Radiosensitization of orthotopic GIC-driven glioblastoma by doxycycline causes skin damage

Abstract

Doxycycline (DXC) is a tetracycline antibiotic which has been proposed as a breast cancer radiosensitizer by specifically reducing the expression of the DNA repair enzyme DNA PK in breast cancer initiating cells. Since DXC presents favorable pharmacokinetics properties including the capacity to cross the blood-brain barrier, it has been hypothesized that it could radiosensitize brain tumors as well. We have investigated the radiosensitizing capacity of DXC towards human glioma initiating cells (GIC)-driven orthotopic glioblastomas (GB) in NOD/SCID mice that faithfully mimic the growth properties of the clinical tumors of origin. DXC at 10 mg/Kg body weight was subcutaneously delivered daily, 5 days/week for 4 weeks. At the same time, radiotherapeutic fractions of 0.25 Gy to the head were delivered every 3–4 days (twice/week) for 15 weeks. No survival advantage was observed in DXC-treated mice as compared to vehicle-treated mice by this radiosensitizing protocol. On the contrary, skin damage with hair loss and deep ulcers were observed after 4 weeks in DXC-treated mice leading to discontinuation of drug treatment. These results do not support the use of DXC as a radiosensitizer for brain tumors and indicate skin damage as an important side effect of DXC.

Ultra‐hyper‐fractionated radiotherapy for high‐grade gliomas

“…Using GIC-driven orthotopic animal models of HGG that closely mimic the growth properties of the clinical tumors of origin, we recently noticed that the administration of 7.5 Gy in fifteen 0.5 Gy fractions was more effective in terms of increased survival of orthotopic HGG-bearing mice subjected to radiosensitization with ATM inhibitors (ATMi), as compared to RT fractions five times higher (3 × 2.5 Gy) (Frosina et al, 2018). We subsequently observed that the same cumulative radiation dose was more effective in terms of animal survival if split in 0.25 rather than 2.5 Gy fractions even in the absence of a radiosensitizing drug (Frosina et al, 2019). By comparing different fractionation schedules in vivo, we show here that with the same total dose, ≤0.5 Gy fractions given twice/week starting at stages of limited tumor progression (a condition that in the clinical setting often occurs at the end of the guidelines RT treatment), confer survival advantages to multiple GIC-driven orthotopic tumors as compared to standard fractions.…”

“…Those experimental drawbacks were dealt with by appropriate treatment randomization. Further, previous studies in our laboratory had shown that the employed total RT doses of 7.5-13.0 Gy were adequate to quantitate relatively small variations in survival among different treatment groups while lacking significant radiation toxicity (Frosina et al, 2019(Frosina et al, , 2018. Ten mice per treatment group were used.…”

“…Occasional longer gaps between doses were linked to the schedule variations illustrated below (Figure 7). Based on preliminary encouraging results using the COMI model, the initially planned RT schedules included a total dose of 7.5 Gy delivered in 3 × 2.5 Gy for hypo-FRT (a fraction size similar to the 2.0 Gy size employed in the clinics) and 30 × 0.25 Gy fractions for ultra-hyper-FRT, each fraction every 3-4 days (Frosina et al, 2019). In the course of the experiments yet, the planned schedules underwent two kinds of variations.…”

Contrast-enhanced, conebeam CT-based, fractionated radiotherapy and follow-up monitoring of orthotopic mouse glioblastoma: a proof-of-concept study

“…Here, we provide proof-of-concept for contrastenhanced, CBCT-based, fractionated radiotherapy and follow-up monitoring of orthotopic mouse glioblastoma with the help of a stand-alone small animal radiotherapy platform with integrated CBCT scanner. The radiation regimen closely resembling glioblastoma radiotherapy in the clinical routine is feasible, well tolerated, and may serve as a basis for combined modality treatment approaches with biologically targeted and/or immunotherapeutic agents in the context of preclinical target validation [20,21]. No other imaging modalities, such as MR, PET, or BL imaging, are needed for tumor localization, treatment planning, dose administration, and/or tumor volume follow-up.…”

“…We have also tested orthotopic xenotransplants of established human glioblastoma cell lines in immunocompromised mice with similar experiences (data not shown). However, the application of this methodology for orthotopic transplants of patient-derived, low-passage-number, glioma stem-like cell isolates which commonly show more invasive growth patterns will require further investigation [20,21,23,24].…”