Abstract:
Oncogenic Ras regulates MAPK, PI3K, and RalGEFs signaling to control cell proliferation, survival, anchorage-independence, and metastasis in cancer. Ral (Ras-like GTPase) activation is known to be essential for Ras-mediated cellular transformation and is regulated primarily through RalGEFs. Cell-matrix adhesion is seen to regulate RalA but not RalB activation, which could have implications for their differential role in anchorage-independent cancer growth. Therefore, targeting RalA without affecting RalB could be an effective means to understand its role in tumor growth and metastasis. Aurora kinase A (AURKA) selectively phosphorylates RalA at Serine 194 residue, affecting its localization and activation. Yet, its relative regulation and role downstream of adhesion and oncogenic Ras in controlling RalA activation and function in solid tumors remains unclear. Targeting AURKA to modulate RalA could provide insight into their crosstalk and effectively target Ral-dependent tumorigenesis in Ras-independent and Ras-dependent cancers. MLN8237 (Alisertib) is a potent AURKA inhibitor, but its clinical benefits are limited by its hydrophobicity and poor water solubility. We have designed an enzyme-biodegradable unimolecular micelle (UMM) polymer nanoparticle platform with significantly improved MLN8237 loading (NPMLN) and solubility. NPMLN treatment of cancer cell lines selectively inhibits AURKA without affecting AURKB and differentially regulates pSer194 RalA. This treatment was found to downregulate RalA activation and anchorage-independent growth (AIG) in Ras-independent (SKVO3) and Ras-dependent (MIA PaCa-2) cancer cells. Furthermore, nanoparticles encapsulated with sulforhodamine B (NPSRB) and IR780 (NPIR780) demonstrated enhanced cellular uptake of NPSRB in vitro and improved localization and retention of NPIR780 within xenograft tumors in mice. Ameliorated solubility and bioavailability offered by this UMM nanoparticle enabled the parenteral administration of MLN8237 at the lowest concentrations than previously reported. Treatment of xenograft tumors with NPMLN demonstrated significantly improved therapeutic potential (compared to free MLN237) in regressing tumor growth, particularly in MIA PaCa-2 over SKVO3. This was accompanied by a significant inhibition of AURKA activation and RalA phosphorylation (pSer194RalA) in both cancers, supporting the role of the AURKA-RalA crosstalk in Ras-independent and Ras-dependent cancers. This further makes it an attractive candidate for regressing tumor growth.
