Discovery, Characterization, and Structure-Based Optimization of Small-Molecule In Vitro and In Vivo Probes for Human DNA Polymerase Theta

Human DNA polymerase theta (Polθ), which is essential for microhomology-mediated DNA double strand break repair, has been proposed as an attractive target for the treatment of BRCA deficient and other DNA repair pathway defective cancers. As previously reported, we recently identified the first selective small molecule Polθ in vitro probe, 22 (ART558), which recapitulates the phenotype of Polθ loss, and in vivo probe, 43 (ART812), which is efficacious in a model of PARP inhibitor resistant TNBC in vivo. Here we describe the discovery, biochemical and biophysical characterization of these probes including small molecule ligand co-crystal structures with Polθ. The crystallographic data provides a basis for understanding the unique mechanism of inhibition of these compounds which is dependent on stabilization of a "closed" enzyme conformation. Additionally, the structural biology platform provided a basis for rational optimization based primarily on reduced ligand conformational flexibility.

P–208 Oleic acid rescues altered autophagy induced by palmitic acid during mouse preimplantation development

Study question

The aim of the study is to identify the autophagic profile and the effects of fatty acid treatments on autophagic activity in preimplantation mouse embryos.

Summary answer

Autophagic activity varies significantly in early stages of mouse preimplantation development; exposure to fatty acids alters the embryonic autophagy profile.

What is known already

Obesity is one of the top comorbidities for infertility, and obese individuals have elevated fatty acid levels. In serum, palmitic acid (PA) and oleic acid (OA) are the most abundant saturated and unsaturated fatty acids, respectively. We recently reported that PA impairs blastocyst development, affects mitochondrial reactive oxygen species, triacylglycerol levels, and endoplasmic reticulum stress pathways during mouse preimplantation development. Interestingly, the addition of OA counteracts those effects. Autophagy plays an essential role in embryo development, as knock-out of a key autophagy protein is embryonic lethal. Little is known about the autophagic profile in fatty acid treated mouse preimplantation embryos.

Study design, size, duration

Pools of 20 – 25 mouse embryos were collected from gonadotrophin super-ovulated and mated CD1 female mice. Two-cell stage embryos were treated with 100 µM PA and 250 µM OA, alone and in combination, and 1.5% bovine serum albumin media (control) within KSOMaa media for 18, 24, and 48 hours in vitro. The detection of various autophagic markers were evaluated by immunofluorescence microscopy and RT-qPCR.

Participants/materials, setting, methods

mRNA levels of autophagic markers were measured using RT-qPCR with the Taqman primers and Universal PCR Mix. Immunofluorescence staining of LC3 puncta (marker for autophagosome formation) was performed using LC3A/B polyclonal antibody (Invitrogen PA1–16931) and DAPI (4′,6-Diamidino–2-phenylindole dihydrochloride) was used to stain for cell nuclei. Analysis of LC3 puncta was performed using ImageJ software. Images were acquired using an LSM 800 laser scanning confocal microscope. Data analysis was completed by GraphPad Prism software.

Main results and the role of chance

Mouse preimplantation embryos showed no change in mRNA levels of autophagic markers (Bcln1, ATG3, ATG5, and LC3) relative to the control group after 48-hours exposure of 100 µM PA and 250 µM OA treatments, alone and in combination.

The number of LC3 puncta was measured and analyzed as a reflection of autophagic activity in mouse preimplantation embryos. Under the fatty acid-free condition, the average number of LC3 puncta per blastomere was significantly decreased after 18 hours of development (p < 0.005). However, the average number of LC3 puncta per blastomere at 18, 24, and 48 hours were not significantly different from each other (p = 0.2724).

Following 100 µM PA and 250 µM OA treatments, alone and in combination, autophagic activity was impacted by the presence of fatty acids. Mouse preimplantation embryos exposed to control and fatty acid treatment groups demonstrated no significant differences in LC3 puncta per blastomere at 18- and 24-hours treatment time (p = 0.5381; p = 0.7829). However, embryos exposed to 48 hours of PA treatment had a significantly greater number of LC3 puncta per blastomere than embryos exposed to 48 hours of OA and PA and OA combination treatments (p < 0.05).

Limitations, reasons for caution

Although LC3 puncta count (autophagosome formation) is impacted by fatty acid treatment, autophagic flux must be measured to fully investigate autophagic activity during mouse preimplantation development. These processes need to be measured in human embryos cultured in vitro.

Wider implications of the findings: Profiling autophagic activity in fatty acid treated mouse preimplantation embryos would guide future investigations on pharmacological modulation of autophagy as a therapeutic intervention for developmentally delayed embryos. With the information gained, we aim to develop strategies to assist overweight and obese patients with their fertility needs.

Trial registration number

Not applicable

Follicular growth, ovulation and embryo recovery in dairy cows given FSH at the beginning or middle of the estrous cycle

Variability in the superovulation response is an important problem for the embryo transfer industry. The objective of this study was to determine whether FSH treatment at the beginning of the cycle would improve the ovulation rate and embryo yield in dairy cows. Twenty-eight postpartum cyclic dairy cows were allocated at random to 4 treatment groups (A, B, C and D). Group A cows (n=10) received FSH (35 mg) at a decreasing dose, starting on Day 9 (Day 0=day of estrus) for 5 days followed by PGF2alpha (35 mg) on Day 12. Cows assigned to Groups B, C and D (n=6 cows each, respectively) were given 35 mg FSH at a decreasing dose from Days 2 to 6 followed by PGF2alpha on Day 7. Group C and D cows received PRID inserts from Day 3 to Day 7. Cows in Group D additionally received 1000 IU hCG 60 hours after PGF2alpha treatment. Ovaries were scanned daily using a real time ultrasound scanner from the beginning of FSH treatment until embryo recovery, to monitor follicular development, ovulation and the number of unovulated follicles. Embryos were recovered from the uterus by a nonsurgical flushing technique 7 days after breeding. There were no differences (P>0.01) in the number of follicles>10 mm at 48 hours after PGF2alpha treatment among the 4 groups. The mean numbers of follicles were 10.6+/-1.2, 9.3+/-1.3, 12.2+/-1.3 and 15.0+/-2.9 for Groups A, B, C and D, respectively. A significantly (P<0.001) higher number of ovulations was observed and a larger number of embryos was recovered in Group A than in the other groups. The results of this study indicate that superovulation with FSH at the beginning of the cycle causes sufficient follicular development but results in very low ovulation and embryo recovery rates.

Mechanistic and stereochemical studies on 3-oxo steroid delta 4-delta 5-isomerase from human placenta

The mechanism of isomerization of delta 5-3-ox steroids to delta 4-3-oxo steroids was examined by using the membrane-bound 3-oxo steroid delta 4-delta 5-isomerase (EC 5.3.3.1) and the 3 beta-hydroxy steroid dehydrogenase present in the microsomal fraction obtained from full-term human placenta. (1) Methods for the preparation of androst-5-ene-3 beta, 17 beta-diol specifically labelled at the 4 alpha-, 4 beta- or 6-positions are described. (2) Incubations with androst-5-ene-3 beta, 17 beta-diol stereospecifically 3H-labelled either in the 4 alpha- or 4 beta-position showed that the isomerization reaction occurs via a stereospecific elimination of the 4 beta hydrogen atom. In addition, the complete retention of 3H in the delta 4-3-oxo steroids obtained from [4 alpha-3H]androst-5-ene-3 beta, 17 beta-diol indicates that the non-enzymic contribution to these experiments was negligible. (3) To study the stereochemistry of the insertion of the incoming proton at C-6, the [6-3H]androst-4-ene-3, 17-dione obtained from the oxidation isomerization of [6-3H]androst-5-ene-3 beta, 17 beta-diol was enzymically hydroxylated in the 6 beta-position by the fungus Rhizopls stolonifer. Retention of 3H in the 6 alpha-position of the isolated 6 beta-hydroxyandrost-4-ene-3, 17-dione indicates that in the isomerase-catalysed migration of the C(5) = C(6) double bond, the incoming proton from the acidic group on the enzyme must enter C-6 from the beta-face, forcing the existing 3H into the 6 alpha-position.