We developed synthetic chemistry to access the marine alkaloid rigidins and over forty synthetic analogues based on the 7-deazaxanthine, 7-deazaadenine, 7-deazapurine and 7-deazahypoxanthine skeletons. Analogues based on the 7-deazahypoxanthine skeleton exhibited nanomolar potencies against cell lines representing cancers with dismal prognoses, tumor metastases and multidrug resistant cells. Studies aimed at elucidating the mode(s) of action of the 7-deazahypoxanthines in cancer cells revealed that they inhibited in vitro tubulin polymerization and disorganized microtubules in live HeLa cells. Experiments evaluating the effects of the 7-deazahypoxanthines on the binding of [3H]colchicine to tubulin identified the colchicine site on tubulin as the most likely target for these compounds in cancer cells. Because many microtubule-targeting compounds are successfully used to fight cancer in the clinic, we believe the new chemical class of antitubulin agents represented by the 7-deazahypoxanthine rigidin analogues have significant potential as new anticancer agents.

Therapeutic payloads remain a challenge for phospholipid-stabilized microbubbles that are currently used as contrast agents in diagnostic ultrasound imaging. High loading is difficult to achieve due to the metastable phospholipid monolayer that lacks cargo volume, requiring lengthy drug-loaded particle tethering strategies or other sophisticated methods. The purpose of this work is to demonstrate that phospholipid conjugation can anchor chemotherapeutics to the microbubble shell with minimal disruption to phospholipid packing, resulting in an ultrasound theranostic agent that requires minimal preparation prior to administration. Using a Steglich esterification reaction, several potent chemotherapeutics were conjugated to phospholipids and were subsequently incorporated into liposomes, microbubbles, and nanodroplets for biological and particle characterization. Prodrug structures were confirmed with 1H and 13C NMR. Retention of biological activity for each phospholipid prodrug was demonstrated with an MTT cell proliferation assay using liposomes. Loading and stability of nanodroplets and microbubbles were measured with UV-Vis spectroscopy. To demonstrate site-specific delivery potential, these solutions were suspended in a submersible cell culture chamber with adhered HeLa cells. A single element transducer was used to apply a radiation force and fragmentation pulse sequence. Ultrasound-exposed and non-exposed areas treated with prodrug-containing microbubbles and nanodroplets were compared, demonstrating local efficacy.