Deregulation and epigenetic modification of BCL2-family genes cause resistance to venetoclax in hematologic malignancies

The BCL2 inhibitor venetoclax has been approved to treat different hematological malignancies. Because there is no common genetic alteration causing resistance to venetoclax in chronic lymphocytic leukemia (CLL) and B-cell lymphoma, we asked if epigenetic events might be involved in venetoclax resistance. Therefore, we employed whole-exome sequencing, methylated DNA immunoprecipitation sequencing, and genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 screening to investigate venetoclax resistance in aggressive lymphoma and high-risk CLL patients. We identified a regulatory CpG island within the PUMA promoter that is methylated upon venetoclax treatment, mediating PUMA downregulation on transcript and protein level. PUMA expression and sensitivity toward venetoclax can be restored by inhibition of methyltransferases. We can demonstrate that loss of PUMA results in metabolic reprogramming with higher oxidative phosphorylation and adenosine triphosphate production, resembling the metabolic phenotype that is seen upon venetoclax resistance. Although PUMA loss is specific for acquired venetoclax resistance but not for acquired MCL1 resistance and is not seen in CLL patients after chemotherapy-resistance, BAX is essential for sensitivity toward both venetoclax and MCL1 inhibition. As we found loss of BAX in Richter's syndrome patients after venetoclax failure, we defined BAX-mediated apoptosis to be critical for drug resistance but not for disease progression of CLL into aggressive diffuse large B-cell lymphoma in vivo. A compound screen revealed TRAIL-mediated apoptosis as a target to overcome BAX deficiency. Furthermore, antibody or CAR T cells eliminated venetoclax resistant lymphoma cells, paving a clinically applicable way to overcome venetoclax resistance.

Results of permanent lead implantation at the His bundle without the use of an electrophysiological unit

Background

His bundle pacing (HBP) promises physiological cardiac stimulation using the conduction system for a synchronous ventricular excitation, excluding the risk of pacing-induced cardiomyopathy. In daily practice, HBP is rather rarely used in Germany, in part because it has been recommended to use an electrophysiological unit (EPU) for registration of the His bundle potential and the HV interval. We attempted HBP replacing the EPU by a normal pacing system analyzer (PSA) with high resolution of the electrogram (EGM) which is used during daily clinical routine (Figs. 1 & 2).

Methods

Consecutive patients (pts) with attempted HBP in our department were included in this prospective study. We used a 4,1F and a 7F lead together with specific sheaths to reach the His bundle. Mapping was performed using a conventional PSA (atrial channel, unipolar mode, 20 mm/mV). We recorded the success of the implantation for HBP, selective versus non-selective His bundle capture, parameters of sensing and pacing performance, operation and fluoroscopy times, the number of lead implantation attempts and QRS duration before and after HBP.

Results

Implantation of a system for HBP was attempted in 265 pts (mean age 78±12 years, 102 female, mean left ventricular ejection fraction 55±8%) and was successful in 244 (92%), selective His bundle capture was achieved in 55%, non-selective in 37%. Implantation success rates increased from 86% (earliest quartile) to 98% (latest quartile). Mean operation time was 95±46 min, mean fluoroscopy time 11±10 min; a mean of 6±7 attempts (median: 3) were necessary. Mean R wave amplitude was 5±4 mV, mean threshold 0,7±0,5 V at 1,0 ms. QRS duration before implantation was 111±29 ms, post implantation 88±20 ms.

Conclusions

HBP in daily clinical routine can be successful in >90% of cases without an EPU. Mean operation and fluoroscopy times were similar to those needed for biventricular pacing. An extremely narrow paced QRS could be achieved that indicates extremely good synchronization with HBP.

Funding Acknowledgement

Type of funding sources: None.

Catchment properties and the photosynthetic trait composition of freshwater plant communities

Unlike in land plants, photosynthesis in many aquatic plants relies on bicarbonate in addition to carbon dioxide (CO2) to compensate for the low diffusivity and potential depletion of CO2 in water. Concentrations of bicarbonate and CO2 vary greatly with catchment geology. In this study, we investigate whether there is a link between these concentrations and the frequency of freshwater plants possessing the bicarbonate use trait. We show, globally, that the frequency of plant species with this trait increases with bicarbonate concentration. Regionally, however, the frequency of bicarbonate use is reduced at sites where the CO2 concentration is substantially above the air equilibrium, consistent with this trait being an adaptation to carbon limitation. Future anthropogenic changes of bicarbonate and CO2 concentrations may alter the species compositions of freshwater plant communities.

Short-term effects of cardiac steroids on intracellular membrane traffic in neuronal NT2 cells

Cardiac steroids (CS) are specific inhibitors of Na+, K+-ATPase activity. Although the presence of CS-like compounds in animal tissues has been established, their physiological role is not clear. In a previous study we showed that in pulse-chase membrane-labeling experiments, long term (hours) interaction of CS at physiological concentrations (nM) with Na+, K+-ATPase, caused changes in endocytosed membrane traffic in human NT2 cells. This was associated with the accumulation of large vesicles adjacent to the nucleus. For this sequence of events to function in the physiological setting, however, CS would be expected to modify membrane traffic upon short term (min) exposure and membrane labeling. We now demonstrate that CS affects membrane traffic also following a short exposure. This was reflected by the CS-induced accumulation of FM1-43 and transferrin in the cells, as well as by changes in their colocalization with Na+, K+-ATPase. We also show that the CS-induced changes in membrane traffic following up to 2 hrs exposure are reversible, whereas longer treatment induces irreversible effects. Based on these observations, we propose that endogenous CS-like compounds are physiological regulators of the recycling of endocytosed membrane proteins and cargo in neuronal cells, and may affect basic mechanisms such as neurotransmitter release and reuptake.

Performance of discrete heat engines and heat pumps in finite time

The performance in finite time of a discrete heat engine with internal friction is analyzed. The working fluid of the engine is composed of an ensemble of noninteracting two level systems. External work is applied by changing the external field and thus the internal energy levels. The friction induces a minimal cycle time. The power output of the engine is optimized with respect to time allocation between the contact time with the hot and cold baths as well as the adiabats. The engine's performance is also optimized with respect to the external fields. By reversing the cycle of operation a heat pump is constructed. The performance of the engine as a heat pump is also optimized. By varying the time allocation between the adiabats and the contact time with the reservoir a universal behavior can be identified. The optimal performance of the engine when the cold bath is approaching absolute zero is studied. It is found that the optimal cooling rate converges linearly to zero when the temperature approaches absolute zero.

Single exchanges of amino acids in the basic region change the specificity of N-Myc

We exchanged specific amino acids in the basic region of the murine N-Myc protein and tested the mutant proteins for their DNA binding specificity. The amino acids we exchanged were chosen in analogy to residues of the homologous basic regions of bHLH and bZIP proteins. Mutant N-Myc peptides were expressed in Escherichia coli and specific DNA binding was monitored by gel shift experiments. For this we used palindromic target sequences with systematic base pair exchanges. Several mutants with altered DNA binding specificity were identified. Amino acid exchanges of residues -14 or -10 of the basic region lead to specificity changes (we define leucine 402 of N-Myc as +1; comparable to GCN4 see (1)). The palindromic N-Myc recognition sequence 5'CACGTG is no longer recognized by the mutant proteins, but DNA fragments with symmetrical exchanges of the target sequence are. Exchanges at position -15 broaden the binding specificity. These data were used to build a computer based model of the putative interactions of the N-Myc basic DNA binding region with its target sequence.

In vitro phagocytosis inhibition assay for the screening of potential candidate antigens for sub-unit vaccines against the asexual blood stage of Plasmodium falciparum

We have previously established a direct correlation between immune protection against the asexual blood stage Plasmodium falciparum infection and the presence of opsonizing antibodies promoting phagocytosis of parasitized red blood cells. In the present communication we describe an in vitro assay for measuring phagocytosis inhibition (PIA) specific for P. falciparum-infected erythrocytes. The phagocytosis inhibition assay is a simple procedure for screening potential candidates for sub-unit vaccines against P. falciparum based on the correlation between opsonizing antibodies and immunoprotection. The assay was used to analyse 18 recombinant molecules, corresponding to 11 distinct antigens of P. falciparum. Pre-incubation and selective antibody depletion experiments demonstrate the antigen-antibody specificity of the PIA. The presence of epitopes participating as targets of opsonic antibodies were demonstrated in six distinct polypeptide antigens.