Design, Synthesis, and Application of a Rapidly Diversifiable Trioxacarcin Pharmacophore in Antibody-Drug Conjugates

Abstract

The trioxacarcin natural products are structurally complex, densely oxygenated bacterial isolates with exquisite biological activity towards a number of different human cancer cell lines. Following an initial isolation report in 1981, a distinct member of the trioxacarcins, LL-D49194α1, was selected for a phase 1 clinical study because of its promising pre-clinical anti-tumor activity. While a number of positive responses were observed in the cohort of 15 patients, the trial was suspended immediately following the death of a woman in the study. Retrospective analysis of the cohort indicated that systemic dosing of trioxacarcins realized non-specific pancarditis at doses that produced any meaningful reduction in tumor volume. In response to the deleterious off-target toxicity natural products like the trioxacarcins typically display, antibody-drug conjugates (ADCs) have emerged as a robust technology to selectively deliver these toxic payloads to a cancer cell. In an ADC, the small molecule warhead is linked to a monoclonal antibody which recognizes a receptor the cancer cell overexpresses relative to normal human cells. Once the entire construct enters the cancer cell, the linkage is engineered to release the payload which as the free drug can then affect cell apoptosis through its distinct mechanism of action. This dissertation presents the most recent step towards the realization of a fully-synthetic trioxacarcin as a suitable payload for an ADC. A halohydrin prodrug of the spiro-epoxide, present in all biologically active trioxacarcins, is utilized as a novel handle upon which to build the first stable trioxacarcin ADC with modest potency against human cancer cell lines. A rapidly diversifiable trioxacarcin pharmacophore is then developed and employed to understand how the linkage site of the trioxacarcin to the antibody effects the resultant properties of the ADC.