Adjuvants that Empower the Action of Photodynamic Therapy

Compounds have been devised whose supportive actions make them important adjuvants in the priming of photosensitization to selectively target cancer cells. Here, we highlight the paper by Maytin and Hasan in this issue of Photochemistry & Photobiology, which describes adjuvants methotrexate, 5-fluorouracil, vitamin D and its analogs leading to improved photodynamic therapy outcome. These small molecule adjuvants act by different mechanisms to enhance the cytotoxicity in tumor cells and the therapeutic effect in cancers. These findings add to the list of strategies for enhancement of photodynamic therapy.

Assessing daylight & low-dose rate photodynamic therapy efficacy, using biomarkers of photophysical, biochemical and biological damage metrics in situ

BACKGROUND

Sunlight can activate photodynamic therapy (PDT), and this is a proven strategy to reduce pain caused byconventional PDT treatment, but assessment of this and other alternative low dose rate light sources, and their efficacy, has not been studied in an objective, controlled pre-clinical setting. This study used three objective assays to assess the efficacy of different PDT treatment regimens, using PpIX fluorescence as a photophysical measure, STAT3 cross-linking as a photochemical measure, and keratinocyte damage as a photobiological measure.

METHODS

Nude mouse skin was used along with in vivo measures of photosensitizer fluorescence, keratinocyte nucleus damage from pathology, and STAT3 cross-linking from Western blot analysis. Light sources compared included a low fluence rate red LED panel, compact fluorescent bulbs, halogen bulbs and direct sunlight, as compared to traditional PDT delivery with conventional and fractionated high fluence rate red LED light delivery.

RESULTS

Of the three biomarkers, two had strong correlation to the PpIX-weighted light dose, which is calculated as the product of the treatment light dose (J/cm²) and the normalized PpIX absorption spectra. Comparison of STAT3 cross-linking to PpIX-weighted light dose had an R=0.74, and comparison of keratinocyte nuclear damage R=0.70. There was little correlation to PpIX fluorescence. These assays indicate most of the low fluence rate treatment modalities were as effective as conventional PDT, while fractionated PDT showed the most damage.

CONCLUSIONS

Daylight or artificial light PDT provides an alternative schedule for delivery of drug-light treatment, and this pre-clinical assay demonstrated that in vivo assays of damage could be used to objectively predict a clinical outcome in this altered delivery process.

Chlorin E6 phototoxicity in L. major and L. braziliensis promastigotes-In vitro study

BACKGROUND

Cutaneous leishmaniasis is a zoonosis caused by protozoa of the genus Leishmania. Conventional treatments are long and aggressive, and they trigger a diversity of side effects. Photodynamic Therapy was originally proposed as a treatment for cancer, and it now appears to be a promising therapy for local treatment with fewer side effects of infectious diseases.

METHODS

This study aimed to evaluate Chlorin e6 internalization by Leishmania major and Leishmania braziliensis promastigotes and its viability and effects on mitochondrial activity. Control groups were kept in the dark, while PDT groups received fluence of 10J/cm(2) (660nm). Chlorin internalization was evaluated using confocal microscopy after one hour of incubation for both species.

RESULTS

The mitochondrial activity was evaluated by MTT assay, and viability was measured by the Trypan blue exclusion test. Giemsa staining was used to observe morphological changes. PS was internalized in both species and mitochondrial activity changed in all groups. However, the obtained MTT and Trypan results indicated that despite the change in mitochondrial activity in the dark groups, their viability was not affected, whereas the PDT treated groups had significantly reduced viability. Morphology was drastically altered in PDT treated groups, while groups kept in the dark exhibited the standard morphology.

CONCLUSIONS

This study demonstrates that Chlorin has great potential for being used in PDT as a treatment for cutaneous leishmaniasis, although more studies are needed to determine in vivo application protocols.

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

Pre-treatment protoporphyrin IX concentration in actinic keratosis lesions may be a predictive biomarker of response to aminolevulinic-acid based photodynamic therapy

BACKGROUND

Although aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) photodynamic therapy (PDT) is an effective FDA-approved therapy for actinic keratosis (AK), a substantial fraction of patients (up to 25%) do not respond to treatment. This study examined the feasibility of using pre-treatment measurements of PpIX concentration in AK lesions to predict response of ALA-PpIX PDT.

METHODS

A non-invasive fiber-optic fluorescence spectroscopy system was used to measure PpIX concentration in patients undergoing standard-of-care ALA-PDT for AK. All patients provided assessments of pain at the time of treatment (n=70), and a subset reported pain and erythema 48-76 h after treatment (n=13).

RESULTS

PpIX concentration was significantly higher in lesions of patients reporting high levels of pain (VAS score ≥5) immediately after treatment vs. patients reporting pain scores below VAS=5 (p<0.022) (n=70). However, pain was not an exclusive indicator of PpIX concentration as many patients with low PpIX concentration reported high pain. In a subpopulation of patients surveyed in the days after treatment (n=13), PpIX concentration measured on the day of treatment was uncorrelated with pain-reported immediately after treatment (r=0.17, p<0.57), but positive correlations were found between PpIX concentration and patient-reported pain (r=0.55, p<0.051) and erythema (r=0.58, p<0.039) in the 48-72 h following treatment.

CONCLUSIONS

These data suggest that in vivo optical measurements of PpIX concentration acquired before light delivery may be an objective predictor of response to ALA-PpIX PDT. Identification of non-responding patients on the day of treatment could facilitate the use of interventions that may improve outcomes.

White light-informed optical properties improve ultrasound-guided fluorescence tomography of photoactive protoporphyrin IX

Subsurface fluorescence imaging is desirable for medical applications, including protoporphyrin-IX (PpIX)-based skin tumor diagnosis, surgical guidance, and dosimetry in photodynamic therapy. While tissue optical properties and heterogeneities make true subsurface fluorescence mapping an ill-posed problem, ultrasound-guided fluorescence-tomography (USFT) provides regional fluorescence mapping. Here USFT is implemented with spectroscopic decoupling of fluorescence signals (auto-fluorescence, PpIX, photoproducts), and white light spectroscopy-determined bulk optical properties. Segmented US images provide a priori spatial information for fluorescence reconstruction using region-based, diffuse FT. The method was tested in simulations, tissue homogeneous and inclusion phantoms, and an injected-inclusion animal model. Reconstructed fluorescence yield was linear with PpIX concentration, including the lowest concentration used, 0.025 μg/ml. White light spectroscopy informed optical properties, which improved fluorescence reconstruction accuracy compared to the use of fixed, literature-based optical properties, reduced reconstruction error and reconstructed fluorescence standard deviation by factors of 8.9 and 2.0, respectively. Recovered contrast-to-background error was 25% and 74% for inclusion phantoms without and with a 2-mm skin-like layer, respectively. Preliminary mouse-model imaging demonstrated system feasibility for subsurface fluorescence measurement in vivo. These data suggest that this implementation of USFT is capable of regional PpIX mapping in human skin tumors during photodynamic therapy, to be used in dosimetric evaluations.

Vitamin D Combined with Aminolevulinate (ALA)-Mediated Photodynamic Therapy (PDT) for Human Psoriasis: A Proof-of-Principle Study

We previously showed that select agents (methotrexate or Vitamin D), when administered as a preconditioning regimen, are capable of promoting cellular differentiation of epithelial cancer cells while simultaneously enhancing the efficacy of 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT). In solid tumors, pretreatment with Vitamin D simultaneously promotes cellular differentiation and leads to selective accumulation of target porphyrins (mainly protoporphyrin IX, PpIX) within diseased tissue. However, questions of whether or not the effects upon cellular differentiation are inexorably linked to PpIX accumulation, and whether these effects might occur in hyperproliferative noncancerous tissues, have remained unanswered. In this paper, we reasoned that psoriasis, a human skin disease in which abnormal cellular proliferation and differentiation plays a major role, could serve as a useful model to test the effects of pro-differentiating agents upon PpIX levels in a non-neoplastic setting. In particular, Vitamin D, a treatment for psoriasis that restores (increases) differentiation, might increase PpIX levels in psoriatic lesions and facilitate their responsiveness to ALA-PDT. This concept was tested in a pilot study of 7 patients with bilaterally-matched psoriatic plaques. A regimen in which calcipotriol 0.005% ointment was applied for 3 days prior to ALA-PDT with blue light, led to preferential increases in PpIX (~130%), and reductions in thickness, redness, scaling, and itching in the pretreated plaques. The results suggest that a larger clinical trial is warranted to confirm a role for combination treatments with Vitamin D and ALA-PDT for psoriasis.

Monitoring the efficacy of antimicrobial photodynamic therapy in a murine model of cutaneous leishmaniasis using L. major expressing GFP

A murine model of cutaneous leishmaniasis with green fluorescent protein positive (GFP+) L. major enables the monitoring of parasitic load via measurements of GFP fluorescence intensity, allowing for a faster and more efficient way of monitoring the clinical outcome of photodynamic therapy (PDT). This model may provide new insights on the phototoxic aspects in PDT. Although PDT regimens may be somewhat different in humans, it is expected that the developed model will facilitate the optimization and clinical translation of PDT as a therapy for cutaneous leishmaniasis and the eventual development of topical PDT treatments for other granulomatous infections.

Optimization of topical photodynamic therapy with 3,7-bis(di-n-butylamino)phenothiazin-5-ium bromide for cutaneous leishmaniasis

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) has evolved as a promising therapeutic measure for the treatment of cutaneous leishmaniasis (CL). In particular, phenothiazine compounds have demonstrated efficacy for PDT of CL. The objective of our present study is to define the use of a new specific phenothiazine photosensitizer, 3,7-bis(di-n-butylamino)phenothiazin-5-ium bromide (PPA904) applied topically as a cream to treat CL.

MATERIALS AND METHODS

To establish the optimal conditions for this treatment, we compared two different ways to improve current regimens of PDT with PPA904 cream (500 microM of PPA904 in Unguentum M) by changing the duration of topical application, and by administration of several consecutive PDT procedures. An initial regimen recommended by the manufacturer (Photopharmica Co. Ltd., Leeds, UK) was maintained as a control: the cream was applied topically for 30 minutes at a final concentration of PPA904 at 500 microM, and the designated treatment area was irradiated with a broad band light source of 665+/-15 nm at a fluence of 50 J/cm(2) (50 mW/cm(2)).

RESULTS

The best curative PPA904-PDT regimen was achieved under the conditions of a longer duration of topical application time (90 minutes) and several (three) consecutive treatments with 4-day intervals between treatments. The mechanisms responsible for such improvements (kinetics of drug penetration, depth of necrosis of the CL lesions after PDT, and daily changes in the parasitic load after PDT) are discussed in the present study.

CONCLUSION

Topical PPA904-PDT, implemented as described above, is a promising treatment for CL, and clinical studies will be initiated to establish efficacy in humans.