Immunotherapy: a useful strategy to help combat multidrug resistance

Using nanotechnology to progress the utilization of marine natural products in combating multidrug resistance in cancer: A prospective strategy

Achieving targeted, customized, and combination therapies with clarity of the involved molecular pathways is crucial in the treatment as well as overcoming multidrug resistance (MDR) in cancer. Nanotechnology has emerged as an innovative and promising approach to address the problem of drug resistance. Developing nano-formulation-based therapies using therapeutic agents poses a synergistic effect to overcome MDR in cancer. In this review, we aimed to highlight the important pathways involved in the progression of MDR in cancer mediated through nanotechnology-based approaches that have been employed to circumvent them in recent years. Here, we also discussed the potential use of marine metabolites to treat MDR in cancer, utilizing active drug-targeting nanomedicine-based techniques to enhance selective drug accumulation in cancer cells. The discussion also provides future insights for developing complex targeted, multistage responsive nanomedical drug delivery systems for effective cancer treatments. We propose more combinational studies and their validation for the possible marine-based nanoformulations for future development.

Acquired immune resistance is associated with interferon signature and modulation of KLF6/c-MYB transcription factors in myeloid leukemia

Resistance to immunity is associated with the selection of cancer cells with superior capacities to survive inflammatory reactions. Here, we tailored an ex vivo immune selection model for acute myeloid leukemia (AML) and isolated the residual subpopulations as "immune-experienced" AML (ieAML) cells. We confirmed that upon surviving the immune reactions, the malignant blasts frequently decelerated proliferation, displayed features of myeloid differentiation and activation, and lost immunogenicity. Transcriptomic analyses revealed a limited number of commonly altered pathways and differentially expressed genes in all ieAML cells derived from distinct parental cell lines. Molecular signatures predominantly associated with interferon and inflammatory cytokine signaling were enriched in the AML cells resisting the T-cell-mediated immune reactions. Moreover, the expression and nuclear localization of the transcription factors c-MYB and KLF6 were noted as the putative markers for immune resistance and identified in subpopulations of AML blasts in the patients' bone marrow aspirates. The immune modulatory capacities of ieAML cells lasted for a restricted period when the immune selection pressure was omitted. In conclusion, myeloid leukemia cells harbor subpopulations that can adapt to the harsh conditions established by immune reactions, and a previous "immune experience" is marked with IFN signature and may pave the way for susceptibility to immune intervention therapies.

Multidrug Resistance in Cancer: Understanding Molecular Mechanisms, Immunoprevention and Therapeutic Approaches

Cancer is one of the leading causes of death worldwide. Several treatments are available for cancer treatment, but many treatment methods are ineffective against multidrug-resistant cancer. Multidrug resistance (MDR) represents a major obstacle to effective therapeutic interventions against cancer. This review describes the known MDR mechanisms in cancer cells and discusses ongoing laboratory approaches and novel therapeutic strategies that aim to inhibit, circumvent, or reverse MDR development in various cancer types. In this review, we discuss both intrinsic and acquired drug resistance, in addition to highlighting hypoxia- and autophagy-mediated drug resistance mechanisms. Several factors, including individual genetic differences, such as mutations, altered epigenetics, enhanced drug efflux, cell death inhibition, and various other molecular and cellular mechanisms, are responsible for the development of resistance against anticancer agents. Drug resistance can also depend on cellular autophagic and hypoxic status. The expression of drug-resistant genes and the regulatory mechanisms that determine drug resistance are also discussed. Methods to circumvent MDR, including immunoprevention, the use of microparticles and nanomedicine might result in better strategies for fighting cancer.

Selectively targeting cancer stem cells: Current and novel therapeutic strategies and approaches in the effective eradication of cancer

Cancer stem cells (CSCs) are a subgroup of cells in malignant cancers, which possess self-renewal capacity, tumor-initiating capability, and pluripotency, as well as being responsible for tumor maintenance, metastasis, relapse, and chemoresistance. The treatment modalities previously established for cancer included surgery, chemotherapy, and radiotherapy. The majority of tumor cells of non-CSCs could be eradicated using conventional chemotherapy and radiotherapy. Therefore, novel and promising therapeutic strategies that selectively target CSCs are of great importance. In this review, we described different therapeutic strategies such as immunotherapy, metabolism-based therapeutic strategies, and additional potential therapeutic approaches (targeting microRNAs [miRNAs], histone deacetylase, and DNA methyl transferase) against CSCs. Taken together, due to the inefficiency of anticancer single therapies, targeting CSCs through their metabolism and using immunotherapy and miRNAs besides classical chemo- and radiotherapy may exert better therapeutic effects.

Amplified antitumor efficacy by a targeted drug retention and chemosensitization strategy-based "combo" nanoagent together with PD-L1 blockade in reversing multidrug resistance

BACKGROUND

Recent studies have demonstrated that multidrug resistance (MDR) is a critical factor in the low efficacy of cancer chemotherapy. The main mechanism of MDR arises from the overexpression of P-glycoprotein (P-gp), which actively enhances drug efflux and limits the effectiveness of chemotherapeutic agents.

RESULTS

In this study, we fabricated a "combo" nanoagent equipping with triple synergistic strategies for enhancing antitumor efficacy against MDR cells. Tumor homing-penetrating peptide endows the nanosystem with targeting and penetrating capabilities in the first stage of tumor internalization. The abundant amine groups of polyethylenimine (PEI)-modified nanoparticles then trigger a proton sponge effect to promote endo/lysosomal escape, which enhances the intracellular accumulation and retention of anticancer drugs. Furthermore, copper tetrakis(4-carboxyphenyl)porphyrin (CuTCPP) encapsulated in the nanosystem, effectively scavenges endogenous glutathione (GSH) to reduce the detoxification mediated by GSH and sensitize the cancer cells to drugs, while simultaneously serving as a photoacoustic imaging (PAI) contrast agent for image visualization. Moreover, we also verify that these versatile nanoparticles in combination with PD-1/PD-L1 blockade therapy can not only activate immunological responses but also inhibit P-gp expression to obliterate primary and metastatic tumors.

CONCLUSION

This work shows a significant enhancement in therapeutic efficacy against MDR cells and syngeneic tumors by using multiple MDR reversing strategies compared to an equivalent dose of free paclitaxel.

Nanocatalytic Innate Immunity Activation by Mitochondrial DNA Oxidative Damage for Tumor-Specific Therapy

The innate immune system plays a key role in protecting the human body from tumors, which, unfortunately, is largely counteracted by their immune-suppression function. Such an immune suppression has been reported to be induced by the immunosuppressive microenvironment, including the exhausted cytotoxic T lymphocytes (CTLs) and tumor-promoting M2-polarized macrophages. Here, a novel tumor-immunotherapeutic modality based on the nanocatalytic innate immunity activation by tumor-specific mitochondrial DNA (mtDNA) oxidative damage is proposed. In detail, a nanocatalytic medicine, Fe²⁺ -Ru²⁺ -loaded mesoporous silica nanoparticle named as MSN-Ru²⁺ /Fe²⁺ (MRF), is constructed to induce oxidative damage in the mtDNA of tumor cells. Such an oxidative mtDNA is able to escape from the tumor cells and acts as an immunogenic damage-associated molecular pattern to M1-polarize tumor-associated macrophages (TAMs), resulting in the reactivated immunoresponse of macrophages against cancer cells, and the subsequent inflammatory response of innate immunity. Most importantly, the treatment strategy based on regulating the innate immune response of TAMs not only stops the primary tumor progression, but also almost completely inhibits the growth of distant tumors in the periods of treatments.

Cancer Stem Cells: Acquisition, Characteristics, Therapeutic Implications, Targeting Strategies and Future Prospects

Since last two decades, the major cancer research has focused on understanding the characteristic properties and mechanism of formation of Cancer stem cells (CSCs), due to their ability to initiate tumor growth, self-renewal property and multi-drug resistance. The discovery of the mechanism of acquisition of stem-like properties by carcinoma cells via epithelial-mesenchymal transition (EMT) has paved a way towards a deeper understanding of CSCs and presented a possible avenue for the development of therapeutic strategies. In spite of years of research, various challenges, such as identification of CSC subpopulation, lack of appropriate experimental models, targeting cancer cells and CSCs specifically without harming normal cells, are being faced while dealing with CSCs. Here, we discuss the biology and characteristics of CSCs, mode of acquisition of stemness (via EMT) and development of multi-drug resistance, the role of tumor niche, the process of dissemination and metastasis, therapeutic implications of CSCs and necessity of targeting them. We emphasise various strategies being developed to specifically target CSCs, including those targeting biomarkers, key pathways and microenvironment. Finally, we focus on the challenges that need to be subdued and propose the aspects that need to be addressed in future studies in order to broaden the understanding of CSCs and develop novel strategies to eradicate them in clinical applications. Graphical Abstract Cancer Stem Cells(CSCs) have gained much attention in the last few decades due to their ability to initiate tumor growth and, self-renewal property and multi-drug resistance. Here, we represent the CSC model of cancer, Characteristics of CSCs, acquisition of stemness and metastatic dissemination of cancer, Therapeutic implications of CSCs and Various strategies being employed to target and eradicate CSCs.

Investigative therapy for advanced esophageal cancer using the option for combined immunotherapy and chemotherapy

Aim: Advanced esophageal cancer has limited therapeutic options and a poor outcome. The efficacy of immunotherapy, as the first-line treatment of advanced esophageal cancer, is uncertain. Results: A stage IV advanced esophageal cancer patient received the first-line treatment with a combination of pembrolizumab and chemotherapy. Partial response (PR) was achieved after three cycles, and the efficacy was evaluated as stable after six cycles of immunochemotherapy and two cycles of maintenance monotherapy. Immune-related adverse events (irAEs) were not obvious. The patient was followed up till November 2019 when he died of gastrointestinal hemorrhage. Conclusion: The combination of an immune checkpoint inhibitor and chemotherapy is effective and safe for the initial treatment of advanced esophageal cancer. To confirm the evidence from this case, larger clinical trials are required in the future.

Antigenic Targets for the Immunotherapy of Acute Myeloid Leukaemia

One of the most promising approaches to preventing relapse is the stimulation of the body’s own immune system to kill residual cancer cells after conventional therapy has destroyed the bulk of the tumour. In acute myeloid leukaemia (AML), the high frequency with which patients achieve first remission, and the diffuse nature of the disease throughout the periphery, makes immunotherapy particularly appealing following induction and consolidation therapy, using chemotherapy, and where possible stem cell transplantation. Immunotherapy could be used to remove residual disease, including leukaemic stem cells from the farthest recesses of the body, reducing, if not eliminating, the prospect of relapse. The identification of novel antigens that exist at disease presentation and can act as targets for immunotherapy have also proved useful in helping us to gain a better understand of the biology that belies AML. It appears that there is an additional function of leukaemia associated antigens as biomarkers of disease state and survival. Here, we discuss these findings.

Structural optimization and additional targets identification of antisense oligonucleotide G3139 encapsulated in a neutral cytidinyl-lipid combined with a cationic lipid in vitro and in vivo

Antisense oligonucleotides (ASOs) usually contain a fully phosphorothioate (PS) backbone, which possibly interact with many genes and proteins under intracellular conditions. G3139 is an ASO that targets Bcl-2 mRNA and induces cell apoptosis. Here, we report a kind of cytidinyl-lipid combined with a cationic lipid (DNCA/CLD, molar ration, 28:3, named mix), which may interact with oligonucleotides via H-bond formation, pi-stacking and electrostatic interaction, accompanied by low zeta potentials. The IC₅₀ value of G3139 delivered by mix-lipid reduced from above 20 μM to 0.158 μM for MCF-7/ADR, and exhibited stronger antiproliferation upon other cancer cell lines. In addition, PS modification in the 3'-half of G3139 (especially at positions 13-16) enhanced serum stability, target specificity and anticancer activity. Also, a locked nucleic acid (LNA) gapmer G3139 (LNA-G3139) showed superior antiproliferation (78.5%) and Bcl-2 mRNA suppression effects (85.5%) at 200 nM, mainly due to its high complementary RNA affinity. More apoptosis-associated targets were identified, and a lower level of non-specific protein binding (HSA) revealed that both antisense and aptamer mechanisms might simultaneously exist. A combination of a new delivery system and chemical modifications, such as in LNA-G3139, may have potential clinical application prospects in the future.

Nanomaterials for modulating innate immune cells in cancer immunotherapy

Cancer immunotherapy has been intensively investigated in both preclinical and clinical studies. Whereas chemotherapies use cytotoxic drugs to kill tumor cells, cancer immunotherapy is based on the ability of the immune system to fight cancer. Tumors are intimately associated with the immune system: they can suppress the immune response and/or control immune cells to support tumor growth. Immunotherapy has yielded promising results in clinical practice, but some patients show limited responses. This may reflect the complexities of the relationship between a tumor and the immune system. In an effort to improve the current immunotherapies, researchers have exploited nanomaterials in creating new strategies to cure tumors via modulation of the immune system in tumor tissues. Although extensive studies have examined the use of immune checkpoint-based immunotherapy, rather less work has focused on manipulating the innate immune cells. This review examines the recent approaches and challenges in the use of nanomaterials to modulate innate immune cells.

Overcoming Multidrug Resistance by Codelivery of MDR1-Targeting siRNA and Doxorubicin Using EphA10-Mediated pH-Sensitive Lipoplexes: In Vitro and In Vivo Evaluation

The therapeutic efficacy of chemotherapy is dramatically hindered by multidrug resistance (MDR), which is induced by the overexpression of P-glycoprotein (P-gp). The codelivery of an antitumor drug and siRNA is an effective strategy recently applied in overcoming P-gp-related MDR. In this study, a multifunctional drug delivery system with both pH-sensitive feature and active targetability was designed, in which MDR1-siRNA and DOX were successfully loaded. The resulting carrier EphA10 antibody-conjugated pH-sensitive doxorubicin (DOX), MDR1-siRNA coloading lipoplexes (shortened as DOX + siRNA/ePL) with high serum stability had favorable physicochemical properties. DOX + siRNA/ePL exhibited an incremental cellular uptake, enhanced P-gp downregulation efficacy, as well as a better cell cytotoxicity in human breast cancer cell line/adriamycin drug-resistant (MCF-7/ADR) cells. The results of the intracellular colocalization study indicated that DOX + siRNA/ePL possessed the ability for pH-responsive rapid endosomal escape in a time-dependent characteristic. Meanwhile, the in vivo antitumor activities suggested that DOX + siRNA/ePL could prolong the circulation time as well as specifically accumulate in the tumor cells via receptor-mediated endocytosis after intravenous administration into the blood system. The histological study further demonstrated that DOX + siRNA/ePL could inhibit the proliferation, induce apoptosis effect, and downregulate the P-gp expression in vivo. Altogether, DOX + siRNA/ePL was expected to be a suitable codelivery system for overcoming the MDR effect.

Identification of an HLA-A2-restricted CD147 epitope that can induce specific CTL cytotoxicity against drug resistant MCF-7/Adr cells

Cluster of differentiation (CD)147 is highly expressed in drug-resistant tumor cell lines and is involved in the formation of tumor drug resistance. Therefore, immunotherapy utilizing CD147 epitope peptides is a promising approach for the elimination of drug-resistant tumor cells. However, like most tumor-associated antigens (TAAs), CD147 belongs to the autoantigen category, and T cells that recognize high affinity, immunodominant epitopes from autoantigens are deleted though thymic negative selection. Furthermore, wild-type autoantigen peptides cannot effectively activate and expand T lymphocytes with lower affinity T cell receptors in vivo. However, mutations of TAA peptides have been demonstrated to increase the affinity of major histocompatibility complex molecules and their binding to T cell receptor molecules, leading to activation of T lymphocytes in vitro. In the present study, a high-affinity point mutation peptide, CD147_126-134L2, was predicted by the human leukocyte antigen (HLA) binding prediction algorithm and its affinity was testified using a T2 binding assay. In addition, when peptide-specific cytotoxic T lymphocytes (CTLs) were stimulated with dendritic cells loaded with the CD147_126-134L2 peptide under HLA-A*02:01 restriction, interferon-γ release and cytotoxicity assays showed that peptide-specific CTLs effectively cross-recognized and lysed T2 target cells loaded either with the wild-type (CD147_126-134) or mutated peptide (CD147_126-134L2). Moreover, the CD147_126-134L2 peptide-specific CTLs exerted strong cytotoxic activity against drug-resistant MCF-7/Adr cells, which express a high level of CD147 and are HLA-A*02:01-positive, but not against normal MCF-7 cells. Thus, this suggests that the wild-type peptide (CD147_126-134) is naturally presented on HLA-A*02:01 of CD147-expressing MCF-7/Adr cells and is cross-recognized by CTLs. In conclusion, an HLA-A*02:01-restricted CD147-point mutant epitope peptide was identified that induces CTLs to efficiently lyse drug-resistant MCF-7 cells that highly express CD147. Therefore, this immunotherapeutic approach should be explored as a potential treatment for drug-resistant tumors.

Vorinostat and hydroxychloroquine improve immunity and inhibit autophagy in metastatic colorectal cancer

Hydroxychloroquine (HCQ) enhances the anti-cancer activity of the histone deacetylase inhibitor, vorinostat (VOR), in pre-clinical models and early phase clinical studies of metastatic colorectal cancer (mCRC). Mechanisms could include autophagy inhibition, accumulation of ubiquitinated proteins, and subsequent tumor cell apoptosis. There is growing evidence that autophagy inhibition could lead to improved anti-cancer immunity. To date, effects of autophagy on immunity have not been reported in cancer patients. To address this, we expanded an ongoing clinical study to include patients with advanced, refractory mCRC to evaluate further the clinical efficacy and immune effects of VOR plus HCQ. Refractory mCRC patients received VOR 400 milligrams orally with HCQ 600 milligrams orally daily, in a 3-week cycle. The primary endpoint was median progression-free survival (mPFS). Secondary endpoints include median overall survival (mOS), adverse events (AE), pharmacodynamic of inhibition of autophagy in primary tumors, immune cell analyses, and cytokine levels. Twenty patients were enrolled (19 evaluable for survival) with a mPFS of 2.8 months and mOS of 6.7 months. Treatment-related grade 3–4 AEs occurred in 8 patients (40%), with fatigue, nausea/vomiting, and anemia being the most common. Treatment significantly reduced CD4⁺CD25^hiFoxp3⁺ regulatory and PD-1⁺ (exhausted) CD4⁺ and CD8⁺ T cells and decreased CD45RO-CD62L⁺ (naive) T cells, consistent with improved anti-tumor immunity. On-study tumor biopsies showed increases in lysosomal protease cathepsin D and p62 accumulation, consistent with autophagy inhibition. Taken together, VOR plus HCQ is active, safe and well tolerated in refractory CRC patients, resulting in potentially improved anti-tumor immunity and inhibition of autophagy.

Stage IV gastric cancer successfully treated by multidisciplinary therapy including chemotherapy, immunotherapy, and surgery: a case report

BACKGROUND

The prognosis of stage IV gastric cancer (GC) still remains unfavorable. Multidisciplinary approaches should therefore be considered to improve the survival of patients with stage IV GC. We report here a case of primary GC with potentially unresectable metastasis, successfully treated by a multidisciplinary approach including chemotherapy, immunotherapy, and surgery.

CASE PRESENTATION

A 74-year-old man presented with multiple left neck masses. Abdominal computed tomography showed a thickened gastric wall and multiple lymphadenopathies including left supraclavicular lymph node. Gastroenterological endoscopy revealed tumor lesions in the gastric cardia. Tumor biopsy indicated a pathological diagnosis of poorly differentiated adenocarcinoma. Open left cervical lymph node biopsy showed histological features identical with the gastric tumor, indicating left clavicle lymph node metastasis of GC. After 2 years of chemo-immunotherapy with S-1/CDDP, paclitaxel, and cytokine-activated killer cells, lesions other than the stomach lesion had regressed to undetectable on imaging studies. The patient then underwent laparoscopy-assisted total gastrectomy with Roux-en-Y reconstruction followed by adjuvant chemo-immunotherapy with paclitaxel and S-1 for 1 year, and immunotherapy with tumor lysate-pulsed dendritic cell-activated killer cells for 5 years. The patient remained well after 5 years and 6 months of follow-up, with no signs of recurrence.

CONCLUSION

Therapeutic combinations including immunotherapy may thus allow surgery to be performed in patients previously considered unsuitable for surgical intervention, potentially leading to a clinical cure, as in the current case.

Co-delivery of doxorubicin and interleukin-2 via chitosan based nanoparticles for enhanced antitumor efficacy

In order to reduce toxicity and improve antitumor therapeutic effects of doxorubicin (DOX) and recombinant human interleukin-2 (rhIL-2), we developed a hydrophilic cationic polymer (N,N,N-trimethyl chitosan, TMC) based nanocomplexes (FTCD/rhIL-2) which could efficiently mediate systemic co-delivery of hydrophobic DOX and water-soluble rhIL-2 to achieve the purpose of combination therapy. DOX was covalently conjugated to TMC through cis-aconitic anhydride (CA) which endowed nanocomplexes a pH-sensitive release of DOX, while rhIL-2 was loaded through electrostatic adsorption without compromise of bioactivity. The resultant nanocomplexes exhibited sub-spherical shape (∼200nm) and positive charge (>20mV). Folate (FA) modification was utilized with the intention of active targeting, which was however correlated with weakened tumor growth inhibition, emphasizing the importance of balance in overcoming diverse delivery barriers for efficacious antitumor therapy. Compared with free drugs, FTCD/rhIL-2 nanocomplexes significantly delayed tumor growth, increased the serum immunoglobulin G (IgG) level and the amount of tumor infiltrated cytotoxic T lymphocytes. These results indicated that the combinational administration of DOX and rhIL-2 based on polymer nanoparticles could serve as an effective strategy in antitumor therapy.

STATEMENT OF SIGNIFICANCE

Combined administration of doxorubicin (DOX) and recombinant human interleukin-2 (rhIL-2) has been utilized for the treatment of tumors. However the traditional administration brought to severe side effects, and the efficiency of current delivery systems were unsatisfactory. Herein we developed a hydrophilic cationic polymer based nanoparticle delivery system which facilitated simultaneous and systemic co-delivery of hydrophobic DOX and water-soluble rhIL-2. This system achieved pH-sensitive release of DOX and sustained release of rhIL-2 in vitro, meanwhile, improved anti-tumor efficacy and reduced side-effect in vivo. Thus, our study provided a solution for combinational administration of DOX and rhIL-2 and could serve as an effective strategy in antitumor therapy.

Current evidence for cancer stem cells in gastrointestinal tumors and future research perspectives

Cancer stem cells (CSCs) are a very heterogeneous subpopulation of "stem-like" cancer cells that have been identified in many cancers, including leukemias and solid tumors. It is believed that CSCs drive tumor growth, malignant behavior and are responsible for the initiation of metastatic spread. In addition, CSCs have been implicated in chemotherapy and radiotherapy resistance. Current evidence supports the theory that CSCs share at least two main features of normal stem cells: self-renewal and differentiation, properties that contribute to tumor survival even in the presence of aggressive chemotherapy; however, the mechanism(s) governing the unique biology of CSCs remain unclear. In the field of gastrointestinal cancer, where we face very low survival rates across different tumor types, unraveling the role of CSCs in gastrointestinal tumors should improve our knowledge of cancer biology and chemoresistance, ultimately benefiting patient survival. Towards this end, much effort is being invested in the characterization of CSCs as a means of overcoming drug resistance and controlling metastatic spread. In this review we will cover the concept of CSCs, the current evidence for CSCs in gastrointestinal tumors and future research directions.

Clinically feasible approaches to potentiating cancer cell-based immunotherapies

The immune system exerts both tumor-destructive and tumor-protective functions. Mature dendritic cells (DCs), classically activated macrophages (M1), granulocytes, B lymphocytes, aβ and ɣδ T lymphocytes, natural killer T (NKT) cells, and natural killer (NK) cells may be implicated in antitumor immunoprotection. Conversely, tolerogenic DCs, alternatively activated macrophages (M2), myeloid-derived suppressor cells (MDSCs), and regulatory T (Tregs) and B cells (Bregs) are capable of suppressing antitumor immune responses. Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. To potentiate immunotherapy, vaccinations can be combined with other modalities that target different immune pathways. These modalities include 1) genetic or chemical modification of cell-based vaccines; 2) cross-priming TAAs to T cells by engaging dendritic cells; 3) T-cell adoptive therapy; 4) stimulation of cytotoxic inflammation by non-specific immunomodulators, toll-like receptor (TLR) agonists, cytokines, chemokines or hormones; 5) reduction of immunosuppression and/or stimulation of antitumor effector cells using antibodies, small molecules; and 6) various cytoreductive modalities. The authors envisage that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

Multiple-purpose immunotherapy for cancer

Anti-cancer vaccination is a useful strategy to elicit antitumor immune responses, while overcoming immunosuppressive mechanisms. Whole tumor cells or lysates derived thereof hold more promise as cancer vaccines than individual tumor-associated antigens (TAAs), because vaccinal cells can elicit immune responses to multiple TAAs. Cancer cell-based vaccines can be autologous, allogeneic or xenogeneic. Clinical use of xenogeneic vaccines is advantageous in that they can be most effective in breaking the preexisting immune tolerance to TAAs. An attractive protocol would be to combine vaccinations with immunostimulating and/or immunosuppression-blocking modalities. It is reasonable to anticipate that combined immunotherapeutic strategies will allow for substantial improvements in clinical outcomes in the near future.

Cytokine-induced killer cells induce apoptosis and inhibit the Akt/nuclear factor-κB signaling pathway in cisplatin-resistant human glioma U87MG cells

Despite advances in the development of treatment methods, glioma remains among the cancer types with a high rate of mortality. Therefore, significant efforts are made to develop novel strategies for the treatment of glioma. Ineffective, long-term cancer chemotherapy can lead to multidrug resistance (MDR), which is one of the most common reasons for the failure of chemotherapy. The present study investigated the effects of cytokine‑induced killer cells (CIK) on reversing MDR in cisplatin-resistant U87MG cells (U87MG/DDP). Mononuclear cells were isolated from the peripheral blood of healthy individuals and cultured in vitro in the presence of a combination of cytokines to generate CIK for the treatment of U87MG/DDP. An MTS assay, flow cytometric analysis of apoptosis, ELISA, western blotting and reverse transcription quantitative polymerase chain reaction were used to investigate the MDR-reversing effects of CIK as well as the underlying mechanisms. The results showed that cisplatin sensitivity and the apoptotic rate following cisplatin treatment were increased, P‑glycoprotein expression was decreased and the intracellular rhodamine‑123 content was increased in U87MG/DDP co‑cultured with CIK. In addition, the present study also identified increased mRNA and protein expression levels of MDR gene 1 (MDR1), MDR‑associated protein 1 (MRP1), B-cell lymphoma 2, Survivin and glutathione S-transferase‑π, while the phosphorylation of AKT and the transcriptional activity of nuclear factor‑κB in CIK co‑cultured U87MG/DDP was decreased. These results indicated that pre‑treatment with CIK reversed the MDR of U87MG/DDP, and that CIK‑induced apoptosis of U87MG/DDP was associated with the inhibition of Akt/NF‑κB. These findings suggested that treatment with CIK may be an effective method to enhance the sensitivity of patients with glioma to chemotherapy.

Cancer stem cells: a challenging paradigm for designing targeted drug therapies

Despite earlier controversies about their role and existence within tumors, cancer stem cells (CSCs) are now emerging as a plausible target for new drug discovery. Research and development (R&D) efforts are being directed against key gene(s) driving initiation, growth, and metastatic pathways in CSCs and the tumor microenvironment (TME). However, the niche signals that enable these pluripotent CSCs to evade radio- and chemotherapy, and to travel to secondary tissues remain enigmatic. Small-molecule drugs, biologics, miRNA, RNA interference (RNAi), and vaccines, among others, are under active investigation. Here, we examine the feasibility of leveraging current knowhow of the molecular biology of CSCs and their cellular milieu to design futuristic, targeted drugs with potentially lower toxicity that can override the multiple drug-resistance issues currently observed with existing therapeutics.

Nanocarrier-mediated drugs targeting cancer stem cells: an emerging delivery approach

INTRODUCTION

Cancer stem cells (CSCs) play an important role in the development of drug resistance, metastasis and recurrence. Current conventional therapies do not commonly target CSCs. Nanocarrier-based delivery systems targeting cancer cells have entered a new era of treatment, where specific targeting to CSCs may offer superior outcomes to efficient cancer therapies.

AREAS COVERED

This review discusses the involvement of CSCs in tumor progression and relevant mechanisms associated with CSCs resistance to conventional chemo- and radio-therapies. It highlights CSCs-targeted strategies that are either under evaluation or could be explored in the near future, with a focus on various nanocarrier-based delivery systems of drugs and nucleic acids to CSCs. Novel nanocarriers targeting CSCs are presented in a cancer-specific way to provide a current perspective on anti-CSCs therapeutics.

EXPERT OPINION

The field of CSCs-targeted therapeutics is still emerging with a few small molecules and macromolecules currently proving efficacy in clinical trials. However considering the complexities of CSCs and existing delivery difficulties in conventional anticancer therapies, CSC-specific delivery systems would face tremendous technical and clinical challenges. Nanocarrier-based approaches have demonstrated significant potential in specific drug delivery and targeting; their success in CSCs-targeted drug delivery would not only significantly enhance anticancer treatment but also address current difficulties associated with cancer resistance, metastasis and recurrence.

MicroRNA-21: a therapeutic target for reversing drug resistance in cancer

INTRODUCTION

Drug resistance is a major clinical obstacle to the successful treatment of human cancer. The microRNAs-21 (miR-21), an oncomiR, may play an important role in the progress of drug resistance.

AREAS COVERED

This review covers all related literature on miR-21 in drug resistance of human cancers and analyzes the expression, biological functions and targets of it. This study also envisages future developments toward its clinical and therapeutic applications in cancer treatment.

EXPERT OPINION

The miR-21 may promote the drug resistance of various cancers. Inhibitors of miR-21 may function as effective approaches for reversing drug resistance in cancer cells. There is a tough way from discovering the function of miR-21 to clinical use. Further understanding of miR-21-mediated signaling pathways will help to promote the therapeutic-clinical use of miR-21 in cancer.

Understanding and targeting cancer stem cells: therapeutic implications and challenges

Cancer stem cells (CSCs) have been identified as rare cell populations in many cancers, including leukemia and solid tumors. Accumulating evidence has suggested that CSCs are capable of self-renewal and differentiation into various types of cancer cells. Aberrant regulation of gene expression and some signaling pathways has been observed in CSCs compared to other tumor cells. CSCs are thought to be responsible for cancer initiation, progression, metastasis, recurrence and drug resistance. The CSC hypothesis has recently attracted much attention due to the potential for discovery and development of CSC-related therapies and the identification of key molecules involved in controlling the unique properties of CSC populations. Over the past several years, a tremendous amount of effort has been invested in the development of new drugs, such as nanomedicines, that can take advantage of the "Achilles' heel" of CSCs by targeting cell-surface molecular markers or various signaling pathways. Novel compounds and therapeutic strategies that selectively target CSCs have been identified, some of which have been evaluated in preclinical and clinical studies. In this article, we review new findings related to the investigation of the CSC hypothesis, and discuss the crucial pathways involved in regulating the development of CSC populations and the advances in studies of drug resistance. In addition, we review new CSC-targeted therapeutic strategies aiming to eradicate malignancies.

Drug conjugates such as Antibody Drug Conjugates (ADCs), immunotoxins and immunoliposomes challenge daily clinical practice

Drug conjugates have been studied extensively in preclinical in vitro and in vivo models but to date only a few compounds have progressed to the clinical setting. This situation is now changing with the publication of studies demonstrating a significant impact on clinical practice and highlighting the potential of this new class of targeted therapies. This review summarizes the pharmacological and molecular background of the main drug conjugation systems, namely antibody drug conjugates (ADCs), immunotoxins and immunoliposomes. All these compounds combine the specific targeting moiety of an antibody or similar construct with the efficacy of a toxic drug. The aim of this strategy is to target tumor cells specifically while sparing normal tissue, thus resulting in high efficacy and low toxicity. Recently, several strategies have been investigated in phase I clinical trials and some have entered phase III clinical development. This review provides a detailed overview of various strategies and critically discusses the most relevant achievements. Examples of the most advanced compounds include T-DM1 and brentuximab vedotin. However, additional promising strategies such as immunotoxins and immunoliposmes are already in clinical development. In summary, targeted drug delivery by drug conjugates is a new emerging class of anti-cancer therapy that may play a major role in the future.