KNK437 is a HSP inhibitor, and inhibits the induction of HSP105, HSP70, and HSP40. IC50 & Target: HSP^[1] In Vitro: KNK437 inhibits the activation of several HSPs including HSP105, HSP70, and HSP40 in COLO 320DM (human colon carcinoma) cells. KNK437 (100 μM) inhibits thermotolerance in COLO 320DM cells after the first heat treatment. KNK437 shows inhibitory effects on thermotolerance dose-dependently in COLO 320DM cells (0-200 μM) and HeLa S3 cells (100, 200 μM)^[1]. KNK437 (100 μM) exhibits inhibitory activities against the methylation of H3-Lys4 before or after heat-treatment in HSC4 cells and KB cells, but does not affect that of H3 Lys9. KNK437 also suppresses the expression of HSP70^[3]. In Vivo: KNK437 is a weakly toxic agent. KNK437 (62.5-400 mg/kg) recovers bodyweight losses of tumor-free CD-1 (ICR) mice. KNK437 (200 mg/kg) alone shows no antitumor effects and does not increase the thermosensitivity of nontolerant tumors. KNK437 improves the antitumor effects of fractionated heat treatment at 44°C at 200 mg/kg in a synergistic manner. KNK437 (200 mg/kg, i.p.) suppresses the induction of thermotolerance when administrated 6 h before the initial heating^[2].