A neutral lipid envelope-type nanoparticle composed of a pH-activated and vitamin E-scaffold lipid-like material as a platform for a gene carrier targeting renal cell carcinoma

Purpose: Cationic gene carriers can mediate cellular uptake but often show poor post-nuclear transcription/translation, toxicity, and aggregation in blood. The study aimed to develop a systemically applicable, tumor-targeting gene carrier that is neutral in blood/cytosol but becomes cationic in endosomes for endosomal escape, using a pH-activated, vitamin E-scaffold lipid-like material.

Hypothesis: If LNPs are formulated with ssPalmE — a vitamin E-scaffolded, pH-activated, disulfide-cleavable lipid-like material — then they will remain neutral and stable in circulation, accumulate in tumors via the EPR effect, escape endosomes, decapsulate pDNA in the cytosol, and produce tumor-specific transgene expression and anti-tumor activity in renal cell carcinoma.

Aims: Prepare and characterize neutral lipid envelope-type nanoparticles using the second-generation ssPalm with vitamin E scaffold (ssPalmE), comparing it with ssPalmM and ssPalmA. - Optimize PEG lipid length/density for blood circulation and tumor accumulation. - Evaluate intratumoral pDNA delivery, transgene expression, and tumor specificity in an OS-RC-2 renal cell carcinoma mouse model. - Test therapeutic efficacy of pDNA encoding sFlt-1 and assess anti-angiogenic effects.

Delivery system: Platform: Neutral lipid envelope-type nanoparticle (LNP) with a pDNA/protamine core. - Key material: ssPalmE, containing vitamin E (α-tocopherol succinate) as a hydrophobic scaffold, tertiary amines for pH-activated endosomal escape, and a disulfide bond cleavable in the cytosol. - Helper lipids: SOPC or SOPE plus cholesterol. - PEG lipids: DMG-PEG2000 and DSG-PEG2000/DSG-PEG5000. - Optimized formulation: ssPalmE/SOPC/Chol (3/4/3) + 3 mol% DMG-PEG2000 + 5 mol% DSG-PEG5000. - Payload: pDNA encoding luciferase or sFlt-1; CpG-free pDNA was used for improved expression. - Targeting mechanism: Passive tumor accumulation via EPR; no active targeting ligand reported.

Approach: Cell line/model: OS-RC-2 renal cell carcinoma cells; BALB/cApl-nu/nu mice bearing OS-RC-2 tumors. - Administration: Intravenous tail-vein injection. - Doses: 40 µg pDNA/mouse for pharmacokinetics, biodistribution, and luciferase expression; 37.5 µg pDNA/mouse for anti-tumor and RT-PCR studies. - Groups: PBS, LNPssPalmM, LNPssPalmA, LNPssPalmE; encapsulated luciferase or sFlt-1; n = 6 for anti-tumor study, triplicate for some assays. - Disease context: Renal cell carcinoma; anti-angiogenic gene therapy.

Key methods: DLS/Zetasizer for size, PDI, and ζ-potential. - [³H]CHE lipid labeling for blood pharmacokinetics. - Real-time PCR for intratumoral pDNA copy number. - Luciferase activity assay and IVIS imaging for transgene expression. - RT-PCR for sFlt-1 mRNA expression. - FTC-GSI-B4 staining for tumor vasculature area. - Tumor volume and body weight monitoring for anti-tumor effect.

Key results: Optimized LNPssPalmE had ~133 nm size, PDI ~0.16, and ζ-potential ~ −6.5 mV. - DSG-PEG5000 modification prolonged blood circulation; 5 mol% was optimal, while 10 mol% did not further improve circulation. - Intratumoral pDNA copy numbers at 24 and 48 h were comparable among ssPalmM, ssPalmA, and ssPalmE. - LNPssPalmE with 5 mol% DSG-PEG5000 showed significantly higher tumor gene expression than LNPssPalmM, with hepatic expression reduced to background. - CpG-free pDNA increased tumor gene expression by about one order of magnitude versus conventional pDNA containing 332 CpG motifs. - LNPssPalmE encapsulating pCpGfree-sFlt-1(0) suppressed tumor growth; anti-tumor effect was significantly higher than LNPssPalmM. - sFlt-1 mRNA was detected in all three treated mice; tumor vascular area was significantly lower than PBS controls (p < 0.05). - No decrease in body weight was observed.

Interpretation: The authors conclude that PEG-modified LNPssPalmE is a promising gene carrier for tumor-targeted RCC therapy. They propose that the therapeutic effect comes from both the expressed sFlt-1 and the intrinsic anti-tumor/apoptotic activity of α-tocopherol succinate generated from ssPalmE degradation, acting synergistically.

Limitations: Only one RCC tumor model (OS-RC-2) was used. - Anti-tumor study followed tumor volume for 10 days; no long-term survival data. - No large-animal validation. - The intrinsic anti-tumor contribution of ssPalmE is proposed but not fully dissected mechanistically. - Optimal PEG density and formulation were identified empirically; broader generalizability remains to be tested.