Factors associated with inoperable cutaneous squamous cell carcinoma.

Inoperable cutaneous squamous cell carcinomas (SCCs) are rare and life-threatening, but few studies have investigated their causal factors. Our aim was to determine factors associated with inoperable SCCs, as well as patient and tumour characteristics, and care pathway-related factors. Based on an observational retrospective study at Reims University Hospital, France, the characteristics of tumours and patients were recorded based on 73 cases of inoperable SCCs and compared with 73 cases of operable SCCs. In addition, the clinical history and care pathway associated with inoperable cases was documented. In patients with inoperable SCCs, the median overall survival (OS) time was 7.6 months and the three-year OS was <5%. Compared to patients with operable tumours, those with inoperable tumours were older (83 vs 78.9; p = 0.018) and more frequently had a history of senile dementia (21.9% vs 8.2%; p = 0.048), cardiovascular disease (75.3% vs 50.7%; p = 0.009) or a tumour with poor or moderate differentiation (30.9% vs 13.3%; p= 0.04). A long delay between tumour appearance and first consultation with a dermatologist (median: five months), failing to attend further medical or surgical appointments (21%), initial refusal of surgery (18%), reluctance to accept doctors' recommendations by the family and/or patient (26%), and absence of surgical revision after a previous incomplete excision (29%) were identified as potentially modifiable factors associated with inoperable SCCs. There is a need for better information for both patients and doctors concerning the potential severity of SCCs and the importance of early and appropriate management, specifically in older and frail patients.

Optimal electrostatic interactions between substrate and protein are essential for radical chemistry in ornithine 4,5-aminomutase.

Ornithine 4,5-aminomutase (OAM) from Clostridium sticklandii is an adenosylcobalamin (AdoCbl) and pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes a 1,2-amino shift, interconverting d-ornithine and 2S, 4R-diaminopentanoate. The reaction occurs via a radical-based mechanism whereby a PLP-bound substrate radical undergoes intramolecular isomerization via an azacyclopropylcarbinyl radical intermediate. Herein, we investigated the catalytic role of active site residues that form non-covalent interactions with PLP and/or substrate, d-ornithine. Kinetic analyses revealed that residues that form salt bridges to the α-carboxylate (R297) or the α-amine (E81) of d-ornithine are most critical for OAM activity as conservative substitutions of these residues results in a 300-600-fold reduction in catalytic turnover and a more pronounced 1000- to 14,000-fold decrease in catalytic efficiency. In contrast, mutating residues that solely interact with the PLP cofactor led to more modest decreases (10-60-fold) in kcat and kcat/Km. All but one variant (S162A) elicited an increase in the kinetic isotope effect on kcat and kcat/Km with d,l-ornithine-3,3,4,4,5,5-d6 as the substrate, which indicates that hydrogen atom abstraction is more rate determining. Electron paramagnetic resonance spectra of the variants reveal that while the substitutions decrease the extent of CoC bond homolysis, they do not affect the structural integrity of the active site. Our experimental results, discussed in context with published computational work, suggests that the protonation state of the PLP cofactor has less of a role in radical-mediated chemistry compared to electrostatic interactions between the substrate and protein.