Heat-activated nanomedicine formulation improves the anticancer potential of the HSP90 inhibitor luminespib in vitro

Abstract

The heat shock protein 90 inhibitor, luminespib, has demonstrated potent preclinical activity against numerous cancers. However, clinical translation has been impeded by dose-limiting toxicities that have necessitated dosing schedules which have reduced therapeutic efficacy. As such, luminespib is a prime candidate for reformulation using advanced drug delivery strategies that improve tumor delivery efficiency and limit off-target side effects. Specifically, thermosensitive liposomes are proposed as a drug delivery strategy capable of delivering high concentrations of drug to the tumor in combination with other chemotherapeutic molecules. Indeed, this work establishes that luminespib exhibits synergistic activity in lung cancer in combination with standard of care drugs such as cisplatin and vinorelbine. While our research team has previously developed thermosensitive liposomes containing cisplatin or vinorelbine, this work presents the first liposomal formulation of luminespib. The physico-chemical properties and heat-triggered release of the formulation were characterized. Cytotoxicity assays were used to determine the optimal drug ratios for treatment of luminespib in combination with cisplatin or vinorelbine in non-small cell lung cancer cells. The formulation and drug combination work presented in this paper offer the potential for resuscitation of the clinical prospects of a promising anticancer agent.

Figure 1

Representative cryo-TEM micrograph of the thermoLUM liposomes.

Figure 2

Long-term stability of thermoLUM stored at room temperature (RT, grey) or 4 °C (black) over 21 days. The liposome-encapsulated drug was separated from unencapsulated drug via size exclusion chromatography. The concentration of LUM was detected via HPLC analysis to determine the amount of drug retained in the liposomes at each timepoint (a). The size (b) and PDI (c) of thermoLUM were determined via DLS. The level of encapsulated drug, size, and PDI of liposomes were found to be stable over the 21-day period.

Figure 3

Drug release from thermoLUM incubated at 37–44 °C in 45 mg/mL BSA over 300 s. Samples were collected at 30 s intervals. The liposome-encapsulated drug was separated from unencapsulated drug via size exclusion chromatography. The concentration of LUM was detected via HPLC analysis to determine the amount of drug release from the liposomes at each timepoint. The liposomes were found to release less than 15% of drug over 5 min below 39 °C, while burst release was observed at 41–44 °C. Data shown represent the mean ± SD (n = 3).

Figure 4

CI values for H460 (a) and H520 (b) cells treated with various molar ratios of LUM + CDDP at fraction affected (FA) = 0.50, 0.75, and 0.90. Data are presented as mean and SD (n = 3). CI values < 0.90 indicate that the two drugs act synergistically (shown in green) while CI values of 0.90–1.10 indicate an additive effect (shown in yellow), and CI values > 1.10 indicate that the two drugs act antagonistically (shown in red). The combination was found to be mostly additive and antagonistic in both cell lines, except 1:10 and 1:20 LUM:CDDP, which were found to have a synergistic effect in H520 cells.

Figure 5

CI values for H460 (a) and H520 (b) cells treated with various molar ratios of LUM + VRL at FA = 0.50, 0.75, and 0.90. Data are presented as mean and SD (n ≥ 3). CI values < 0.90 indicate that the two drugs act synergistically (shown in green) while CI values of 0.90–1.10 indicate an additive effect (shown in yellow), and CI values > 1.10 indicate that the two drugs act antagonistically (shown in red). The combination was found to be additive and antagonistic in H460 cells, while most ratios were additive and synergistic in H520 cells.