Sterigmatocystine is a precursor of aflatoxins and a mycotoxin produced by common mold strains from Aspergillus versicolor^[1][2]. Sterigmatocystine, a inhibitor of G1 Phase and DNA synthesis, is used to inhibit p21 activity. Sterigmatocystine has teratogenic, and carcinogenic effects in animals^[3]. In Vitro: Sterigmatocystine-induced DNA damage activates the ATM/53-dependent signaling pathway, which contributes to the induction of G2 arrest in GES-1 cells^[4]. In Vivo: Sterigmatocystine (ip; 3 mg/kg once daily for 14 days) inhibits p21^WAF1/CIP1[3].