LPV/r induces p53 DDR in lung cells by upregulating anti-proliferative and growth-arrest genes, while downregulating pro-survival genes. Subsequently, cell cycle arrest and or cell death mechanisms are induced, resulting in reduced cell proliferation.

The Sub-Saharan countries, particularly South Africa has the largest number of people living with HIV, accompanied by the largest antiretroviral treatment (ART) programme in the world. The Highly Active Antiretroviral Treatment (HAART) is the most effective regimen against HIV/AIDS and has improved the lifespan and quality of life of HIV positive patients. HAART has also led to a decrease in the incidence of AIDS defining cancers (ADCs) while there is an increased incidence of the non-AIDS Defining Cancers (NADCs), such as lung cancer in the HAART era. The association between lung tumourigenesis and the use of HAART components such as the dual protease inhibitor (PI) lopinavir/ritonavir (LPV/r) is poorly understood. Using cell and molecular biological approaches, this study aimed at elucidating the effects of LPV/r on the regulation of the cell cycle related genes in normal (MRC-5) and adenocarcinoma (A549) lung cells. Initially, the nuclear integrity of these cells in response to LPV/r was determined using DAPI staining. The effect of LPV/r on cell cycle genes was evaluated through the use of a RT2 PCR gene array of 84 genes related to the cell cycle signaling pathway. The PCR array data was validated by Real-Time Quantification PCR (RT-qPCR). Ingenuity Pathway Analysis (IPA) bio-informatics tool was employed to disclose the molecular mechanism/s observed at cellular and gene expression levels. Loss of nuclear integrity and the upregulation of the p53 DNA damage response (DDR) pathway was revealed by DAPI staining, differential gene expression and IPA core analysis. Furthermore, MAD2L2 and AURKB which also play a role in the DDR pathway were shown to be differentially expressed. The activation of the CASP3 gene in response to LPV/r in A549 cells was also observed. The findings of this study suggest genotoxic properties of LPV/r in healthy normal lung fibroblasts cells and anti-tumour properties in the A549 cells.