PT  - JOURNAL ARTICLE
AU  - Sunday Okutachi
AU  - Ganesh babu Manoharan
AU  - Daniel Abankwa
TI  - Potential of phenothiazines to synergistically block calmodulin and reactivate PP2A in cancer cells
AID  - 10.1101/2021.06.16.448716
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.06.16.448716
4099  - http://biorxiv.org/content/early/2021/06/17/2021.06.16.448716.short
4100  - http://biorxiv.org/content/early/2021/06/17/2021.06.16.448716.full
AB  - Phenothiazines (PTZ) are well known as inhibitors of monoamine neurotransmitter receptors, notably dopamine receptors. Because of this activity they are used for decades as antipsychotic drugs. In addition, significant anti-cancer properties have been ascribed to them. Several attempts for their repurposing were made, however, their incompletely understood polypharmacology is challenging.Here we examined the potential of PTZ to synergistically act on two cancer associated targets, calmodulin (CaM) and the tumor suppressor protein phosphatase 2A (PP2A). Both proteins are known to modulate the Ras-MAPK pathway activity. Consistently, combinations of a CaM inhibitor and a PP2A activator synergistically inhibited cancer cells with KRAS or BRAF mutations. We identified the covalently reactive PTZ derivative fluphenazine mustard as an inhibitor of Ras driven proliferation and Ras membrane organization. We confirmed its anti-CaM activity in vitro and through a cellular CaM target engagement bioluminescence resonance energy transfer (BRET) assay. Our results suggest that improved PTZ derivatives retaining their synergistic CaM inhibitory and PP2A activating properties, but without neurological side-effects, may be interesting to pursue further as anti-cancer agents.