Bone Microenvironment-Suppressed T Cells Increase Osteoclast Formation and Osteolytic Bone Metastases in Mice.

Immunotherapies use components of the immune system, such as T cells, to fight cancer cells, and are changing cancer treatment, causing durable responses in some patients. Bone metastases are a debilitating complication in advanced breast and prostate cancer patients. Approved treatments fail to cure bone metastases or increase patient survival and it remains unclear whether immunotherapy could benefit patients. The bone microenvironment combines various immunosuppressive factors, and combined with T cell products could increase bone resorption fueling the vicious cycle of bone metastases. Using syngeneic mouse models, our study revealed that bone metastases from 4T1 breast cancer contain tumor-infiltrating lymphocyte (TILs) and their development is increased in normal mice compared to immunodeficient and T-cell depleted mice. This effect seemed caused by the TILs specifically in bone, because T-cell depletion increased 4T1 orthotopic tumors and did not affect bone metastases from RM-1 prostate cancer cells, which lack TILs. T cells increased osteoclast formation ex vivo and in vivo contributing to bone metastasis vicious cycle. This pro-osteoclastic effect is specific to unactivated T cells, because activated T cells, secreting interferon γ (IFNγ) and interleukin 4 (IL-4), actually suppressed osteoclastogenesis, which could benefit patients. However, non-activated T cells from bone metastases could not be activated in ex vivo cultures. 4T1 bone metastases were associated with an increase of functional polymorphonuclear and monocytic myeloid-derived suppressor cells (MDSCs), potent T-cell suppressors. Although effective in other models, sildenafil and zoledronic acid did not affect MDSCs in bone metastases. Seeking other therapeutic targets, we found that monocytic MDSCs are more potent suppressors than polymorphonuclear MDSCs, expressing programmed cell death receptor-1 ligand (PD-L1)+ in bone, which could trigger T-cell suppression because 70% express its receptor, programmed cell death receptor-1 (PD-1). Collectively, our findings identified a new mechanism by which suppressed T cells increase osteoclastogenesis and bone metastases. Our results also provide a rationale for using immunotherapy because T-cell activation would increase their anti-cancer and their anti-osteoclastic properties. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

TIE2 Induces Breast Cancer Cell Dormancy and Inhibits the Development of Osteolytic Bone Metastases.

Breast cancer (BCa) cells disseminating to the bone can remain dormant and resistant to treatments for many years until relapsing as bone metastases. The tyrosine kinase receptor TIE2 induces the dormancy of hematopoietic stem cells, and could also induce the dormancy of BCa cells. However, TIE2 is also a target for anti-angiogenic treatments in ongoing clinical trials, and its inhibition could then restart the proliferation of dormant BCa cells in bone. In this study, we used a combination of patient data, in vitro, and in vivo models to investigate the effect of TIE2 in the dormancy of bone metastases. In BCa patients, we found that a higher TIE2 expression is associated with an increased time to metastases and survival. In vitro, TIE2 decreased cell proliferation as it increased the expression of cyclin-dependent kinase inhibitors CDKN1A and CDKN1B and arrested cells in the G0/G1 phase. Expression of TIE2 also increased the resistance to the chemotherapeutic 5-Fluorouracil. In mice, TIE2 expression reduced tumor growth and the formation of osteolytic bone metastasis. Together, these results show that TIE2 is sufficient to induce dormancy in vitro and in vivo, and could be a useful prognostic marker for patients. Our data also suggest being cautious when using TIE2 inhibitors in the clinic, as they could awaken dormant disseminated tumor cells.

In silico-designed mutations increase variable new-antigen receptor single-domain antibodies for VEGF165 neutralization.

The stability, binding, and tissue penetration of variable new-antigen receptor (VNAR) single-domain antibodies have been tested as part of an investigation into their ability to serve as novel therapeutics. V13 is a VNAR that recognizes vascular endothelial growth factor 165 (VEGF165). In the present study V13 was used as a parental molecule into which we introduced mutations designed in silico. Two of the designed VNAR mutants were expressed, and their ability to recognize VEGF165 was assessed in vitro and in vivo. One mutation (Pro98Tyr) was designed to increase VEGF165 recognition, while the other (Arg97Ala) was designed to inhibit VEGF165 binding. Compared to parental V13, the Pro98Tyr mutant showed enhanced VEGF165 recognition and neutralization, as indicated by inhibition of angiogenesis and tumor growth. This molecule thus appears to have therapeutic potential for neutralizing VEGF165 in cancer treatment.

A response regulator interfaces between the Frz chemosensory system and the MglA/MglB GTPase/GAP module to regulate polarity in Myxococcus xanthus.

How cells establish and dynamically change polarity are general questions in cell biology. Cells of the rod-shaped bacterium Myxococcus xanthus move on surfaces with defined leading and lagging cell poles. Occasionally, cells undergo reversals, which correspond to an inversion of the leading-lagging pole polarity axis. Reversals are induced by the Frz chemosensory system and depend on relocalization of motility proteins between the poles. The Ras-like GTPase MglA localizes to and defines the leading cell pole in the GTP-bound form. MglB, the cognate MglA GTPase activating protein, localizes to and defines the lagging pole. During reversals, MglA-GTP and MglB switch poles and, therefore, dynamically localized motility proteins switch poles. We identified the RomR response regulator, which localizes in a bipolar asymmetric pattern with a large cluster at the lagging pole, as important for motility and reversals. We show that RomR interacts directly with MglA and MglB in vitro. Furthermore, RomR, MglA, and MglB affect the localization of each other in all pair-wise directions, suggesting that RomR stimulates motility by promoting correct localization of MglA and MglB in MglA/RomR and MglB/RomR complexes at opposite poles. Moreover, localization analyses suggest that the two RomR complexes mutually exclude each other from their respective poles. We further show that RomR interfaces with FrzZ, the output response regulator of the Frz chemosensory system, to regulate reversals. Thus, RomR serves at the functional interface to connect a classic bacterial signalling module (Frz) to a classic eukaryotic polarity module (MglA/MglB). This modular design is paralleled by the phylogenetic distribution of the proteins, suggesting an evolutionary scheme in which RomR was incorporated into the MglA/MglB module to regulate cell polarity followed by the addition of the Frz system to dynamically regulate cell polarity.