(T1530-01-02) Development of a pH-Responsive Nanocarrier to Deliver Phenelzine for Prostate Cancer Treatment

Purpose: Prostate cancer (PCa) is characterized by overexpression of monoamine oxidase-A (MAO-A), which promotes tumor growth, progression, and metastasis as well as treatment resistance [1-5].Consequently, repurposing monoamine oxidase inhibitors (MAOIs) such as phenelzine for prostate cancer management has emerged as a promising strategy. However, preliminary research indicates that systemic administration of phenelzine at doses effective for anti-tumor activity also impacts the brain. This presents a significant challenge due to potential central nervous system side effects [6]. Therefore, there is a pressing need to develop a drug delivery platform that can precisely and systematically transport phenelzine to PCa cells.

Methods: We developed a pH-responsive drug delivery platform that incorporates a hydrazone bond to ensure the delivery of phenelzine in a targeted and controlled manner. Synthesis of polyethylene glycol-hydrazone-phenelzine (PEG-HZ-PHE) was performed as previously described [7], by reacting PEG₂₀₀₀-aldehyde and phenelzine in a 1:5 mole ratio in anhydrous methanol. The formed product (PEG-HZ-PHE) was characterized using LC/MS. PEG-HZ-PHE was incorporated in a lipid nanocarrier system which was characterized using dynamic light scattering (DLS). pH-dependent release of phenelzine from the formulation was evaluated by dialysis at different pH ranges (pH 5.4, 6.4 and 7.4) at 0.5, 1, 2, 4, 6, and 18 hours each. Stability of the formulation over a period of 14 days at pH 5.4, 6.4 and 7.4, respectively, was also assessed. The cytocompatibility of the formulation was examined in fresh human red blood cells (RBCs).

Results: The pH-responsive nanocarriers demonstrated a particle size of 168.9 ± 1.595 nm, polydispersity index (PDI) of 0.16 ± 0.02, and a zeta potential of -41.7 ± 1.83. From the pH dependent release study, it was observed that at 18 h, phenelzine release was highest at pH 5.4 (74.70 ± 0.56 %) and lowest at pH 7.4 (11.30 ± 0.14 %), while the phenelzine release at pH 6.4 was 42.32 ± 0.57 %. The formulation was stable over a period of two weeks at pH 7.4 as demonstrated by particle size consistently remaining in the range of 168-180nm.  Conversely, at pH 5.4 and 6.4, formation of aggregates as evident in the >1000nm hydrodynamic diameter and 1.0 PDI measurements after 2 days was an indication of instability within this pH range. From the RBCs hemolysis assay, there was no significant difference in the hemolytic activity of the formulation compared to the negative control (PBS buffer). On the other hand, the positive control (0.5% Triton X-100) showed a significant hemolytic activity against RBCs compared with the formulation.

Conclusion: We have developed a pH responsive nanocarrier that is stable at physiological pH (i.e., pH 7.4) but rapidly hydrolyzed in acidic environment (pH 5.4 and 6.4). This formulation did not exert any gross hemolytic activity against human RBCs. Considering that the tumor microenvironment is acidic, these results suggest that our delivery platform will potentially enhance tumor specificity and drug accumulation at the cancer site, minimizing non-specific distribution while reducing side effects.

References: 1. Wang, K., et al., The MAO inhibitors phenelzine and clorgyline revert enzalutamide resistance in castration resistant prostate cancer. Nature communications, 2020. 11(1): p. 1-14.
2. Chen, L., et al., High monoamine oxidase a expression predicts poor prognosis for prostate cancer patients. BMC urology, 2023. 23(1): p. 112.
3. Wu, J.B., et al., MAOA-dependent activation of Shh-IL6-RANKL signaling network promotes prostate cancer metastasis by engaging tumor-stromal cell interactions. Cancer cell, 2017. 31(3): p. 368-382.
4. Peehl, D.M., et al., The significance of monoamine oxidase-A expression in high grade prostate cancer. The Journal of urology, 2008. 180(5): p. 2206-2211.
5. Flamand, V., H. Zhao, and D.M. Peehl, Targeting monoamine oxidase A in advanced prostate cancer. Journal of cancer research and clinical oncology, 2010. 136: p. 1761-1771.
6. Brown, J., et al., Nanoformulation improves antitumor efficacy of MAOI immune checkpoint blockade therapy without causing aggression-related side effects. Frontiers in Pharmacology, 2022. 13: p. 970324.
7. Ding, X., et al., Hydrazone-bearing PMMA-functionalized magnetic nanocubes as pH-responsive drug carriers for remotely targeted cancer therapy in vitro and in vivo. ACS applied materials & interfaces, 2014. 6(10): p. 7395-7407.