Cerium oxide nanoparticles for prevention of therapy-induced prostate cancer progression

Cerium oxide nanoparticles (CNPs) are unique multifunctional nanozymes, exerting redox and non-redox simil-enzymatic activities, promising acting as unprecedented anticancer agents, in particular radio-senstitizing cancer cells. Prostate cancer (PCa) is a fatal disease when metastatic, both at the hormone-sensitive (HSPC), clinically (treated with the cytostatic androgen deprivation therapy, ADT), and at the castration resistant (CRPC) stage, treated with cytotoxic chemotherapy. Both treatments efficiently achieve tumor regression, but eventually the disease comes back more aggressive, up to the fatal conclusion. It is therefore important to find adjuvant strategies that stabilize the initial positive response to both therapies. In this scenario, as a main objective of my PhD research project, I wanted to explore whether CNPs, in the same guise as they ameliorate radiotherapy response, may also ameliorate the response of HSPC to the cytostatic hormone therapy, and of CRPC to the cytotoxic chemotherapy. The rationale is that both hormone- and chemo-therapy promote strong inflammatory responses, a phenomenon where CNPs may theoretically exert their anticancer effect. The model systems where I tested the hypothesis are in vitro models of human prostate cancer, and specifically the hormone-sensitive PCa cells LNCaP, and the castration-resistant PCa cells PC3, treated as to recapitulate clinical schedules. We mimicked ADT by culturing LNCaP cells in media deprived of androgen, whereas etoposide was used on PC3 to mimic pulsed chemotherapy. CNPs were added as pristine nanoparticles, stabilized as aqueous colloidal suspension, at different times post-treatment. The effect of CNPs was evaluated based on their ability to modulate cell survival, proliferation, type of paracrine signaling, inflammatory state of the culture, and cancer markers. An unexpected achievement was the isolation of a clone of hormone-insensitive cells from the hormone-sensitive LNCaP, namely the AR-PA cells, which appeared after 23 days of androgen deprivation therapy (ADT). AR-PA display features distinct from the parental LNCaP, rather closely resembling PC3 in terms of morphology and behavior. This rare event not only provided insights into the epigenetic rearrangements underlying the progression from HSPC to CRPC but also allowed validating the CRAC model on a CRPC cell line produced in vitro. Remarkably indeed, despite minimal exceptions, this new line mirrored the behavior of the extensively studied PC3 cells despite the modality through which androgen independence was reached, i.e., in a patient as disease progression, for PC3; in vitro, for ARPA. In this cell system, CNPs reduced post-therapy repopulation and, notably, prevented acquisition of resistance and other malignant features. Mechanistically, CNPs block chemotherapy-induced malignant progression by disrupting the proinflammatory milieu induced by chemotherapy itself. This indicates that CNPs can modulate the tumor microenvironment and inhibit key pathways involved in cancer progression. The effects of CNP on ADT-treated LNCaP cells were instead less straightforward. The inflammatory profile induced by ADT was strongly different from that observed in chemo-treated AR-PA and PC3 cells. A main difference is the levels of prostaglandin E2, a major mediator of CRPC progression, and a primary target of CNP action: PGE2 is extremely increased by chemotherapy, whereas in ADT the levels are viceversa reduced. Also in the context of ADT however, CNPs alter the profile of inflammatory mediators. This does not lead to an effect on cancer cell survival, but it cannot be excluded that CNPs may help stabilizing the senescence/cytostasis state induced by ADT through the establishment of an anti-inflammatory tumor environment. We will address such unexpected scenario in the next future. Overall, the lesson we learned from these findings is the complex and context-dependent nature of CNP effects on prostate cancer cells. The ability of CNPs to modulate inflammatory pathways and enhance the efficacy of chemotherapy underscores their potential as a versatile tool in cancer therapy. However, their impact during hormone therapy requires further investigation to fully understand the mechanisms and design their therapeutic application.