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.

Purpose: This work investigates X‐PACT (X‐ray Psoralen Activated Cancer Therapy): a new approach for the treatment of cancer. X‐PACT utilizes psoralen, a potent anti‐cancer therapeutic with immunogenic anti‐cancer potential. Psoralen therapies have been limited due to the requirement for psoralen activation by UVA light. 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 reradiate (phosphoresce) at UV wavelengths. Methods: 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 to investigate treatment induced apoptosis. Methylene blue staining, and WST assays were also used. X‐PACT was then evaluated in an in‐vivo pilot study on BALBc mice with syngeneic 4T1 tumors, including control arms for X‐PACT components. Analysis focused on tumor growth delay. Results: A multivariable regression analysis of 36 independent in‐vitro irradiation experiments demonstrated that X‐PACT induces significant tumor cell apoptosis and cytotoxicity on all three tumor cell lines in‐vitro (p<0.0001). Neither psoralen nor phosphor alone had a strongly significant effect. The in‐vivo studies show a pronounced tumor growth delay when compared to controls (42% reduction at 25 days, p=0.0002). Conclusions: These studies demonstrate for the first time a therapeutic effect for X‐PACT, and provide a foundation and rationale for future studies. X‐PACT represents a novel treatment approach in which well‐tolerated low doses of x‐ray radiation generate UVA light in‐situ (including deep seated lesions) which in‐turn photo‐activates powerful anticancer therapeutics which may lead to short and long term therapeutic effect. This work was supported by Immunolight Llc

Purpose: Psoralen is a UV‐light activated anti‐cancer biotherapeutic used for treating skin lesions (PUVA) and advanced cutaneous T‐cell lymphoma (ECP). To date psoralen has not been used to treat deep seated tumors due to difficulty in generating UV‐light at depth. We recently demonstrated psoralen activation at depth by introducing energy converting particles that absorb kV x‐ray radiation and re‐emit UV‐light. Our in‐vitro work found that 0.2–1Gy using 40–100kVp x‐rays combined with psoralen and particles can induce a substantial apoptotic response beyond that expected from the sum of individual components. In preparation for a phase I clinical trial of canine companion animals, we address the physics and dosimetry considerations for applying this new teletherapy paradigm to an in‐vivo setting. Methods: The kV on‐board imaging (OBI) system mounted on a medical linear accelerator (Varian) was commissioned to deliver the prescribed dose (0.6Gy) using 80 and 100kVp. Dosimetric measurements included kVp, HVL, depth dose, backscatter factors, collimator and phantom scatter factors, field size factors, and blade leakage. Absolute dosimetry was performed following AAPM TG61 recommendations and verified with an independent kV dose meter. We also investigated collimated rotational delivery to minimize skin dose using simple dose calculations on homogeneous cylindrical phantoms. Results: Single beam delivery is feasible for shallow targets (<5cm) without exceeding skin tolerance, while a rotational delivery may be utilized for deeper targets; skin dose is ∼75% of target dose for 80kVp collimated rotational delivery to a 3cm target within a 20cm phantom. Heat loading was tolerable; 0.6Gy to 5cm can be delivered before the anode reaches 75% capacity. Conclusion: KV teletherapy for Psoralen activation in deep seated tissue was successfully commissioned for a Varian OBI machine for use in a phase I clinical trial in canines. Future work will use Monte Carlo dosimetry to investigate dose in presence of bone. Research funded by Immunolight LLC. H. Walder, Z. Fathi, & W. Beyer are employees of Immunolight LLC which holds a patent on the technology. Drs. Adamson and Oldham are consultants to Immunolight LLC.