Amit K. Mittal

Hedgehog-induced survival of B-cell chronic lymphocytic leukemia cells in a stromal cell microenvironment: a potential new therapeutic target.

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by an accumulation of neoplastic B cells due to their resistance to apoptosis and increased survival. Among various factors, the tumor microenvironment is known to play a role in the regulation of cell proliferation and survival of many cancers. However, it remains unclear how the tumor microenvironment contributes to the increased survival of B-CLL cells. Therefore, we studied the influence of bone marrow stromal cell–induced hedgehog (Hh) signaling on the survival of B-CLL cells. Our results show that a Hh signaling inhibitor, cyclopamine, inhibits bone marrow stromal cell–induced survival of B-CLL cells, suggesting a role for Hh signaling in the survival of B-CLL cells. Furthermore, gene expression profiling of primary B-CLL cells (n = 48) indicates that the expression of Hh signaling molecules, such as GLI1, GLI2, SUFU, and BCL2, is significantly increased and correlates with disease progression of B-CLL patients with clinical outcome. In addition, SUFU and GLI1 transcripts, as determined by real-time PCR, are significantly overexpressed and correlate with adverse indicators of clinical outcome in B-CLL patients, such as cytogenetics or CD38 expression. Furthermore, selective down-regulation of GLI1 by antisense oligodeoxynucleotides (GLI1-ASO) results in decreased BCL2 expression and cell survival, suggesting that GLI1 may regulate BCL2 and, thereby, modulate cell survival in B-CLL. In addition, there was significantly increased apoptosis of B-CLL cells when cultured in the presence of GLI1-ASO and fludarabine. Together, these results reveal that Hh signaling is important in the pathogenesis of B-CLL and, hence, may be a potential therapeutic target. (Mol Cancer Res 2008;6(12):1928–36)

ATM, CTLA4, MNDA, and HEM1 in High versus Low CD38–Expressing B-Cell Chronic Lymphocytic Leukemia

Purpose: In B-cell chronic lymphocytic leukemia (CLL), high CD38 expression has been associated with unfavorable clinical course, advanced disease, resistance to therapy, shorter time to first treatment, and shorter survival. However, the genes associated with CLL patient subgroups with high and low CD38 expression and their potential role in disease progression is not known. Experimental Design: To identify the genes associated with the clinical disparity in CLL patients with high versus low CD38 expression, transcriptional profiles were obtained from CLL cells from 39 different patients using oligonucleotide microarray. Gene expression was also compared between CLL cells and B cells from healthy individuals. Results: Gene expression analysis identified 76 differentially expressed genes in CD38 high versus low groups. Out of these genes, HEM1, CTLA4, and MNDA were selected for further studies and their differential expression was confirmed by real-time PCR. HEM1 overexpression was associated with poor outcome, whereas the overexpression of CTLA4 and MNDA was associated with good outcome. Down-regulation of HEM1 expression in patient CLL cells resulted in a significant increase in their susceptibility to fludarabine-mediated killing. In addition, when gene expression patterns in CD38 high and low CLL cells were compared with normal B-cell profiles, ATM expression was found to be significantly lower in CD38 high compared with CD38 low CLL as confirmed by real-time reverse transcription-PCR. Conclusions: These results identify the possible genes that may be involved in cell proliferation and survival and, thus, determining the clinical behavior of CLL patients expressing high or low CD38.

Chronic lymphocytic leukemia cells in a lymph node microenvironment depict molecular signature associated with an aggressive disease.

Chronic lymphocytic leukemia (CLL) cells survive longer in vivo than in vitro, suggesting that the tissue microenvironment provides prosurvival signals to tumor cells. Primary and secondary lymphoid tissues are involved in the pathogenesis of CLL, and the role of these tissue microenvironments has not been explored completely. To elucidate host-tumor interactions, we performed gene expression profiling (GEP) of purified CLL cells from peripheral blood (PB; n = 20), bone marrow (BM; n = 18), and lymph node (LN; n = 15) and validated key pathway genes by real-time polymerase chain reaction, immunohistochemistry and/or TCL1 trans-genic mice. Gene signatures representing several pathways critical for survival and activation of B cells were altered in CLL cells from different tissue compartments. Molecules associated with the B-cell receptor (BCR), B cell-activating factor/a proliferation-inducing ligand (BAFF/APRIL), nuclear factor (NF)-κB pathway and immune suppression signature were enriched in LN-CLL, suggesting LNs as the primary site for tumor growth. Immune suppression genes may help LN-CLL cells to modulate antigen-presenting and T-cell behavior to suppress antitumor activity. PB CLL cells overexpressed chemokine receptors, and their cognate ligands were enriched in LN and BM, suggesting that a chemokine gradient instructs B cells to migrate toward LN or BM. Of several chemokine ligands, the expression of CCL3 was associated with poor prognostic factors. The BM gene signature was enriched with antiapoptotic, cytoskeleton and adhesion molecules. Interestingly, PB cells from lymphadenopathy patients shared GEP with LN cells. In Eμ-TCL1 transgenic mice (the mouse model of the disease), a high percentage of leukemic cells from the lymphoid compartment express key BCR and NF-κB molecules. Together, our findings demonstrate that the lymphoid microenvironment promotes survival, proliferation and progression of CLL cells via chronic activation of BCR, BAFF/APRIL and NF-κB activation while suppressing the immune response.

Lymph node‐induced immune tolerance in chronic lymphocytic leukaemia: a role for caveolin‐1

Emerging evidence indicates that the tumour microenvironment (TME) regulates the behaviour of chronic lymphocytic leukaemia (CLL). However, the precise mechanism and molecules involved in this process remain unknown. Gene expression profiles of CLL cells from lymph node (LN), bone marrow (BM) and peripheral blood (PB) indicate overexpression of a tolerogenic signature in CLL cells in lymph nodes (LN‐CLL). Based on their role in B cell biology, the progression of CLL, or immune regulation, a few genes of this 83‐gene signature were selected for further analyses. We observed a significant correlation between the clinical outcomes and the expression of CAV1 (P = 0·041), FGFR1 isoform 8 (P = 0·032), PTPN6 (P = 0·031) and ZWINT (P < 0·001). CAV1, a molecule involved in the regulation of tumour progression in other cancers, was seven‐fold higher in LN‐CLL cells compared to BM‐ and PB‐CLL cells. Knockdown of CAV1 expression in CLL cells resulted in significantly decreased migration (P = 0·016) and proliferation (P = 0·04). When CAV1 was knocked down in B and T cell lines, we observed an inability to form immune synapses. Furthermore, CAV1 knockdown in CLL cells impaired their ability to form immune synapses with autologous T lymphocytes and allogeneic, healthy T cells. Subsequent analyses of microarray data showed differential expression of cytoskeletal genes, specifically those involved in actin polymerization. Therefore, we report a novel role for CAV1 in tumour‐induced immunosuppression during the progression of CLL.

Tumor-specific peptide-based vaccines containing the conformationally biased, response-selective C5a agonists EP54 and EP67 protect against aggressive large B cell lymphoma in a syngeneic murine model

Vaccines to large B cell lymphoma were made by the covalent attachment of an epitope from the gp70 glycoprotein (SSWDFITV) to the N-termini of the conformationally biased, response-selective C5a agonists EP54 (YSFKPMPLaR) and EP67 (YSFKDMP(MeL)aR). Syngeneic Balb/c mice were immunized with these EP54/EP67-containing vaccines and challenged with a lethal dose of the highly liver metastatic and gp70-expressing lymphoma cell line RAW117-H10 to evaluate the ability of these vaccines to induce protective immune outcomes. All mice immunized with SSWDFITVRRYSFKPMPLaR (Vaccine 2) and SSWDFITVRRYSFKDMP(MeL)aR (Vaccine 3) were protected to a lethal challenge of RAW117-H10 lymphoma (>170 days survival) and exhibited no lymphoma infiltration or solid tumor nodules in the liver relative to unvaccinated controls (<18 days survival). Vaccines 2 and 3 contained the protease-sensitive double-Arg (RR) linker sequence between the epitope and the EP54/EP67 moieties in order to provide a site for intracellular proteases to separate the epitope from the EP54/EP67 moieties once internalized by the APC and, consequently, enhance epitope presentation in the context of MHC I/II. These protected mice exhibited an immune outcome consistent with increased involvement of CD8(+) and/or CD4(+) T lymphocytes relative to controls and mice that did not survive or showed low survival rates as with Vaccines 1 and 4, which lacked the RR linker sequence. CD8(+) T lymphocytes activated in response to Vaccines 2 and 3 express cytotoxic specificity for gp70-expressing RAW117-H10 lymphoma cells, but not antigen-irrelevant MDA-MB231A human breast cancer cells. Results are discussed against the backdrop of the ability of EP54/EP67 to selectively target antigens to and activate C5a receptor-bearing antigen presenting cells and the prospects of using such vaccines therapeutically against lymphoma and other cancers.

Novel therapy for therapy‐resistant mantle cell lymphoma: Multipronged approach with targeting of hedgehog signaling

Mantle cell lymphoma (MCL) is one of the most aggressive B‐cell lymphomas with a median patient survival of only 5–7 years. The failure of existing therapies is mainly due to disease relapse when therapy‐resistant tumor cells remain after chemotherapy. Therefore, development and testing of novel therapeutic strategies to target these therapy‐resistant MCL are needed. Here, we developed an in vivo model of therapy‐resistant MCL by transplanting a patient‐derived MCL cell line (Granta 519) into NOD/SCID mice followed by treatment with combination chemotherapy. Cytomorphologic, immunophenotypic, in vitro and in vivo growth analyses of these therapy‐resistant MCL cells confirm their MCL origin and resistance to chemotherapy. Moreover, quantitative real‐time PCR revealed the upregulation of GLI transcription factors, which are mediators of the hedgehog signaling pathway, in these therapy‐resistant MCL cells. Therefore, we developed an effective therapeutic strategy for resistant MCL by treating the NOD/SCID mice bearing Granta 519 MCL with CHOP chemotherapy to reduce tumor burden combined with GLI‐antisense oligonucleotides or bortezomib, a proteosome inhibitor, to target therapy‐resistant MCL cells that remained after chemotherapy. This regimen was followed by treatment with MCL‐specific cytotoxic T lymphocytes to eliminate all detectable leftover minimal residual disease. Mice treated with this strategy showed a significantly increased survival and decreased tumor burden compared to the mice in all other groups. Such therapeutic strategies that combine chemotherapy with targeted therapy followed by tumor‐specific immunotherapy are effective and have excellent potential for clinical application to provide long‐term, disease‐free survival in MCL patients.

Role of CTLA4 in the Proliferation and Survival of Chronic Lymphocytic Leukemia

Earlier, we reported that CTLA4 expression is inversely correlated with CD38 expression in chronic lymphocytic leukemia (CLL) cells. However, the specific role of CTLA4 in CLL pathogenesis remains unknown. Therefore, to elucidate the possible role of CTLA4 in CLL pathogenesis, CTLA4 was down-regulated in primary CLL cells. We then evaluated proliferation/survival in these cells using MTT, 3H-thymidine uptake and Annexin-V apoptosis assays. We also measured expression levels of downstream molecules involved in B-cell proliferation/survival signaling including STAT1, NFATC2, c-Fos, c-Myc, and Bcl-2 using microarray, PCR, western blotting analyses, and a stromal cell culture system. CLL cells with CTLA4 down-regulation demonstrated a significant increase in proliferation and survival along with an increased expression of STAT1, STAT1 phosphorylation, NFATC2, c-Fos phosphorylation, c-Myc, Ki-67 and Bcl-2 molecules. In addition, compared to controls, the CTLA4-downregulated CLL cells showed a decreased frequency of apoptosis, which also correlated with increased expression of Bcl-2. Interestingly, CLL cells from lymph node and CLL cells co-cultured on stroma expressed lower levels of CTLA4 and higher levels of c-Fos, c-Myc, and Bcl-2 compared to CLL control cells. These results indicate that microenvironment-controlled-CTLA4 expression mediates proliferation/survival of CLL cells by regulating the expression/activation of STAT1, NFATC2, c-Fos, c-Myc, and/or Bcl-2.

Stromal Tumor Microenvironment in Chronic Lymphocytic Leukemia: Regulation of Leukemic Progression

Chronic Lymphocytic Leukemia (CLL), the most prevalent adult leukemia in western countries, which is highly heterogeneous with a very variable clinical outcome. Emerging evidence indicates that the stromal tumor microenvironment (STME) and stromal associated genes (SAG) play important roles in the pathogenesis and progression of CLL. However, the precise mechanisms by which STME and SAG are involved in this process remain unknown. In an attempt to explore the role of STME in this process, we examined the expression levels of stromal associated genes using gene expression profiling (GEP) of CLL cells from lymph nodes (LN) (n=15), bone marrow (BM) (n=18), and peripheral blood (PB) (n=20). Interestingly, LUM, MMP9, MYLK, ITGA9, CAV1, CAV2, FBN1, PARVA, CALD1, ITGB5 and EHD2 were found to be overexpressed while ITGB2, DLC1 and ITGA6 were under expressed in LN-CLL compared to BM-CLL and PB-CLL. This is suggestive of a role for LN-mediated TME in CLL cell survival/progression. Among these genes, expression of MYLK, CAV1 and CAV2 correlated with clinical outcome as determined by time to first treatment. Together, our studies show that members of the stromal signature, particularly in the CLL cells from lymph nodes, regulate CLL cell survival and proliferation and thus leukemic progression.

Differential gene expression in murine large cell B-cell lymphoma metastatic variants

Previous studies from this laboratory have characterized RAW117-P murine large cell B-cell lymphoma and its in vivo selected highly malignant and liver metastatic RAW117-H10 subline for their biological and biochemical properties. In this study, to understand the molecular basis of low and high metastatic behavior of these variant sublines, we have investigated the molecular phenotypes of these cells using differential display techniques and cDNA array analysis. Differential display analysis indicated a significant difference in expression of several genes between these two metastatic variant lymphoma cells. Further analyses of these cells using microarray showed an increased expression of several genes including uPAR1, CRE-BP1, Chop-10, IGF, insulin-like growth factor-IA, STAT6, Cyclin-D1, Cyclin-E, ERBB-3, Alpha NGF, Kruppel-like factor LKLF, (P)19INK4 in metastatic RAW117-H10 cells compared to parental RAW117-P cells. On the other hand, MIP1beta, CD14 antigen, Cathepsin B and MOD are expressed more in RAW117-P cells compared to RAW117-H10 cells. Differential expression of the selected genes was confirmed using semiquantitative RT-PCR techniques. The combination of plasminogen activator and its receptor and IGF-like growth factors, cell cycle regulatory molecules and transcription factors might provide an ideal environment for RAW117-H10 cells to metastasize to distant organs and colonize. Thus these results identify certain differentially expressed genes that are involved in the metastatic properties of these lymphoma cells and lay foundation for further in depth analyses to use this information to develop therapy for metastatic lymphoma.