齋藤 心平

BACKGROUND: To clarify the clinical roles of changes in testosterone (T) levels with a cut-off level of 20 ng/dL as predictive factors for prostate cancer patients treated with degarelix acetate. METHODS: A total of 120 prostate cancer patients who received hormone therapies with gonadotropin-releasing hormone antagonist degarelix acetate were retrospectively analyzed. The predictive values of nadir T levels, max T levels, T bounce, and other clinical factors were evaluated for overall survival (OS), cancer-specific survival (CSS), and progression-free survival (PFS). T bounce was defined as satisfying both nadir serum T levels of <20 ng/dL and max serum T levels of ≥20 ng/dL during hormone therapies. RESULTS: In 120 prostate cancer patients, 16 (13%) patients did not achieve nadir T < 20 ng/dL, and 76 (63%) patients had max T ≥ 20 ng/dL. The median times to nadir T and max T are 108 and 312 days, respectively. T bounce was shown in 60 (50%) patients and is associated with favorable prognoses both for OS (p = 0.0019) and CSS (p = 0.0013) but not for PFS (p = 0.92). While in the subgroup analyses of the patients with the progression of the first-line hormone therapies, T bounce predicts favorable OS (p = 0.0015) and CSS (p = 0.0013) after biochemical recurrence. CONCLUSIONS: The present study revealed that T bounce with cut-off levels of 20 ng/dL is a promising biomarker that predicts OS and CSS for prostate cancer patients treated with degarelix acetate.

L-type amino acid transporter 1 (LAT1) is specifically expressed in many malignancies, contributes to the transport of essential amino acids, such as leucine, and regulates the mammalian target of rapamycin (mTOR) signaling pathway. We investigated the expression profile and functional role of LAT1 in prostate cancer using JPH203, a specific inhibitor of LAT1. LAT1 was highly expressed in castration-resistant prostate cancer (CRPC) cells, including C4-2 and PC-3 cells, but its expression level was low in castration-sensitive LNCaP cells. JPH203 significantly inhibited [14C] leucine uptake in CRPC cells but had no effect in LNCaP cells. JPH203 inhibited the proliferation, migration, and invasion of CRPC cells but not of LNCaP cells. In C4-2 cells, Cluster of differentiation (CD) 24 was identified by RNA sequencing as a novel downstream target of JPH203. CD24 was downregulated in a JPH203 concentration-dependent manner and suppressed activation of the Wnt/β-catenin signaling pathway. Furthermore, an in vivo study showed that JPH203 inhibited the proliferation of C4-2 cells in a castration environment. The results of this study indicate that JPH203 may exert its antitumor effect in CRPC cells via mTOR and CD24.

L-type amino acid transporter 1 (LAT1, SLC7A5) is an amino acid transporter expressed in various carcinomas, and it is postulated to play an important role in the proliferation of cancer cells through the uptake of essential amino acids. Cabazitaxel is a widely used anticancer drug for treating castration-resistant prostate cancer (CRPC); however, its effectiveness is lost when cancer cells acquire drug resistance. In this study, we investigated the expression of LAT1 and the effects of a LAT1-specific inhibitor, JPH203, in cabazitaxel-resistant prostate cancer cells. LAT1 was more highly expressed in the cabazitaxel-resistant strains than in the normal strains. Administration of JPH203 inhibited the growth, migration, and invasive ability of cabazitaxel-resistant strains in vitro. Phosphoproteomics using liquid chromatography-mass spectrometry to comprehensively investigate changes in phosphorylation due to JPH203 administration revealed that cell cycle-related pathways were affected by JPH203, and that JPH203 significantly reduced the kinase activity of cyclin-dependent kinases 1 and 2. Moreover, JPH203 inhibited the proliferation of cabazitaxel-resistant cells in vivo. Taken together, the present study results suggest that LAT1 might be a valuable therapeutic target in cabazitaxel-resistant prostate cancer.

BACKGROUND/AIM: The prognostic significance of androgen receptor amplification (AR amp) in cell-free DNA (cfDNA) was studied in Japanese patients with castration-resistant prostate cancer (CRPC). PATIENTS AND METHODS: A total of 120 serum samples were obtained from 38 patients with CRPC. Serum cfDNA was purified and the AR copy number was determined. Factors associated with progression-free survival (PFS) and overall survival (OS) were statistically investigated. RESULTS: The number of patients administered enzalutamide (Enza)/abiraterone (Abi)/docetaxel (DTX) was 33/25/11, respectively. The median PSA was 16.5 ng/ml. Thirty patients (79%) had bone metastases and three patients (7.9%) had lung metastases. The median follow-up was 655 days. The median initial AR copy number was 1.27 (1.10-11.50); an AR copy number of 1.27 or higher was defined as an AR-amp. Regarding PFS, the presence of AR-amp, Gleason score (GS), and ALP were significant factors in univariate analysis. In multivariate analysis, AR amplification was an independent prognostic factor (hazard ratio=7.7, p=0.0035). For OS, PSA and AR-amp were significant factors. In multivariate analysis, AR-amp (hazard ratio=4.65, p=0.0188) was the only independent prognostic factor. CONCLUSION: AR-amp was associated with high nadir PSA and low iPSA/PSA ratio. AR-amp was significantly associated with poor prognosis in Japanese patients with CRPC.

BACKGROUND: The prognostic nutritional index (PNI) based on the serum albumin level and the lymphocyte count has been investigated as a prognostic factor in patients with malignant tumors. However, it has been poorly studied in prostate cancer (PCa), and little is known about its clinical utility. METHODS: Clinical data of 353 patients with de novo, metastatic, hormone-sensitive PCa (mHSPC) who received androgen deprivation therapy (ADT) were obtained from multiple institutions between 2000 and 2019. The impacts of the pretreatment PNI level on treatment response and survival, together with clinical parameters, were examined. The Mann-Whitney U test, Cox proportional hazards models, and Kaplan-Meier methods were used to evaluate significance. RESULTS: The median age and initial prostate-specific antigen level were 73 and 266.18 ng/mL, respectively. Patients with a low PNI had shorter progression-free survival (PFS), cancer-specific survival (CSS), and overall survival (OS) (p < 0.0001). On multivariate analysis, low PNI was an independent prognostic factor for OS (p = 0.0027, HR = 1.65), as well as advanced age (p = 0.049, HR = 1.38), the International Society of Urological Pathology (ISUP) grade group (GG) 5 (p = 0.0027, HR = 1.69), and elevated lactate dehydrogenase (LDH) (p < 0.0001, HR = 2.08). A propensity score-matching analysis showed that the PNI level remained a significant prognostic biomarker for PFS (p = 0.0263), CSS (p = 0.0006), and OS (p = 0.0015). Furthermore, a novel risk classification using PNI, LDH, and the ISUP GG was established to stratify patients' prognosis. An increase in the number of risk factors was significantly correlated with poor outcomes. CONCLUSIONS: A low pretreatment PNI might be an effective biomarker of poor treatment response and survival in patients with mHSPC undergoing ADT.