Chemotherapy-induced Resistance Research Articles

Blockade of chemo-resistance to 5-FU by a CK2-targeted combination via attenuating AhR-TLS-promoted genomic instability in human colon cancer cells

As highly expressed in several human cancers, Casein Kinase 2 (CK2) is involved in chemotherapy-induced resistance. As a new potent CK2 inhibitor, DN701 is used to overcome chemoresistance through its synergistic antitumor effect with 5-fluorouracil (5-FU). Translesion DNA synthesis (TLS) has drawn our attention because it is associated with the development of chemo-resistance and tumor recurrence. The in vitro biological properties of 5-FU-resistant colon cancer cells revealed that DN701 combined with 5-FU could overcome chemo-resistance via blocking CK2-mediated aryl hydrocarbon receptor (AhR) and TLS-induced DNA damage repair (DDR). Moreover, pharmacologic and genetic inhibitions of AhR potently reduced TLS-promoted genomic instability. The mechanistic studies showed that combined DN701 with 5-FU was investigated to inhibit CK2 expression level and AhR-TLS-REV1 pathway. Meanwhile, DN701 combined with 5-FU could reduce CK2-AhR-TLS genomic instability, thus leading to superior in vivo antitumor effect. The insights provide a rationale for combining DN701 with 5-FU as a therapeutic strategy for patients with colon cancer.

A redox-responsive self-assembling COA-4-arm PEG prodrug nanosystem for dual drug delivery suppresses cancer metastasis and drug resistance by downregulating hsp90 expression.

Metastasis and resistance are main causes to affect the outcome of the current anticancer therapies. Heat shock protein 90 (Hsp90) as an ATP-dependent molecular chaperone takes important role in the tumor metastasis and resistance. Targeting Hsp90 and downregulating its expression show promising in inhibiting tumor metastasis and resistance. In this study, a redox-responsive dual-drug nanocarrier was constructed for the effective delivery of a commonly used chemotherapeutic drug PTX, and a COA-modified 4-arm PEG polymer (4PSC) was synthesized. COA, an active component in oleanolic acid that exerts strong antitumor activity by downregulating Hsp90 expression, was used as a structural and functional element to endow 4PSC with redox responsiveness and Hsp90 inhibitory activity. Our results showed that 4PSC/PTX nanomicelles efficiently delivered PTX and COA to tumor locations without inducing systemic toxicity. By blocking the Hsp90 signaling pathway, 4PSC significantly enhanced the antitumor effect of PTX, inhibiting tumor proliferation and invasiveness as well as chemotherapy-induced resistance invitro. Remarkable results were further confirmed invivo with two preclinical tumor models. These findings demonstrate that the COA-modified 4PSC drug delivery nanosystem provides a potential platform for enhancing the efficacy of chemotherapies.

Copper Increases the Sensitivity of Cholangiocarcinoma Cells to Tripterine by Inhibiting TMX2-Mediated Unfolded Protein Reaction Activation.

Chemotherapy-induced adaptive resistance is a significant factor that contributes to low therapeutic efficacy in tumor cells. The unfolded protein response (UPR) is a key mechanism in the development of drug resistance and serves as a critical reactive system for endoplasmic reticulum stress. Cu(II) can reduce the abundance of 60S ribosomal subunits and inhibit rRNA processing, leading to a decrease in the translation efficiency of the GRP78/BiP mRNA, which serves as a primary sensor for UPR activation. In this study, CuET-Lipid@Cela, composed of CuET and tripterine (Cela), demonstrates a significant synergistic antitumor effect on cholangiocarcinoma (CCA) cells. RNA-Seq is used to investigate the underlying mechanism, which suggests that the transmembrane protein 2 (TMX2) gene may be crucial in Cu(II) regulation of UPR by inhibiting the activation of GRP78/BiP and PERK/eIF2α. The synergistic antitumor efficacy of CuET-Lipid@Cela via inhibition of TMX2 is also confirmed in a myrAKT/YapS127A plasmid-induced primary CCA mouse model, providing new insights into the reversal of acquired chemotherapy-induced resistance in CCA.

The Prognostic and Therapeutic Implications of the Chemoresistance Gene BIRC5 in Triple-Negative Breast Cancer.

Chemoresistance affects TNBC patient treatment responses. Therefore, identifying the chemoresistant gene provides a new approach to understanding chemoresistance in TNBC. BIRC5 was examined in the current study as a tool for predicting the prognosis of TNBC patients and assisting in developing alternative therapies using online database tools. According to the examined studies, BIRC5 was highly expressed in 45 to 90% of TNBC patients. BIRC5 is not only abundantly expressed but also contributes to resistance to chemotherapy, anti-HER2 therapy, and radiotherapy. Patients with increased expression of BIRC5 had a median survival of 31.2 months compared to 85.8 months in low-expression counterparts (HR, 1.73; CI, 1.4-2.13; p = 2.5 × 10-7). The overall survival, disease-free survival, relapse-free survival, distant metastasis-free survival, and the complete pathological response of TNBC patients with high expression of BIRC5 who received any chemotherapy (Taxane, Ixabepilone, FAC, CMF, FEC, Anthracycline) and anti-HER2 therapy (Trastuzumab, Lapatinib) did not differ significantly from those patients receiving any other treatment. Data obtained indicate that the BIRC5 promoter region was substantially methylated, and hypermethylation was associated with higher BIRC5 mRNA expression (p < 0.05). The findings of this study outline the role of BIRC5 in chemotherapy-induced resistance of TNBC, further indicating that BIRC5 may serve as a promising prognostic biomarker that contributes to chemoresistance and could be a possible therapeutic target. Meanwhile, several in vitro studies show that flavonoids were highly effective in inhibiting BIRC5 in genetically diverse TNBC cells. Therefore, flavonoids would be a promising strategy for preventing and treating TNBC patients with the BIRC5 molecule.

Efficacy and safety of ibrutinib in mantle cell lymphoma: A systematic review and meta-analysis.

Since the US Food and Drug Administration (FDA) approved ibrutinib to treat patients with refractory/relapsed mantle cell lymphoma (R/R MCL), it is used in clinical trials, whether as a single agent or in combination with other chemotherapy agents. The efficacy and safety of ibrutinib administration alone or in combinations have not been studied systematically. This study systematically reviewed the efficacy and safety of ibrutinib-containing regimens for the treatment of patients with MCL. We performed a systematic search in PubMed, Cochrane CENTRAL, Embase, Web of Science, and Scopus. Then, a team of independent reviewers selected relevant studies and extracted the data. From a total of 1,436 studies, 12 trials were eligible. The overall response rates (ORRs) of patients with R/R MCL receiving single-agent ibrutinib ranged between 62.7% to 93.8%, and the ORRs of ibrutinib combinations ranged from 74 to 88%. In patients with newly diagnosed MCL receiving ibrutinib and rituximab, ORR ranged from 84 to 100%. The highest progression-free survival (PFS) was reported in patients receiving ibrutinib and rituximab (43months). The meta-analysis performed on adverse events (AEs) demonstrated that single-agent ibrutinib had a high risk of bleeding, nausea, and diarrhea. Single-agent ibrutinib showed acceptable efficacy and safety in the treatment of patients with MCL. Moreover, combining ibrutinib with other agents such as rituximab, venetoclax, and ublituximab can increase its efficacy and reduce chemotherapy-induced resistance in most cases; however, in the case of combination therapy, patients need to be monitored more strictly in terms of AEs. In our review, the ibrutinib and rituximab combination showed promising results in patients with R/R MCL. Also, this combination showed favorable efficacy and safety in patients with newly diagnosed untreated MCL, making it a great candidate to be studied more in large and well-designed trials.

Dysregulated Metabolism in Cancer

Metabolism describes the cellular bioenergetic pathways that provide energy and macromolecules for protein, lipid, and nucleic acid syntheses. In cancer, malignant cells alter the metabolic pathways to acquire nutrients needed for proliferation and survival. The various metabolic modifications exhibited by cancer cells include aerobic glycolysis, decreased oxidative phosphorylation, and elevated production of biosynthetic intermediates. To support the increasing need for these metabolic modifications, cancer cells increase the expressions of plasma membrane transporters and enzymes involved in the metabolic pathways. Additionally, some cancer cells escape chemotherapy treatment by reprogramming their metabolic activities. This chemotherapy-induced resistance mechanism allows malignant cells to promote their survival as well as to provide defense against cell damage by engaging various metabolic shunt pathways. Therefore, understanding metabolic reprogramming in cancer may provide useful information that can further be exploited to strategize potential treatment interventions and subsequently foster better outcomes among patients with cancer.

AdipoRon and Pancreatic Ductal Adenocarcinoma: a future perspective in overcoming chemotherapy-induced resistance?

The latest scientific knowledge has provided additional insights accountable for the worst prognosis for pancreatic ductal adenocarcinoma (PDAC). Among the causative factors, the aptitude to develop resistance towards approved medications denotes the master key for understanding the lack of improvement in PDAC survival over the years. Even though several compounds have achieved encouraging results at preclinical stage, no new adjuvant agents have reached the bedside of PDAC patients lately. The adiponectin receptor agonist AdipoRon is emerging as a promising anticancer drug in different cancer models, particularly in PDAC. Building on the existing findings, we recently reinforced its candidacy in PDAC cells, proposing AdipoRon either as a suitable partner in gemcitabine-based treatment or as an effective drug in resistant cells. Crossing the current state-of-the-art, herein we provide a critical perspective on AdipoRon to figure out whether this receptor agonist can potentially be considered a future therapeutic choice in overcoming chemotherapy-induced resistance, expressly in PDAC.

A novel oncotherapy strategy: Direct thrombin inhibitors suppress progression, dissemination and spontaneous metastasis in non-small cell lung cancer.

Cancer cachexia and cancer-associated thrombosis are potentially fatal outcomes of advanced cancer. Nevertheless, thrombin expression in non-small cell lung cancer (NSCLC) primary tumour tissues and the association between prognosis of NSCLC patients remain largely unknown. Clinical pathological analysis was performed to determine the relationship between thrombin and tumour progression. Effects of r-hirudin and direct thrombin inhibitor peptide (DTIP) on cancer progression were evaluated. Western blotting, immunohistochemistry, and immunofluorescence were used to explore the inhibition mechanism of r-hirudin and DTIP. The therapeutic effect of the combination of DTIP and chemotherapy was determined. Thrombin expression in NSCLC tissues was closely related to clinicopathological features and the prognosis of patients. Thrombin deficiency inhibited tumour progression. The novel thrombin inhibitors, r-hirudin and DTIP, inhibited cell invasion and metastasis in vitro. They inhibited tumour growth and metastasis in orthotopic lung cancer model, inhibited cell invasion, and prolonged survival after injection of tumour cells via the tail vein. They also inhibited angiogenesis and spontaneous metastases from subcutaneously inoculated tumours. The promotion by thrombin of invasion and metastasis was abolished in PAR-1-deficient NSCLC cells. r-hirudin and DTIP inhibited tumour progression through the thrombin-PAR-1-mediated RhoA and NF-κB signalling cascades via inhibiting MMP9 and IL6 expression. DTIP potentiated chemotherapy-induced growth and metastatic inhibition and inhibited chemotherapy-induced resistance in mice. Thrombin makes a substantial contribution, together with PAR-1, to NSCLC malignancy. The anti-coagulants, r-hirudin and DTIP, could be used in anti-tumour therapy and a combination of DTIP and chemotherapy might improve therapeutic effects.

MicroRNAs Involved in Small-cell Lung Cancer as Possible Agents for Treatment and Identification of New Targets.

Small-cell lung cancer, a neuro-endocrine type of lung cancers, responds very well to chemotherapy-based agents. However, a high frequency of relapse due to adaptive resistance is observed. Immunotherapy-based treatments with checkpoint inhibitors has resulted in improvement of treatment but the responses are not as impressive as in other types of tumor. Therefore, identification of new targets and treatment modalities is an important issue. After searching the literature, we identified eight down-regulated microRNAs involved in radiation- and chemotherapy-induced resistance, as well as three up-regulated and four down-regulated miRNAs with impacts on proliferation, invasion and apoptosis of small-cell lung cancer cells in vitro. Furthermore, one up-regulated and four down-regulated microRNAs with in vivo activity in SCLC cell xenografts were identified. The identified microRNAs are candidates for inhibition or reconstitution therapy. The corresponding targets are candidates for inhibition or functional reconstitution with antibody-based moieties or small molecules.

Abstract 66: MHC class I polypeptide related sequence A as contributing factor to chemotherapy-induced resistance

Abstract MHC class I polypeptide related sequence A (MICA) is a cell surface protein associated to tumor immunosurveillance activity, due to its ability to activate natural killer (NK) cells. Cleavage of MICA and generation of its soluble form (sMICA) has been described as an immunoevasion mechanism presented by aggressive tumors. In agreement with the role of MICA on tumor immunoevasion, recent studies correlated better prognosis for patients with higher levels of MICA expression in different types of cancer. Chemotherapeutic drugs are used to treat a great variety of malignant diseases. However, a fraction of patients under chemotherapy regimen stop responding to the treatment and develop recurrent tumors. We postulate that MICA can be a factor contributing to chemotherapy-induced resistance. To test our hypothesis, we tested the expression of MICA in prostate cancer-derived LNCaP and E006AA-hT cell lines were treated with bortezomib, a chemotherapeutic drug that inhibits proteasome activity. MTT cell viability assays showed that both cells had similar sensitivity to bortezomib, with IC50 of 10 nM and 8 nM for LNCaP and E006AA-hT, respectively. Flow cytometry analysis showed baseline difference in the cell fraction expressing surface MICA with 67% in LNCaP cells against 18% in E006AA-hT (p<000.1). Following treatment with bortezomib, the fraction of LNCaP cells expressing surface MICA increased 1.3-fold (p<0.01), while in the fraction of E006AA-hT cells expressing MICA yielded 2.3-fold increase (p<0.001). Baseline release rate of sMICA, assessed by ELISA analysis of culture supernatants, was 54 pg/ml/106cells for LNCaP and 5 pg/ml/106cells in E006AA-hT cells. Relative to baseline, sMICA release rate dropped 2-fold with bortezomib in LNCaP cells to 22 pg/ml/106cells (p<0.01). However, sMICA release rate in E006AA rose to 531 pg/ml/106cells (p<0.0001), more than 100-fold increase. Our findings show that, despite similar sensitivity to the killing effects of bortezomib in LNCaP and E006AA-hT, the release rate of sMICA in response to bortezomib is significantly distinct. These evidences lead us to propose that MICA is a contributing factor of resistance to chemotherapy, probably related to soluble MICA's immunoevasion properties. Further studies, testing cell specific ability of MICA's to affect cytotoxic activity in the context of chemotherapy-induced resistance will allow us to assess the value of this premise. This studies can open opportunities for new targeted immunotherapies, enhancing the innate immune system and avoiding the undesired effect of chemotherapy resistance. Citation Format: Marcelo Jun Sakiyama, Ingrid Espinoza, Deepak Kumar, Amit Reddy, Eldrin Bhanat, Krista Syrigos, Roya Gordji, Christian Gomez. MHC class I polypeptide related sequence A as contributing factor to chemotherapy-induced resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 66.

Analysis of temozolomide resistance in low-grade gliomas using a mechanistic mathematical model.

Understanding how tumors develop resistance to chemotherapy is a major issue in oncology. When treated with temozolomide (TMZ), an oral alkylating chemotherapy drug, most low-grade gliomas (LGG) show an initial volume decrease but this effect is rarely long lasting. In addition, it has been suggested that TMZ may drive tumor progression in a subset of patients as a result of acquired resistance. Using longitudinal tumor size measurements from 121 patients, the aim of this study was to develop a semi-mechanistic mathematical model to determine whether resistance of LGG to TMZ was more likely to result from primary and/or from chemotherapy-induced acquired resistance that may contribute to tumor progression. We applied the model to a series of patients treated upfront with TMZ (n=109) or PCV (procarbazine, CCNU, vincristine) chemotherapy (n=12) and used a population mixture approach to classify patients according to the mechanism of resistance most likely to explain individual tumor growth dynamics. Our modeling results predicted acquired resistance in 51% of LGG treated with TMZ. In agreement with the different biological effects of nitrosoureas, none of the patients treated with PCV were classified in the acquired resistance group. Consistent with the mutational analysis of recurrent LGG, analysis of growth dynamics using mathematical modeling suggested that in a subset of patients, TMZ might paradoxically contribute to tumor progression as a result of chemotherapy-induced resistance. Identification of patients at risk of developing acquired resistance is warranted to better define the role of TMZ in LGG.

Nanomedicine based curcumin and doxorubicin combination treatment of glioblastoma with scFv-targeted micelles: In vitro evaluation on 2D and 3D tumor models

NF-κB is strongly associated with poor prognosis of different cancer types and an important factor responsible for the malignant phenotype of glioblastoma. Overcoming chemotherapy-induced resistance caused by activation of PI3K/Akt and NF-κB pathways is crucial for successful glioblastoma therapy. We developed an all-in-one nanomedicine formulation for co-delivery of a chemotherapeutic agent (topoisomerase II inhibitor, doxorubicin) and a multidrug resistance modulator (NF-κB inhibitor, curcumin) for treatment of glioblastoma due to their synergism. Both agents were incorporated into PEG-PE-based polymeric micelles. The glucose transporter-1 (GLUT1) is overexpressed in many tumors including glioblastoma. The micellar system was decorated with GLUT1 antibody single chain fragment variable (scFv) as the ligand to promote blood brain barrier transport and glioblastoma targeting. The combination treatment was synergistic (combination index, CI of 0.73) against U87MG glioblastoma cells. This synergism was improved by micellar encapsulation (CI: 0.63) and further so with GLUT1 targeting (CI: 0.46). Compared to non-targeted micelles, GLUT1 scFv surface modification increased the association of micelles (>20%, P<0.01) and the nuclear localization of doxorubicin (∼3-fold) in U87MGcells, which also translated into enhanced cytotoxicity. The increased caspase 3/7 activation by targeted micelles indicates successful apoptosis enhancement by combinatory treatment. Moreover, GLUT1 targeted micelles resulted in deeper penetration into the 3D spheroid model. The increased efficacy of combination nanoformulations on the spheroids compared to a single agent loaded, or to non-targeted formulations, reinforces the rationale for selection of this combination and successful utilization of GLUT1 scFv as a targeting agent for glioblastoma treatment.

Abstract 5201: Identification of growth factors that promote the proliferation and drug resistance of human primary acute B lymphoblastic cells

Abstract Bone marrow mesenchymal stem cells (BMMSCs) contribute the survival, expansion, and drug resistance of leukemic cells. However, how BMMSCs promote the proliferation and drug resistance of leukemia remains to be poorly understood. Here, we derived a BM-derived stromal cell line that supported unlimited growth of human primary acute B lymphoblastic leukemic cells (B-ALL) by physical contacts with B-ALL cells and secreting growth factors. Nevertheless, its capacity of promoting primary B-ALL proliferation was abolished once the cell line was induced to differentiate into adipocytes. In xenograft models, we demonstrate that the presence of adipocytes suppressed the engraftment of primary B-ALL cells while the decrease of adipocytes enhanced the reconstitution of B-ALL. Consistently, we observed that the increase of numbers and diameters of adipocytes was correlated with remission after chemotherapy treatments in B-ALL patients. By comparing the global transcription profiles between the BM stromal cells and the adipocytes that were derived from the cell line, we identified a combination of cytokines and adherent proteins that were able to support the long-term growth of human primary B-ALL cells and desensitize them to chemotherapy drugs in a stromal-free culture condition. Furthermore, we showed that the PI3K/AKT pathways were involved in chemotherapy-induced resistance because targeting these signaling pathways increased the chemotherapy sensitivity of B-ALL in xenografts. Collectively, our results uncovered the mechanisms of BMMSCs supporting the survival, expansion, and drug resistance of human B-ALL cells. Citation Format: Peng Li, Zhiwu Jiang. Identification of growth factors that promote the proliferation and drug resistance of human primary acute B lymphoblastic cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5201.

NKP-1339: Maximum tolerated dose defined for first-in-human GRP78 targeted agent.

3033 Background: NKP-1339 is a first-in-class small molecule anti-cancer compound that down-regulates GRP78, a key regulator of misfolded protein processing and tumor survival/anti-apoptosis. GRP78 up-regulation occurs in many tumors, and is associated with intrinsic and chemotherapy-induced resistance. Preclinically, single agent NKP-1339 demonstrates activity against multiple tumor types, including chemoresistant lines. This phase I trial evaluates the safety, tolerability, maximum tolerated dose (MTD), pharmacokinetics, and pharmacodynamics (PD) of NKP-1339. Methods: Patients (pts) with advanced solid tumors, adequate organ function, ECOG 0-1 are enrolled. NKP-1339 is infused on day 1, 8, and 15 of 28 day cycles. Single pt cohorts are enrolled until grade 2 toxicity, then adjusted to standard 3+3 design. Doses from 20-780 mg/m2 are evaluated. PD samples for plasma GRP78 are collected. At MTD, an expanded cohort of 25 pts is enrolled. Results: 34 pts are enrolled for dose escalation: 30 evaluable for dose determination; 4 replaced due to tumor progression in cycle 1. Demographics: 19M/15F; median age 62 yrs (range 28 to 79). Tumor types: colorectal (CRC, 10), non-small cell lung (NSCLC, 8); neuroendocrine (NET, 5); head and neck (H&amp;N, 3); and other cancer (8). Dose limiting toxicity of grade (gr) 2-3 nausea, with gr 2 creatinine in 1 pt, occurred at 780 mg/m2; MTD is 625 mg/m2. Gr 1 fever/chills is observed above 420 mg/m2, but is prevented by steroid premedication. The most common drug-related events are gr 1 nausea, gr 1-2 vomiting, and gr 1-2 fatigue. No lab abnormalities were noted except reversible creatinine elevation in 4 pts: 3 pt with gr 1; 1 pt with gr 2 secondary to DLT. Partial response was in 1 pt (NET); stable disease in 7 pts, including NET (2), NSCLC (2), CRC (1), sarcoma (1), and unknown primary (1). Therapy duration 14+-88+ weeks. Soluble GRP78 is detected in the plasma of patients at baseline. Conclusions: NKP-1339is well tolerated with manageable side effects. Single agent activity is noted in multiple tumors including NET. Results from the expanded cohort and pre/post-therapy PD will be presented. Phase II single agent NKP-1339 and phase I NKP-1339 combination trials are planned.

Proteomic analysis of gemcitabine-induced drug resistance in pancreatic cancer cells

Currently, the most effective agent against pancreatic cancer is gemcitabine (GEM), which inhibits tumor growth by interfering with DNA replication and blocking DNA synthesis. However, GEM-induced drug resistance in pancreatic cancer compromises the therapeutic efficacy of GEM. To investigate the molecular mechanisms associated with GEM-induced resistance, 2D-DIGE and MALDI-TOF mass spectrometry were performed to compare the proteomic alterations of a panel of differential GEM-resistant PANC-1 cells with GEM-sensitive pancreatic cells. The proteomic results demonstrated that 33 proteins were differentially expressed between GEM-sensitive and GEM-resistant pancreatic cells. Of these, 22 proteins were shown to be resistance-specific and dose-dependent in the regulation of GEM. Proteomic analysis also revealed that proteins involved in biosynthesis and detoxification are significantly over-expressed in GEM-resistant PANC-1 cells. In contrast, proteins involved in vascular transport, bimolecular decomposition, and calcium-dependent signal regulation are significantly over-expressed in GEM-sensitive PANC-1 cells. Notably, both protein-protein interaction of the identified proteins with bioinformatic analysis and immunoblotting results showed that the GEM-induced pancreatic cell resistance might interplay with tumor suppressor protein p53. Our approach has been shown here to be useful for confidently detecting pancreatic proteins with differential resistance to GEM. Such proteins may be functionally involved in the mechanism of chemotherapy-induced resistance.

Identification of gene signatures involved in the mechanisms of multidrug resistance.

Identification of gene signatures involved in the mechanisms of multidrug resistance.

Downregulation of Notch signaling by γ-secretase inhibition can abrogate chemotherapy-induced apoptosis in T-ALL cell lines

Activation of Notch1 signaling plays an important role in the pathogenesis of precursor T-cell lymphoblastic leukemia (T-ALL). The Notch1 receptor is cleaved and activated via the gamma-secretase complex. Downregulation of Notch1 signaling by gamma-secretase inhibitors (GSIs) thus represents a potential novel therapeutic approach. In this study, we analyzed the response of four T-ALL cell lines to compound E, a potent gamma-secretase inhibitor, and to the combination of compound E with vincristine, daunorubicin, L-asparaginase (L-ASP), and dexamethasone (DEX). We identified two distinct types of responses: In type 1 cell lines, represented by TALL1 and HSB2, GSI-induced apoptosis followed cell cycle arrest and enhanced the induction of apoptosis caused by DEX and L-ASP. In type 2 cell lines, represented by CEM and Jurkat J6, GSI caused neither cell cycle block nor cell death. Notably, the combination of GSI with chemotherapy-induced resistance by decreasing apoptosis. In type 2 cells, GSI induced the upregulation of Bcl-xl mRNA and protein, which was thus identified as a candidate mechanism for the inhibition of apoptosis. In conclusion, the data presented here caution against clinical use of a combination treatment of GSI and chemotherapy in T-ALL.

Lysosomes and endoplasmic reticulum: Targets for improved, selective anticancer therapy

Most currently used anticancer agents are active against proliferating cells. Apoptosis signaling mechanisms induced by many such agents are impaired in tumor cells, leading to therapy resistance. Lysosomes and the endoplasmic reticulum (ER) hold promise as drug targets and mediators of apoptosis signaling which may be less affected by intrinsic or chemotherapy-induced resistance mechanisms. Tumor cell lysosomes contain increased levels of cathepsins, and the release of these enzymes into the cytosol may result in apoptosis or necrosis, as has been reported for TNF-alpha. It is also reported that tumor transformation leads to increased sensitivity to cathepsin B-dependent apoptosis. Tumor cells often show evidence of constitutive ER stress, possibly due to hypoxia and glucose depletion. Various anticancer drugs, including cisplatin and proteasome inhibitors, have been shown to induce ER stress. Manipulating the ER stress response of tumor cells is an interesting therapeutic strategy. We conclude that organelle damage responses can be used to trigger tumor cell death, and that the response to such damage may be triggered in cells that are resistant to conventional DNA-damaging agents.