Immune checkpoint inhibitors (ICIs) are widely used for various malignancies. However, their safety and efficacy in patients with a kidney transplant have not been defined. To delineate this, we conducted a multicenter retrospective study of 69 patients with a kidney transplant receiving ICIs between January 2010 and May 2020. For safety, we assessed the incidence, timing, and risk factors of acute graft rejection. For efficacy, objective response rate and

The heme-containing Cytochrome P450s (CYPs) are a major enzymatic determinant of drug clearance and drug-drug interactions. The CYP3A4 isoform is inhibited by antifungal imidazoles or triazoles, which form low spin heme iron complexes via formation of a nitrogen-ferric iron coordinate bond. However, CYP3A4 also slowly oxidizes the antifungal itraconazole (ITZ) at a site that is ∼ 25 Å from the triazole nitrogens, suggesting that large antifungal azoles can adopt multiple orientations within the CYP3A4 active site. Here, we report a surface plasmon resonance (SPR) analysis with kinetic resolution of two binding modes of ITZ, and the related drug ketoconazole (KTZ). SPR reveals a very slow off-rate for one binding orientation. Multiphasic binding kinetics are observed and one of the two binding components resolved by curve-fitting exhibits 'equilibrium overshoot'. Pre-loading of CYP3A4 with the heme ligand imidazole abolishes this component of the antifungal azole binding trajectories, and it eliminates the conspicuously slow off-rate. The fractional populations of CYP3A4 complexes corresponding to different drug orientations can be manipulated by altering the duration of the pulse of drug exposure. UV-vis difference absorbance titrations yield low spin spectra and K D values that are consistent with the high affinity complex resolved by SPR. These results demonstrate that ITZ and KTZ bind in multiple orientations, including a catalytically productive mode and a slowly-dissociating inhibitory mode. Most importantly, they provide the first example of an SPR-based method for the kinetic characterization of drug binding to any human CYP, including mechanistic insight not available from other methods. Keywords protein-ligand interactions; tight binding inhibitors; drug metabolism; drug interactionsThe hepatic and intestinal heme-containing Cytochrome P450s (CYPs) 1 oxidize most drugs, and thus play a critical role in their metabolism and disposition [1][2][3]. Among the various human CYP isoforms, CYP3A4 contributes most to drug metabolism. CYP3A4 exhibits complex allosteric kinetics, which may result from drug-drug interactions on a single CYP molecule through multiple drug binding, as suggested by steady state kinetic behavior [4][5][6], large active sites observed in crystal structures [7][8][9][10] and spectroscopic studies [11]. Complex kinetics † This work was supported by NIH grants GM32165 (WMA, NI, KLK) and GM07750 (JTP). * Corresponding author: Tel: (206) FAX: (206) [12][13][14][15], and equilibrium optical titrations that rely on the inhibitor-or substrate-dependent changes in ferric spin state equilibrium [16][17][18]. The complexity of CYP kinetics severely impedes prediction of drug clearance and drug-drug interactions [12][13][14][15]19]. Clearly, new methods are required to elucidate the molecular basis of CYP allosterism and complex inhibitor or substrate binding.The antifungal azoles, including ketoconazole (KTZ) and itraconazole (ITZ), historically have been considered to be potent inh...

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