Targeting HOX/PBX dimer formation as a potential therapeutic option in esophageal squamous cell carcinoma

Abstract

Homeobox genes are known to be classic examples of the intimate relationship between embryogenesis and tumorigenesis, which are a family of transcriptional factors involved in determining cell identity during early development, and also dysregulated in many malignancies. Previously, HOXB7 , HOXC6 and HOXC8 were found abnormally upregulated in esophageal squamous cell carcinoma (ESCC) tissues compared with normal mucosa and seen as poor prognostic predictors for ESCC patients, and were shown to promote cell proliferation and anti‐apoptosis in ESCC cells. These three HOX members have a high level of functional redundancy, making it difficult to target a single HOX gene. The aim of the present study was to explore whether ESCC cells are sensitive to HXR9 disrupting the interaction between multiple HOX proteins and their cofactor PBX, which is required for HOX functions. ESCC cell lines (KYSE70, KYSE150, KYSE450) were treated with HXR9 or CXR9, and coimmunoprecipitation and immunofluorescent colocalization were carried out to observe HOX/PBX dimer formation. To further investigate whether HXR9 disrupts the HOX pro‐oncogenic function, CCK‐8 assay and colony formation assay were carried out. Apoptosis was assessed by flow cytometry, and tumor growth in vivo was investigated in a xenograft model. RNA‐seq was used to study the transcriptome of HXR9‐treated cells. Results showed that HXR9 blocked HOX/PBX interaction, leading to subsequent transcription alteration of their potential target genes, which are involved in JAK‐signal transducer and activator of transcription (STAT) activation and apoptosis inducement. Meanwhile, HXR9 showed an antitumor phenotype, such as inhibiting cell proliferation, inducing cell apoptosis and significantly retarding tumor growth. Therefore, it is suggested that targeting HOX/PBX may be a novel effective treatment for ESCC.

HOXB7 mediates cisplatin resistance in esophageal squamous cell carcinoma through involvement of DNA damage repair

“…Regarding the safety of the peptide HXR9, we found that it was not cytotoxic to the nonmalignant esophagus epithelial cell line HEEC and bodyweight loss in mice treated with HXR9 was not significantly greater than the control. 28 Meanwhile, the combination of HXR9 with cisplatin did not lead to significant weight loss in mice. In addition, previous studies have indicated that there is a rapid accumulation of HXR9 in the first few hours and it then remains stable beyond 24 hours and local delivery of HXR9 into tumors in mice has not resulted in a local inflammatory response.…”

“…Moreover, it was found that disruption of HOXB7/PBX by HXR9 caused transcription alteration of genes such as MPL, IL-15, IL-23A and IL-24, which encode cytokines involved in regulating the activation of JAK-STAT signaling pathway or induction of apoptosis in our previous study. 28 It suggested that HXR9 may disrupt HOX/PBX functions through modifying cyctokine-JAK-STAT pathway activation to sensitize ESCC cells to cisplatin. However, the underlying exact mechanism is to be investigated in the future.…”

“…Extensive researches have demonstrated that HXR9 causes apoptosis and inhibits tumor survival in a variety of tumor types, including ESCC. [23][24][25][26][27][28] To validate the hypothesis that HXR9 enhances the efficacy of cisplatin in ESCC cells, we performed a CCK-8 assay and clonal formation assay to evaluate the cell viability after exposure to cisplatin, or HXR9, or the combination of cisplatin with HXR9 and to determine the effect of these treatments on tumor growth in ESCC mouse xenograft models. The results showed that a combination of HXR9 and cisplatin synergistically inhibited cell viability (Fig 7a, b).…”

Direct and Indirect Targeting of HOXA9 Transcription Factor in Acute Myeloid Leukemia

“…Such interaction shuts down the expression of various genes involved in apoptosis [8,237,238]. Disruption of HOX/PBX interaction impacts cell proliferation and restores cell death in various solid tumor cell models [238], including melanoma [236,239], renal cell carcinoma [240], ovarian cancer (such as the SK-OV3 cell model or primary samples [241,242]), breast cancer [243], prostate cancer [244], asbestos-associated mesothelioma [245], and oral and esophageal squamous cell carcinoma [246,247]. HXR9 was also evaluated in AMLs based on the relevance of HOXA9 and PBX3 interaction in AML [29,75,248,249], but other expressed HOX/PBX3 interfaces may also be disrupted by HXR9 in AML.…”

Roles of the HOX Proteins in Cancer Invasion and Metastasis

“…Cancer cells' sensitivity to this peptide is highly correlated to their HOX expression profile, albeit the subset of HOX genes which act as oncosuppressors is not affected [34]. This peptide has shown to be effective in oesophageal and oral squamous cell carcinomas [36,37], melanoma [35,38], ovarian cancer (OC) [39], breast cancer [40], meningioma [41], prostate cancer [42], and leukaemia [43]. The use of RNA interference mechanisms [44,45] and the control of HOX methylation status [46] are additional tools that can control HOX expression with therapeutic function.…”