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Prolactin (PRL) is elevated in B-cell-mediated lymphoproliferative diseases and promotes B-cell survival. Whether PRL or PRL receptors drive the evolution of B-cell malignancies is unknown. We measure changes in B cells after knocking down the pro-proliferative, anti-apoptotic long isoform of the PRL receptor (LFPRLR) in vivo in systemic lupus erythematosus (SLE)- and B-cell lymphoma-prone mouse models, and the long plus intermediate isoforms (LF/IFPRLR) in human B-cell malignancies. To knockdown LF/IFPRLRs without suppressing expression of the counteractive short PRLR isoforms (SFPRLRs), we employ splice-modulating DNA oligomers. In SLE-prone mice, LFPRLR knockdown reduces numbers and proliferation of pathogenic B-cell subsets and lowers the risk of B-cell transformation by downregulating expression of activation-induced cytidine deaminase. LFPRLR knockdown in lymphoma-prone mice reduces B-cell numbers and their expression of BCL2 and TCL1. In overt human B-cell malignancies, LF/IFPRLR knockdown reduces B-cell viability and their MYC and BCL2 expression. Unlike normal B cells, human B-cell malignancies secrete autocrine PRL and often express no SFPRLRs. Neutralization of secreted PRL reduces the viability of B-cell malignancies. Knockdown of LF/IFPRLR reduces the growth of human B-cell malignancies in vitro and in vivo. Thus, LF/IFPRLR knockdown is a highly specific approach to block the evolution of B-cell neoplasms.

Studying mechanisms of malignant transformation of human pre-B cells, we found that acute activation of oncogenes induced immediate cell death in the vast majority of cells. Few surviving pre-B cell clones had acquired permissiveness to oncogenic signaling by strong activation of negative feedback regulation of Erk signaling. Studying negative feedback regulation of Erk in genetic experiments at three different levels, we found that Spry2, Dusp6, and Etv5 were essential for oncogenic transformation in mouse models for pre-B acute lymphoblastic leukemia (ALL). Interestingly, a small molecule inhibitor of DUSP6 selectively induced cell death in patient-derived pre-B ALL cells and overcame conventional mechanisms of drug-resistance.

The unfolded protein response (UPR) pathway, a stress-induced signaling cascade emanating from the endoplasmic reticulum (ER), regulates the expression and activity of molecules including BiP (HSPA5), IRE1 (ERN1), Blimp-1 (PRDM1), and X-box binding protein 1 (XBP1). These molecules are required for terminal differentiation of B cells into plasma cells and expressed at high levels in plasma cell-derived multiple myeloma. Although these molecules have no known role at early stages of B-cell development, here we show that their expression transiently peaks at the pre-B-cell receptor checkpoint. Inducible, Cre-mediated deletion of Hspa5, Prdm1, and Xbp1 consistently induces cellular stress and cell death in normal pre-B cells and in pre-B-cell acute lymphoblastic leukemia (ALL) driven by BCR-ABL1- and NRAS(G12D) oncogenes. Mechanistically, expression and activity of the UPR downstream effector XBP1 is regulated positively by STAT5 and negatively by the B-cell-specific transcriptional repressors BACH2 and BCL6. In two clinical trials for children and adults with ALL, high XBP1 mRNA levels at the time of diagnosis predicted poor outcome. A small molecule inhibitor of ERN1-mediated XBP1 activation induced selective cell death of patient-derived pre-B ALL cells in vitro and significantly prolonged survival of transplant recipient mice in vivo. Collectively, these studies reveal that pre-B ALL cells are uniquely vulnerable to ER stress and identify the UPR pathway and its downstream effector XBP1 as novel therapeutic targets to overcome drug resistance in pre-B ALL.

The reaction of substituted acylthiourea derivatives (L1–L4) with [(PPh3)2Cu(μ‐Cl)2Cu(PPh3)] in a proper stoichiometric proportion gave the complexes (1–4) in good yields. The structures of the compounds (ligands and complexes) were advocated through spectroscopic analyses and x‐ray diffraction (XRD) studies; the latter confirmed their molecular structures. The complexes (1–4) were assessed for their cytotoxic potential through MTT assay against A549, T24, and HepG2 cancer cells, and their toxicity was evaluated using Vero and MCF‐10a normal cells. The complexes (1–4) displayed better cytotoxic action toward HepG2 cancer cells than cisplatin. Complexes 3 and 4 significantly destroyed A549 cancer cells with the IC50 values of 16.25 and 4.90 μM, respectively, which were lower than that of cisplatin (IC50 = 17.73 μM). Furthermore, the higher IC50 values in normal cells showed that the complexes were less hazardous to the normal cells except complex 3. The biocompatibility study showed that the complexes had minimal impact on normal human dermal fibroblast (NHDF) cells. The mode of cell death of complexes 3 and 4 against cancer cells was evaluated using staining assays. Both compounds demonstrated a significant reduction in live cells, an increase in early apoptotic cells, and pronounced proapoptotic effects, as evidenced by fragmented nuclei. Flow cytometry revealed a distinctive subpopulation in the subG0 phase, highlighting the compounds' ability to induce apoptosis and inhibit cell cycle progression. [ABSTRACT FROM AUTHOR]

The B cell-specific transcription factor BACH2 is required for affinity maturation of B cells. Here we show that Bach2-mediated activation of p53 is required for stringent elimination of pre-B cells that failed to productively rearrange immunoglobulin VH-DJH gene segments. After productive VH-DJH gene rearrangement, pre-B cell receptor signaling ends BACH2-mediated negative selection through B cell lymphoma 6 (BCL6)-mediated repression of p53. In patients with pre-B acute lymphoblastic leukemia, the BACH2-mediated checkpoint control is compromised by deletions, rare somatic mutations and loss of its upstream activator, PAX5. Low levels of BACH2 expression in these patients represent a strong independent predictor of poor clinical outcome. In this study, we demonstrate that Bach2(+/+) pre-B cells resist leukemic transformation by Myc through Bach2-dependent upregulation of p53 and do not initiate fatal leukemia in transplant-recipient mice. Chromatin immunoprecipitation sequencing and gene expression analyses carried out by us revealed that BACH2 competes with BCL6 for promoter binding and reverses BCL6-mediated repression of p53 and other cell cycle checkpoint-control genes. These findings identify BACH2 as a crucial mediator of negative selection at the pre-B cell receptor checkpoint and a safeguard against leukemogenesis.

Tyrosine kinase inhibitors (TKIs) are widely used to treat patients with leukaemia driven by BCR-ABL1 (ref. 1) and other oncogenic tyrosine kinases. Recent efforts have focused on developing more potent TKIs that also inhibit mutant tyrosine kinases. However, even effective TKIs typically fail to eradicate leukaemia-initiating cells (LICs), which often cause recurrence of leukaemia after initially successful treatment. Here we report the discovery of a novel mechanism of drug resistance, which is based on protective feedback signalling of leukaemia cells in response to treatment with TKI. We identify BCL6 as a central component of this drug-resistance pathway and demonstrate that targeted inhibition of BCL6 leads to eradication of drug-resistant and leukaemia-initiating subclones.

BCL6 protects germinal center (GC) B cells against DNA damage-induced apoptosis during somatic hypermutation and class-switch recombination. Although expression of BCL6 was not found in early IL-7-dependent B cell precursors, we report that IL-7Ralpha-Stat5 signaling negatively regulates BCL6. Upon productive VH-DJH gene rearrangement and expression of a mu heavy chain, however, activation of pre-B cell receptor signaling strongly induces BCL6 expression, whereas IL-7Ralpha-Stat5 signaling is attenuated. At the transition from IL-7-dependent to -independent stages of B cell development, BCL6 is activated, reaches expression levels resembling those in GC B cells, and protects pre-B cells from DNA damage-induced apoptosis during immunoglobulin (Ig) light chain gene recombination. In the absence of BCL6, DNA breaks during Ig light chain gene rearrangement lead to excessive up-regulation of Arf and p53. As a consequence, the pool of new bone marrow immature B cells is markedly reduced in size and clonal diversity. We conclude that negative regulation of Arf by BCL6 is required for pre-B cell self-renewal and the formation of a diverse polyclonal B cell repertoire.

Three Pd(II) complexes (1–3) containing tridentate chromone-based thiosemicarbazones (SVSHL1–3) have been investigated as potential anticancer agents. The complexes of the type [Pd(PPh3)(ONS-(SVSHL1–3)-OCH3)] were synthesized by the reaction of [PdCl2(PPh3)2] with the corresponding TSC ligands under inert conditions; the formation of the complexes occurred with the ligands undergoing in situ Michael addition. The characterization of complexes was achieved with the aid of analytical and various spectroscopic techniques. The molecular structure of complex 3 was determined using a single crystal X-ray diffraction (XRD) method, confirming the Michael addition pathway as well. The complexes were screened against a panel of cancer and normal cell lines to evaluate their anticancer activity; complexes 2 and 3 with a phenyl or cyclohexyl substituent on the N-terminal of the ligands exhibited IC50 values of 2.87 and 4.01 μM against HeLa cancer cells, respectively. The apoptotic mode of cell death was confirmed using microscopic and flow cytometry studies. Interestingly, normal cell architecture was seen in the tissues of mice treated with the active Pd(II) complexes, in contrast with those treated with cisplatin which induced severe damage to the normal tissues in mice. [ABSTRACT FROM AUTHOR]

Memory B cells are a dynamic subset of the mature B cell population that in some cases can reenter germinal centers (GCs) in response to iterative infections. Such a reactivation can lead to accumulation of genetic lesions in these cells, potentially from repetitive activation of the B cell mutator enzyme AID. Normal memory B cells do not survive repeated reentries into GCs. In this issue, Sungalee et al. demonstrate that memory B cells harboring the oncogenic BCL2:IGH translocation, which results in constitutive BCL2 expression, survive multiple GC entries upon repetitive immunization. Through these multiple GC reentries, the hallmark BCL2:IGH translocation enables AID-induced hypermutation and propagates clonal evolution toward malignant follicular lymphoma., Clonal evolution of follicular lymphomas Follicular lymphoma (FL) is an indolent subtype of non-Hodgkin's lymphoma (1) that clonally evolves over decades (2) before presenting as overt disease. In almost all [...]