Colorectal cancer (CRC) is a common cause of cancer and cancer-related death. Surgery is the only curative modality. Fluorescence-enhanced visualization of CRC with targeted fluorescent probes that can delineate boundaries and target tumor-specific biomarkers can increase rates of curative resection. Approaches to enhancing visualization of the tumor-to-normal tissue interface are active areas of investigation. Nonspecific dyes are the most-used approach, but tumor-specific targeting agents are progressing in clinical trials. The present narrative review describes the principles of fluorescence targeting of CRC for diagnosis and fluorescence-guided surgery with molecular biomarkers for preclinical or clinical evaluation.

Tumor-specific targeting with fluorescent probes can enhance contrast for identification of cancer during surgical resection and visualize otherwise invisible tumor margins. Nanobodies are the smallest naturally-occurring antigen-binding molecules with rapid pharmacokinetics. The present work demonstrates the efficacy of a fluorescent anti-CEA nanobody conjugated to an IR800 dye to target and label patient derived pancreatic cancer xenografts. After intravenous administration, the probe rapidly localized to the pancreatic cancer tumors within an hour and had a tumor-to-background ratio of 2.0 by 3 h. The fluorescence signal was durable over a prolonged period of time. With the rapid kinetics afforded by fluorescent nanobodies, both targeting and imaging can be performed on the same day as surgery.

Background/Aim: The alkylating agent trabectedin, which binds the minor groove of DNA, is second-line therapy for soft-tissue sarcoma but has only moderate efficacy. The aim of the present study was to determine the synergistic efficacy of recombinant methioninase (rMETase) and trabectedin on fibrosarcoma cells in vitro, compared with normal fibroblasts. Materials and Methods: HT1080 human fibrosarcoma cells expressing green fluorescent protein (GFP) in the nucleus and red fluorescent protein (RFP) in the cytoplasm and Hs27 normal human fibroblasts, were used. Each cell line was cultured in vitro and divided into four groups: no-treatment control; trabectedin treated; rMETase treated; and trabectedin plus rMETase treated. The dual-color HT1080 cells were used to quantitate nuclear fragmentation in each treatment group. Results: The combination of rMETase and trabectedin was highly synergistic to decrease HT1080 cell viability. In contrast, there was no synergy on Hs27 cells. Moreover, nuclear fragmentation occurred synergistically with the combination of trabectedin and rMETase on dual-color HT1080 cells. Conclusion: The combination treatment of trabectedin plus rMETase was highly synergistic on fibrosarcoma cells in vitro suggesting that the combination can improve the outcome of trabectedin alone in future clinical studies. The lack of synergy of rMETase and trabectedin on normal fibroblasts suggests the combination is not toxic to normal cells. Synergy of the two drugs may be due to the high rate of nuclear fragmentation on treated HT1080 cells, and the late-S/G₂ cell-cycle block of cancer cells by rMETase, which is a target for trabectedin. The results of the present study suggest the future clinical potential of the combination of rMETase and trabectedin for soft-tissue sarcoma.

Background/Aim: Doxorubicin is first-line therapy for soft-tissue sarcoma, but patients can develop resistance which is usually fatal. As a novel therapeutic strategy, the present study aimed to determine the synergy of recombinant methioninase (rMETase) and doxorubicin against HT1080 fibrosarcoma cells compared to Hs27 normal fibroblasts, and rMETase efficacy against doxorubicin-resistant HT1080 cells in vitro. Materials and Methods: The 50% inhibitory concentrations (IC₅₀) of doxorubicin and rMETase, as well as their combination efficacy, against HT1080 human fibrosarcoma cells, Hs27 normal human fibroblasts and doxorubicin-resistant HT1080 (DR-HT1080) cells were determined. Dual-color HT1080 cells which expressed red fluorescent protein (RFP) in the cytoplasm and green fluorescent protein (GFP) in the nuclei were used to visualize nuclear fragmentation during treatment. Nuclear fragmentation was observed with an IX71 fluorescence microscope. Results: The IC₅₀ for doxorubicin was 3.3 μM for HT1080 cells, 12.4 μM for DR-HT1080 cells, and 7.25 μM for Hs27 cells. The IC₅₀ for rMETase was 0.75 U/ml for HT1080 cells, 0.42 U/ml for DR-HT1080 cells, and 0.93 U/ml for Hs27 cells. The combination of rMETase and doxorubicin was synergistic against fibrosarcoma cells but not against normal fibroblasts. The combination of doxorubicin plus rMETase also caused more fragmented nuclei than either treatment alone in HT1080 cells. rMETase alone was highly effective against the DR-HT1080 cells as well as the parental HT1080 cells. Conclusion: The present results indicate the future clinical potential of rMETase in combination with doxorubicin for fibrosarcoma, including doxorubicin-resistant fibrosarcoma.

Background/Aim: Methionine addiction is a fundamental and general hallmark of cancer and is targeted by methionine restriction. The aim of the present study was to examine whether methionine restriction can eliminate cancer cells co-cultured with normal cells that remain healthy. Materials and Methods: The IC₅₀ for recombinant methioninase (rMETase) was determined for HC116 colon-cancer cells using the WST-8 viability assay. HCT-116 cells and Hs27 human normal skin fibroblasts were co-cultured and treated with rMETase at the IC₅₀ concentration for HCT-116 cells. Cell morphology and viability were monitored over 16 days via phase-contrast microscopy. Results: The IC₅₀ for rMETase was 0.46 U/ml for HCT-116 cancer cells. In the untreated control co-cultures, the HCT-116 colon cancer cells overgrew Hs27 normal fibroblasts from day 2. In contrast, rMETase-treated cultures showed elimination of HCT-116 cells by day 8, while Hs27 fibroblasts remained viable and proliferative throughout the experiment. Conclusion: The differential sensitivity of cancer and normal cells to rMETase at 0.46 U/ml was so extensive that cancer cells were essentially eliminated from the co-cultures while the normal cells remained viable and proliferating. The difference in sensitivity of normal and cancer cells growing together suggests that rMETase selectively and precisely targets methionine addiction of cancer and can be a safe and effective clinical anti-cancer agent.

Background/Aim: Methionine addiction, known as the Hoffman effect, makes cancer cells more sensitive to methionine restriction than normal cells. However, the long-term effects of methionine restriction on cancer and normal cells have not been thoroughly studied. Materials and Methods: HCT-116 human colorectal-cancer cells and Hs27 normal skin fibroblasts were treated with 0-8 U/ml of recombinant methioninase (rMETase) for 12 days. The cells were cultured in Dulbecco’s modified Eagle’s medium in 96-well tissue-culture plates. Results: HCT-116 cells were sensitive to all concentrations of rMETase from 0.125 U/ml to 8 U/ml. After day-8 of treatment, HCT-116 cells were acutely sensitive to rMETase, especially at rMETase concentrations of 0.5 U/ml or higher. Normal Hs27 fibroblasts were much less sensitive to rMETase: In the range of 0.125 U/ml to 0.5 U/ml, rMETase had no effect on Hs27 cells. rMETase concentrations up to 2 U/ml had a slight initial effect on Hs27 cells, whereas at concentrations ranging from 4 U/ml to 8 U/ml, rMETase reduced Hs27 viability over the 12-day test period, with acute loss of viability observed after eight days of exposure. Conclusion: Cancer cells were significantly more sensitive to rMETase than normal cells, with an acute loss of cell viability observed in cancer cells after eight days of treatment at concentrations of 0.5 U/ml or higher. These findings highlight the large difference in sensitivity between cancer and normal cells to rMETase and introduce the phenomenon of acute cell death in methionine restriction, which we term “methionine-depletion catastrophe”.