Evaluation of photothermal effects induced by laser heating of gold nanorods in suspensions and inoculated tumors

G.S. Terentyuk, D.S. Chumakov, I.L. Maksimova

Saratov State University

M.V. Basko Saratov State Medical University A.V. Ivanov N.N. Blokchin Russian Cancer Research Centre B.N. Khlebtsov, N.G. Khlebtsov IBPPM RAS, Saratov Russia

SFM'13 September 25-28, 2013, Saratov, Russia

Background

Thermal ablation of cancer is gaining increasing attention as an alternative to standard surgical therapies , especially for patients with contraindications.

Potential benefits of thermal ablation include reduced morbidity and mortality in comparison with standard surgical resection and the ability to treat nonsurgical patients. There is a wide range of ablation techniques that include : cryoablation, radiofrequency ablation, microwave ablation, ultrasound ablation and laser ablation.

Plasmonic photothermal therapy (PPTT)

is a technique of cancer thermal therapy based on the laser heating of gold nanoparticles. One of the main advantages of this therapeutic technology is its high spatial selectivity that prevents surrounding healthy tissues from thermal damage.

Advantages of gold nanoparticles as antitumor photothermal agents:

1) Unique optical properties 2) Photostability 3) Low toxicity 4) Well-known synthesis protocols

Manthe R.L. et al . Mol . Pharm (2010) Dickerson et al. Chem. Soc Rev (2011)

Goal of the research

To study photothermal effects under laser irradiation of aqueous suspensions of gold nanorods (in vitro experiments) and mice inoculated Erlich carcinoma after intravenous injections of gold nanorods (in vivo experiments)

Characteristics of nanoparticles Gold nanorods (GNR) were synthesized by a seed-mediated approach and functionalized with PEG Geometrical parameters : L = 41 ± 8 nm d= 10,2 ± 2 nm r = 4,03 ± 0,7 Plasmon resonance at the wavelength 820 nm Transmission electron microscopic image of gold nanorods

Scheme of in vitro experiments

Suspension volume – 1,5 ml Duration of irraditaion – 5 min Power density - 1 W/сm 2 Wavelength - 810 nm IRYSYS thermal imager was placed at the distance 37 cm of the test tube

Dependence of the temperature increment ∆T on the concentration of gold nanorods in the suspension after irradiation with laser light (810 nm, 1 W/сm 2 ) during 5 min.

Distribution of temperature T along the axis x of test tubes under the laser heating of gold nanorod suspensions with concentrations 8 (а) and 100 (b) mg/ml.

(А) (B)

Laboratory animals and tumour model

Laboratory animals

Female linear mice BALB /с Age : 3 months Body mass : 20-22 g

Tumour model

: Ehrlich’s ascites carcinoma The mean volume of the tumour was 1,7 ± 0,3 см 2

Experimental group № 1 14 animals

Scheme of in vivo experiments

Experimental group № 2 14 animals

7 animals (ААS)

Laser irradiation Wavelength - 810 nm Duration - 5 min Power Density- 1 W/cm 2

Evaluation of tumor growth dynamic (7 animals)

Control group № 1 6 animals

Scheme of in vivo experiments

Control group № 2 6 animals Laser irradiation Wavelength - 810 nm Duration - 5 min Power Density- 1 W/cm 2 No irradiation

2 animals (AAS) Evaluation of tumor growth dynamic (4 animals) 2 animals (AAS) Evaluation of tumor growth dynamic (4 animals)

2 D distribution of temperature over the surface of mice skin before the laser irradiation, in 1 min and in 5 min. before laser irradiation 1 min 5 min

Kinetics of laser heating of tumor (1) and healthy (2) tissue in the vicinity of it maximum in 24 houres after intravenous injection of gold nanorods in the dose 2 (а) and 8 (b) mg /kg. Curve 3 shows the kinetics of the maximal heating of healthy muscle tissue without injecting the nanoparticles .

Biodistribution of gold nanorods in tumour and muscle (a) in liver and spleen (b) in 24 houres after intravenous injection of nanoparticles in doses 2 (1) and 8 (2) mg/kg. Curve 3 shows the corresponding distribution when injecting saline instead of nanoparticles .

Dependences of the tumour mean volume on the number of the days passed after perfoming a PPTT in the experimental groups with the dose of injected gold nanorods 8 (1) and 2 mg/kg (2) and for control groups with laser irradiation without injecting nanoparticles (3) and without laser irradiation (4).

Conclusion

1) PEG-coated nanorods with the size 40 × 10 nm in 24 houres after systemic injection to mice with inoculated Ehrlich carcinoma are accumulated in the tumor in the amount 4 mkg/g. In 24 houres after injection the concentration of nanoparticles is maximal in the spleen and liver. 2) Too high concentrations of gold nanoparticles in tumour may lead to undesirable effect of light absorption in surface layers and extremely nonuniform heat release 3) Even in the case of significant photothermal action on the tumour tissue , its complete resorption was not achieved and in 12 days after PPTT the growth of tumours recommenced. These results again emphasise the necessity to use photothermotherapy in combination with chemotherapy and radiotherapy in order to provide high efficiency of the complex therapy.