Focused Ultrasound Hyperthermia Mediated Drug Delivery Using Thermosensitive Liposomes and Visualized With in vivo Two-Photon Microscopy

Abstract

The future of nanomedicines in oncology requires leveraging more than just the passive drug accumulation in tumors through the enhanced permeability and retention effect. Promising results combining mild hyperthermia (HT) with lyso-thermosensitive liposomal doxorubicin (LTSL-DOX) has led to improved drug delivery and potent antitumor effects in pre-clinical studies. The ultimate patient benefit from these treatments can only be realized when robust methods of HT can be achieved clinically. One of the most promising methods of non-invasive HT is the use of focused ultrasound (FUS) with MRI thermometry for anatomical targeting and feedback. MRI-guided focused ultrasound (MRgFUS) is limited by respiratory motion and large blood vessel cooling. In order to translate exciting pre-clinical results to the clinic, novel heating approaches capable of overcoming the limitations on clinical MRgFUS+HT must be tested and evaluated on their ability to locally release drug from LTSL-DOX.Methods: In this work, a new system is described to integrate focused ultrasound (FUS) into a two-photon microscopy (2PM) setting to image the release of drug from LTSL-DOX in real-time during FUS+HT in vivo. A candidate scheme for overcoming the limitations of respiratory motion and large blood vessel cooling during MRgFUS+HT involves applying FUS+HT to 42°C in short ~30s bursts. The spatiotemporal drug release pattern from LTSL-DOX as a result is quantified using 2PM and compared against continuous (3.5min and 20min at 42°C) FUS+HT schemes and unheated controls.Results: It was observed for the first time in vivo that these short duration temperature elevations could produce substantial drug release from LTSL-DOX. Ten 30s bursts of FUS+HT was able to achieve almost half of the interstitial drug concentration as 20min of continuous FUS+HT. There was no significant difference between the intravascular area under the concentration-time curve for ten 30s bursts of FUS+HT and 3.5min of continuous FUS+HT.Conclusion: We have successfully combined 2PM with FUS+HT for imaging the release of DOX from LTSL-DOX in vivo in real-time, which will permit the investigation of FUS+HT heating schemes to improve drug delivery from LTSL-DOX. We have evaluated the ability to release DOX in short 30s FUS+HT bursts to 42°C as a method to overcome limitations on clinical MRgFUS+HT and have found that such exposures are capable of releasing measurable amounts of drug. Such an exposure has the potential to overcome limitations that hamper conventional MRgFUS+HT treatments in targets that are associated with substantial tissue motion.

Effect of Liposomal Doxorubicin in Pressurized Intra-Peritoneal Aerosol Chemotherapy (PIPAC)

“…It has been determined that these particles are better tolerated and show higher maximal tolerated doses compared to free drug solutions due to slower drug release 25 , 26 . Drug release can then be mediated with time or enhanced by ultrasound, hyperthermia or other means as previously described 27 , 28 . However, this could be complicated by the fact that intraperitoneal liposomal particles are in partial systemically absorbed.…”

Concurrent visual and acoustic tracking of passive and active delivery of nanobubbles to tumors

“…The integrated intravital visual and acoustic setup further provides powerful spatiotemporal insights. Such real-time monitoring of acute vascular effects resulting from ultrasound-stimulated bubble-based therapeutic approaches has only been utilized in a handful of studies in simplified models 68 - 70 , in the absence of tumors 71 - 73 , and without 52 , 71 - 73 or with 50 recording acoustic response. However, these studies utilized microbubbles; no study to date has provided real-time intravital monitoring of acute vascular effects upon ultrasound stimulation of NBs.…”

“…All animal procedures were approved and conducted in compliance with the Animal Care Committee guidelines at Sunnybrook Research Institute, Canada. Six- to eight-week old BALB/c nude mice (Charles River) underwent dorsal skinfold window chamber implantation as in 50 , 52 . This technique involved the surgical implantation of a titanium frame to support the dorsal skinfold within a transparent window ( Figure 3 A).…”

“…As in 52 , 50 , the objective lens and ring transducer were colocalized and imaging was completed near the surface of the dorsal skinfold (up to a depth of 150 µm) to both maintain a high signal-to-noise ratio for the microscope and remain close to the transducer acoustic focus (with a lateral FWHM of ~500 µm). Prior to agent injections and laser scanning, baseline cavitation data was acquired with the same pulse sequences as would be utilized later.…”

Microscale direct measurement of localized photothermal heating in tissue-mimetic hydrogels

“…The presented technique is also applicable with other NPs operating in visible light 59 or IR regions 60,61 in spectrum. Finally, our developed system for localized photothermal investigations is compatible with other local hyperthermia techniques such as magnetic hyperthermia [62][63][64] , ultrasound hyperthermia 65,66 and microwave hyperthermia 67,68 with minor modifications. Also, this method can be modified to incorporate secondary effects like mechanical expansion and deformation because of photothermal heating by integrating a thin film stain sensor 69 .…”