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Summary: High-grade serous ovarian cancers (HGSOCs) with homologous recombination deficiency (HRD) are initially responsive to poly (ADP-ribose) polymerase inhibitors (PARPi), but resistance ultimately emerges. HGSOC with CCNE1 amplification (CCNE1amp) are associated with resistance to PARPi and platinum treatments. High replication stress in HRD and CCNE1amp HGSOC leads to increased reliance on checkpoint kinase 1 (CHK1), a key regulator of cell cycle progression and the replication stress response. Here, we investigated the anti-tumor activity of the potent, highly selective, orally bioavailable CHK1 inhibitor (CHK1i), SRA737, in both acquired PARPi-resistant BRCA1/2 mutant and CCNE1amp HGSOC models. We demonstrated that SRA737 increased replication stress and induced subsequent cell death in vitro. SRA737 monotherapy in vivo prolonged survival in CCNE1amp models, suggesting a potential biomarker for CHK1i therapy. Combination SRA737 and PARPi therapy increased tumor regression in both PARPi-resistant and CCNE1amp patient-derived xenograft models, warranting further study in these HGSOC subgroups.

Abstract Background Dogs infected with canine parvovirus (CPV) have compromised intestinal epithelial barrier integrity. Production of D‐lactate by enteric bacteria may directly reflect disease severity or contribute to metabolic acid‐base status in these dogs. Hypothesis Serum D‐lactate concentration will be increased in CPV dogs compared to healthy controls and correlate with markers of disease severity and acid‐base status. Animals Dogs with CPV undergoing treatment (n = 40) and healthy control dogs (n = 9). Methods Prospective observational study. Dogs with CPV had a baseline and daily CBC, venous blood gas with serum electrolyte concentrations, composite clinical severity score, and serum D‐lactate concentration performed. A single serum D‐lactate measurement was obtained from healthy control dogs. Results The CPV dogs had a higher D‐lactate concentration (mean ± SD) of 469 ± 173 μM compared to controls, 306 ± 45 μM (P

Lilly PCSK9 antibody LY3015014 (LY) is a monoclonal antibody (mAb) that neutralizes proprotein convertase subtilisin-kexin type 9 (PCSK9). LY decreases LDL cholesterol in monkeys and, unlike other PCSK9 mAbs, does not cause an accumulation of intact PCSK9 in serum. Comparing the epitope of LY with other clinically tested PCSK9 mAbs, it was noted that the LY epitope excludes the furin cleavage site in PCSK9, whereas other mAbs span this site. In vitro exposure of PCSK9 to furin resulted in degradation of PCSK9 bound to LY, whereas cleavage was blocked by other mAbs. These other mAbs caused a significant accumulation of serum PCSK9 and displayed a shorter duration of LDL-cholesterol lowering than LY when administered to mice expressing the WT human PCSK9. In mice expressing a noncleavable variant of human PCSK9, LY behaved like a cleavage-blocking mAb, in that it caused significant PCSK9 accumulation, its duration of LDL lowering was reduced, and its clearance (CL) from serum was accelerated. Thus, LY neutralizes PCSK9 and allows its proteolytic degradation to proceed, which limits PCSK9 accumulation, reduces the CL rate of LY, and extends its duration of action. PCSK9 mAbs with this property are likely to achieve longer durability and require lower doses than mAbs that cause antigen to accumulate.

O6-methylguanine DNA methyltransferase (MGMT) deficiency is associated with an increased susceptibility to alkylating agent toxicity. To understand the contribution of MGMT in protecting against cyclophosphamide (CP)-induced toxicity, mutagenesis and tumorigenesis, we compared the biological effects of this agent in transgenic Mgmt knockout and wild-type mice. In addition, neurofibromin (Nf1)+/− background was used to increase the likelihood of CP-induced tumorigenesis. Cohorts of Mgmt-proficient or -deficient mice (either Nf1+/+ or Nf1+/−) were given 6 weekly injections of a maximally tolerated dose of CP (250 mg/kg) or vehicle and followed for 15 months. CP-treated mice had more deaths than control mice but there was no difference in the long-term survival between Mgmt+/+ and Mgmt−/− mice (12 of 83 Mgmt+/+ mice died compared to 12 of 80 Mgmt−/− mice, disregarding Nf1 status). Lymphomas and adrenal tumours were the most frequent malignancies. Interestingly, CP-treated, Mgmt-deficient mice developed fewer tumours than controls. Ten of 71 (14%) Mgmt-proficient mice developed tumours after CP treatment compared to only 2 of 68 (3%) Mgmt-deficient mice (P = 0.02). Mgmt−/−, Nf1+/− mice developed fewer tumours (1 of 35, 3%) following CP compared to Mgmt+/+, Nf1+/− mice (7 of 37, 19%) (P = 0.03). Hypoxanthine–guanine phosphoribosyltransferase mutation assays showed no significant increases in mutant frequencies in Mgmt−/− (18.1 × 106) compared to Mgmt+/+ mice (12.9 × 106). These data indicate that MGMT deficiency does not protect against long-term toxicity or mutagenicity from CP and appears to attenuate the occurrence of CP-induced tumours in an Nf1+/− background. [ABSTRACT FROM AUTHOR]

The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) protects from toxicity and mutations incurred following alkylating agents by removing O6-alkylguanine lesions. Using Mgmt-/- mice, we examined MGMTs role in protecting from in vivo mutations induced by three different alkylating agents, temozolomide (TMZ), 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) and cyclophosphamide. Mutant frequencies were determined in the hypoxanthine–guanine phosphoribosyltransferase gene of splenic T-lymphocytes from C57BL/6 mice (Mgmt+/+ and Mgmt-/-) following TMZ, BCNU or cyclophosphamide. Following TMZ, the mutation frequency was significantly greater in Mgmt-/- mice (5.5 and 9.8 × 10-6 for 7 and 10 mg/kg TMZ, respectively) compared with vehicle-treated mice (1.0 × 10-6, P = 0.05). In contrast, TMZ-induced mutations were not increased over vehicle in Mgmt+/+ mice. The mutation frequency of mice treated with BCNU (7.5 mg/kg) was the same regardless of Mgmt status. Similarly, pretreatment of Mgmt+/+ mice with 30 mg/kg O6-benzylguanine, a potent inactivator of MGMT, prior to BCNU (15 mg/kg) did not result in significantly more mutations than mice treated with BCNU alone. Following cyclophosphamide, mutation frequencies significantly increased from 1.8 × 10-6 in control-treated mice to 12.9 × 10-6 in Mgmt+/+ and 18.1 × 10-6 in Mgmt-/- mice, although the difference in Mgmt-/- compared with Mgmt+/+ was not significant. Acrolein and chloroacetaldehyde, metabolites of cyclophosphamide, were not mutagenic in Mgmt+/+ and Mgmt-/- mice. These results demonstrate that MGMT significantly protects against in vivo TMZ-induced mutations and that MGMT deficiency does not result in greater mutation frequency following cyclophosphamide or BCNU compared with wild-type mice. [ABSTRACT FROM AUTHOR]

Activation of the unfolded protein response (UPR) in eukaryotic cells represents an evolutionarily conserved response to physiological stress. Here, we report that the mTOR inhibitors rapamycin (sirolimus) and structurally related temsirolimus are capable of inducing UPR in sarcoma cells. However, this effect appears to be distinct from the classical role for these drugs as mTOR inhibitors. Instead, we detected these compounds to be associated with ribosomes isolated from treated cells. Specifically, temsirolimus treatment resulted in protection from chemical modification of several rRNA residues previously shown to bind rapamycin in prokaryotic cells. As an application for these findings, we demonstrate maximum tumor cell growth inhibition occurring only at doses which induce UPR and which have been shown to be safely achieved in human patients. These results are significant because they challenge the paradigm for the use of these drugs as anticancer agents and reveal a connection to UPR, a conserved biological response that has been implicated in tumor growth and response to therapy. As a result, eIF2 alpha phosphorylation and Xbp-1 splicing may serve as useful biomarkers of treatment response in future clinical trials using rapamycin and rapalogs.