###### Abstract  
Several cancers are induced by microbial infections or chronic inflammation. _Ptaeroxylon obliquum_ is traditionally used to treat various infections characterized by inflammation. The in vitro antiproliferativeative and antioxidant activity of _P. obliquum_ leaf extracts, fractions and isolated compounds were determined. Antiproliferative activity was assessed against normal Vero cells, and several cancerous human cells, including human breast cancer (MCF-7), hepatocarcinoma (HepG2), lung adenocarcinoma (A549) and human cervical cancer cells (HeLa) using a colorimetric tetrazolium bromide assay. Radical scavenging activity was tested using the 2,2-diphenyl-1-inspricrylhydraz1 (DPPH) and 2,2-azineo-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. Obliquumol, O-methylalloptaeroxylin and a mixture of lupeol and \(\beta\)-amyrin were isolated from the chloroform fraction using silica gel open column chromatography. Acetone extracts were toxic to HepG2 cells with IC\({}_{50}\) values from 8 to 200 \(\mu\)g/mL but were less toxic to other cells with selectivity index as high as 14. Aqueous extracts and fractions were non-toxic at concentrations tested against all the cell lines (IC\({}_{50}>\) 100 \(\mu\)g/mL). Isolated compounds had IC\({}_{50}\) values ranging from 52 to 539 \(\mu\)g/mL and 189 to 247 \(\mu\)g/mL against HepG2 and HeLa cells, respectively. Light microscopy showing changes in HepG2 and HeLa cell morphology supported the cytotoxicity of the acetone extracts. Water extracts scavenged ABTS and DPPH radicals with IC\({}_{50}\) values as low as 29.06 \(\mu\)g/mL and 43.4 \(\mu\)g/mL. _P. obliquum_ extracts may be useful as sources of anticancer therapy, as they have selective cytotoxicity against cancer cell lines. Ptaeroxylon obliquum; cancer; antiproliferative; Vero; HepG2; HeLa +
Footnote †: journal: Applied Sciences  
1  
to 29.5 million of new cancer diagnoses and 16.5 million cancer-related deaths yearly across the globe [5; 6; 7]. In South Africa, cancer is emerging as a critical public health problem with an estimated 107,467 new reported cancer cases and a total of 57,373 deaths occurring in 2018 [8; 9]. The incidence rate of breast cancer is the highest (14,097 cases, 13.1%), followed by cervical (12,983 cases, 12.1%) and prostate cancers (12,452 cases, 11.6%) and the incidence of lung cancer was reported at 7.7%, ranking fourth among all the cancers, which gives it the highest mortality rate of 13.5%. Lung and prostate cancers are the most predominant types in males while breast and cervical cancers are the predominant types in females [9; 10]. Treatment options for cancer include chemotherapy, radiation, hormone and gene therapy; however, they all have various negative side effects such as fatigue, nausea, vomiting, weight loss and bleeding [11]. Chemotherapy is one of the most commonly used anticancer treatments, but some cancers are resistant to cytotoxic/chemotherapeutic agents, which poses a major threat to anticancer therapy. The limitation in the efficacy of the therapeutic agents leads to non-satisfactory treatment outcomes and eventually death [12]. Cancer cells may be resistant by evading potential apoptotic mechanisms, such as down-regulated pro-apoptotic signals, up-regulated anti-apoptotic signals, and faulty apoptosis initiation and implementation. There is a need to seek alternative anticancer therapeutics such as phytochemicals, as there is increasing evidence that suggest they could exhibit anticancer effects. Scientific evidence suggests that phytochemicals have substantial anticancer potential that may be considered for drug development [13]. Modern medicine has embraced plants used in traditional medicine as potential leads for the development of therapeutic drugs. South Africa has a large variety of plant species, which are yet to be investigated for their potential in treating cancer.