Anti-tumour activity of fotemustine and protons in combination with bevacizumab

BACKGROUND

Metastatic melanoma is one of the most aggressive tumours and is also very resistant to current therapeutic approaches. The aim of this investigation was the in vitro study of the anti-proliferative effects of fotemustine (FM; 100 and 250 microM), bevacizumab (5 microg/ml) and proton irradiation (12 and 16 Gy) on resistant HTB140 human melanoma cells.

METHODS

Viability was estimated by sulphorhodamine B assay, while cell proliferation was analyzed by 5-bromo-2-deoxyuridine assay. Cell cycle distribution and apoptosis were examined using flow cytometry.

RESULTS

Cell viability and proliferation were reduced after all applied treatments. The level of apoptosis significantly increased after treatment with FM, protons or a combination of all agents, while the apoptotic index ranged from 1.2 to 9.2. Proton irradiation, as well as combined treatment with bevacizumab and protons or 100 microM FM, bevacizumab and protons, have reduced melanoma cell proliferation through the induction of G1 phase arrest. Single FM (250 microM) or bevacizumab treatment and their combination, as well as the joint application of these 2 agents with protons, reduced cell proliferation and provoked G2 phase accumulation.

CONCLUSION

The analyzed treatments reduced cell viability and proliferation, triggered G1 or G2 cell cycle phase accumulation and stimulated apoptotic cell death.

Effects of fotemustine or dacarbasine on a melanoma cell line pretreated with therapeutic proton irradiation

Background

Considering that HTB140 melanoma cells have shown a poor response to either protons or alkylating agents, the effects of a combined use of these agents have been analysed.

Methods

Cells were irradiated in the middle of the therapeutic 62 MeV proton spread out Bragg peak (SOBP). Irradiation doses were 12 or 16 Gy and are those frequently used in proton therapy. Four days after irradiation cells were treated with fotemustine (FM) or dacarbazine (DTIC). Drug concentrations were 100 and 250 μM, values close to those that produce 50% of growth inhibition. Cell viability, proliferation, survival and cell cycle distribution were assessed 7 days after irradiation that corresponds to more than six doubling times of HTB140 cells. In this way incubation periods providing the best single effects of drugs (3 days) and protons (7 days) coincided at the same time.

Results

Single proton irradiations have reduced the number of cells to ~50%. FM caused stronger cell inactivation due to its high toxicity, while the effectiveness of DTIC, that was important at short term, almost vanished with the incubation of 7 days. Cellular mechanisms triggered by proton irradiation differently influenced the final effects of combined treatments. Combination of protons and FM did not improve cell inactivation level achieved by single treatments. A low efficiency of the single DTIC treatment was overcome when DTIC was introduced following proton irradiation, giving better inhibitory effects with respect to the single treatments. Most of the analysed cells were in G1/S phase, viable, active and able to replicate DNA.

Conclusion

The obtained results are the consequence of a high resistance of HTB140 melanoma cells to protons and/or drugs. The inactivation level of the HTB140 human melanoma cells after protons, FM or DTIC treatments was not enhanced by their combined application.