Pomalidomide, Bortezomib, and Dexamethasone in Lenalidomide-Pretreated Multiple Myeloma: A Subanalysis of OPTIMISMM by Frailty and Bortezomib Dose Adjustment.

INTRODUCTION: A proportion of patients with multiple myeloma (MM) are older and/or have comorbidities, requiring dose adjustments. Data from OPTIMISMM (NCT01734928) supported the use of pomalidomide, bortezomib, and dexamethasone (PVd) for treating relapsed/refractory MM. This subanalysis of OPTIMISMM assessed outcome by frailty and/or bortezomib dose adjustment. METHODS: Patient frailty (nonfrail vs. frail) was classified using age, Charlson Comorbidity Index, and Eastern Cooperative Oncology Group performance status. Data from patients requiring a bortezomib dose reduction, interruption, and/or withdrawal during PVd treatment were assessed. RESULTS: Among 559 patients, 93 of 281 (33.1%) and 93 of 278 (33.5%) patients who received PVd and bortezomib and dexamethasone (Vd), respectively, were frail. Overall response rate (ORR) and median progression-free survival (PFS) were higher in nonfrail vs. frail with PVd treatment (ORR, 82.8% vs. 79.6%; PFS, 14.7 vs. 9.7 months); significantly higher than with Vd regardless of frailty. Grade ≥ 3 treatment-emergent adverse events (TEAEs) were higher with PVd vs. Vd, regardless of frailty. Discontinuations of PVd were lower in nonfrail vs. frail patients (19.2% vs. 30.1%); the median duration of treatment was similar (DoT; 8.8 vs. 8.9 months, respectively). Patients who received PVd with a bortezomib dose adjustment (n = 240) had a longer median DoT (9.3 vs. 4.5 months) and PFS (12.1 vs. 8.4 months) vs. those without. CONCLUSION: Frail patients treated with PVd demonstrated a higher ORR and a longer PFS and DoT vs. Vd, despite a higher frequency of grade ≥ 3 TEAEs leading to pomalidomide, bortezomib, and/or dexamethasone discontinuation. Therefore, PVd treatment may improve patient outcomes, regardless of frailty.

The human Exonuclease-1 interactome and phosphorylation sites.

Error-free repair of DNA double-strand breaks is orchestrated by homologous recombination (HR) pathways and requires the concerted action of several factors. Among these, Exonulcease-1 (EXO1) and DNA2/BLM execute extensive resection of DNA ends to produce 3'-overhangs, which are key intermediates for downstream steps of HR. To help shedding light on regulatory aspects of DNA repair pathways in which EXO1 participates, we set out to identify proteins interacting with EXO1. Affinity purification of EXO1 followed by Orbitrap mass spectrometry led to the identification of novel partners that are involved in RNA processing or that are the causative agents of rare X-linked disorders. Depletion of a selected subset of EXO1 interacting proteins led to reduction of the DNA damage response. Among those, we examined the RRP5-homologue and NF-kappa-B-interacting protein PDCD11/ALG-4, which has roles in apoptosis and is a putative driver gene in cutaneous T-cell lymphoma. We provide evidence that depletion of PDCD11 decreased the formation of γ-H2AX foci and the phosphorylation of DNA damage response (DDR) signaling intermediates in response to camptothecin or bleomycin, resulting in increased cellular resistance to DNA damage. Furthermore, extensive coverage of EXO1 sequence by mass spectrometry allowed conducting an in-depth analysis of its phosphorylation sites, with the identification of 26 residues that are differentially modified in untreated conditions or upon induction of DNA damage.

Aurora A depletion reveals centrosome-independent polarization mechanism in Caenorhabditis elegans.

How living systems break symmetry in an organized manner is a fundamental question in biology. In wild-type Caenorhabditis elegans zygotes, symmetry breaking during anterior-posterior axis specification is guided by centrosomes, resulting in anterior-directed cortical flows and a single posterior PAR-2 domain. We uncover that C. elegans zygotes depleted of the Aurora A kinase AIR-1 or lacking centrosomes entirely usually establish two posterior PAR-2 domains, one at each pole. We demonstrate that AIR-1 prevents symmetry breaking early in the cell cycle, whereas centrosomal AIR-1 instructs polarity initiation thereafter. Using triangular microfabricated chambers, we establish that bipolarity of air-1(RNAi) embryos occurs effectively in a cell-shape and curvature-dependent manner. Furthermore, we develop an integrated physical description of symmetry breaking, wherein local PAR-2-dependent weakening of the actin cortex, together with mutual inhibition of anterior and posterior PAR proteins, provides a mechanism for spontaneous symmetry breaking without centrosomes.

Pharmacophore-guided discovery of CDC25 inhibitors causing cell cycle arrest and tumor regression.

CDC25 phosphatases play a key role in cell cycle transitions and are important targets for cancer therapy. Here, we set out to discover novel CDC25 inhibitors. Using a combination of computational methods, we defined a minimal common pharmacophore in established CDC25 inhibitors and performed virtual screening of a proprietary library. Based on the availability of crystal structures for CDC25A and CDC25B, we implemented a molecular docking strategy and carried out hit expansion/optimization. Enzymatic assays revealed that naphthoquinone scaffolds were the most promising CDC25 inhibitors among selected hits. At the molecular level, the compounds acted through a mixed-type mechanism of inhibition of phosphatase activity, involving reversible oxidation of cysteine residues. In 2D cell cultures, the compounds caused arrest of the cell cycle at the G1/S or at the G2/M transition. Mitotic markers analysis and time-lapse microscopy confirmed that CDK1 activity was impaired and that mitotic arrest was followed by death. Finally, the compounds induced differentiation, accompanied by decreased stemness properties, in intestinal crypt stem cell-derived Apc/K-Ras-mutant mouse organoids, and led to tumor regression and reduction of metastatic potential in zebrafish embryo xenografts used as in vivo model.

Dual mode of cell death upon the photo-irradiation of a RuII polypyridyl complex in interphase or mitosis.

Photodynamic therapy (PDT) is an attractive, complementary medical technique to chemotherapy. Among the different photosensitizers (PSs) employed, Ru(ii) polypyridyl complexes were found to be valid substitutes to porphyrin-based or phthalocyanine-based PSs. Here, we confirm that one such complex, namely [Ru(bipy)2-dppz-7-methoxy][PF6]2 (Ru65), which localizes in the nucleus of various cancer and normal cells, displays cytotoxicity only upon UV-A irradiation. Importantly, we disclose the molecular mechanism of the UV-A mediated cytotoxic action of Ru65. We demonstrate that Ru65 intercalates in DNA and, upon light irradiation, promotes guanine oxidation, resulting in nicks in the double helix. We confirm this mechanism of action in living cells, showing that the UV-A irradiation of cells loaded with Ru65 results in a transient DNA damage response and cell death. Strikingly, the photo-irradiation of Ru65 triggered distinct mechanisms of cell death in interphase or mitotic cells. The former underwent cell cycle arrest at the G2/M phase and massive cytoplasmic vacuolation, which was paralleled by an unfolded-protein stress response, resulting in a reduction of viability and cell death through a paraptosis-like mechanism. On the other hand, the UV-A irradiation of Ru65 in cells synchronized by G2/M block-release with a selective CDK1 inhibitor led to blocking mitotic entry and rapid cell death through classic apoptotic pathways. Importantly, targeting mitotic cells with Ru65 allowed increasing its photo-toxicity by a factor of 3.6. Overall, our findings show that the use of a combination of a cell cycle inhibitor and a PS targeting the nucleus could open up new avenues in PDT.

Maintaining Genome Stability in Defiance of Mitotic DNA Damage.

The implementation of decisions affecting cell viability and proliferation is based on prompt detection of the issue to be addressed, formulation and transmission of a correct set of instructions and fidelity in the execution of orders. While the first and the last are purely mechanical processes relying on the faithful functioning of single proteins or macromolecular complexes (sensors and effectors), information is the real cue, with signal amplitude, duration, and frequency ultimately determining the type of response. The cellular response to DNA damage is no exception to the rule. In this review article we focus on DNA damage responses in G2 and Mitosis. First, we set the stage describing mitosis and the machineries in charge of assembling the apparatus responsible for chromosome alignment and segregation as well as the inputs that control its function (checkpoints). Next, we examine the type of issues that a cell approaching mitosis might face, presenting the impact of post-translational modifications (PTMs) on the correct and timely functioning of pathways correcting errors or damage before chromosome segregation. We conclude this essay with a perspective on the current status of mitotic signaling pathway inhibitors and their potential use in cancer therapy.

Chromosome Missegregation Associated with RUVBL1 Deficiency.

RUVBL1 (RuvB-like1) and RUVBL2 (RuvB-like 2) are integral components of multisubunit protein complexes involved in processes ranging from cellular metabolism, transcription and chromatin remodeling to DNA repair. Here, we show that although RUVBL1 and RUVBL2 are known to form heterodimeric complexes in which they stabilize each other, the subunits separate during cytokinesis. In anaphase-to-telophase transition, RUVBL1 localizes to structures of the mitotic spindle apparatus, where it partially co-localizes with polo-like kinase 1 (PLK1). The ability of PLK1 to phosphorylate RUVBL1-but not RUVBL2-in vitro and their physical association in vivo suggest that this kinase differentially regulates the function of the RuvB-like proteins during mitosis. We further show that siRNA-mediated knock-down of RuvB-like proteins causes severe defects in chromosome alignment and segregation. In addition, we show that the ATPase activity of RUVBL1 is indispensable for cell proliferation. Our data thus demonstrate that RUVBL1 is essential for efficient mitosis and proliferation.

Sumoylation regulates EXO1 stability and processing of DNA damage.

DNA double-strand break repair by the error-free pathway of homologous recombination (HR) requires the concerted action of several factors. Among these, EXO1 and DNA2/BLM are responsible for the extensive resection of DNA ends to produce 3'-overhangs, which are essential intermediates for downstream steps of HR. Here we show that EXO1 is a SUMO target and that sumoylation affects EXO1 ubiquitylation and protein stability. We identify an UBC9-PIAS1/PIAS4-dependent mechanism controlling human EXO1 sumoylation in vivo and demonstrate conservation of this mechanism in yeast by the Ubc9-Siz1/Siz2 using an in vitro reconstituted system. Furthermore, we show physical interaction between EXO1 and the de-sumoylating enzyme SENP6 both in vitro and in vivo, promoting EXO1 stability. Finally, we identify the major sites of sumoylation in EXO1 and show that ectopic expression of a sumoylation-deficient form of EXO1 rescues the DNA damage-induced chromosomal aberrations observed upon wt-EXO1 expression. Thus, our study identifies a novel layer of regulation of EXO1, making the pathways that regulate its function an ideal target for therapeutic intervention.

AmotL2 links VE-cadherin to contractile actin fibres necessary for aortic lumen expansion.

The assembly of individual endothelial cells into multicellular tubes is a complex morphogenetic event in vascular development. Extracellular matrix cues and cell-cell junctional communication are fundamental to tube formation. Together they determine the shape of endothelial cells and the tubular structures that they ultimately form. Little is known regarding how mechanical signals are transmitted between cells to control cell shape changes during morphogenesis. Here we provide evidence that the scaffold protein amotL2 is needed for aortic vessel lumen expansion. Using gene inactivation strategies in zebrafish, mouse and endothelial cell culture systems, we show that amotL2 associates to the VE-cadherin adhesion complex where it couples adherens junctions to contractile actin fibres. Inactivation of amotL2 dissociates VE-cadherin from cytoskeletal tensile forces that affect endothelial cell shape. We propose that the VE-cadherin/amotL2 complex is responsible for transmitting mechanical force between endothelial cells for the coordination of cellular morphogenesis consistent with aortic lumen expansion and function.