Bispecific T-cell Engager (BiTE) Immunotherapy of Ovarian Cancer Based on MIL-88A MOF/MC Gene Delivery System

Component: MOF Nanoparticles; Description: MIL-88A (Fe-based MOF) — FeCl₃ + fumaric acid; synthesized via microwave-assisted hydrothermal method (100°C, 1 h); spindle-shaped, ~300 nm length × ~100 nm width (DLS: 187.8 nm average)

Component: Surface Charge; Description: Positively charged: +24.7 mV (in water)

Component: Degradation; Description: pH-dependent; faster degradation at pH 4.0 vs. pH 7.0; biocompatible (no cytotoxicity in 293T cells up to 100 mg/L)

Component: Genetic Payload; Description: Minicircle DNA (MC) — enhanced non-viral vector lacking bacterial backbone; smaller size, higher transgene efficiency, reduced immunogenicity

Component: Therapeutic Gene; Description: MC.BiTE — encodes anti-CD3/anti-EpCAM bispecific T-cell engager; contains eukaryotic secretion signal (N-terminal), scFv domains (anti-CD3 + anti-EpCAM) linked by (G₄S) linker, 6× His-tag (C-terminal)

Component: Reporter Gene; Description: MC.luc — encodes firefly luciferase (for transfection efficiency studies)

Component: Loading Mechanism; Description: • Electrostatic interactions (positive MOF + negative DNA)<br>• Metal-phosphate bonds (Fe—O—P coordination) confirmed by XPS (red shift in Fe 2p peaks)

Component: Loading Capacity; Description: Complete DNA binding at MOF/MC mass ratio of 50:1

Component: Zeta Potential After Loading; Description: -9.16 mV (MOF/MC complex)

Component: Cell Line; Description: SKOV3 (human ovarian cancer), SKOV3-luc (luciferase-transfected), 293T, human PBMC-derived T cells

Component: Mouse Model; Description: NOD/SCID mice (immune-deficient; lacks T, B, NK cells); intraperitoneal SKOV3-luc xenograft

Component: Administration Route; Description: Intraperitoneal (i.p.) — preferred for local BiTE expression in peritoneal cavity

Parameter: In Vivo Transfection Study; Details: BALB/c mice; MOF/MC.luc (20 μg MC, MOF amounts 0.25-2 mg); routes: i.p., i.v., i.m., s.c.; IVIS imaging at various time points; organs harvested at 24 h for biodistribution

Parameter: In Vitro BiTE Characterization; Details: • Binding specificity: SKOV3 (EpCAM⁺) and human T cells (CD3⁺) incubated with BiTE (0-10 μg/mL); His-tag APC antibody detection by flow cytometry<br>• Cytotoxicity: SKOV3 + T cells at varying E:T ratios (1:1 to 20:1); BiTE concentrations (0.01-10 ng/mL); LDH release assay; cytokine ELISA (IL-2, TNF-α, IFN-γ, granzyme B)

Parameter: In Vivo Therapy Study; Details: NOD/SCID mice; i.p. injection of 5×10⁶ SKOV3-luc cells (day -7); treatment started day 0 (day 8 post-tumor engraftment)

Parameter: Treatment Groups; Details: • PBS control (n=5)<br>• T cells only (1×10⁷ human T cells, i.p., twice weekly)<br>• MOF/MC.BiTE + T cells (1 mg MOF + 20 μg MC.BiTE i.p., followed by T cells twice weekly)<br>• Additional controls: MOF alone, MOF/MC (no T cells)

Parameter: Treatment Schedule; Details: Two cycles: day 0 and day 6 of therapy; T cells infused twice weekly after each MOF/MC.BiTE dose

Parameter: Efficacy Readouts; Details: • IVIS bioluminescence imaging (tumor burden)<br>• Survival curves<br>• Serum/ascites BiTE concentration (His ELISA)<br>• Immunohistochemistry (anti-CD3 for T cell infiltration)<br>• H&E staining (toxicity)

Parameter: Safety Assessment; Details: Serum biochemistry (ALT, AST, creatinine, urea); H&E of major organs (heart, liver, spleen, lung, kidney) at day 14 post-injection

Parameter: Replicates; Details: n=3 per group (transfection studies); n=5 per group (therapy study)

Analysis Category: MOF Characterization; Methods: • TEM, SEM (morphology)<br>• DLS (size, zeta potential)<br>• Elemental mapping (EDX)<br>• ICP (Fe release, degradation)<br>• TGA (thermal stability, DNA loading)

Analysis Category: DNA Binding Studies; Methods: • Agarose gel electrophoresis (binding at various MOF/MC ratios)<br>• XPS (Fe 2p, O 1s, C 1s chemical states before/after loading)<br>• Zeta potential (surface charge changes)

Analysis Category: In Vivo Imaging; Methods: IVIS Spectrum (Xenogen); luciferase bioluminescence (photons/sec); ROI analysis

Analysis Category: BiTE Detection; Methods: His-tag ELISA kit (serum, ascites)

Analysis Category: Cytotoxicity; Methods: LDH release assay (Promega)

Analysis Category: Cytokine Analysis; Methods: ELISA (IL-2, TNF-α, IFN-γ, granzyme B; RayBiotech)

Analysis Category: Immunohistochemistry; Methods: Anti-CD3 antibody (ab17143); HRP/DAB staining; hematoxylin counterstain

Analysis Category: Safety; Methods: Serum biochemistry (ALT, AST, creatinine, urea); H&E histopathology

Analysis Category: Cell Viability; Methods: CCK-8 assay

Parameter: MOF size (TEM); Result: ~300 nm length × ~100 nm width

Parameter: MOF size (DLS); Result: 187.8 nm

Parameter: Zeta potential (MOF); Result: +24.7 mV

Parameter: Zeta potential (MC); Result: -19.7 mV

Parameter: Zeta potential (MOF/MC); Result: -9.16 mV (electrostatic interaction confirmed)

Parameter: DNA binding; Result: Complete at MOF/MC mass ratio 50:1

Parameter: Degradation; Result: Faster at pH 4.0 vs. pH 7.0; pH-responsive

Parameter: Cytotoxicity (in vitro); Result: No toxicity up to 100 mg/L (293T cells)

Route: Intraperitoneal (i.p.); Naked MC: No signal; MOF/MC: Strong bioluminescence; Effect: MOF enhances transfection

Route: Intravenous (i.v.); Naked MC: No signal; MOF/MC: No signal; Effect: No effect

Route: Intramuscular (i.m.); Naked MC: Strong signal; MOF/MC: Strong signal; Effect: MOF not needed (muscle uptake)

Route: Subcutaneous (s.c.); Naked MC: Weak signal; MOF/MC: Enhanced signal; Effect: MOF improves transfection

Route: i.p. biodistribution; Naked MC: -; MOF/MC: Liver > spleen > intestines > stomach; Effect: No signal in heart/kidney

Route: i.p. duration; Naked MC: -; MOF/MC: Peak at 24 h; baseline by day 5; Effect: -

Parameter: Binding to CD3⁺ T cells; Result: Concentration-dependent (0.1-10 μg/mL)

Parameter: Binding to EpCAM⁺ SKOV3; Result: Concentration-dependent (0.1-10 μg/mL)

Parameter: Optimal BiTE concentration; Result: 1 ng/mL

Parameter: Optimal incubation time; Result: 12 h

Parameter: Optimal E:T ratio; Result: 10:1

Parameter: Cytokine release (1 ng/mL, 12 h); Result: IL-2, TNF-α, IFN-γ, granzyme B significantly increased (P < 0.001)

Parameter: Tumor progression (bioluminescence); PBS Control: Uncontrolled; T Cells Only: Slight control at day 14, then progression; MOF/MC.BiTE + T Cells: Suppressed through day 21

Parameter: Median survival; PBS Control: 26 days; T Cells Only: 30 days; MOF/MC.BiTE + T Cells: 39 days

Parameter: BiTE in serum (peak); PBS Control: N/A; T Cells Only: N/A; MOF/MC.BiTE + T Cells: 77.3 ng/mL (8 h post-transfection)

Parameter: BiTE in ascites (peak); PBS Control: N/A; T Cells Only: N/A; MOF/MC.BiTE + T Cells: 51.0 ng/mL (8 h post-transfection)

Parameter: T cell infiltration (IHC); PBS Control: Minimal; T Cells Only: Moderate; MOF/MC.BiTE + T Cells: Strong CD3⁺ infiltration

Parameter: MOF alone / MOF/MC (no T cells); PBS Control: -; T Cells Only: -; MOF/MC.BiTE + T Cells: No therapeutic effect (Fig. S4)

Parameter: ALT, AST, creatinine, urea; MOF vs. Control: No significant difference; MOF/MC vs. Control: No significant difference

Parameter: H&E of major organs; MOF vs. Control: No histopathological changes; MOF/MC vs. Control: No histopathological changes

1. Xenograft model limitations: NOD/SCID mice lack functional T, B, and NK cells; human T cells were adoptively transferred, but this does not fully recapitulate an intact human immune system or the tumor-immune microenvironment. The authors note these mice are "deficient in three typical kinds of immune cells."

2. Short-term treatment: Only two cycles of MOF/MC.BiTE treatment were administered; long-term efficacy, optimal dosing schedule, and durability of response were not studied.

3. Modest survival extension: Median survival extended from 26 days (control) and 30 days (T cells alone) to 39 days (MOF/MC.BiTE) — a ~13-day extension over T cells alone, which is modest but statistically significant.

4. No treatment of established large tumors: Therapy was started at day 7 post-tumor engraftment when "4 mm cancer lesions were already established" — relatively early intervention; efficacy against more advanced disease was not tested.

5. Transfection efficiency limited to i.p. and s.c.: i.v. administration showed no transfection, limiting systemic applications; the approach is best suited for localized peritoneal cancers (e.g., ovarian cancer).

6. EpCAM target expression: SKOV3 cells express EpCAM; the approach assumes EpCAM expression on target tumors, but EpCAM expression can be heterogeneous or downregulated in some cancers.

7. Potential immunogenicity of BiTE: The BiTE contains scFv domains and a 6×His tag; potential immunogenicity in immunocompetent hosts was not evaluated (NOD/SCID mice are immune-deficient).

8. No direct comparison to recombinant BiTE protein therapy: The study does not benchmark MOF/MC.BiTE against directly injected BiTE protein (though this is implied as the clinical alternative).

9. Repeated dosing feasibility: The study shows that a second dose at day 6 was effective, but the potential for anti-MOF antibody responses or loss of efficacy with repeated dosing was not assessed.

10. MOF degradation products: While no acute toxicity was observed, the long-term fate and clearance of MOF degradation products (Fe ions, fumarate) were not thoroughly investigated.

11. T cell source: Human T cells were expanded from PBMCs; the quality, phenotype, and persistence of these adoptively transferred T cells in NOD/SCID mice were not fully characterized.

12. No antigen-specific T cell activation data: While T cell infiltration was shown, direct evidence of T cell activation, proliferation, or persistence at the tumor site was limited to IHC for CD3.

Report prepared based on the published Applied Materials Today article. For full experimental details, supplementary figures, and complete references, please refer to the original publication.