A personalized and long-acting local therapeutic platform combining photothermal therapy and chemotherapy for the treatment of multidrug-resistant colon tumor

Abstract

Background: Local photothermal therapy (PTT) provides an easily applicable, noninvasive adjunctive therapy for colorectal cancer (CRC), especially when multidrug resistance (MDR) occurs. However, using PTT alone does not result in complete tumor ablation in many cases, thus resulting in tumor recurrence and metastasis.

Materials and methods: In this study, we aim to develop a personalized local therapeutic platform combining PTT with long-acting chemotherapy for the treatment of MDR CRC. The platform consists of polyethylene glycol (PEG)-coated gold nanorods (PEG-GNRs) and D-alpha-tocopheryl PEG 1000 succinate (TPGS)-coated paclitaxel (PTX) nanocrystals (TPGS-PTX NC), followed by the incorporation into an in situ hydrogel (gel) system (GNRs-TPGS-PTX NC-gel) before injection. After administration, PEG-GNRs can exert quick and efficient local photothermal response under near-infrared laser irradiation to shrink tumor; TPGS-PTX NC then provides a long-acting chemotherapy due to the sustained release of PTX along with the P-glycoprotein inhibitor TPGS to reverse the drug resistance.

Results: The cytotoxicity studies showed that the IC₅₀ of GNRs-TPGS-PTX NC-gel with laser irradiation decreased to ~178-folds compared with PTX alone in drug-resistant SW620 AD300 cells. In the in vivo efficacy test, after laser irradiation, the GNRs-TPGS-PTX NC-gel showed similar tumor volume inhibition compared with GNRs-gel at the beginning. However, after 14 days, the tumor volume of the mice treated with GNRs-gel quickly increased, while that of the mice treated with GNRs-TPGS-PTX NC-gel remained controllable due to the long-term chemotherapeutic effect of TPGS-PTX NC. The mice treated with GNRs-TPGS-PTX NC-gel also showed no weight loss and obvious organ damages and lesions during the treatment, indicating a low systemic side effect profile and a good biocompatibility.

Conclusion: Overall, the nano-complex may serve as a promising local therapeutic patch against MDR CRC with one-time dosing to achieve a long-term tumor control. The doses of PEG-GNRs and TPGS-PTX NC can be easily adjusted before use according to patient-specific characteristics potentially making it a personalized therapeutic platform.

Keywords: TPGS; gold nanorods; in situ hydrogel; paclitaxel nanocrystals; tumor recurrence.

Figure 1

The illustration of the dose-adjustable in situ hydrogel platform containing PEG-GNRs and TPGS-PTX NC for the combination of PTT and long-acting chemotherapy. Notes: CTAB-GNRs, CTAB-coated GNRs; PEG-GNRs, PEG-coated GNRs; TPGS-PTX NC, TPGS-coated PTX NC. Abbreviations: CTAB, hexadecyl trimethyl ammonium bromide; GNRs, gold nanorods; LCST, low critical solution temperature; mPEG-SH, thiol-terminated methoxypoly-(ethylene glycol); NC, nanocrystal; NIR, near-infrared; PEG, polyethylene glycol; P-gp, P-glycoprotein; PTT, photothermal therapy; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 2

Characterization of PEG-GNRs. Notes: TEM images of (A) CTAB-GNRs (×60K) and (B) PEG-GNRs (×80K). (C) Absorption spectra of CTAB-GNRs and PEG-GNRs (Au: 20 µg mL⁻¹). (D) Zeta potentials of CTAB-GNRs and PEG-GNRs (n=3). (E) The stability of CTAB-GNRs and PEG-GNRs in 10% FBS diluted with PBS or PBS, respectively. CTAB-GNRs, CTAB-coated GNRs; PEG-GNRs, PEG-coated GNRs. Abbreviations: CTAB, hexadecyl trimethyl ammonium bromide; GNRs, gold nanorods; PEG, polyethylene glycol; TEM, transmission electron microscopy.

Figure 3

TEM images of (A) TPGS-PTX NC (×30K) and (B) GNRs-TPGS-PTX NC-gel (×15K; the red arrows represent TPGS-PTX NC; the blue arrows represent PEG-GNRs). Notes: PEG-GNRs, PEG-coated GNRs; TPGS-PTX NC, TPGS-coated PTX NC. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TEM, transmission electron microscopy; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 4

Storage modulus (G′) and loss modulus (G″) changes of gel with temperature from 20°C to 50°C. (A) Blank; (B) F127-PTX NC-gel; (C) TPGS-PTX NC-gel; (D) GNRs-TPGS-PTX NC-gel. (E) Photographs of various gels at different temperatures; (A₁) F127-PTX NC-gel, (A₂) GNRs-TPGS-PTX NC-gel, and (A₃) TPGS-PTX NC-gel. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 5

The photothermal efficacy and in vitro drug release of the gel. Notes: (A) Temperature change of GNRs-TPGS-PTX NC-gel at various Au element concentrations during NIR laser irradiation for 25 minutes. (B) In vitro release of PTX from gel at 37°C. Laser irradiation (808 nm, 2 W cm⁻², 5 minutes). The results represent mean ± SD (n=3). Abbreviations: GNRs, gold nanorods; NC, nanocrystal; NIR, near-infrared; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 6

Photographs during gel erosion in vitro. Notes: At various time points, the tubes were photographed by a digital camera. (A) Blank; (B) TPGS-PTX NC-gel; (C) GNRs-gel; (D) GNRs-TPGS-PTX NC-gel; (E) GNRs-TPGS-PTX NC-gel (laser). (F) The height of the remaining gel in the tube. Arrows imply gel formulation interfaces (n=3). Abbreviations: d, days; GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 7

In vitro cytotoxicity assessments by MTT assay in SW620 and SW620 AD300 cells after treatment for 24 hours. Notes: (A) The inhibitory effects of PTX on the proliferations of SW620 cells. Cytotoxicities of PTX (B), F127-PTX NC (C), TPGS-PTX NC (D), and GNRs-TPGS-PTX NC (E) in SW620 AD300 cells (n=6). (F) IC₅₀ values of PTX of different formulations against SW620 AD300 cells. TPGS-PTX NC, TPGS-coated PTX NC. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 8

In vitro cytotoxicity assessments by MTT assay in SW620 and SW620 AD300 cells after treatment for 72 hours. Notes: (A) The inhibitory effects of PTX on the proliferations of SW620 cells. Cytotoxicities of PTX (B), F127-PTX NC (C), TPGS-PTX NC (D), and GNRs-TPGS-PTX NC (E) in SW620 AD300 cells (n=6). (F) IC₅₀ values of PTX of different formulations against SW620 AD300 cells. TPGS-PTX NC, TPGS-coated PTX NC. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 9

Infrared theamal images and average temperature changes at the tumor site over time. Notes: (A) Infrared thermal images of tumors after 808 nm laser irradiation at 0, 1, 3, and 5 minutes in PBS-, GNRs-gel-, and GNRs-TPGS-PTX NC-gel-injected mice under 2 W cm⁻² irradiation (the arrows represent the location of the tumor; WL). (B) The changes of average temperature in tumor region with time during NIR laser (808 nm, 2 W cm⁻²) irradiation (n=2 for PBS group, n=3 for GNRs-gel and GNRs-TPGS-PTX NC-gel group). Abbreviations: GNRs, gold nanorods; NC, nanocrystal; NIR, near-infrared; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate; WL, white light.

Figure 10

In vivo antitumor efficacy against SW620 AD300 tumor-bearing mice. Notes: (A) Tumor volume growth of the tumor-bearing mice with different treatments (three purple *** represent the TPGS-PTX NC group, a blue * represents the GNRs-gel [laser] group). (B) Changes in tumor volume in each group in the first 14 days. (C) The mean weight of the excised SW620 AD300 tumors from the mice. (D) The images of excised tumors at the end of the treatment. ***P<0.001 and *P<0.05 vs the GNRs-TPGS-PTX NC-gel group. ^#P<0.05 and ^##P<0.01 vs PBS group. Student’s t-test was used to analyze the data and a P-value of <0.05 was considered statistically significant. The results represent mean ± SD (n=8). TPGS-PTX NC, TPGS-coated PTX NCs. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.

Figure 11

Systemic toxicity studies of the GNRs-TPGS-PTX NC-gel with laser. Notes: (A) The body weight changes of SW620 AD300 tumor-bearing mice with different treatments (n=8). (B) H&E-stained images of major tissue sections including hearts, livers, spleens, lungs, and kidneys of mice after the treatments. The magnification used was 20×. Abbreviations: GNRs, gold nanorods; NC, nanocrystal; PEG, polyethylene glycol; PTX, paclitaxel; TPGS, D-alpha-tocopheryl PEG 1000 succinate.