Radiation-induced effects on murine kidney tumor cells: role in the interaction of local irradiation and immunotherapy

Animal models of spontaneous renal carcinoma: A possible rebirth?

Introduction and Objectives The animal models for renal carcinogenesis have allowed researchers to better understand the physiopathological, genetic, molecular, and immunological mechanisms underlying the development of human renal cancers from the induction of precancerous lesions to the metastatic process. Our study aimed to review and discuss the characteristics of all the spontaneous animal models of renal carcinogenesis described in scientific literature to date and see how they could address future challenges in the field of personalized medicine. Methods and Materials We reviewed all the papers on PubMed which focus on spontaneous animal models of renal carcinogenesis. To do so, we used the keywords "spontaneous" AND "animal model" AND "renal cancer" in the PubMed search engine. We also conducted a search using the keywords "spontaneous" AND "animal model" AND "kidney cancer." PRISMA recommendations were used for the literature review. Results A total of 213 publications were found on PubMed with the keywords "spontaneous" AND "animal model" AND "kidney cancer." 219 publications were found on PubMed with the keywords "spontaneous" AND "animal model" AND "renal cancer." After pooling these 2 searches and removing the duplicate publications, 233 publications remained. Among these, 220 full-text articles were assessed for eligibility; 160 were removed because they were irrelevant to our topic, and the remaining 60 studies were included in our qualitative synthesis. Conclusions Many spontaneous animal models have been developed to study renal cancer. So far, these models have enabled the understanding of pathophysiological mechanisms underlying renal cancer. Though less appropriate than patient xenografts from the perspective of personalized medicine, we believe animal models can help medical professionals better understand the hows and whys of the genetic events underlying the intratumoral heterogeneity and spatial distribution of metastatic subclones.

Radiation as an immune modulator

Radiation therapy is currently one of the most widely utilized treatment strategies in the clinical management of cancer. Classically, radiation therapy was developed as an anticancer treatment on the basis of its capacity to induce DNA double strand breaks in exposed cancer cells, ultimately resulting in tumor cell death. Recently, our understanding of radiation effects has expanded widely in terms of the consequences of radiation-induced tumor cell death and the pertinent cells, signaling pathways, and molecular sensors that modify the tumor response to radiation. It is now well accepted that inflammation plays a complex dual role in promoting or inhibiting tumor growth. The capacity of inflammatory responses to alter the tumor response to radiation therapy, and vice versa, is now the subject of intense scientific and clinical investigation. Herein, we review the concepts regarding the immunostimulatory properties of radiation therapy with particular focus on the effects of radiation therapy on the tumor microenvironment.

Prolonged low dose IL-2 and thalidomide in progressive metastatic renal cell carcinoma with concurrent radiotherapy to bone and/or soft tissue metastasis: a phase II study

Metastatic renal cell cancer is one of the immuno-sensitive tumors. Apart from the immuno-modulating agents IFNalpha and IL-2, thalidomide has been reported to be effective in this type of cancer. However, bone metastases and bulky metastases, show limited response to immunotherapy, are often site of recurrent disease and are therefore often treated later with radiotherapy. In this phase II study, we evaluated toxicity and efficacy of the combination of continuous low dose (1 mIU/m2) s.c. IL-2 and thalidomide (200 mg once daily) in 22 patients with progressive metastatic renal cell cancer. In addition, 13 soft tissue lesions and two bone metastases in 13 patients were concurrently treated with fractionated radiotherapy. T cell number and activation in blood was measured by immunoflowcytometry. Nearly all patients developed grade 1-2 toxicity consisting of fatigue, sensory neuropathy, constipation and dizziness. Five patients had a grade 3-4 toxic event: four patients with deep venous thrombosis requiring anticoagulant therapy, and one patient who developed radiation myelopathy. On systemic response evaluation ten patients showed ongoing SD with a mean progression free survival of 9 months. One patient showed a PR (at an irradiated site). Regarding local response to irradiation, seven lesions showed a PR for a mean time period of 8.7 months, whereas seven were stable for 6 months. The radiation response of one lesion was not evaluable. Immunoflowcytometry showed an increase in number and activation of lymphocytes (mainly Natural Killer--NK-cells), which was absent or even decreased in irradiated patients. The combination of sc. low dose IL-2, thalidomide and radiotherapy is feasible, but relatively toxic and does not lead to higher responses at non-irradiated sites. The combination of immunotherapy and concurrent radiotherapy is effective at 60% of the relatively large evaluable sites. Progressive myelopathy developed in one patient, possibly due to radiotherapy in combination with thalidomide.

The controversial abscopal effect

The abscopal effect is potentially important for tumor control and is mediated through cytokines and/or the immune system, mainly cell-mediated immunity. It results from loss of growth stimulatory and/or immunosuppressive factors from the tumor. Until recently, the abscopal effect referred to the distant effects seen after local radiation therapy. However, the term should now be used interchangeably with distant bystander effect. Through analysis of distant bystander effects of other local therapies, we discuss the poorly understood and researched radiation-induced abscopal effect. Although the abscopal effect has been described in various malignancies, it is a rarely recognized clinical event. The abscopal effect is still extremely controversial with known data that both support and refute the concept.

Treatment of bone metastases and local recurrence from renal cell carcinoma with immunochemotherapy and radiation

Immunotherapies using interferons and/or interleukins are currently the treatment of choice for metastatic renal cell carcinoma (RCC). Bone metastases and non-resectable local recurrence are negative predictors for successful immunotherapy and signs of poor prognosis. The present study was designed to evaluate the effectiveness of combined immunochemotherapy (ICT) and radiation therapy (RT) for bone metastases or local recurrence from RCC in a prospective fashion. From September 1997 to September 1999, 20 patients with progressive RCC were treated with a combination of RT and ICT [s.c. interleukin-2a (IL-2), s.c. interferon alpha (IFN-alpha) and i.v. 5-fluorouracil]. RT started in week 2 of ICT. The radiation field was limited to the symptomatic bone metastases (15 patients) or the local recurrence (five patients). The total dosages of the RT ranged between 45 and 50 Gy, administered in fractions of from 1.8 to 2 Gy daily. In case of objective response or stable disease, the patients received up to two further ICT courses. All patients had good pain relief. Three out of 20 achieved complete remission, three had a partial remission, nine were stable and five patients had progressive disease under the combined treatment. Median survival was 21 months, mean survival 24 months (range: 5-59 months). The side effects of the combined treatment are in the same range as with ICT alone (World Health Organisation grade 2 and 3). Of 20 patients, 19 had their pain medication reduced after treatment. The combination of ICT and RT is feasible. There is remarkable pain relief. Our data suggest that the combination of immunochemotherapy and radiation therapy may induce a synergistic antitumor effect for the treatment of bone metastases or local recurrence from RCC compared to data from the literature for ICT or RT alone.

Ionizing radiation inhibition of distant untreated tumors (abscopal effect) is immune mediated

PURPOSE

Ionizing radiation can reduce tumor growth outside the field of radiation, known as the abscopal effect. Although it has been reported in multiple malignancies, the abscopal effect remains a rare and poorly understood event. Ionizing radiation generates inflammatory signals and, in principle, could provide both tumor-specific antigens from dying cells and maturation stimuli that are necessary for dendritic cells' activation of tumor-specific T cells. We therefore tested the hypothesis that the abscopal effect elicited by radiation is immune mediated. This was directly tested by enhancing the number of available dendritic cells using the growth factor Flt3-Ligand (Flt3-L).

METHODS AND MATERIALS

Mice bearing a syngeneic mammary carcinoma, 67NR, in both flanks were treated with Flt3-L daily for 10 days after local radiation therapy (RT) to only 1 of the 2 tumors at a single dose of 2 or 6 Gy. The second nonirradiated tumor was used as indicator of the abscopal effect. Data were analyzed using repeated measures regression.

RESULTS

RT alone led to growth delay exclusively of the irradiated 67NR tumor, as expected. Surprisingly, growth of the nonirradiated tumor was also impaired by the combination of RT and Flt3-L. As control, Flt3-L had no effect without RT. Importantly, the abscopal effect was shown to be tumor specific, because growth of a nonirradiated A20 lymphoma in the same mice containing a treated 67NR tumor was not affected. Moreover, no growth delay of nonirradiated 67NR tumors was observed when T cell deficient (nude) mice were treated with RT plus Flt3-L.

CONCLUSIONS

These results demonstrate that the abscopal effect is in part immune mediated and that T cells are required to mediate distant tumor inhibition induced by radiation.

Local low-dose interleukin-2 induces systemic immunity when combined with radiotherapy of cancer. A pre-clinical study

Tumor recurrence and outgrowth of metastases limit the therapeutical effect of radiotherapy. We have tested whether these problems can be overcome by supplementing radiotherapy with locoregional interleukin-2 (IL-2) treatment. The SL2 lymphoma and the M8013 mammary carcinoma were used. Mice bearing a 10-day-old s.c. tumor were locally irradiated and were treated daily with IL-2 peritumorally for 5 or 10 days. Low-dose IL-2 therapy improved local response (LR) and increased disease-free survival (DFS) in both tumor models following either single-dose irradiation or fractionated irradiation. For example, 93% of SL2-bearing mice treated with single-dose irradiation and 10 days of IL-2 experienced long-term DFS, compared with 17% for irradiation alone (p < 0.0001). Additionally, treatment of one tumor with irradiation +IL-2 led to anti-tumor effects in a second, untreated tumor in 80% of SL2-bearing mice. LR was increased to 100% and DFS to 70% when the second, non-irradiated tumor was also treated with peritumoral IL-2. We conclude that supplementing local radiotherapy with low doses of IL-2 results in increased local tumor control and regression of distant, non-irradiated tumors. This type of radioimmunotherapy is a promising new approach for the clinic.