Anti-malarial drug Pyronaridine modulates microenvironment leading to potent anti-cancer activity against GBM

Glioblastoma multiforme (GBM) is a commonly diagnosed primary brain tumor with median survival of about one year. GBM is highly aggressive malignancy with limited treatment options. The standard of care for GBM is Temozolomide (TMZ), given as first-line therapy, however, 90% of recurrent gliomas acquire TMZ resistance. Treatment to GBM remains greatest challenge in the management of cancer patients worldwide due to inherent tumor heterogeneity and drug resistant nature leading to high unmet medical need. New drug development is challenging and takes an enormous amount of time, money and effort. Drug repurposing, the application of an existing therapeutic to a new disease indication holds the promise of rapid clinical impact at a lower cost than de novo drug development. This study reports the anti-cancer efficacy of Pyronaridine (PYR), a benzonaphthyridine derivative, used as an agent for the treatment of malaria. Anti-malarial action of PYR therapy is known to target haematin formation and inhibit activity of P. falciparum DNA topoisomerase II. PYR was earlier reported to show in vitro anticancer activity in combination with other drugs in breast and haematological cancer. However, in this study we report its anticancer activity in GBM with novel mechanism of action selective against GBM resistant cells. In our studies, anticancer activity of PYR was confirmed in panel of cancer cell lines comprising of kidney, pancreatic, ovarian, glioma and bladder cancer (IC50: 0.907 - 11 µM). Interestingly, PYR demonstrated dose dependant anti-proliferative and pro-apoptotic activity in both TMZ sensitive and TP53 and PTEN mutated resistant GBM cells (IC50: 1.82-4.2 µM). The 3D culture multicellular spheroid model (MCS) is important and relevant as it is predictive of in vivo antitumor efficacy, PYR inhibited MCS developed from TMZ resistant cells. Additionally, PYR also showed potent activity against glioma stem cell line and primary culture derived from high grade glioma. Cell cycle analysis indicated G1 and G2/M phase arrest and increased sub G0 population when GBM cells were treated with PYR. While deciphering the mechanism of action of PYR, we astoundingly invented a novel role for PYR as an inducer of Prostate Apoptosis Response-4 (PAR-4), a pro-apoptotic tumor suppressor protein. The expression of PAR-4 is known to be downregulated in most tumors including GBM. Here, we demonstrate that PYR modulates microenvironment by inducing PAR-4 in normal fibroblast cells in a dose dependent manner. The conditioned medium from these cells induced profound cytotoxicity against cancer cells. PYR is relatively safe to use in humans and our data clearly indicates its anti-cancer potential and hence is a promising therapeutic candidate. The detailed studies focusing on its novel mechanism of action alone and in combination in drug resistant models will be discussed. Citation Format: Jeevan D. Ghosalkar, Vinay R. Sonawane, Siddhika R. Raut, Mariamma Thekkumpurath, Radha Pujari, Padma Shastri, Geena Malhotra, Kalpana S. Joshi. Anti-malarial drug Pyronaridine modulates microenvironment leading to potent anti-cancer activity against GBM [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 251.