M1 macrophages increase production of reactive oxygen species (ROS), while M2 macrophages decrease ROS accumulation. Bisantrene shifts M2b macrophages to M1 macrophages, therefore increasing ROS production/accumulation.
The tumor microenvironment is made up of many, many things, although it is densely populated with m2 macrophages (the blue compounds). Whereby, tumor-associated macrophages are considered to be the most critical component of the tumor microenvironment.
If some of those M2 macrophages preventing ROS accumulation (and subsequent cancer cell damage) at the tumor site were to suddenly be converted into M1 macrophages (the pink), then the increase in ROS activity can begin to cause cancer cell damage.
There are many other things that M1 and M2 macrophages do to be anti- and pro-tumorigenic.
