Optimization of liposomal topotecan for use in treating neuroblastoma

Abstract

The purpose of this work was to develop an optimized liposomal formulation of topotecan for use in the treatment of patients with neuroblastoma. Drug exposure time studies were used to determine that topotecan (Hycamtin) exhibited great cytotoxic activity against SK-N-SH, IMR-32 and LAN-1 neuroblastoma human cell lines. Sphingomyelin (SM)/cholesterol (Chol) and 1,2-dis tearoyl-sn-glycero-3-phosphocholine (DSPC)/Chol liposomes were prepared using extrusion methods and then loaded with topotecan by pH gradient and copper-drug complexation. In vitro studies showed that SM/Chol liposomes retained topotecan significantly better than DSPC/Chol liposomes. Decreasing the drug-to-lipid ratio engendered significant increases in drug retention. Doserange finding studies on NRG mice indicated that an optimized SM/Chol liposomal formulation of topotecan prepared with a final drug-to-lipid ratio of 0.025 (mol: mol) was better tolerated than the previously described DSPC/Chol topotecan formulation. Pharmacokinetic studies showed that the optimized SM/ Chol liposomal topotecan exhibited a 10-fold increase in plasma half-life and a 1000-fold increase in AUC 0-24 h when compared with Hycamtin administered at equivalent doses (5 mg/kg). In contrast to the great extension in exposure time, SM/Chol liposomal topotecan increased the life span of mice with established LAN-1 neuroblastoma tumors only modestly in a subcutaneous and systemic model. The extension in exposure time may still not be sufficient and the formulation may require further optimization. In the future, liposomal topotecan will be assessed in combination with high-dose radiotherapy such as 131 I-metaiodobenzylguanidine, and immunotherapy treatment modalities currently used in neuroblastoma therapy. Cancer Medicine Open Access 1241

In vitro assay for measuring real time topotecan release from liposomes: release kinetics and cellular internalization

“…Interestingly, a different study from our laboratory showed that the in vivo release rate of topotecan from an optimized liposomal formulation [25] was 25% per hour, which was faster than the maximum release rate of 17% per hour (see Fig. 4c) demonstrated using the present in vitro assay.…”

“…Comparing the cytotoxicity of topotecan to liposomal topotecan Given that the liposomal topotecan formulation retained drug over extended time periods [25], it was expected that the liposomal formulation would be less active in vitro when compared to free topotecan. The cytotoxicity of liposomal topotecan was compared to topotecan when tested on different cell lines and over different incubation times (Fig.…”

The liposomal delivery of hydrophobic oxidovanadium complexes imparts highly effective cytotoxicity and differentiating capacity in neuroblastoma tumour cells

“…Liposomes can penetrate some solid tumours by 'passive targeting' through the enhanced permeability and retention (EPR) effect 67 . Although this appears feasible in neuroblastoma xenograft models 68,69 , it is unclear whether EPR is relevant here clinically. The delivery of oxidovanadium complexes in vivo for neuroblastoma would likely need more advanced liposomal technology, such as tumour targeting with RGD-based peptides 60,69 , or antibodies specific for disialoganglioside 2 (GD2), a key antigen on neuroblastoma cells 70,71 .…”

Therapeutic Opportunities in Neuroblastoma Using Nanotechnology

“…Topotecan undergoes a pH-dependent, reversible hydrolysis into a nonactive carboxylate at physiologic pH (Devriese et al, 2015). With this in mind, a liposomal topotecan formulation was prepared to protect the cytostatic drug from this pH-induced hydrolysis (Chernov et al, 2017;Gilabert-Oriol et al, 2017). Pharmacokinetic studies showed that the nanoformulation exhibited a 10-fold increase in plasma half-life values in comparison with equivalent doses of topotecan (Hycamtin); however, encapsulated topotecan only modestly increased the life span of NB mice.…”