The Novel Nucleoside Analogue ProTide NUC-7738 Overcomes Cancer Resistance Mechanisms <i>In Vitro</i> and in a First-In-Human Phase I Clinical Trial.

Abstract

Nucleoside analogues form the backbone of many therapeutic regimens in oncology and require the presence of intracellular enzymes for their activation. A ProTide is comprised of a nucleoside fused to a protective phosphoramidate cap. ProTides are easily incorporated into cells whereupon the cap is cleaved and a preactivated nucleoside released. 3'-Deoxyadenosine (3'-dA) is a naturally occurring adenosine analogue with established anticancer activity <i>in vitro</i> but limited bioavailability due to its rapid <i>in vivo</i> deamination by the circulating enzyme adenosine deaminase, poor uptake into cells, and reliance on adenosine kinase for its activation. In order to overcome these limitations, 3'-dA was chemically modified to create the novel ProTide NUC-7738. We describe the synthesis of NUC-7738. We determine the IC₅₀ of NUC-7738 using pharmacokinetics (PK) and conduct genome-wide analyses to identify its mechanism of action using different cancer model systems. We validate these findings in patients with cancer. We show that NUC-7738 overcomes the cancer resistance mechanisms that limit the activity of 3'-dA and that its activation is dependent on ProTide cleavage by the enzyme histidine triad nucleotide-binding protein 1. PK and tumor samples obtained from the ongoing first-in-human phase I clinical trial of NUC-7738 further validate our <i>in vitro</i> findings and show NUC-7738 is an effective proapoptotic agent in cancer cells with effects on the NF-κB pathway. Our study provides proof that NUC-7738 overcomes cellular resistance mechanisms and supports its further clinical evaluation as a novel cancer treatment within the growing pantheon of anticancer ProTides.