Co-encapsulation of PI3-Kδ/HDAC6 dual inhibitor and Navitoclax in Quatramer™ nanoparticles for synergistic effect in ER+ breast cancer

Progression and metastasis of ER⁺ breast cancer depend on multiple signaling cascades. The available conventional treatment options have limited efficacy in ER⁺ breast cancer due to overexpression of AKT, c-Myc and BCL-2 proteins. Simultaneous targeting and inhibition of these targets in ER⁺ cancer may result in effective therapeutic outcomes. However, combining two or more free drug molecules to treat cancer leads to unsynchronised pharmacokinetics, toxicity, and eventual resistance development. To overcome these limitations, a novel nanoformulation of PI3-Kδ/HDAC6 dual inhibitor in combination with Navitoclax is developed using Pluronic modified PLA based hybrid block copolymer. The prepared dual drug loaded PI3-Kδ/HDAC6-NAV-NPs (1:3-NPs) have shown high encapsulation efficiency, hydrodynamic size, and polydispersity of ∼ 93 %, 159 ± 2.6 nm, and 0.19 ± 0.03, respectively. These PI3-Kδ/HDAC6-NAV-NPs exhibit slow and sustained release profiles of PI3-Kδ/HDAC6 inhibitor and NAV in phosphate buffer saline (PBS, pH 7.4). The in-vitro cytotoxicity studies done with PI3-Kδ/HDAC6-NAV-NPs in ER⁺ breast cancer cell lines have shown a synergistic effect with lower IC₅₀ values compared to individual NAV-NPs and PI3-Kδ/HDAC6-NPs. The PI3-Kδ/HDAC6-NAV-NPs treatment (4 mg/kg, I.V., twice a week for three weeks) of ER⁺ breast cancer syngeneic mice tumor model resulted in complete tumor eradication without any overt toxicity. These results demonstrate that a unique formulation of a novel PI3-Kδ/HDAC6 dual inhibitor in combination with Navitoclax represents an approach for an efficient treatment option for ER⁺ breast cancer.