Applying Optical Approaches to the Drug Delivery Problem

Division Of Basic Sciences - Nci

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Abstract

In previous work, we developed an uncaging reaction sequence initiated by near-IR light using readily synthesized C4'-dialkylamine-substituted heptamethine cyanines. We have shown that a variety of phenol- and amine- containing small molecules are quickly uncaged upon irradiation with low energy light. Detailed mechanistic studies involving mass spectrometry, NMR, and absorbance techniques have shown that release occurs through regioselective C-C cleavage and then hydrolysis of the C4'-amine. We are currently broadening the scope of the release process and examining aspects of the mechanism in detail using computational (collaboration with Dr. Joseph Ivanic) and experimental techniques. In this effort, we have developed an approach that enables the control release of amine payload through an approach that involves cyanine photooxidation followed by beta-elimination. Existing methods that use light for therapeutic interventions typically rely on the local generation of reactive oxygen species (ROS). The local delivery of potent therapeutic agents elicit alternative mechanistic paradigms, while achieving otherwise unattainable potency. We are applying our light-cleavable chemistry for targeted drug delivery. This approach merges the unique potency of small molecule drugs with the high spatial control afforded by light release and molecular targeting. The use of tissue penetrant, cytocompatible near-IR light is critical because existing uncaging chemistries using UV or blue light would not be suitable for this application. In this area, we reported the first example of near-IR light cleavable antibody drug conjugate strategy. We have developed conjugates that release the potent anticancer natural product, duocarmycin. These conjugates can be tracked in vivo using fluorescence and uncaged attainable flux from an external CW laser source. These compounds have shown excellent antitumor activity in various in vivo models. Building on these efforts, we are using optical imaging to guide the design of novel antibody targeted drug delivery strategies. Our prior studies (Aim 1.1) established that tuning cyanine structure can have a profound impact on tumor and off-target uptake of antibody-fluorophore conjugates. The key insight to emerge from these efforts, is that highly charged, but net-neutral (i.e., zwitterionic) probes dramatically improve tumor targeting. To define the rules of optimal mAb targeting, we assembled and quantitatively compared a series of substituted cyanines. These efforts provide additional support for the notion that highly polar, zwitterionic substituents dramatically improve the in vivo properties of mAb conjugates. Ongoing efforts are testing the role of labeling chemistry on tumor targeting. In addition to antibody properties, the cleavable linker plays a critical role in the properties of ADCs. Conventional always-ON probes are not suitable for addressing the site and extent of ADC-linker cleavage. We hypothesized that our activatable CyBam probes would allow us to compare linker chemistries in animal models. We created mAb-targeted variants that were applied to quantitatively compare a series of broadly employed ADC linkers. Going forward, we will apply this strategy to identify ADC linker-mAb combinations that harness proteases found in the tumor-microenvironment (TME) to enable tumor-selective drug release. We are also developing and applying strategies to enable the quantitative in vivo measurement of mAb internalization kinetics. Overall the goal of this project is to develop an "imaging-first" approach that will allow us to create exceptionally well-tolerated, potent ADCs.