Role of the splenic microenvironment in chronic lymphocytic leukemia development in Eµ-TCL1 transgenic mice.

The chronic lymphocytic leukemia (CLL) microenvironment has been receiving an increasing amount of attention, but there is currently limited data surrounding how the microenvironment affects initial development of CLL. We determined that the spleen is the initial site of CLL growth through monitoring of transgenic Eµ-TCL1 mice that develop CLL. Subsequently, we isolated stromal cells from the spleens of Eµ-TCL1 mice (EMST cells) that induce CLL cell division in vitro. Both cell-cell contact and soluble factors were involved in EMST-induced CLL cell division. These stromal cells are present in significantly larger numbers in the spleen than other lymphoid organs. We also noted that splenectomy delayed CLL development in Eµ-TCL1 mice and completely prevented CLL development in adoptive transfer mice. Our findings will allow future studies surrounding the CLL microenvironment to focus upon the splenic stromal cells.

Targeted Oral Delivery of Paclitaxel Using Colostrum-Derived Exosomes.

Lung cancer is the leading cause of cancer-related deaths worldwide. Non-small-cell lung cancer (NSCLC) is the most common type accounting for 84% of all lung cancers. Paclitaxel (PAC) is a widely used drug in the treatment of a broad spectrum of human cancers, including lung. While efficacious, PAC generally is not well tolerated and its limitations include low aqueous solubility, and significant toxicity. To overcome the dose-related toxicity of solvent-based PAC, we utilized bovine colostrum-derived exosomes as a delivery vehicle for PAC for the treatment of lung cancer. Colostrum provided higher yield of exosomes and could be loaded with higher amount of PAC compared to mature milk. Exosomal formulation of PAC (ExoPAC) showed higher antiproliferative activity and inhibition of colony formation against A549 cells compared with PAC alone, and also showed antiproliferative activity against a drug-resistant variant of A549. To further enhance its efficacy, exosomes were attached with a tumor-targeting ligand, folic acid (FA). FA-ExoPAC given orally showed significant inhibition (>50%) of subcutaneous tumor xenograft while similar doses of PAC showed insignificant inhibition. In the orthotopic lung cancer model, oral dosing of FA-ExoPAC achieved greater efficacy (55% growth inhibition) than traditional i.v. PAC (24-32% growth inhibition) and similar efficacy as i.v. Abraxane (59% growth inhibition). The FA-ExoPAC given i.v. exceeded the therapeutic efficacy of Abraxane (76% growth inhibition). Finally, wild-type animals treated with p.o. ExoPAC did not show gross, systemic or immunotoxicity. Solvent-based PAC caused immunotoxicity which was either reduced or completely mitigated by its exosomal formulations. These studies show that a tumor-targeted oral formulation of PAC (FA-ExoPAC) significantly improved the overall efficacy and safety profile while providing a user-friendly, cost-effective alternative to bolus i.v. PAC and i.v. Abraxane.

Chronic Lymphocytic Leukemia-Derived IL-10 Suppresses Antitumor Immunity.

Chronic lymphocytic leukemia (CLL) patients progressively develop an immunosuppressive state. CLL patients have more plasma IL-10, an anti-inflammatory cytokine, than healthy controls. In vitro human CLL cells produce IL-10 in response to BCR cross-linking. We used the transgenic Eµ-T cell leukemia oncogene-1 (TCL1) mouse CLL model to study the role of IL-10 in CLL associated immunosuppression. Eµ-TCL mice spontaneously develop CLL because of a B cell-specific expression of the oncogene, TCL1. Eµ-TCL1 mouse CLL cells constitutively produce IL-10, which is further enhanced by BCR cross-linking, CLL-derived IL-10 did not directly affect survival of murine or human CLL cells in vitro. We tested the hypothesis that the CLL-derived IL-10 has a critical role in CLL disease in part by suppressing the host immune response to the CLL cells. In IL-10R-/- mice, wherein the host immune cells are unresponsive to IL-10-mediated suppressive effects, there was a significant reduction in CLL cell growth compared with wild type mice. IL-10 reduced the generation of effector CD4 and CD8 T cells. We also found that activation of BCR signaling regulated the production of IL-10 by both murine and human CLL cells. We identified the transcription factor, Sp1, as a novel regulator of IL-10 production by CLL cells and that it is regulated by BCR signaling via the Syk/MAPK pathway. Our results suggest that incorporation of IL-10 blocking agents may enhance current therapeutic regimens for CLL by potentiating host antitumor immune response.

Novel role of prostate apoptosis response-4 tumor suppressor in B-cell chronic lymphocytic leukemia.

Prostate apoptosis response-4 (Par-4), a proapoptotic tumor suppressor protein, is downregulated in many cancers including renal cell carcinoma, glioblastoma, endometrial, and breast cancer. Par-4 induces apoptosis selectively in various types of cancer cells but not normal cells. We found that chronic lymphocytic leukemia (CLL) cells from human patients and from Eµ-Tcl1 mice constitutively express Par-4 in greater amounts than normal B-1 or B-2 cells. Interestingly, knockdown of Par-4 in human CLL-derived Mec-1 cells results in a robust increase in p21/WAF1 expression and decreased growth due to delayed G1-to-S cell-cycle transition. Lack of Par-4 also increased the expression of p21 and delayed CLL growth in Eµ-Tcl1 mice. Par-4 expression in CLL cells required constitutively active B-cell receptor (BCR) signaling, as inhibition of BCR signaling with US Food and Drug Administration (FDA)-approved drugs caused a decrease in Par-4 messenger RNA and protein, and an increase in apoptosis. In particular, activities of Lyn, a Src family kinase, spleen tyrosine kinase, and Bruton tyrosine kinase are required for Par-4 expression in CLL cells, suggesting a novel regulation of Par-4 through BCR signaling. Together, these results suggest that Par-4 may play a novel progrowth rather than proapoptotic role in CLL and could be targeted to enhance the therapeutic effects of BCR-signaling inhibitors.

Oxidative stress-induced JNK/AP-1 signaling is a major pathway involved in selective apoptosis of myelodysplastic syndrome cells by Withaferin-A.

Myelodysplastic syndromes (MDS) are a diverse group of malignant clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis, dysplastic cell morphology in one or more hematopoietic lineages, and a risk of progression to acute myeloid leukemia (AML). Approximately 50% of MDS patients respond to current FDA-approved drug therapies but a majority of responders relapse within 2-3 years. There is therefore a compelling need to identify potential new therapies for MDS treatment. We utilized the MDS-L cell line to investigate the anticancer potential and mechanisms of action of a plant-derived compound, Withaferin A (WFA), in MDS. WFA was potently cytotoxic to MDS-L cells but had no significant effect on the viability of normal human primary bone marrow cells. WFA also significantly reduced engraftment of MDS-L cells in a xenotransplantation model. Through transcriptome analysis, we identified reactive oxygen species (ROS)-activated JNK/AP-1 signaling as a major pathway mediating apoptosis of MDS-L cells by WFA. We conclude that the molecular mechanism mediating selective cytotoxicity of WFA on MDS-L cells is strongly associated with induction of ROS. Therefore, pharmacologic manipulation of redox biology could be exploited as a selective therapeutic target in MDS.

Milk-derived exosomes for oral delivery of paclitaxel.

In this report milk-derived exosomes have been investigated for oral delivery of the chemotherapeutic drug paclitaxel (PAC) as an alternative to conventional i.v. therapy for improved efficacy and reduced toxicity. PAC-loaded exosomes (ExoPAC) were found to have a particle size of ~108 nm, a narrow particle size distribution (PDI ~0.190), zeta potential (~ -7 mV) and a practical loading efficiency of ~8%. Exosomes and ExoPAC exhibited excellent stability in the presence of simulated-gastrointestinal fluids, and during the storage at -80 °C. A sustained release of PAC was also observed up to 48 h in vitro using PBS (pH 6.8). Importantly, ExoPAC delivered orally showed significant tumor growth inhibition (60%; P<0.001) against human lung tumor xenografts in nude mice. Treatment with i.p. PAC at the same dose as ExoPAC, however, showed modest but statistically insignificant inhibition (31%). Moreover, ExoPAC demonstrated remarkably lower systemic and immunologic toxicities as compared to i.v. PAC.

Radiation Induced Apoptosis of Murine Bone Marrow Cells Is Independent of Early Growth Response 1 (EGR1).

An understanding of how each individual 5q chromosome critical deleted region (CDR) gene contributes to malignant transformation would foster the development of much needed targeted therapies for the treatment of therapy related myeloid neoplasms (t-MNs). Early Growth Response 1 (EGR1) is a key transcriptional regulator of myeloid differentiation located within the 5q chromosome CDR that has been shown to regulate HSC (hematopoietic stem cell) quiescence as well as the master regulator of apoptosis-p53. Since resistance to apoptosis is a hallmark of malignant transformation, we investigated the role of EGR1 in apoptosis of bone marrow cells; a cell population from which myeloid malignancies arise. We evaluated radiation induced apoptosis of Egr1+/+ and Egr1-/- bone marrow cells in vitro and in vivo. EGR1 is not required for radiation induced apoptosis of murine bone marrow cells. Neither p53 mRNA (messenger RNA) nor protein expression is regulated by EGR1 in these cells. Radiation induced apoptosis of bone marrow cells by double strand DNA breaks induced p53 activation. These results suggest EGR1 dependent signaling mechanisms do not contribute to aberrant apoptosis of malignant cells in myeloid malignancies.

Role of B cell receptor signaling in IL-10 production by normal and malignant B-1 cells.

B-1 cells are considered innate immune cells, which produce the majority of natural antibodies. B-1 cell responses to B cell receptor (BCR) and Toll-like receptor ligation are tightly regulated owing to the cross-reactivity to self-antigens. CD5 has been shown to play a major role in downregulation of BCR responses in B-1 cells. Here, we provide evidence for another mechanism by which BCR response is regulated in B-1 cells. B-1 cells, as well as their malignant counterpart, B cell chronic lymphocytic leukemia (B-CLL) cells, produce interleukin-10 (IL-10) constitutively. IL-10 secretion by normal B-1 cells downregulates their proliferation responses to BCR ligation. However, we found that CLL cells appear to be unique in not responding to IL-10-mediated feedback-suppressive effects in comparison to normal B-1 cells. In addition, we describe a novel role of the BCR signaling pathway in constitutive IL-10 secretion by normal and malignant B-1 cells. We found that inhibition of Src family kinases, spleen tyrosine kinase, Syk, or Bruton's tyrosine kinase reduces constitutive IL-10 production by both normal and malignant B-1 cells.