The antiapoptotic member of the Bcl-2 family Mcl-1 is a CTL target in cancer patients

A Synthetic Overview of Benzoxazines and Benzoxazepines as Anticancer Agents

Benzoxazines and benzoxazepines are nitrogen and oxygen-containing six and seven-membered benzo-fused heterocyclic scaffolds, respectively. Benzoxazepines and benzoxazines are well-known pharmacophores in pharmaceutical chemistry, which are of significant interest and have been extensively studied because of their promising activity against various diseases including their wide range of anticancer activity. Several reports are known for synthesizing benzoxazine and benzoxazepine-based compounds in the literature. Herein this review provides a critical analysis of synthetic strategies towards benzoxazines and benzoxazepines along with various ranges of anticancer activities based on these molecules that have been reported from 2010 onwards. This review also focuses on the structure-activity relationship of the benzoxazine and benzoxazepine scaffolds containing bioactive compounds and describes how the structural modification affects their anticancer activity.

Tumor microenvironment antigens

The identification and characterization of tumor antigens are central objectives in developing anti-cancer immunotherapy. Traditionally, tumor-associated antigens (TAAs) are considered relatively restricted to tumor cells (i.e., overexpressed proteins in tumor cells), whereas tumor-specific antigens (TSAs) are considered unique to tumor cells. Recent studies have focused on identifying patient-specific neoantigens, which might be highly immunogenic because they are not expressed in normal tissues. The opposite strategy has emerged with the discovery of anti-regulatory T cells (anti-Tregs) that recognize and attack many cell types in the tumor microenvironment, such as regulatory immune cells, in addition to tumor cells. The term proposed in this review is "tumor microenvironment antigens" (TMAs) to describe the antigens that draw this attack. As therapeutic targets, TMAs offer several advantages that differentiate them from more traditional tumor antigens. Targeting TMAs leads not only to a direct attack on tumor cells but also to modulation of the tumor microenvironment, rendering it immunocompetent and tumor-hostile. Of note, in contrast to TAAs and TSAs, TMAs also are expressed in non-transformed cells with consistent human leukocyte antigen (HLA) expression. Inflammation often induces HLA expression in malignant cells, so that targeting TMAs could additionally affect tumors with no or very low levels of surface HLA expression. This review defines the characteristics, differences, and advantages of TMAs compared with traditional tumor antigens and discusses the use of these antigens in immune modulatory vaccines as an attractive approach to immunotherapy. Different TMAs are expressed by different cells and could be combined in anti-cancer immunotherapies to attack tumor cells directly and modulate local immune cells to create a tumor-hostile microenvironment and inhibit tumor angiogenesis. Immune modulatory vaccines offer an approach for combinatorial therapy with additional immunotherapy including checkpoint blockade, cellular therapy, or traditional cancer vaccines. These combinations would increase the number of patients who can benefit from such therapeutic measures, which all have optimal efficiency in inflamed tumors.

Mcl-1 Inhibition: Managing Malignancy in Multiple Myeloma

Multiple myeloma (MM) is a plasma cells neoplasm. The overexpression of Bcl-2 family proteins, particularly myeloid cell leukemia 1 (Mcl-1), plays a critical role in the pathogenesis of MM. The overexpression of Mcl-1 is associated with drug resistance and overall poor prognosis of MM. Thus, inhibition of the Mcl-1 protein considered as a therapeutic strategy to kill the myeloma cells. Over the last decade, the development of selective Mcl-1 inhibitors has seen remarkable advancement. This review presents the critical role of Mcl-1 in the progression of MM, the most prominent BH3 mimetic and semi-BH3 mimetic that selectively inhibit Mcl-1, and could be used as single agent or combined with existing therapies.

Synthesis and structure-activity relationship of coumarins as potent Mcl-1 inhibitors for cancer treatment

Myeloid cell leukemia-1 (Mcl-1) is a validated and attractive target for cancer therapy. Over-expression of Mcl-1 in many cancers allows cancer cells to evade apoptosis and contributes to their resistance to current chemotherapeutics. In this study, more than thirty coumarin derivatives with different substituents were designed and synthesized, and their Mcl-1 inhibitory activities evaluated using a fluorescence polarization-based binding assay. The results showed that the catechol group was a key constituent for Mcl-1 inhibitory activity of the coumarins, and methylation of the catechol group led to decreased inhibitory activity. The introduction of a hydrophobic electron-withdrawing group at the C-4 position of 6,7-dihydroxycoumarin, enhanced Mcl-1 inhibitory capacity, and a hydrophilic group in this position was unbeneficial to the inhibitory potency. In addition, the introduction of a nitrogen-containing group to the C-5 or C-8 position, which allowed an intramolecular hydrogen bond, was also unfavorable for Mcl-1 inhibition. Among all coumarins tested, 4-trifluoromethyl-6,7-dihydroxycoumarin (Cpd 4) displayed the most potent inhibitory activity towards Mcl-1 (Ki = 0.21 ± 0.02 μM, IC50 = 1.21 ± 0.56 μM, respectively), for which the beneficial effect on taxol resistance was also validated in A549 cells. A strong interaction between Cpd 4 and Mcl-1 in docking simulations further supported the observed potent Mcl-1 inhibition ability of Cpd 4. 3D-QSAR analysis of all tested coumarin derivatives further provides new insights into the relationships linking the inhibitory effects on Mcl-1 and the steric-electrostatic properties of coumarins. These findings could be of great value for medicinal chemists for the design and development of more potent Mcl-1 inhibitors for biomedical applications.

How Good is Jarzynski's Equality for Computer-Aided Drug Design?

Accurate determination of the binding affinity of the ligand to the receptor remains a difficult problem in computer-aided drug design. Here, we study and compare the efficiency of Jarzynski’s equality (JE) combined with steered molecular dynamics and the linear interaction energy (LIE) method by assessing the binding affinity of 23 small compounds to six receptors, including β-lactamase, thrombin, factor Xa, HIV-1 protease (HIV), myeloid cell leukemia-1, and cyclin-dependent kinase 2 proteins. It was shown that Jarzynski’s nonequilibrium binding free energy ΔG_neq^Jar correlates with the available experimental data with the correlation levels R = 0.89, 0.86, 0.83, 0.80, 0.83, and 0.81 for six data sets, while for the binding free energy ΔG_LIE obtained by the LIE method, we have R = 0.73, 0.80, 0.42, 0.23, 0.85, and 0.01. Therefore, JE is recommended to be used for ranking binding affinities as it provides accurate and robust results. In contrast, LIE is not as reliable as JE, and it should be used with caution, especially when it comes to new systems.

Unraveling survivin expression in chronic myeloid leukemia: Molecular interactions and clinical implications

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the BCR-ABL oncoprotein, known to drive leukemogenesis by orchestrating multiple signaling pathways ultimately involved in cell survival. Despite successful response rates of CML patients to tyrosine kinase inhibitors (TKIs), resistance eventually arises due to BCR-ABL-dependent and independent mechanisms. Survivin is an inhibitor of apoptosis protein acting in the interface between apoptosis deregulation and cell cycle progression. In CML, high levels of survivin have been associated with late stages of disease and therapy resistance. In this review, we provide an overview of important aspects concerning survivin subcellular localization and expression pattern in CML patients and cell lines. Moreover, we highlight the relevance of molecular networks involving survivin for disease progression and treatment resistance. Finally, we discuss the mechanisms accounting for survivin overexpression, as well as novel therapeutic interventions that have been designed to counteract survivin-associated malignancy in CML.

Exploring indole derivatives as myeloid cell leukaemia-1 (Mcl-1) inhibitors with multi-QSAR approach: a novel hope in anti-cancer drug discovery

In humans, the over-expression of Mcl-1 protein causes different cancers and it is also responsible for cancer resistance to different cytotoxic agents.

BAG2 Overexpression Correlates with Growth and Poor Prognosis of Esophageal Squamous Cell Carcinoma

Previous studies have suggested that Bcl2-associated athanogene 2 (BAG2) serves as a crucial regulator for tumorigenesis in multiple tumors. However, little is known about the effect of BAG2 on esophageal squamous cell carcinoma (ESCC). This study focused on investigating whether BAG2 functions as a cancer-promoting gene in ESCC. In this work, gene expression data and clinical information from the NCBI Gene Expression Omnibus (GEO), Oncomine and The Cancer Genome Atlas (TCGA) were collected and analyzed. Expression of BAG2 in ESCC was determined using quantitative reverse transcription polymerase chain reaction (qRT-PCR). BAG2 was knocked down using small interference RNA (si-RNA) approach. Cell proliferation, migration and invasion were assessed by Cell Counting Kit-8 (CCK-8) and transwell assays. Molecular mechanism was detected by western blotting assay. The expression of BAG2 both in ESCC tissues and cells was upregulated and overexpression was associated with worsened prognosis. BAG2 silencing inhibited ESCC cell proliferation, migration and invasion, which was regulated by the phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (AKT) signaling pathway. These results reveal contributions of BAG2 as a predictor and potential therapeutic target in ESCC.

Optimization of Potent and Selective Tricyclic Indole Diazepinone Myeloid Cell Leukemia-1 Inhibitors Using Structure-Based Design

Myeloid cell leukemia 1 (Mcl-1), an antiapoptotic member of the Bcl-2 family of proteins, has emerged as an attractive target for cancer therapy. Mcl-1 upregulation is often found in many human cancers and is associated with high tumor grade, poor survival, and resistance to chemotherapy. Here, we describe a series of potent and selective tricyclic indole diazepinone Mcl-1 inhibitors that were discovered and further optimized using structure-based design. These compounds exhibit picomolar binding affinity and mechanism-based cellular efficacy, including growth inhibition and caspase induction in Mcl-1-sensitive cells. Thus, they represent useful compounds to study the implication of Mcl-1 inhibition in cancer and serve as potentially useful starting points toward the discovery of anti-Mcl-1 therapeutics.

Peptide vaccination against multiple myeloma using peptides derived from anti-apoptotic proteins: a phase I trial

The B-cell lymphoma-2 (Bcl-2) family of proteins play a crucial role in multiple myeloma (MM), contributing to lacking apoptosis which is a hallmark of the disease. This makes the Bcl-2 proteins interesting targets for therapeutic peptide vaccination. We report a phase I trial of therapeutic vaccination with peptides from the proteins Bcl-2, Bcl-XL and Mcl-1 in patients with relapsed MM. Vaccines were given concomitant with bortezomib. Out of 7 enrolled patients, 4 received the full course of 8 vaccinations. The remaining 3 patients received fewer vaccinations due to progression, clinical decision of lacking effect and development of hypercalcemia, respectively. There were no signs of toxicity other than what was to be expected from bortezomib. Immune responses to the peptides were seen in all 6 patients receiving more than 2 vaccinations. Three patients had increased immune responses after vaccination. Vaccination against Bcl-2 was well tolerated and was able to induce immune responses in patients with relapsed MM.

Structural Re-engineering of the α-Helix Mimetic JY-1-106 into Small Molecules: Disruption of the Mcl-1-Bak-BH3 Protein-Protein Interaction with 2,6-Di-Substituted Nicotinates

The disruption of aberrant protein-protein interactions (PPIs) with synthetic agents remains a challenging goal in contemporary medicinal chemistry but some progress has been made. One such dysregulated PPI is that between the anti-apoptotic Bcl-2 proteins, including myeloid cell leukemia-1 (Mcl-1), and the α-helical Bcl-2 homology-3 (BH3) domains of its pro-apoptotic counterparts, such as Bak. Herein, we describe the discovery of small-molecule inhibitors of the Mcl-1 oncoprotein based on a novel chemotype. Particularly, re-engineering of our α-helix mimetic JY-1-106 into 2,6-di-substituted nicotinates afforded inhibitors of comparable potencies but with significantly decreased molecular weights. The most potent inhibitor 2-(benzyloxy)-6-(4-chloro-3,5-dimethylphenoxy)nicotinic acid (1 r: Ki =2.90 μm) likely binds in the p2 pocket of Mcl-1 and engages R263 in a salt bridge through its carboxylic acid, as supported by 2D (1) H-(15) N HSQC NMR data. Significantly, inhibitors were easily accessed in just four steps, which will facilitate future optimization efforts.

Discovery of tricyclic indoles that potently inhibit Mcl-1 using fragment-based methods and structure-based design

Myeloid cell leukemia-1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family of proteins that is overexpressed and amplified in many cancers. Overexpression of Mcl-1 allows cancer cells to evade apoptosis and contributes to the resistance of cancer cells to be effectively treated with various chemotherapies. From an NMR-based screen of a large fragment library, several distinct chemical scaffolds that bind to Mcl-1 were discovered. Here, we describe the discovery of potent tricyclic 2-indole carboxylic acid inhibitors that exhibit single digit nanomolar binding affinity to Mcl-1 and greater than 1700-fold selectivity over Bcl-xL and greater than 100-fold selectivity over Bcl-2. X-ray structures of these compounds when complexed to Mcl-1 provide detailed information on how these small-molecules bind to the target, which was used to guide compound optimization.

Small molecule Mcl-1 inhibitors for the treatment of cancer

The Bcl-2 family of proteins serves as primary regulators of apoptosis. Myeloid cell leukemia 1 (Mcl-1), a pro-survival member of the Bcl-2 family of proteins, is overexpressed and the Mcl-1 gene is amplified in many tumor types. Moreover, the overexpression of Mcl-1 is the cause of resistance to several chemotherapeutic agents. Thus, Mcl-1 is a promising cancer target. This review highlights the current progress on the discovery of small molecule Mcl-1 inhibitors.

Discovery of potent myeloid cell leukemia 1 (Mcl-1) inhibitors using fragment-based methods and structure-based design

Myeloid cell leukemia 1 (Mcl-1), a member of the Bcl-2 family of proteins, is overexpressed and amplified in various cancers and promotes the aberrant survival of tumor cells that otherwise would undergo apoptosis. Here we describe the discovery of potent and selective Mcl-1 inhibitors using fragment-based methods and structure-based design. NMR-based screening of a large fragment library identified two chemically distinct hit series that bind to different sites on Mcl-1. Members of the two fragment classes were merged together to produce lead compounds that bind to Mcl-1 with a dissociation constant of <100 nM with selectivity for Mcl-1 over Bcl-xL and Bcl-2. Structures of merged compounds when complexed to Mcl-1 were obtained by X-ray crystallography and provide detailed information about the molecular recognition of small-molecule ligands binding Mcl-1. The compounds represent starting points for the discovery of clinically useful Mcl-1 inhibitors for the treatment of a wide variety of cancers.

Tumor associated antigen specific T-cell populations identified in ex vivo expanded TIL cultures

Ex vivo expanded tumor infiltrating lymphocytes (TILs) from malignant melanoma (MM) and head & neck squamous cell carcinoma (HNSCC) share a similar oligoclonal composition of T effector memory cells, with HLA class I restricted lysis of tumor cell lines. In this study we show that ex vivo expanded TILs from MM and HNSCC demonstrate a heterogeneous composition in frequency and magnitude of tumor associated antigen specific populations by Elispot IFNγ quantitation. TILs from MM and HNSCC shared reactivity towards NY ESO-1, cyclin B1 and Bcl-x derived peptides. Additionally we show that dominating T-cell clones and functionality persists through out expansion among an oligoclonal composition of T-cells. Our findings mirror prior results on the oligoclonal composition of TIL cultures, further indicating a potential for a broader repertoire of specific effector cells recognizing the heterogeneous tumors upon adoptive transfer; increasing the probability of tumor control by minimizing immune evasion by tumor cell escape variants.

The anti-apoptotic members of the Bcl-2 family are attractive tumor-associated antigens

Anti-apoptotic members of the Bcl-2 family (Bcl-2, Bcl-X(L) and Mcl-2) are pivotal regulators of apoptotic cell death. They are all highly overexpressed in cancers of different origin in which they enhance the survival of the cancer cells. Consequently, they represent prime candidates for anti-cancer therapy and specific antisense oligonucleotides or small molecule inhibitors have shown broad anti-cancer activities in pre-clinical models and are currently tested in clinical trials. In addition, immune-mediated tumor destruction is emerging as an interesting modality to treat cancer patients. Notably, spontaneous cellular immune responses against the Bcl-2 family proteins have been identified as frequent features in cancer patients underscoring that these proteins are natural targets for the immune system. Thus, Bcl-2 family may serve as an important and widely applicable target for anti-cancer immunotherapeutic strategies, alone or in the combination with conventional therapy. Here, we summarize the current knowledge of Bcl-2 family proteins as T-cell antigens, which has set the stage for the first explorative trial using these antigens in therapeutic vaccinations against cancer, and discuss future opportunities.

Role of cytotoxic protease granzyme-b in neuronal degeneration during human stroke

Infiltration of leukocytes into post-ischemic cerebrum is a well-described phenomenon in stroke injury. Because CD-8(+) T-lymphocytes secrete cytotoxic proteases, including granzyme-b (Gra-b) that exacerbates post-ischemic brain damage, we investigated roles of Gra-b in human stroke. To study the role of Gra-b in stroke, ischemic and non-ischemic tissues (from post-mortem stroke patients) were analyzed using immunoblotting, co-immunoprecipitation, terminal deoxy uridine nick end labeling (TUNEL) and Annexin-V immunostaining, and in vitro neuron survival assays. Activated CG-SH cells and supernatants were used to model leukocyte-dependent injury. Non-ischemic brain tissues were used as non-pathological controls. Non-activated CG-SH cells and supernatants were used as controls for in vitro experiments. Human stroke (ischemic) samples contained significantly higher levels of Gra-b and interferon-gamma inducible protein-10 (IP-10/CXCL10) than non-ischemic controls. In stroke, poly (ADP-ribose) polymerase-1 and heat shock protein-70 were cleaved to canonical proteolytic "signature" fragments by Gra-b. Gra-b was also found to bind to Bid and caspase-3. Gra-b also co-localized with Annexin-V(+) /TUNEL(+) in degenerating neurons. Importantly, Gra-b inhibition protected both normal and ischemia-reperfused neurons against in vitro neurotoxicity mediated by activated CG-SH cells and supernatants. These results suggest that increased leukocyte infiltration and elevated Gra-b levels in the post-stroke brain can induce contact-dependent and independent post-ischemic neuronal death to aggravate stroke injury.

The anti-apoptotic members of the Bcl-2 family are attractive tumor-associated antigens

Anti-apoptotic members of the Bcl-2 family (Bcl-2, Bcl-X(L) and Mcl-2) are pivotal regulators of apoptotic cell death. They are all highly overexpressed in cancers of different origin in which they enhance the survival of the cancer cells. Consequently, they represent prime candidates for anti-cancer therapy and specific antisense oligonucleotides or small molecule inhibitors have shown broad anti-cancer activities in pre-clinical models and are currently tested in clinical trials. In addition, immune-mediated tumor destruction is emerging as an interesting modality to treat cancer patients. Notably, spontaneous cellular immune responses against the Bcl-2 family proteins have been identified as frequent features in cancer patients underscoring that these proteins are natural targets for the immune system. Thus, Bcl-2 family may serve as an important and widely applicable target for anti-cancer immunotherapeutic strategies, alone or in the combination with conventional therapy. Here, we summarize the current knowledge of Bcl-2 family proteins as T-cell antigens, which has set the stage for the first explorative trial using these antigens in therapeutic vaccinations against cancer, and discuss future opportunities.

Treatment combinations targeting apoptosis to improve immunotherapy of melanoma

Immunotherapy based on T cell responses to the tumor is believed to involve killing of cancer cells by induction of apoptosis. The predominant mechanisms are death ligand-induced signaling mainly by TNF-related apoptosis-inducing ligand (TRAIL) mediated by CD4 T cells, monocytes and dendritic cells, and perforin/granzyme mediated apoptosis mediated by CD8 T cells and NK cells. Resistance against TRAIL involves loss of TRAIL death receptors and/or activation of the MEK and/or Akt signal pathways. Resistance to CD8 CTL responses also involves activation of the MEK and/or Akt pathways. Apoptosis induced by immune responses is regulated by the Bcl-2 family of proteins. Many reagents have been developed against the Bcl-2 antiapoptotic proteins and clinical trials combining them with immunotherapy are awaited. The second group of agents that regulate the Bcl-2 family of proteins are the signal pathway inhibitors. Clinical trials with inhibitors of RAS, RAF or MEK are in progress and would appear an exciting combination with immunotherapy. One of the main drivers of resistance to apoptosis are adaptive mechanisms that allow cancer cells to overcome endoplasmic reticulum (ER) stress. These adaptive mechanisms inhibit practically all known apoptotic pathways and create an acidic environment that may reduce infiltration of lymphocytes against the tumor. The signal pathway inhibitors may be effective against these adaptive processes but additional agents that target ER stress pathways are in development. In conclusion, combination of immunotherapy with agents that target antiapoptotic mechanisms in cancer cells offers a new approach that requires evaluation in clinical trials.

Down-regulation of mcl-1 by small interfering RNA sensitizes resistant melanoma cells to fas-mediated apoptosis

Resistance of malignant melanoma cells to Fas-mediated apoptosis is among the mechanisms by which they escape immune surveillance. However, the mechanisms contributing to their resistance are not completely understood, and it is still unclear whether antiapoptotic Bcl-2-related family proteins play a role in this resistance. In this study, we report that treatment of Fas-resistant melanoma cell lines with cycloheximide, a general inhibitor of de novo protein synthesis, sensitizes them to anti-Fas monoclonal antibody (mAb)-induced apoptosis. The cycloheximide-induced sensitization to Fas-induced apoptosis is associated with a rapid down-regulation of Mcl-1 protein levels, but not that of Bcl-2 or Bcl-xL. Targeting Mcl-1 in these melanoma cell lines with specific small interfering RNA was sufficient to sensitize them to both anti-Fas mAb-induced apoptosis and activation of caspase-9. Furthermore, ectopic expression of Mcl-1 in a Fas-sensitive melanoma cell line rescues the cells from Fas-mediated apoptosis. Our results further show that the expression of Mcl-1 in melanoma cells is regulated by the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) and not by phosphatidylinositol 3-kinase/AKT signaling pathway. Inhibition of ERK signaling with the mitogen-activated protein/ERK kinase-1 inhibitor or by expressing a dominant negative form of mitogen-activated protein/ERK kinase-1 also sensitizes resistant melanoma cells to anti-Fas mAb-induced apoptosis. Thus, our study identifies mitogen-activated protein kinase/ERK/Mcl-1 as an important survival signaling pathway in the resistance of melanoma cells to Fas-mediated apoptosis and suggests that its targeting may contribute to the elimination of melanoma tumors by the immune system.

Design and development of synthetic peptide vaccines: past, present and future

Synthetic peptide vaccines aiming at the induction of a protective CD8(+) T-cell response against infectious or malignant diseases are widely used in the clinic but, despite their success in animal models, they do not yet live up to their promise in humans. This review assesses the development of synthetic peptide vaccines, weighs it against the immunological concepts that have emerged, and identifies the key issues that play a role in the failure or success of a synthetic peptide vaccine. The current state-of-the-art peptide vaccine is a complete synthetic inflammatory product that is ingested by professional antigen-presenting cells and stimulates both CD4(+) and CD8(+) T cells.

BCR-ABL Activity Is Critical for the Immunogenicity of Chronic Myelogenous Leukemia Cells

Chronic myelogenous leukemia (CML) is a myeloproliferative disorder caused by excessive granulopoiesis due to the formation of the constitutively active tyrosine kinase BCR-ABL. An effective drug against CML is imatinib mesylate, a tyrosine kinase inhibitor acting on Abl kinases, c-KIT, and platelet-derived growth factor receptor. Recently, a study revealed that patients treated with imatinib showed impaired CTL responses compared with patients treated with IFN-alpha, which might be due to a treatment-induced reduction in immunogenicity of CML cells or immunosuppressive effects. In our study, we found that inhibition of BCR-ABL leads to a down-regulation of immunogenic antigens on the CML cells in response to imatinib treatment, which results in the inhibition of CML-directed immune responses. By treating CML cells with imatinib, we could show that the resulting inhibition of BCR-ABL leads to a decreased expression of tumor antigens, including survivin, adipophilin, hTERT, WT-1, Bcl-x(L), and Bcl-2 in correlation to a decreased development of CML-specific CTLs. In contrast, this reduction in immunogenicity was not observed when a CML cell line resistant to the inhibitory effects of imatinib was used, but could be confirmed by transfection with specific small interfering RNA against BCR-ABL or imatinib treatment of primary CML cells.

Epothilone-paclitaxel resistant leukemic cells CEM/dEpoB300 are sensitive to albendazole: Involvement of apoptotic pathways

Altered or deficient activation of apoptosis signalling pathways may contribute to drug resistance. Here, we assess the role of apoptotic mediators in eliciting an anti-proliferative response to paclitaxel (PTX) in a T cell acute lymphoblastic leukemia (ALL) cell line CEM and its epothilone-paclitaxel resistant sub-line CEM/dEpoB300. Furthermore, the cellular response to PTX was compared to those elicited by cells in response to treatment with albendazole (ABZ; a microtubule depolymerizing agent). In cell proliferation studies, CEM cells were sensitive to both PTX and ABZ, while the CEM/dEpoB300 cells were highly resistant to PTX (IC(50) 2.86 nM versus 30.26 nM, respectively). In contrast, the resistant cells showed a 2-fold increase in sensitivity to ABZ (0.32 microM in CEM compared to 0.16 microM in CEM/dEpoB300). Analysis of caspase-3 activity and cytochrome c release in response to PTX or ABZ treatment (24, 48 and 72 h) revealed that, compared to the parent cells, the resistant cells have diminished response to PTX and enhanced response to ABZ. A similar pattern was observed for the pro-apoptotic protein Bax. Levels of the anti-apoptotic protein Bcl-2 was highly elevated in CEM/dEpoB300 cells and in these cells, ABZ was more effective in lowering the Bcl-2 levels than PTX. Similarly, ABZ treatment led to profound down regulation of the Mcl-1 protein. These results reveal for the first time, the changes in apoptotic mediators following development of resistance to PTX in an ALL cell and the significantly increased sensitivity of these PTX resistant cells to ABZ.

Spontaneous Immunity against Bcl-xL in Cancer Patients

It is well-established that peptide epitopes derived from human tumor-associated Ags can be recognized by CTL in the context of the MHC molecule. However, the vast majority of Ags described are not vital for survival and growth of the tumor cells, and immunoselection of Ag-loss variants during immunotherapy has been demonstrated in several cases. Malfunctions in death pathways observed in human cancers are often due to overexpression of antiapoptotic proteins in the Bcl-2 protein family, i.e., Bcl-2, Mcl-1, and Bcl-xL. These antiapoptotic proteins are implicated in cancer development, tumor progression, and drug resistance. The general overexpression of the antiapoptotic members of the Bcl-2 family in cancer and the fact that down-regulation or loss of expression of these proteins as a means of immune escape would impair sustained tumor growth makes them very attractive targets for anticancer immunotherapy. Recently, we identified spontaneous T cell responses against Bcl-2- and Mcl-1-derived peptides in patients suffering from cancers of different origin. In this study, we demonstrate that Bcl-xL is a target for T cell recognition in cancer patients. Thus, we describe spontaneous HLA-A2-restricted cytotoxic T cell responses against peptide epitopes derived from Bcl-xL by means of ELISPOT and flow cytometry stainings, whereas no responses were detected against any of the Bcl-xL epitopes in any healthy controls. Moreover, Bcl-xL-specific T cells are cytotoxic against HLA-matched cancer cells of different origin. Thus, cellular immune responses against apoptosis inhibitors like the Bcl-2 family proteins appear to represent a general feature in cancer.

Regulators of apoptosis: suitable targets for immune therapy of cancer

Harnessing the immune system in the battle against cancer has been the focus of tremendous research efforts during the past two decades. Several means for achieving this goal, including adoptive transfer of tumour-reactive T cells, systemic or localized administration of immune modulating cytokines and the use of 'therapeutic' vaccines, have been explored. Anti-apoptotic molecules that enhance the survival of cancer cells and facilitate their escape from cytotoxic therapies represent prime candidates as vaccination antigens. Notably, spontaneous cellular immune responses against these proteins have frequently been identified in cancer patients. Here, we summarize current knowledge of IAP and BCL2 family proteins as T-cell antigens, report the results of the first explorative trial using these antigens in therapeutic vaccinations against cancer and discuss future opportunities.