This Conference Presentation, "Much more than an impactful cancer scientist: Tom Dougherty as a graduate student advisor, mentor, advocate, and friend," was recorded at the International Photodynamic Association World Congress 2019 in Boston, Massachusetts, United States.
The results of experiments combining laser hyperthermia (LHT) wit photodynamic therapy (PDT) in the treatment of cancerous tumors have been very encouraging. Typically treatments have been sequential, employing separate hyperthermia and PDT systems. Sequential application of these therapies, however, fails to maximize the synergistic effects of combined, simultaneous treatment. This paper reports the results of an SBIR funded Phase I project intended to develop a system for precise simultaneous delivery of both LHT and PDT light, and to measure the synergistic effects os simultaneously applied LHT and PDT with both Photofrin II- and SnET2-mediated PDT. A system was developed that would allow the use to specify all treatment parameters and then deliver the combined light to the treatment site. Thermal and optical feedback in the system provide stability and precise control during the treatment. The system architecture, the computer control system, and the results obtained from bench-testing the system are presented in this paper. The system was then tested in a small animal tumor model. This paper will discuss the study protocol and the experimental results.
The porphyrin derivative Photofrin-Il (PH-Il) is associated with positive photodynarnic therapy (PDT) responses (1,5) . However several properties of this photosensitizer, such as minimal absorption above 600 nm, chemical impurity and prolonged in-vivo retention, are not optimal. New photosensitizers are being synthesized and evaluated in an attempt to improve the efficacy of PDT (6) . Compounds with increased absorption further in the near infrared will improve photon utilization and depth of light penetration within tissue (7) . Derivatives of porphyrins, chlorins and phthalocyanines are among the compounds being examined (8, 9) . One second generation compound, mono-l--aspartyl chiorin e6 (NPe6), is an hydrophilic chlorin which exhibits promising in-vitro and in-vivo photosensitizing properties (8, 10-14) . N2e6 is chemically pure and has significant absorption at 664 nm. The photosensitizer appears to localize in the lysosomal compartment in cells and has in-vivo tissue distribution properties similar to PH-Il (12,14) . NPe6 mediated PDT is effective against a mouse mammary carcinoma when short time intervals (4-6 hours) between drug injection and light exposure are used (8) . Clearance of N2e6 from blood accounts for the minimal tumor and skin photosensitivity when a 24 hr interval between drug administration and light treatment is used. In the current study, we evaluated in-vivo metabolic properties of NPe6 and quantified PDT responsiveness as a function of the time interval between drug administration and light treatment.
Experimental results for the optical properties of ocular tumors in the red to near infrared region from 600-900 nm and at the near infrared wavelength of 1064 nm are presented. The tumor models have been human retinoblastoma heterotransplanted in athyinic mice and B16 melanotic melanoma in athymic mice. The steady state retinal and tumor temperature rise during 1064 nm laser irradiation have been examined in vivo in normal albino and pigmented rabbits eye and in Greene''s melanoma inoculated in the retinachoroidal layers. 2.
In-vitro sensitivity to porphyrin mediated photodynamic therapy (PDT) has
been examined in cell lines resistant to hyperthermia. Parental (HA-i) and
heat resistant (3012) Chinese hamster fibroblasts as well as parental (RIF-i)
and temperature resistant (TR-4, TR-5 and TR-iO) mouse radiation-induced
fibrosarcoma cells were evaluated for thermal and PDT sensitivity.
Quantitative survival curves were generated and porphyrin uptake properties
were obtained for all cell lines. Significant resistance to hyperthermia
(450C for varying exposure periods) was documented for the 3012 and TR cell
strains when compared to 'the parent lines. However, normal and heat resistant
clones exhibited comparable levels of porphyrin uptake and photosensitivity.
Our results indicate that cross resistance between hyperthermia and PDT is not
observed and that members of the 70 kD heat shock protein family (which are
elevated in the thermal resistant cells and may be associated with the heat
resistant phenotype) do not play a significant role in modulating PDT
sensitivity. Mechanisms of in-vitro cytotoxicity appear to be different for
PDT and hyperthermia even though possible subcellular targets (such as the
plasma membrane) and types of damage (protein denaturation) may be similar for
the two modalities.
KEYWORDS: Photodynamic therapy, Tumors, Tissue optics, Luminescence, In vivo imaging, Animal model studies, Oxygen, Tissues, Natural surfaces, Space reconnaissance
A fiberoptic isotropic probe system has been developed to
measure both the Space Irradiance (SI) and Fluorescence (F)
within tissue during Photodynamic Therapy (PDT). The probe
is 0.8mm in diameter. The system has a SI sensitivity of
0.1 mW/cm2 and a F sensitivity of 0.1 microgram per
milliliter of DHE in a tissue phantom solution. It also
provides for the time integrated SI and F and a ratio of the
F to SI. A biological response study is being undertaken
using DHE to determine the correlation of therapeutic
response with drug dose, light dose, integrated space
irradiance, and integrated fluorescence in a standardized
animal tumor model. Description of the device and its
performance will be presented along with preliminary results
of animal tumor model studies.
KEYWORDS: Tissues, Tumors, Scattering, Tissue optics, Absorption, Near infrared, In vivo imaging, Photodynamic therapy, Laser scattering, In vitro testing
The optical properties of neoplastic and normal tissues have
been evaluated in the wavelength region from red to near
infrared. The tumor models have been human retinoblastoina and
B16 melanotic iuelanoma transplanted in athymic mice and mammary
adenocarcinoma in C3H mice. The normal tissue results include in
vivo measurements in human and rabbit muscle.
The continued examination of injury sites and mechanisms of cytotoxicity associated with photodynamic therapy (PDT) can take advantage of current molecular and/or biochemical techniques. The increased expression of oxidative stress proteins can be studied as a function of photosensitizer type, treatment conditions and cell type. However, while in-vitro studies can address questions regarding subcellular PDT targets there is growing evidence that in-vivo effects of PDT are mediated by both vascular and direct tumor cell injury. Preclinical PDT studies using mono-l-aspartyl chlorin e6 (NPe6) confirm that the efficacy of this photosensitizer is correlated with plasma levels of this compound and not tumor cell levels.
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