Microvascular Free Flap Outcomes in Maxillectomy Defects from Invasive Fungal Sinusitis.

OBJECTIVES: Microvascular free tissue transfer is routinely used for reconstructing midface defects in patients with malignancy, however, studies regarding reconstructive outcomes in invasive fungal sinusitis (IFS) are lacking. We aim to describe outcomes of free flap reconstruction for IFS defects, determine the optimal time to perform reconstruction, and if anti-fungal medications or other risk factors of an immunocompromised patient population affect reconstructive outcomes. METHODS: Retrospective review of reconstruction for IFS (2010-2022). Age, BMI, hemoglobin A1c, number of surgical debridements, and interval from the last debridement to reconstruction were compared between patients with delayed wound healing versus those without. Predictor variables for delayed wound healing and the effect of time on free flap reconstruction were analyzed. RESULTS: Twenty-seven patients underwent free flap reconstruction for IFS. Three patients were immunocompromised from leukemia and 21 had diabetes mellitus (DM). Patients underwent an average of four surgical debridements for treatment of IFS. The interval from the last IFS debridement to flap reconstruction was 5.58 months (±5.5). Seven flaps (25.9%) had delayed wound healing. A shorter interval of less than 2 months between the last debridement for IFS and reconstructive free flap procedure was associated with delayed wound healing (Fisher Exact Test p = 0.0062). Other factors including DM, BMI, HgA1c, and bone reconstruction were not associated with delayed wound healing. CONCLUSION: Patients with maxillectomy defects from IFS can undergo microvascular-free flap reconstruction with good outcomes while on anti-fungal medication. Early reconstruction in the first 2 months after the last IFS debridement is associated with delayed wound healing. LEVEL OF EVIDENCE: 4 Laryngoscope, 134:1642-1647, 2024.

Site-specific PEGylation of human thyroid stimulating hormone to prolong duration of action.

Recombinant human thyroid stimulating hormone (rhTSH or Thyrogen) has been approved for thyroid cancer diagnostics and treatment under a multidose regimen due to its short circulating half-life. To reduce dosing frequency, PEGylation strategies were explored to increase the duration of action of rhTSH. Lysine and N-terminal PEGylation resulted in heterogeneous product profiles with 40% or lower reaction yields of monoPEGylated products. Eleven cysteine mutants were designed based on a structure model of the TSH-TSH receptor (TSHR) complex to create unique conjugation sites on both α and ß subunits for site-specific conjugation. Sequential screening of mutant expression level, oligomerization tendency, and conjugation efficiency resulted in the identification of the αG22C rhTSH mutant for stable expression and scale-up PEGylation. The introduced cysteine in the αG22C rhTSH mutant was partially blocked when isolated from conditioned media and could only be effectively PEGylated after mild reduction with cysteine. This produced a higher reaction yield, ~85%, for the monoPEGylated product. Although the mutation had no effect on receptor binding, PEGylation of αG22C rhTSH led to a PEG size-dependent decrease in receptor binding. Nevertheless, the 40 kDa PEG αG22C rhTSH showed a prolonged duration of action compared to rhTSH in a rat pharmacodynamics model. Reverse-phase HPLC and N-terminal sequencing experiments confirmed site-specific modification at the engineered Cys 22 position on the α-subunit. This work is another demonstration of successful PEGylation of a cysteine-knot protein by an engineered cysteine mutation.

Carbohydrate-mediated polyethylene glycol conjugation of TSH improves its pharmacological properties.

Thyrogen (thyrotropin alfa for injection), recombinant human TSH (rhTSH), has been successfully used to enhance diagnostic radioiodine scanning and thyroglobulin testing in the follow-up of patients with thyroid cancer and as an adjunctive treatment for radioiodine thyroid remnant ablation. However, the short half-life of rhTSH in the circulation requires a multidose regimen. We developed novel sialic acid-mediated and galactose-mediated conjugation chemistries for targeting polyethylene glycol (PEG) to the three N-linked glycosylation sites on the protein, to prolong plasma half-life by eliminating kidney filtration and potential carbohydrate-mediated clearance. Conjugates of different PEG sizes and copy numbers were screened for reaction yield, TSH receptor binding, and murine phamacokinetics/pharmacodynamics studies. The best performing of these products, a 40-kDa mono-PEGylated sialic acid-mediated conjugate, exhibited a 3.5-fold longer duration of action than rhTSH in rats, as a 5-fold lower affinity was more than compensated by a 23-fold extension of circulation half-life. Biochemical characterization confirmed conjugation through the sialic acids. Correlation of PEG distribution on the three N-linked glycosylation sites and the PEG effect on receptor binding supported the previously reported structure-function relationship of rhTSH glycosylation. This long-acting rhTSH has the potential to significantly improve patient convenience and provider flexibility while reducing potential side effects associated with a sudden elevation of serum TSH.