In Vivo Treatment with CPT-11 Leads to Differentiation of Neuroblastoma Xenografts and Topoisomerase I Alterations

Abstract

Topoisomerase I inhibitors, such as CPT-11, are potent anticancer drugs against neuroblastoma (NB). Differentiating agents, such as retinoids, improve the survival of children with metastatic NB. To characterize the biological effects associated with exposure to CPT-11 in vivo, athymic mice bearing a human NB xenograft, named IGR-NB8 and characterized as an immature NB with poor prognostic markers, were treated with CPT-11. Prolonged stable disease was observed, resulting in an overall tumor growth delay of 115 days. During treatment, tumors differentiated into ganglioneuroblastomas (GGNB), which reverted into an immature phenotype when treatment was discontinued. In contrast, 13-cis retinoic acid failed to induce differentiation of IGR-NB8 in vivo. Tumor differentiation was associated with decreased N-myc expression, induction of p73 expression in the perinuclear area and cytoplasm, and a dramatic 35-fold decrease in topoisomerase I (topo I) catalytic activity. The full-length M r 100,000 topo I protein was present in both pre and post-treatment immature NB xenografts. In contrast, differentiated GGNBs did not contain the M r 100,000 protein but an intense M r 48,000 topo I fragment. Furthermore, redistribution of the M r 48,000 and 68,000 forms to the cytoplasm was observed in differentiated tumors. The same pattern of topo I expression and catalytic activity was observed in NBs and GGNBs obtained from pediatric patients. Our data suggest that prolonged in vivo exposure to CPT-11 induces differentiation of NB xenografts, which is associated with truncation of the topo I enzyme, relocation of the degraded forms to the cytoplasm, and decreased catalytic activity.

No topoisomerase I alteration in a neuroblastoma model with in vivo acquired resistance to irinotecan

“…The parental xenografts displayed the histological features of a poorly differentiated NB composed of undifferentiated neuroblastic cells (small uniform rounded cells) containing a high number of mitotic figures per high-power field and very little schwannian stroma ( Figure 4A). During the first two passages, the stabilisation state was associated with tumour differentiation exhibiting features of a maturing ganglioneuroma (Santos et al, 2004) However, the IGR-NB8-R-resistant xenografts showed similar histological features to those observed in the parental xenografts ( Figure 4A), namely those of a poorly differentiated NB ( Figure 4B). These results indicate that there was no modification of histological features during the acquisition of resistance.…”

“…Moreover Western blot analysis of topoisomerase I showed no difference between the tumours studied ( Figure 7). The human polyclonal anti-topoisomerase I antibody revealed two main bands located at 100 kDa, corresponding to a full-length enzyme and at 54 kDa, a form specific to human tissues (Santos et al, 2004) and perhaps the heavy chain of the immunoglobulin molecule (Bronstein et al, 1996). Thus, topoisomerase expression and activity was not implicated in the in vivo resistance acquisition.…”

Differentiation-Inducing Activity of Hydroxycamptothecin on Cancer Stem-Like Cells Derived from Hepatocellular Carcinoma

“…Low concentration of HCPT and its analogs have been proven to have potent differentiation-inducing activity in several kinds of human cancer cells in vitro. Therefore, we chose HCPT as a differentiation-inducing agent and used the concentration of 0.02 lg/ml, as described in previous studies [15,16,21,22].…”

“…Moreover, HCPT and its analogs have been proven to have potent differentiation-inducing activity in human cancer cells [14][15][16]. CSCs play important roles in the development and progression of malignancies.…”

Antitumor activity and pharmacokinetics of oral gimatecan on pediatric cancer xenografts

“…The active metabolite of CPT-11, SN-38, stabilizes a ternary complex between the nuclear enzyme topoisomerase I and double-stranded DNA [7]. As reported by Santos et al, CPT-11 shows marked antitumoral activity against pediatric xenografts in preclinical studies [8,9]. Topotecan is used as a standard treatment in ovarian cancer, and it was recently reported to be eVective in a small percentage of patients with relapsed or refractory neuroblastoma [10][11][12].…”