociclib and cisplatin therapy followed by Ribociclib maintenance was synergistic. Evaluation of the cell cycle suggested that Ribociclib may also act at the G2/M check point via dephosphorylation of ATR and CHK1. Consistent with this mechanism, Ribociclib demonstrated clear activity in both platinum-resistant and platinum-sensitive tumor models in vivo. This work supports clinical trials using Ribociclib in combination with cisplatin and as a maintenance therapy in ovarian cancer.

Aspirin regulation of c-myc and cyclinD1 proteins to overcome tamoxifen resistance in estrogen receptor-positive breast cancer cells

Tamoxifen is still the most commonly used endocrine therapy drug for estrogen receptor (ER)-positive breast cancer patients and has an excellent outcome, but tamoxifen resistance remains a great impediment to successful treatment. Recent studies have prompted an anti-tumor effect of aspirin. Here, we demonstrated that aspirin not only inhibits the growth of ER-positive breast cancer cell line MCF-7, especially when combined with tamoxifen, but also has a potential function to overcome tamoxifen resistance in MCF-7/TAM. Aspirin combined with tamoxifen can down regulate cyclinD1 and block cell cycle in G0/G1 phase. Besides, tamoxifen alone represses c-myc, progesterone receptor (PR) and cyclinD1 in MCF-7 cell line but not in MCF-7/TAM, while aspirin combined with tamoxifen can inhibit the expression of these proteins in the resistant cell line. When knocking down c-myc in MCF-7/TAM, cells become more sensitive to tamoxifen, cell cycle is blocked as well, indicating that aspirin can regulate c-myc and cyclinD1 proteins to overcome tamoxifen resistance. Our study discovered a novel role of aspirin based on its anti-tumor effect, and put forward some kinds of possible mechanisms of tamoxifen resistance in ER-positive breast cancer cells, providing a new strategy for the treatment of ER-positive breast carcinoma.

Mitoketoscins: Novel mitochondrial inhibitors for targeting ketone metabolism in cancer stem cells (CSCs)

Previous studies have now well-established that epithelial cancer cells can utilize ketone bodies (3-hydroxybutyrate and aceto-acetate) as mitochondrial fuels, to actively promote tumor growth and metastatic dissemination. The two critical metabolic enzymes implicated in this process are OXCT1 and ACAT1, which are both mitochondrial proteins. Importantly, over-expression of OXCT1 or ACAT1 in human breast cancer cells is sufficient to genetically drive tumorigenesis and/or lung metastasis, validating that they indeed behave as metabolic “tumor promoters”. Here, we decided to target these two enzymes, which give cancer cells the ability to recycle ketone bodies into Acetyl-CoA and, therefore, to produce increased ATP. Briefly, we used computational chemistry (in silico drug design) to select a sub-set of potentially promising compounds that spatially fit within the active site of these enzymes, based on their known 3D crystal structures. These libraries of compounds were then phenotypically screened for their effects on total cellular ATP levels. Positive hits were further validated by metabolic flux analysis. Our results indicated that four of these compounds effectively inhibited mitochondrial oxygen consumption. Two of these compounds also induced a reactive glycolytic phenotype in cancer cells. Most importantly, using the mammosphere assay, we showed that these compounds can be used to functionally inhibit cancer stem cell (CSC) activity and propagation. Finally, our molecular modeling studies directly show how these novel compounds are predicted to bind to the active catalytic sites of OXCT1 and ACAT1, within their Coenzyme A binding site. As such, we speculate that these mitochondrial inhibitors are partially mimicking the structure of Coenzyme A. Thus, we conclude that OXCT1 and ACAT1 are important new therapeutic targets for further drug development and optimization. We propose that this new class of drugs should be termed “mitoketoscins”, to reflect that they were designed to target ketone re-utilization and mitochondrial function.

Mitochondrial mRNA transcripts predict overall survival, tumor recurrence and progression in serous ovarian cancer: Companion diagnostics for cancer therapy

Here, we performed a systematic analysis to discover new biomarkers of overall survival and tumor progression in ovarian cancer patients. More specifically, we determined whether nuclear-encoded mitochondrial genes related to mitochondrial biogenesis and function are effective in predicting clinical outcome in ovarian cancer. As a consequence, we are able to provide in silico validation of the prognostic value of these mitochondrial markers, in a well-defined population of ovarian cancer patients. Towards this end, we used a group of N=111 ovarian cancer patients (serous type; stage III), with optimal de-bulking. Importantly, in this group of cancer patients, CA125 and PCNA (conventional markers) were associated with poor overall survival, as would be expected. Using this approach, we identified >100 new individual mitochondrial gene probes that effectively predicted significantly reduced overall survival, with hazard-ratios (HR) of up to 3.68 (p < 9.8e-05). These mitochondrial mRNA transcripts included membrane proteins, chaperones, anti-oxidant enzymes, as well as mitochondrial ribosomal proteins (MRPs) and key members of the OXPHOS (I-V) complexes. Based on this bioinformatics analysis and in silico validation, we conclude that mitochondrial biogenesis and OXPHOS should both be considered as new therapeutic targets, for the more effective treatment of human ovarian cancers. The mitochondrial biomarkers that we have identified could also be employed as new companion diagnostics to assist oncologists in: i) more accurately predicting clinical outcomes and ii) improving the response to therapy, in ovarian cancer patients.

Mitochondrial biomarkers predict tumor progression and poor overall survival in gastric cancers: Companion diagnostics for personalized medicine

Here, we employed a bioinformatics approach to identify novel molecular determinants to predict tumor progression and overall survival in gastric cancer patients. In particular, we directly assessed whether nuclear-derived mRNA species encoding proteins involved in mitochondrial protein translation and OXPHOS are able to successfully predict clinical outcome in gastric cancer. As such, using in silico validation, we have now established the prognostic value of these mitochondrial biomarkers, in a defined population of gastric cancer patients. In this context, we interrogated 5 year follow-up data collected from a group of N = 359 gastric cancer patients. Importantly, in this group of cancer patients, Ki67 and PCNA (conventional markers of cell proliferation) were associated with tumor progression, as might be expected. Using this simplified informatics approach, we identified ∼75 new individual mitochondrial gene probes that effectively predicted tumor progression, with hazard-ratios (HR) of up to 2.22 (p < 2.1e-10). These mitochondrial mRNA transcripts included heat shock proteins/chaperones, membrane proteins, anti-oxidants, enzymes involved in genome maintenance, as well as mitochondrial ribosomal proteins (MRPs) and numerous members of the OXPHOS complexes. In addition, we combined 8 mitochondrial protein transcripts (NDUFS5, VDAC3, ATP5O, IMMT, MRPL28, COX5B, MRPL52, PRKDC), to generate a compact gastric mitochondrial gene signature, associated with a HR of 2.77 (p = 1.4e-14). As a result of this analysis and validation, we strongly suggest that proteins involved in mitochondrial protein translation and OXPHOS should be considered as targets for new drug discovery, for the treatment of gastric cancers. The mitochondrial markers we identified here could also be used as companion diagnostics, to predict clinical outcomes, as well as the patient response to therapy. This should allow a more successful and personalized approach to gastric cancer diagnosis and therapy.

Mitochondrial markers predict survival and progression in non-small cell lung cancer (NSCLC) patients: Use as companion diagnostics

Here, we used an informatics-based approach to identify novel biomarkers of overall survival and tumor progression in non-small cell lung cancer (NSCLC) patients. We determined whether nuclear-encoded genes associated with mitochondrial biogenesis and function can be used to effectively predict clinical outcome in lung cancer. This strategy allowed us to directly provide in silico validation of the prognostic value of these mitochondrial components in large, clinically-relevant, lung cancer patient populations. Towards this end, we used a group of 726 lung cancer patients, with negative surgical margins. Importantly, in this group of cancer patients, markers of cell proliferation (Ki67 and PCNA) were associated with poor overall survival, as would be expected. Similarly, key markers of inflammation (CD163 and CD68) also predicted poor clinical outcome in this patient population. Using this approach, we identified >180 new individual mitochondrial gene probes that effectively predicted significantly reduced overall survival, with hazard-ratios (HR) of up to 4.89 (p<1.0e-16). These nuclear-encoded mitochondrial genes included chaperones, membrane proteins as well as ribosomal proteins (MRPs) and components of the OXPHOS (I-V) complexes. In this analysis, HSPD1, a key marker of mitochondrial biogenesis, had the highest predictive value and was also effective in predicting tumor progression in both smokers and non-smokers alike. In fact, it had even higher predictive value in non-smokers (HR=5.9; p=3.9e-07). Based on this analysis, we conclude that mitochondrial biogenesis should be considered as a new therapeutic target, for the more effective treatment of human lung cancers. The mitochondrial biomarkers that we have identified could serve as new companion diagnostics to assist clinicians in more accurately predicting clinical outcomes in lung cancer patients, driving more personalized cancer therapy.

Mitochondrial markers predict recurrence, metastasis and tamoxifen-resistance in breast cancer patients: Early detection of treatment failure with companion diagnostics

Here, we used a data-mining and informatics approach to discover new biomarkers of resistance to hormonal therapy in breast cancer. More specifically, we investigated whether nuclear-encoded genes associated with mitochondrial biogenesis can be used to predict tumor recurrence, distant metastasis and treatment failure in high-risk breast cancer patients. Overall, this strategy allowed us to directly provide in silico validation of the prognostic value of these mitochondrial components in large and clinically relevant patient populations, with >15 years of follow-up data. For this purpose, we employed a group of 145 ER(+) luminal A breast cancer patients, with lymph-node (LN) metastasis at diagnosis, that were treated with tamoxifen, but not any chemotherapy agents. Using this approach, we identified >60 new individual mitochondrial biomarkers that predicted treatment failure and tumor recurrence, with hazard-ratios (HR) of up to 4.17 (p=2.2e-07). These include mitochondrial chaperones (HSPD1, HSPA9), membrane proteins (VDAC2, TOMM70A) and anti-oxidants (SOD2), as well as 18 different mitochondrial ribosomal proteins (MRPs) and >20 distinct components of the OXPHOS complexes. In addition, we combined 4 mitochondrial proteins (HSPD1, UQCRB, MRPL15, COX17), to generate a compact mitochondrial gene signature, associated with a HR of 5.34 (p=1e-09). This signature also successfully predicted distant metastasis and was effective in larger groups of ER(+) (N=2,447), basal (N=540) and HER2(+) (N=193) breast cancers. It was also effective in all breast cancers (N=3,180), if considered together as a single group. Based on this analysis, we conclude that mitochondrial biogenesis should be considered as a new therapeutic target for overcoming tumor recurrence, distant metastasis and treatment failure in patients with breast cancer. In summary, we identified individual mitochondrial biomarkers and 2 compact mitochondrial gene signatures that can be used to predict tamoxifen-resistance and tumor recurrence, at their initial diagnosis, in patients with advanced breast cancer. In the long-term, these mitochondrial biomarkers could provide a new companion diagnostics platform to help clinicians to accurately predict the response to hormonal therapy in ER(+) breast cancer patients, facilitating more personalized and effective treatment. Similarly, these mitochondrial markers could be used as companion diagnostics, to determine which breast cancer patients would benefit most from clinical treatments with mitochondrially-targeted anti-cancer therapeutics. Finally, we also showed that these mitochondrial markers are superior when directly compared with conventional biomarkers, such as Ki67 and PCNA.

[Pollution of the environment with lead]

Elevated mitochondrial biogenesis and/or metabolism are distinguishing features of cancer cells, as well as Cancer Stem Cells (CSCs), which are involved in tumor initiation, metastatic dissemination, and therapy resistance. In fact, mitochondria-impairing agents can be used to hamper CSCs maintenance and propagation, toward better control of neoplastic disease. Tri-Phenyl-Phosphonium (TPP)-based mitochondrially-targeted compounds are small non-toxic and biologically active molecules that are delivered to and accumulated within the mitochondria of living cells. Therefore, TPP-derivatives may represent potentially “powerful” candidates to block CSCs. Here, we evaluate the metabolic and biological effects induced by the TPP-derivative, termed Dodecyl-TPP (d-TPP) on breast cancer cells. By employing the 3D mammosphere assay in MCF-7 cells, we demonstrate that treatment with d-TPP dose-dependently inhibits the propagation of breast CSCs in suspension. Also, d-TPP targets adherent “bulk” cancer cells, by decreasing MCF-7 cell viability. The analysis of metabolic flux using Seahorse Xfe96 revealed that d-TPP potently inhibits the mitochondrial oxygen consumption rate (OCR), while simultaneously shifting cell metabolism toward glycolysis. Thereafter, we exploited this ATP depletion phenotype and strict metabolic dependency on glycolysis to eradicate the residual glycolytic CSC population, by using additional metabolic stressors. More specifically, we applied a combination strategy based on treatment with d-TPP, in the presence of a selected panel of natural and synthetic compounds, some of which are FDA-approved, that are known to behave as glycolysis (Vitamin C, 2-Deoxy-Glucose) and OXPHOS (Doxycyline, Niclosamide, Berberine) inhibitors. This two-hit scheme effectively decreased CSC propagation, at concentrations of d-TPP toxic only for cancer cells, but not for normal cells, as evidenced using normal human fibroblasts (hTERT-BJ1) as a reference point. Taken together, d-TPP halts CSCs propagation and targets “bulk” cancer cells, without eliciting the relevant undesirable off-target effects in normal cells. These observations pave the way for further exploring the potential of TPP-based derivatives in cancer therapy. Moreover, TPP-based compounds should be investigated for their potential to discriminate between “normal” and “malignant” mitochondria, suggesting that distinct biochemical, and metabolic changes in these organelles could precede specific normal or pathological phenotypes. Lastly, our data validate the manipulation of the energetic machinery as useful tool to eradicate CSCs.

[Congenital abnormalities of the atrioventricular ostia and the annexed valves: report of a case of an extra hole in the posterolateral cuspis of the mitral valve]

Here, we developed a new synthetic lethal strategy for further optimizing the eradication of cancer stem cells (CSCs). Briefly, we show that chronic treatment with the FDA-approved antibiotic Doxycycline effectively reduces cellular respiration, by targeting mitochondrial protein translation. The expression of four mitochondrial DNA encoded proteins (MT-ND3, MT-CO2, MT-ATP6 and MT-ATP8) is suppressed, by up to 35-fold. This high selection pressure metabolically synchronizes the surviving cancer cell sub-population towards a predominantly glycolytic phenotype, resulting in metabolic inflexibility. We directly validated this Doxycycline-induced glycolytic phenotype, by using metabolic flux analysis and label-free unbiased proteomics.

Next, we identified two natural products (Vitamin C and Berberine) and six clinically-approved drugs, for metabolically targeting the Doxycycline-resistant CSC population (Atovaquone, Irinotecan, Sorafenib, Niclosamide, Chloroquine, and Stiripentol). This new combination strategy allows for the more efficacious eradication of CSCs with Doxycycline, and provides a simple pragmatic solution to the possible development of Doxycycline-resistance in cancer cells. In summary, we propose the combined use of i) Doxycycline (Hit-1: targeting mitochondria) and ii) Vitamin C (Hit-2: targeting glycolysis), which represents a new synthetic-lethal metabolic strategy for eradicating CSCs.

This type of metabolic Achilles’ heel will allow us and others to more effectively “starve” the CSC population.