EPR-Effect Enhancers Strongly Potentiate Tumor-Targeted Delivery of Nanomedicines to Advanced Cancers: Further Extension to Enhancement of the Therapeutic Effect

Abstract

For more than three decades, enhanced permeability and retention (EPR)-effect-based nanomedicines have received considerable attention for tumor-selective treatment of solid tumors. However, treatment of advanced cancers remains a huge challenge in clinical situations because of occluded or embolized tumor blood vessels, which lead to so-called heterogeneity of the EPR effect. We previously developed a method to restore impaired blood flow in blood vessels by using nitric oxide donors and other agents called EPR-effect enhancers. Here, we show that two novel EPR-effect enhancers-isosorbide dinitrate (ISDN, Nitrol^®) and sildenafil citrate-strongly potentiated delivery of three macromolecular drugs to tumors: a complex of poly(styrene-co-maleic acid) (SMA) and cisplatin, named Smaplatin^® (chemotherapy); poly(N-(2-hydroxypropyl)methacrylamide) polymer-conjugated zinc protoporphyrin (photodynamic therapy and imaging); and SMA glucosamine-conjugated boric acid complex (boron neutron capture therapy). We tested these nanodrugs in mice with advanced C26 tumors. When these nanomedicines were administered together with ISDN or sildenafil, tumor delivery and thus positive therapeutic results increased two- to four-fold in tumors with diameters of 15 mm or more. These results confirmed the rationale for using EPR-effect enhancers to restore tumor blood flow. In conclusion, all EPR-effect enhancers tested showed great potential for application in cancer therapy.

Keywords: EPR effect; EPR-effect enhancers; heterogeneity of the EPR effect; isosorbide dinitrate; nitric oxide donors; sildenafil citrate; tumor blood flow.

Figure 1

Enhancement of delivery of PZP to tumors by using EPR-effect enhancers. Male, 6-week-old, BALB/c mice bearing Colon 26 tumor were given 10 mg/kg PZP iv; ISDN at 30 mg/kg intraperitoneally or sildenafil citrate at 30 mg/kg subcutaneously immediately after PZP. The amount of drug in each tissue was quantified by using fluorescence spectroscopy, with the excitation wavelength of 422 nm (corresponding to ZnPP). Data are expressed as means ± SD. See text for details.

Figure 2

ISDN-enhanced accumulation of SGB-complex (A) and Smaplatin^® (B) in C26 tumor tissues. SGB-complex at 15 mg/kg (boric acid equivalent) or Smaplatin at 10 mg/kg (Cisplatin equivalent) was administered iv; 30 mg/kg ISDN was administered ip as an EPR-effect enhancer. At 24 h after drug treatment, the amounts of ¹⁰B and platinum in tissues were quantified by means of ICP-MS according to the manufacturer’s procedure. Data are expressed as means ± SD. (n = 5) See text for details.

Figure 3

Ex vivo imaging of advanced mouse tumors after treatment with PZP plus ISDN or sildenafil. To study EPR-effect enhancers, we used late-stage C26 tumors (about 18 mm in diameter). PZP, 5 mg/kg, was injected iv, after which ISDN or sildenafil was administered. After 24 h of iv infusion, tumors were removed from mice, and fluorescence images were obtained by IVIS. Both enhancers augmented drug delivery to tumors about two- to three-fold (A). (B) shows the comparison quantitative measurement of PZP drug accumulation with/without EPR-effect enhancers based on the fluorescence intensity. Data are expressed as means ± SD (n = 3).

Figure 4

Improvement in the therapeutic effect of different concentrations of Smaplatin^® by using ISDN (A) and sildenafil (B) in C26 tumors. When tumor diameters measured about 12 mm, 6 mg/kg or 3 mg/kg Smaplatin^® was injected iv; ISDN (30 mg/kg, ip) or sildenafil (30 mg/kg sc) was given with 3 mg/kg Smaplatin^®. The 3 mg/kg Smaplatin^® given with ISDN showed improved therapeutic efficacy compared with 6 mg/kg Smaplatin^® given alone (A); the result for 3 mg/kg Smaplatin^® plus sildenafil was similar to that for 6 mg/kg Smaplatin^® given alone (B). Arrows indicate times of drug administration. * p < 0.05, ** p < 0.01, *** p < 0.001, combination group vs Smaplatin^® 3 mg/kg group. Data are expressed as means ± SD. (n = 5).

Figure 5

Improvement in the antitumor effect of SGB-complex by using EPR-effect enhancers in the C26 tumor model. (A) Antitumor effect of the SGB-complex given with ISDN. (B) Antitumor efficacy of the SGB-complex given with sildenafil. ISDN increased the antitumor effect of the SGB-complex about 3-fold; sildenafil, 1.5- to 2-fold. Arrows indicate times of drug administration. Data are expressed as means ± SD. * p < 0.05, ** p <0.01, *** p < 0.001, combination group vs. SGB 5 mg/kg group. See text for details.