Targeting Oncogenic NOTCH1 in T-cell Acute Lymphoblastic Leukemia With a Selective SERCA Inhibitor CAD204520

The identification of SERCA (sarco/endoplasmic reticulum calcium ATPase) as a target for modulating gain-of-function NOTCH1 mutations in Notch dependent cancers has spurred the development of this compound class for cancer therapeutics. SERCA plays a critical role in Ca2+ regulation particularly in myocytes, thus inhibiting it may increase the risk of heart failure, limiting the development of this compound class for cancer therapeutics. Considering this toxicity challenge, discovery and early optimization of small molecules with better drug-like properties and reduced off-target toxicity is warranted. Despite the innate toxicity challenge associated with SERCA inhibition, we identified CAD204520, a small molecule with better drug-like properties and reduced off-target Ca2+ toxicity compared with the SERCA inhibitor thapsigargin. Similar to the SERCA inhibitor thapsigargin, CAD204520 inhibits Notch signaling in T cell acute lymphoblastic leukemia (T-ALL) cells causing a cell cycle arrest and induction of apoptosis. CAD204520 also preferentially targets mutated over wild type NOTCH1 proteins in T-ALL and mantle cell lymphoma (MCL), thereby overcoming the therapeutic limitation associated with the use of pan-Notch inhibitors. Remarkably, CAD204520 resulted in an effective treatment in a NOTCH1-mutated T-ALL in vivo model without causing overt Ca2+-related cardiac toxicity. To anticipate the potential mechanism of resistance to SERCA inhibitors, we generated a T-ALL cell line resistant to the effect of thapsigargin. A subsequent small molecule library screening identified glucocorticoids among the top hits in the resistant cell line. This effect is at least in part mediated by the specific upregulation of glucocorticoid receptor. Consequently, the association of SERCA inhibitors and glucocorticoids displayed a synergistic effect in multiple preclinical models. This study supports the development of SERCA inhibitors for Notch-dependent cancers and extends their application to cases with isolated mutations in the PEST degradation domain of NOTCH1, such as MCL or chronic lymphocytic leukemia (CLL). Furthermore, this study suggests that SERCA-Ca2+ modulation mediates glucocorticoid signaling and that innovative SI can pharmacologically modulate glucocorticoid resistance in T-ALL.