Review Papers Against Their Own Results

Quick verdict

The 2025 Pharmaceutics review Recent Advances in the Development of Pro-PROTAC for Selective Protein Degradation (DOI 10.3390/pharmaceutics17091160) summarizes and organizes emerging prodrug strategies for PROTACs (photocaging/opto-PROTAC, enzyme/ROS/hypoxia activation, in cell click/CLIPTAC, folate targeting, polymer/nanoparticle delivery and Poly-PROTAC/SPNpro). It is a comprehensive, up-to-date synthesis (searches to 1 April 2025) that highlights both promising selective-activation chemistries and clear translational gaps (limited in vivo validation, PK/PKD concerns, activation depth and off-target promoiety toxicity) Pro-PROTAC review (Pharmaceutics)

Detailed review and critique

Paper identity and scope

The paper Recent Advances in the Development of Pro-PROTAC for Selective Protein Degradation (Pharmaceutics, published 4 September 2025; DOI 10.3390/pharmaceutics17091160) is a focused literature review (Reaxys searches to 1 April 2025) that compiles pro-PROTAC strategies designed to confer cell or tissue selectivity or controlled activation to heterobifunctional degraders (PROTACs) Pro-PROTAC review (Pharmaceutics)

What the review does well

• Comprehensive taxonomy: organizes pro-PROTACs by activation trigger (light, ROS, hypoxia, enzymes, bioorthogonal in-cell assembly) and by delivery strategy (folate targeting, polymeric nanoparticles/Poly-PROTAC, SPNpro) Pro-PROTAC taxonomy and examples
• Concrete, literature-grounded examples: cites specific constructs (e.g., DMNB/DEACM/NPOM photocages on glutarimide or hydroxyproline VHL motifs; aryl boronic acid boronate cages for ROS activation of lenalidomide or VHL ligands; NTR or nitroimidazole hypoxia triggers; CLIPTAC tetrazine-TCO systems; Poly-PROTAC RAFT polymers and SPNpro) with mechanistic descriptions and reported model systems (cells, zebrafish, mice) Representative pro-PROTAC examples
• Balanced discussion of translational barriers: recognizes synthesis complexity, increased molecular weight and lipophilicity, potential pharmacokinetic liabilities, activation depth constraints (UV vs NIR), and unknown toxicity of promoieties and metabolites Translational limitations

Key weaknesses and blindspots

1. Limited primary-data critique and quantitative comparison — the review summarizes many designs but stops short of extracting or tabulating comparative quantitative metrics (DC50/DC90, degradation kinetics, in vivo exposure, tumor:plasma ratios) across studies that would let readers compare activation efficiency and selectivity systematically. This undermines the ability to prioritize approaches for translation Lack of harmonized quantitative metrics
2. Under-addressed safety assessment of promoieties — while the authors note promoiety toxicity as a limitation, the review would be stronger with a structured assessment (known reactive metabolites, immunogenicity risks, off-target enzymatic cleavage) and recommended preclinical assays to screen promoiety liabilities Promoiety toxicity noted but underdeveloped
3. Clinical feasibility and manufacturability gaps — the review mentions synthetic complexity and low yields but does not estimate scale-up feasibility, costs, or outline synthetic strategies likely to be compatible with GMP and medicinal chemistry optimization for clinic-ready pro-PROTACs Manufacturing and scale-up concerns
4. Bias toward cancer microenvironment cues — the review focuses largely on tumor-selective activation (ROS, hypoxia, enzymes, folate receptors) but gives less attention to other disease contexts (neurology, fibrosis, immune diseases) where pro-PROTACs could be valuable and where activation cues differ; this risks overgeneralizing tumor findings to other fields without evidence Cancer focus and limited nononcology scope

Concrete, evidence-based recommendations

• Provide a harmonized performance table: extract DC50/EC50, activation half-life, fold tumor selectivity, in vivo tumor:plasma ratios and reported toxicities from each primary study and display as sortable datatable (this would materially increase the review utility).
• Systematic promoiety risk matrix: categorize common cages/linkers (DMNB, DEACM, NPOM, aryl boronates, nitroimidazoles, disulfides, MAC self-immolative linkers) by predicted metabolite reactivity, propensity for immunogenic hapten formation, and recommended in vitro assays (hepatocyte metabolism, Ames, cytokine release in PBMCs) before in vivo studies.
• Early PK/PD frameworks: recommend standardizing brief PK/PD paradigms (single-dose activation kinetics, active PROTAC plasma vs tumor concentration over time, target engagement via degradation assay and downstream functional readouts) to allow cross-study comparison.
• Assessment of activation depth: for photochemical systems prioritize NIR-cleavable cages or two-photon activation chemistry and provide experimental penetration-depth data (mouse skin vs internal organs) and genotoxicity assays for repeated activation regimes.

Where the field should go next

Top priorities for the pro-PROTAC field are (i) head-to-head in vivo performance benchmarking across common POIs and activation modalities, (ii) systematic toxicity profiling of promoieties and nano-formulations, (iii) improved activation chemistries compatible with deep tissue (NIR/biorthogonal enzyme triggers) and (iv) early GMP-aware synthetic route optimization (shorter sequences, convergent assembly, stable intermediates) to reduce translational friction Field priorities from review

Confidence and falsifiability note

The central conclusions (pro-PROTACs are promising but translationally immature) rest on collated published examples and the review authors assessment; this judgement would be falsified if rigorous in vivo studies show poor selectivity or if promoieties consistently produce unacceptable toxicity in preclinical GLP studies — both outcomes are plausible and must be tested experimentally Falsifiability and caveats

Methods appraisal

The methods are appropriate for a literature review: two Reaxys searches gave coverage to April 1 2025 and the authors screened titles/abstracts; chemical depictions used ACD Chemsketch. Limitations of a review format apply: no new experiments or meta-analysis were performed, and selection/positive-result publication biases in primary literature could inflate perceived success rates of activation strategies Review methods described

Useful figures and data I would add

• Datatable comparing activation modality, trigger, POI, cell models, in vivo models, DC50/Dmax, activation fold selectivity, and reported toxicity (unique id proprotac_table_1).
• Plotly scatter: tumor selectivity (fold) versus activation depth (qualitative scale: surface, shallow organ, deep organ) to visualize which modalities are promising for internal tumors (unique id proprotac_graph_1).