The permeability-glycoprotein (P-gp) efflux transporter is densely expressed at the blood-brain barrier (BBB) and its resultant ‘spare capacity’ requires substantial blockade to increase the uptake of avid substrates. This has blunted the ability of investigators to measure clinically meaningful alterations in P-gp function. This study, conducted in humans, examined two P-gp inhibitors (tariquidar, a known inhibitor, and disulfiram, a putative inhibitor) and two routes of administration (intravenous and oral) to maximally increase brain uptake of the avid and selective P-gp substrate 11C-desmethyl-loperamide (dLop), while avoiding side effects associated with high doses of tariquidar. Methods Forty-two 11C-dLop positron emission tomography (PET) scans were obtained from 37 healthy volunteers. PET was performed with 11C-dLop under five conditions: 1) injected under baseline conditions without P-gp inhibition; 2) injected one hour after IV tariquidar infusion; 3) injected during IV tariquidar infusion; 4) injected after oral tariquidar; and 5) injected after disulfiram. 11C-dLop uptake was quantified with kinetic modeling using metabolite-corrected arterial input function or by measuring the area under the time-activity curve in brain from 10 to 30 minutes. Results Neither oral tariquidar nor oral disulfiram increased brain uptake of 11C-dLop. Injecting 11C-dLop during tariquidar infusion, when plasma tariquidar concentrations reach their peak, resulted in brain uptake of radioligand approximately five-fold greater than baseline. Brain uptake was similar with 2 and 4 mg/kg IV tariquidar; however, the lower dose was better tolerated. Injecting 11C-dLop after tariquidar infusion also increased brain uptake, though higher doses (up to 6 mg/kg) were required. Brain uptake of 11C-dLop increased fairly linearly with increasing plasma tariquidar concentrations, but we are uncertain whether maximal uptake was achieved. Conclusion We sought to increase the dynamic range of P-gp function measured after blockade. Performing 11C-dLop PET during peak plasma concentrations of tariquidar, achieved with concurrent administration of IV tariquidar, resulted in greater P-gp inhibition at the human BBB than delayed administration, and allowed use of a lower, more tolerable dose of tariquidar. Based on prior monkey studies, we suspect that plasma concentrations of tariquidar did not fully block P-gp; however, higher doses of tariquidar would likely be associated with unacceptable side effects.

We sought to develop a PET radioligand that would be useful for imaging human brain metabotropic subtype 1 receptors (mGluR1) in neuropsychiatric disorders and in drug development. 4-Fluoro-N-methyl-N-(4-(6-(methylamino)pyrimidin-4-yl)thiazol-2-yl)benzamide (FIMX, 11) was identified as having favorable properties for development as a PET radioligand. We developed a method for preparing [18F]11 in useful radiochemical yield and in high specific activity from [18F]fluoride ion and an N-Boc-protected (phenyl)aryliodonium salt precursor (15). In baseline experiments in rhesus monkey, [18F]11 gave high brain radioactivity uptake reflecting the expected distribution of mGluR1 with notably high uptake in cerebellum which became 47% lower by 120 min after radioligand injection. Pharmacological challenges demonstrated a very high proportion of the radioactivity in monkey brain to be bound specifically and reversibly to mGluR1. [18F]11 is concluded to be an effective PET radioligand for imaging mGluR1 in monkey brain and therefore merits further evaluation in human subjects.

The hormone prolactin (PRL) and its receptor (hPRLr) are significantly involved in breast cancer pathogenesis. The intermediate hPRLr (hPRLrI) is an alternatively-spliced isoform, capable of stimulating cellular viability and proliferation. An analogous truncated mouse PRLr (mPRLr) was recently found to be oncogenic when co-expressed with wild-type mPRLr. The goal of this study was to determine if a similar transforming event occurs with the hPRLr in human breast epithelial cells and to better understand the mechanism behind such transformation. hPRLrL+I co-expression in MCF10AT cells resulted in robust in vivo and in vitro transformation, while hPRLrI knock-down in MCF7 cells significantly decreased in vitro malignant potential. hPRLrL+I heterodimers displayed greater stability than hPRLrL homodimers, and while being capable of activating Jak2, Ras, and MAPK, they were unable to induce Stat5a tyrosine phosphorylation. Both immunohistochemical breast cancer tissue microarray data and RNA sequencing analyses using The Cancer Genome Atlas (TCGA) identified that higher hPRLrI expression associates with triple-negative breast cancer. These studies indicate the hPRLrI, when expressed alongside hPRLrL, participates in mammary transformation, and represents a novel oncogenic mechanism.

Introduction Metabotropic glutamate subtype receptor 1 (mGluR1) is implicated in several neuropsychiatric disorders and is a target for drug development. [18F]FIMX ([18F]4-fluoro-N-methyl-N-(4-(6-(methylamino)pyrimidin-4-yl)thiazol-2-yl)benzamide) is an effective radioligand for imaging brain mGluR1 with PET. A similarly effective radioligand with a shorter half-life would usefully allow PET studies of mGluR1 at baseline and after pharmacological or other challenge on the same day. Here we describe the preparation of [11C]FIMX for evaluation in monkey with PET. Methods [11C]FIMX was prepared via Pd-promoted carbonylation of 1-fluoro-4-iodobenzene with [11C]carbon monoxide, aminolysis of the [11C]acyl-palladium complex with the requisite Boc-protected amine, and deprotection with HCl in THF. PET scans of [11C]FIMX injected into a monkey were performed at baseline and after preblock of mGluR1 with measurement of the arterial input function. Results The radiosynthesis required 42 min and gave [11C]FIMX in about 5% overall decay-corrected radiochemical yield and with a specific activity of about 100 GBq/μmol. PET in rhesus monkey at baseline showed that radioactivity peaked high in receptor-rich cerebellum and much lower in receptor-poor occipital cortex. Radioactivity in cerebellum declined to 32% of peak at 85 min. VT at baseline appeared stable in all brain regions after 60 min. Under mGluR1 pre-blocked condition, radioactivity uptake in all regions declined more rapidly to a low level. Receptor pre-block reduced VT from 13.0 to 1.5 in cerebellum and from 2.9 to 1.4 in occipital cortex. Conclusion [11C]FIMX is an effective radioligand for imaging mGluR1 in monkey with PET.