| NHP |
(Kroth et al. 2019, PMID 31264169) Nonradioactive test compound(s) ranging from 0.61 nM to 1000 nM Bavarostat: (Strebl, 2017 #475) HDAC6 A tracer mass will cause a maximal receptor occupancy of 1-5%. | ||||
|---|---|---|---|---|---|
| Specific activity (fixed) Specific activity can be convertd to molarity if we know MW (https://www.perkinelmer.com/lab-products-and-services/application-support-knowledgebase/radiometric/radiochemical-calculations.html#Radiochemicalcalculations-Molarityofacarrer-freeradionuclide) | If dose | Then Activity | Receptor occupancy | ||
| 11C raclopride (Yao 2012) | Mice | 0.3 MBq | 1% | ||
| rat | 5.2 MBq | 1% | |||
| 11C raclopride (Kung 2005) | 1,000 Ci/mmol (1 uCi=1 pmol) | human | 10 mCi | <1% | |
| a high-affinity brain ligand (Kd 0.1 nM), (Lancelot 2010) | mice | ~5 nmol/kg | 0.1 MBq (=2.7 uCi) | 1% | |
| HDAC6 | Cyno) | 3.8 mCi/4.9kg | |||
| 11C CFT (Kung 2005) | Human | 459 mCi/70kg | <1% | ||
| mouse | 130 uCi/25g | <1% | |||
| rat | 2 mCi/300g | <1% | |||
| Paul McQuade | mouse | 100 uCi (=25 ng/25g?) | |||
(usually 11C or 18F)
Preclinical study
| Baseline scan (tracer 봄) | Blocking (pretreatment) scan (약의 특성을 봄) | |
|---|---|---|
| Radioligand only |
- Radioligand + drug candidate (two doses) (mice 의 TO study와 마찬가지로 drug dose 를 변화시키면서 ligand 후보 molecule 의 dose 는 고정) - Two animals each | |
| deliverables | Brain penetrability, Regional distribution (of ligand) | Target occupancy (blocking) of drug canditate, quantitative relationship between drug plasma exposure and target occupancy |
| Cost | 20210120 Paul: $250K | |
| example | Takeda HDAC6 [18F]EKZ-001 ([18F]Bavarostat), 2020 cELEN | (fig5) EKZ-317 achieves higher target occupancy than ACY-775 EKZ-317 achieved full HDAC6 occupancy at 2 mg/kg and greater than 90% occupancy at 0.1 mg/kg, demonstrating a higher level of target engagement than ACY-775 in brain |
In vivo PET imaging to assess regional distribution and blocking by drug candidate
- Once candidate has been selected and radiolabeled, next step in development process is to conduct baseline scan in NHP to validate that the compound shows brain penetrability and that regional uptake matches known distribution
Structure of [18F]MNI-1054
[18F]MNI-1054 Fused MRI/PET
Selected TACs
- [18F]MNI-1054 identified as potential LSD-1 targeting PET ligand whose regional brain distribution in NHP correlated with LSD-1 expression levels
In vivo PET imaging to assess regional distribution and blocking by drug candidate
- Establish quantitative relationship between drug plasma exposure and target occupancy in NHP via PET tracer
Compound 1
Compound 2
- Blocking studies performed using structurally diverse compounds
- Correlation between plasma levels of drug candidates and target occupancy
Clinical study
| Baseline scan (tracer를 봄) | Blocking (pretreatment) scan (약의 특성을 봄) | |
|---|---|---|
| Radioligand only |
- Radioligand + drug candidate (several doses to cover the expected occupancy range) - Several subjects for each dose | |
| Objective (2014 Honer) |
Typically, examination of regional tissue time-activity curves (TAC) from a minimum of two subjects will allow one to determine:• whether the ligand enters the brain (ideally with peak brain uptake occurring approximately coincident with the peak activity in the plasma); whether distribution is consistent with the known distribution of the target (based on post-mortem data); whether the kinetic profile is consistent with an appropriate balance between specific and nonspecific binding, and an absence of radiolabelled metabolites amuleg the brain (i.e. a clear uptake and washout phase, as opposed to continuing accumulation); if it is susceptible to any unwanted defluorination (for 18F labelled tracers) |
ii) to evaluate in vivo selectivity and iii) to assess possible reference regions This is important because the collection of arterial blood samples and construction of a metabolite-corrected blood curve is invasive and technically demanding; repeatability is limited and measurement and processing of metabolite data is often the weakest link in the analysis chain. So being able to replace the arterial input curve by an indirect input curve derived from an area of the brain with little or no target binding in which the radiotracer kinetics represent the free and nonspecific contribution to the signal in the target region(s) is highly desirable. |
| − |
- Kinetics, - Regional distribution - Test-retest reproducibility |
- Drug's occupancy : was calculated as the percent change of the binding specific to PDE10A (Vs) total distribution volume (VT), (which was calculated as the VT of the putamen minus the VT of the cerebellum.) |
| − | - 그런데, Patient or HE 꼭 포함되어야 하나? |
Multiple timepoints 를 하면, TO의 TIME course (ie TO Kinetics)를 알아서, dosing regimen 정하는데 도울수 있음. In general, HV are appropriate for human PET occupancy studies. Dose-PK-TO (of drug canditate) (occupancy study), js: if the test drug and the radioligand do not bind the same site, this study cannot be done. : so 'the range of doses' can be deduced for dose ranging study - Time course for target interaction in CNS can be different from plasma pharmacokinetics e! |
| deliverables | Regional distribution (of ligand ie the target protein, not drug!), (js: so this study is not called 'biodistribution study') | |
| timing | 이게 clinical validation study 겠군, 그런데 1b with patient cohort 에서 clinical blocking study 를 하려면, IND review 중에 (혹은 적어도 SAD) 까지는 이 baseline scan 도 되어야 할텐데. 약없이 HV & AD 에서 해야 할텐데, (SAD는 PK불확실하니 좀 그렇더라도), MAD에서 할 수 있을 것 같은데? |
Phase 1 MAD에서 환자 cohort 써서 할 수 있겠군. (cf: 2상에서는 confirm dose 함) Logic: Desired occupancy (eg. >80%) is defined from preclinical study, & Toxicity is defined (below vertical line) → From human TO study, the therapeutic index (below gray area) can be estimated Principle] assuming that the in vitro and in vivo KD are equivalent. Calculation of the tissue 'free' concentration from the total tissue concentration is typically not feasible from PET data alone. 항상 X축은 plasma concentration! - Target occupancy = O = Cfree plasma / (Cfree plasma + KD) - when a reference region exists, BPND is the outcome measure. (2016 Takano) - (2016 Takano) when a reference region don't exists: VT is the outcome measure. → However, VT consists of a specifically bound part (VS) and a nondisplacable part (VND), which means that occupancy not directly proportional to the change in VT. There are several methods to estimate VND, for example, the method proposed by Lassen et al. [13] in which VND is derived from the various VT values obtainpeted in a PET occupancy study. Although this Occ (%) = 100 × (BPNDbaseline − BPNDdrug) / BPNDbaseline method is easy to apply, it is important to check whether the underlying assumptions of identical occupancy levels and VND values across the brain are still valid for the study. Studies typically use 3-5 single doses of drug candidate, 3-4 time points per dose level (baseline and 2-3 postdose time points), and 2-4 subjects per dose level. Typically in HV. (book: translational medicine in CNS drug development) |
| example | [18F]MK-6240 |
FIH (NCT02562989): 1) assess safety and tolerability; 2) determine radiation safety profile; 3) determine optimal imaging protocol parameters for quantification of brain NFTs in AD; 4) compare tracer binding in brain PET scans from AD patients, MCI participants, and healthy elderly participants; and 5) evaluate intra-subject test-retest variability of tracer uptake in brain regions of interest. (→ 그런데 이 연구의 결과인 (Lohith, 2019 #1627)보면 test-retest 안 했다고 함. - Part 1: healthy young participants - Part 2: healthy elderly, AD, MCI patients Enpoints: AE, Effective dose of tracer (from healthy young), SUVR, t-rt variability |
| PDE10 (Takano et al. 2016, …) | - HV | |
| [18F]EKZ-001 ([18F]Bavarostat), 2020 Koole: The primary objectives of this open-label phase 1 study were threefold (cohorts A, B, and C). - In cohort A, we estimated biodistribution … | my book: |
Uncertain Spans
- “amuleg the brain” — Objective (2014 Honer) 셀의 ‘absence of radiolabelled metabolites amuleg the brain’ 구문에서 ‘amuleg’가 OCR/시각 모두 모호. ‘among’ 또는 ‘all the’ 등 후보가 있을 수 있으나 글자 그대로 전사.
- “EKZ-317 achieves higher target occupancy than ACY-775 / 90% occupancy at 0.1 mg/kg” — 사진의 작은 글자 부분에서 ‘0.1’ 또는 ‘01’ 모호. 시각적으로 0.1로 판단해 전사.
- “Cyno)” — ‘Dose of PET tracer’ 표 species 셀이 ‘Cyno)’ 닫는 괄호만 보임. 이전 페이지 (184816)와 동일한 source 텍스트로 추정.
- “[18F]EKZ-001 ([18F]Bavarostat), 2020 cELEN” — Preclinical study example 셀의 저자 부분 ‘cELEN’ 또는 ‘eLEN’ 모호. OCR ‘cELEN’ 그대로 전사.
- 하단 example 행 [18F]EKZ-001 ([18F]Bavarostat), 2020 Koole 셀 — ‘In cohort A, we estimated biodistribution …’까지만 보이며 나머지는 photo 잘림으로 미가시.