Site dependent response of tumours to combined heat and radiation

A gentle introduction to understanding preclinical data for cancer pharmaco-omic modeling

A central goal of precision oncology is to administer an optimal drug treatment to each cancer patient. A common preclinical approach to tackle this problem has been to characterize the tumors of patients at the molecular and drug response levels, and employ the resulting datasets for predictive in silico modeling (mostly using machine learning). Understanding how and why the different variants of these datasets are generated is an important component of this process. This review focuses on providing such introduction aimed at scientists with little previous exposure to this research area.

THERMAL DOSE REQUIREMENT FOR TISSUE EFFECT: EXPERIMENTAL AND CLINICAL FINDINGS

In this review we have summarized the basic principles that govern the relationships between thermal exposure (Temperature and time of exposure) and thermal damage, with an emphasis on normal tissue effects. We have also attempted to identify specific thermal dose information (for safety and injury) for a variety of tissues in a variety of species. We address the use, accuracy and difficulty of conversion of an individual time and temperature (thermal doses) to a standardized value (eg equivalent minutes at 43 degrees C) for comparison of thermal treatments. Although, the conversion algorithm appears to work well within a range of moderately elevated temperatures (2-15 deg C) above normal physiologic baseline (37-39 deg C) there is concern that conversion accuracy does not hold up for temperatures which are minimally or significantly above baseline. An extensive review of the literature suggests a comprehensive assessment of the "thermal does-to-tissue effect" has not previously been assembled for most individual tissues and never been viewed in a semi-comprehensive (tissues and species) manner. Finally, we have addressed the relationship of thermal does-to-effect vs. baseline temperature. This issues is important since much of the thermal dose-to-effect information has been accrued in animal models with baseline temperatures 1-2 deg higher than that of humans.

Tumour blood flow changes induced by application of electric pulses

The effect of electric pulses on tumour blood flow was investigated in the murine fibrosarcoma SA-1. After the application of short intense electric pulses, relative tumour perfusion was measured using an 86RbC1 extraction technique. A significant reduction of tumour perfusion (approximately 30% of control) was observed within 1 h following the application of eight electric pulses to the tumour. Thereafter, tumour blood flow slowly recovered, almost reaching the pretreatment level by 24 h. No change in perfusion was induced in the untreated contralateral normal leg muscle. A similar pattern of blood flow reduction was induced when a second set of electric pulses was applied to the tumour following a 24 h interval. The degree of tumour blood flow reduction was dependent upon the number of electric pulses applied, at 1040 V, and less effect was observed if less than eight pulses were applied. A modification of the amplitude of the electric pulses resulted in changes in the direction of tumour blood flow response. Tumour blood flow increased following pulses in the range between 80 and 560 V and decreased at amplitudes higher than 640 V. These results demonstrate that the local application of electric pulses to solid tumours can modify tumour blood flow. Pulses of increased amplitude resulted in the progressive reduction of tumour blood flow with a corresponding increase in tumour cytotoxicity as measured by growth delay. Tumour blood flow reduction by electric pulses could have potential in exploiting modalities mediated by tumour hypoxia, e.g. activation of bioreductive agents.

Anti-vascular approaches to solid tumour therapy: evaluation of vinblastine and flavone acetic acid

Several agents have now been identified which exert their anti-tumour effects in large part via the tumour vasculature; these include TNF alpha and flavone acetic acid (FAA). More recently, Vincristine and Vinblastine have also been shown to cause a prolonged and selective decrease in tumour perfusion. Vinblastine, unlike, FAA, causes no increase in plasma TNF alpha levels in mice bearing the CaNT tumour, suggesting 2 distinct mechanisms of anti-vascular activity for these structurally diverse agents. Since FAA and Vinblastine also show quite different normal tissue toxicities, which are separately dose-limiting, we have examined the strategy of combining these 2 agents. When Vinblastine preceded FAA by 24 hr or less, tumour growth delay was significantly enhanced without a concomitant increase in toxicity. The level of enhancement was not significantly reduced by a 5-fold decrease in Vinblastine dose, though any reduction in the dose of FAA caused a rapid reduction in treatment effectiveness. Investigation of the functional vasculature of treated tumours suggested that increased anti-vascular effects may contribute to the enhanced growth inhibition of the combined treatment. Our results demonstrate the potential benefit of combining 2 different classes of anti-vascular agent, using Vinblastine and FAA (or 5,6-MeXAA) as prototype drugs.

Temperature differentials between treatment and pretreatment temperatures correlate with local control following radiotherapy and hyperthermia

PURPOSE

To evaluate the influence of pretreatment tumor temperatures and the temperature differential between treatment and pretreatment temperatures on local tumor control in patients who underwent combined radiation therapy and hyperthermia.

METHODS AND MATERIALS

Mapped intratumoral temperatures were measured immediately prior to and during hyperthermia in 138 hyperthermia fields among 59 patients with nodular (60 fields) or diffuse (78 fields) superficially-located tumors. In the nodular subgroup there were 40 fields with adenocarcinomas (31 breast, two prostate, seven other primary sites), six melanomas, nine squamous cell carcinomas, and five other histologies. The fields with diffuse tumor involvement consisted of 77 adenocarcinomas (67 breast, 10 other) and one melanoma. The maximum, minimum, and average temperatures were determined for both the pretreatment (pTmax, pTmin, pTave) and treatment (Tmax, Tmin, Tave) distributions and the differences, Dm = Tmin-pTmax, and Da = Tmin-pTave, computed. These quantities were averaged over treatments to produce the corresponding mean quantities for each hyperthermia field. Univariate and multivariate analyses were performed to determine treatment and pretreatment parameters which best correlated with the duration of local control.

RESULTS

Pretreatment tumor temperatures were significantly lower than the oral temperatures with mean pTmax, mean pTmin, and mean pTave of 36.2 degrees C, 34.2 degrees C, and 35.4 degrees C, respectively. For the adenocarcinomas with diffuse involvement within the hyperthermia field, the covariates best correlating with local control duration on univariate analysis were concurrent radiation dose (p = 0.0026), Dm (p = 0.009), pTmax (p = 0.012) and Da (p = 0.036). Lower pTmax and larger Dm and Da were predictive for longer local control. In multivariate analyses, all thermal parameters lost power, however, the best model included Dm which was significant at the p = 0.040 level. For the nodular subgroup, nonthermal parameters and dichotomized thermal parameters were of prognostic significance for local control.

CONCLUSION

For fields diffusely involved with adenocarcinoma significant correlations with duration of local control have been demonstrated both for a) low pretreatment temperatures and b) large differentials between treatment and pretreatment intratumoral temperatures. These correlations were also found in a dichotomized description for fields with nodular tumors. The results support the concept that pretreatment hypothermic conditions can lead to an increase in thermal sensitization and may help explain the excellent clinical results noted in the treatment of superficial tumors with radiation and hyperthermia. Further exploitation of this approach by planned cooling of superficially-located recurrent tumors prior to hyperthermia treatment warrants investigation.

Vinca alkaloids: anti-vascular effects in a murine tumour

We have investigated the blood flow modifying effects of the vinca alkaloids, vincristine and vinblastine in the murine carcinoma CaNT. Vinblastine at doses of 7.5 or 10 mg/kg induced profound and chronic reductions in tumour blood flow as measured by 86RbCl extraction. Following the maximum tolerated dose of 10 mg/kg, blood flow was reduced to 10% of pretreatment values after 2 h and remained below 20% of pretreatment values 24 h after drug administration. These findings are consistent with the early induction of necrosis by vinblastine and suggest that vascular-mediated cell death may account for a large part of the 11 day growth delay induced by this drug dose. In contrast to the large reductions in tumour blood flow, in skin, kidney, liver and muscle, blood flow reductions did not, at any time examined, exceed 40%. In all the normal tissues studied, blood flow had fully recovered by 6 h after vinblastine administration. Similar results, albeit less pronounced, have been obtained with vincristine at the maximum tolerated dose of 3 mg/kg. The results clearly show that both vinblastine and vincristine can induce, with some selectivity, a dramatic and prolonged reduction in tumour blood flow and that this may contribute to the anti-tumour effects against the CaNT tumour.

A comparison of vascular-mediated tumor cell death by the necrotizing agents GR63178 and flavone acetic acid

A vascular component of tumor damage has been identified for the anticancer agent GR63178. The necrotizing activity of this drug and of flavone acetic acid has been compared with their ability to induce growth delay in six murine tumor models. At 24 hr, after a fixed dose of flavone acetic acid (200 mg/kg), all six tumor types appeared 80-100% necrotic histologically, although growth delays ranging from 3 to 79 days were measured. GR63178 (200 mg/kg) induced more variable degrees of necrosis (10 to 95%), but a uniformly small delay in growth (0 to 4 days). These data illustrate that the absence of a tumor-growth response should not be automatically equated with an absence of drug activity. Without assessing tumor response histologically, agents with unusual mechanisms of action may be missed, despite their potential for killing large numbers of tumor cells.

A review of hypoxic cell radiosensitization

Despite an enormous laboratory and clinical effort, advance in patient care has not yet been achieved by hypoxic cell radiosensitization. The reasons for this are considered and suggestions made as to the future direction of work in this important field.

Effect of hyperthermia and/or nicotinamide on the radiation response of a C3H mammary carcinoma

The effect of hyperthermia and/or nicotinamide (200 mg/kg of body weight) on the tumour growth delay induced by radiation was evaluated in a C3H mouse mammary adenocarcinoma. The study showed a radiosensitizing effect of hyperthermia and of nicotinamide but the combination of all three modalitites showed no increased tumor growth delay compared to hyperthermia and radiation alone. The tumour growth delay induced by hyperthermia was not modified by nicotinamide.

Vascular collapse after flavone acetic acid: a possible mechanism of its anti-tumour action

Flavone acetic acid (FAA, LM 975) causes regression and growth retardation in several solid murine tumours. The mechanism of action is unknown, although various lines of evidence suggest an indirect cytotoxic effect. We have carried out preliminary studies on the effect of FAA on relative blood flow in six experimental murine tumours using 86RbCl extraction. We have also measured growth delay after treatment with the same dose of FAA (200 mg/kg). The data show that the drug induces a drop in tumour perfusion within 6 h of treatment in all of the tumours, and that this can be correlated with the growth delay measured. We conclude that vascular collapse may be an important component of the action of this drug, and that further investigation of this phenomenon is warranted.

Cell line and growth site as relevant parameters governing tumor tissue oxygenation

Tumors commonly exhibit pronounced inter-individual and intra-individual differences in the oxygenation status. Paramount factors contributing to this variability are the tumor growth stage or size, changes in the O2 transport capacity of the arterial blood (e.g., during tumor-induced anemia) as well as inherent properties of the tumor cell line investigated and different tumor growth sites as shown in the present study. In most cases, variations of nutritive tumor blood flow and changes in the amount of arterio-venous shunt perfusion within the tumor tissue have to be considered as basic pathomechanisms for these inter-tumor variations of tissue oxygenation.

The influence of pre-treatment temperature on the thermal sensitivity of a mouse tumour

The response of tumours to hyperthermia was tested by giving graded heat treatments and assessing local control at 90 days. Mice were divided into three groups which were pre-treated for 3 days in ambient temperatures of 4, 21 or 35 degrees C. This enabled the mean tumour resting temperature to be varied by up to 11 degrees C, before subsequent heat treatment. For the heat treatments, the tumours were clamped in order to eliminate blood flow, resulting in uniform temperature distributions and hence more uniform thermal sensitivity. TCD50 values were used to construct Arrhenius plots. For all three pre-treatment temperatures, these plots demonstrated a factor of 1.6 increase in heating time per degree Celsius reduction in heating temperature. However, tumours kept in a 4 degrees C environment before treatment were more thermally sensitive than those kept in 21 degrees C conditions, while those in a 35 degrees C environment were more resistant. Pretreatment at 4 degrees C was equivalent to an increase of either 0.5 degree C in heating temperature or 28 per cent in heating time, compared with pre-treatment at 21 degrees C. Pre-treatment at 35 degrees C was equivalent to a reduction of either 0.6 degree C in heating temperature or 25 per cent in heating time. These data indicate that the pre-treatment tumour temperature is an important parameter, but the effect of heat treatment is more closely related to absolute heating temperature rather than to the increase in temperature above the normal resting level.