HC-1119 is a new second-generation AR antagonist that has been used in clinical trials to treat prostate cancer [29, 30]. Although lacking sufficient pharmacokinetics data, the effective concentrations of HC-1119 for inhibiting AR function are 0.5 µM in Hs578T cells and 10 µM in SUM159PT cells, which are much lower than the 4 to 50 µM of the regular Enzalutamide  and the 25 µM to 10 mM of bicalutamide used for TNBC cells [32, 33, 34]. The usage of lower dose may help to reduce side effects.
We found that HC-1119 treatment could inhibit DHT-promoted migration and invasion capabilities of the AR-positive TNBC cells, and this inhibition might be a consequence of reduced EMT plasticity of these TNBC cells. Previous studies have shown that DHT-activated AR interacts with demethylase LSD1 to repress E-cadherin transcription and upregulate vimentin transcription in the ER and AR positive MCF7 breast cancer cells, leading to EMT that increases cell migration and invasion . Furthermore, AR activation can enhance the viability of cancer stem-like cells (CSCs) through an androgen paracrine action, and also facilitates the steaminess features of AR-positive cancer cells . Our results indicate that HC-1119 could be an effective AR inhibitor to suppress androgen-promoted migration and invasion of AR-positive TNBCs.
HC-1119 at a dose of 7 mg/kg given to mice every 2 days could reduce DHT-promoted metastasis of TNBC cells in vivo. Early studies showed that testosterone levels are fluctuating, and plasma concentration of DHT is maintained in a dynamic balance during menstrual cycle, which is higher in premenopause women and lower in postmenopause women [35, 36]. Hence, it should be meaningful to examine plasma concentration of DHT (PC-DHT) routinely in TNBC patients. Furthermore, since the DHT-induced nuclear translocation of AR is a key step for AR signaling to promote metastasis of TNBC [8, 9], the ratio of nuclear AR to cytoplasmic AR, together with the PC-DHT, may be used to assess whether a patient with AR-positive TNBC is sensitive to HC-1119 treatment and can receive benefits from HC-1119 treatment.
It is known that DHT binds and activates AR, which in turn increases AR protein through multiple pathways [37, 38, 39, 40]. Our results suggest that HC-1119 can completely block the increase in AR protein induced by DHT, indicating that HC-1119 can effectively suppress AR function in TNBC cells. In addition, our assays suggest that either DHT or HC-1119 treatment did not significantly alter the proliferation or apoptosis of TNBC cells (data not shown), suggesting that AR function is not essential for the growth or survival of TNBC cells. A previous study also demonstrated that DHT treatment of the patient-derived xenografts developed from patients with AR-positive TNBCs mainly inhibits EMT, angiogenesis, and WNT/β-catenin signaling .
In this study, we have evaluated the efficacy of HC-1119 in inhibition of DHT-activated AR function in AR-positive TNBC cells. However, we have not compared the efficacy of HC-1119 with the regular enzalutamide in these cells, which will be planned in our future experiments. Furthermore, we only studied the response of DHT-treated TNBC cells, but accumulating evidence suggests that AR also plays an important role in ER-positive breast cancer cells [20, 38, 42, 43]. Thus, it will be interesting to test the inhibitory effects of HC-1119 on ER-positive breast cancer cells. Moreover, the crosstalk between AR signaling and other pathways such as PI3K/AKT/mTOR, WNT/β-catenin and MAPK has been shown being involved in the abnormal activation of AR and the resistance to AR antagonist [37, 44, 45]. It would be important to test whether combinatorial treatment with HC-1119 and other pathway inhibitors can achieve a better result. Finally, the pharmacokinetics, safety and tolerability of HC-1119 should be further studied.
In summary, this study demonstrated that HC-1119 can effectively inhibit DHT-increased AR protein and DHT binding-induced AR-nuclear translocation, and thus block DHT-promoted migration, invasion and metastasis of TNBC cells. These results suggest that HC-1119 is a new second-generation AR inhibitor that might be used to treat AR-positive TNBCs. This is the first study showing that HC-1119 may be used to treat other types of AR-positive cancers such as AR-positive TNBC in addition to the prostate cancer.