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. 2023 Mar 10;6(4):614-632.
doi: 10.1021/acsptsci.3c00003. eCollection 2023 Apr 14.

Discovery of a High-Affinity Fluoromethyl Analog of [11C]5-Cyano- N-(4-(4-methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide ([11C]CPPC) and Their Comparison in Mouse and Monkey as Colony-Stimulating Factor 1 Receptor Positron Emission Tomography Radioligands

Stefano Altomonte  1 , Xuefeng Yan  1 , Cheryl L Morse  1 , Jeih-San Liow  1 , Madeline D Jenkins  1 , Jose A Montero Santamaria  1 , Sami S Zoghbi  1 , Robert B Innis  1 , Victor W Pike  1
Affiliations

Discovery of a High-Affinity Fluoromethyl Analog of [11C]5-Cyano- N-(4-(4-methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl)furan-2-carboxamide ([11C]CPPC) and Their Comparison in Mouse and Monkey as Colony-Stimulating Factor 1 Receptor Positron Emission Tomography Radioligands

Stefano Altomonte et al. ACS Pharmacol Transl Sci. .

Abstract

[11C]CPPC has been advocated as a radioligand for colony-stimulating factor 1 receptor (CSF1R) with the potential for imaging neuroinflammation in human subjects with positron emission tomography (PET). This study sought to prepare fluoro analogs of CPPC with higher affinity to provide the potential for labeling with longer-lived fluorine-18 (t 1/2 = 109.8 min) and for delivery of higher CSF1R-specific PET signal in vivo. Seven fluorine-containing analogs of CPPC were prepared and four were found to have high inhibitory potency (IC50 in low to sub-nM range) and selectivity at CSF1R comparable with CPPC itself. One of these, a 4-fluoromethyl analog (Psa374), was investigated more deeply by labeling with carbon-11 (t 1/2 = 20.4 min) for PET studies in mouse and monkey. [11C]Psa374 showed high peak uptake in monkey brain but not in mouse brain. Pharmacological challenges revealed no CSF1R-specific binding in either species at baseline. [11C]CPPC also failed to show specific binding at baseline. Moreover, both [11C]Psa374 and [11C]CPPC showed brain efflux transporter substrate behavior in both species in vivo, although Psa374 did not show liability toward human efflux transporters in vitro. Further development of [11C]Psa374 in non-human primate models of neuroinflammation with demonstration of CSF1R-specific binding would be required to warrant the fluorine-18 labeling of Psa374 with a view to possible application in human subjects.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Some previously reported candidate radioligands for PET imaging of brain CSF1R.
Scheme 1
Scheme 1. Synthesis of CSF1R Ligands 8a–8g, Psa374, and CPPC
Reagents and conditions: (a) EtOH, 0 °C for 1 h, then rt for 16 h, (b) 140 °C, 16 h, (c) H2 (70 psi), Pd/C 10%, MeOH, rt, 16 h, (d) HATU, DIPEA, DMF, rt, 16 h.
Scheme 2
Scheme 2. Synthesis of Secondary Amine Precursors for Radiolabeling
Reagents and conditions: (a) tert-butyl piperazine-1-carboxylate, K2CO3, 130 °C, 16 h, (b) H2 (70 psi), Pd/C 10%, MeOH, rt, 16 h, (c) HATU, DIPEA, DMF, rt, 16 h, (d) 1. TFA, DCM, rt; 2. aq. NaHCO3.
Scheme 3
Scheme 3. Radiosyntheses of Radioligands [11C]CPPC, [11C]Psa374, [11C]8e, and [11C]8g
Figure 2
Figure 2
Ex vivo reverse-phase HPLC analysis of radioactivity in plasma (panel A) and brain (panel B) at 30 min after intravenous injection of [11C]Psa374 into a rat. See Experimental Section for HPLC conditions.
Figure 3
Figure 3
Whole brain time–activity curves from PET in wild-type and dual P-gp and BCRP knockout mice after intravenous injection of [11C]CPPC (panel A) or [11C]Psa374 (panel B) at baseline and after homologous treatments. Error bars are mean ± SD and within symbol size if not shown.
Figure 4
Figure 4
Time–activity curves in the brain after intravenous injection of [11C]8e (panel A), [11C]8g (panel B), [11C]CPPC (panel C), and [11C]Psa374 (panel D) into monkey at baseline and after treatment with CPPC or Psa374. Solid lines show fits of the data to a 2-tissue compartmental model. Error bars are SD values for n ≥ 3 or half range for n = 2 and are within symbol size if not shown.
Figure 5
Figure 5
Time–activity data fitted (solid lines) using the two-tissue compartmental model in monkey brain for [11C]CPPC (panel A) and [11C]Psa374 (panel B) at baseline and after partial blocking of efflux transporters with elacridar (3 mg/kg, i.v.). For each radioligand, the same monkey was used in the baseline and blocking experiment in 1 day (n = 1).
Figure 6
Figure 6
Reverse-phase HPLC analysis of radioactivity in monkey plasma at 30 min after intravenous injection of [11C]CPPC (panel A) and [11C]Psa374 (panel B). See Experimental Section for HPLC conditions.
Figure 7
Figure 7
Whole brain VT (panel A) and VT/fP (panel B) values for [11C]CPPC and [11C]Psa374 in monkeys at baseline (n = 3 for [11C]Psa374 and n = 2 for [11C]CPPC) and after intravenous pharmacological challenge with either CPPC (n = 2 for [11C]Psa374 and n = 1 for [11C]CPPC) or Psa374 (n = 1). Error bars are mean ± SD for n > 2, and mean ± half of the range for n = 2. See Tables S7 and S8 for respective VT and VT/fP values for individual brain regions.
Figure 8
Figure 8
Parametric images of one monkey brain derived from Logan plots at baseline and after self-block at 4 mg/kg (i.v.) for [11C]CPPC (panel A) and [11C]Psa374 (panel B). VT values for these images were derived from Logan plots. Left images are coronal, middle are sagittal, and right are horizontal.
Figure 9
Figure 9
Monkey whole brain VT (panel A, n = 1) and VT/fP values (panel B, n = 1) for [11C]CPPC and [11C]Psa374 in monkeys at baseline and after challenge with elacridar. See Tables S9 and S10 for respective VT and VT/fP values for individual brain regions.
Figure 10
Figure 10
Parametric images of monkey brain at baseline and after intravenous administration of elacridar at 3 mg/kg for [11C]CPPC (panel A) and [11C]Psa374 (panel B). VT values for these images were derived from Logan plots. Left images are coronal, middle are sagittal, and right are horizontal.
See this image and copyright information in PMC

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