Reactivated memory undergoes a rebuilding process that depends on de novo protein synthesis. This suggests that retrieval is dynamic and serves to incorporate new information into preexisting memories. However, little is known about whether or not protein degradation is involved in the reorganization of retrieved memory. We found that postsynaptic proteins were degraded in the hippocampus by polyubiquitination after retrieval of contextual fear memory. Moreover, the infusion of proteasome inhibitor into the CA1 region immediately after retrieval prevented anisomycin-induced memory impairment, as well as the extinction of fear memory. This suggests that ubiquitin- and proteasome-dependent protein degradation underlies destabilization processes after fear memory retrieval. It also provides strong evidence for the existence of reorganization processes whereby preexisting memory is disrupted by protein degradation, and updated memory is reconsolidated by protein synthesis.

Purpose PARP inhibition (PARPi) has modest clinical activity in recurrent BRCA mutant (BRCAMUT) high-grade serous ovarian cancers (HGSOC). We hypothesized that PARPi increases dependence on ATR/CHK1 such that combination PARPi with ATR/CHK1 blockade results in increased cell death and tumor regression. Experimental Design Effects of PARPi (olaparib), CHK1 inhibition (CHK1i;MK8776) or ATR inhibition (ATRi;AZD6738) alone or in combination on survival, colony formation, cell-cycle, genome instability and apoptosis were evaluated in BRCA1/2MUT HGSOC cells. Tumor growth in vivo was evaluated using a BRCA2MUT patient-derived-xenograft (PDX) model. Results PARPi monotherapy resulted in a decrease in BRCAMUT cell survival, colony formation and suppressed but did not eliminate tumor growth at the maximum-tolerated dose in a BRCAMUT PDX. PARPi treatment increased pATR and pCHK1 indicating activation of the ATR-CHK1 fork protection pathway is relied upon for genome stability under PARPi. Indeed, combination of ATRi or CHK1i with PARPi synergistically decreased survival and colony formation compared to single agent treatments in BRCAMUT cells. Notably, PARPi led to G2 phase accumulation, and the addition of ATRi or CHK1i released cells from G2 causing premature mitotic entry with increased chromosomal aberrations and apoptosis. Moreover, the combinations of PARPi with ATRi or CHK1i were synergistic in causing tumor suppression in a BRCAMUT PDX with the PARPi-ATRi combination inducing tumor regression and in most cases, complete remission. Conclusions PARPi causes increased reliance on ATR/CHK1 for genome stability and combination PARPi with ATR/CHK1i is more effective than PARPi alone in reducing tumor burden in BRCAMUT models.

Ovarian cancer (OVCA) inevitably acquires resistance to platinum chemotherapy and PARP inhibitors (PARPi). We show that acquisition of PARPi-resistance is accompanied by increased ATR-CHK1 activity and sensitivity to ATR inhibition (ATRi). However, PARPi-resistant cells are remarkably more sensitive to ATRi when combined with PARPi (PARPi-ATRi). Sensitivity to PARPi-ATRi in diverse PARPi and platinum-resistant models, including BRCA1/2 reversion and CCNE1 -amplified models, correlate with synergistic increases in replication fork stalling, double-strand breaks, and apoptosis. Surprisingly, BRCA reversion mutations and an ability to form RAD51 foci are frequently not observed in models of acquired PARPi-resistance, suggesting the existence of alternative resistance mechanisms. However, regardless of the mechanisms of resistance, complete and durable therapeutic responses to PARPi-ATRi that significantly increase survival are observed in clinically relevant platinum and acquired PARPi-resistant patient-derived xenografts (PDXs) models. These findings indicate that PARPi-ATRi is a highly promising strategy for OVCAs that acquire resistance to PARPi and platinum.

50% of patients with HRD respond to PARPi therapy (3). Moreover, patients without known HRD have also shown a clinical benefit from PARPis, as seen in recent trials assessing niraparib, olaparib, or rucaparib, as maintenance therapy in platinum-sensitive recurrent ovarian cancer (5-8). Given that not all patients will respond to PARPi therapy, improved clinical tools for predicting which patients will respond are urgently needed.Numerous clinical trials have led to FDA approval of 3 PARPis since 2014 and there is continued development of 2 additional drugs within this class (9-13). Despite growth in the BACKGROUND. Poly(ADP-ribose) polymerase (PARP) inhibitors are effective in a broad population of patients with ovarian cancer; however, resistance caused by low enzyme expression of the drug target PARP-1 remains to be clinically evaluated in this context. We hypothesize that PARP-1 expression is variable in ovarian cancer and can be quantified in primary and metastatic disease using a novel PET imaging agent. METHODS.We used a translational approach to describe the significance of PET imaging of PARP-1 in ovarian cancer. First, we produced PARP1-KO ovarian cancer cell lines using CRISPR/Cas9 gene editing to test the loss of PARP-1 as a resistance mechanism to all clinically used PARP inhibitors. Next, we performed preclinical microPET imaging studies using ovarian cancer patient-derived xenografts in mouse models. Finally, in a phase I PET imaging clinical trial we explored PET imaging as a regional marker of PARP-1 expression in primary and metastatic disease through correlative tissue histology. RESULTS.We found that deletion of PARP1 causes resistance to all PARP inhibitors in vitro, and microPET imaging provides proof of concept as an approach to quantify PARP-1 in vivo. Clinically, we observed a spectrum of standard uptake values (SUVs) ranging from 2-12 for PARP-1 in tumors. In addition, we found a positive correlation between PET SUVs and fluorescent immunohistochemistry for PARP-1 (r 2 = 0.60).CONCLUSION. This work confirms the translational potential of a PARP-1 PET imaging agent and supports future clinical trials to test PARP-1 expression as a method to stratify patients for PARP inhibitor therapy.TRIAL REGISTRATION. Clinicaltrials.gov NCT02637934. 22-24). Furthermore, PARP-1 has been development and application of PARPis, the primary drug target poly(ADP-ribose) polymerase 1 (PARP-1) has never been evaluated in vivo, even though loss of expression in vitro is a wellcharacterized resistance mechanism (3,(14)(15)(16)(17)(18)(19). It was first hypothesized that PARPis work primarily through a synthetic lethality pathway where loss of BRCA1 or BRCA2 combined with chemical inhibition of PARP-1 results in cell death (20, 21). However, it was later shown that deletion of PARP1 did not result in BRCA1-restored cells showed no increase in γH2AX compared with DMSO controls. Olaparib-treated OVCAR8 PARP1-KO G1 and G3 cells showed a 1.3 times increase (ANOVA, **P < 0.01 and ***P < 0.001, respectively) in γH2AX...

MUC1 is a glycoprotein overexpressed in tumors as a hypoglycosylated form. A vaccine composed of a 100-amino acid peptide corresponding to five 20-amino acid long repeats, and SB-AS2 adjuvant, was tested in a phase I study for safety, toxicity, and ability to elicit or boost MUC1-specific immune responses. Patients with resected or locally advanced pancreatic cancer without prior chemotherapy or radiotherapy were eligible. Escalating doses of the peptide (100, 300, 1,000, and 3,000 mug) were admixed with SB-AS2 and administered intramuscularly every 3 weeks for three doses, in cohorts of four patients. Sixteen patients were enrolled. Common adverse effects were grade 1 flu-like symptoms, tenderness, and erythema at the injection site. Delayed-type hypersensitivity (DTH) sites showed few or no T cells prevaccination (Pre V), but increased T-cell infiltration postvaccination (Post V). There was an increase in the percentage of CD8(+) T cells in the peripheral blood Post V. An increase in total MUC1-specific antibody was seen in some patients, and several patients developed IgG antibody. Two of 15 resected pancreatic cancer patients are alive and disease free at follow-up of 32 and 61 months. MUC1 100mer peptide with SB-AS2 adjuvant is a safe vaccine that induces low but detectable mucin-specific humoral and T-cell responses in some patients. No difference was seen between different peptide doses. Further evaluation is warranted to examine the effect on disease-free survival and overall survival, especially in early disease and in the absence of immunosuppressive standard therapy.

The APOBEC3 family of antiviral DNA cytosine deaminases is implicated as the second largest source of mutation in cancer. This mutational process may be a causal driver or inconsequential passenger to the overall tumor phenotype. We show that human APOBEC3A expression in murine colon and liver tissues increases tumorigenesis. All other APOBEC3 family members, including APOBEC3B, fail to promote liver tumor formation. Tumor DNA sequences from APOBEC3A-expressing animals display hallmark APOBEC signature mutations in TCA/T motifs. Bioinformatic comparisons of the observed APOBEC3A mutation signature in murine tumors, previously reported APOBEC3A and APOBEC3B mutation signatures in yeast, and reanalyzed APOBEC mutation signatures in human tumor datasets support cause-and-effect relationships for APOBEC3A-catalyzed deamination and mutagenesis in driving multiple human cancers.

No abstract

Cofilin-actin rods are inclusion-like structures that are induced by certain chemical or physical stresses in cultured cells, and the rods formed in neurons are thought to be associated with neurodegeneration. Here, we cloned an Aplysia cofilin homolog and overexpressed it in cultured neurons. Overexpressed cofilin formed rod-like structures that included actin. The overall neuronal morphology was unaffected by cofilin overexpression; however, a decrease in number of synaptic varicosities was observed. Consistent with this structural change by cofilin overexpression, the synaptic strength was reduced, and furthermore, the long-term facilitation elicited by repeated pulses of 5-hydroxytryptamine was impaired in sensory-to-motor synapses. However, cofilin overexpression did not induce programmed cell death. These findings suggest that the formation of cofilin-actin rod-like structures can lead to neurodegeneration, and this might be a mechanism of rundown of neuronal and synaptic function without cell death in neurodegenerative diseases.neurodegeneration ͉ Hirano body ͉ long-term facilitation