Tissino et al. demonstrate that in chronic lymphocytic leukemia, the VLA-4 (CD49d/CD29) integrin remains activable by B cell receptor stimulation also upon in vitro and in vivo ibrutinib exposure. Clinically, ibrutinib-treated CD49d-positive CLL patients experience reduced recirculation lymphocytosis and nodal response and inferior outcomes.

Recent studies have shown that metals such as copper, zinc, aluminum, cadmium, chromium, iron and lead cause severe dose-dependent disturbances in growth, morphogenesis, photosynthetic and respiratory activity as well as on ultrastructure and function of organelles in the algal model system Micrasterias denticulata (Volland et al., 2011, 2012; Andosch et al., 2012). In the present investigation we focus on amelioration of these adverse effects of cadmium, chromium and lead by supplying the cells with different antioxidants and essential micronutrients to obtain insight into metal uptake mechanisms and subcellular metal targets. This seems particularly interesting as Micrasterias is adapted to extremely low-concentrated, oligotrophic conditions in its natural bog environment.The divalent ions of iron, zinc and calcium were able to diminish the effects of the metals cadmium, chromium and lead on Micrasterias. Iron showed most ameliorating effects on cadmium and chromium in short- and long-term treatments and improved cell morphogenesis, ultrastructure, cell division rates and photosynthesis. Analytical transmission electron microscopic (TEM) methods (electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI)) revealed that chromium uptake was decreased when Micrasterias cells were pre-treated with iron, which resulted in no longer detectable intracellular chromium accumulations. Zinc rescued the detrimental effects of chromium on net-photosynthesis, respiration rates and electron transport in PS II. Calcium and gadolinium were able to almost completely compensate the inhibiting effects of lead and cadmium on cell morphogenesis after mitosis, respectively. These results indicate that cadmium is taken up by calcium and iron transporters, whereas chromium appears to enter the algae cells via iron and zinc carriers. It was shown that lead is not taken up into Micrasterias at all but exerts its adverse effects on cell growth by substituting cell wall bound calcium. The antioxidants salicylic acid, ascorbic acid and glutathione were not able to ameliorate any of the investigated metal effects on the green alga Micrasterias when added to the culture medium.

Acute myeloid leukemia (AML) has a poor prognosis under the current standard of care. In recent years, venetoclax, a BCL-2 inhibitor, was approved to treat patients, ineligible for intensive induction chemotherapy. Complete remission rates with venetoclax-based therapies are, however, hampered by minimal residual disease (MRD) in a proportion of patients, leading to relapse. MRD is due to leukemic stem cells retained in bone marrow protective environments; activation of the CXCL12/CXCR4 pathway was shown to be relevant to this process. An important role is also played by cell adhesion molecules such as CD44, which has been shown to be crucial for AML development. Here we show that CD44 is involved in CXCL12 promotion of resistance to venetoclax-induced apoptosis in human AML cell lines and AML patient samples which could be abrogated by CD44 knockdown, knockout or blocking with an anti-CD44 antibody. Split-Venus biomolecular fluorescence complementation showed that CD44 and CXCR4 physically associate at the cell membrane upon CXCL12 induction. In the venetoclax-resistant OCI-AML3 cell line, CXCL12 promoted an increase in the proportion of cells expressing high levels of embryonic-stem-cell core transcription factors (ESC-TFs: Sox2, Oct4, Nanog), abrogated by CD44 knockdown. This ESC-TF-expressing subpopulation which could be selected by venetoclax treatment, exhibited a basally-enhanced resistance to apoptosis, and expressed higher levels of CD44. Finally, we developed a novel AML xenograft model in zebrafish, showing that CD44 knockout sensitizes OCI-AML3 cells to venetoclax treatment in vivo. Our study shows that CD44 is a potential molecular target to sensitize AML cells to venetoclax-based therapies.

Extracellular vesicles (EVs) released by a variety of cell types have been shown to act as a natural delivery system for bioactive molecules such as RNAs and proteins. EV therapy holds great promise as a safe and cell‐free therapy for many immunological and degenerative diseases. However, translation to clinical application is limited by several factors, including insufficient large‐scale manufacturing technologies and low yield. We have developed a novel drug delivery platform technology, BioDrone™, based on cell‐derived vesicles (CDVs) produced from diverse cell sources by using a proprietary extrusion process. This extrusion technology generates nanosized vesicles in far greater numbers than naturally obtained EVs. We demonstrate that the CDVs are surrounded by a lipid bilayer membrane with a correct membrane topology. Physical, biochemical and functional characterisation results demonstrate the potential of CDVs to act as effective therapeutics. Umbilical cord mesenchymal stem cell (UCMSC)‐derived CDVs exhibit a biological activity that is similar to UCMSCs or UCMSC‐derived EVs. Lastly, we present the establishment of a GMP‐compliant process to allow the production of a large number of UCMSC‐CDVs in a reproducible manner. GMP‐compliant manufacturing of CDVs will facilitate the preclinical and clinical evaluation of these emerging therapeutics in anti‐inflammatory or regenerative medicine. This study also represents a crucial step in the development of this novel drug delivery platform based on CDVs.

Adhesive properties of leukemia cells shape the degree of organ infiltration and the extent of leukocytosis. CD44 and the integrin VLA-4, a CD49d/CD29 heterodimer, are important factors of progenitor cell adhesion in bone marrow (BM). Here, we report their cooperation in acute myeloid leukemia (AML) by a novel non-classical CD44-mediated way of inside-out VLA-4 activation. In primary AML BM samples from patients and the OCI-AML3 cell line, CD44 engagement by hyaluronan induced inside-out activation of VLA-4 resulting in enhanced leukemia cell adhesion on VCAM-1. This was independent from VLA-4 affinity regulation but based on ligand-induced integrin clustering on the cell surface. CD44-induced VLA-4 activation could be inhibited by the Src family kinase inhibitor PP2 and the multikinase inhibitor midostaurin. In further consequence, the increased adhesion on VCAM-1 allowed AML cells to strongly bind stromal cells. Thereby VLA-4/VCAM-1 interaction promoted activation of Akt, MAPK, NF-kB and mTOR signaling and decreased AML cell apoptosis. Collectively, our investigations provide a mechanistic description of an unusual CD44 function in regulating VLA-4 avidity in AML, supporting AML cell retention in the supportive BM microenvironment.