Drug Delivery Using Nano-Pore Zeolites and Ultrasound

Dear Editor: Ultrasound is a mechanical wave with frequencies greater than 20 KHz. Biological effects of ultrasound can often be attributed either to temperature rise or to cavitation activity.¹ Ultrasound is adopted in drug delivery such as supplying chemotherapeutic drugs into tumors. Several drugs, such as hydrocortisone, salicylic acid, and lidocaine have been delivered in clinical applications using sonophoresis. Ultrasound is also used to release drugs at the site of interest to perform minimally invasive, localized therapy. A lot of studies show that ultrasound improves drug uptake in cells, tumors, and other solid tissues, such as the brain.²

On the other hand, zeolites are crystalline solids with well-defined structures. Zeolites contain a network of nano-pores with diameters usually less than 20 nm. Substitution of drugs into nano-zeolites is practical and achievable. The arbitrary drug is trapped into the nano-pores of the zeolite, which can be recovered in due time. Many in-vitro and in-vivo experiments are executed on natural and artificial zeolites. A study has shown the anti-diarrheic application of purified natural clinoptilolite zeolite into the body.³ Another work showed that surfactant can use zeolites as drug-carriers to release chloroquin.⁴ Also, Zn²⁺-exchanged natural zeolite is used as an active carrier for antibiotics in anti-acne topical therapy.⁵

None of the previous studies have focused on the combined effect of ultrasound on zeolites for drug delivery into the brain. We hypothesize that drug-substituted zeolite solution can be prepared and injected into the blood. This solution can cross the blood–brain barrier and reach tumors. Then the trapped drug can be released by using ultrasonic waves to vibrate the structure of the nano-pore zeolite. It seems that this vibration will augment drug-release in the damaged location, and side effects may diminish. Surely, this hypothesis needs clinical data to confirm it.