| Summary |
With the advancement of chemotherapy drugs, the general life expectancy of cancer patients has drastically improved. However, persistent side effects, such as chemotherapy-induced peripheral neuropathy (CIPN), often severely devastate patients' quality of life post chemotherapy. Since the mechanisms underlying CIPN remain unclear, no effective method of preventing or treating CIPN is currently available. In the current study, we aim to determine the potential therapeutic effects of targeting small GTPases of Rho family (Rho GTPases) in the prevention of CIPN, as well as suppression of tumor progression by utilizing Rho GTPases modulators. The Rho GTPases are master regulators in many critical cellular functions, which include cellular differentiation, cytoskeleton remodeling, cell motility, and vesicle transport. Rho GTPases can be activated by binding to guanosine triphosphate (GTP) and deactivated by binding to guanosine diphosphate (GDP). Two groups of regulators tightly control the activity of Rho GTPases: guanine nucleotide exchange factors (GEFs) induce Rho GTPases activation by facilitating GDP to GTP exchange, whereas GTPase activating proteins (GAPs) induce Rho GTPases deactivation by accelerating GTP hydrolysis. Additionally, abnormal activity of Rho GTPases is reported in a wide variety of human diseases ranging from neurological diseases to cancers. Therefore, Rho GTPases have become valuable targets for therapeutic intervention due to their unique "on and off" molecular switch mechanisms and their broad involvement in human diseases. We used a syngeneic immunocompetent mouse line with transplanted Lewis Lung Carcinoma (LLCab) to create a novel tumor-bearing CIPN animal model and examined the therapeutic effect of RhoA signaling pathway suppression. Y-27632, a selective inhibitor of Rho kinase/p160ROCK directly downstream of RhoA modulating actin dynamics, was used to treat both tumorigenesis and cisplatin-induced peripheral neuropathy. Several key findings were observed from our experiments. First, Y-27632 enhanced the antineoplastic effect of cisplatin in both our in vitro and in vivo studies by promoting cellular apoptosis in the tumor. Second, Y-27632 alleviated the reduction of touch sensitivity induced by cisplatin treatment. Third, crucial touch sensitivity-associated peripheral nervous structures, such as epidermal nerve fibers (ENFs) and Meissner corpuscles (MCs), were protected from cisplatin-induced impairment by Y-27632 treatment. Importantly, quantitative proteomic studies of mouse footpad tissues revealed that Y-27632 attenuated cisplatin-induced dysregulation of cellular stress-associated proteins and suppressed the hyper-activation of NF-kB. Lastly, in order to understand the potential mechanism of cisplatin on the dynamic changes of actin polymerization in live cells, we utilized advanced molecular tools to record both nuclear and cytoplasmic actin reorganization in mitotic and non-mitotic cells. We found that cisplatin caused nuclear actin polymerization in the mitotic cells, and concomitantly induced cytoplasmic actin reorganization in the non-mitotic cells. In summary, these studies, for the first time, highlighted a dual anti-neoplastic and neuroprotective effects of Rho kinase/p160ROCK inhibition in a syngeneic immunocompetent tumor-bearing mouse model, as well as demonstrated the differential influence of cisplatin on the actin dynamics in both mitotic and non-mitotic cells. Due to the close association between Rho GTPases and cellular actin regulation, it is possible that Rho GTPases mediate the cisplatin-induced differential actin reorganization in the mitotic and non-mitotic cells, providing a potential explanation for the mechanism underlying cisplatin-induced neurotoxicity in the cancer patients. Finally, since Y-27632 cooperates with cisplatin to curtail tumor growth while protecting the host from CIPN through RhoA-NF-kB axis to inflammation and cellular stress, Y-27632 or its optimized modulators should be further investigated for the development of clinical adjuvants to improve chemotherapeutic outcomes. |
