Tumour thermotolerance, a physiological phenomenon involving vessel normalisation

Figures & data

Figure 1. Tumour oxygenation as a function of daily fractionated mild temperature hyperthermia (41.5°C, 60 min). Tumour oxygenation is transiently increased by fractionated mild temperature hyperthermia (MTH) treatment in B16F10 and SCK tumors as measured in real time by Eppendorf histograph. -▪- control and -•- 41.5°C (60 min) heatings.

Figure 2. Vascular thermal tolerance. Pre-treatment of tumours with mild temperature hyperthermia (41.5°C, 60 min) increases tumour oxygenation by conventional hyperthermia (43°C, 60 min) treatment in B16F10 (A) and SCK (B) tumours. Representative pimonidazole stainings of control, and different hyperthermia schedules in B16F10 tumours (C). A minimum of 3 tumours and 10 randomly chosen images per treatment group were acquired. Original magnification, ×200; Scale bar 50 µM. *p < 0.05 versus control; **p < 0.05 versus 43°C treatment group.

Figure 3. Histological analysis of pericytes and microvessel density (MVD) after hyperthermia treatment schedules. Co-localisation staining of pericytes (α-SMA, green) and microvessel density (CD31, red) in B16F10 tumours (A). Quantification of IF staining for microvessel density (CD31) (B), pericytes (α-SMA) (C) and pericyte covered vessels (D) by morphometric analysis. Original magnification, ×200; scale bar 50 µM. *p < 0.05 versus control; *^#p < 0.05 versus 43°C treatment group. After binarisation of the images, microvessel density or pericytes were estimated by scoring the total number of representative coloured pixels per field. A pericyte-covered tumour blood vessel is considered a mature, normalised vessel.

Figure 4. Fractionated radiation treatment enhancement by rational scheduling of mild temperature hyperthermia. B16F10 tumour volumes after hyperthermia, radiation or combination treatments (A). Tumour-bearing animals were treated with control (-▪-), heat (-▾-, 41.5°C 60 min on days 7 and 8; indicated by arrowhead), radiation (-▴-, 5 Gy, day 8 and 9, indicated by diamond arrow tail), or combined (-♦-). Data are plotted as means ± SEM over time with third order polynomial line fitting. Efficacy determination of combination therapy of heat and fractionated radiation (B). The following formula was applied to determine efficacy [21]: the expected tumour growth inhibition from combination treatment (tumour growth inhibition by hyperthermia × tumour growth inhibition by radiation) / observed tumour growth inhibition. A ratio >1 indicates a synergistic (greater than additive) effect.

Figure 5. Clonogenic potential of parenchymal and stromal cells after different hyperthermia schedules. Survival of B16F10 (A), HUVEC (B), fibroblasts (C), and 10T½ pericyte cells (D), after different hyperthermia treatments as indicated. Acquisition of thermotolerance (E). Treatment schedules were as follows: (1) mild temperature hyperthermia (MTH), where the flasks were heated at 41.5°C for 60 min two consecutive days in a row, day 1 and 2; (2) a single treatment of 43°C for 60 min on the third day of heat treatments; (3) pretreatment of MTH followed by treatment with 43°C for 60 min on day 3. Thermal tolerance was determined by the following formula [21]: the observed fraction of colony formation after MTH pretreatment/the expected fraction of colony formation (i.e. fraction of colonies after MTH × fraction of colonies after 43°C for 60 min). A ratio >1 indicates induced thermal tolerance by MTH pretreatment, whereas a ratio of <1 indicates an induction of thermal sensitisation by MTH pretreatment.

Dings RP, Yokoyama Y, Ramakrishnan S, Griffioen AW, Mayo KH. The designed angiostatic peptide anginex synergistically improves chemotherapy and antiangiogenesis therapy with angiostatin. Cancer Res 2003; 63: 382–385

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