title: Photo activation of HPPH encapsulated in "Pocket" liposomes triggers multiple drug release and tumor cell killing in mouse breast cancer xenografts.
abstract: We recently reported laser-triggered release of photosensitive compounds from liposomes containing dipalmitoylphosphatidylcholine (DPPC) and 1,2 bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC(8,9)PC). We hypothesized that the permeation of photoactivated compounds occurs through domains of enhanced fluidity in the liposome membrane and have thus called them "Pocket" liposomes. In this study we have encapsulated the red light activatable anticancer photodynamic therapy drug 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH) (Ex/Em410/670 nm) together with calcein (Ex/Em490/517 nm) as a marker for drug release in Pocket liposomes. A mole ratio of 7.6:1 lipid:HPPH was found to be optimal, with >80% of HPPH being included in the liposomes. Exposure of liposomes with a cw-diode 660 nm laser (90 mW, 0-5 minutes) resulted in calcein release only when HPPH was included in the liposomes. Further analysis of the quenching ratios of liposome-entrapped calcein in the laser treated samples indicated that the laser-triggered release occurred via the graded mechanism. In vitro studies with MDA-MB-231-LM2 breast cancer cell line showed significant cell killing upon treatment of cell-liposome suspensions with the laser. To assess in vivo efficacy, we implanted MDA-MB-231-LM2 cells containing the luciferase gene along the mammary fat pads on the ribcage of mice. For biodistribution experiments, trace amounts of a near infrared lipid probe DiR (Ex/Em745/840 nm) were included in the liposomes. Liposomes were injected intravenously and laser treatments (90 mW, 0.9 cm diameter, for an exposure duration ranging from 5-8 minutes) were done 4 hours postinjection (only one tumor per mouse was treated, keeping the second flank tumor as control). Calcein release occurred as indicated by an increase in calcein fluorescence from laser treated tumors only. The animals were observed for up to 15 days postinjection and tumor volume and luciferase expression was measured. A significant decrease in luciferase expression and reduction in tumor volume was observed only in laser treated animal groups injected with liposomes containing HPPH. Histopathological examination of tumor tissues indicated tumor necrosis resulting from laser treatment of the HPPH-encapsulated liposomes that were taken up into the tumor area.
authors.affiliation: Membrane Structure and Function Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute - Frederick, Frederick, MD, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Sine
authors.affiliation: Department of Radiology, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Cordula
authors.initials: C
authors.lastname: Urban
authors.affiliation: Membrane Structure and Function Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute - Frederick, Frederick, MD, USA.
authors.forename: Derek
authors.initials: D
authors.lastname: Thayer
authors.affiliation: Department of Radiology, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Charron
authors.affiliation: Department of Radiology, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Niksa
authors.initials: N
authors.lastname: Valim
authors.affiliation: US Food and Drug Administration, CDRH/OSEL/Division of Physics, White Oak Campus, MD, USA.
authors.forename: Darrell B
authors.initials: DB
authors.lastname: Tata
authors.affiliation: Lester and Sue Smith Breast Center, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Schiff
authors.affiliation: Membrane Structure and Function Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute - Frederick, Frederick, MD, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Blumenthal
authors.affiliation: Department of Radiology, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Joshi
authors.affiliation: Membrane Structure and Function Section, Basic Research Laboratory, Center for Cancer Research, National Cancer Institute - Frederick, Frederick, MD, USA.
authors.forename: Anu
authors.initials: A
authors.lastname: Puri
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000493:pharmacokinetics*; D001943:Breast Neoplasms / Q000188:drug therapy; D045744:Cell Line, Tumor; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D065546:Drug Liberation; D005260:Female; D005452:Fluoresceins / Q000737:chemistry / Q000493:pharmacokinetics; D006801:Humans; D007834:Lasers; D008027:Light; D008081:Liposomes / Q000737:chemistry*; D008163:Luminescent Measurements; D051379:Mice; D008819:Mice, Nude; D010778:Photochemotherapy / Q000379:methods; D014018:Tissue Distribution; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D005452:Fluoresceins; D008081:Liposomes; D002734:Chlorophyll; C083998:2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; C007740:fluorexon
keywords: laser-triggered payload release; photo-agents; photopolymerizable phospholipids; phototriggering; tumor regression