Sequences and combinations of multifaceted therapy in advanced prostate cancer

A conjugate of methotrexate and an analog of luteinizing hormone releasing hormone shows increased efficacy against prostate cancer

LHRH receptor, is over-expressed in a variety of human tumors and, is a potential binding site for targeted metastatic prostate cancer therapy. The objectives of our study were to synthesize a bioconjugate of the LHRH analog [DLys⁶]-LHRH and the anti-tumor agent methotrexate and test the hypothesis that [DLys⁶]-LHRH-MTX targets and inhibits prostate cancer cell growth in vitro and in vivo. The results of in vitro studies, showed that both [DLys⁶]-LHRH-MTX and MTX displayed superior cytotoxicity against prostate cancer cells in a concentration-dependent manners, with IC₅₀ concentrations for PC-3 cells of, 1.02 ± 0.18 μmol/L and 6.34 ± 1.01 μmol/L; for DU-145 cells, 1.53 ± 0.27 μmol/L and 8.03 ± 1.29 μmol/L; and for LNCaP cells, 1.93 ± 0.19 μmol/L and 9.68 ± 1.24 μmol/L, respectively. The IC₅₀ values of [DLys⁶]-LHRH-MTX and MTX were 110.77 ± 15.31 μmol/L and 42.33 ± 7.25 μmol/L, respectively. Finally, [DLys⁶]-LHRH-MTX significantly improved the anti-tumor activity of MTX in nude mice bearing PC-3 tumor xenografts. The inhibition ratios of tumor volume and tumor weight in the [DLys⁶]-LHRH-MTX treated group were significantly higher than those in the MTX-treated group. Tumor volume doubling time was also significantly extended from 6.13 days in control animals to 9.67 days in mice treated with [DLys⁶]-LHRH-MTX. In conclusion, [DLys⁶]-LHRH -MTX may be useful in treating prostate cancer.

Multifaceted and personalized therapy of advanced prostate cancer

PURPOSE OF REVIEW

A number of molecular and genomic biomarkers that possess the ability to guide treatment or 'actionable targets' are being reported in metastatic prostate cancer. In addition, pathways of resistance to existing therapies and novel agents to overcome them are currently under active investigation. The next wave of investigations is focused on personalized therapy of prostate cancer. The focus of this review article is to provide an update on clinical development in advanced prostate cancer and to highlight the ongoing investigations of biomarker discovery, and ways of overcoming therapeutic resistance. The next generation of clinical trials developing novel targets and compounds promises to be in populations enriched with specific marker expression.

RECENT FINDINGS

The breakthrough report, of the ability of the androgen receptor variant 7 mutation, detected in circulating tumor cells, to predict the lack of response to abiraterone or enzalutamide, and the remarkable responses of poly adenosine diphosphate ribose polymerase inhibitors in prostate cancer with DNA repair mutations have elevated hopes of a bright future in the biomarker-driven therapeutic arena. Novel targets such as bromodomain extra terminal-1 and phosphatidylinositol 3-kinase hold promise for the possibility of overcoming resistance. Novel hormone agents are also under active study.

SUMMARY

As the clinical application of the multifaceted therapies narrows down to enriched patient populations selected by genomic testing, the therapeutic efficiency will escalate considerably. Novel targets, resistance mechanisms and relevant agents are being avidly tested, and the dream of personalized medicine is emerging into reality.

Lin28 induces resistance to anti-androgens via promotion of AR splice variant generation

BACKGROUND

Prostate cancer (PCa) is androgen-dependent initially and progresses to a castration-resistant state after androgen deprivation therapy. Treatment options for castration-resistant PCa include the potent second-generation anti-androgen enzalutamide or CYP17A1 inhibitor abiraterone. Recent clinical observations point to the development of resistance to these therapies which may be mediated by constitutively active alternative splice variants of the androgen receptor (AR).

METHODS

Sensitivity of LNCaP cells overexpressing Lin28 (LN-Lin28) to enzalutamide, abiraterone, or bicalutamide was compared to that of control LN-neo cells using cell growth assays, proliferation assays using MTT, anchorage-dependent clonogenic ability assays and soft agar assays. Ability of LN-Lin28 cells to maintain AR activation after treatment with enzalutamide, abiraterone, or bicalutamide was tested using immunofluorescence, Western blotting, ChIP assays, and qRT-PCR. Importance of Lin28 in enzalutamide resistance was assessed by the downregulation of Lin28 expression in C4-2B and 22Rv1 cells chronically treated with enzalutamide. Requirement for sustained AR signaling in LN-Lin28 cells was examined by the downregulation of either full length AR or AR-V7 using siRNA.

RESULTS

We show that Lin28 promotes the development of resistance to currently used targeted therapeutics by enhancing the expression of AR splice variants such as AR-V7. PCa cells overexpressing Lin28 exhibit resistance to treatment with enzalutamide, abiraterone, or bicalutamide. Downregulation of Lin28 resensitizes enzalutamide-resistant PCa cells to enzalutamide treatment. We also show that the upregulation of splicing factors such as hnRNPA1 by Lin28 may mediate the enhanced generation of AR splice variants in Lin28-expressing cells.

CONCLUSIONS

Our findings suggest that Lin28 plays a key role in the acquisition of resistance to AR-targeted therapies by PCa cells and establish the importance of Lin28 in PCa progression.