ALBERT

Description: XRCC1 mutation is associated with PARP1 hyperactivation and cerebellar ataxia Nature 541, 7635 (2017). doi:10.1038/nature20790 Authors: Nicolas C. Hoch, Hana Hanzlikova, Stuart L. Rulten, Martine Tétreault, Emilia Komulainen, Limei Ju, Peter Hornyak, Zhihong Zeng, William Gittens, Stephanie A. Rey, Kevin Staras, Grazia M. S. Mancini, Peter J. McKinnon, Zhao-Qi Wang, Justin D. Wagner, Grace Yoon & Keith W. Caldecott XRCC1 is a molecular scaffold protein that assembles multi-protein complexes involved in DNA single-strand break repair. Here we show that biallelic mutations in the human XRCC1 gene are associated with ocular motor apraxia, axonal neuropathy, and progressive cerebellar ataxia. Cells from a patient with mutations in XRCC1 exhibited not only reduced rates of single-strand break repair but also elevated levels of protein ADP-ribosylation. This latter phenotype is recapitulated in a related syndrome caused by mutations in the XRCC1 partner protein PNKP and implicates hyperactivation of poly(ADP-ribose) polymerase/s as a cause of cerebellar ataxia. Indeed, remarkably, genetic deletion of Parp1 rescued normal cerebellar ADP-ribose levels and reduced the loss of cerebellar neurons and ataxia in Xrcc1-defective mice, identifying a molecular mechanism by which endogenous single-strand breaks trigger neuropathology. Collectively, these data establish the importance of XRCC1 protein complexes for normal neurological function and identify PARP1 as a therapeutic target in DNA strand break repair-defective disease.

Description: Functional activation of the PI3K/AKT signaling pathway provides survival signals to leukemic cells and pathway blockade may facilitate cell death. We have previously demonstrated that activation of AKT (phosphorylated on threonine 308 and serine 473 [pAKT308 & pAKT473]) pathway is a frequent event with adverse prognostic consequences in AML. To further explore the upstream regulation and downstream consequences of activation of this pathway in AML we assessed the level of expression and activation of PTEN/phosphoPTEN (pPTEN) (which controls AKT activation), P53 and DJ1 (which regulates PTEN), along with targets of activated AKT including proteins regulating proliferation (S6RP, Cyclin D1, GSK3, MTOR), and apoptosis (MCL, BAD, XIAP, BCL2). Total and phospho-protein levels from 258 leukemia-enriched samples of newly diagnosed, untreated AML patients were measured using high-throughput reverse phase protein array technology (RPPA). High P53 expression negatively correlated with PTEN levels (p=0.001). Almost all cases with very high P53 had unfavorable cytogenetics with complex karyotypes, and P53 mutations were found in 54% cases (see accompanying abstract). AKT activation, determined as high ratios of phospho to total (P/T) pAKT473 and pAKT308 were strongly correlated with loss of PTEN expression or increased PTEN phosphorylation,(p=0.0006 & 0.006) but not with increased levels of PTEN suppressor DJ1 (P=0.33 & 0.34). AKT activation (pAKT473 & pAKT308 P/T ratios) was associated with increased signaling through mTOR kinase (increased phosphorylation of S6RP on p236, p240, p244, p

Description: Abstract 2358 Allogeneic stem cell transplantation (alloSCT) is an effective treatment for pts with acute myeloid leukemia (AML) in first remission. However, only 10–20% of pts with relapsed disease achieve a durable remission. Microenvironment/leukemia interactions play a major role in chemoresistance of leukemic stem cells residing in the bone marrow niches. In pre-clinical in vivo leukemia models, inhibition of chemokine receptor CXCR4 results in mobilization of leukemic cells into circulation and sensitization to chemotherapy. We hypothesized that mobilization of leukemic stem cells by CXCR4 inhibition and G-CSF will result in improved anti-leukemia activity of a standard preparative regimen followed by alloSCT. In this Phase I/II study, G-CSF is administered at a standard dose beginning on day -9 daily for 6 days, and the CXCR4 inhibitor plerixafor (Mozobil®) from day -7 at one of the 4 dose levels 0 (control), 0.08, 0.16, or 0.24 mg/kg, 8 hours prior of each four daily doses of a standard preparative regimen (Fludarabine, 40mg/m2 and IV Busulfan, 130mg/m2, days -6 through -3). Twenty seven pts have been enrolled in the study to date with a median age of 48 yrs (range 25–65). Baseline characteristics include 13 pts (48%) with de novo AML, 6 (22%) with secondary AML, 5 with MDS and 3 with CML. Among the 24 AML/MDS pts, 14 (58%) had intermediate and 10 (42%) poor risk cytogenetics. Twelve pts (50%) had primary refractory AML, 5 were in 1st or 2nd relapse, 2 were untreated, 3 were in CR1 and 2 in CR2. The source of stem cells was sibling donor in 16 and unrelated donor in 11. After phase I plerixafor dose escalation in 16 pts, 11 pts received 0.24 mg/kg in Phase II. Common grade ≥ 3 adverse events which consisted primarily of neutropenic fever, infections, or rash were seen in 24/27 (89%) pts. There were no toxicities ascribed to the G-CSF/plerixafor component of the regimen. No evidence of significant delays in neutrophil (ANC 〉500/mm3, median 12.5d, range 10–19) or platelet recovery (plt 〉20k/mm3, median 12d, range 9–74d) were observed. Grade I-II GVHD was seen in 10/27 pts (37%), with no occurrences of Grade III-IV GVHD. Of the 19 pts with active disease at study entry, 18 achieved a CR. Treatment failure was due to persistent disease in 1 pt (4%), relapsed disease in 10 pts (37%) and early death due to complications from intracranial hemorrhage in 1 pt (4%). Median progression-free survival (PFS) for all pts was 26.6 wks (95%CI: 18.1–33.9 wks) and 15.7 wks (95% CI: 12.1–26.6 wks) in relapsed pts. Median follow-up for all study pts was 19.14 wks (range: 0.7–54.6 wks). Correlative studies analyzed from 16 pts enrolled in the Phase I portion of the trial demonstrate that G-CSF/plerixafor mobilizes CD34+ cells, with the mean fold increase of 5.9-fold at 0.08 mg/kg plerixafor; at 0.16 mg/kg, 13-fold; and at 0.24 mg/kg, 14.2-fold. Based on fitted longitudinal linear mixed models, G-CSF had a significant effect on cell mobilization over time (WBC and CD34+). In contrast, plerixafor at the doses of 0.16 and 0.24 mg/kg was significantly associated with increased cellular CXCR4 expression levels and with mobilization of CXCR4+ cells over time (p