P-800 Plerixafor for endogenous mobilisation of mesenchymal stem cells to induce endometrial regeneration
Authors: Rossato S , Ishimura R , Rosa e Silva J.C , Rosa e Silva A.C.J.D.S 
Published: June 2022

Abstract

Study question
Will the treatment with plerixafor alone or associated with β3 agonist cause endometrial regeneration and consequently improve the reproductive outcome of mice with thin endometrium?

Summary answer
The combined treatment with plerixafor and β3 agonist improved the reproductive outcomes, indicating a potential therapeutic option for infertility related to thin endometrium.

What is known already
Thin endometrium represents a huge challenge in assisted reproduction, since it is related to decreased endometrial receptivity and consequent implantation failure. The treatments with mesenchymal stem cells (MSC) have regenerative properties that improve endometrial thickness and expression of receptivity biomarkers.
Plerixafor is a CXCR4 antagonist receptor that disrupts the CXCL12-CXCR4 axis, which is directly related to stem cell migration, and has been used in tissue regeneration studies to increase the influx of stem cells to the site of injury. In addition, its combined use with β3 adrenergic agonist receptors leads to selective recruitment of MSC with better regenerative results.

Study design, size, duration
Experiments were carried out on female C57Bl/6 mice (age 9 weeks; 20g). Forty-eight individuals were assigned for either thin endometrium induction or sham procedure; then, mice in each group were randomly divided into three treatment subgroups (n = 8): (1) Placebo - phosphate-buffered saline, (2) plerixafor, (3) plerixafor and BRL37344 (rodent-selective β3 adrenergic receptor agonist). Two estrous cycles after modelling and treatment, all groups were mated with proven C57Bl/6 male mice for four weeks.

Participants/materials, setting, methods
Thin endometrium was induced by direct injection (50 μl) of 95% ethanol in the surgically exposed uterus, while Phosphate-buffered saline (PBS) was used in the sham procedure. Regarding the treatments, the groups received: (1) PBS (5 mg/kg sc) single-dose after surgery, (2) plerixafor (5 mg/kg sc) single-dose after surgery, (3) BRL37344 (rodent-selective β3 adrenergic receptor agonist) (10 mg/kg sc) for four consecutive days previous to surgery plus plerixafor (5 mg/kg sc) single-dose.

Main results and the role of chance
The pregnancy rate and litter size were analysed in order to establish the impact on the reproductive outcomes. In addition, a macroscopic anatomic analysis was performed on the offspring to evaluate possible teratogenic effects.
Concerning pregnancy rates, 23 out of 24 sham mice got pregnant (despite the treatment group). The thin endometrium model reproduced the literature results, with under 30% of failure in inducing endometrial damage, represented by a pregnancy rate of 25% (2/8) in the PBS group in comparison to all sham groups (p &lt; 0,05).
The plerixafor plus β3 agonist treatment completely restored the endometrial function, promoting pregnancy rates similar to all sham groups (p &gt; 0,05). There was no difference between the plerixafor alone group and all the other groups (p &gt; 0.05) in terms of pregnancy, although a clinically relevant difference between placebo and plerixafor alone group was found (25% versus 62,5%, respectively). The litter size was similar between the treatment groups, except for the plerixafor group with a smaller number of newborns. Regarding the teratogenic potential of the tested drugs (plerixafor and β3 agonist), we did not observe any relevant macroscopic malformations (internal and external) in the treated groups.

Limitations, reasons for caution
There is a need to establish the biological mechanisms responsible for endometrial recovery. Moreover, this study provided treatment for an acute injury; therefore, future work should evaluate the application on long term endometrial damage. The long term effect of the single-dose treatment should also be assessed.

Wider implications of the findings
Our findings indicate a potential therapy for thin endometrium. Plerixafor and β3 agonist treatment resulted in an expressive improvement in reproductive outcomes, without a detrimental impact on offspring. Moreover, this treatment utilises two clinical approved classes of drugs, which could reduce the timeline and cost of translational applications in future.

Trial registration number
not applicable