In other studies, it was observed that VPA could decrease proliferation of Metformin-resistant human renal cell carcinoma cells and inhibit invasiveness in bladder cancer (Wei et al., 2018[44]; Yagi et al., 2010[50]; Tang et al., 2004[39]). and cisplatin (8 M) to evaluate cytotoxicity. IC50 of the drugs, when they were applied separately and in combination, were calculated using the COMPUSYN software. DNA electrophoresis, TUNEL assay, and Hoechst staining were performed to investigate apoptosis induction. RT-PCR was utilized for the evaluation of apoptotic genes expression. The results of the MTT assay showed that cell viability decreased at all applied doses of NG and VPA. It was noticed that the cytotoxic effects of these drugs were dose- and time-dependent. Based on the COMPUSYN output, the combination of the drugs (VPA Frentizole and NG) in a certain ratio concentration synergistically decreased cell viability. Cisplatin significantly decreased cell viability of PBMCs and K562 cells. Also, the combination drug experienced cytotoxic effect and Frentizole significantly reduced viability of K562 cells compared with PBMCs and control cells. In the target cells treated with this combination, Bax and caspase-3 expression increased but Bcl-2 expression decreased. These results suggest that NG, VPA, and their combination decreased cell viability and induced apoptosis via the intrinsic apoptotic pathway. This study suggests that this combination therapy can be considered for further Frentizole evaluation as an effective chemotherapeutic strategy for patients with chronic myeloid leukemia. strong class=”kwd-title” Keywords: apoptosis, combination therapy, cytotoxicity, K562 cells, nitroglycerine, valproic acid Introduction The main reason for failure in the treatment of cancer is the occurrence of resistance to chemotherapy. However, chemotherapy is still an effective approach for treating malignancy. For the majority of anti-cancer drugs, apoptosis appears to be initiated by the extrinsic (death receptor) pathway or the intrinsic (mitochondrial) pathway. In the intrinsic apoptosis pathway, the Bcl-2 family of proteins functions as a central regulator. The Bcl-2 protein, as a member of the Bcl-2 family, resides in the outer mitochondrial membrane or around the endoplasmic reticulum. It removes pro-apoptotic members such as Bax from mitochondria, which ultimately prevents apoptotic cell death. Increased Bax expression in malignancy cells induces cell death and eliminates tumor cells. In contrast, increased Bcl-2 expression prevents apoptosis and prospects to tumor progression. It is generally believed that chemotherapeutic drugs eliminate malignancy cells by inducing apoptosis (Letai, 2017[25]). The discovery and synthesis of biologically active molecules with cytotoxic KIR2DL5B antibody properties has been considered as a potential new therapy for destroying tumor cells. Targeting histone deacetylases (HDACs), Frentizole which have important functions in regulating cell proliferation, cell migration, and cell death via their inhibitors is one of the goals in malignancy drug development. A wide variety of HDAC inhibitors (HDACIs) have shown anticancer effects used either singly (Wetzel et al., 2005[45]) or in combination with other brokers (Seah et al., 2018[34]; Almenara et al., 2002[2]). Due to the sensitivity of tumor cells and relative resistance of normal cells to HDACIs, inhibiting these proteins is usually highlighted not only in clinical treatments but also in chemoprevention of malignancy (Dong et al., 2018[11]; Ahrens et al., 2016[1]). Therefore, we suggest that inhibiting these targets provides normal cells with compensatory capabilities and relative resistance to induced cell death compared to the sensitive malignancy cells. VPA, which belongs to the class of aliphatic acids, has been recently shown to inhibit HDACs activity, have antiproliferative and anticancer effects, and to be responsible for tissue-dependent changes in the transcriptome (Matthews et al., 2001[27]; Ho et al., 2012[18]; Frederiksen et al., 2007[13]; Brodie and Brandes, 2014[5]; Van Leeuwen et al., 2011[43]; Heers et al., 2018[16]; Witt et al., 2013[46]; Yarmohamadi et al., 2018[51]; Ni et al., 2017[28]). In addition to its effect on histone proteins, VPA can also influence the protein levels of nonhistone proteins such as p53 (Cook et al., 2004[8]), Ku70 (Jordan et al., 2000[22]), Bcl-2, Bax, and caspase-3 that are important in malignancy growth, apoptosis, DNA repair, differentiation, and cell cycle control (Huang et al., 1999[19]; Takabuchi et al., 2004[38]; Thomas et al., 2004[41]). Numerous studies have shown that VPA in combination with other drugs has increased anticancer effects. The combinatory effects of VPA and Fluvastatin demonstrate that they take action synergistically in inducing -H2AX and apoptosis accompanied by higher acetylated histones H3 and H4 in GBM8401 cells. In addition, it has been revealed that VPA in combination with Mitomycin C consistently induces synergistic growth inhibition and decreases viability of colon carcinoma cells (Friedmann et al., 2006[14]). Numerous studies show that the combination of VPA and Metformin (MET) can synergistically decrease the viability of prostate malignancy cells more efficiently than either drug used individually. Moreover, MET combined with VPA reduced proliferation and induced apoptosis in tumor cells (Tran et al., 2017[42]). Several studies have shown that combination of Cytarabine and VPA has significant anticancer effects in non-acute myeloid leukemia cases. Moreover, Cytarabine and VPA cooperatively Frentizole induced DNA double-strand breaks, reflected in induction of -H2AX and apoptosis, accompanied by activation of.