Defined media reveal the essential role of lipid scavenging in supporting cancer cell proliferation

Fetal bovine serum (FBS) is an undefined additive that is ubiquitous to mammalian cell culture media and whose functional contributions to promoting cell proliferation remain poorly understood. Efforts to replace serum supplementation in culture media have been hindered by an incomplete understanding of the environmental requirements fulfilled by FBS. Here, we use a combination of live-cell imaging and quantitative lipidomics to elucidate the role of serum in supporting proliferation. We show that serum provides consumed factors that enable proliferation, with serum metal and lipid components serving as crucial metabolic resources. Despite access to a wide range of lipid classes available in serum, we find albumin-bound lipids are the primary species consumed by cancer cells. Furthermore, we find that supplementing with additives that contain necessary metals and any of the albumin-associated lipid classes can obviate the FBS requirement for cancer cell proliferation. Using this defined system, we investigated cancer cell lipid consumption dynamics, finding that albumin-associated lipids are primarily consumed through a mass-action mechanism with minimal competition within or amongst lipid classes. We also find that lipid scavenging is a dominant lipid acquisition route and is necessary for cancer cell proliferation. This work therefore identifies metabolic contributions of serum and provides a framework for building defined culture systems that sustain cell proliferation without the undefined contributions of serum.