The latrunculins are commonly used to experimentally disrupt the actin cytoskeleton of cells. Latrunculin B causes concentration-dependent changes in cell shape and actin organization. It sequesters G-actin and prevents F-actin assembly. It binds monomeric actin with 1:1 stoichiometry and can be used to block actin polymerization both in vitro and in cells (Kd = 60 nM).[1] The short-term effects of latrunculin B are comparable to those of latrunculin A, although latrunculin B is slightly less potent.[2] However, latrunculin B is gradually inactivated by serum so that induced changes are transient in the continued presence of the compound. For this reason, latrunculin B may have fewer unwanted effects than latrunculin A and may be preferred for short-term studies.

Reference:
[1]. Wakatsuki, T., Schwab, B., Thompson, N.C., et al. Effects of cytochalasin D and latrunculin B on mechanical properties of cells. Journal of Cell Science 114, 1025-1036 (2000).
[2]. Spector, I., Schochet, N.R., Blasberger, D., et al. Latrunculins-novel marine macrolides that disrupt microfilament organization and affect cell growth: I. comparison with cytochalasin D. Cell Motility and the Cytoskeleton 13, 127-144 (1989).