Dibenzyl trisulfide induces caspase-independent death and lysosomal membrane permeabilization of triple-negative breast cancer cells

The Petiveria alliacea L. (P. alliacea) plant is traditionally used in folklore medicine throughout tropical regions of the world to treat arthritis, asthma, and cancer. Dibenzyl trisulfide (DTS) is one of the active ingredients within the P. alliacea plant. Triple-negative breast cancer (TNBC) is associated with a poor prognosis, particularly among women of West African ancestry, due in part to limited effective therapy. Though potent anticancer actions of DTS have been reported in a TNBC cell line, the mechanism of DTS-mediated cytotoxicity and cell death remains ill-defined. In the current study, we show that DTS exhibits cytotoxicity in a panel of triple-negative breast cancer (TNBC) cells derived from patients of European and West African ancestry. We found that DTS inhibits proliferation and migration of CRL-2335 cells derived from a patient of West African ancestry. DTS induces the expression of pro-apoptotic genes BAK1, GADD45a, and LTA in CRL2335 cells though it primarily promotes caspase-independent CRL-2335 cell death. DTS also promotes destabilization of the lysosomal membrane resulting in cathepsin B release in CRL-2335 cells. Finally, Kaplan-Meier survival curves reveal that higher expression of BAK1 and LTA in tumors from patients with TNBC is associated with longer relapse-free survival. Collectively, our data suggest that DTS confers promising antitumor efficacy in TNBC, in part, via lysosomal-mediated, caspase-independent cell death to warrant furthering its development as an anticancer agent.

Abstract PO-110: Plant isolate dibenzyl trisulfide induces caspase-independent death in triple negative breast cancer cells derived from patients of West African descent

Patients with triple negative breast cancer (TNBC) possess tumors that lack estrogen receptor, progesterone receptor, and human epidermal growth receptor expression. While these patients traditionally receive chemotherapy to combat this aggressive breast cancer subtype, others use natural remedies. Dibenzyl trisulfide (DTS) is derived from Petiveria alliacea, a perennial shrub that grows in tropical regions of the world. Many TNBC patients residing in the tropics are of West African descent. Therefore, we evaluated the anticancer actions of DTS in TNBC cells, including those derived from patients of West African descent. We found that DTS inhibited TNBC cell viability, migration and proliferation in a dose-dependent manner. Interestingly, DTS blocked the propensity of pro-carcinogen benzo-A-pyrene to induce proliferation of immortalized breast epithelial cells. Moreover, we found that DTS induced early apoptosis in TNBC cells, which was only partially attenuated following pretreatment with pan-caspase inhibitor zVAD-fmk. Though DTS induced pro-apoptotic gene and protein expression along with PARP cleavage, it failed to produce appreciable caspase 3 cleavage and promote significant apoptotic body formation. This suggests that this plant isolate induces caspase-independent and non-apoptotic death of TNBC cells. Furthermore, DTS promoted lysosomal membrane destabilization and cathepsin B release in TNBC cells. Taken together, DTS exhibits promising chemotherapeutic and chemopreventive ability by inducing non-apoptotic TNBC cell death and thwarting TNBC progression, supporting its evaluation in clinical trials as an agent to combat TNBC among patients of West African descent.

Citation Format: Jonathan Wooten, Shaniece Wooten, Cristina Araújo, Joyce Aja, Nicole Mavingire, Rupika Delgoda, Eileen Brantley. Plant isolate dibenzyl trisulfide induces caspase-independent death in triple negative breast cancer cells derived from patients of West African descent [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-110.

Cancer stem cells: Culprits in endocrine resistance and racial disparities in breast cancer outcomes

Breast cancer stem cells (BCSCs) promote endocrine therapy (ET) resistance, also known as endocrine resistance in hormone receptor (HR) positive breast cancer. Endocrine resistance occurs via mechanisms that are not yet fully understood. In vitro, in vivo and clinical data suggest that signaling cascades such as Notch, hypoxia inducible factor (HIF), and integrin/Akt promote BCSC-mediated endocrine resistance. Once HR positive breast cancer patients relapse on ET, targeted therapy agents such as cyclin dependent kinase inhibitors are frequently implemented, though secondary resistance remains a threat. Here, we discuss Notch, HIF, and integrin/Akt pathway regulation of BCSC activity and potential strategies to target these pathways to counteract endocrine resistance. We also discuss a plausible link between elevated BCSC-regulatory gene levels and reduced survival observed among African American women with basal-like breast cancer which lacks HR expression. Should future studies reveal a similar link for patients with luminal breast cancer, then the use of agents that impede BCSC activity could prove highly effective in improving clinical outcomes among African American breast cancer patients.

Abstract 6553: Plant power: Plant isolate dibenzyl trisulfide induces death of triple-negative breast cancer cells derived from an African American patient

Triple negative breast cancer (TNBC), characterized by tumors that lack estrogen receptor, progesterone receptor, and human epidermal growth receptor expression, represents one of the most aggressive subtypes of breast cancer. TNBC carries a poor prognosis due, in part, to a lack of clinically available targeted therapy. Novel therapeutic strategies to combat TNBC primarily involve the use of synthetic small molecules. However, the World Health Organization reports that there is increased use of natural remedies and traditional medicine to treat diseases. Our lab has investigated the chemotherapeutic and chemopreventive effects of a variety of plant isolates. Dibenzyl trisulfide (DTS) is derived from Petiveria alliacea, a perennial shrub that grows in tropical regions of the world. Previous investigations surrounding DTS are limited to anticancer actions in European American breast cancer cells. The purpose of this study was to evaluate the anticancer actions of DTS in CRL-2335 cells which are derived from an African American patient with TNBC. We found that DTS inhibited TNBC cell migration and proliferation using wound healing and colony forming assays. Furthermore, we found DTS induced apoptotic body formation and nuclear fragmentation using relief contrast and fluorescence microscopy respectively. Moreover, using the Annexin V/PI assay we found that DTS induced early apoptosis, which was partially attenuated in cells pretreated with pan-caspase inhibitor zVAD-fmk. Finally, quantitative polymerase chain reaction analyses revealed that DTS induced the expression of pro-apoptotic genes BAK1, LTA and GADD45A. Our data suggest that DTS effectively induces caspase-independent death of TNBC cells derived from an African American patient and represents a promising agent to treat more refractory forms of breast cancer.

Citation Format: Jonathan Wooten, Cristina Araújo, Shaniece Wauchope, Joyce Aja, Nicole Mavingire, Rupika Delgoda, Eileen Brantley. Plant power: Plant isolate dibenzyl trisulfide induces death of triple-negative breast cancer cells derived from an African American patient [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6553.