Differential immune landscapes in appendicular versus axial skeleton.

Roughly 400,000 people in the U.S. are living with bone metastases, the vast majority occurring in the spine. Metastases to the spine result in fractures, pain, paralysis, and significant health care costs. This predilection for cancer to metastasize to the bone is seen across most cancer histologies, with the greatest incidence seen in prostate, breast, and lung cancer. The molecular process involved in this predilection for axial versus appendicular skeleton is not fully understood, although it is likely that a combination of tumor and local micro-environmental factors plays a role. Immune cells are an important constituent of the bone marrow microenvironment and many of these cells have been shown to play a significant role in tumor growth and progression in soft tissue and bone disease. With this in mind, we sought to examine the differences in immune landscape between axial and appendicular bones in the normal noncancerous setting in order to obtain an understanding of these landscapes. To accomplish this, we utilized mass cytometry by time-of-flight (CyTOF) to examine differences in the immune cell landscapes between the long bone and vertebral body bone marrow from patient clinical samples and C57BL/6J mice. We demonstrate significant differences between immune populations in both murine and human marrow with a predominance of myeloid progenitor cells in the spine. Additionally, cytokine analysis revealed differences in concentrations favoring a more myeloid enriched population of cells in the vertebral body bone marrow. These differences could have clinical implications with respect to the distribution and permissive growth of bone metastases.

Targeted Notch1 inhibition with a Notch1 antibody, OMP-A2G1, decreases tumor growth in two murine models of prostate cancer in association with differing patterns of DNA damage response gene expression.

Notch plays a protumorigenic role in many cancers including prostate cancer (PCa). Global notch inhibition of multiple Notch family members using γ-secretase inhibitors has shown efficacy in suppressing PCa growth in murine models. However, global Notch inhibition is associated with marked toxicity due to the widespread function of many different Notch family members in normal cell physiology. Accordingly, in the current study, we explored if specific inhibition of Notch1 would effectively inhibit PCa growth in a murine model. The androgen-dependent VCaP and androgen-independent DU145 cell lines were injected subcutaneously into mice. The mice were treated with either control antibody 1B7.11, anti-Notch1 antibody (OMP-A2G1), docetaxel or the combination of OMP-A2G1 and docetaxel. Tumor growth was measured using calipers. At the end of the study, tumors were assessed for proliferative response, apoptotic response, Notch target gene expression, and DNA damage response (DDR) expression. OMP-A2G1 alone inhibited tumor growth of both PCa cell lines to a greater extent than docetaxel alone. There was no additive or synergistic effect of OMP-A2G1 and docetaxel. The primary toxicity was weight loss that was controlled with dietary supplementation. Proliferation and apoptosis were affected differentially in the two cell lines. OMP-A2G1 increased expression of the DDR gene GADD45α in VCaP cells but downregulated GADD45α in Du145 cells. Taken together, these data show that Notch1 inhibition decreases PCa xenograft growth but does so through different mechanisms in the androgen-dependent VCaP cell line vs the androgen-independent DU145 cell line. These results provide a rationale for further exploration of targeted Notch inhibition for therapy of PCa.

Loss of DNA polymerase ß induces cellular senescence.

We aim to establish that accelerated aging and premature cellular senescence seen in individuals with Down syndrome is related to reduced DNA polymeraseß. We report here that primary fibroblasts from Down syndrome individuals exhibit greater SA-ß-gal staining (fourfold increase, P < 0.001), increased p16 transcript abundance (threefold increase, P < 0.01), and reduced HMGB1 nuclear localization (1.5-fold lower, P < 0.01). We also find that DNA polymerase ß expression is significantly reduced in Down syndrome primary fibroblasts (53% decline, P < 0.01). To evaluate whether DNA polymerase ß might be causative in senescence induction, we evaluated the impact of murine DNA polymerase ß nullizygosity on senescence. We find that unexposed DNA polymerase ß -null primary fibroblasts exhibit a robust increase in the number of senescent cells compared to wild-type (11-fold, P < 0.001), demonstrating that loss DNA polymerase ß is sufficient to induce senescence. We also see an additional increase in response to hydroxyurea (threefold greater than WT-HU, P < 0.05). These data demonstrate that loss of DNA polymerase ß is sufficient to induce senescence. Additionally, we report a significant induction in spontaneous DNA double strand breaks in DNA polymerase ß null MEFs (fivefold increase from wild-type, P < 0.0001). Our findings strongly suggest that DNA polymerase ß is causative in senescence induction, reasonably pointing to DNA polymerase ß as a likely factor driving the premature senescence in Down syndrome. Environ. Mol. Mutagen. 59:603-612, 2018. © 2018 Wiley Periodicals, Inc.