Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells <em>In Vitro</em>

In recent years, there has been the difficulty in finding more effective therapies against cancer with less systemic side effects. Therefore Photodynamic ...

Balgrist University Hospital, Zurich, Switzerland

To redirect the lytic activity of cytotoxic T lymphocytes (CTL) toward tumor vascular endothelial cells, we prepared bifunctional proteins with specificity for both alphavbeta3 and CD3. Monocyclic RGD peptides (cRGDfK) were covalently coupled to an anti-CD3 monoclonal antibody at different peptide:protein ratios. The resulting RGDpep-anti-CD3 conjugates bound specifically to alphavbeta3-expressing endothelial cells. Displacement studies with radiolabeled alphavbeta3 ligand demonstrated that the alphavbeta3 binding affinity of RGDpep-anti-CD3 conjugates was elevated as compared to the non-conjugated RGDpep. IC50 values ranged from 150-1.1 nM, depending on the amount of coupled RGDpep molecules per antibody molecule. RGD modification did not affect the ability of anti-CD3 antibodies to bind to CTL. Furthermore, RGDpep-anti-CD3 was fully capable of activating T cells upon CD3 binding as was shown in a Jurkat/NFAT reporter-gene activation assay. All RGDpep-anti-CD3 conjugates were able to induce RGDpep, CD3-dependent lysis of human primary endothelial cells by anti-CD3/IL-2 activated human peripheral blood mononuclear cells (PBMC), with a significant induction of cytotoxicity observed at an E/T ratio as low as 10. Redirecting cytolytic activity reached up to 50% cytotoxicity using the conjugate with the highest RGD peptide load. Combining the good accessibility of tumor blood vessel endothelium for CTL with the efficiency of target cell killing warrants further investigations on anti-tumor effects of this type of conjugates in vivo.

RGD-modified anti-CD3 antibodies redirect cytolytic capacity of cytotoxic T lymphocytes toward alphavbeta3-expressing endothelial cells.

The increasing average age in developed societies is paralleled by an increase in the prevalence of many age-related diseases such as osteoarthritis (OA), which is characterized by deformation of the joint due to cartilage damage and increased turnover of subchondral bone. Consequently, deficiency in DNA repair, often associated with premature aging, may lead to increased pathology of these two tissues. To examine this possibility, we analyzed the bone and cartilage phenotype of male and female knee joints derived from 52- to 104-week-old WT C57Bl/6 and trichothiodystrophy (TTD) mice, who carry a defect in the nucleotide excision repair pathway and display many features of premature aging. Using micro-CT, we found bone loss in all groups of 104-week-old compared to 52-week-old mice. Cartilage damage was mild to moderate in all mice. Surprisingly, female TTD mice had less cartilage damage, proteoglycan depletion, and osteophytosis compared to WT controls. OA severity in males did not significantly differ between genotypes, although TTD males had less osteophytosis. These results indicate that in premature aging TTD mice age-related changes in cartilage were not more severe compared to WT mice, in striking contrast with bone and many other tissues. This segmental aging character may be explained by a difference in vasculature and thereby oxygen load in cartilage and bone. Alternatively, a difference in impact of an anti-aging response, previously found to be triggered by accumulation of DNA damage, might help explain why female mice were protected from cartilage damage. These findings underline the exceptional segmental nature of progeroid conditions and provide an explanation for pro- and anti-aging features occurring in the same individual.

Analysis of osteoarthritis in a mouse model of the progeroid human DNA repair syndrome trichothiodystrophy.

In osteoarthritis (OA), changes occur in both cartilage and subchondral bone. The subchondral bone plate facilitates normal cross-talk between articular cartilage and trabecular subchondral bone, and adaptive changes in the plate due to OA may therefore disturb cross-talk homeostasis. To investigate these changes over time, we examined the cartilage-subchondral bone interface using a combined approach of histologic analysis and in vivo microfocal computed tomography.

Osteoarthritis induction leads to early and temporal subchondral plate porosity in the tibial plateau of mice: an in vivo microfocal computed tomography study.

Trichothiodystrophy (TTD) is a rare, autosomal recessive nucleotide excision repair (NER) disorder caused by mutations in components of the dual functional NER/basal transcription factor TFIIH. TTD mice, carrying a patient-based point mutation in the Xpd gene, strikingly resemble many features of the human syndrome and exhibit signs of premature aging. To examine to which extent TTD mice resemble the normal process of aging, we thoroughly investigated the bone phenotype. Here, we show that female TTD mice exhibit accelerated bone aging from 39 weeks onwards as well as lack of periosteal apposition leading to reduced bone strength. Before 39 weeks have passed, bones of wild-type and TTD mice are identical excluding a developmental defect. Albeit that bone formation is decreased, osteoblasts in TTD mice retain bone-forming capacity as in vivo PTH treatment leads to increased cortical thickness. In vitro bone marrow cell cultures showed that TTD osteoprogenitors retain the capacity to differentiate into osteoblasts. However, after 13 weeks of age TTD females show decreased bone nodule formation. No increase in bone resorption or the number of osteoclasts was detected. In conclusion, TTD mice show premature bone aging, which is preceded by a decrease in mesenchymal stem cells/osteoprogenitors and a change in systemic factors, identifying DNA damage and repair as key determinants for bone fragility by influencing osteogenesis and bone metabolism.

Bone fragility and decline in stem cells in prematurely aging DNA repair deficient trichothiodystrophy mice.

Osteosarcoma (OS) is a rare bone neoplasm that affects mainly adolescents. It is associated with poor prognosis in case of metastases formation. The search for metastasis predicting markers is therefore imperative to optimize treatment strategies for patients at risk and important for the search of new drugs for the treatment of this devastating disease. Here, we have analyzed by microarray the differential gene expression in four human and two mouse OS cell line systems consisting of parental cell lines with low metastatic potential and derivatives thereof with increased metastatic potential. Using two osteoblastic cell line systems, the most common OS phenotype, we have identified forty-eight common genes that are differentially expressed in metastatic cell lines compared to parental cells. The identified subset of metastasis relevant genes in osteoblastic OS overlapped only minimally with differentially expressed genes in the other four preosteoblast or nonosteoblastic cell line systems. The results imply an OS phenotype specific expression pattern of metastasis regulating proteins and form a basis for further investigation of gene expression profiles in patients' samples combined with survival analysis with the aim to optimize treatment strategies to develop new drugs and to consequently improve the survival of patients with the most common form of osteoblastic OS.

Sander M. Botter

Laboratory for Orthopedic Research

Balgrist University Hospital, Zurich, Switzerland

Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells In Vitro

Sander M. Botter

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Balgrist University Hospital, Zurich, Switzerland

Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells In Vitro

Laboratory for Orthopedic Research