The effect of ultrasound pulse length on microbubble cavitation induced antibody accumulation and distribution in a mouse model of breast cancer

Abstract

In solid tumors, the limited diffusion of therapeutic molecules in the perivascular space is a known limitation impacting treatment efficacy. Ultrasound Targeted Microbubble Cavitation (UTMC) has been shown to increase vascular permeability and improve the delivery of therapeutic compounds including small molecules, antibodies (mAb), nanoparticles and even cells, notably across the blood-brain-barrier (BBB). In this study, we hypothesized that UTMC could improve the accumulation and biodistribution of mAb targeting the adenosinergic pathway (i.e. CD73) in mice bearing bilateral subcutaneous 4T1 mammary carcinoma. METHODS: A bolus of fluorescently labeled mAb was given intravenously, followed by a slow infusion of microbubbles. UTMC therapy (1 MHz, 850 kPa) was given under ultrasound image guidance for 5 minutes to the right side tumor only, using three different pulse lengths with identical ultrasound energy (5000cyc "long", 125x40cyc "mid" and 500x10cyc "short"), and leaving the left tumor as a paired control. Longitudinal accumulation at 0 h, 4 h and 24 h was measured using whole-body biofluorescence and confocal microscopy. RESULTS: Our data support an increase in antibody accumulation and extravasation (# extravasated vessels and extravasated signal intensity) at 0 h for all pulses and at 4 h for the mid and short pulses when compared to the control non treated side. However, this difference was not found at 24 h post UTMC, indicative of the transient nature of UTMC. Interestingly, confocal data supported that the highest extravasation range was obtained at 0 h with the long pulse and that the short pulse caused no increase in the extravasation range. Overall, the mid pulse was the only pulse to increase all our metrics (biofluorescence, fraction of extravasated vessels, amount of extravasated Ab, and extravasation range) at 0 h and 4 h time points. CONCLUSIONS: Our results support that UTMC can enhance antibody accumulation in solid tumors at the macroscopic and microscopic levels. This preferential accumulation was evident at early time points (0 h and 4 h) but had started to fade by 24 h, a time dependence that is consistent with the ultrasound blood brain barrier opening literature. Further development and optimization of this theranostic platform, such as repeated UTMC, could help improve antibody based therapies against solid cancer.

A Single Short ‘Tone Burst’ Results in Optimal Drug Delivery to Tumours Using Ultrasound-Triggered Therapeutic Microbubbles

“…A 5 s trigger, as we have previously used [ 22 ], is very short compared to most triggers used [ 21 , 26 , 27 , 28 ]. Therefore, the total duration of the trigger was increased to 120 s to burst more of the injected thMB population and potentially deliver more drug to the tumour (see Figure 1 for a schematic of the US parameters).…”

“…RaSP pulses were similarly shown to improve microbubble-mediated liposomal uptake in the brain over that obtained with long pulses [ 20 ]. The use of MBs and US was studied in 4T1 breast cancer xenografts to improve the delivery of a fluorescently labelled antibody to the tumour [ 21 ]. The total number of acoustic cycles per pulse (5000 cycles) and acoustic energy were the same in all three groups.…”

Targeted Anti-Cancer Provascular Therapy Using Ultrasound, Microbubbles, and Nitrite to Increase Radiotherapy Efficacy

“…In addition to keeping alive healthy cells close to the perfused tumor, which limits damage to healthy surrounding tissues, the tumor vasculature could be used to transport synergistic antitumor agents, such as chemotherapeutic agents or immunostimulants. In addition, it should be noted that cavitation near the endothelial cells causes temporary permeabilization of the vessels, which can be used to improve the delivery of therapeutic molecules to the tumor site, ,− which could not be possible with antivascular therapy. To the best of our knowledge, this is the first demonstration that UTMC + nitrite can improve RT.…”

Lytic Release of Cellular ATP: Physiological Relevance and Therapeutic Applications

“…However, the systemic administration of these powerful inhibitors can lead to harsh side effects [ 51 ], which could be alleviated by a local potentiation of these active compounds. Interestingly, ultrasound (US)-targeted microbubble (MB) cavitation (UTMC) offers an externally triggered, spatially controlled and image-guided approach that is promising for local drug release [ 52 , 53 ] and for improving antibody extravasation and efficacy [ 54 , 55 , 56 , 57 ]. However, these exciting results overshadow the fact that the biological effects and signalling pathways stimulated by MB–cell interactions are still poorly understood.…”