Concise Review: Targeting Cancer Stem Cells Using Immunologic Approaches

FOXD1-ALDH1A3 Signaling Is a Determinant for the Self-Renewal and Tumorigenicity of Mesenchymal Glioma Stem Cells

Glioma stem-like cells (GSC) with tumor-initiating activity orchestrate the cellular hierarchy in glioblastoma and engender therapeutic resistance. Recent work has divided GSC into two subtypes with a mesenchymal (MES) GSC population as the more malignant subtype. In this study, we identify the FOXD1-ALDH1A3 signaling axis as a determinant of the MES GSC phenotype. The transcription factor FOXD1 is expressed predominantly in patient-derived cultures enriched with MES, but not with the proneural GSC subtype. shRNA-mediated attenuation of FOXD1 in MES GSC ablates their clonogenicity in vitro and in vivo Mechanistically, FOXD1 regulates the transcriptional activity of ALDH1A3, an established functional marker for MES GSC. Indeed, the functional roles of FOXD1 and ALDH1A3 are likely evolutionally conserved, insofar as RNAi-mediated attenuation of their orthologous genes in Drosophila blocks formation of brain tumors engineered in that species. In clinical specimens of high-grade glioma, the levels of expression of both FOXD1 and ALDH1A3 are inversely correlated with patient prognosis. Finally, a novel small-molecule inhibitor of ALDH we developed, termed GA11, displays potent in vivo efficacy when administered systemically in a murine GSC-derived xenograft model of glioblastoma. Collectively, our findings define a FOXD1-ALDH1A3 pathway in controling the clonogenic and tumorigenic potential of MES GSC in glioblastoma tumors. Cancer Res; 76(24); 7219-30. ©2016 AACR.

Therapeutic Implications of Cellular Heterogeneity and Plasticity in Breast Cancer

Cellular heterogeneity represents one of the greatest challenges in cancer therapeutics. In many malignancies, this heterogeneity is generated during tumor evolution through a combination of genetic alterations and epigenetic events that recapitulate normal developmental processes including stem cell self-renewal and differentiation. Many, if not most, tumors display similar hierarchal organization, at the apex of which are "stem-like cells" that drive tumor growth, mediate metastasis, and contribute to treatment resistance. Using breast cancer as a model, we discuss how an improved understanding of tumor cellular heterogeneity and plasticity may lead to development of more effective therapeutic strategies.

Towards a biofunctionalized vascular prosthesis: immune cell trapping via a growth factor receptor

To improve the clinical performance of vascular prostheses, which is inacceptably low for implants with small diameters (< 6 mm), biofunctionalization of synthetic implants by endothelialization has become a major, although still unreached, aim. In order to be able to recruit native endothelial progenitor cells (EPCs) to luminal implant surfaces from the blood stream, we generated monoclonal antibodies against the EPC-specific vascular endothelial growth factor receptor 2 (VEGFR-2). Employing the very efficient genetic immunization strategy, > 10 000 hybridoma clones were generated. Screening with various deletion mutants of VEGFR-2, 49 highly-specific monoclonal antibodies (mAbs) covering all seven Ig domains of VEGFR-2 were selected. mAb 9H10 was characterized in detail. Once immobilized on synthetic surfaces, mAb 9H10 allowed, within min, nearly 100-fold enrichment of VEGFR-2-expressing cells under continuous flow conditions. Cell trapping was cell-type specific and essentially not affected by competing VEGFR-2-negative cells. To exclude that the antibody would adversely modify receptor responses, four different in vitro assays were employed. Cell proliferation, angiogenic tube formation, acetylated low-density lipoprotein uptake and VEGFR-2 phosphorylation remained unaffected, suggesting that the antibody did not interfere with the receptor functioning of human umbilical vascular endothelial cells. The molecular and cellular characteristics make the selected monoclonal antibody a very promising tool for the biofunctionalization of vascular implants. Copyright © 2016 John Wiley & Sons, Ltd.

Reversing drug resistance of soft tumor-repopulating cells by tumor cell-derived chemotherapeutic microparticles

Developing novel approaches to reverse the drug resistance of tumor-repopulating cells (TRCs) or stem cell-like cancer cells is an urgent clinical need to improve outcomes of cancer patients. Here we show an innovative approach that reverses drug resistance of TRCs using tumor cell-derived microparticles (T-MPs) containing anti-tumor drugs. TRCs, by virtue of being more deformable than differentiated cancer cells, preferentially take up T-MPs that release anti-tumor drugs after entering cells, which in turn lead to death of TRCs. The underlying mechanisms include interfering with drug efflux and promoting nuclear entry of the drugs. Our findings demonstrate the importance of tumor cell softness in uptake of T-MPs and effectiveness of a novel approach in reversing drug resistance of TRCs with promising clinical applications.

The double-edge role of B cells in mediating antitumor T-cell immunity: Pharmacological strategies for cancer immunotherapy

Emerging evidence reveals the controversial role of B cells in antitumor immunity, but the underlying mechanisms have to be explored. Three latest articles published in the issue 521 of Nature in 2015 reconfirmed the puzzling topic and put forward some explanations of how B cells regulate antitumor T-cell responses both positively and negatively. This paper attempts to demonstrate that different B-cell subpopulations have distinct immunological properties and that they are involved in either antitumor responses or immunosuppression. Recent studies supporting the positive and negative roles of B cells in tumor development were summarized comprehensively. Several specific B-cell subpopulations, such as IgG(+), IgA(+), IL-10(+), and regulatory B cells, were described in detail. The mechanisms underlying the controversial B-cell effects were mainly attributed to different B-cell subpopulations, different B-cell-derived cytokines, direct B cell-T cell interaction, different cancer categories, and different malignant stages, and the immunological interaction between B cells and T cells is mediated by dendritic cells. Promising B-cell-based antitumor strategies were proposed and novel B-cell regulators were summarized to present interesting therapeutic targets. Future investigations are needed to make sure that B-cell-based pharmacological strategies benefit cancer immunotherapy substantially.

Does primary neoadjuvant systemic therapy eradicate minimal residual disease? Analysis of disseminated and circulating tumor cells before and after therapy

BACKGROUND

Patients with breast cancer (BC) undergoing neoadjuvant chemotherapy (NACT) may experience metastatic relapse despite achieving a pathologic complete response. We analyzed patients with BC before and after NACT for disseminated tumor cells (DTCs) in the bone marrow(BM); comprehensively characterized circulating tumor cells (CTCs), including stem cell-like CTCs (slCTCs), in blood to prove the effectiveness of treatment on these cells; and correlated these findings with response to therapy, progression-free survival (PFS), and overall survival (OS).

METHODS

CTCs (n = 135) and slCTCs (n = 91) before and after NACT were analyzed using the AdnaTest BreastCancer, AdnaTest TumorStemCell, and epithelial-mesenchymal transition (QIAGEN Hannover GmbH Germany). The expression of estrogen receptor, progesterone receptor, and the resistance marker excision repair cross-complementing rodent repair deficiency, complementation group 1 (ERCC1), nuclease were studied in separate single-plex reverse transcription polymerase chain reaction experiments. DTCs were evaluated in 142 patients before and 165 patients after NACT using the pan-cytokeratin antibody A45-B/B3 for immunocytochemistry.

RESULTS

The positivity rates for DTCs, CTCs, and slCTCs were 27 %, 24 %, and 51 % before and 20 %, 8 %, and 20 % after NACT, respectively. Interestingly, 72 % of CTCs present after therapy were positive for ERCC1, and CTCs before (p = 0.005) and after NACT (p = 0.05) were significantly associated with the presence of slCTCs. Whereas no significant associations with clinical parameters were found for CTCs and slCTCs, DTCs were significantly associated with nodal status (p = 0.03) and histology (0.046) before NACT and with the immunohistochemical subtype (p = 0.02) after NACT. Univariable Cox regression analysis revealed that age (p = 0.0065), tumor size before NACT (p = 0.0473), nodal status after NACT (p = 0.0137), and response to NACT (p = 0.0136) were significantly correlated with PFS, whereas age (p = 0.0162) and nodal status after NACT (p = 0.0243) were significantly associated with OS. No significant correlations were found for DTCs or any CTCs before and after therapy with regard to PFS and OS.

CONCLUSIONS

Although CTCs were eradicated more effectively than DTCs, CTCs detected after treatment seemed to be associated with tumor cells showing tumor stem cell characteristics as well as with resistant tumor cell populations that might indicate a worse outcome in the future. Thus, these patients might benefit from additional second-line treatment protocols including bisphosphonates for the eradication of DTCs.

Decreasing lncRNA HOTAIR expression inhibits human colorectal cancer stem cells

Research on the relationship between aberrant long non-coding RNA (lncRNA) and cancer stem cell (CSC) biology in cancer patients has been recently gaining attention. The goal of this study was to investigate whether the decreasing lncRNA HOTAIR expression would inhibit human colorectal cancer (CRC) stem cells. CD133(+)CSCs were isolated from human CRC LoVo cell line by using a magnetic-activated cell sorting system, and were transfected with the expression vector-based small hairpin RNA targeting HOTAIR (shHOTAIR). The ability of cellular proliferation, migration, invasion, colony-forming, and the epithelial-mesenchymal transition (EMT)-associated molecule expression as well as the tumorigenicity of CD133(+)-shHOTAIR were evaluated by the MTT, wound-healing, cellular invasion, colony formation and Western blot assays, respectively. This study found that, when compared with control cells in vitro, CD133(+)-shHOTAIR exhibited the decreased HOTAIR expression, suppressed cellular proliferation, migration, invasion, colony-forming, and inhibited the Vimentin expression with increased E-cadherin expression. In particular, the down-regulation of the HOTAIR expression in CD133(+)CSCs markedly attenuated the tumor growth and lung metastasis in xenograft nude mice. Taken together, this study found that down-regulating the HOTAIR expression in CD133(+)CSCs could serve as a potential anti-cancer regimen to inhibit the invasiveness and metastasis of CRC CSCs.

Cancer Stem Cell Plasticity Drives Therapeutic Resistance

The connection between epithelial-mesenchymal (E-M) plasticity and cancer stem cell (CSC) properties has been paradigm-shifting, linking tumor cell invasion and metastasis with therapeutic recurrence. However, despite their importance, the molecular pathways involved in generating invasive, metastatic, and therapy-resistant CSCs remain poorly understood. The enrichment of cells with a mesenchymal/CSC phenotype following therapy has been interpreted in two different ways. The original interpretation posited that therapy kills non-CSCs while sparing pre-existing CSCs. However, evidence is emerging that suggests non-CSCs can be induced into a transient, drug-tolerant, CSC-like state by chemotherapy. The ability to transition between distinct cell states may be as critical for the survival of tumor cells following therapy as it is for metastatic progression. Therefore, inhibition of the pathways that promote E-M and CSC plasticity may suppress tumor recurrence following chemotherapy. Here, we review the emerging appreciation for how plasticity confers therapeutic resistance and tumor recurrence.

Evolving Strategies for Therapeutically Targeting Cancer Stem Cells

Cancer is a multifactor and multistep process that is affected intrinsically by the genetic and epigenetic makeup of tumor cells and extrinsically by the host microenvironment and immune system. A key component of cancer involves a unique subpopulation of highly malignant cancerous cells referred to as cancer stem cells (CSCs). CSCs are positioned at the apex of the tumor hierarchy with an ability to both self-renew and also generate non-CSC/differentiated progeny, which contribute to the majority of the tumor mass. CSCs undergo functional changes and show plasticity that is stimulated by specific microenvironmental cues and interactions in the tumor niche, which contribute to the complexity and heterogeneity of the CSC population. The prognostic value of CSCs in the clinic is evident since there are many examples in which CSCs serve as markers for poor patient prognosis. CSCs are innately resistant to many standard therapies and they display anoikis resistance, immune evasion, tumor dormancy, and field cancerization, which may result in metastasis and relapse. Many academic laboratories and biotechnology companies are currently focusing on strategies that target CSCs. Combination therapies, epigenetic modifiers, stemness inhibitors, CSC surface marker-based therapies, and immunotherapy-based CSC-targeting drugs are currently undergoing clinical trials. Potential new targets/strategies in CSC-targeted therapy include MDA-9/Syntenin (SDCBP), Patched (PTCH), epigenetic targets, noncoding RNAs, and differentiation induction. Defining ways of targeting and destroying CSCs holds potential to impact significantly on cancer therapy, including prevention of metastasis and cancer recurrence.

Therapies targeting cancer stem cells: Current trends and future challenges

Traditional therapies against cancer, chemo- and radiotherapy, have multiple limitations that lead to treatment failure and cancer recurrence. These limitations are related to systemic and local toxicity, while treatment failure and cancer relapse are due to drug resistance and self-renewal, properties of a small population of tumor cells called cancer stem cells (CSCs). These cells are involved in cancer initiation, maintenance, metastasis and recurrence. Therefore, in order to develop efficient treatments that can induce a long-lasting clinical response preventing tumor relapse it is important to develop drugs that can specifically target and eliminate CSCs. Recent identification of surface markers and understanding of molecular feature associated with CSC phenotype helped with the design of effective treatments. In this review we discuss targeting surface biomarkers, signaling pathways that regulate CSCs self-renewal and differentiation, drug-efflux pumps involved in apoptosis resistance, microenvironmental signals that sustain CSCs growth, manipulation of miRNA expression, and induction of CSCs apoptosis and differentiation, with specific aim to hamper CSCs regeneration and cancer relapse. Some of these agents are under evaluation in preclinical and clinical studies, most of them for using in combination with traditional therapies. The combined therapy using conventional anticancer drugs with CSCs-targeting agents, may offer a promising strategy for management and eradication of different types of cancers.

Cancer stem cell vaccine expressing ESAT-6-gpi and IL-21 inhibits melanoma growth and metastases

Tumor vaccines may induce antitumor efficacy, however, weak immunogenicity of tumor antigens is one of the prime obstacles for excitation of the antitumor immune responses. Therefore, strategies that enhance immunogenicity of tumor vaccines are of particular interest. In this study, a novel melanoma B16F10 CD133(+)CD44(+) cancer stem cell (CSC) vaccine expressing 6 kDa early secreted antigenic target (ESAT-6) in the glycosylphosphatidylinositol (GPI)-anchored form and secreting interleukin (IL)-21 was developed. Its anti-melanoma efficacy and mechanisms were investigated in mice. The results demonstrated that the B16F10-ESAT-6-gpi/IL-21 CD133(+)CD44(+) CSC vaccine exhibited enhanced anti-melanoma efficacy as determined by inhibited melanoma growth, prolonged survival of melanoma bearing mice. The anti-melanoma immunity was associated with elevated levels of serum anti-ESAT-6 and interferon (IFN)-γ as well as increased cytotoxic activities of natural killer cells, splenocytes, and complement dependent cytotoxicity. Furthermore, this CSC-based vaccine apparently inhibited melanoma lung metastasis by decreasing the level of Vimentin while increasing the level of E-cadherin expression, suggesting an inhibited epithelial mesenchymal transition. Thus, the B16F10-ESAT-6-gpi/IL-21 CD133(+)CD44(+) CSC vaccine may be used to reactivate the anti-tumor immunity and for treatment of melanoma.

Nanomedicine-mediated cancer stem cell therapy

Circumstantial evidence suggests that most tumours are heterogeneous and contain a small population of cancer stem cells (CSCs) that exhibit distinctive self-renewal, proliferation and differentiation capabilities, which are believed to play a crucial role in tumour progression, drug resistance, recurrence and metastasis in multiple malignancies. Given that the existence of CSCs is a primary obstacle to cancer therapy, a tremendous amount of effort has been put into the development of anti-CSC strategies, and several potential approaches to kill therapeutically-resistant CSCs have been explored, including inhibiting ATP-binding cassette transporters, blocking essential signalling pathways involved in self-renewal and survival of CSCs, targeting CSCs surface markers and destroying the tumour microenvironment. Meanwhile, an increasing number of therapeutic agents (e.g. small molecule drugs, nucleic acids and antibodies) to selectively target CSCs have been screened or proposed in recent years. Drug delivery technology-based approaches hold great potential for tackling the limitations impeding clinical applications of CSC-specific agents, such as poor water solubility, short circulation time and inconsistent stability. Properly designed nanocarrier-based therapeutic agents (or nanomedicines) offer new possibilities of penetrating CSC niches and significantly increasing therapeutic drug accumulation in CSCs, which are difficult for free drug counterparts. In addition, intelligent nanomedicine holds great promise to overcome pump-mediated multidrug resistance which is driven by ATP and to decrease detrimental effects on normal somatic stem cells. In this review, we summarise the distinctive biological processes related to CSCs to highlight strategies against inherently drug-resistant CSCs. We then focus on some representative examples that give a glimpse into state-of-the-art nanomedicine approaches developed for CSCs elimination. A perspective on innovative therapeutic strategies and the potential direction of nanomedicine-based CSC therapy in the near future is also presented.

Lability and diversity of circadian rhythms of cotton rats Sigmodon hispidus

Tumor initiating cells (TIC) have been suggested as a mechanism for driving chemoresistance and tumor recurrence in human cancers including triple negative breast cancer (TNBC). Significant progress has been made in targeting TICs. However, methods for simultaneously targeting heterogeneous TIC populations are lacking. In this study, we found that treating TNBC cells with chemotherapeutic agents led to a significant accumulation of the ALDH⁺ TIC population. Treating TNBC cells with a disulfiram and copper mixture (DSF/Cu) specifically decreased the ALDH⁺ TIC population and treatment with BKM120, a pan-PI3K inhibitor, significantly decreased the CD44⁺/CD24⁻ TIC population. Furthermore, treatment with DSF/Cu or BKM120 induced higher levels of apoptosis in ALDH⁺ or CD44⁺/CD24⁻ populations, respectively, than in bulk tumor cells. Combining DSF/Cu and BKM120 treatment simultaneously decreased the ALDH⁺ and CD44⁺/CD24⁻ TICs. Using a TNBC tumor xenograft mouse model, we found that DSF/BKM in combination with Taxol significantly reduced the tumor burden and delayed tumor recurrence compared to Taxol treatment alone. Our study is the first of its kind to use two different drugs to abolish two major TIC subtypes simultaneously and inhibit tumor recurrence. These results lay a foundation for developing a novel therapy that can improve chemotherapeutic efficacy.