The mechanism of inhibition of HIV-1 reverse transcriptase by three nonnucleoside inhibitors is described. Nevirapine, O-TIBO, and CI-TIBO each bind to a hydrophobic pocket in the enzyme-DNA complex close to the active site catalytic residues. Pre-steady-state kinetic analysis was used to establish the mechanism of inhibition by these noncompetitive inhibitors. Analysis of the pre-steady-state burst of DNA polymerization indicated that inhibitors blocked the chemical reaction, but did not interfere with nucleotide binding or the nucleotide-induced conformational change. Rather, in the presence of saturating concentrations of the inhibitors, the nucleoside triphosphate bound tightly (Kd, 100 nM), but nonproductively. The data suggest that an inhibitor combining the functionalities of a nonnucleoside inhibitor and a nucleotide analog could bind very tightly and specifically to reverse transcriptase and could be effective in the treatment of AIDS.

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The parameters governing the polymerization mechanism of reverse transcriptase containing the tyrosine to cysteine mutation at position 181 (Y181C) were determined using pre-steady-state techniques. The pathway for single nucleotide incorporation catalyzed by Y181C is similar to that determined for wild-type RT where a rate-limiting conformational change precedes fast chemistry and is followed by slow steady-state release of the primer/template. The Y181C mutant enzyme binds a 25/45-mer duplex DNA tightly with a Kd of 11 nM. However, the Y181C mutation weakens the nucleotide affinity 2-3-fold relative to the wild-type complex. We also determined the parameters governing the mechanism of nonnucleoside inhibitor resistance with Y181C. The Kd value of Nevirapine with the mutant E.DNA complex increased approximately 500-fold. The decreased affinity of Nevirapine for the mutant enzyme is a consequence of a faster inhibitor dissociation rate from the enzyme complex of Y181C relative to that of the wild-type. The E.DNA complex of Y181C may be saturated with Nevirapine, and the I.E.DNA complex is capable of a maximum incorporation rate of 0.1 s-1 (a 10-fold faster rate than that of the wild-type I.E.DNA complex). The overall two-step binding of nucleotide to Y181C in the presence of Nevirapine remains unaffected.

Oncologist well-being is critical to initiating and maintaining the physician-patient relationship, yet many oncologists suffer from symptoms of burnout. Burnout has been linked to poor physical and mental health, as well as increased medical errors, patient dissatisfaction, and workforce attrition. In this Call to Action article, we discuss causes of and interventions for burnout and moral distress in oncology, highlight existing interventions, and provide recommendations for addressing burnout and improving well-being at the individual and organizational levels to deliver ethical, quality cancer care.