Induction thermochemotherapy increases therapeutic gain factor for the fractionated radiotherapy given to a mouse fibrosarcoma

Host Acid Sphingomyelinase Regulates Microvascular Function Not Tumor Immunity

Previous studies provided evidence that MCA/129 fibrosarcomas and B16 melanomas grow 2- to 4-fold faster in acid sphingomyelinase (asmase)-deficient mice than in asmase(+/+) littermates and are resistant to single-dose irradiation due to inability to mount an apoptotic response in tumor microvascular endothelium. However, others postulated the differences might be associated with a host antitumor immune response in asmase(+/+) mice that is not expressed in asmase(-/-) mice due to phenotypic deficiency in antitumor immunity. The present studies demonstrate that none of the tumor-host combinations displayed the classic criteria of an immunogenic tumor because they lacked endotumoral or peritumoral infiltrates almost entirely. Furthermore, neither MCA/129 fibrosarcoma nor B16 melanoma tumors showed differences in growth or radioresponsiveness when implanted into mutant mouse models (Rag(-/-) and MEF(-/-)) lacking functional immune cell [natural killer (NK), NK-T, T, and B cells] populations. Additionally, development and function of B-, T-, and NK-cell populations in asmase(-/-) mice were normal, indistinguishable from their wild-type littermates. These data provide definitive evidence that MCA/129 fibrosarcomas and B16F1 melanomas do not elicit a host immune response in wild-type mice and that the asmase(-/-) phenotype is not deficient in antitumor immunity, supporting the notion that the patterns of tumors growth and radiation response are conditionally linked to the ability of the tumor endothelium to undergo ASMase-mediated apoptosis.

Malignant pleural mesothelioma

Malignant pleural mesothelioma remains a difficult tumor to treat, much less cure. Currently, the best chance for long-term survival lies with early diagnosis and aggressive surgical extirpation, but given the typically long delay between the onset of symptoms and diagnosis, this is only possible with a high index of suspicion and an aggressive diagnosis workup. Early referral to a tertiary center experienced in the treatment of MPM may be important for several reasons: (1) decreased risk of tumor spread along multiple thoracenesis/biopsy tracts, (2) the availability of specialized pathologic assays for definitive diagnosis, (3) the availability of critical staging modalities (aggressive mediastinoscopy +/- thoracoscopy, MRI scans performed according to specific mesothelioma protocols, and perhaps PET scans), (4) surgical experience with pleurectomy/decortication and/or extrapleural pneumonectomy, that may decrease morbidity and mortality, and (5) the availability of novel adjuvant protocols. Single-modality therapy is unlikely to result in long-term survival. Aggressive surgery is required for optimal debulking, and extrapleural pneumonectomy may offer better local control compared with pleurectomy/ecortication. Delivery of optimal radiation schedules, which may involve large fractions as well as large total doses, is limited by the presence of nearby dose-limiting structures. Current chemotherapy is severely lacking in producing objective responses and improved survival although gemcitabine and IL-2 may be active agents to be combined with radiation and/or other agents. Hyperthermia, photodynamic therapy, intracavitary therapy, and gene therapy are all relatively new techniques under active investigation that should be supported by enrollment in on-going protocols. Predictably, many of these techniques provide greater benefit when used in the setting of adjuvant protocols or minimal residual disease, emphasizing the importance of multimodality therapy.

For the clinical application of thermochemotherapy given at mild temperatures

It has been demonstrated in vitro and in vivo that hyperthermia can enhance the cytotoxicity of some chemotherapeutic agents. This paper summarizes the authors' own laboratory studies on the effect of chemotherapeutic agents given at elevated temperatures, experimental results obtained using animal tumour systems in other laboratories, and clinical trials of thermochemotherapy reported in literature. The in vivo studies have demonstrated that the thermal enhancement of cytotoxicity of many chemotherapeutic agents is maximized at mild temperatures such as at 40.5-43 degrees C. Comparison of in vitro and in vivo results using five agents show that the in vivo thermal enhancement increases with an increase in the activation energy obtained in the temperature range between 40.5 and 43.0 degrees C. A summary of experimental results obtained by various investigators indicates a potentially wide variation in the thermal enhancement of a given agent among the different types of tumours and suggests potential agents useful at moderately elevated temperatures. In vivo studies on nine different agents indicate that the drug(s) of choice at physiological temperatures may not be the drug(s) of choice at elevated temperatures. It is also shown that drug concentration in the target must be high for sufficient thermal enhancement. Clinical trials of thermochemotherapy have employed various heating methods, including local heating, hyerthermic perfusion and whole body hyperthermia. Extensive trials have been made in the treatment of melanoma and soft tissue sarcoma in the extremity. Hyperthermic isolated perfusion with chemotherapeutic(s) provides much higher drug concentration than a systemic drug administration in the target(s), resulting in a high tumour response rate and an increased survival of the patients. It is of interest that the most successful agent used in the treatment of both melanomas and sarcomas is melphalan and is the drug of choice at moderately elevated temperatures among the nine agents tested in the in vivo studies. Current results using the tumour necrosis factor with melphalan are impressive. In several institutes, techniques have been developed to uniformly heat the localized tumour, but studies are needed to find an agent effective at elevated temperatures to each type of tumours and to establish the methods for obtaining a sufficient drug concentration in the target tissue.

Are hypoxic cells critical for the outcome of fractionated radiotherapy in a slow-growing mouse tumor?

PURPOSE

To investigate the significance of hypoxic cells, reoxygenation and repopulation for the outcome of fractionated radiotherapy of a slow-growing subline of a murine fibrosarcoma and to compare the results with those previously obtained from the original fast-growing tumor.

MATERIALS AND METHODS

A slow-growing subline, 457-O, was obtained among the tumors that recurred after a single irradiation to the third generation isotransplants of a mouse fibrosarcoma, FSa-II. The single cell suspensions were transplanted into the mouse foot and when the tumors reached an average diameter of 4 mm, they were subjected to one to 20 equal daily y-ray doses given in air (A) or under hypoxic conditions (H). The TCD50 (50% tumor control radiation dose) was calculated according to the tumor control frequency within 180 days. The linear-quadratic plus time model was fitted to these data by logistic regression analysis.

RESULTS

The volume doubling time of the 457-O tumors was approximately 2.2 times slower than that of the original FSa-II tumors. The TCD50(H) (single dose) was 52.3 Gy and increased with an increasing number of fractions to a TCD50(H) (20 doses) of 90.8 Gy. This increase of 38.5 Gy was much smaller than that of 149 Gy for the original FSa-II. The TCD50(A) (single dose) and TCD50(A) (20 doses) were 41.3 and 50.6 Gy, respectively. This small difference of 9.3 Gy contrasted with a significant increase of 52.9 Gy for the FSa-II.

DISCUSSION

These results suggested no repopulation of 457-O tumor clonogens during the course of up to 20 daily doses, while the original FSa-II tumor cells repopulated substantially. Hypoxic clonogens in the slow-growing tumor reoxygenated but some fractions remained critical.

CONCLUSION

The present data together with those obtained from the fast-growing FSa-II suggested that hypoxic clonogens were critical for the outcome of fractionated radiotherapy. Repopulation was insignificant in this slow-growing tumor during five to 20 daily doses.