FDA-approved drug screening in patient-derived organoids demonstrates potential of drug repurposing for rare cystic fibrosis genotypes

BACKGROUND

Preclinical cell-based assays that recapitulate human disease play an important role in drug repurposing. We previously developed a functional forskolin induced swelling (FIS) assay using patient-derived intestinal organoids (PDIOs), allowing functional characterization of CFTR, the gene mutated in people with cystic fibrosis (pwCF). CFTR function-increasing pharmacotherapies have revolutionized treatment for approximately 85% of people with CF who carry the most prevalent F508del-CFTR mutation, but a large unmet need remains to identify new treatments for all pwCF.

METHODS

We used 76 PDIOs not homozygous for F508del-CFTR to test the efficacy of 1400 FDA-approved drugs on improving CFTR function, as measured in FIS assays. The most promising hits were verified in a secondary FIS screen. Based on the results of this secondary screen, we further investigated CFTR elevating function of PDE4 inhibitors and currently existing CFTR modulators.

RESULTS

In the primary screen, 30 hits were characterized that elevated CFTR function. In the secondary validation screen, 19 hits were confirmed and categorized in three main drug families: CFTR modulators, PDE4 inhibitors and tyrosine kinase inhibitors. We show that PDE4 inhibitors are potent CFTR function inducers in PDIOs where residual CFTR function is either present, or created by additional compound exposure. Additionally, upon CFTR modulator treatment we show rescue of CF genotypes that are currently not eligible for this therapy.

CONCLUSION

This study exemplifies the feasibility of high-throughput compound screening using PDIOs. We show the potential of repurposing drugs for pwCF carrying non-F508del genotypes that are currently not eligible for therapies.

ONE-SENTENCE SUMMARY

We screened 1400 FDA-approved drugs in CF patient-derived intestinal organoids using the previously established functional FIS assay, and show the potential of repurposing PDE4 inhibitors and CFTR modulators for rare CF genotypes.

Cross-species genetics converge to TLL2 for mouse avoidance behavior and human bipolar disorder

Interspecies genetic analysis of neurobehavioral traits is critical for identifying neurobiological mechanisms underlying psychiatric disorders, and for developing models for translational research. Recently, after screening a chromosome substitution strain panel in an automated home cage environment, chromosomes 15 and 19 were identified in female mice for carrying genetic loci that contribute to increased avoidance behavior (sheltering preference). Furthermore, we showed that the quantitative trait locus (QTL) for baseline avoidance behavior on chromosome 15 is homologous with a human linkage region for bipolar disorder (8q24). Similarly, we now performed comparative analysis on the QTL for avoidance behavior found on chromosome 19 and correspondingly revealed an overlap of the mouse interval and human homologous region 10q23-24, which has been previously linked to bipolar disorders. By means of a comparative genetic strategy within the human homologous region, we describe an association for TLL2 with bipolar disorder using the genome-wide association study (GWAS) data set generated by the Wellcome Trust Case Control Consortium (WTCCC). On the basis of genetic homology and mood stabilizer sensitivity, our data indicate the intriguing possibility that mouse home cage avoidance behavior may translate to a common biochemical mechanisms underlying bipolar disorder susceptibility. These findings pave new roads for the identification of the molecular mechanisms and novel treatment possibilities for this psychiatric disorder, as well as for the validity of translational research of associated psychiatric endophenotypes.

NPY receptor subtype specification for behavioral adaptive strategies during limited food access

The neuropeptide Y (NPY) system in the brain regulates a wide variety of behavioral, metabolic and hormonal homeostatic processes required for energy balance control. During times of limited food availability, NPY promotes behavioral hyperactivity necessary to explore and prepare for novel food resources. As NPY can act via 5 different receptor subtypes, we investigated the path through which NPY affects different behavioral components relevant for adaptation to such conditions. We tested NPY Y1 and Y2 receptor knockout mice and their wild-type littermate controls in a daily scheduled limited food access paradigm with unlimited access to running wheel. Here we show that NPY Y1 receptor deficient mice lack the expression of appetitive behavior and that NPY Y2 receptors control the level of hyperactive behavior under these conditions. Thus, receptor specificity determines the differential expression of NPY-mediated behavioral adaptations to overcome a negative energy status.

Chromosomal mapping of excessive physical activity in mice in response to a restricted feeding schedule

Excessive physical activity plays an important role in the progression of anorexia nervosa (AN) by accelerating weight loss during dietary restriction. To search for mechanisms underlying this trait, a panel of mouse chromosome substitution strains derived from C57BL/6J and A/J strains was exposed to a scheduled feeding paradigm and to voluntary running wheel (RW) access. Here, we showed that A/J chromosomes 4, 12 and 13 contribute to the development of a disrupted RW activity in response to daily restricted feeding. This pattern is characterized by intense RW activity during the habitual rest phase and leads to accelerated body weight loss. Regions on mouse chromosomes 4, 12 and 13 display homology with regions on human chromosomes linked with anxiety and obsessionality in AN cohorts. Therefore, our data open new roads for interspecies genetic studies of AN and for unraveling novel mechanisms and potential effective treatment strategies for these neurobehavioral traits.

Variations in ventral root axon morphology and locomotor behavior components across different inbred strains of mice

Locomotion is a complex behavior affected by many different brain- and spinal cord systems, as well as by variations in the peripheral nervous system. Recently, we found increased gene expression for EphA4, a gene intricately involved in motor neuron development, between high-active parental strain C57BL/6J and the low-active chromosome substitution strain 1 (CSS1). CSS1 mice carry chromosome 1 from A/J mice in a C57BL/6J genetic background, allowing localization of quantitative trait loci (QTL) on chromosome 1. To find out whether differences in motor neuron anatomy, possibly related to the changes in EphA4 expression, are involved in the motor activity differences observed in these strains, motor performance in various behavioral paradigms and anatomical differences in the ventral roots were investigated. To correlate the behavioral profiles to the spinal motor neuron morphology, not only CSS1 and its parental strains C57BL/6J (host) and A/J (donor) were examined, but also a set of other mouse inbred strains (AKR/J, 129x1/SvJ and DBA/2J). Significant differences were found between inbred strains on home cage motor activity levels, the beam balance test, grip test performance, and on alternating versus synchronous hind limb movement (hind limb hopping). Also, considerable differences were found in spinal motor neuron morphology, with A/J and CSS1 showing smaller, possibly less developed, motor neuron axons compared to all other inbred strains. For CSS1 and C57BL/6J, only genetically different for chromosome 1, a correlation was found between motor activity levels, synchronous hind limb movement and neuro-anatomical differences in spinal motor neurons. Inclusion of the other inbred strains, however, did not show this direct correlation. These data verifies the complex nature of the mammalian motor system that may be further dissected using genetic mapping populations derived from these inbred strains.

High-resolution genetic mapping of mammalian motor activity levels in mice

The generation of motor activity levels is under tight neural control to execute essential behaviors, such as movement toward food or for social interaction. To identify novel neurobiological mechanisms underlying motor activity levels, we studied a panel of chromosome substitution (CS) strains derived from mice with high (C57BL/6J strain) or low motor activity levels (A/J strain) using automated home cage behavioral registration. In this study, we genetically mapped the expression of baseline motor activity levels (horizontal distance moved) to mouse chromosome 1. Further genetic mapping of this trait revealed an 8.3-Mb quantitative trait locus (QTL) interval. This locus is distinct from the QTL interval for open-field anxiety-related motor behavior on this chromosome. By data mining, an existing phenotypic and genotypic data set of 2445 genetically heterogeneous mice (http://gscan.well.ox.ac.uk/), we confirmed linkage to the peak marker at 79 970 253 bp and refined the QTL to a 312-kb interval containing a single gene (A830043J08Rik). Sequence analysis showed a nucleotide deletion in the 3' untranslated region of the Riken gene. Genome-wide microarray gene expression profiling in brains of discordant F(2) individuals from CS strain 1 showed a significant upregulation of Epha4 in low-active F(2) individuals. Inclusion of a genetic marker for Epha4 confirmed that this gene is located outside of the QTL interval. Both Epha4 and A830043J08Rik are expressed in brain motor circuits, and similar to Epha4 mutants, we found linkage between reduced motor neurons number and A/J chromosome 1. Our findings provide a novel QTL and a potential downstream target underlying motor circuitry development and the expression of physical activity levels.

Foscan uptake and tissue distribution in relation to photodynamic efficacy

Clinical photodynamic therapy (PDT) schedules are based on the assumption that optimum drug-light intervals are times at which there is a maximum differential between photosensitiser retention in the tumour and surrounding normal tissue. However, vascular-mediated effects contribute to tumour destruction by PDT; therefore, plasma sensitiser levels and endothelial cell drug exposure could also be important determinants of PDT response. The purpose of this study was to investigate the influence of tumour, tissue and plasma concentrations of the photosensitiser Foscan (meta-tetrahydroxyphenylchlorin, mTHPC) on PDT response. Groups of BalbC nude mice, bearing human mesothelioma xenografts (H-MESO1) were injected (i.v.) with a single dose of (14)C-labelled mTHPC, or with two doses, separated by 72 h. Drug levels in plasma, tumour and normal tissues were measured at 5 min to 120 h after drug administration. The PDT tumour and skin responses were evaluated by illuminating separate groups mice at intervals of 5 min to 120 h after injection of Foscan (nonlabelled). Drug levels in both tumour and skin increased during the first 24 h after a single injection, and remained almost constant for at least 120 h. The second injection produced a further, rapid increase in mTHPC levels in tumours and skin, with steady state being maintained from 20 min to 120 h. By contrast, PDT response of both tumours and skin were maximal for illumination at 1-3 h after drug, with very little response when illumination was given 48-120 h after drug. There was no significant correlation between tumour or skin drug level and PDT response. There was, however, a significant correlation between plasma drug levels and tumour or skin response, excluding an initial distribution time of 20 min. These studies demonstrate a pronounced disassociation between tumour drug levels and optimum drug-light intervals for PDT response with Foscan. We suggest that the PDT effect, in both tumours and normal tissues, is largely mediated via vascular damage and that the selectivity of PDT is not based on differential tumour drug uptake.

Intraoperative photodynamic therapy after pleuropneumonectomy in patients with malignant pleural mesothelioma: dose finding and toxicity results

OBJECTIVE

To determine the optimal administered dose of meta-tetrahydroxyphenylchlorin (mTHPC) for intraoperative photodynamic therapy (IPDT) in resected malignant pleural mesothelioma (MPM). The primary objective of this combination treatment was to improve local tumor control.

DESIGN

Phase I/II dose escalation study.

SETTING

Two Dutch cancer centers.

PATIENTS

The study included 28 patients (2 women, 26 men), with pathologically confirmed MPM. The mean age was 57 years (age range, 37 to 68 years), and the World Health Organization performance score was 0 to 1. Epithelial mesotheliomas were found in 17 patients, a sarcomatous mesothelioma was found in 1 patient, and mixed epithelial sarcomatous mesotheliomas were found in 10 patients.

METHODS

Patients were injected with 0.075 mg/kg (4 patients), 0.10 mg/kg (19 patients), or 0.15 mg/kg (5 patients) mTHPC 4 or 6 days before undergoing surgery and IPDT. Complete surgical resection (i.e., pleuropneumonectomy) was followed by integral illumination with monochromatic light of 652 nm (10 J/cm(2)). The real-time fluence rate measurements were performed using four isotropic detectors in the chest cavity to calculate the total light dose.

RESULTS

Dose-limiting toxicity was reached at the level of 0.15 mg/kg mTHPC. Three patients died in the perioperative period, and one death was directly related to photodynamic therapy. Real-time dosimetry identified 12 patients in whom additional illumination had to be given to the diaphragmatic sinuses, which were unavoidably shielded during integral illumination. In two patients, illumination was cancelled due to the insufficient resectability of the tumor. The median survival time for all 28 patients was 10 months. Local tumor control, 9 months after treatment, was achieved in 13 of the 26 patients treated with IPDT.

CONCLUSION

IPDT using mTHPC, combined with a pleuropneumonectomy, resulted in local control of disease in 50% of the treated cases. The considerable toxicity associated with the procedure, however, precludes its recommendation for widespread use. Stricter patient selection and improvements of the IPDT technique may reduce the toxicity.

Photodynamic therapy with meta-tetrahydroxyphenylchlorin for basal cell carcinoma: a phase I/II study

BACKGROUND

Photodynamic therapy (PDT) is a convenient and effective method of treating small superficial tumours. New second-generation photosensitizers offer some advantages over first-generation sensitizers such as haematoporphyrin derivatives.

OBJECTIVES

To define the optimal treatment parameters (drug dose, light dose and time interval) using meta-tetrahydroxyphenylchlorin (mTHPC) as a photosensitizer in patients with multiple basal cell carcinomas (BCCs).

METHODS

Light of 652 nm (100 mW cm(-2)) was used for illuminating different tumours (n = 187) with light doses of 5--15 J cm(-2). Following an intravenous injection of 0.1 mg kg(-1) mTHPC each patient (n = 5) was illuminated on 4 consecutive days. Each day at least three BCCs per patient were treated with PDT.

RESULTS

Response evaluation at 6, 12 and 18 months showed maximum responses for illumination with 10 or 15 J cm(-2) on days 1 or 2 after injection (86% complete responses). Normal tissue reactions (oedema and erythema) around the treatment site were more severe on day 1 than after longer intervals.

CONCLUSIONS

mTHPC is a very effective photosensitizer; short illumination times can result in long-term cures with good cosmetic healing and with skin phototoxicity of short duration.

Photodynamic therapy for malignant mesothelioma: preclinical studies for optimization of treatment protocols

Effective photodynamic therapy (PDT) depends on the optimization of factors such as drug dose, drug-light interval, fluence rate and total light dose (or fluence). In addition sufficient oxygen has to be present for the photochemical reaction to occur. Oxygen deficits may arise during PDT if the photochemical reaction consumes oxygen more rapidly than it can be replenished, and this could limit the efficacy of PDT. In this study we investigated the influence of the drug-light interval, illumination-fluence rate and total fluence on PDT efficacy for the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC). The effect of increasing the oxygenation status of tumors during PDT was also investigated. PDT response was assessed from tumor-growth delay and from cures for human malignant mesothelioma xenografts grown in nude mice. Tumor-bearing mice were injected intravenously with 0.15 or 0.3 mg.kg-1 mTHPC, and after intervals of 24-120 h, the subcutaneous tumors were illuminated with laser light (652 nm) at fluence rates of 20, 100 or 200 mW.cm-2. Tumor response was strongly dependent on the drug-light interval. Illumination at 24 h after photosensitization was always significantly more effective than illumination at 72 or 120 h. For a drug-light interval of 24 h the tumor response increased with total fluence, but for longer drug-light intervals even high total fluences failed to produce a significant delay in tumor regrowth. No fluence-rate dependence of PDT response was demonstrated in these studies. Nicotinamide injection and carbogen breathing significantly increased tumor oxygenation and increased the tumor response for PDT schedules with illumination at 24 h after photosensitizer injection.

Targeting of aluminum (III) phthalocyanine tetrasulfonate by use of internalizing monoclonal antibodies: improved efficacy in photodynamic therapy

The use of monoclonal antibodies (MAbs) directed against tumor-associated antigens for targeting of photosensitizers is an interesting option to improve the selectivity of photodynamic therapy (PDT). Hydrophilic photosensitizers are most suitable for conjugation to MAbs because of their water solubility. The photosensitizer aluminum (III) phthalocyanine tetrasulfonate [AlPc(SO3H)4] has many ideal photochemical properties; however, because of its hydrophilicity, the free form of this sensitizer does not readily reach the critical intracellular target and, therefore, is ineffective in PDT. On the basis of our previous studies, we hypothesized that AlPc(SO3H)4 might be suitable for PDT when coupled to internalizing tumor-selective MAbs. In this study, a reproducible procedure is presented for coupling of AlPc(SO3H)4 to MAbs via the tetra-glycine derivative AlPc(SO2Ngly)4. Conjugation was performed to chimeric MAb (cMAb) U36 and murine MAbs (mMAb) E48 and 425 using a labile ester. Conjugates showed preservation of integrity and immunoreactivity and full stability in serum in vitro. At molar ratios >4, the solubility of the conjugates decreased. Data on the in vitro efficacy of PDT showed that in the chosen experimental setup the internalizing AlPc(SO2Ngly)4-mMAb 425 conjugate was about 7500 times more toxic to A431 cells than the free sensitizer (IC50s, 0.12 nM versus 900 nM). The AlPc(SO2Ngly)4-mMAb 425 conjugate was also more toxic than meta-tetrahydroxyphenylchlorin-mMAb 425 conjugates and free meta-tetrahydroxyphenylchlorin that had been tested previously (M. B. Vrouenraets et al., Cancer Res., 59: 1505-1513, 1999) in the same system (IC50s, 7.3 nm and 2.0 nM, respectively). Biodistribution analysis of AlPc(SO2Ngly)4-125I-labeled cMAb U36 conjugates with different sensitizer:MAb ratios in squamous cell carcinoma-bearing nude mice revealed selective accumulation in the tumor, although to a lesser extent than for the unconjugated 125I-labeled cMAb U36, whereas tumor:blood ratios were similar. These findings indicate that AlPc(SO3H)4 has high potential for use in PDT when coupled to internalizing tumor-selective MAbs.

Targeting of a hydrophilic photosensitizer by use of internalizing monoclonal antibodies: A new possibility for use in photodynamic therapy

Coupling of photosensitizers to tumor-selective monoclonal antibodies (MAbs) is an attractive option for improving the selectivity of photodynamic therapy (PDT). For this purpose, hydrophilic sensitizers would be most suitable because of their solubility in water. However, such sensitizers are known to be ineffective in PDT, probably because they cannot readily pass the cell membrane and reach the critical intracellular target. We used the model compound TrisMPyP-PhiCO(2)H, a hydrophilic porphyrin derivative, to test the hypothesis that hydrophilic photosensitizers might become of therapeutic value when directed into the tumor cell by use of internalizing MAbs. TrisMPyP-PhiCO(2)H was conjugated using a labile ester. Conjugates showed no impairment of integrity on SDS-PAGE, full stability in serum in vitro, and optimal immunoreactivity when the sensitizer:MAb ratio was </=3. At higher molar ratios, the solubility of the conjugates decreased. In vitro internalization experiments showed that TrisMPyP-PhiCONH-(125)I-cMAb U36 and TrisMPyPPhiCONH-(125)I-mMAb 425 conjugates were internalized by A431 cells, in contrast to TrisMPyP-PhiCONH-(125)I-mMAb E48 conjugates. Data on the in vitro efficacy of PDT with MAb-conjugated TrisMPyP-PhiCO(2)H showed that the internalizing cMAb U36 and mMAb 425 conjugates were phototoxic to A431 cells, while the non-internalizing E48 conjugate and the unconjugated sensitizer were not. Biodistribution data of conjugates with sensitizer:(125)I-cMAb U36 ratios varying from 1:1 to 3:1 in tumor-bearing nude mice revealed selective accumulation in the tumor. Conjugates with higher molar ratios were cleared more rapidly from the blood than the unconjugated (125)I-cMAb U36, resulting in lower tumor uptake but similar tumor-to-blood ratios. Our data suggest that hydrophilic photosensitizers might have therapeutic value when targeted to tumors by internalizing MAbs.

The importance of in situ light dosimetry for photodynamic therapy of oral cavity tumors

BACKGROUND

Photodynamic therapy (PDT) is being evaluated for treatment of localized head and neck cancer. "Light dose" is usually prescribed as incident fluence, which takes no account of reflected and scattered light. This study investigates variations in total tissue fluence for a given incident fluence in the oral cavity.

METHODS

Light dosimetry was performed in 19 patients treated with PDT for cancers in the oral cavity and in 5 volunteers. Illumination was with 652 nm laser light delivered via a microlens. In situ dosimetry was performed with isotropic probes held against the tissue in the illuminated area.

RESULTS

Tissue fluences of 254% to 305% of the incident fluence were measured in the illuminated area in healthy volunteers. In the patient population tissue fluences were 133% to 545% of the incident fluence.

CONCLUSION

The relationship between incident and total tissue fluence depended on the location and pigmentation of the target area and was not predictable. In situ dosimetry during cavity illumination allows for more controlled tissue illumination and should be employed as the basis for light dose prescription in PDT for head and neck cancer.

Development of meta-tetrahydroxyphenylchlorin-monoclonal antibody conjugates for photoimmunotherapy

A limitation of photodynamic therapy is the lack of tumor selectivity of the photosensitizer. To overcome this problem, a protocol was developed for coupling of meta-tetrahydroxyphenylchlorin (mTHPC), one of the most promising photosensitizers, to tumor-selective monoclonal antibodies (MAbs). mTHPC was radiolabeled with 131I to facilitate the assessment of the in vitro and in vivo behavior. After the modification to 131I-mTHPC-(CH2COOH)4, thus increasing the water solubility and creating a functional moiety suitable for coupling, conjugation was performed using a labile ester. Insoluble aggregates were not formed when mTHPC-MAb conjugates with a molar ratio of up to 4 were prepared. These conjugates showed a minimal impairment of the integrity on SDS-PAGE, full stability in serum in vitro, and an optimal immunoreactivity. To test the in vivo behavior of the mTHPC-MAb conjugates, the head and neck squamous cell carcinoma-selective chimeric MAb U36 was used in head and neck squamous cell carcinoma-bearing nude mice. Biodistribution data showed that the tumor selectivity of cMAb U36-conjugated mTHPC was increased in comparison with free mTHPC, despite the fact that conjugates with a higher mTHPC:MAb ratio were more rapidly cleared from the blood. Preliminary results on the in vitro efficacy of photodynamic therapy with MAb-conjugated mTHPC showed that mTHPC coupled to the internalizing murine MAb 425 exhibited more phototoxicity than when coupled to the noninternalizing chimeric MAb U36.

Does tumour uptake of Foscan determine PDT efficacy?

Preferential retention of photosensitizers in tumours has always been one of the major goals in the search for new photosensitizers and has determined the design of clinical trials with respect to the interval between drug administration and illumination. The purpose of this study was to investigate the importance of tumour and plasma concentrations of Foscan (mTHPC, meta-tetrahydroxyphenylchlorin) in relation to PDT effect. Both pharmacokinetic and tumour response studies were carried out in mice bearing s.c. RIF1 tumours. mTHPC was injected in 1 or 2 doses of 0.3 mg x kg-1. For distribution studies, 14C-labelled mTHPC was given 5 min to 48 hr before determination of plasma and tumour drug levels. Non-labelled sensitizer was used to determine the PDT efficacy for illumination at 5 min to 48 hr after drug administration. PDT efficacy was greatest for illumination at 1 to 3 hr, and for an interval of 48 hr there was no significant tumour-growth delay. In contrast, mTHPC tumour drug levels reached a maximum 6 hr after injection and remained high for 48 hr. A comparison of pharmacokinetics and response studies revealed no significant correlation between tumour mTHPC levels and tumour response. There was, however, a significant correlation between plasma drug levels and tumour response for time intervals of 1 to 48 hr. This association may imply that PDT protocols should use shorter drug-light intervals in combination with lower drug doses. This would increase safety and decrease the extent and duration of normal tissue photosensitization.

Foscan-mediated photodynamic therapy for a peritoneal-cancer model: drug distribution and efficacy studies

Distribution of the photosensitizer Foscan (meta-tetrahydroxyphenylchlorin, mTHPC), after i.v. or i.p. injection, was investigated in Wag/Rij rats bearing i.p. tumours. These results were compared with the efficacy of mTHPC-mediated photodynamic therapy for illumination intervals of 4 hr to 3 days. For the distribution experiments a single tumour (CC53I colon carcinoma) was implanted intra-abdominally in a fat pad, or a cell suspension (1 x 10(6) CC531 cells) was injected into the peritoneal cavity, which results in a dissemination of tumour nodules on the peritoneum. 14C-mTHPC was not selectively taken up in the single-tumour model after i.v. or i.p. injection, but higher concentrations were achieved for i.p. administration. For this tumour model the concentration ratios between tumour and normal tissue never exceeded a value of 3. In the disseminated-tumour model, an uptake of up to 40% of the injected dose was found per gram tumour at 4 hr after an i.p. injection and this resulted in very high (> 14) concentration ratios of tumour to normal tissues. Low uptake was found after the i.v. injection route (1% of the injected dose per gram tumour) with lower tumour/normal tissue ratios (<8). The efficacy of i.p. photodynamic therapy (IPPDT) was evaluated using the single-tumour model only. The lower abdomen was illuminated at 4 hr to 3 days after mTHPC, and tumour size was repeatedly measured via a small laparoscopy. Significant delay in tumour regrowth was achieved for 6 J x cm-2 at 1 day after i.v., or at 4 hr after i.p. mTHPC (p values 0.019 and 0.045 respectively). Response to PDT, of tumours implanted in the fat pad, was not greater for i.p. administration of the photosensitizer and there was a poor correlation between times of maximum drug uptake in tumours and optimal illumination times for PDT efficacy.

Intraperitoneal photodynamic therapy: comparison of red and green light distribution and toxicity

The aim of this study was to compare red (652 nm) and green (514 nm) light for photodynamic therapy (PDT) of the peritoneal cavity with emphasis on light distribution and toxicity. Red-light PDT was limited by intestinal toxicity and it was hypothesized that less penetrating green light would allow higher light doses to be used in the peritoneal cavity. Female non-tumor-bearing rats were photosensitized with mTHPC (meta-tetrahydroxyphenylchlorin, Foscan) intravenously or intraperitoneally and the peritoneum was illuminated using a minimally invasive technique. For both red and green light, the time of illumination was varied to give the required dose. Light fluence rate was measured in situ at multiple sites within the abdominal cavity. The toxicity experiments were carried out with a total of 160 J incident red or 640 J incident green light and a drug dose of 0.15 mg/kg Foscan. For red light a mean fluence rate of 55.2 +/- 38.5 mW cm-2 was measured, with a peak fluence rate of 128 mW cm-2 on the intestines. For green light the mean and peak fluence rates were 8.2 +/- 9.0 (i.e. including zero fluence rate measurements) and 28 mW cm-2, respectively. Intestines were most vulnerable to red light illumination. The intravenous injection route resulted in increased toxicity for red light, but for green light there were no major differences between intravenous and intraperitoneal routes. The 4 h interval between drug and illumination resulted in very little toxicity for both wavelengths. We conclude that for intraperitoneal PDT green light allows higher light doses than red light, but the light distribution over the peritoneum is much less favorable and may not be suitable for whole peritoneal illumination using a minimal-access technique.

Receptor-mediated uptake of low-density lipoprotein by B16 melanoma cells in vitro and in vivo in mice

Selective delivery of cytotoxic anti-neoplastic drugs can diminish the severe side-effects associated with these drugs. Many malignant tumours express high levels of low-density lipoprotein (LDL) receptors on their membranes. Therefore, LDL may be used as a carrier to obtain selective delivery of anti-neoplastic drugs to tumours. The present study was performed to investigate the feasibility of the murine B16 tumour/mouse model for the evaluation of LDL-mediated tumour therapy. LDL binds with high affinity to LDL receptors on cultured B16 cells (Kd, 5.9 +/- 2.3 micrograms ml-1; Bmax 206 +/- 23 ng LDL mg-1 cell protein). After binding and internalisation, LDL was very efficiently degraded: 724 +/- 19 ng LDL mg-1 cell protein h-1. Chloroquine and ammonium chloride completely inhibited the degradation of LDL by the B16 cells, indicating involvement of lysosomes. LDL receptors were down-regulated by 70% after preincubation of B16 cells with 300 micrograms ml-1 LDL, indicating that their expression is regulated by intracellular cholesterol. To evaluate the uptake of LDL by the B16 tumour in vivo, tissue distribution studies were performed in C57/B1 mice inoculated with B16 tumours. For these experiments, LDL was radiolabelled with tyramine cellobiose, a non-degradable label, which is retained in cells after uptake. At 24 h after injection of LDL, the liver, adrenals and the spleen were found to be the major organs involved in LDL uptake, with tissue-serum (T/S) ratios of 0.82 +/- 0.08, 1.17 +/- 0.20 and 0.69 +/- 0.08 respectively. Of all the other tissues, the tumour showed the highest uptake of LDL (T/S ratio of 0.40 +/- 0.07). A large part of the LDL uptake was receptor mediated, as the uptake of methylated LDL was much lower. Although the LDL uptake by the liver, spleen and adrenals is higher than that by the tumour, the LDL receptor-mediated uptake by these organs may be selectively down-regulated by methods that do not affect the expression of LDL receptors on tumour cells. It is concluded that the B16 tumour-bearing mouse constitutes a good model to evaluate the effectiveness of LDL-mediated delivery of cytotoxic (pro)drugs to tumours in vivo.

Influence of fractionation and fluence rate in photodynamic therapy with Photofrin or mTHPC

Various schedules of fractionated photodynamic therapy (PDT), delivered at two different light fluence rates, were investigated in the RIF1 tumor model in an attempt to minimize the development of hypoxia during PDT and thereby improve tumor response relative to single treatments. The photosensitizers Photofrin and meta-tetrahydroxyphenylchlorin (mTHPC) were used in combination with either interstitial or superficial illumination. For both methods of illumination, equal volumetric light doses gave similar tumor responses, as measured by tumor regrowth times and number of cures. Fractionation of superficial illumination did not generally improve tumor response compared with a single illumination with the same total light dose. The only fractionated schedules which demonstrated a trend for increased cure were six fractions of superficial illumination given with short (1 h) dark periods between illuminations. Using both photosensitizers, an increase in tumor regrowth time occurred when tumors were illuminated interstitially with continuous light at a linear diffuser output of 50 mW compared with 100 mW per cm diffuser length. Discontinuous illumination with alternating light and dark periods of 30 s improved the tumor response further for mTHPC-mediated PDT at a fluence rate of 100 mW cm(-1). No improvement in response was seen by discontinuous interstitial illumination after Photofrin-mediated PDT. These results demonstrate that lower fluence rates and/or fractionating the light dose delivered can improve the response of the RIF1 tumor to PDT but that the choice of dark intervals between fractions is critical.

Enhancement of photodynamic therapy by mitomycin C: a preclinical and clinical study

Photodynamic therapy (PDT) using Photofrin was used in combination with a hypoxic toxin (mitomycin C, MMC) to treat four patients with recurrent skin metastasis of a mammary carcinoma. In preclinical experiments an additive effect was found for the combination of MMC and PDT for treating subcutaneous RIF1 tumours in mice. When interstitial PDT was combined with a low dose of MMC (administered 15 min before illumination), the Photofrin dose or light dose could be reduced by a factor of 2 in order to obtain equivalent cure rate or growth delay. In the clinical pilot study, a low dose of Photofrin (0.75 mg kg-1) was used for PDT alone (superficial illumination) or combined with low-dose MMC (5 mg m-2). Different tumour areas were illuminated with or without a preceding infusion of MMC. Both tumour response and skin photosensitivity were scored. After 8-12 weeks of treatment, tumour cure could be achieved by administering light doses > or = 150 J cm-2 for PDT alone and similar effects were obtained when light doses of 75-87.5 J cm-2 were given after infusion with MMC. In all cases necrotic tissue of both tumour and surrounding skin was observed, which lasted for a mean of 5 months (range 2-20 months). Skin phototoxicity, tested by using a standardised illumination of skin patches on the back, lasted maximally 3 weeks. Three main conclusions could be drawn from these studies: (1) The enhanced effects of the combination of PDT and MMC observed in mouse tumours can be extrapolated to patients with mammary skin metastasis. (2) The combination of PDT and hypoxic toxins facilitates treatment by permitting lower doses of photosensitiser to be used (thereby reducing skin phototoxicity) or lower light doses (thereby reducing illumination times and allowing the possibility to treat larger tumour areas). (3) Restoration of skin after PDT in previously treated tumour areas (chemotherapy, radiation therapy and surgery) is very low.

Vascular perfusion and hypoxic areas in RIF-1 tumours after photodynamic therapy

The influence of photodynamic therapy (PDT) on vascular perfusion and the development of hypoxia was investigated in the murine RIF-1 tumour. Image analysis was used to quantify changes in perfusion and hypoxia at 5 min after interstitial Photofrin-mediated PDT. The fluorescent stain Hoechst 33342 was used as an in vivo marker of functional vascular perfusion and the antibody anti-collagen type IV as a marker of the tumour vasculature. The percentage of total tumour vasculature that was perfused decreased to less than 30% of control values after PDT. For the lower light doses this decrease was more pronounced in the centre of the tumour. The observed reduction in vascular perfusion showed a good linear correlation (r = 0.98) with previously published tumour perfusion data obtained with the 86Rb extraction technique. The image analysis technique provides extra information concerning the localisation of (non)-perfused vessels. To detect hypoxic tumour areas in vivo, an immunohistochemical method was used employing NITP [7-(4'-(2-nitroimidazol-1-yl)-butyl)-theophylline]. A large increase in hypoxic areas was found for PDT-treated tumours. More than half the total tumour area was hypoxic after PDT, compared with < 4% for control tumours. Our studies illustrate the potential of image analysis systems for monitoring the functional consequences of PDT-mediated vascular damage early after treatment. This provides direct confirmation that the perfusion changes lead to tissue hypoxia, which has implications for the combined treatment of PDT with bioreductive drugs.

Mechanisms for optimising photodynamic therapy: second-generation photosensitisers in combination with mitomycin C

Mechanisms for improving photodynamic therapy (PDT) were investigated in the murine RIF1 tumour using meso-tetrahydroxyphenylchlorin (m-THPC) or bacteriochlorin a (BCA) as photosensitisers and comparing these results with Photofrin-mediated PDT. The 86Rb extraction technique was used to measure changes in perfusion at various times after interstitial PDT. Non-curative combinations of light doses with m-THPC and BCA PDT markedly decreased vascular perfusion. This decrease was more pronounced for both new photosensitisers than for Photofrin. Comparison of tumour perfusion after PDT with tumour response revealed an inverse correlation for all three photosensitisers, but the relationship was less clear for m-THPC and BCA. In vivo/in vitro experiments were performed after Photofrin or m-THPC PDT in order to assess direct tumour kill (immediate plating) vs indirect vascular effects (delayed plating). For both photosensitisers, there was little direct cell killing but clonogenic survival decreased as the interval between treatment and excision increased. When m-THPC PDT was combined with mitomycin C (MMC), light doses could be decreased by a factor of 2 for equal tumour effects. Lower light and m-THPC doses could be used compared with Photofrin PDT in combination with MMC. BCA PDT with MMC did not result in a greater tumour response compared with BCA PDT alone. Reduction in both light and photosensitiser does for effective PDT regimes in combination with MMC offers substantial clinical advantages, since both treatment time and skin photosensitisation will be reduced.

Photosensitizing efficacy of MTHPC-PDT compared to photofrin-PDT in the RIF1 mouse tumour and normal skin

The new photosensitizer, meso-tetrahydroxyphenylchlorin (mTPHC) was compared with Photofrin in the murine RIF1 tumour and in normal mouse skin. A range of mTHPC or Photofrin doses were given at intervals of 1 hr to 7 days before illumination. mTHPC-PDT resulted in much higher tumour phototoxicity with longer regrowth delays and more cures. The RIF1 tumour could be effectively treated with 30 J cm-1 (interstitial illumination) at 1 day after mTHPC, whereas 4 to 13 times higher light doses were required with Photofrin for an equivalent anti-tumour effect. High doses of mTHPC also caused more skin phototoxicity (superficial illumination) than Photofrin for the 1-day illumination interval. Evaluating both tumour and normal skin photosensitization, the largest therapeutic gain factor (TGF) for mTHPC-PDT was achieved with a low drug dose (0.15 mg kg-1) at 1 day before illumination (TGF = 5.6, relative to Photofrin PDT). The duration of cutaneous photosensitivity for mTHPC was shorter than for Photofrin. The light dose required to produce a desquamation response in 50% of the animals increased more than 20-fold over the period 1 to 7 days after high doses of mTHPC, whereas this light dose only increased by a factor of 2 from 1 to 7 days after Photofrin. The large therapeutic gains seen for mTHPC-mediated PDT compared to Photofrin, plus the rapid fading of skin photosensitization, suggest that mTHPC is a potent photosensitizer suitable for clinical testing.

Partial protection of photodynamic-induced skin reactions in mice by N-acetylcysteine: a preclinical study

The major side effect of photodynamic therapy (PDT) using Photofrin is enhanced skin sensitivity for sunlight, which persists for 3-8 weeks after injection. Formation of singlet oxygen and radicals is believed to be involved in the basic mechanism of inducing skin damage. Reducing this side effect would make PDT more widely acceptable, particularly for palliative use. Hairless dorsal skin patches of mice, injected with 10 mg kg-1 photofrin intraperitoneally (i.p.) 24 h before illumination, were used to evaluate the effect of increasing light doses. The light was obtained from a halogen lamp and transmitted via a fiber optic to illuminate a field of 2.5 cm2. After establishing a dose-response relationship for single or fractionated light dose illumination of the skin, drugs known to scavenge radicals, quench singlet oxygen or interfere with histamine release were tested for their protective effect. N-acetyl-cysteine (NAC), a radical scavenger, administered i.p. (1000 and 2000 mg kg-1) 1 h before illumination produced a significant decrease in skin damage at light doses > 50 J cm-2 (protection factor of 1.3-1.8). When NAC was administered in a dose of 500 mg kg-1, no protection was observed. Fractionated illumination experiments in combination with multiple injections of NAC (1000 mg kg-1) also failed to show any protection. The addition of Ranitidine, a histamine blocking agent (25-100 mg kg-1), given prior to illumination, resulted in a limited protection at higher light doses. From this study we conclude that NAC could be of value in amelioration of the photosensitivity in patients treated with PDT.

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.

Changes in perfusion of mouse tumours after photodynamic therapy

The influence of photodynamic therapy (PDT) on vascular perfusion was investigated in 2 s.c. mouse tumours, a radiation-induced fibrosarcoma (RIF I) and a squamous-cell carcinoma (SCCVII). The 86Rb extraction technique was used to measure changes in perfusion relative to cardiac output at various intervals after interstitial PDT. Control groups showed that vascular perfusion in the RIF I tumours decreased with increasing tumour size. For both tumours, of constant size, vascular perfusion decreased to less than 10% of control values within 5 min after high PDT doses. Significant decreases in vascular perfusion were also seen after lower, sub-curative doses. Thereafter there was slow recovery towards control levels. Photofrin given at shorter intervals before illumination generally resulted in even larger decreases in tumour perfusion, and slower recovery. Comparison of tumour perfusion measurements after PDT with tumour response revealed an inverse correlation with tumour growth delay both for the RIF I and for the SCCVII tumours. PDT with sub-curative light doses appears to decrease vascular perfusion in the RIF I and SCCVII for a period of at least 24 hr. The most severe reductions in tumour blood flow were associated with the longest regrowth delays, indicating a major role of vascular damage in tumour response to PDT.

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.