Aldehyde dehydrogenase enzymes (ALDHs) have a broad spectrum of biological activities through the oxidation of both endogenous and exogenous aldehydes. Unbalanced expression levels of ALDHs have been associated with a variety of disease states such as alcoholic liver disease, Parkinson’s disease, obesity, and multiple types of cancers. ALDH1A1 also plays a major role in preserving the tumor microenvironment via differentiation, self-protection, and proliferation of cancer stem cells. The cancer cell stemness is associated with cancer relapse and poor prognosis, raising the potential of ALDH1A1 as an attractive therapeutic target.

We performed a systematic medicinal chemistry optimization and biological characterization of newly designed quinoline series that ultimately led to potent ALDH1A1 inhibitors with excellent enzymatic potency and Aldefluor cellular activity (e.g., MIA PaCa-2, OV-90, HT-29 cancer cell lines), as well as improved pharmacokinetic (PK) properties. This chemotype also demonstrated a high degree of selectivity over other ALDH isozymes (ALDH1A2, ALDH1A3, ALDH1B1, ALDH3A1, and ALDH2) and other dehydrogenases (HPGD and HSD17ß4).

Further development of the series indicated that NCATS-101 and NCATS-102 exhibit low nanomolar potency in both enzymatic and cellular assays, demonstrate target engagement in a cellular thermal shift assay (CETSA), and can inhibit the formation of 3D spheroid cultures of OV-90 ovarian cancer cells. In addition, lead compounds potentiated the cytotoxicity of Paclitaxel in SKOV-3-TR, a Taxol-resistant ovarian cancer cell line, which suggest the potential feasibility of combined treatment with existing cancer drugs. PK studies demonstrated that NCATS-101 and NCATS-102 have good drug exposure via oral administration and should be suitable for in vivo studies or testing in other disease-relevant models.