BCL-2 inhibition in haematological malignancies: Clinical application and complications

B-cell lymphoma-2 (BCL-2) family proteins are fundamental regulators of the intrinsic apoptotic pathway which modulate cellular fate. In many haematological malignancies, overexpression of anti-apoptotic factors (BCL-2, BCL-XL and MCL-1) circumvent apoptosis. To address this cancer hallmark, a concerted effort has been made to induce apoptosis by inhibiting BCL-2 family proteins. A series of highly selective BCL-2 homology 3 (BH3) domain mimetics are in clinical use and in ongoing clinical trials for acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM). These inhibitors serve as promising candidates, both as single agents or in combination therapy to improve patient outcomes. In other diseases such as follicular lymphoma, efficacy has been notably limited. There are also clinical problems with BCL-2 family inhibition, including drug resistance, disease relapse, tumour lysis syndrome, and clinically relevant cytopenias. Here, we provide a balanced view on both the clinical benefits of BCL-2 inhibition as well as the associated challenges.

Panhematopoietic RNA barcoding enables kinetic measurements of nucleate and anucleate lineages and the activation of myeloid clones following acute platelet depletion

BACKGROUND

Platelets and erythrocytes constitute over 95% of all hematopoietic stem cell output. However, the clonal dynamics of HSC contribution to these lineages remains largely unexplored.

RESULTS

We use lentiviral genetic labeling of mouse hematopoietic stem cells to quantify output from all lineages, nucleate, and anucleate, simultaneously linking these with stem and progenitor cell transcriptomic phenotypes using single-cell RNA-sequencing. We observe dynamic shifts of clonal behaviors through time in same-animal peripheral blood and demonstrate that acute platelet depletion shifts the output of multipotent hematopoietic stem cells to the exclusive production of platelets. Additionally, we observe the emergence of new myeloid-biased clones, which support short- and long-term production of blood cells.

CONCLUSIONS

Our approach enables kinetic studies of multi-lineage output in the peripheral blood and transcriptional heterogeneity of individual hematopoietic stem cells. Our results give a unique insight into hematopoietic stem cell reactivation upon platelet depletion and of clonal dynamics in both steady state and under stress.

Plasma cell-derived mtDAMPs activate the macrophage STING pathway, promoting myeloma progression

Mitochondrial damage-associated molecular patterns (mtDAMPs) include proteins, lipids, metabolites, and DNA and have various context-specific immunoregulatory functions. Cell-free mitochondrial DNA (mtDNA) is recognized via pattern recognition receptors and is a potent activator of the innate immune system. Cell-free mtDNA is elevated in the circulation of trauma patients and patients with cancer; however, the functional consequences of elevated mtDNA are largely undefined. Multiple myeloma (MM) relies upon cellular interactions within the bone marrow (BM) microenvironment for survival and progression. Here, using in vivo models, we describe the role of MM cell-derived mtDAMPs in the protumoral BM microenvironment and the mechanism and functional consequence of mtDAMPs in myeloma disease progression. Initially, we identified elevated levels of mtDNA in the peripheral blood serum of patients with MM compared with those of healthy controls. Using the MM1S cells engrafted into nonobese diabetic severe combined immunodeficient gamma mice, we established that elevated mtDNA was derived from MM cells. We further show that BM macrophages sense and respond to mtDAMPs through the stimulator of interferon genes (STING) pathway, and inhibition of this pathway reduces MM tumor burden in the KaLwRij-5TGM1 mouse model. Moreover, we found that MM-derived mtDAMPs induced upregulation of chemokine signatures in BM macrophages, and inhibition of this signature resulted in egress of MM cells from the BM. Here, we demonstrate that malignant plasma cells release mtDNA, a form of mtDAMPs, into the myeloma BM microenvironment, which in turn activates macrophages via STING signaling. We establish the functional role of these mtDAMP-activated macrophages in promoting disease progression and retaining MM cells in the protumoral BM microenvironment.

You are what you eat: How to best fuel your immune system

Normal bone marrow (BM) homeostasis ensures consistent production of progenitor cells and mature blood cells. This requires a reliable supply of nutrients in particular free fatty acids, carbohydrates and protein. Furthermore, rapid changes can occur in response to stress such as infection which can alter the demand for each of these metabolites. In response to infection the haematopoietic stem cells (HSCs) must respond and expand rapidly to facilitate the process of emergency granulopoiesis required for the immediate immune response. This involves a shift from the use of glycolysis to oxidative phosphorylation for energy production and therefore an increased demand for metabolites. Thus, the right balance of each dietary component helps to maintain not only normal homeostasis but also the ability to quickly respond to systemic stress. In addition, some dietary components can drive chronic inflammatory changes in the absence of infection or immune stress, which in turn can impact on overall immune function. The optimal nutrition for the best immunological outcomes would therefore be a diet that supports the functions of immune cells allowing them to initiate effective responses against pathogens but also to resolve the response rapidly when necessary and to avoid any underlying chronic inflammation. In this review we discuss how these key dietary components can alter immune function, what is their impact on bone marrow metabolism and how changes in dietary intake of each of these can improve the outcomes of infections.

PGC-1α induced mitochondrial biogenesis in stromal cells underpins mitochondrial transfer to melanoma

INTRODUCTION

Progress in the knowledge of metabolic interactions between cancer and its microenvironment is ongoing and may lead to novel therapeutic approaches. Until recently, melanoma was considered a glycolytic tumour due to mutations in mitochondrial-DNA, however, these malignant cells can regain OXPHOS capacity via the transfer of mitochondrial-DNA, a process that supports their proliferation in-vitro and in-vivo. Here we study how melanoma cells acquire mitochondria and how this process is facilitated from the tumour microenvironment.

METHODS

Primary melanoma cells, and MSCs derived from patients were obtained. Genes' expression and DNA quantification was analysed using Real-time PCR. MSC migration, melanoma proliferation and tumour volume, in a xenograft subcutaneous mouse model, were monitored through bioluminescent live animal imaging.

RESULTS

Human melanoma cells attract bone marrow-derived stromal cells (MSCs) to the primary tumour site where they stimulate mitochondrial biogenesis in the MSCs through upregulation of PGC1a. Mitochondria are transferred to the melanoma cells via direct contact with the MSCs. Moreover, inhibition of MSC-derived PGC1a was able to prevent mitochondrial transfer and improve NSG melanoma mouse tumour burden.

CONCLUSION

MSC mitochondrial biogenesis stimulated by melanoma cells is prerequisite for mitochondrial transfer and subsequent tumour growth, where targeting this pathway may provide an effective novel therapeutic approach in melanoma.

Acute Myeloid Leukaemia Drives Metabolic Changes in the Bone Marrow Niche

Acute myeloid leukaemia (AML) is a highly proliferative cancer characterised by infiltration of immature haematopoietic cells in the bone marrow (BM). AML predominantly affects older people and outcomes, particularly in this difficult to treat population remain poor, in part due to inadequate response to therapy, and treatment toxicity. Normal haematopoiesis is supported by numerous support cells within the BM microenvironment or niche, including adipocytes, stromal cells and endothelial cells. In steady state haematopoiesis, haematopoietic stem cells (HSCs) primarily acquire ATP through glycolysis. However, during stress-responses HSCs rapidly transition to oxidative phosphorylation, enabled by mitochondrial plasticity. Historically it was thought that cancer cells preferentially used glycolysis for ATP production, however recently it has become evident that many cancers, including AML primarily use the TCA cycle and oxidative phosphorylation for rapid proliferation. AML cells hijack the stress-response pathways of their non-malignant counterparts, utilising mitochondrial changes to drive expansion. In addition, amino acids are also utilised by leukaemic stem cells to aid their metabolic output. Together, these processes allow AML cells to maximise their ATP production, using multiple metabolites and fuelling rapid cell turnover which is a hallmark of the disease. This review of AML derived changes in the BM niche, which enable enhanced metabolism, will consider the important pathways and discuss future challenges with a view to understanding how AML cells are able to hijack metabolic pathways and how we may elucidate new targets for potential therapies.

LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation

The bone marrow (BM) microenvironment regulates acute myeloid leukemia (AML) initiation, proliferation, and chemotherapy resistance. Following cancer cell death, a growing body of evidence suggests an important role for remaining apoptotic debris in regulating the immunologic response to and growth of solid tumors. Here, we investigated the role of macrophage LC3–associated phagocytosis (LAP) within the BM microenvironment of AML. Depletion of BM macrophages (BMMs) increased AML growth in vivo. We show that LAP is the predominate method of BMM phagocytosis of dead and dying cells in the AML microenvironment. Targeted inhibition of LAP led to the accumulation of apoptotic cells (ACs) and apoptotic bodies (ABs), resulting in accelerated leukemia growth. Mechanistically, LAP of AML-derived ABs by BMMs resulted in stimulator of IFN genes (STING) pathway activation. We found that AML-derived mitochondrial damage–associated molecular patterns were processed by BMMs via LAP. Moreover, depletion of mitochondrial DNA (mtDNA) in AML-derived ABs showed that it was this mtDNA that was responsible for the induction of STING signaling in BMMs. Phenotypically, we found that STING activation suppressed AML growth through a mechanism related to increased phagocytosis. In summary, we report that macrophage LAP of apoptotic debris in the AML BM microenvironment suppressed tumor growth.

Metabolic Regulation of Macrophages by SIRT1 Determines Activation During Cholestatic Liver Disease in Mice

BACKGROUND & AIMS

Inflammation is the hallmark of chronic liver disease. Metabolism is a key determinant to regulate the activation of immune cells. Here, we define the role of sirtuin 1 (SIRT1), a main metabolic regulator, in controlling the activation of macrophages during cholestatic liver disease and in response to endotoxin.

METHODS

We have used mice overexpressing SIRT1, which we treated with intraperitoneal lipopolysaccharides or induced cholestasis by bile duct ligation. Bone marrow-derived macrophages were used for mechanistic in vitro studies. Finally, PEPC-Boy mice were used for adoptive transfer experiments to elucidate the impact of SIRT1-overexpressing macrophages in contributing to cholestatic liver disease.

RESULTS

We found that SIRT1 overexpression promotes increased liver inflammation and liver injury after lipopolysaccharide/GalN and bile duct ligation; this was associated with an increased activation of the inflammasome in macrophages. Mechanistically, SIRT1 overexpression associated with the activation of the mammalian target of rapamycin (mTOR) pathway that led to increased activation of macrophages, which showed metabolic rewiring with increased glycolysis and broken tricarboxylic acid cycle in response to endotoxin in vitro. Activation of the SIRT1/mTOR axis in macrophages associated with the activation of the inflammasome and the attenuation of autophagy. Ultimately, in an in vivo model of cholestatic disease, the transplantation of SIRT1-overexpressing myeloid cells contributed to liver injury and fibrosis.

CONCLUSIONS

Our study provides novel mechanistic insights into the regulation of macrophages during cholestatic disease and the response to endotoxin, in which the SIRT1/mTOR crosstalk regulates macrophage activation controlling the inflammasome, autophagy and metabolic rewiring.

Schizophrenia-associated variation at ZNF804A correlates with altered experience-dependent dynamics of sleep slow waves and spindles in healthy young adults

The rs1344706 polymorphism in ZNF804A is robustly associated with schizophrenia and schizophrenia is, in turn, associated with abnormal non-rapid eye movement (NREM) sleep neurophysiology. To examine whether rs1344706 is associated with intermediate neurophysiological traits in the absence of disease, we assessed the relationship between genotype, sleep neurophysiology, and sleep-dependent memory consolidation in healthy participants. We recruited healthy adult males with no history of psychiatric disorder from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. Participants were homozygous for either the schizophrenia-associated 'A' allele (N = 22) or the alternative 'C' allele (N = 18) at rs1344706. Actigraphy, polysomnography (PSG) and a motor sequence task (MST) were used to characterize daily activity patterns, sleep neurophysiology and sleep-dependent memory consolidation. Average MST learning and sleep-dependent performance improvements were similar across genotype groups, albeit more variable in the AA group. During sleep after learning, CC participants showed increased slow-wave (SW) and spindle amplitudes, plus augmented coupling of SW activity across recording electrodes. SW and spindles in those with the AA genotype were insensitive to learning, whilst SW coherence decreased following MST training. Accordingly, NREM neurophysiology robustly predicted the degree of overnight motor memory consolidation in CC carriers, but not in AA carriers. We describe evidence that rs1344706 polymorphism in ZNF804A is associated with changes in the coordinated neural network activity that supports offline information processing during sleep in a healthy population. These findings highlight the utility of sleep neurophysiology in mapping the impacts of schizophrenia-associated common genetic variants on neural circuit oscillations and function.

Free fatty-acid transport via CD36 drives β-oxidation-mediated hematopoietic stem cell response to infection

Acute infection is known to induce rapid expansion of hematopoietic stem cells (HSCs), but the mechanisms supporting this expansion remain incomplete. Using mouse models, we show that inducible CD36 is required for free fatty acid uptake by HSCs during acute infection, allowing the metabolic transition from glycolysis towards β-oxidation. Mechanistically, high CD36 levels promote FFA uptake, which enables CPT1A to transport fatty acyl chains from the cytosol into the mitochondria. Without CD36-mediated FFA uptake, the HSCs are unable to enter the cell cycle, subsequently enhancing mortality in response to bacterial infection. These findings enhance our understanding of HSC metabolism in the bone marrow microenvironment, which supports the expansion of HSCs during pathogenic challenge.

Siglec-7 Mediates Immunomodulation by Colorectal Cancer-Associated Fusobacterium nucleatum ssp. animalis

Fusobacterium nucleatum is involved in the development of colorectal cancer (CRC) through innate immune cell modulation. However, the receptors of the interaction between F. nucleatum ssp. and immune cells remain largely undetermined. Here, we showed that F. nucleatum ssp. animalis interacts with Siglecs (sialic acid-binding immunoglobulin-like lectins) expressed on innate immune cells with highest binding to Siglec-7. Binding to Siglec-7 was also observed using F. nucleatum-derived outer membrane vesicles (OMVs) and lipopolysaccharide (LPS). F. nucleatum and its derived OMVs or LPS induced a pro-inflammatory profile in human monocyte-derived dendritic cells (moDCs) and a tumour associated profile in human monocyte-derived macrophages (moMϕs). Siglec-7 silencing in moDCs or CRISPR-cas9 Siglec-7-depletion of U-937 macrophage cells altered F. nucleatum induced cytokine but not marker expression. The molecular interaction between Siglec-7 and the LPS O-antigen purified from F. nucleatum ssp. animalis was further characterised by saturation transfer difference (STD) NMR spectroscopy, revealing novel ligands for Siglec-7. Together, these data support a new role for Siglec-7 in mediating immune modulation by F. nucleatum strains and their OMVs through recognition of LPS on the bacterial cell surface. This opens a new dimension in our understanding of how F. nucleatum promotes CRC progression through the generation of a pro-inflammatory environment and provides a molecular lead for the development of novel cancer therapeutic approaches targeting F. nucleatum-Siglec-7 interaction.

Abstract 2799: Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion

Multiple myeloma (MM) is an incurable malignancy of antibody (Ig) secreting differentiated B cells (plasma cells) characterized by the accumulation and localization of tumor cells in the bone marrow microenvironment (BMM). Mitochondrial DNA (mtDNA) is a damage associated molecular pattern (DAMP), as the mitochondrial genome contains islands of unmethylated CpG nucleotide motifs that have been shown to activate and promote memory B cell proliferation and antibody secretion. Recent studies have indicated that mtDNA is elevated in the circulation of trauma and cancer patients. Here we investigate the functional purpose of elevated mtDNA within the BM microenvironment of MM.We hypothesize that multiple myeloma cells secrete mitochondrial DAMPs into the bone marrow microenvironment promoting a state of chronic inflammation that drives the progression and expansion of multiple myeloma. NSG immunocompromised mice engrafted with human MM1S myeloma cell line showed elevated levels of MM derived mtDNA in the serum, detected by real-time PCR. Next we engrafted C57BL/6 mice with murine 5TGM1 myeloma cell line to establish a syngeneic mouse model. Flow cytometry analysis of the haematopoietic stem and progenitor cell (HSPC) populations showed that 5TGM1 induced an inflammatory expansion of the stem cell niche To determine the role of mtDNA in HSPC expansion we treated C57BL/6 mice with multiple doses of CpG oligodeoxynucleotides to mimic mtDNA export by MM. Results showed similar expansion of haematopoietic stem and progenitor cell populations. To understand the effects of mtDAMPs on the inflammatory cells of the BMM, we show that bone marrow derived macrophages treated with mtDNA and CpG had increased expression of pro-inflammatory cytokines including IL-6. In vivo, isolated F4/80+ bone marrow macrophages from 5TGM1 and CpG treated mice also showed increased expression of pro-inflammatory cytokines. Finally, to understand the role of mtDAMPs in regulating HSPC expansion we used blocking antibodies to TLR9 (toll-like receptor 9 for mtDNA) and FPR1 (receptor for formylated mitochondrial proteins) in 5TGM1 engrafted animals. Blocking these receptors resulted in reduced myeloma tumor burden compared to control animals. Here we establish that MM releases mtDNA into the microenvironment and highlight the involvement of mtDAMPs in creating a pro-inflammatory BMM that aids in MM disease progression. This data suggests the potential for the targeting of TLR9 or FPR1 signaling pathways as a novel therapeutic approach for MM.

Citation Format: Aisha Jibril, Prakrit Kumar, Charlotte Hellmich, Jamie A. Moore, Jayna J. Mistry, Victoria Willimott, Kristian M. Bowles, Stuart A. Rushworth. Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2799.

Abstract 2752: LC3-associated phagocytosis in bone marrow macrophages suppresses AML progression through TIM-4 mediated STING activation

Acute myeloid leukemia (AML) is a tumor dependent on its interactions within the bone marrow (BM) microenvironment. LC3-associated phagocytosis (LAP) maintains tissue homeostasis by regulating immune responses, including in tumor immunity. Here we investigate the function of LAP in the AML BM microenvironment.

We used two syngeneic leukemia models (HOXA9/Meis1 and MN1)to investigate the role of LAP on AML proliferation. AML cells were injected into LAP deficient (LAP-/-; ATG16E230-/-) and wild-type (WT) mice. LAP-/- mice had increased AML engraftment in the BM compared to WT mice, as well as reduced animal survival. Flow cytometry (Annexin+) of the BM microenvironment showed an increase in apoptosis in the BM compartment of mice engrafted with AML. This was further increased in LAP-/- mice with AML.

The number of BM macrophages (MØ) (CD45+, GR1-, F4/80+ CD115INT) did not differ between the WT and LAP-/- mice. Next, we quantified MØ numbers in the BM of WT and LAP-/- mice with AML. We found increased numbers of tumor associated CD206+ BM MØ in LAP-/- mice with AML compared to WT animals with AML. Gene expression analysis showed up-regulation of type I interferons (IFNs) relating to the STING pathway in the WT engrafted mice. Inhibition of the STING pathway reversed the LAP dependent AML suppression of inflammatory cytokines, suggesting LAP processing of apoptotic cells is important for STING activation.

AML has high mtDNA content compared to non-malignant cells, and as mtDNA can activate the STING pathway via cGAS we studied the effects of AML cells without mtDNA (AML ρ0) on STING pathway activation. Induction of apoptosis in AML ρ0 cells followed by co-culture with BM derived MØ (BMDM) for 24 hours did not activate the STING pathway in the MØ. In contrast, MØ co-culture with mitochondria containing apoptotic AML cells did activate the MØ STING pathway.

STING pathway activation via type I IFNs induces recruitment of cytotoxic T cells, but no increase in CD8+ T cell numbers or activation (Granzyme-B and IFN-γ) was observed in the BM between LAP-/- and WT animals engrafted with AML. Type I IFNs produced by MØ have been shown to act in an autocrine manner, we therefore investigated MØ phagocytic capacity in AML. Ex-vivo analysis showed enhanced phagocytosis and LAP processing of Zymosan fluorescent beads and LC3 association in MØ from AML engrafted mice compared to controls. Engulfment of apoptotic cells by MØ requires recognition of phosphatidylserine by surface TIM-4 which mediates LAP. We found TIM-4 inhibition increased AML proliferation in vivo. Finally, ex vivo analysis of TIM-4 inhibited MØ confirmed reduced LAP.

We report that BM MØ process apoptotic AML cells via LAP through TIM-4. Furthermore, AML apoptotic bodies containing mtDNA initiate MØ STING activation and inhibit AML proliferation.

Citation Format: Jamie Aaron Moore, Jayna J. Mistry, Charlotte Hellmich, Aisha Jibril, Tom Wileman, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. LC3-associated phagocytosis in bone marrow macrophages suppresses AML progression through TIM-4 mediated STING activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2752.

Abstract 1048: Targeting BCL-2 and CD38 in models of acute myeloid leukemia reduces tumour burden

The prognosis for patients with acute myeloid leukemia (AML) remains poor with high mortality rates. It is often not possible to achieve complete remission with current therapy and relapse following treatment is common. New and more targeted treatment approaches are therefore needed to improve outcomes for patients. AML progression and treatment resistance has been associated with overexpression of BCL2. Venetoclax, a BH3 mimetic targeting BCL2, has been shown to effectively target AML cells and induce cell death. It has been approved for the treatment of AML but as with other AML treatments not all patients respond, and others develop treatment resistance. Research has therefore focussed on exploring combination therapies for Venetoclax. Our group has previously shown that mitochondrial transfer from mesenchymal stromal cells (MSC) to AML blasts promotes AML growth and is mediated by CD38. Daratumumab targets CD38 and inhibits this transfer, which results in impaired AML growth and improved animal survival. Here, we investigate the effect of inhibiting both CD38 with daratumumab and BCL2 with Venetoclax on the survival of AML. Primary AML blasts and MSC were isolated from patients' bone marrow in accordance with the Declaration of Helsinki. Flow cytometry was used to measure CD38 and BCL2 expression in AML blasts compared to normal CD34+ progenitor cells. BCL2 expression was significantly higher in AML blasts and CD38 expression was also increased. Cell viability was significantly reduced following treatment with Venetoclax alone, whilst Daratumumab alone or in combination with Venetoclax did not affect AML survival further. However, the action of daratumumab relies on the bone marrow microenvironment and AML blasts were therefore co-cultured with MSC and then treated with Venetoclax or daratumumab or in combination. After 24 hours cells were stained with Annexin V-FITC/PI and flow cytometry was used to assess levels of apoptosis. Combination treatment with Venetoclax and Daratumumab resulted in significantly more apoptosis in AML cells compared to AML cells treated with single agent. Finally, the effect of combination treatment with Venetoclax and Daratumumab was assessed in vivo using an NSG xenograft mouse model of AML. Mice were engrafted with MV411-luc or patient derived AML and then treated with vehicle control (PBS) or daratumumab alone (5mg/kg on day 7 and 14) or Venetoclax alone (100mg/kg/day) or both daratumumab and Venetoclax. Bioluminescence imaging was used to assess disease engraftment and progression before and after treatment. Combining treatment with Daratumumab and Venetoclax in vivo significantly reduced tumour burden and improved animal survival compared to control or single agent.

This data supports that combination treatment with Venetoclax and Daratumumab could have an important clinical application in the treatment of AML.

Citation Format: Charlotte Hellmich, Jayna J. Mistry, Amelia Lambert, Jamie A. Moore, Aisha Jibril, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. Targeting BCL-2 and CD38 in models of acute myeloid leukemia reduces tumour burden [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1048.

Venetoclax and Daratumumab combination treatment demonstrates pre-clinical efficacy in mouse models of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains an incurable malignancy despite recent advances in treatment. Recently a number of new therapies have emerged for the treatment of AML which target BCL-2 or the membrane receptor CD38. Here, we show that treatment with Venetoclax and Daratumumab combination resulted in a slower tumor progression and a reduced leukemia growth both in vitro and in vivo. These data provide evidence for clinical evaluation of Venetoclax and Daratumumab combination in the treatment of AML.

Abstract 2643: ROS dependent PGC1alpha driven mitochondrial biogenesis within the melanoma microenvironment is a pre-requisite for mitochondrial transfer from MSC to malignant cells

The tumor microenvironment is essential for the growth and proliferation of melanoma. Recently, reports have shown that mitochondria are transferred from mesenchymal stromal cells (MSCs) to melanoma tumor cells through tunneling nanotubes (TNTs), a process which supports their proliferation in-vitro and in-vivo. Moreover, we have shown in leukemia that tumor superoxide provides the stimulus to drive mitochondrial transfer in this way. In the present study we specifically examine the effects of melanoma cells on MSC mitochondrial biogenesis and subsequent mitochondrial transfer to the malignant cell. Primary melanoma cells, and MSCs derived from the bone marrow of patients without melanoma were obtained after informed consent and under approval from the UK Health Research Authority, and in accordance with the Declaration of Helsinki. Primary cells were characterized using flow cytometry. Genes involved in mitochondria biogenesis, fission/fusion and activity were analysed using Real-time PCR and Western blotting. Mitochondrial transfer was assessed and quantified in-vitro using a MitoTracker green FM staining and flow cytometry. Melanoma signals were quenched by various inhibitors including glutathione and diphenyleneiodonium (DPI). Melanoma proliferation and tumor volume, in an NSG xenograft subcutaneous model, were monitored through bioluminescent live animal imaging. First, we confirmed primary melanoma cell identity using CD45-, CD31-, CD166+ and CD146+ staining using flow cytometry. Next, we quantified levels of mitochondrial transfer from MSC to melanoma, with and without inhibition of superoxide activity. We found that the anti-oxidants glutathione and DPI significantly reduced levels of mitochondrial transfer from MSCs to melanoma. We next quantified mitochondrial biogenesis within MSCs, showing that MSCs had increased mitochondrial DNA and increased MitoTracker green FM staining in response to co-culture with melanoma. Next, we found that this increase in mitochondrial content also occurred in response to hydrogen peroxide, which mimics the effects of melanoma-derived ROS. In addition, we show that PGC1α (master regulator of mitochondrial biogenesis) levels in the nucleus of MSCs increased when cultured with melanoma. Moreover, knockdown of PGC1α inhibited mitochondrial biogenesis in MSCs when cultured with melanoma or activated with hydrogen peroxide. Furthermore, transfer of mitochondria from MSCs to melanoma was substantially reduced when MSC-derived PGC1α was silenced. Finally, we engrafted control or PGC1α knockdown MSCs together with melanoma cell lines into the sub-cutaneous tissue of NSG mice. We found significantly reduced tumor volume when the melanoma was transplanted with the PGC1α knockdown MSCs compared to transplant of melanoma with the control knockdown MSC. Here we report that the ROS generated by melanoma cells drives MSC mitochondrial biogenesis and subsequent mitochondrial transfer from MSCs to melanoma cells. Targeting this pathway may provide an effective novel therapeutic approach in melanoma.

Citation Format: Prakrit Kumar, Jayna Mistry, Jamie Moore, Charlotte Hellmich, Aisha Jibril, Christopher Morris, Marc Moncrieff, Kristian Bowles, Stuart Rushworth. ROS dependent PGC1alpha driven mitochondrial biogenesis within the melanoma microenvironment is a pre-requisite for mitochondrial transfer from MSC to malignant cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2643.

Abstract 2974: Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment

Acute myeloid leukaemia (AML) causes 85,000 global deaths per year, which is estimated to double by 2040. AML has been shown to be highly dependent on the bone marrow (BM) microenvironment. Mesenchymal stromal cells (MSC) specifically, play an important pro-tumoral role. We previously demonstrated AML blasts rely on higher mitochondrial content and are more dependent on oxidative phosphorylation compared to non-malignant unstimulated CD34+ progenitor cells. To achieve this high metabolic demand, functional mitochondria are transferred from the MSC to the AML blasts. Mitochondrial transfer has also been demonstrated in myeloma in a pro-tumoral process regulated by CD38. Taken together, these data indicate that mitochondria are a biologically plausible and attractive drug target in the treatment of AML.We investigated the role mitochondrial transfer and the subsequent metabolic consequences of inhibiting CD38 using daratumumab on the AML BM microenvironment.Primary AML blasts and MSC were isolated from patient's BM. Mitochondrial transfer was assessed by coculture of AML and MSC in vitro using both qPCR DNA analysis and flow cytometry analysis. We used an NSG xenograft mouse model of AML, we transplanted OCI-AML3-luc, and treated the animals with either vehicle control (PBS) or daratumumab (5mg/kg) on day 9 and 16 followed by bioluminescence imaging. Post transplantation, AML mitochondrial transfer was assessed by murine mitochondrial DNA in human AML blasts by species specific PCR analysis. Post transplantation mitochondrial health and function was measured by TMRM and Seahorse analysis.Targeting CD38 using daratumumab inhibits the transfer of mitochondria from MSC to AML in vitro. In vivo, treatment with daratumumab significantly reduced tumor burden and improved survival compared to untreated controls. Additionally, we found two doses of daratumumab resulted in reduced mitochondrial potential, mitochondrial content and oxygen consumption rate in the AML cells sorted from the human xenograft mouse model. Finally, analysis of human AML cells sorted from NSG mouse BM showed reduced levels of mouse mitochondrial DNA in the human AML blasts from daratumumab treated mice compared to mice with AML treated with vehicle control.CD38 inhibition by daratumumab treatment inhibits mitochondrial transfer from MSC to AML blasts in the BM microenvironment. This results in a reduction in oxidative phosphorylation in AML blasts and subsequent reduced leukemia growth, which in turn results in improved NSG/AML animal survival. Whilst it is probable that daratumumab has a number of mechanisms of action, here we demonstrate inhibition of mitochondrial transfer is an addition to the list for this drug in AML. These data support the further clinical investigation of daratumumab based chemotherapeutic strategies as a therapeutic approach for the treatment AML.

Citation Format: Jayna J. Mistry, Jamie A. Moore, Christopher R. Marlein, Charlotte Hellmich, Genevra Pillinger, Federica Di Palma, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2974.

Bone Marrow Senescence and the Microenvironment of Hematological Malignancies

Senescence is the irreversible arrest of cell proliferation that has now been shown to play an important role in both health and disease. With increasing age senescent cells accumulate throughout the body, including the bone marrow and this has been associated with a number of age-related pathologies including malignancies. It has been shown that the senescence associated secretory phenotype (SASP) creates a pro-tumoural environment that supports proliferation and survival of malignant cells. Understanding the role of senescent cells in tumor development better may help us to identify new treatment targets to impair tumor survival and reduce treatment resistance. In this review, we will specifically discuss the role of senescence in the aging bone marrow (BM) microenvironment. Many BM disorders are age-related diseases and highly dependent on the BM microenvironment. Despite advances in drug development the prognosis particularly for older patients remains poor and new treatment approaches are needed to improve outcomes for patients. In this review, we will focus on the relationship of senescence and hematological malignancies, how senescence promotes cancer development and how malignant cells induce senescence.

CD38-Driven Mitochondrial Trafficking Promotes Bioenergetic Plasticity in Multiple Myeloma

Metabolic adjustments are necessary for the initiation, proliferation, and spread of cancer cells. Although mitochondria have been shown to move to cancer cells from their microenvironment, the metabolic consequences of this phenomenon have yet to be fully elucidated. Here, we report that multiple myeloma cells use mitochondrial-based metabolism as well as glycolysis when located within the bone marrow microenvironment. The reliance of multiple myeloma cells on oxidative phosphorylation was caused by intercellular mitochondrial transfer to multiple myeloma cells from neighboring nonmalignant bone marrow stromal cells. This mitochondrial transfer occurred through tumor-derived tunneling nanotubes (TNT). Moreover, shRNA-mediated knockdown of CD38 inhibits mitochondrial transfer and TNT formation in vitro and blocks mitochondrial transfer and improves animal survival in vivo. This study describes a potential treatment strategy to inhibit mitochondrial transfer for clinical benefit and scientifically expands the understanding of the functional effects of mitochondrial transfer on tumor metabolism. SIGNIFICANCE: Multiple myeloma relies on both oxidative phosphorylation and glycolysis following acquisition of mitochondria from its bone marrow microenvironment.See related commentary by Boise and Shanmugam, p. 2102.

Abstract 2449: Superoxide regulates protumoral p16-driven senescence in the bone marrow microenvironment of acute myeloid leukemia

Acute myeloid leukemia (AML) is primarily a disease of the elderly and depends on the bone marrow microenvironment. The aging bone marrow accumulates senescent cells, characterized by an irreversible arrest of cell proliferation and the secretion of numerous pro-inflammatory cytokines, chemokines and growth factors, termed the secretary associated senescence profile (SASP). Previously we showed that AML is capable of reprogramming bone marrow stromal cells (BMSC) and induces oxidative stress in the BMSC (via superoxide) to support blast survival and proliferation. Here, we hypothesize that AML derived superoxide induces a senescent aging phenotype in the BMSC, generating a SASP in the BMSC which then feed back to promote AML blast proliferation in the bone marrow niche. We isolated primary AML cells and BMSCs from the bone marrow of patients attending our clinic. To assess senescence of BMSC we measured p16 mRNA and protein levels and senescence associated β-Galactosidase activity. Primary AML was engrafted into NSG mice and CD105+ / CD45- cells (BMSC) were sorted and analysed for SASP. We transplanted syngeneic AML blasts (generated from lineage negative cells transduced with the oncogene MN1) into p16-3MR, WT C57Bl/6 and NOX2 (CYBB) deficient mice. Patient samples were taken in accordance with the Declaration of Helsinki and animal studies performed under approval of the UK Home Office. We report that human AML cells induce SASP in vivo as measured by RT-PCR of sorted BMSC cells from NSG mice engrafted with human AML. Next, we engrafted p16-3MR mice with MN1 cells and flow cytometry analysis of isolated BSMC (CD105+ CD45-) showed AML cells induce micro-environment senescence in vivo. Furthermore, depletion of p16 positive stromal cells through treating MN1 engrafted p16-3MR animals with ganciclovir significantly increased survival of MN1 engrafted mice compared with animals treated with vehicle control. In addition, we show that MN1 AML cells, transplanted into NOX2 deficient mice, generate high levels of superoxide in the bone marrow, which results in oxidative stress in the BMSC. Finally NOX2-KD in MN1 AML reduces BMSC senescence in the BM of p16-3MR recipient mice and results in improved animal survival. Here we show that the AML derived superoxide induces a senescent phenotype in the bone marrow micro-environment which then feeds back to enhance the growth capacity of AML. Targeting the senescent microenvironment may therefore provide novel therapeutic approaches for the treatment of this disease in the future.

Citation Format: Charlotte Hellmich, Amina Abdul-Aziz, Christopher Marlein, Yu Sun, Manar Shafat, Angela Collins, Rachel Piddock, Judith Campisi, Kristian Bowles, Stuart Rushworth. Superoxide regulates protumoral p16-driven senescence in the bone marrow microenvironment of acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2449.

Abstract 4970: Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells which is highly dependent on the bone marrow microenvironment (BMM). MM tumor survival, proliferation and drug resistance is reliant on ATP production however the mechanisms by which the malignant cells generate ATP are poorly defined. In this study, we investigate the contributions of oxidative phosphorylation and aerobic glycolysis to tumor cell ATP generation within BMM. Furthermore, we address whether ATP generation within tumor cells is enabled by the transfer of mitochondria from the non-malignant stromal cells of the BMM to the malignant plasma cell.

Bone marrow was obtained from patients under approval from the UK Health Research Authority. In-vivo experiments were performed with local Animal Welfare and Ethical Review Board approval and under license from the UK Home Office.

Using Seahorse extracellular flux analysis we show that primary MM cells have high baseline rates of mitochondrial respiration compared to MM cell lines. Furthermore, mitochondrial respiration rates increased ex-vivo after co-culture with non-malignant bone marrow stromal cells (BMSC). We engrafted the malignant MM1S cell line into NSG mice and examined the mitochondrial respiration rate from isolated tumor cells compared to MM1S cells cultured in-vitro. We found increased rates of mitochondrial respiration in MM1S cells isolated from mouse BM. To determine whether the increase in tumor oxidative phosphorylation observed in the presence of micro-environment cells was a result of mitochondrial transfer from BMSC to MM, we used three methods. Firstly we stained BMSC with the mitochondrial stain MitoTracker Green and cultured these with primary MM cells. Using a combination of flow cytometry and confocal microscopy we detected MitoTracker fluorescence in the MM cells after co-culture, showing that the stained mitochondria are transferred from BMSC to MM cells in-vitro. Secondly, mitochondrial transfer was directly observed between BMSC and MM cells, visualized by the acquisition of a mCherry labeled mitochondrial protein we transfected into BMSC. Finally, using a human MM cell line engrafted into an NSG mouse xenograft model, we detected murine mitochondrial DNA in sorted human MM1S and U266 tumor cells post-transplant. Through fixed cell confocal microscopy we found that mitochondria move through tunnelling nanotubes (TNTs), and inhibition of TNT formation by treatment with cytochalasin B resulted in reduced mitochondrial transfer and tumor cell oxidative phosphorylation.

Here we show that MM cellular metabolism favors oxidative phosphorylation over glycolysis, in the setting of the BMM. This is due to mitochondrial transfer occurring between non-malignant BMSC and malignant plasma cells. This process is necessary for optimum tumor growth in-vivo and forms part of the malignant phenotype of MM.

Citation Format: Christopher R. Marlein, Rachel E. Piddock, Charlotte Hellmich, Lyubov Zaitseva, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4970.

Genetics, sleep and memory: a recall-by-genotype study of ZNF804A variants and sleep neurophysiology

BACKGROUND

Schizophrenia is a complex, polygenic disorder for which over 100 genetic variants have been identified that correlate with diagnosis. However, the biological mechanisms underpinning the different symptom clusters remain undefined. The rs1344706 single nucleotide polymorphism within ZNF804A was among the first genetic variants found to be associated with schizophrenia. Previously, neuroimaging and cognitive studies have revealed several associations between rs1344706 and brain structure and function. The aim of this study is to use a recall-by-genotype (RBG) design to investigate the biological basis for the association of ZNF804A variants with schizophrenia. A RBG study, implemented in a population cohort, will be used to evaluate the impact of genetic variation at rs1344706 on sleep neurophysiology and procedural memory consolidation in healthy participants.

METHODS/DESIGN

Participants will be recruited from the Avon Longitudinal Study of Parents and Children (ALSPAC) on the basis of genotype at rs1344706 (n = 24). Each participant will be asked to take part in two nights of in-depth sleep monitoring (polysomnography) allowing collection of neurophysiological sleep data in a manner not amenable to large-scale study. Sleep questionnaires will be used to assess general sleep quality and subjective sleep experience after each in-house recording. A motor sequencing task (MST) will be performed before and after the second night of polysomnography. In order to gather additional data about habitual sleep behaviour participants will be asked to wear a wrist worn activity monitor (actiwatch) and complete a sleep diary for two weeks.

DISCUSSION

This study will explore the biological function of ZNF804A genotype (rs1344706) in healthy volunteers by examining detailed features of sleep architecture and physiology in relation to motor learning. Using a RBG approach will enable us to collect precise and detailed phenotypic data whilst achieving an informative biological gradient. It would not be feasible to collect such data in the large sample sizes that would be required under a random sampling scheme. By dissecting the role of individual variants associated with schizophrenia in this way, we can begin to unravel the complex genetic mechanisms of psychiatric disorders and pave the way for future development of novel therapeutic approaches.

Is trabecular bone permeability governed by molecular ordering-induced fluid viscosity gain? Arguments from re-evaluation of experimental data in the framework of homogenization theory

It is generally agreed on that trabecular bone permeability, a physiologically important quantity, is governed by the material׳s (vascular or intertrabecular) porosity as well as by the viscosity of the pore-filling fluids. Still, there is less agreement on how these two key factors govern bone permeability. In order to shed more light onto this somewhat open issue, we here develop a random homogenization scheme for upscaling Poiseuille flow in the vascular porosity, up to Darcy-type permeability of the overall porous medium "trabecular bone". The underlying representative volume element of the macroscopic bone material contains two types of phases: a spherical, impermeable extracellular bone matrix phase interacts with interpenetrating cylindrical pore channel phases that are oriented in all different space directions. This type of interaction is modeled by means of a self-consistent homogenization scheme. While the permeability of the bone matrix equals to zero, the permeability of the pore phase is found through expressing the classical Hagen-Poiseuille law for laminar flow in the format of a "micro-Darcy law". The upscaling scheme contains pore size and porosity as geometrical input variables; however, they can be related to each other, based on well-known relations between porosity and specific bone surface. As two key results, validated through comprehensive experimental data, it appears (i) that the famous Kozeny-Carman constant (which relates bone permeability to the cube of the porosity, the square of the specific surface, as well as to the bone fluid viscosity) needs to be replaced by an again porosity-dependent rational function, and (ii) that the overall bone permeability is strongly affected by the pore fluid viscosity, which, in case of polarized fluids, is strongly increased due to the presence of electrically charged pore walls.

The role of endplate poromechanical properties on the nutrient availability in the intervertebral disc

OBJECTIVE

To investigate the relevance of the human vertebral endplate poromechanics on the fluid and metabolic transport from and to the intervertebral disc (IVD) based on educated estimations of the poromechanical parameter values of the bony endplate (BEP).

METHODS

50 micro-models of different BEP samples were generated from μCTs of lumbar vertebrae and allowed direct determination of porosity values. Permeability values were calculated by using the micro-models, through the simulation of permeation via computational fluid dynamics. These educated ranges of porosity and permeability values were used as inputs for mechano-transport simulations to assess their effect on both the distributions of metabolites within an IVD model and the poromechanical calculations within the cartilaginous part of the endplate i.e., the cartilage endplate (CEP).

RESULTS

BEP effective permeability was highly correlated to local variations of porosity (R(2) ≈ 0.88). Universal patterns between bone volume fraction and permeability arose from these results and from other experimental data in the literature. These variations in BEP permeability and porosity had negligible effects on the distributions of metabolites within the disc. In the CEP, the variability of the poromechanical properties of the BEP did not affect the predicted consolidation but induced higher fluid velocities.

CONCLUSIONS

The present paper provides the first sets of thoroughly identified BEP parameter values that can be further used in patient-specific poromechanical studies. Representing BEP structural changes through variations in poromechanical properties did not affect the diffusion of metabolites. However, attention might be paid to alterations in fluid velocities and cell mechano-sensing within the CEP.

Mathematical modeling of postmenopausal osteoporosis and its treatment by the anti-catabolic drug denosumab

Denosumab, a fully human monoclonal antibody, has been approved for the treatment of postmenopausal osteoporosis. The therapeutic effect of denosumab rests on its ability to inhibit osteoclast differentiation. Here, we present a computational approach on the basis of coupling a pharmacokinetics model of denosumab with a pharmacodynamics model for quantifying the effect of denosumab on bone remodeling. The pharmacodynamics model comprises an integrated systems biology-continuum micromechanics approach, including a bone cell population model, considering the governing biochemical factors of bone remodeling (including the action of denosumab), and a multiscale micromechanics-based bone mechanics model, for implementing the mechanobiology of bone remodeling in our model. Numerical studies of postmenopausal osteoporosis show that denosumab suppresses osteoclast differentiation, thus strongly curtailing bone resorption. Simulation results also suggest that denosumab may trigger a short-term bone volume gain, which is, however, followed by constant or decreasing bone volume. This evolution is accompanied by a dramatic decrease of the bone turnover rate by more than one order of magnitude. The latter proposes dominant occurrence of secondary mineralization (which is not anymore impeded through cellular activity), leading to higher mineral concentration per bone volume. This explains the overall higher bone mineral density observed in denosumab-related clinical studies.

Microchimerism: covert genetics?

While the world of genetics has been dominated over the last decade by technological advances allowing the identification of common variants underlying the major complex diseases, it is increasingly clear that other genetic mechanisms are also involved in genetic susceptibility and resistance to disease. One understudied contender is microchimerism (maternal and foetal), resulting from bi-directional transfer of cells across the placental barrier in pregnancy. Data from several diseases suggest that elevated levels of microchimerism are associated with autoimmunity. Theories differ however on the role of these cells in the disease process. Some suggest that they increase genetic susceptibility while others suggest that these cells are effectors of the immune response, or that they represent the target of the immune response while another proposes that elevated levels in disease are caused by ongoing repair of damaged tissue. Intriguingly these semi allogeneic cells are tolerated in healthy individuals, albeit at a lower level than in disease scenarios and recent studies in cancer suggest that foetal microchimeric cells may provide surveillance and repair. Many questions remain to be answered about this new avenue of genetics. It is likely that as technology advances our understanding of, and ability to manipulate these cells for therapeutic gain, will push forward new frontiers in medicine.

Characterization of the deformation behavior of intermediate porosity interconnected Ti foams using micro-computed tomography and direct finite element modeling

Under load-bearing conditions metal-based foam scaffolds are currently the preferred choice as bone/cartilage implants. In this study X-ray micro-computed tomography was used to discretize the three-dimensional structure of a commercial titanium foam used in spinal fusion devices. Direct finite element modeling, continuum micromechanics and analytical models of the foam were employed to characterize the elasto-plastic deformation behavior. These results were validated against experimental measurements, including ultrasound and monotonic and interrupted compression testing. Interrupted compression tests demonstrated localized collapse of pores unfavorably oriented with respect to the loading direction at many isolated locations, unlike the Ashby model, in which pores collapse row by row. A principal component analysis technique was developed to quantify the pore anisotropy which was then related to the yield stress anisotropy, indicating which isolated pores will collapse first. The Gibson-Ashby model was extended to incorporate this anisotropy by considering an orthorhombic, rather than a tetragonal, unit cell. It is worth noting that the natural bone is highly anisotropic and there is a need to develop and characterize anisotropic implants that mimic bone characteristics.

Finite element simulation of the human mandible: the role of (natural) teeth

INTRODUCTION

Individual bone quality depends on genetic, biological, and mechanical influencing factors, where the latter is accessible via Finite Element Simulation. This work is part of an interdisciplinary research project with the purpose of stepwise refinement towards anatomical reality. This approach opened the door for many interrelated applications such as atrophy of the jaw bone, periodontology, implantology, or TMJ disorders. This lecture is dedicated to the influence of dental anatomy on mandibular biomechanics.

MATERIALS AND METHODS

In general, biomechanical simulation requires reconstruction of the individual anatomy, implementation of the inhomogeneous and anisotropic material law of bone, and realization of the load case due to tooth, muscle and joint forces. The simulation chain ranges from image processing of CT data up to specifically adapted post-processing of the simulation results. In spite of ongoing research, there is still a fundamental difference of dental implants compared to natural teeth: the periodontal ligament (PDL) present at the interface between teeth and mandibular corpus. Due to its thickness of about 0.2 mm, the PDL was introduced to the simulation model by a special semiautomatic procedure.

RESULTS

Simulations "with and without PDL" proved remarkable force absorption due to the PDL, as well as qualitative changes of the stress/strain profiles of the alveolar ridge. Concerning the simulation without PDL, the observed high compressive strains at the adjacent bone were in agreement with regions of frequent implant failure.

CONCLUSION

The PDL is essential for the structural behavior of the human mandible. Based on the mechanical adaptation of bone, the comparison of the simulation with and without PDL provided special insight to the changes due to dental implants, in particular implant loss and bone resorption. Finally, the simulation will serve as a virtual platform for further evaluation (a) of implant design (b) of implant placement.

Mandibular finite element simulation as a tool for trauma surgery

PURPOSE

Despite remarkable progress within the last decade, the treatment of mandibular fractures is still a highly discussed topic in oral and cranio-maxillofacial surgery. The possible traumatologic scenarios are characterized by high variability. A current project is focused on "resimulation" of traumatologic cases given by clinical radiographs by means of finite element method.

METHODS

The applied finite element model of the mandible is very refined, providing detailed dental anatomy especially of the periodontal ligament. The mandible was modelled as inhomogeneous and anisotropic. The temporomandibular joints were realized as simplified joint capsules, wherein the mandibular condyles are freely mobile with certain limitations. The user has the choice of 5 regions on the mandibular surface where the virtual injury can be inflicted. Power and direction of the impact force vector can be set at will. The masticatoy system including the digastrics and the mylohyoid muscles can be activated.

RESULTS

The situations given by radiographs could be "reproduced" by a simulation scenario characterized by high compressive strain at the location of fractures. If masticatory muscles were activated and teeth clenched, the stress/strain profiles were qualitatively changed.

DISCUSSION

The approach may be of benefit for optimized behavior with regard to certain sports or vocations. For forensic analysis, the method will contribute by elimination of scenarios not matching the given fracture locations. Nevertheless, the immediate purpose of our approach is a better understanding of the injured organ's condition. Fractures of bone as an adaptive biological tissue differ fundamentally from mechanical failure in engineering. Many of our trauma simulations showed elevated stress/strain around the fracture, leading to the suggestion of weakened bone there. This finding was confirmed by surgical observation.

Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

Average hydroxyapatite concentration is uniform in the extracollagenous ultrastructure of mineralized tissues: evidence at the 1-10-microm scale

At the ultrastructural observation scale of fully mineralized tissues (l=1-10 mum), transmission electron micrographs (TEM) reveal that hydroxyapatite (HA) is situated both within the fibrils and extrafibrillarly, and that the majority of HA lies outside the fibrils. The extrafibrillar amount of HA varies from tissue to tissue. By means of mathematical modeling, we here provide strong indications that there exists a physical quantity that is the same inside and outside the fibrils, for all different fully mineralized tissues. This quantity is the average mineral concentration in the non-collagenous space. This space is the sum of the extrafibrillar volume and of the volume of the fibrils that is not occupied by collagen molecules. Two independent sets of experimental observations covering a large range of tissue mass densities establish the relevance of our proposition: (i) mass density measurements and diffraction spacing measurements, re-analyzed through a dimensionally consistent packing model; (ii) optical density measurements of TEMs. The aforementioned average uniform HA-concentration in the extracollagenous space of the ultrastructure may emphasize the putative role played by a number of non-collagenous organic molecules in providing the chemical boundary conditions for mineralization of HA in the extracollagenous space. The probable existence of an average uniform extracollagenous HA concentration has far-reaching consequences for the mechanical behavior of mineralized tissues.

[The efficacy of oral betamimetics using an oxytocin-stimulated puerperal model (author's transl)]

Puerperal uteri were stimulated by oxytocin, the uterine motility was recorded by transcervical catheter techniques, maternal pulse and blood-pressure were recorded continuously or intermittently. Oral tocolytics as Gynipral (Hexoprenaline), Partusisten (Fenoterol), Spiropent (Clenbuterol) and Prepar (Ritodrine) were administered orally in single or double dose. The inhibitory effect of these drugs were recorded, evaluated from the records and calculated statistically concerning their significant differences. It could be demonstrated that only Hexoprenaline in a three time higher dose than used usually and Partusisten in a dose of 10 and 20 mg were able to reduce uterine motility for more than 50%. All other substances definitely had an inhibitory effect on the puerperal uterus, but inhibition was not stronger than 30%. Cardiovascular side-effects were discussed. The question, if oral given betamimetics are effective in the treatment of threatening premature labour could not be answered definitively, but there are doubts according this study concerning the dose and the repetition of it for this purpose.