Local hyperthermic treatment does not enhance mitoxantrone effectiveness for responses of a rat solid tumour regrowing after irradiation

Human tumor xenografts recurring after radiotherapy are more sensitive to anti-vascular endothelial growth factor receptor-2 treatment than treatment-naive tumors

The effects of antiangiogenic therapy on tumors relapsing after irradiation are not known. To this end, we irradiated human tumors growing s.c. in nude mice with a single dose of 20 or 30 Gy. Compared with primary (treatment-naive) xenografts, the growth rate of recurrent tumors was 1.6-fold slower, which is consistent with the known "tumor bed effect." For similar size tumors, recurrences had fewer functional vessels, a reduced vessel coverage by perivascular cells, and were more necrotic. Placenta growth factor concentration was significantly lower in relapses, whereas vascular endothelial growth factor (VEGF) levels were similar between primary and recurrent tumors. On the other hand, fibrillar collagen deposition was significantly increased in recurrent tumors. This radiation-induced fibrosis was partially responsible for the slower growth of recurrences; the i.t. injection of collagenase increased the growth rate of tumor relapses without affecting primary tumor growth. The mouse-specific VEGF receptor 2-blocking antibody DC101 induced a 2.2-fold longer growth delay in recurrent tumors compared with treatment-naive tumors. DC101 significantly decreased the interstitial fluid pressure and did not change the functional vessel density and perivascular cell coverage in both tumor variants. Interestingly, DC101 induced a rapid (2 days after treatment initiation) and significant decrease in tumor cell proliferation in recurrent but not in primary tumors. Thus, our results show that the stromal compartment and the response to antiangionenic therapy of primary and in-field recurrent tumors are significantly different. Our findings suggest that antiangiogenic agents could be effective in the treatment of patients with relapses after radiotherapy.

Local hyperthermia enhances the effect of cis-diamminedichloro-platinum(II) on nonirradiated and preirradiated rat solid tumors

PURPOSE

We have investigated differences in the efficacy of combined treatment with cis-diamminedichloroplatinum(II) (cDDP) and local hyperthermia (HT) in nonirradiated and preirradiated experimental tumors.

METHODS AND MATERIALS

Survival of R-1 rhabdomyosarcoma cells was assessed after treatment with various cDDP-concentrations at 37 degrees C and 42 degrees C in vitro. Rats bearing R-1 rhabdomyosarcomas of 190 mm3 (SE 15 mm3) were treated with cDDP (6 mg/kg i.p.), HT (1 h at 43 degrees C), or cDDP+HT (45 min interval) without preirradiation or at day 16 after the first dose of fractionated irradiation. Fractionated irradiation consisted of four daily doses of 5 Gy of x-rays each and tumor volumes had regrown to their original volume at the time of treatment. Experimental endpoint was tumor growth delay (TGD).

RESULTS

Hyperthermia-enhanced cDDP cytotoxicity in vitro by a factor of about 5. Treatment with cDDP or HT alone resulted in a similar TGD in non- and preirradiated tumors (7.2 vs. 7.4 days and 1.1 vs. 0.9 days, respectively). In non- as well as in preirradiated tumors, HT given in combination with cDDP significantly enhanced the effect of cDDP, prolonging the TGD (11.1 days (p = 0.0001) and 16.2 days (p < 0.0001), respectively) corresponding to a TGD-enhancement of 1.54 and 2.19, respectively. The TGD after cDDP+HT in preirradiated tumors was significantly longer than in nonirradiated tumors (p = 0.0003).

CONCLUSIONS

In this tumor model, HT enhanced the antitumor effect of cDDP. Previous radiation treatment did not reduce the HT-enhanced effect of cDDP. Combined cDDP and HT may be useful in the treatment of nonirradiated tumors as well as previously irradiated tumors.