Confronting the central challenge of beta cell regeneration : cell lineage-selective activity

Pancreatic β-cells are solely responsible for secreting insulin in response to blood glucose. Loss of β-cell mass and function is a hallmark of diabetes, and reversal of this β-cell deficit is a towering goal in regenerative therapy for diabetes. Thus, the development of new β-cell-directed diabetes therapeutics to preserve and/or enhance β-cell mass and function (insulin secretion) has exceptional human health impact potential. Unfortunately, advancement in this arena is stymied by a dearth of β-cell-specific therapeutic targets. Translation of numerous promising, but un-targeted, diabetes therapeutics to the clinic has thus far failed because of systemic effects. Consequently, the next generation of β-cell-directed imaging and therapeutic modalities must be reimagined with β-cell selective targeting in mind. Chapter 1 begins by outlining the urgent need for selective β-cell targeting. A clinically successful β-cell targeting paradigm could dramatically transform diabetes care, most notably by allowing β-cell regeneration to be translated into humans. This chapter introduces current diabetes therapeutics and their potential for selective targeting to β-cells. Next, it surveys the literature of targeted β-cell delivery, highlighting successful β-cell imaging applications and their potential application to targeted drug delivery. Further, all exemplified β-cell targeting methods are reviewed, which include, most successfully, Zn2+-based targeting (Chapter 3). Finally, the potential of selective prodrug release, which has heretofore been largely unexplored in β-cells, is assessed. Within the area of β-cell therapeutics is the relatively recent idea of restoring healthy blood glucose homeostasis by stimulating β-cells to self-replicate. Chapter 2 conveys a completed research project whose goal was to overcome poor potency, a central limitation of all available pro-β-cell replication compounds. This project involved repurposing a toxic compound (OTS167) with promiscuous binding across all human kinases, and honed in using substantial synthetic chemistry, biochemistry, and cell biology to generate a highly potent, yet non-toxic, lead compound. This chapter is evidence of the medicinal chemistry aspects of this dissertation research. Chapter 3 exemplifies β-cell targeted drug delivery of a zinc-chelating small molecule. It describes assays that were established and the synthesis of a hybrid replication-promoting/zinc-chelating small molecule. New assays were developed or adapted to assess chelation in β-cells, accumulation in primary islets, and selective replication, using microscopy, liquid chromatography/mass spectrometry, and quantitative immunofluorescence. Finally, the central hypothesis that this molecule accumulates in β-cells and selectively biases replication toward β-cells relative to non β-cells was confirmed. This chapter embodies the power of the chemistry-biology interface to prod discovery in medicinal research. Chapter 4 clarifies the experimental steps involved in designing and performing the assays in Chapter 3 and elaborates some of the most crucial steps. Ensuring a high level of reproducibility is critical for capitalizing on the broad applicability of Zn2+-chelator-based targeted β-cell delivery. Chapter 5, while not directly related to either β-cell targeted delivery or β-cell replication, demonstrates that neuroendocrine neoplasms, which share commonalities with β-cells, show staining intensity for an enzyme expressed by neuroendocrine cells. This finding was robust and repeatable. This discovery illustrates the utility of examining neuroendocrine markers in real human tissues. Additionally, the presence of this chapter backs up the highly interdisciplinary nature of this dissertation, reaching from synthetic organic chemistry all the way to clinical research

Keywords: Chemistry.
Advisor: Annes Justin
Bertozzi Carolyn R.
Khosla Chaitan