Placental transfer of temsavir, an HIV-1 attachment inhibitor, in the ex vivo human cotyledon model
This study utilized an ex vivo human placental perfusion model to demonstrate that temsavir, the active metabolite of the HIV-1 attachment inhibitor fostemsavir, exhibits low placental transfer and limited fetal exposure, though further in vivo research is required to confirm fetal safety.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Every year, more than a million women living with HIV give birth. For these mothers, the primary goal of medical care is twofold: to protect their own health and to prevent passing the virus to their child during pregnancy or delivery. To achieve this, doctors prescribe antiretroviral therapy, a combination of medicines that keeps the virus under control. While many of these drugs have been studied extensively for use during pregnancy, some newer treatments lack this crucial safety data. When a woman has a form of HIV that is resistant to standard medicines, doctors may turn to a newer drug called fostemsavir. This medication works by stopping the virus from attaching to and entering human cells. However, because it is a relatively new treatment, there is very little information about whether it crosses the barrier between a mother and her unborn baby, or what level of exposure the fetus might experience.
The active ingredient that actually fights the virus is a substance called temsavir. When a person takes fostemsavir, their body quickly converts it into temsavir. To understand if this drug is safe for a developing baby, researchers needed to know how easily temsavir can pass through the placenta. The placenta is the organ that connects a pregnant woman to her fetus, acting as a selective filter that allows nutrients and oxygen to pass while blocking many harmful substances. Determining how much of a drug gets through this filter is essential for assessing risk, but testing this directly in pregnant women is ethically impossible. Instead, scientists use a model that mimics the human placenta outside the body to observe how drugs move from the maternal side to the fetal side.
In a recent study, researchers set out to measure exactly how much temsavir crosses the human placenta. They collected placentas from healthy women who had just given birth at full term. In a laboratory setting, they isolated a small, intact section of the placenta, known as a cotyledon, and connected it to two separate circuits of fluid. One circuit represented the mother's blood supply, and the other represented the baby's. They pumped a fluid containing temsavir into the maternal side, simulating the drug levels found in a treated adult, while keeping the fetal side free of the drug at the start. To ensure the placenta tissue was alive and functioning correctly throughout the experiment, they also added a harmless marker substance called antipyrine, which is known to cross the placenta easily.
The team ran these experiments for about an hour, carefully maintaining the temperature and chemical balance to match the conditions inside a human body. They took samples from both the maternal and fetal sides at regular intervals to measure how much temsavir had moved across. The results showed that the drug did not cross the barrier very well. On average, only about 8 percent of the temsavir present in the maternal fluid appeared in the fetal fluid. For comparison, the marker substance that crosses easily showed a transfer rate of about 28 percent. This means that temsavir moves across the placenta at a rate roughly one-quarter as fast as a substance that passes through freely. The researchers noted that the drug's tendency to stick to proteins in the blood and its chemical properties likely contribute to this low transfer rate, effectively limiting the amount that reaches the fetus.
These findings suggest that when a pregnant woman takes fostemsavir, her unborn baby is exposed to very low levels of the active drug. While the study provides a clear picture of how the drug behaves in a controlled, term-placenta model, the researchers emphasize that this is not the final word on safety. The experiment was conducted using placentas from full-term pregnancies, which may differ from those in earlier stages of development, and it did not account for how the drug might be processed inside the fetus itself. Consequently, while the low transfer rate is a reassuring sign that the drug may pose minimal risk of toxicity, more research is needed. Future studies involving real-world data from pregnant women and their infants will be necessary to confirm these findings and to guide doctors on the safest ways to treat this specific group of patients.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.