Erica A. Steen

Chemical inducers of proximity (CIPs) stabilize biomolecular interactions, often causing an emergent rewiring of cellular biochemistry. While rational design strategies can expedite the discovery of heterobifunctional CIPs, monovalent, molecular glue-like CIPs have relied predominantly on serendipity. Envisioning a prospective approach to discover molecular glues for a pre-selected target, we hypothesized that pre-existing ligands could be systematically decorated with chemical modifications to empirically discover protein-ligand surfaces that are tuned to cooperatively engage another protein interface. Here, we used sulfur(VI)-fluoride exchange (SuFEx)-based high-throughput chemistry (HTC) to install 3,163 structurally diverse chemical building blocks onto ENL and BRD4 ligands and then screened the crude products for degrader activity. This revealed dHTC1, a potent, selective, and stereochemistry-dependent degrader of ENL. It recruits CRL4 ^CRBN to ENL through an extended interface of protein-protein and protein-ligand contacts, but only after pre-forming the ENL:dHTC1 complex. We also characterized two structurally distinct BRD4 degraders, including dHTC3, a molecular glue that selectively dimerizes the first bromodomain of BRD4 to SCF ^FBXO3 , an E3 ligase not previously accessible for chemical rewiring. Altogether, this study introduces HTC as a facile tool to discover new CIPs and actionable cellular effectors of proximity pharmacology.

Summary: A 6.6-year-old female presented to endocrinology with precocious puberty for evaluation and management. Workup was initiated, and a diagnosis of central precocious puberty was confirmed. A decision was made to initiate pubertal blockade using gonadotropin-releasing hormone agonist (GnRHa) therapy with depot leuprolide acetate injections every 3 months. The patient received the first depot leuprolide acetate injection in the right ventrogluteal area. Six hours following the injection, the patient was reported to be inconsolable in pain, which was localized to the right hip site of the earlier injection and associated with a refusal to ambulate. The pain and discomfort continued to progress over the next 24 h despite an alternating regimen of Tylenol and ibuprofen prompting admission to the emergency department. Vital signs demonstrated a low-grade fever and elevated C-reactive protein. An ultrasound of the right hip demonstrated fluid accumulation within the joint. Over the next week, the patient was unable to walk independently and required assistance for activities of daily living. By 2 weeks after the injection, the pain began to remit, and the patient resumed activities of daily living. Following consultation with allergy, a decision was made to continue GnRHa suppressive therapy with an alternative analog (Triptodur). The patient tolerated subsequent treatment without reaction. Learning points: Although gonadotropin-releasing hormone agonists (GnRHa) have a generally good safety profile, there is a history of both local and systemic hypersensitivity reactions associated with their use. Despite the long-acting formulation of depot leuprolide acetate, the systemic reaction in this case appears to be self-limited. Discontinuation of therapy or a change to an alternative formulation of GnRHa analog should be considered based on the need for therapy versus the potential risk of rechallenge.

Summary: An 11-year-old girl with past medical history of septic shock and multi-organ failure at age 5 presented to her primary care doctor with concern for pallor of the lips. Laboratory studies demonstrated low free thyroxine (T4) and normal thyroid-stimulating hormone (TSH). A referral to endocrinology was made where the patient was evaluated, and laboratory evaluation was repeated. The patient was asymptomatic and clinically euthyroid with a height consistent with her mid-parental height and was in mid- to late-puberty. The repeated laboratory evaluation demonstrated a pattern suggestive of primary hypothyroidism with low free T4 and an elevated TSH. However, the magnitude of elevation of TSH was less than expected, given the degree of lowering of free T4; therefore, central hypothyroidism was considered. Workup was initiated, and laboratory studies and MRI imaging confirmed an underlying diagnosis of panhypopituitarism in the setting of pituitary stalk interruption syndrome. Learning points: Pituitary stalk interruption syndrome is a rare but important cause of panhypopituitarism. Central hypothyroidism should be suspected in patients with low free thyroxine with an inappropriate degree of elevation of thyroid-stimulating hormone. Workup of central hypothyroidism should include multi-pituitary hormone assessment, and, if evident, MRI imaging should be done. Adrenal insufficiency should be suspected in a hypotensive, critically ill patient who is failing to improve on standard-of-care therapy.