Hanne Verswyvel

Chapter 2 │ Page 47 3 RESULTS 3.1 Fluorescently-Transduced Cells Acquire Increases Sensitivity to NTP To determine the e ects of fluorescence-induced photodamage on NTP therapy response, both the parental (SC263) and fluorescently-transduced (SC263T) cell lines were treated with NTP and analyzed 24 hours later for cell survival. While no significant di erences in NTP sensitivity were observed between the SC263T cell line (SC263T-PL) and the parental cells at low passages (SC263-PL) (Figure 3a), at higher passages (PH), the SC263T-PH cells became more sensitive to NTP compared to their parental counterpart (Figure 3b). At NTP treatments of 0.4 J and higher, cellular survival was reduced in the SC263T-PH group compared to parental SC263PH, within the same treatment condition (p ≤ 0.003). Indeed, it is apparent that nontransduced SC263 cells retained their original sensitivity to NTP, regardless of how long they remained in culture (Figure 3c), thus suggesting the absence of genetic drift/instability or selection pressures resulting in phenotypic changes. However, following continuous culturing, the transduced SC263T-PH cells became more sensitive to NTP compared to their early passage counterparts, SC263T-PL (Figure 3d). Quantification of transduced cancer cell survival showed that with higher passages, NTP treatment at 0.9 J and higher, further decreased cell viability by 12% compared to the lower passage cells (p = 0.0135). In summary, our results revealed that viral transduction for live-cell imaging renders cancer cells more sensitive to applied NTP treatment, following prolonged cell culture and passaging. In the following experiments, we aimed to investigate which sources of light could introduce these sensitizing e ects.

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