Apoptosis-resistant Cancer Cells Research Articles

Sphaeropsidin A C15-C16 Cross-Metathesis Analogues with Potent Anticancer Activity.

We recently discovered that sphaeropsidin A (SphA), a fungal metabolite from Diplodia cupressi, overcomes apoptosis resistance in cancer cells by inducing cellular shrinkage by impairing regulatory volume increase. Previously, we prepared a pyrene-conjugated derivative of SphA by a cross-metathesis reaction involving the phytotoxin's C15,C16-alkene. This derivative's evaluation in a cancer cell panel revealed a significant increase in potency, with the IC50 values 5-10× lower than those displayed by the original natural product. Herein, we describe the preparation and anticancer evaluation of fifteen novel C15,C16-alkene cross-metathesis analogues in which the pyrene moiety was replaced with other aromatic or non-aromatic hydrophobic groups. The idea for this replacement was to prepare a family of compounds that would not be predicted to be mutagenic compared with the original pyrene analogue. We predict several of our new compounds to be non-mutagenic, while retaining the high potency of the original pyrene-containing analogues. Examples of these potential lead compounds included those containing pentamethylphenyl and triphenylethylene pendant groups. As an additional feature of the current investigation, we prepared several deuterated pyrene-containing compounds to overcome intellectual property issues associated with non-patentability of the original pyrene derivative.

Caffeic Acid Enhances Anticancer Drug-induced Apoptosis in Acid-adapted HCT116 Colon Cancer Cells.

Apoptosis resistance in cancer cells adapted to acidic microenvironments poses a challenge for effective treatment. This study investigated the potential use of caffeic acid as an adjunct therapy to overcome drug resistance in colorectal cancer cells under acidic conditions. Long-term exposure to low-pH conditions induced resistance in HCT116 colorectal cancer cells. The effects of caffeic acid on proliferation, clonogenicity, and apoptosis induction were assessed alone and in combination with oxaliplatin and 5-Fluorouracil. The signaling pathways involved in drug resistance were examined by assessing the activities of PI3K/Akt and ERK1/2. Caffeic acid inhibited the proliferation and clonogenicity of acid-adapted cancer cells, and enhanced apoptosis when combined with anticancer drugs. Mechanistically, caffeic acid attenuated the hyperactivation of the PI3K/Akt and ERK1/2 signaling pathways associated with drug resistance. Caffeic acid is a promising therapeutic agent for targeting resistant cancer cells in acidic microenvironments. Its ability to inhibit proliferation, sensitize cells to apoptosis, and modulate signaling pathways highlights its potential for overcoming drug resistance in cancer therapy.

α-Hederin induces paraptosis by targeting GPCRs to activate Ca2+/MAPK signaling pathway in colorectal cancer.

Non-apoptotic cell death is presently emerging as a potential direction to overcome the apoptosis resistance of cancer cells. In the current study, a natural plant agent α-hederin (α-hed) induces caspase-independent paraptotic modes of cell death. The present study is aimed to investigate the role of α-hed induces paraptosis and the associated mechanism of it. The cell proliferation was detected by CCK-8. The cytoplasm organelles were observed under electron microscope. Calcium (Ca2+) level was detected by flow cytometry. Swiss Target Prediction tool analyzed the potential molecule targets of α-hed. Molecular docking methods were used to evaluate binding abilities of α-hed with targets. The expressions of genes and proteins were analyzed by RT-qPCR, western blotting, immunofluorescence, and immunohistochemistry. Xenograft models in nude mice were established to evaluate the anticancer effects invivo. α-hed exerted significant cytotoxicity against a panel of CRC cell lines by inhibiting proliferation. Besides, it induced cytoplasmic vacuolation in all CRC cells. Electron microscopy images showed the aberrant dilation of endoplasmic reticulum and mitochondria. Both mRNA and protein expressions of Alg-2 interacting proteinX (Alix), the marker of paraptosis, were inhibited by α-hed. Besides, both Swiss prediction and molecular docking showed that the structure of α-hed could tightly target to GPCRs. GPCRs were reported to activate the phospholipase C (PLC)-β3/ inositol 1,4,5-trisphosphate receptor (IP3R)/ Ca2+/ protein kinase C alpha (PKCα) pathway, and we then found all proteins and mRNA expressions of PLCβ3, IP3R, and PKCα were increased by α-hed. After blocking the GPCR signaling, α-hed could not elevate Ca2+ level and showed less CRC cell cytotoxicity. MAPK cascade is the symbol of paraptosis, and we then demonstrated that α-hed activated MAPK cascade by elevating Ca2+ flux. Since non-apoptotic cell death is presently emerging as a potential direction to overcome chemo-drug resistance, we then found α-hed also induced paraptosis in 5-fluorouracil-resistant (5-FU-R) CRC cells, and it reduced the growth of 5-FU-R CRC xenografts. Collectively, our findings proved α-hed as a promising candidate for inducing non-apoptotic cell death, paraptosis. It may overcome the resistance of apoptotic-based chemo-resistance in CRC.

Abstract PR002: Ferroptosis inducers can antagonize prostate cancer-bone interactions

Abstract Prostate cancer (PCa) is a leading cause of mortality, primarily due to its ability to metastasize to the bone. The incidence, rates of metastasis and mortality rates are higher in men of African descent compared to other races. The transcription factor High Mobility Group AT-Hook 2 (HMGA2) plays a crucial role in regulating gene expression and has been implicated in tumorigenesis and the metastatic process. Our recent study revealed that overexpression of the wild-type/full-length HMGA2 isoform in PCa cells promotes cancer progression by triggering epithelial mesenchymal transition (EMT), whereas truncated HMGA2 isoform promotes progression through oxidative stress signaling. Ferroptosis is a regulated form of cell death induced by the accumulation of iron-dependent lipid reactive oxygen species (ROS). Exploiting this oxidative stress pathway offers a promising therapeutic approach for cancer treatment, especially for apoptosis-resistant cancer cells. In our investigation, we aimed to assess the effectiveness of RSL3, a known ferroptosis inducer, in inhibiting interactions between prostate cancer cells and bone. To achieve this, we co-cultured various human PCa cell lines: C4-2B (Caucasian/bone metastatic), C4-2B MDVR (enzalutamide-resistant), MDAPCa-2b (African American/bone metastatic), LNCaP (Caucasian/non-metastatic) that stably overexpresses Neo control, HMGA2 wild-type or truncated isoform with human ground bone matrix powder (GBM) to recapitulate the bone microenvironment. We collected the conditioned media (CM) from these co-cultures and subsequently added it to parental LNCaP cells, with or without RSL3 ferroptosis inducer, plus or minus Ferrostatin-1 (Fer-1) ferroptosis inhibitor. We then assessed cell viability, migration, and lipid ROS levels. Our results demonstrated that LNCaP cells treated with CM from cancer cells co-cultured with GBM exhibited increased cell viability and migration. However, the addition of RSL3 effectively inhibited cell viability by inactivating GPX4 antioxidant and triggering lipid ROS production; this could be reversed by Fer-1. This suggests that ferroptosis inducers such as RSL3 hold potential as a treatment strategy for prostate cancer bone metastasis. Further investigation is necessary to comprehensively evaluate the impact of RSL3 treatments and elucidate the underlying mechanisms involved. By exploring these avenues, we can advance our understanding and potentially develop targeted therapies to combat the devastating effects of prostate cancer bone metastasis. Acknowledgements: These studies were supported by NIH/NIGMS/RISE SR25GM060414 and NIH/NIMHD 2U54MD007590; 5U54MD013376. Citation Format: Precious Elechi Dike, Taaliah Campbell, Valerie Odero-Marah. Ferroptosis inducers can antagonize prostate cancer-bone interactions [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr PR002.

Pomiferin targets SERCA, mTOR, and P-gp to induce autophagic cell death in apoptosis-resistant cancer cells, and reverses the MDR phenotype in cisplatin-resistant tumors in vivo

Drug resistance in cancer has been classified as innate resistance or acquired resistance, which were characterized by apoptotic defects and ABC transporters overexpression respectively. Therefore, to preclude or reverse these resistance mechanisms could be a promising strategy to improve chemotherapeutic outcomes. In this study, a natural product from Osage Orange, pomiferin, was identified as a novel autophagy activator that circumvents innate resistance by triggering autophagic cell death via SERCA inhibition and activation of the CaMKKβ-AMPK-mTOR signaling cascade. In addition, pomiferin also directly inhibited the P-gp (MDR1/ABCB1) efflux and reversed acquired resistance by potentiating the accumulation and efficacy of the chemotherapeutic agent, cisplatin. In vivo study demonstrated that pomiferin triggered calcium-mediated tumor suppression and exhibited an anti-metastatic effect in the LLC-1 lung cancer-bearing mouse model. Moreover, as an adjuvant, pomiferin potentiated the anti-tumor effect of the chemotherapeutic agent, cisplatin, in RM-1 drug-resistant prostate cancer-bearing mouse model by specially attenuating ABCB1-mediated drug efflux, but not ABCC5, thereby promoting the accumulation of cisplatin in tumors. Collectively, pomiferin may serve as a novel effective agent for circumventing drug resistance in clinical applications.

Investigating the Expression of Genes Involved in Apoptosis and Mutation in Ovarian Cancer Cell Line and Possible Hepatotoxicity in Rats Induced by New Green Synthesized Ag-NPs

Silver nanoparticles (Ag-NPs) can enter tumor cells through endocytosis and transfer to mitochondria, then disrupt mitochondrial function, damage deoxyribonucleic acid (DNA), and finally lead to cell death and apoptosis. As the Ag-NPs synthesized by Moringa peregrina leaf extract contain biomolecules such as flavonoids and terpenoids, they may suppress cancer by disrupting the flow of autophagy and inhibiting the differentiation of cancer cells, especially in apoptosisresistant cancer cells. Accordingly, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid (MTT) assay proved that Ag-NPs could inhibit the OVCAR-3 cell line in a time- and concentrationdependent manner. Real-time polymerase chain reaction (PCR) results showed that the ratio of the pro-apoptotic Bak1 gene to the anti-apoptotic Bclx gene increased about 10 times compared to the control. Also, the expression of the caspase-3 gene has increased about 18 times compared to the control. In addition, it was found that Ag-NPs can inhibit the progression of ovarian cancer cell lines and decrease the expression of the AKT1 gene by 0.08. And the more important point was the safety of Ag-NPs, which was checked by the lipid peroxidation method and it was confirmed that the treated hepatocytes did not have any significant difference in the production of malondialdehyde with the control and probably do not cause hepatotoxicity.

Mixed lineage kinase domain-like pseudokinase: Conventional (necroptosis) and unconventional (necroptosis-independent) functions and features.

Mixed lineage kinase domain-like pseudokinase (MLKL) is the terminal and indispensable mediator of necroptosis. Necroptosis, also known as programmed cell necrosis, is a caspase-independent cell death mechanism involved in various pathologic and inflammatory processes. Triggering necroptosis could be an alternative approach in treating apoptosis-resistant cancer cells to prevent recurrent disease. In addition to its function in necroptosis, MLKL plays a role as a regulator in many cellular processes independent of necroptosis. A better understanding of the intracellular function of MLKL and its role in various diseases and pathologic conditions is needed to enable discovery of new targeted therapies. Various necroptosis-dependent and independent functions of MLKL are reviewed in this chapter, with a focus on functions of MLKL in necroptosis, autophagy, inflammation, tissue regeneration, and endosomal trafficking.

Investigation of Apoptotic Effect of Klotho Protein on Human Colorectal Cancer Cells via TRAIL Death Receptors

Klotho is a transmembrane protein which is deficiency has pleiotropic effects in a number of aging-related disease processes and various cancers. In some recent studies about klotho protein disorders, it has been shown to klotho is effective in various cancers including lung, liver, breast, kidney, and colon. TNF-related apoptosis-inducing ligand (TRAIL), a TNF family molecule, is a cytokine that stimulates apoptosis through death receptors in many cancer types and therefore attracts attention for tumor therapies in various preclinical models. Interaction with TRAIL death receptors create an apoptotic effect in cancer treatments by reducing the proliferation of cancer cells. In this study, it was aimed to investigate the effects of exogen klotho administration on cell viability and apoptosis on TRAIL death receptors (TRAIL1 and TRAILR2) in human healthy colon cells (CCD 841 CoN) and TRAIL-resistant human colorectal cancer cells (caco2). For this purpose, cells were treated with different concentrations of klotho for 24 and 48 hours. To determine the cell viability, proliferation, and death receptors effects of klotho protein on cancer and healthy cells evaluations with WST-8 and Real-Time qRT-PCR analysis were performed. Our results showed that the increase in klotho protein concentration did not have a significant effect on cell viability in healthy colon cells, whereas it decreased cell viability and proliferation in apoptosis-resistant human colorectal cancer cells. Relative gene expression of TRAIL1 and TRAILR2 death receptors increased with klotho applied to the apoptosis-resistant colorectal cancer cell line caco-2. Therefore, targeting the ligand-receptors that induce TNF-related apoptosis with the klotho protein can be considered as a potential therapeutic approach for cancer therapy.

Luteolin induces pyroptosis in HT-29 cells by activating the Caspase1/Gasdermin D signalling pathway.

Luteolin, which is a natural flavonoid, has anti-inflammatory, antioxidant, and anticancer properties. Numerous studies have proven that luteolin inhibits the growth of many types of cancer cells by promoting apoptosis, autophagy, and cell cycle arrest in tumour cells. However, in vivo research on this topic has been limited. In addition, other studies have shown that luteolin exerts a good inhibitory effect on apoptosis-resistant cancer cells. While existing studies have not completely elucidated the mechanism underlying this phenomenon, we assume that luteolin, which is a natural compound that exerts its effects through various mechanisms, may have the potential to inhibit tumour growth. In our study, we proved that luteolin exerted a good inhibitory effect on the proliferation of colon cancer cells according to CCK8 and EdU fluorescence assays, and the same conclusion was drawn in animal experiments. In addition, we found that luteolin, which is an antioxidant, unexpectedly promoted oxidative stress as shown by measuring the levels of oxidative balance-related indicators, such as reactive oxygen species (ROS), SOD, H2O2 and GSH. However, the decreased oxidation of luteolin-treated HT-29 cells after treatment with the active oxygen scavenger NAC did not reverse the inhibition of cell growth. However, the Caspase1 inhibitor VX765 did reverse the inhibition of cell growth. Western blotting analysis showed that luteolin treatment increased the expression of Caspase1, Gasdermin D and IL-1β, which are members of the pyroptosis signalling pathway, in colon cancer cells. We further intuitively observed NLRP3/Gasdermin D colocalization in luteolin-treated HT-29 cells and mouse tumour tissues by immunofluorescence. These results suggest that luteolin inhibits the proliferation of colon cancer cells through a novel pathway called pyroptosis. This study provides a new direction for the development of natural products that inhibit tumour growth by inducing pyroptosis.

Relative refractoriness of breast cancer cells to tumour necrosis factor-α induced necroptosis.

Necroptosis, a recently identified programmed cell death pathway, has attracted attention as an alternative route to target apoptosis-resistant cancer cells. The status of the necroptosis pathway in different subtypes of breast cancer has not been well explored. Stimulating the cells by TNF-α can trigger cell survival or death depending on the combination of downstream players involved. In this work, we attempted to induce necroptosis in them using a combination of TNF-α and Z-VAD-FMK with and without chemotherapy. Cell viability, apoptosis, and necroptosis were assessed using MTT and Annexin-V/PI assays, respectively. Gene and protein expression was analysed by qPCR and immunophenotyping. Both the cell lines were resistant to induction of cell death by necroptosis. There was no enhancement in cell death when chemotherapeutic drugs were combined with necroptosis induction. Expression studies showed reduced translational expression of key necroptosis molecules like RIP kinases and MLKL in breast cancer cells compared to positive control cell line L929. Also, cell survival molecules were expressed more in MDA-MB-231 in contrast to death pathway molecules which were expressed more in T47D cells. In this work, the two breast cancer cell lines were observed to be resistant to TNF-α induced necroptosis with or without chemotherapy. Expression of key necroptosis players revealed relative insufficiency of the molecular machinery involved in the above pathway. In our opinion this may be the cause for resistance to necroptosis and novel strategies to upregulate these molecules need to be developed to sensitize the breast cancer cells towards cell death by necroptosis.

A REVIEW OF ADVANCED NANOTECHNOLOGIES AND DRUG DELIVERY SYSTEMS OF SALINOMYCIN AND THEIR ROLE IN TRIPLE-NEGATIVE BREAST CANCER

Cancer cells spread to other tissues and organs when they divide incorrectly. Breast cancer (BC) is the main cause of cancer-related mortality globally. Some recent studies on cancer stem cells (CSCs), drug resistance, tumor recurrence and metastasis, and the significance of CD44+in targeted treatment for breast cancer are covered. Breast cancer stem cells (BCSCs) and bulk BC cells must be eliminated for the disease to be eliminated. Researchers have shown that Streptomyces Albus-derived monocarboxylic polyether antibiotic salinomycin kills human cancer stem cells (CSCs) and prevents the spread and growth of breast cancer cells. Several drug and apoptosis resistance mechanisms may also trigger apoptosis in breast cancer cells when salinomycin is used in combination with the treatment. Apoptosis-resistant cancer cells and cancer stem cells are both susceptible to the anticancer drug salinomycin. Salinomycin may be able to inhibit CSCs, as well as the source and structure modification of salinomycin analog exhibit potent anticancer activity, the effect of salinomycin on chemotherapeutic-resistant CSCs, and the various mechanisms by which salinomycin inhibits cancer stem cells in this study. Method and delivery technique for salinomycin Nano formulation in triple-negative breast cancer and also contains pharmacokinetics and toxicity of salinomycin. Salinomycin-based drug delivery system is the subject of the patent information. Tumor genesis, development, and invasion are all aided by salinomycin. It's possible to boost the effectiveness of cancer therapy by focusing on cancer stem cells (CSCs).

Co-targeting of BAX and BCL-XL proteins broadly overcomes resistance to apoptosis in cancer

Deregulation of the BCL-2 family interaction network ensures cancer resistance to apoptosis and is a major challenge to current treatments. Cancer cells commonly evade apoptosis through upregulation of the BCL-2 anti-apoptotic proteins; however, more resistant cancers also downregulate or inactivate pro-apoptotic proteins to suppress apoptosis. Here, we find that apoptosis resistance in a diverse panel of solid and hematological malignancies is mediated by both overexpression of BCL-XL and an unprimed apoptotic state, limiting direct and indirect activation mechanisms of pro-apoptotic BAX. Both survival mechanisms can be overcome by the combination of an orally bioavailable BAX activator, BTSA1.2 with Navitoclax. The combination demonstrates synergistic efficacy in apoptosis-resistant cancer cells, xenografts, and patient-derived tumors while sparing healthy tissues. Additionally, functional assays and genomic markers are identified to predict sensitive tumors to the combination treatment. These findings advance the understanding of apoptosis resistance mechanisms and demonstrate a novel therapeutic strategy for cancer treatment.

Suppression of non-small-cell lung cancer A549 tumor growthby an mtDNA mutation-targeting pyrrole-imidazole polyamide-triphenylphosphonium and a senolytic drug.

Certain somatic mutations in mtDNA were associated with tumor progression and frequently found in a homoplasmic state. We recently reported that pyrrole‐imidazole polyamide conjugated with the mitochondria‐delivering moiety triphenylphosphonium (PIP‐TPP) targeting an mtDNA mutation efficiently induced apoptosis in cancer cells with the mutation but not normal cells. Here, we synthesized the novel PIP‐TPP, CCC‐021‐TPP, targeting ND6 14582A > G homoplasmic missense mutation that is suggested to enhance metastasis of non‐small‐cell lung cancer A549 cells. CCC‐021‐TPP did not induce apoptosis but caused cellular senescence in the cells, accompanied by a significant induction of antiapoptotic BCL‐XL. Simultaneous treatment of A549 cells with CCC‐021‐TPP and the BCL‐XL selective inhibitor A‐1155463 resulted in apoptosis induction. Importantly, the combination induced apoptosis and suppressed tumor growth in an A549 xenografted model. These results highlight the potential of anticancer therapy with PIP‐TPPs targeting mtDNA mutations to induce cell death even in apoptosis‐resistant cancer cells when combined with senolytics.

Enhancement of Apo2L/TRAIL signaling pathway receptors by theactivation of Klotho genewithCRISPR/Cas9 in Caco-2 colon cancer cells.

Human Klotho gene has many known functions such as anti-aging and anti-tumor, and decreased expression of this gene causes malignant formations in most types of cancer, including colon cancer. Interacting with TRAIL death receptors (DR4 and DR5) induces an apoptotic effect in cancer treatments by reducing the proliferation of cancer cells. The present study aimed to investigate downstream effect of overexpression of Klotho gene, which is known to have an antitumor effect on resistant human colon cancer cells, by examining its action on TRAIL death and decoy (DcR1 and DcR2) receptors for the first time. For this purpose, upregulation of human Klotho gene was achieved with CRISPR/Cas9-mediated system in resistant human colon cancer Caco-2 cells. To determine the effect of upregulation of Klotho gene on cancer cells evaluations with flow cytometry, WST-8, qRT-PCR, ELISA, and immunohistochemical analysis were performed. Then, Klotho gene was knocked out and its apoptotic effect was tested to find out whether it is due to overexpression of Klotho gene or not. Our results indicate that overexpression of Klotho gene in Caco-2 cells via CRISPR/Cas9-sensitized TRAIL death receptor DR4 suppresses the proliferation of cells by leading to apoptosis. Thus, this study conducted on apoptosis-resistant colon cancer cells may bring new insights about the role of Klotho gene in colon cancer.

Polygodial and Ophiobolin A Analogues for Covalent Crosslinking of Anticancer Targets.

In a search of small molecules active against apoptosis-resistant cancer cells, including glioma, melanoma, and non-small cell lung cancer, we previously prepared α,β- and γ,δ-unsaturated ester analogues of polygodial and ophiobolin A, compounds capable of pyrrolylation of primary amines and demonstrating double-digit micromolar antiproliferative potencies in cancer cells. In the current work, we synthesized dimeric and trimeric variants of such compounds in an effort to discover compounds that could crosslink biological primary amine containing targets. We showed that such compounds retain the pyrrolylation ability and possess enhanced single-digit micromolar potencies toward apoptosis-resistant cancer cells. Target identification studies of these interesting compounds are underway.

Metformin and sodium dichloroacetate effects on proliferation, apoptosis, and metabolic activity tested alone and in combination in a canine prostate and a bladder cancer cell line.

An important approach in tumor therapy is combining substances with different action mechanisms aiming to enhance the antineoplastic effect, decrease the therapeutic dosage, and avoid resistance mechanisms. Moreover, evaluating compounds already approved for the treatment of non-neoplastic diseases is promising for new antineoplastic therapies. Sodium dichloroacetate (DCA) reactivates oxidative phosphorylation in the cancer cell mitochondria, reducing apoptosis resistance in cancer cells. Furthermore, metformin inhibits the proliferation of tumor cells and CD133+ cancer -stem-like cells. In the present study, we evaluated the independent and synergistic effect of metformin and DCA on the metabolic activity, cell proliferation, and apoptosis of a canine prostate adenocarcinoma (Adcarc1258) and a transitional cell carcinoma cell line (TCC1506) in comparison to a primary canine fibroblast culture. Determining metformin uptake in tumor cells was performed by quantitative HPLC. Depending on the dosage, metformin as a single agent inhibited the metabolic activity and cell proliferation of the tumor cells, showing only minor effects on the fibroblasts. Furthermore, 1 mM metformin increased apoptosis over 96 h in the tumor cell lines but not in fibroblasts. Additionally, metformin uptake into the tumor cells in vitro was measurable by quantitative HPLC. Synergistic effects for the combination therapy were observed in both neoplastic cell lines as well as in the fibroblasts. Based on these results, metformin might be a promising therapeutic agent for canine urogenital tumors. Further studies on kinetics, toxicology, bioavailability, and application of metformin in dogs are necessary.

The Multifaceted Role of Flavonoids in Cancer Therapy: Leveraging Autophagy with a Double-Edged Sword.

Flavonoids are considered as pleiotropic, safe, and readily obtainable molecules. A large number of recent studies have proposed that flavonoids have potential in the treatment of tumors by the modulation of autophagy. In many cases, flavonoids suppress cancer by stimulating excessive autophagy or impairing autophagy flux especially in apoptosis-resistant cancer cells. However, the anti-cancer activity of flavonoids may be attenuated due to the simultaneous induction of protective autophagy. Notably, flavonoids-triggered protective autophagy is becoming a trend for preventing cancer in the clinical setting or for protecting patients from conventional therapeutic side effects in normal tissues. In this review, focusing on the underlying autophagic mechanisms of flavonoids, we hope to provide a new perspective for clinical application of flavonoids in cancer therapy. In addition, we highlight new research ideas for the development of new dosage forms of flavonoids to improve their various pharmacological effects, establishing flavonoids as ideal candidates for cancer prevention and therapy in the clinic.

Bcl-2/Bcl-xL inhibitor ABT-263 overcomes hypoxia-driven radioresistence and improves radiotherapy

Hypoxia, a characteristic of most human solid tumors, is a major obstacle to successful radiotherapy. While moderate acute hypoxia increases cell survival, chronic cycling hypoxia triggers adaptation processes, leading to the clonal selection of hypoxia-tolerant, apoptosis-resistant cancer cells. Our results demonstrate that exposure to acute and adaptation to chronic cycling hypoxia alters the balance of Bcl-2 family proteins in favor of anti-apoptotic family members, thereby elevating the apoptotic threshold and attenuating the success of radiotherapy. Of note, inhibition of Bcl-2 and Bcl-xL by BH3-mimetic ABT-263 enhanced the sensitivity of HCT116 colon cancer and NCI-H460 lung cancer cells to the cytotoxic action of ionizing radiation. Importantly, we observed this effect not only in normoxia, but also in severe hypoxia to a similar or even higher extent. ABT-263 furthermore enhanced the response of xenograft tumors of control and hypoxia-selected NCI-H460 cells to radiotherapy, thereby confirming the beneficial effect of combined treatment in vivo. Targeting the Bcl-2 rheostat with ABT-263, therefore, is a particularly promising approach to overcome radioresistance of cancer cells exposed to acute or chronic hypoxia with intermittent reoxygenation. Moreover, we found intrinsic as well as ABT-263- and irradiation-induced regulation of Bcl-2 family members to determine therapy sensitivity. In this context, we identified Mcl-1 as a resistance factor that interfered with apoptosis induction by ABT-263, ionizing radiation, and combinatorial treatment. Collectively, our findings provide novel insights into the molecular determinants of hypoxia-mediated resistance to apoptosis and radiotherapy and a rationale for future therapies of hypoxic and hypoxia-selected tumor cell fractions.

Alternative approaches to overcome chemoresistance to apoptosis in cancer.

Apoptosis, or programmed cell death, is a form of regulated cell death (RCD) that is essential for organogenesis and homeostatic maintenance of normal cell populations. Apoptotic stimuli activate the intrinsic and/or extrinsic pathways to induce cell death due to perturbations in the intracellular and extracellular microenvironments, respectively. In patients with cancer, the induction of apoptosis by anticancer drugs and radiation can produce cancer cell death. However, tumor cells can adapt and become refractory to apoptosis-inducing therapies, resulting in the development of clinical resistance to apoptosis. Drug resistance facilitates the development of aggressive primary tumors that eventually metastasize, leading to therapy failure and mortality. To overcome the resistance to apoptosis to neoadjuvant chemotherapy or targeted therapy, alternative targets of RCD can be induced in apoptosis-resistant cancer cells. Alternatively, cell death can be independent of apoptosis and this strategy could be utilized to develop novel anti-cancer therapies. This chapter discusses approaches that could be employed to overcome clinical resistance to apoptosis in cancer cells.

Anoikis resistance conferred by tenascin-C-derived peptide TNIIIA2 and its disruption by integrin inactivation

Glioblastoma multiforme (GBM), the most common brain tumor in adults, has an extremely poor prognosis, which is attributed to the aggressive properties of GBM cells, such as dysregulated proliferation and disseminative migration. We recently found that peptide TNIIIA2, derived from tenascin-C (TNC), which is highly expressed in GBM, contributes to the acquisition of these aggressive properties through β1-integrin activation. In general, cancer cells often acquire an additional malignant property that confers resistance to apoptosis due to loss of adhesion to the extracellular matrix, termed anoikis resistance. Our present results show that regulation of β1-integrin activation also plays a key role in both the development and loss of anoikis resistance in GBM cells. Despite being derived from a GBM with an extremely poor prognosis, the human GBM cell line T98G was susceptible to anoikis but became anoikis resistant via treatment with peptide TNIIIA2, which is able to activate β1-integrin. The TNIIIA2-conferred anoikis resistance of T98G cells was disrupted by further addition of peptide FNIII14, which has the ability to inactivate β1-integrin. Moreover, anchorage-independent survival of GBM cells in suspension culture was abrogated by peptide FNIII14, but not by RGD and CS-1 peptides, which are antagonistic for integrins α5β1, αvβ3, and α4β1. These results suggest that GBM cells develop anoikis resistance through activation of β1-integrin by TNC-derived peptide TNIIIA2, which is abundantly released into the tumor microenvironment of GBM. Inactivation of β1-integrin may provide a promising strategy to overcome the apoptosis resistance of cancer cells, including GBM.