CAL-101 (Idelalisib GS-1101 CAS 870281-82-6) is a selective inhibitor targeting the p110 isoform of phosphatidylinositol 3-kinase (PI3K) an enzyme involved in signaling pathways critical for proliferation and survival of malignant B cells By inhibiting PI3K p110 CAL-101 reduces PI3K-mediated phosphorylation of Akt and other downstream factors leading to enhanced PARP cleavage and caspase activation ultimately inducing apoptosis in malignant B cells CAL-101 has been demonstrated to counteract survival signals initiated by molecules such as CD40 ligand (CD40L) TNF- and fibronectin This agent is valuable in investigating B-cell malignancies