Human Serum Enhances Biomimicry of Engineered Tissue Models of Bone and Cancer

Zika virus infects human osteoclasts and blocks differentiation and bone resorption

Bone-related complications are commonly reported following arbovirus infection. These arboviruses are known to disturb bone-remodeling and induce inflammatory bone loss via increased activity of bone resorbing osteoclasts (OCs). We previously showed that Zika virus (ZIKV) could disturb the function of bone forming osteoblasts, but the susceptibility of OCs to ZIKV infection is not known. Here, we investigated the effect of ZIKV infection on osteoclastogenesis and report that infection of pre- and early OCs with ZIKV significantly reduced the osteoclast formation and bone resorption. Interestingly, infection of pre-OCs with a low dose ZIKV infection in the presence of flavivirus cross-reacting antibodies recapitulated the phenotype observed with a high viral dose, suggesting a role for antibody-dependent enhancement in ZIKV-associated bone pathology. In conclusion, we have characterized a primary in vitro model to study the role of osteoclastogenesis in ZIKV pathogenesis, which will help to identify possible new targets for developing therapeutic and preventive measures.

Synthesis and ex vivo biodistribution of two 68Ga-labeled tetrazine tracers: Comparison of pharmacokinetics

Pretargeted PET imaging allows the use of radiotracers labeled with short-living PET radionuclides for tracing drugs with slow pharmacokinetics. Recently, especially methods based on bioorthogonal chemistry have been under intensive investigation for pretargeted PET imaging. The pharmacokinetics of the radiotracer is one of the factors that determine the success of the pretargeted strategy. Here, we report synthesis and biological evaluation of two ⁶⁸Ga-labeled tetrazine (Tz)-based radiotracers, [⁶⁸Ga]Ga-HBED-CC-PEG₄-Tz ([⁶⁸Ga]4) and [⁶⁸Ga]Ga-DOTA-PEG₄-Tz ([⁶⁸Ga]6), aiming for development of new tracer candidates for pretargeted PET imaging based on the inverse electron demand Diels-Alder (IEDDA) ligation between a tetrazine and a strained alkene, such as trans-cyclooctene (TCO). Excellent radiochemical yield (RCY) was obtained for [⁶⁸Ga]4 (RCY > 96%) and slightly lower for [⁶⁸Ga]6 (RCY > 88%). Radiolabeling of HBED-CC-Tz proved to be faster and more efficient under milder conditions compared to the DOTA analogue. The two tracers exhibited excellent radiolabel stability both in vitro and in vivo. Moreover, [⁶⁸Ga]4 was successfully used for radiolabeling two different TCO-functionalized nanoparticles in vitro: Hepatitis E virus nanoparticles (HEVNPs) and porous silicon nanoparticles (PSiNPs).

Human Platelet Lysate as Alternative of Fetal Bovine Serum for Enhanced Human In Vitro Bone Resorption and Remodeling

Introduction

To study human physiological and pathological bone remodeling while addressing the principle of replacement, reduction and refinement of animal experiments (3Rs), human in vitro bone remodeling models are being developed. Despite increasing safety-, scientific-, and ethical concerns, fetal bovine serum (FBS), a nutritional medium supplement, is still routinely used in these models. To comply with the 3Rs and to improve the reproducibility of such in vitro models, xenogeneic-free medium supplements should be investigated. Human platelet lysate (hPL) might be a good alternative as it has been shown to accelerate osteogenic differentiation of mesenchymal stromal cells (MSCs) and improve subsequent mineralization. However, for a human in vitro bone model, hPL should also be able to adequately support osteoclastic differentiation and subsequent bone resorption. In addition, optimizing co-culture medium conditions in mono-cultures might lead to unequal stimulation of co-cultured cells.

Methods

We compared supplementation with 10% FBS vs. 10%, 5%, and 2.5% hPL for osteoclast formation and resorption by human monocytes (MCs) in mono-culture and in co-culture with (osteogenically stimulated) human MSCs.

Results and Discussion

Supplementation of hPL can lead to a less donor-dependent and more homogeneous osteoclastic differentiation of MCs when compared to supplementation with 10% FBS. In co-cultures, osteoclastic differentiation and resorption in the 10% FBS group was almost completely inhibited by MSCs, while the supplementation with hPL still allowed for resorption, mostly at low concentrations. The addition of hPL to osteogenically stimulated MSC mono- and MC-MSC co-cultures resulted in osteogenic differentiation and bone-like matrix formation, mostly at high concentrations.

Conclusion

We conclude that hPL could support both osteoclastic differentiation of human MCs and osteogenic differentiation of human MSCs in mono- and in co-culture, and that this can be balanced by the hPL concentration. Thus, the use of hPL could limit the need for FBS, which is currently commonly accepted for in vitro bone remodeling models.

Engineering complexity in human tissue models of cancer

Major progress in the understanding and treatment of cancer have tremendously improved our knowledge of this complex disease and improved the length and quality of patients' lives. Still, major challenges remain, in particular with respect to cancer metastasis which still escapes effective treatment and remains responsible for 90% of cancer related deaths. In recent years, the advances in cancer cell biology, oncology and tissue engineering converged into the engineered human tissue models of cancer that are increasingly recapitulating many aspects of cancer progression and response to drugs, in a patient-specific context. The complexity and biological fidelity of these models, as well as the specific questions they aim to investigate, vary in a very broad range. When selecting and designing these experimental models, the fundamental question is "how simple is complex enough" to accomplish a specific goal of cancer research. Here we review the state of the art in developing and using the human tissue models in cancer research and developmental drug screening. We describe the main classes of models providing different levels of biological fidelity and complexity, discuss their advantages and limitations, and propose a framework for designing an appropriate model for a given study. We close by outlining some of the current needs, opportunities and challenges in this rapidly evolving field.