The station was the site of a containment breach sometime in December 2137. A Xenomorph broke free of its restraints and slaughtered the entirety of the station's crew. As a result Mendel Station was destroyed by a special corporate order to cover up the evidence of what happened on the station.
While the exact details of the research carried out aboard the station are never revealed it can be assumed that it is something to do with the Xenomorph species. This theory is backed up by the presence of a Xenomorph drone that, in the words of Amanda Ripley, can only have been born on the station.
This is also in line with Weyland-Yutani's long history of intense interest in the Xenomorph species.
In December 2137, a Xenomorph Drone broke loose and began slaughtering the crew of the station in a fit of bloodthirsty rage. For whatever reason, perhaps due to the absence of the controlling influence of a Queen, it did not attempt to incapacitate the crew for implantation but instead killed them all outright.
During the outbreak and subsequent killing spree Amanda Ripley, following in the experiences of her mother, worked against the Xenomorph using the station's engineering access points to survive in the vents while directing the crew of the USCSS Haldin which had docked with the station. She eventually escaped the station aboard the Haldin shortly before it was destroyed.