Sonrotoclax overcomes BCL2 G101V mutation-induced venetoclax resistance in preclinical models of hematologic malignancy.

ABSTRACT: Venetoclax, the first-generation inhibitor of the apoptosis regulator B-cell lymphoma 2 (BCL2), disrupts the interaction between BCL2 and proapoptotic proteins, promoting the apoptosis in malignant cells. Venetoclax is the mainstay of therapy for relapsed chronic lymphocytic leukemia and is under investigation in multiple clinical trials for the treatment of various cancers. Although venetoclax treatment can result in high rates of durable remission, relapse has been widely observed, indicating the emergence of drug resistance. The G101V mutation in BCL2 is frequently observed in patients who relapsed treated with venetoclax and sufficient to confer resistance to venetoclax by interfering with compound binding. Therefore, the development of next-generation BCL2 inhibitors to overcome drug resistance is urgently needed. In this study, we discovered that sonrotoclax, a potent and selective BCL2 inhibitor, demonstrates stronger cytotoxic activity in various hematologic cancer cells and more profound tumor growth inhibition in multiple hematologic tumor models than venetoclax. Notably, sonrotoclax effectively inhibits venetoclax-resistant BCL2 variants, such as G101V. The crystal structures of wild-type BCL2/BCL2 G101V in complex with sonrotoclax revealed that sonrotoclax adopts a novel binding mode within the P2 pocket of BCL2 and could explain why sonrotoclax maintains stronger potency than venetoclax against the G101V mutant. In summary, sonrotoclax emerges as a potential second-generation BCL2 inhibitor for the treatment of hematologic malignancies with the potential to overcome BCL2 mutation-induced venetoclax resistance. Sonrotoclax is currently under investigation in multiple clinical trials.

Characterization and functional analysis of a novel glutathione S-transferase gene potentially associated with the abamectin resistance in Panonychus citri (McGregor).

The citrus red mite, Panonychus citri (McGregor), a major citrus pest distributed worldwide, has been found to be resistant to various insecticides and acaricides used in China. However, the molecular mechanisms associated with the abamectin resistance in this species have not yet been reported. In this study, results showed over-expression of a novel glutathione S-transferases (GSTs) gene (PcGSTm5) in abamectin-resistant P. citri. Quantitative real-time PCR analysis showed that the transcripts of PcGSTm5 were also significantly up-regulated after exposure to abamectin and the maximum mRNA expression level at nymphal stage. The recombinant protein of PcGSTm5-pET-28a produced by Escherichia coli showed a pronounced activity toward the conjugates of 1-chloro-2,4 dinitrobenzene (CDNB) and glutathione (GSH). The kinetics of CDNB and GSH and its optimal pH and thermal stability were also determined. Reverse genetic study through a new method of leaf-mediated dsRNA feeding further support a link between the expression of PcGSTm5 and abamectin resistance. However, no direct evidence was found in metabolism or inhibition assays to confirm the hypothesis that PcGSTm5 can metabolize abamectin. Finally, it is here speculated that PcGSTm5 may play a role in abamectin detoxification through other pathway such as the antioxidant protection.

Functional analysis of a chitinase gene during the larval-nymph transition in Panonychus citri by RNA interference.

Chitinases are hydrolytic enzymes that are required for chitin degradation and reconstruction in arthropods. In this study, we report a cDNA sequence encoding a putative chitinase (PcCht1) from the citrus red mite, Panonychus citri. The PcCht1 (564 aa) possessed a signal peptide, a conserver domain, and a chitin-binding domain. Structural and phylogenetic analyses found that PcCht1 had high sequence similarity to chitinases in Tetranychus urticae. Real-time quantitative PCR analyses showed that the transcript levels of PcCht1 peaked periodically in larval and nymph stages. Moreover, significant increase of PcCht1 transcript level in the larvae was observed upon the exposure of diflubenzuron. In contrast, exposures of the larvae to diflubenzuron resulted in the decreased chitin content. Furthermore, through a feeding-based RNA interference approach, we were able to reduce the PcCht1 transcript level by 59.7 % in the larvae, and consequently the treated larvae showed a very low molting rate compared with the control. Our results expanded the understanding of the important role of PcCht1 in the growth and development of P. citri.

Reference Gene Validation for Quantitative PCR Under Various Biotic and Abiotic Stress Conditions in Toxoptera citricida (Hemiptera, Aphidiae).

The regulation of mRNA expression level is critical for gene expression studies. Currently, quantitative reverse transcription polymerase chain reaction (qRT-PCR) is commonly used to investigate mRNA expression level of genes under various experimental conditions. An important factor that determines the optimal quantification of qRT-PCR data is the choice of the reference gene for normalization. To advance gene expression studies in Toxoptera citricida (Kirkaldy), an important citrus pest and a main vector of the Citrus tristeza virus, we used five tools (GeNorm, NormFinder, BestKeeper, ΔCt methods, and RefFinder) to evaluate seven candidate reference genes (elongation factor-1 alpha [EF1α], beta tubulin [ß-TUB], 18S ribosomal RNA [18S], RNA polymerase II large subunit (RNAP II), beta actin (ß-ACT), alpha tubulin, and glyceraldhyde-3-phosphate dehydrogenase) under different biotic (developmental stages and wing dimorphism) and abiotic stress (thermal, starvation, and UV irradiation) conditions. The results showed that EF1α and 18S were the most stable genes under various biotic states, ß-ACT and ß-TUB during thermal stress, EF1α and RNAP II under starvation stress, and RNAP II, ß-ACT, and EF1α under UV irradiation stress conditions. This study provides useful resources for the transcriptional profiling of genes in T. citricida and closely related aphid species.

Regulation of three isoforms of SOD gene by environmental stresses in citrus red mite, Panonychus citri.

Superoxide dismutase (SOD) is a family of enzymes with multiple isoforms that possess antioxidative abilities in response to environmental stresses. Panonychus citri is one of the most important pest mites and has a global distribution. In this study, three distinct isoforms of SOD were cloned from P. citri and identified as cytoplasmic Cu-ZnSOD (PcSOD1), extracellular Cu-ZnSOD (PcSOD2), and mitochondrial MnSOD (PcSOD3). mRNA expression level analysis showed that all three isoforms were up-regulated significantly after exposure to the acaricide abamectin and to UV-B ultraviolet irradiation. In particular, PcSOD3 was up-regulated under almost all environmental stresses tested. The fold change of PcSOD3 expression was significantly higher than those of the two Cu-ZnSOD isoforms. Taken together, the results indicate that abamectin and UV-B can induce transcripts of all three SOD isoforms in P. citri. Furthermore, PcSOD3 seems to play a more important role in P. citri tolerance to oxidative stress.

BGB-A445, a novel non-ligand-blocking agonistic anti-OX40 antibody, exhibits superior immune activation and antitumor effects in preclinical models.

OX40 is a costimulatory receptor that is expressed primarily on activated CD4+, CD8+, and regulatory T cells. The ligation of OX40 to its sole ligand OX40L potentiates T cell expansion, differentiation, and activation and also promotes dendritic cells to mature to enhance their cytokine production. Therefore, the use of agonistic anti-OX40 antibodies for cancer immunotherapy has gained great interest. However, most of the agonistic anti-OX40 antibodies in the clinic are OX40L-competitive and show limited efficacy. Here, we discovered that BGB-A445, a non-ligand-competitive agonistic anti-OX40 antibody currently under clinical investigation, induced optimal T cell activation without impairing dendritic cell function. In addition, BGB-A445 dose-dependently and significantly depleted regulatory T cells in vitro and in vivo via antibody-dependent cellular cytotoxicity. In the MC38 syngeneic model established in humanized OX40 knock-in mice, BGB-A445 demonstrated robust and dose-dependent antitumor efficacy, whereas the ligand-competitive anti-OX40 antibody showed antitumor efficacy characterized by a hook effect. Furthermore, BGB-A445 demonstrated a strong combination antitumor effect with an anti-PD-1 antibody. Taken together, our findings show that BGB-A445, which does not block OX40-OX40L interaction in contrast to clinical-stage anti-OX40 antibodies, shows superior immune-stimulating effects and antitumor efficacy and thus warrants further clinical investigation.

Tislelizumab uniquely binds to the CC' loop of PD-1 with slow-dissociated rate and complete PD-L1 blockage.

Programmed cell death protein 1 (PD-1), an immune checkpoint receptor expressed by activated T, B, and NK cells, is a well-known target for cancer immunotherapy. Tislelizumab (BGB-A317) is an anti-PD-1 antibody that has recently been approved for treatment of Hodgkin's lymphoma and urothelial carcinoma. Here, we show that tislelizumab displayed remarkable antitumor efficacy in a B16F10/GM-CSF mouse model. Structural biology and Surface plasmon resonance (SPR) analyses revealed unique epitopes of tislelizumab, and demonstrated that the CC' loop of PD-1, a region considered to be essential for binding to PD-1 ligand 1 (PD-L1) but not reported as targeted by other therapeutic antibodies, significantly contributes to the binding of tislelizumab. The binding surface of tislelizumab on PD-1 overlaps largely with that of the PD-L1. SPR analysis revealed the extremely slow dissociation rate of tislelizumab from PD-1. Both structural and functional analyses align with the observed ability of tislelizumab to completely block PD-1/PD-L1 interaction, broadening our understanding of the mechanism of action of anti-PD-1 antibodies.

Discovery of Pamiparib (BGB-290), a Potent and Selective Poly (ADP-ribose) Polymerase (PARP) Inhibitor in Clinical Development.

Poly (ADP-ribose) polymerase (PARP) plays a significant role in DNA repair responses; therefore, this enzyme is targeted by PARP inhibitors in cancer therapy. Here we have developed a number of fused tetra- or pentacyclic dihydrodiazepinoindolone derivatives with excellent PARP enzymatic and cellular PARylation inhibition activities. These efforts led to the identification of pamiparib (BGB-290, 139), which displays excellent PARP-1 and PARP-2 inhibition with IC50 of 1.3 and 0.9 nM, respectively. In a cellular PARylation assay, this compound inhibits PARP activity with IC50 = 0.2 nM. Cocrystal of pamiparib shows similar binding sites with PARP with other PARP inhibitors, but pamiparib is not a P-gp substrate and shows excellent drug metabolism and pharmacokinetics (DMPK) properties with significant brain penetration (17-19%, mice). The compound is currently being investigated in phase III clinical trials as a maintenance therapy in platinum-sensitive ovarian cancer and gastric cancer.

Antioxidant Role of PcGSTd1 in Fenpropathrin Resistant Population of the Citrus Red Mite, Panonychus citri (McGregor).

The citrus red mite, Panonychus citri, a major citrus pest distributed worldwide, has evolved severe resistance to various classes of chemical acaricides/insecticides including pyrethroids. It is well known that the resistance to pyrethroids is mainly caused by point mutations of voltage-gated sodium channel gene in a wide range of pests. However, increasing number of evidences support that pyrethroids resistance might also be resulted from the integrated mechanisms including metabolic mechanisms. In this study, firstly, comparative analysis of RNA-seq data showed that multiple detoxification genes, including a GSTs gene PcGSTd1, were up-regulated in a fenpropathrin-resistant population compared with the susceptible strain (SS). Quantitative real time-PCR results showed that the exposure of fenpropathrin had an induction effect on the transcription of PcGSTd1 in a time-dependent manner. In vitro inhibition and metabolic assay of recombinant PcGSTd1 found that fenpropathrin might not be metabolized directly by this protein. However, its antioxidant role in alleviating the oxidative stress caused by fenpropathrin was demonstrated via the reversely genetic experiment. Our results provide a list of candidate genes which may contribute to a multiple metabolic mechanisms implicated in the evolution of fenpropathrin resistance in the field population of P. citri. Furthermore, during the detoxification process, PcGSTd1 plays an antioxidant role by detoxifying lipid peroxidation products induced by fenpropathrin.

BGB-283, a Novel RAF Kinase and EGFR Inhibitor, Displays Potent Antitumor Activity in BRAF-Mutated Colorectal Cancers.

Oncogenic BRAF, which drives cell transformation and proliferation, has been detected in approximately 50% of human malignant melanomas and 5% to 15% of colorectal cancers. Despite the remarkable clinical activities achieved by vemurafenib and dabrafenib in treating BRAF(V600E) metastatic melanoma, their clinical efficacy in BRAF(V600E) colorectal cancer is far less impressive. Prior studies suggested that feedback activation of EGFR and MAPK signaling upon BRAF inhibition might contribute to the relative unresponsiveness of colorectal cancer to the first-generation BRAF inhibitors. Here, we report characterization of a dual RAF kinase/EGFR inhibitor, BGB-283, which is currently under clinical investigation. In vitro, BGB-283 potently inhibits BRAF(V600E)-activated ERK phosphorylation and cell proliferation. It demonstrates selective cytotoxicity and preferentially inhibits proliferation of cancer cells harboring BRAF(V600E) and EGFR mutation/amplification. In BRAF(V600E) colorectal cancer cell lines, BGB-283 effectively inhibits the reactivation of EGFR and EGFR-mediated cell proliferation. In vivo, BGB-283 treatment leads to dose-dependent tumor growth inhibition accompanied by partial and complete tumor regressions in both cell line-derived and primary human colorectal tumor xenografts bearing BRAF(V600E) mutation. These findings support BGB-283 as a potent antitumor drug candidate with clinical potential for treating colorectal cancer harboring BRAF(V600E) mutation.

Cloning and characterization of the 14-3-3 protein gene from the halotolerant alga Dunaliella salina.

Previous studies have demonstrated that 14-3-3 proteins exist in all the eukaryotic organisms studied; however, studies on the 14-3-3 proteins have not been involved in the halotolerant, unicellular green alga Dunaliella salina so far. In the present study, a cDNA encoding 14-3-3 protein of D. salina was cloned and sequenced by PCR and rapid amplification of cDNA end (RACE) technique based on homologous sequences of the 14-3-3 proteins found in other organisms. The cloned cDNA of 1485 bp in length had a 29.2 kDa of molecular weight and contained a 774 bp of open reading frame encoding a polypeptide of 258 amino acids. Like the other 14-3-3 proteins, the deduced amino acid sequences of the D. salina 14-3-3 protein also contained two putative phosphorylation sites within the N-terminal region (positions 62 and 67). Furthermore, an EF hand motif characteristic for Ca(2+)-binding sites was located within the C-terminal part of this polypeptide (positions 208-219). Analysis of bioinformatics revealed that the 14-3-3 protein of D. salina shared homology with that of other organisms. Real-time quantitative PCR demonstrated that expression of the 14-3-3 protein gene is cell cycle-dependent.

Structural insights into host GTPase isoform selection by a family of bacterial GEF mimics.

The Escherichia coli type III effector Map belongs to a large family of bacterial virulence factors that activate host Rho GTPase signaling pathways through an unknown molecular mechanism. Here we report direct evidence that Map functions as a potent and selective guanine-nucleotide exchange factor (GEF) for Cdc42. The 2.3-A structure of the Map-Cdc42 complex revealed that Map mimics the GEF strategy of the mammalian Dbl family but has a three-dimensional architecture that is nearly identical to the bacterial GEF Salmonella spp. SopE. A comparative analysis between human and bacterial GEFs revealed a previously uncharacterized pairing mechanism between Map and the variable beta2-3 interswitch region of Cdc42. We propose a GTPase selection model that is experimentally validated by the preferential activation Rac1 and RhoA by the Shigella spp. effectors IpgB1 and IpgB2, respectively. These results significantly expand the repertoire of bacterial GEF mimics and unify a GEF selection mechanism for host GTPase substrates.

Structural basis for activation and inhibition of the secreted chlamydia protease CPAF.

The obligate intracellular pathogen Chlamydia trachomatis is the most common cause of sexually transmitted bacterial disease. It secretes a protease known as chlamydial protease/proteasome-like activity factor (CPAF) that degrades many host molecules and plays a major role in Chlamydia pathogenesis. Here, we show that mature CPAF is a homodimer of the catalytic domains, each of which comprises two distinct subunits. Dormancy of the CPAF zymogen is maintained by an internal inhibitory segment that binds the CPAF active site and blocks its homodimerization. CPAF activation is initiated by trans-autocatalytic cleavage, which induces homodimerization and conformational changes that assemble the catalytic triad. This assembly leads to two autocatalytic cleavages and removal of the inhibitory segment, enabling full CPAF activity. CPAF is covalently bound and inhibited by the proteasome inhibitor lactacystin. These results reveal the activation mechanism of the CPAF serine protease and suggest new opportunities for anti-Chlamydia drug development.