Radiolabeled PSMA Inhibitors

PSMA has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. We have reviewed developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin, GRPr and integrin αvβ3. An overview of the regulatory status of PSMA-targeting radiopharmaceuticals in the USA and Europe is also provided. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new emerging radiolabeling strategies are discussed. Furthermore, insights are given into the production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional refinement of radiopharmaceuticals is required in order to further improve dose-limiting factors, such as nephrotoxicity and salivary gland uptake during endoradiotherapy. The improvement of patient treatment achieved by the advantageous combination of radionuclide therapy with alternative therapies is also a special focus of this review.

Fibroblast Activation Protein Targeted Photodynamic Therapy Selectively Kills Activated Skin Fibroblasts from Systemic Sclerosis Patients and Prevents Tissue Contraction

Systemic sclerosis (SSc) is a rare, severe, auto-immune disease characterized by inflammation, vasculopathy and fibrosis. Activated (myo)fibroblasts are crucial drivers of this fibrosis. By exploiting their expression of fibroblast activation protein (FAP) to perform targeted photodynamic therapy (tPDT), we can locoregionally deplete these pathogenic cells. In this study, we explored the use of FAP-tPDT in primary skin fibroblasts from SSc patients, both in 2D and 3D cultures. Method: The FAP targeting antibody 28H1 was conjugated with the photosensitizer IRDye700DX. Primary skin fibroblasts were obtained from lesional skin biopsies of SSc patients via spontaneous outgrowth and subsequently cultured on plastic or collagen type I. For 2D FAP-tPDT, cells were incubated in buffer with or without the antibody-photosensitizer construct, washed after 4 h and exposed to λ = 689 nm light. Cell viability was measured using CellTiter Glo®®. For 3D FAP-tPDT, cells were seeded in collagen plugs and underwent the same treatment procedure. Contraction of the plugs was followed over time to determine myofibroblast activity. Results: FAP-tPDT resulted in antibody-dose dependent cytotoxicity in primary skin fibroblasts upon light exposure. Cells not exposed to light or incubated with an irrelevant antibody-photosensitizer construct did not show this response. FAP-tPDT fully prevented contraction of collagen plugs seeded with primary SSc fibroblasts. Even incubation with a very low dose of antibody (0.4 nM) inhibited contraction in 2 out of 3 donors. Conclusions: Here we have shown, for the first time, the potential of FAP-tPDT for the treatment of fibrosis in SSc skin.

Decision Regret and Quality of Life after Focal Therapy with Vascular-Targeted Photodynamic Therapy (TOOKAD®) for Localized Prostate Cancer

<b><i>Purpose:</i></b> The aim of the study was to assess quality of life (QoL), decision involvement, and decisional regret after treatment with vascular-targeted photodynamic therapy (VTP) (TOOKAD®) for unilateral low-risk prostate cancer. <b><i>Methods:</i></b> Validated questionnaires (EORTC QLQ-C30 and QLQ-PR25) capturing QoL post-treatment, involvement in decision-making (Control Preferences Scale) and decision regret (Decisional Regret Scale), were given to patients at the 12-month visit after undergoing VTP at our institution between May 2018 and February 2021. <b><i>Results:</i></b> Out of 44 patients, 36 patients were included in this study and 31 (86.1%) responded to the questionnaires. Mean overall health score capturing QoL at 12 months was 79.3 (standard deviation: ±18.1). 70.9% of the patients (<i>n</i> = 22) had no decision regret, and 67.8% of men (<i>n</i> = 21) had an active role in decision-making. In control biopsy at 12 months post-treatment, 19.4% of patients (<i>n</i> = 7) presented with local recurrence and progression to higher Gleason score (GS) was found in 13.8% of patients (<i>n</i> = 5). Patients (<i>n</i> = 3) presenting with tumor recurrence or progression to higher GS in control biopsy showed a significantly higher level of decision regret (<i>p</i> &#x3c; 0.009). <b><i>Conclusion:</i></b> Only 9.7% of men (<i>n</i> = 3) felt a strong emotion of regret at 12 months after VTP. Level of decision regret was significantly higher in patients with local recurrence or tumor progression detected in control biopsy. QoL was stable after VTP.