BH3 mimetics are small molecules designed or discovered to mimic the binding of BH3-only proteins to the hydrophobic groove of antiapoptotic BCL2 proteins. The selectivity of these molecules for BCL2, BCL-X L , or MCL1 has been established in vitro; whether they inhibit these proteins in cells has not been rigorously investigated. In this study, we used a panel of leukemia cell lines to assess the ability of seven putative BH3 mimetics to inhibit antiapoptotic proteins in a cell-based system. We show that ABT-737 is the only BH3 mimetic that inhibits BCL2 as assessed by displacement of BAD and BIM from BCL2. The other six BH3 mimetics activate the endoplasmic reticulum stress response inducing ATF4, ATF3, and NOXA, which can then bind to and inhibit MCL1. In most cancer cells, inhibition of one antiapoptotic protein does not acutely induce apoptosis. However, by combining two BH3 mimetics, one that inhibits BCL2 and one that induces NOXA, apoptosis is induced within 6 h in a BAX/BAK-dependent manner. Because MCL1 is a major mechanism of resistance to ABT-737, these results suggest a novel strategy to overcome this resistance. Our findings highlight a novel signaling pathway through which many BH3 mimetics inhibit MCL1 and suggest the potential use of these agents as adjuvants in combination with various chemotherapy strategies.

Chemotherapeutic agents modify intracellular signaling that culminates in the inhibition of Bcl-2 family members and initiates apoptosis. Inhibition of the extracellular signal-regulated kinase by PD98059 dramatically accelerates vinblastine-mediated apoptosis in ML-1 leukemia with cells dying in 4 hours from all phases of the cell cycle. Inhibition of protein synthesis by cycloheximide also markedly accelerated vinblastineinduced apoptosis, showing that the proteins required for this acute apoptosis are constitutively expressed. Vinblastine induced the rapid induction of Mcl-1 that was inhibited by PD98059 and cycloheximide. No change in Bcl-2 or Bcl-X was observed. We hypothesize that ML-1 cells use Mcl-1 for protection from the rapid vinblastine-induced apoptosis. This was confirmed by targeting Mcl-1 with short hairpin RNA. We also investigated the response of 13 other leukemia and lymphoma cell lines and cells from seven chronic lymphocytic leukemia patients. Four cell lines and all chronic lymphocytic leukemia cells were killed in 6 hours by vinblastine alone. Two additional cell lines were sensitized to vinblastine by PD98059, which suppressed Mcl-1. This acute apoptosis either alone or in combination with PD98059 required vinblastine-mediated activation of c-Jun-NH 2 -terminal kinase. PD98059 did not suppress Mcl-1 in other cell lines whereas sorafenib did, but this did not sensitize the cells to vinblastine, suggesting that the acute apoptosis varies depending on which Bcl-2 protein mediates protection. Most of the cell lines were sensitized to vinblastine by cycloheximide, suggesting that inhibition of a short-lived protein in addition to Mcl-1 can acutely sensitize cells. These results suggest several clinical strategies that might provide an effective therapy for selected patients. Mol Cancer Ther; 9(4); 791-802. ©2010 AACR.

Our previous studies found that B16-F10 melanoma growth in the rear footpad of immunocompetent mice induces marked B cell accumulation within tumor-draining popliteal lymph nodes (TDLN). This B cell accumulation drives TDLN remodeling that precedes and promotes metastasis, indicating a tumor-promoting role for TDLN B cells. Here we show that phenotypic characterization of lymphocytes in mice bearing B16-F10 melanomas identifies preferential accumulation of T2-MZP B cells in the TDLN. Comparison of non-draining LNs and spleens of tumor-bearing mice with LNs and spleens from naïve mice determined that this pattern of B cell accumulation was restricted to the TDLN. B cell-deficient and immunocompetent mice reconstituted with T2-MZP B cells but not with other B cell subsets displayed accelerated tumor growth, demonstrating that T2-MZP B cells possess regulatory activity in tumor-bearing mice. Unlike splenic regulatory B cells, however, these TDLN B cells did not exhibit increased IL-10 production, nor did they promote Treg generation in the TDLN. These findings demonstrate that tumors initially signal via the lymphatic drainage to stimulate the preferential accumulation of T2-MZP regulatory B cells. This local response may be an early and critical step in generating an immunosuppressive environment to permit tumor growth and metastasis.

We have engineered an integration-deficient lentiviral vector, LV305, to deliver the tumor antigen NY-ESO-1 to human dendritic cells in vivo through pseudotyping with a modified Sindbis virus envelop protein. Mice immunized once with LV305 developed strong, dose-dependent, multifunctional, and cytotoxic NY-ESO-1-specific cluster of differentiation 8 (CD8) T cells within 14 days post-immunization and could be boosted with LV305 at least twice to recall peak-level CD8 T-cell responses. Immunization with LV305 protected mice against tumor growth in an NY-ESO-1-expressing CT26 lung metastasis model, with the protective effect abrogated upon depletion of CD8 T cells. Adoptive transfer of CD8 T cells, alone or together with CD4 T cells or natural killer cells, from LV305-immunized donor mice to tumor-bearing recipient mice conferred significant protection against metastatic tumor growth. Biodistribution of injected LV305 in mice was limited to the site of injection and the draining lymph node, and injected LV305 exhibited minimal excretion. Mice injected with LV305 developed little to no adverse effects, as evaluated by toxicology studies adherent to good laboratory practices. Taken together, these data support the development of LV305 as a clinical candidate for treatment against tumors expressing NY-ESO-1.

Normalization to a reference gene is the method of choice for quantitative PCR analysis. The stability of reference genes is critical for accurate gene expression analysis, as significant variations in reference gene expression can alter experimental results and conclusions. In this study, we evaluated the expression stability of five commonly used reference genes found in mouse lymphocytes. Using NormFinder and BestKeeper algorithms, we consistently show that ubiquitin C (Ubc) is the optimal reference gene for normalizing qPCR data obtained from mouse lymphocytes, whereas beta-actin (Actb) is not a suitable reference gene due to its extensive variability in expression. Our findings emphasize the importance of validating reference genes for qPCR analyses. We provide a shortlist of reference genes to use for normalization and recommend freely available software programs as a rapid approach to validate potential reference genes.