Complementary Targeting of Rb Phosphorylation and Growth in Cervical Cancer Cell Cultures and a Xenograft Mouse Model by SHetA2 and Palbociclib.

Amy L Kennedy,Rajani Rai,Doris M Benbrook,Zitha Redempta Isingizwe,Yan Daniel Zhao,Stanley A Lightfoot

doi:10.3390/cancers12051269

Amy L Kennedy, Rajani Rai + Show 4 more

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https://doi.org/10.3390/cancers12051269

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Journal: Cancers	Publication Date: May 17, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of Oklahoma Health Sciences Center

Abstract

Cervical cancer is caused by high-risk human papillomavirus (HPV) types and treated with conventional chemotherapy with surgery and/or radiation. HPV E6 and E7 proteins increase phosphorylation of retinoblastoma (Rb) by cyclin D1/cyclin dependent kinase (CDK)4/6 complexes. We hypothesized that cyclin D1 degradation by the SHetA2 drug in combination with palbociclib inhibition of CDK4/6 activity synergistically reduces phosphorylated Rb (phospho-Rb) and inhibits cervical cancer growth. The effects of these drugs, alone, and in combination, were evaluated in SiHa and CaSki HPV-positive and C33A HPV-negative cervical cancer cell lines using cell culture, western blots and ELISA, and in a SiHa xenograft model. Endpoints were compared by isobolograms, ANOVA, and Chi-Square. In all cell lines, combination indexes documented synergistic interaction of SHetA2 and palbociclib in association SHetA2 reduction of cyclin D1 and phospho-Rb, palbociclib reduction of phospho-Rb, and enhanced phospho-Rb reduction upon drug combination. Both drugs significantly reduced phospho-Rb and growth of SiHa xenograft tumors as single agents and acted additively when combined, with no evidence of toxicity. Dilated CD31-negative blood vessels adjacent to, or within, areas of necrosis and apoptosis were observed in all drug-treated tumors. These results justify development of the SHetA2 and palbociclib combination for targeting phospho-Rb in cervical cancer treatment.

Highlights

While promising new molecularly targeted agents have been FDA-approved for other cancer types, there are none currently approved for first line cervical cancer therapy
Our findings validate the in vivo complementarity of SHetA2 and palbociclib against phospho-Rb and growth of cervical cancer xenograft tumors
We tested this interaction based on our hypothesized model (Graphical Abstract) that SHetA2-induced degradation of cyclin D1 is complemented by palbociclib inhibition of cyclin dependent kinase 4/6 (CDK4/6) kinase activity to more fully inhibit the cyclin D1/CDK4/6 complex phosphorylation of Rb in comparison to the singular activities of the individual drugs

Summary

Introduction

While promising new molecularly targeted agents have been FDA-approved for other cancer types, there are none currently approved for first line cervical cancer therapy. In 2014, the US FDA approved addition of the anti-vascular endothelial growth factor (VEGF), angiogenesis inhibitor bevacizumab to chemotherapy for advanced cases of cervical cancer only [3]. A decrease in the cervical cancer death. Cancers 2020, 12, 1269 rate by more than half in 2016 compared to 1975 is attributed to implementation of screening programs that have reduced incidence and increased early detection [4]. Between 2007 and 2016 the decrease in cervical cancer death rate leveled out to only 1% per year in women over the age of 50 with no decrease in women less than 50 years old [4,5]. There are over one hundred types of HPV which can be categorized into high or low risk for causing cervical cancer [6]. High risk HPV examples include HPV-16 and HPV-18, while low risk examples include

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