Photodynamic therapy of C3H tumours in mice: Effect of drug/light dose fractionation and misonidazole

Effects of photodynamic therapy in combination with Adriamycin

The combination of photodynamic therapy (PDT) and Adriamycin (ADM) was studied in the animal model system. Photohem (PH) was used as a photosensitizer. Mice bearing carcinoma epidermoides LL of the lung received PH once at a dose 10 mg/kg and after 24 h ADM was injected i.p. at a dose 3 mg/kg and tumors were illuminated with laser light after three different time intervals, 15 min, 3 and 24 h. To evaluate the effect of PDT and PDT combined with ADM the intensity of lipid peroxidation in tumor tissue and in blood serum was determined using the thiobarbituric acid assay. PDT induces an increase of malondialdehyde (MDA) concentration in tumor tissue as well as in blood serum. When PDT is combined with ADM, the MDA level in tumor tissue is similar to the level of this product as in the PDT alone. No enhancement of the efficiency of the combined treatment was observed at these experimental conditions. This is also confirmed by the tumor growth dynamics, survival time of animals and flow cytometric DNA analysis of tumor cells. For the successful combination of PDT with chemotherapy it is suggested to apply the drugs at the regimen which will allow to avoid the interaction between two agents since the ground state interaction between PH and ADM is stated spectroscopically. It should lead to the conclusion that the sequence of the combination of two treatment modalities is an important factor for synergistic effect.

What does photodynamic therapy have to offer radiation oncologists (or their cancer patients)?

Major advances have recently been made in photodynamic therapy (PDT) for clinical application, including the development of more powerful photosensitizers and light sources and suitable light applicators. PDT is emerging as an attractive new form of cancer therapy, suitable for treating superficial lesions (less than 1 cm in depth) and carcinoma in situ, or as an adjuvant to surgery for more bulky disease. PDT is therefore complementary to radiotherapy which is better suited to treating larger tumours. There are some qualitative similarities between light distribution in tissue during superficial illumination and ionizing radiation dose distributions during external beam irradiation, or between interstitial PDT and brachytherapy, although the geometric scale is very different (visible light penetrates a maximum of 5-10 mm in tissue). The contribution of scattered light to tissue irradiance is much greater than for ionizing radiation and in situ light dosimetry is very important (although rather complicated) to ensure adequate illumination without over-treating. Dosimetry and treatment planning are highly advanced for ionizing radiation and are routine in all radiotherapy departments. Proper in situ light dosimetry and dose distribution calculation for PDT is in its infancy. Physicists have an important role to play in the further optimization of clinical PDT and much of the infrastructure and expertise present in the radiotherapy department is ideally suited to accommodate PDT. In this review, parallels and contrasts are made between PDT and ionizing radiation for both mechanistic and dosimetric aspects of the therapies. A summary of the most interesting clinical applications is also given.

Adjuvant intraoperative photodynamic therapy in experimental colorectal cancer

A reliable animal model for quantitative assessment of local recurrence of colorectal cancer was developed using colo26 tumour in BALB/c mice. The effect of adjuvant intraoperative photodynamic therapy to potentially curative surgery on local recurrence was examined in four study and four control groups. Study groups received 15 mg kg-1 Photofrin (a photosensitizing drug) 24 h before surgery. After 'curative' tumour excision, the tumour beds were illuminated with either 630 nm or 510 nm laser light each at 40 and 70 J/cm-2. Controls received surgery only, surgery and Photofrin only or surgery and either 630 nm or 510 nm light. The local recurrence rates at 70 days were 17-33 per cent in the study groups compared with 83-100 per cent in the control groups (P < 0.001; log rank test). Photodynamic therapy is capable of reducing local recurrence following potentially curative excision of tumour in this model.

The use of porphyrins and non-ionizing radiation for treatment of cancer

Photodynamic therapy (PDT) is the treatment of malignant lesions with visible light following systemic or local administration of a photosensitizer or its precursor. Initially, hematoporphyrin derivative and a purified component called Photofrin II was used for clinical PDT. Later on interest has focused on new sensitizers with more favourable absorption as regards light transmission in tissues. Twenty years of clinical experience has revealed that PDT is best applied to early stage cancers. The present review discusses the basic components of PDT and its clinical use in treatment of cancer.

Comparing the anti-tumor effect of several bioreductive drugs when used in combination with photodynamic therapy (PDT)

PURPOSE

To compare the effect on the RIF-1 murine sarcoma of nine bioreductive agents from five different classes when used in combination with either photodynamic therapy or clamping.

METHODS AND MATERIALS

RIF-1 tumors implanted intradermally in C3H mice were treated with either 50J photodynamic therapy or with 120 min clamping in combination with either misonidazole, pimonidazole, metronidazole, nimorazole, RB6145, RSU1069, SR4233, mitomycin-C, or RB90740. The tumors were measured 3 times-per-week until reaching 4 x their initial treatment volume.

RESULTS

RSU1069 produced the greatest anti-tumor activity in combination with both photodynamic therapy and clamping. RB6145 also substantially enhanced the effect of photodynamic therapy and clamping whereas misonidazole induced a smaller, but significant increase. Mitomycin-C had no effect under clamped conditions, but greatly increased the tumorcidal effect of photodynamic therapy. Mitomycin-C also induced an effect when given with light alone. None of the other agents showed any augmentation of the tumor cell killing induced by photodynamic therapy.

CONCLUSION

Of the bioreductive agents studied RSU1069, RB6145 and mitomycin-C showed the greatest anti-tumor response in combination with photodynamic therapy.

Enhancement of interstitial photodynamic therapy by mitomycin C and EO9 in a mouse tumour model

The tumoricidal effect of interstitial photodynamic therapy (IPDT) using Photofrin was found to increase when combined with the bioreductive alkylating agent mitomycin C (MMC) and, to a lesser extent, with the indoloquinone EO9. When MMC was given prior to IPDT or RIF1 tumours, the light dose required for a given regrowth time or for 50% cure was reduced by a factor of 2 compared with IPDT alone. MMC given immediately after illumination did not increase the effects of IPDT, although MMC plus illumination without photosensitizer produced a significant increase in regrowth time compared with MMC or light alone. Combination of IPDT with EO9, given directly before illumination, only marginally increased the tumour regrowth times at non-toxic doses. These results demonstrate that combining IPDT with MMC greatly improves the tumour response. Factors such as PDT-induced hypoxia, pH changes, temperature increases and production of toxic reactive oxygen species by both drugs may play a role in the enhanced MMC cytotoxicity.

Interaction of the bioreductive drug SR 4233 and photodynamic therapy using photofrin in a mouse tumor model

PURPOSE

Combining the bioreductive drug SR 4233 with interstitial photodynamic therapy to improve efficacy.

METHODS AND MATERIALS

RIF1 tumors were implanted subcutaneously in mice and treated with interstitial photodynamic therapy. The bioreductive drug SR 4233 (a benzotriazine which exhibits preferential cell killing under hypoxic conditions) was combined with photodynamic therapy to exploit the induced hypoxia. SR 4233 was given to mice prior to or just after illumination. The effect of multiple SR 4233 injections given over the first 3 days after treatment was also evaluated.

RESULTS

The results from experiments with a 24 hr interval between Photofrin and illumination showed that SR 4233 produced only a small additional growth delay compared with photodynamic therapy alone (light doses of 300 or 400 J/cm, combined with 6 x 15 mg/kg SR 4233). Some cures (6/60), however, were found in groups treated with 200 to 400 J/cm with SR 4233, whereas only two cures (2/77) occurred at light doses up to 400 J/cm after photodynamic therapy alone. Reducing the interval between Photofrin injection and illumination increased the number of cures in the combination group, although this was associated with a marked increase in toxicity. A small increase in cure rate was observed for the combination of photodynamic therapy (6 hr interval) and SR 4233, although this was not significant due to the limited number of mice that survived treatment.

CONCLUSION

Only a limited effect of combining SR 4233 and interstitial photodynamic therapy was observed in this tumor model. A possible explanation could be the rapid conversion of SR 4233 into inactive metabolites.

New drugs and future developments in photodynamic therapy

New photosensitizing drugs are becoming available which should improve on some of the disadvantages of haematoporphyrin derivates for photodynamic therapy (PDT). The main features are shorter duration of systemic photosensitisation, activation by longer and more penetrating light and better tumour to normal tissue drug uptake ratios. These drugs together with better understanding of in vivo light dosimetry promise to improve both results and clinical acceptability for PDT in future studies.

Tumor hypoxia, reoxygenation and oxygenation strategies: possible role in photodynamic therapy

The concept of hypoxia and its role in tumor therapy are currently under re-evaluation. Poor oxygenation is no longer visualized as an independent feature promoting necrosis and resistance to treatments, but rather as one of the several interdependent microenvironmental parameters associated with impaired blood perfusion. Tumor cells display several survival strategies and remain clonogenic for long periods in nutrient-deprived situations. Reoxygenation may cause lethal damage, improve the response to therapy, or else allow the cell variants adapted to hypoxia to resume proliferation with enhanced aggressiveness and resistance to treatment. The blood supply parameters, oxygenation status and metabolism of malignant cells are discussed here from the standpoint of tumor photodynamic therapy. The role of the tumor interstitial fluid as oxygen- and sensitizer-carrier is discussed. Techniques for assessing tumor oxygenation and for mapping hypoxic territories are described. Strategies for locally improving the oxygenation levels or for selectively destroying the hypoxic populations are outlined.

Phthalocyanine fluorescence in tumors during PDT

Athymic nude mice with human tumors transplanted to one of the hind legs were given aluminium phthalocyanine disulfonate (AlPcS2) intraperitoneally. Twenty-four hours after the injection the mice were placed with the tumor in the sample position in a fluorescence spectrometer with modulated excitation. Exposure of the tumors to laser light at a fluence rate of 50-200 mW/cm2 led to a rapid transient reduction by up to 50% of the phthalocyanine fluorescence of the tumor. After the laser irradiation the fluence rate of the fluorescence increased almost up to the initial value within a few minutes. This finding should be taken into account when optimal fluence rates and dose fractionation schemes are sought for photodynamic therapy.