Towards Targeted Photodynamic Therapy: Synthesis and Characterization of Aziridine Aldehyde-cyclized Cancer-targeting Peptides and Bacteriochlorin Photosensitizers

This thesis presents the contributions we made towards achieving targeted photodynamic therapy (PDT) by synthesizing and characterizing new aziridine aldehyde-cyclized cancer-targeting peptides and bacteriochlorin photosensitizers (PSs). The new peptides are based on the integrin-targeting sequence, arginine-glycine-aspartic acid (RGD), and were cyclized by aziridine aldehyde-driven macrocyclization chemistry. We developed a versatile conjugation strategy, and created two useful RGD macrocycles that specifically bound to integrin receptors in vitro. Computer modeling and competitive binding studies found that this macrocyclization chemistry modulated the binding affinity of these peptides by tuning the geometry of peptides of different lengths. The new PSs described herein include bacteriochlorophyll derivatives that efficiently produced reactive oxygen species (ROS) upon illumination with red light. We discovered two simple structural modifications that enhanced the photogeneration of ROS, and suggest that future studies make use of these design parameters to create next generation bacteriochlorin PSs with superior photoactivity compared to known derivatives. In addition, we optimized a facile synthetic reaction for creating a new natural product analog with a distinct exocyclic F-ring, and found it was capable of PDT. Unlike some of its natural chlorin counterparts, our bacteriochlorin was not a potent antioxidant. Yet, we suggest that future efforts make use of our simple reaction to expand the library of F-ring containing bacteriochlorins to elucidate key structural modifications that can tune the PDT efficacy and antioxidant activity of this distinct class of bacteriochlorins. Finally, this thesis presents preliminary investigations that attempted to develop new cancer-targeting PDT agents. While the goal of achieving optimal cancer-targeted PDT was not accomplished in this work, it is envisioned that this thesis will provide useful data and insights that will contribute to the development of optimal aziridine aldehyde-cyclized peptide-bacteriochlorin PS conjugates for efficient in vivo cancer-specific PDT.Ph.D

68Ga-Labeled [Leu13ψThz14]Bombesin(7–14) Derivatives: Promising GRPR-Targeting PET Tracers with Low Pancreas Uptake

The gastrin-releasing peptide receptor (GRPR) is a G-protein-coupled receptor that is overexpressed in many solid cancers and is a promising target for cancer imaging and therapy. However, high pancreas uptake is a major concern in the application of reported GRPR-targeting radiopharmaceuticals, particularly for targeted radioligand therapy. To lower pancreas uptake, we explored Ga-complexed TacsBOMB2, TacsBOMB3, TacsBOMB4, TacsBOMB5, and TacsBOMB6 derived from a potent GRPR antagonist sequence, [Leu13ψThz14]Bombesin(7–14), and compared their potential for cancer imaging with [68Ga]Ga-RM2. The Ki(GRPR) values of Ga-TacsBOMB2, Ga-TacsBOMB3, Ga-TacsBOMB4, Ga-TacsBOMB5, Ga-TacsBOMB6, and Ga-RM2 were 7.08 ± 0.65, 4.29 ± 0.46, 458 ± 38.6, 6.09 ± 0.95, 5.12 ± 0.57, and 1.51 ± 0.24 nM, respectively. [68Ga]Ga-TacsBOMB2, [68Ga]Ga-TacsBOMB3, [68Ga]Ga-TacsBOMB5, [68Ga]Ga-TacsBOMB6, and [68Ga]Ga-RM2 clearly show PC-3 tumor xenografts in positron emission tomography (PET) images, while [68Ga]Ga-TacsBOMB5 shows the highest tumor uptake (15.7 ± 2.17 %ID/g) among them. Most importantly, the pancreas uptake values of [68Ga]Ga-TacsBOMB2 (2.81 ± 0.78 %ID/g), [68Ga]Ga-TacsBOMB3 (7.26 ± 1.00 %ID/g), [68Ga]Ga-TacsBOMB5 (1.98 ± 0.10 %ID/g), and [68Ga]Ga-TacsBOMB6 (6.50 ± 0.36 %ID/g) were much lower than the value of [68Ga]Ga-RM2 (41.9 ± 10.1 %ID/g). Among the tested [Leu13ψThz14]Bombesin(7–14) derivatives, [68Ga]Ga-TacsBOMB5 has the highest tumor uptake and tumor-to-background contrast ratios, which is promising for clinical translation to detect GRPR-expressing tumors. Due to the low pancreas uptake of its derivatives, [Leu13ψThz14]Bombesin(7–14) represents a promising pharmacophore for the design of GRPR-targeting radiopharmaceuticals, especially for targeted radioligand therapy application

Seasonal accumulation of acetylated triacylglycerols by a freeze-tolerant insect

© 2014. Published by The Company of Biologists Ltd. Most animals store energy as long-chain triacylglycerols (lcTAGs). Trace amounts of acetylated triacylglycerols (acTAGs) have been reported in animals, but are not accumulated, likely because they have lower energy density than lcTAGs. Here we report that acTAGs comprise 36% of the neutral lipid pool of overwintering prepupae of the goldenrod gall fly, Eurosta solidaginis, while only 17% of the neutral lipid pool is made up of typical lcTAGs. These high concentrations of acTAGs, present only during winter, appear to be synthesized by E. solidaginis and are not found in other freezetolerant insects, nor in the plant host. The mixture of acTAGs found in E. solidaginis has a significantly lower melting point than equivalent lcTAGs, and thus remains liquid at temperatures at which E. solidaginis is frozen in the field, and depresses the melting point of aqueous solutions in a manner unusual for neutral lipids. We note that accumulation of acTAGs coincides with preparation for overwintering and the seasonal acquisition of freeze tolerance. This is the first observation of accumulation of acTAGs by an animal, and the first evidence of dynamic interconversion between acTAGs and lcTAGs during development and in response to stress