**1. Introduction**

Polyhydroxylated steroids have been found in diverse marine species of ophiuroids, gorgonians, sponges, and other marine invertebrates. However, the class Asteroidea (also known as starfish or sea stars) is the richest source of these kind of steroids [1–7]. These substances generally contain from four to nine hydroxyl groups in the steroid nucleus and side chains and are characterized by a wide variety of chemical structures. Polyhydroxylated steroids are present in starfish in both free, sulfated, or glycosylated by one to three monosaccharide residues forms. These compounds usually occur in very complicated mixtures that are often difficult to separate into individual components by chromatographic methods. In addition to the original chemical structure, polyhydroxylated steroids attract attention with a wide diversity of biological effects including neuritogenic, neuroprotective, antiviral, anti-inflammatory, immunomodulatory, and other activities [7,8]. Recently, new knowledge

about the cancer preventive activity and toxicity against different human tumor cell lines and molecular mechanisms of action of some starfish steroid compounds has been acquired [9]. Moreover, for the first time, it has been shown that starfish polyhydroxylated compounds demonstrated the radio sensitizing activity that was realized through apoptosis induction by the regulation of anti- and pro-apoptotic protein expression followed by activation of caspases and DNA degradation [10]. On the basis of the data obtained, we assume that the study of polyhydroxylated steroids from the starfish could lead to new promising results on their biological activities.

The search for new metabolites from starfish is a long-term direction of the studies of G.B. Elyakov Pacific Institute of Bioorganic Chemistry which celebrated its 55th anniversary in 2019. Continuing our research on biologically active steroid metabolites from the starfish species inhabiting the Vietnamese sea waters [11–15], herein, we describe the results of our investigation of steroid constituents from the methanolic extract of the starfish *Anthenoides laevigatus* Liao & A.M. Clark, 1989 (order Valvatida, family Goniasteridae), collected off the coastal waters of the Qui Nhon Province, Vietnam. We have isolated and structurally studied four new polyhydroxylated steroids **1**−**4,** along with two previously known related steroids **5** and **6**. Additionally, the action of compounds **1**, **5**, and **6** on cell viability and proliferation of normal and cancer cells, as well as colony formation of cancer cells in a soft agar clonogenic assay *in vitro*, have been investigated.
