Abstract
This work investigates X-PACT (X-ray Psoralen Activated Cancer Therapy): a new approach for the treatment of solid cancer. X-PACT utilizes psoralen, a potent anti-cancer therapeutic with current application to proliferative disease and extracorporeal photopheresis (ECP) of cutaneous T Cell Lymphoma. An immunogenic role for light-activated psoralen has been reported, contributing to long-term clinical responses. Psoralen therapies have to-date been limited to superficial or extracorporeal scenarios due to the requirement for psoralen activation by UVA light, which has limited penetration in tissue. X-PACT solves this challenge by activating psoralen with UV light emitted from novel non-tethered phosphors (co-incubated with psoralen) that absorb x-rays and re-radiate (phosphoresce) at UV wavelengths. The efficacy of X-PACT was evaluated in both in-vitro and in-vivo settings. In-vitro studies utilized breast (4T1), glioma (CT2A) and sarcoma (KP-B) cell lines. Cells were exposed to X-PACT treatments where the concentrations of drug (psoralen and phosphor) and radiation parameters (energy, dose, and dose rate) were varied. Efficacy was evaluated primarily using flow cell cytometry in combination with complimentary assays, and the in-vivo mouse study. In an in-vitro study, we show that X-PACT induces significant tumor cell apoptosis and cytotoxicity, unlike psoralen or phosphor alone (p<0.0001). We also show that apoptosis increases as doses of phosphor, psoralen, or radiation increase. Finally, in an in-vivo pilot study of BALBc mice with syngeneic 4T1 tumors, we show that the rate of tumor growth is slower with X-PACT than with saline or AMT + X-ray (p<0.0001). Overall these studies demonstrate a potential therapeutic effect for X-PACT, and provide a foundation and rationale for future studies. In summary, X-PACT represents a novel treatment approach in which well-tolerated low doses of x-ray radiation are delivered to a specific tumor site to generate UVA light which in-turn unleashes both short- and potentially long-term antitumor activity of photo-active therapeutics like psoralen.
Highlights
Psoralens are naturally occurring compounds found in plants with anticancer [1,2,3,4] and immunogenic [5,6,7,8] properties
In this work we introduce a new approach, X-Ray Psoralen Activated Cancer Therapy (X-PACT) (X-ray Psoralen Activated Cancer Therapy), which has potential to extend psoralen therapy to a wide range of solid tumors, at deep seated sites in the body
X-PACT is a novel treatment based on photo-activation of a drug in-situ, using very low doses of x-rays, and is not a radiation treatment that relies upon direct radiation cell kill
Summary
Psoralens are naturally occurring compounds found in plants (furocoumarin family) with anticancer [1,2,3,4] and immunogenic [5,6,7,8] properties. They freely penetrate the phospholipid cellular bilayer membranes and intercalate into DNA between nucleic acid pyrimidines, where they are biologically inert (unless photo-activated) and excreted within 24 hours.
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