Taselisib

Drug Overview

Taselisib is a p110-alpha isoform-specific PI3K inhibitor. PI3K signaling plays a fundamental role in
tumorigenesis, governing cell proliferation, survival, and motility, as well as angiogenesis. Mechanisms
that contribute to PI3K dysregulation include aberrant activation of upstream receptors of PI3K,
amplification mutations in the phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha
(PIK3CA) gene that encodes the catalytic subunit of PI3K, as well as inactivation of the phosphatase
and tensin homolog (PTEN) tumor suppressor protein (Massacesi et al., 2013; Wymann et al., 2003).

Analyst Outlook

Taselisib (Roche/Chugai) is a phosphoinositide 3-kinase (PI3K) inhibitor predicted to be the second
such drug to reach the market behind Novartis’s late-phase candidate buparlisib. Despite early signs
of efficacy as a combination treatment with letrozole, taselisib’s commercial attractiveness will be
limited by the potentially high cost of treatment and its small patient population, which is limited to
hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast
cancers with PI3K mutations.