Chemical Oral Cancerogenesis Is Impaired in PI3Kγ Knockout and Kinase-Dead Mice.

Emilio Hirsch,Barbara Mognetti,Federica Romano,Giuliana Abbadessa,Federica Di Scipio,Zhiqian Yang,Alessandra Oberto,Adriano Ceccarelli,Giovanni Nicolao Berta,Maria Elisabetta Carere

doi:10.3390/cancers13164211

Abstract

Simple SummaryOral carcinoma remains one of the most challenging cancers to be cured and the pharmacological approach is often ineffective. The identification of novel molecular targets will greatly improve its management. We wondered if PI3Kγ might be looked at as a target in oral cancer handling. In this preclinical study, we analyzed the role of PI3Kγ in a murine transgenic model. We demonstrated that the absence/inhibition of PI3Kγ might be a reasonable strategy to impair the development of preneoplastic and neoplastic lesions of the oral cavity. PI3Kγ is not required for normal development, life span, or basic immune responses, unless under stress conditions; therefore, low toxicity and few side effects are expected by acting on PI3Kγ as a therapeutic target.We investigated the role of PI3Kγ in oral carcinogenesis by using a murine model of oral squamous carcinoma generated by exposure to 4-nitroquinoline 1-oxide (4NQO) and the continuous human cancer cell line HSC-2 and Cal-27. PI3Kγ knockout (not expressing PI3Kγ), PI3Kγ kinase-dead (carrying a mutation in the PI3Kγ gene causing loss of kinase activity) and wild-type (WT) C57Bl/6 mice were administered 4NQO via drinking water to induce oral carcinomas. At sacrifice, lesions were histologically examined and stained for prognostic tumoral markers (EGFR, Neu, cKit, Ki67) and inflammatory infiltrate (CD3, CD4, CD8, CD19 and CD68). Prevalence and incidence of preneoplastic and exophytic lesions were significantly and similarly delayed in both transgenic mice versus the control. The expression of prognostic markers, as well as CD19+ and CD68+ cells, was higher in WT, while T lymphocytes were more abundant in tongues isolated from transgenic mice. HSC-2 and Cal-27 cells were cultured in the presence of the specific PI3Kγ-inhibitor (IPI-549) which significantly impaired cell vitality in a dose-dependent manner, as shown by the MTT test. Here, we highlighted two different mechanisms, namely the modulation of the tumor-infiltrating cells and the direct inhibition of cancer-cell proliferation, which might impair oral cancerogenesis in the absence/inhibition of PI3Kγ.

Highlights

Phosphoinositide 3-kinases (PI3Ks) are a group of eight plasma membrane-associated lipid kinases grouped into three classes [1]
Oral 4-nitroquinoline 1-oxide (4NQO)-Carcinogenesis Is Delayed in PI3KγKD/KD and PI3Kγ−/− Mice
Delayed the development of OPLs during the exposure to 4NQO: between week 11 and 15 (Figure 1A), the difference between control and transgenic mice was of utmost significance, since at least 70% of wild type (WT) mice showed OPLS, while both PI3KγKD/KD and PI3Kγ−/− mice had null or scarce lesions

Summary

Introduction

Phosphoinositide 3-kinases (PI3Ks) are a group of eight plasma membrane-associated lipid kinases grouped into three classes (based on their primary structure, regulation, and in vitro lipid substrate specificity) [1]. Class I kinases received great attention because of their involvement in important processes such as cell proliferation and survival [2]: they are heterodimers composed by a 110-kDa catalytic subunit (p110 α, β, γ, δ) complexed with a regulatory part, which allows the interaction with membrane receptors. The main product of class I PI3Ks is phosphatidylinositol-3,4,5-trisphosphate (PIP3): it initiates one of the most important signaling pathways essential for cell growth, proliferation, survival, and migration downstream of growth factors and oncoproteins. Class I PI3Ks are further subgrouped into class IA and IB. Distinct expression patterns are shown in the four different class I PI3K isoforms [3]

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