Radiosensitizing Effect of Novel Phenylpyrimidine Derivatives on Human Lung Cancer Cells via Cell Cycle Perturbation

Abstract

Radiotherapy is one of the most common treatments for cancer, but radioresistance and injury to normal tissue are considered major obstacles to successful radiotherapy. Thus, there is an urgent need to develop radiosensitizers to improve the therapeutic outcomes of radiotherapy in cancer patients. Our previous efforts to identify novel radiosensitizers, using high-throughput screening targeting p53 and Nrf2 revealed a promising N-phenylpyrimidin-2-amine (PPA) lead compound. In the present study, 17 derivatives of this lead compound were examined, and it was found that 4-(4-fluorophenyl)-N-(4-nitrophenyl)-6-phenylpyrimidin-2-amine (PPA5), 4-((4-(4fluorophenyl)pyrimidin-2-yl)amino)-3-methoxy-N-methyl-benzamide (PPA13), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA14), 4-((4-(2-chlorophenyl)pyrimidin-2-yl) amino)benzenesulfonamide (PPA15), and 4-((4-(2-chlorophenyl) pyrimidin-2-yl)amino)-N-methylbenzamide (PPA17) inhibited cell viability by more than 50%, with a marked increase in the proportion of cells arrested at the G 2 /M phase of cell cycle. Among these compounds, PPA15 markedly increased the sub-G 1 cell population and increased the levels of cyclin B1 and the phosphorylation levels of cyclin-dependent kinase (CDK) 1. Combined treatment with radiation and PPA14 or PPA15 significantly decreased clonogenic survival. An in vitro kinase assay revealed that PPA15 inhibited multiple CDKs involved in cell cycle regulation. Compared with drug or radiation treatment alone, combined treatment with PPA15 and radiation resulted in the suppression of A549 tumor growth in mice by 59.5% and 52.7%, respectively. Treatment with PPA15 alone directly inhibited tumor growth by 25.7%. These findings suggest that the novel pan CDK inhibitor, PPA15, may be a promising treatment to improve the effectiveness of radiotherapy for the treatment of cancer. SIGNIFICANCE STATEMENT Several inhibitors of CDK have been successfully evaluated in combination with other chemotherapeutics in clinical trials, but negative side effects have partially restricted their clinical use. In this study, we identified a novel pan-CDK inhibitor to increase radiosensitivity, and we hope this work will encourage the development of promising small-molecule radiosensitizers.

CDK4, CDK6/cyclin-D1 Complex Inhibition and Radiotherapy for Cancer Control: A Role for Autophagy

“…These results were partially confirmed in clinical trials for brain cancer, when the use of CDKIs in combination with RT or temozolomyde or other anticancer agents showed promising results in terms of PFS and OS [38]. Similarly, the efficacy of CDKIs in combination with IR was also preliminarily tested in patients with lung [36], prostate, cervical, and breast cancer, suggesting a broad activity of this combination across these tumor types [38,39]. Notably, multiple pre-clinical studies have demonstrated the ability of CD-KIs to promote apoptosis in tumor tissues exposed to IR, presumably by engaging p53 independent mechanisms Interestingly, these studies also revealed the ability of CDKI to protect normal tissues by IR as well as chemotherapy-mediated damage by reducing the frequency of treatment associated intestinal injuries and hematological toxicity [40,41].…”

“…Although the precise mechanisms of these events have not been completely elucidated, several pre-clinical models provide the scientific rationale to investigate the combination pharmacological CDKIs [2,24,[32][33][34][35][36] with IR [37] and suggest that it could be a paramount new avenue to achieve a better clinical performance of this class of drugs.…”

Coordination of anti-CTLA-4 with whole-brain radiation therapy decreases tumor burden during treatment in a novel syngeneic model of lung cancer brain metastasis

“…EGFR signaling is associated with diverse functions in lung cancer cells, including increased radioresistance, metastatic capabilities [ 26 – 28 ], DNA synthesis, proliferation, and cell cycle arrest [ 29 ]. It is well documented that phases of the cell cycle are a determinant of radiotherapy response, with cells in late S phase being most radioresistant and cells in M phase most radiosensitive [ 30 , 31 ]. A study in 2020 demonstrated inhibition of EGFR/HER2 signaling in LLC cells results in decreased proliferation, reduced metastasis, and increased radiosensitivity [ 32 ].…”

The Renaissance of Cyclin Dependent Kinase Inhibitors

“…They discovered the small molecule radiosensitizer PPA15. It was found to be a pan-CDKI which, combined with radiation, resulted in suppression of A549 (lung adenocarcinoma) tumor growth in mice by 50–60% [ 193 ].…”