STAT3 and STAT5A are potential therapeutic targets in castration-resistant prostate cancer

Abstract

Mechanisms of castration-resistant prostate cancer (CRPC) are not well understood, thus hindering rational-based drug design. Activation of STAT3/5A, key components of the JAK/STAT pathway, is implicated in aggressive PC, yet their clinical relevance in CRPC remains elusive. Here, we evaluated the possible role of STAT3/5A in CRPC using immunological, quantitative mRNA expression profiling, and pharmacological methods. We observed a strong nuclear immunoreactivity for STAT3 and STAT5A in 93% (n=14/15) and 80% (n=12/15) of CRPC cases, respectively, compared with benign prostatic hyperplasia (BPH). We demonstrated that PC cells express varying levels of STAT3 and STAT5A transcripts. In addition, we demonstrate that pimozide, a psychotropic drug and an indirect inhibitor of STAT5, attenuated PC cells growth, and induced apoptosis in a dose-dependent manner. Furthermore, our analysis of the PC public data revealed that the STAT3/5A genes were frequently amplified in metastatic CRPC. These findings suggest that STAT3/5A potentially serves as a predictive biomarker to evaluate the therapeutic efficacy of a cancer drug targeting the JAK/STAT pathway. Since the JAK/STAT and AR pathways are suggested to be functionally synergistic, inhibition of the JAK/STAT signaling alone or together with AR may lead to a novel treatment modality for patients with advanced PC.

Keywords: STAT3; STAT5A; castration-resistance; pimozide; prostate cancer.

Figure 1

Bar diagram showing the expression patterns of STAT3 (A) and STAT5A (B) in castration-resistant prostate cancer (CRPC) and benign prostatic hyperplasia (BPH) clinical cases as analyzed by IHC.

Figure 2. IHC staining of STAT3/5A in CRPC cases

(A) Hematoxylin and Eosin (H&E). (B) Diffuse and strong nuclear immunoreactivity for STAT3. (C) Diffuse and strong nuclear immunoreactivity for STAT5A. (D) A case of H&E staining in CRPC. (E) Negative staining for STAT3 in CRPC. (F) Negative staining for STAT5A in CRPC. Original magnification was x200. Micrographs are representation of multiple images.

Figure 3. IHC staining of STAT3/5A in BPH cases

(A) Hematoxylin and Eosin (H&E) staining of BPH cases. (B) Diffuse and strong nuclear immunoreactivity for STAT3. (C) Diffuse and moderate to strong nuclear immunoreactivity for STAT5A. (D) A case of H&E staining in BPH. (E) Negative staining for STAT3 in BPH. (F) Negative staining for STAT5A in BPH. Original magnification was x200. Micrographs are representation of multiple images.

Figure 4. Alterations of STAT3/5A mRNA and genes in PC

(A) Quantitative RT-PCR analysis of STAT3 and STAT5A transcripts in LNCaP, C4-2, 22Rv1, and PC3 cells. *p<0.0002, **p>0.05 ***p<0.002. 24h after cell seeding, total RNA was isolated from cells that were grown in serum-fed conditions. (B) Alterations of the STAT3 and STAT5A genes in metastatic CRPC clinical cases. The data were accessed through the www.cbioportal.org online platform. Data (±SD) are representation of two independent experiments in triplicates.

Figure 5. The effects of pimozide on PC cells growth and apoptosis in vitro

(A) The dose-dependent effects of pimozide on LNCaP (*p<0.001), C4-2 (*p>0.06; **p<0.002), 22Rv1 (*p<0.02), and PC3 (*p>0.15; **p<0.002) cell growth. (B) Dose-dependent effects of pimozide on LNCaP (*p<0.01) and C4-2 (*p<0.01) apoptosis. Cell proliferation by CCK-8 and apoptosis by PI staining were analyzed at 48h post pimozide treatment. Data (±SD) are representation of two independent experiments in triplicates.