Therapeutic Potential of Synergistic Targeted Inhibition of HSP90AB1 and PARP1 in Prostate Cancer Cells: A Review of Celastrol and Olaparib Combination Therapy

Background

Prostate Cancer (PCA) is one of the most common malignancies among men worldwide, with its incidence continually rising in recent years, making early screening and treatment crucial. The causes and pathology of prostate cancer are complex, involving a variety of genetic, environmental, and lifestyle factors. Despite some advancements in detection and treatment, prostate cancer still faces high recurrence rates and poor survival expectations, especially in patients with advanced castration-resistant prostate cancer (CRPC), where treatment becomes more challenging. Existing treatments such as Androgen Deprivation Therapy (ADT) are typically effective initially but diminish in efficacy with the development of resistance. Thus, overcoming the limitations of current drugs and exploring new effective treatment strategies has become a research focus.

Research into genes and molecular mechanisms has found that Heat Shock Protein 90 (HSP90) family member HSP90AB1 plays a significant role in intracellular protein homeostasis and folding, with its overexpression associated with various solid tumors. Moreover, Poly (ADP-ribose) polymerase 1 (PARP1) is also highly expressed in prostate cancer cells and as a key enzyme in the DNA repair process, its inhibition can induce apoptosis in cancer cells. The PARP inhibitor Olaparib has drawn attention for its significant anti-cancer effects in DNA repair-deficient cancer cells, especially those with BRCA mutations. However, single therapies may be limited by factors such as resistance, making combined targeted therapies an effective strategy to enhance therapeutic outcomes.

Research Overview and Methodology

This study, conducted by a collaborative team from Guizhou University, Zunyi Medical University Affiliated Hospital, and Guizhou Institute of Technology, was published in the 2024 edition of “Cancer Cell International”. The research primarily explored the expression of HSP90AB1 and PARP1 in prostate cancer and their impact on cell resistance. It further investigated the therapeutic effects of combining the HSP90 inhibitor Celastrol with the PARP inhibitor Olaparib on prostate cancer, particularly their potential in inhibiting cell survival, migration, and proliferation. Additionally, the team validated the synergistic anti-tumor effect of combining these two drugs in vivo using a mouse xenograft model.

Research Methods and Process

1. Gene Expression Analysis: The research team obtained expression data for HSP90AB1 and PARP1 from The Cancer Genome Atlas (TCGA) and analyzed their expression levels in various cancer types and prostate adenocarcinoma (PRAD) through the R2 platform and GEPIA database. The results showed significant overexpression of HSP90AB1 and PARP1 in prostate cancer cells, with high expression correlating with poor prognosis for patients.

2. Cell Experiments: The study selected prostate cancer cell lines such as RWPE-1, 22RV1, PC3, and DU145, utilizing Western Blotting and clonogenic assays to verify the overexpression of HSP90AB1 and PARP1. To further explore the impact of HSP90AB1 on sensitivity to PARP inhibitors, the team used short hairpin RNA (shRNA) to knockdown the HSP90AB1 gene, finding that its inhibition significantly increased prostate cancer cell sensitivity to Olaparib.

3. Combined Effects of Celastrol and Olaparib: The research used clonogenic assays, scratch assays, EdU fluorescence staining, and CCK-8 cell proliferation testing to further investigate the impact of combined Celastrol and Olaparib treatment on prostate cancer cell growth, migration, and viability. The results showed the combination treatment significantly inhibited the cells’ clonogenic ability, migration speed, and proliferation activity.

4. DNA Damage Detection: The study detected DNA damage through γH2AX immunofluorescence staining and alkaline comet assays, finding significant increases in the DNA double-strand break marker γH2AX following combined treatment with Celastrol and Olaparib, indicating accrued DNA damage and enhanced cell death.

5. Signaling Pathway Analysis: The study also explored the effects of Celastrol and Olaparib combination therapy on the PI3K/AKT signaling pathway. Western Blot results demonstrated significant reductions in the phosphorylation levels of PI3K and AKT with combination treatment, suggesting that inhibition of this pathway may further sensitize cancer cells to treatment.

6. In Vivo Xenograft Model: The anti-tumor effect of the combined drugs was validated through mouse xenograft experiments. Results showed that the combination treatment group had significantly reduced tumor volume and weight compared to single-drug groups, with no apparent toxic reactions, further supporting the therapeutic potential of their combined use.

Data Analysis

All experimental results were statistically analyzed using GraphPad Prism software, employing t-tests and analysis of variance (ANOVA) to assess data significance. A P-value less than 0.05 was considered statistically significant.

Research Results and Discussion

1. Overexpression of HSP90AB1 and PARP1: The study found significant overexpression of HSP90AB1 and PARP1 in prostate cancer cell lines, which negatively correlates with patient survival rates. This indicates that these proteins may play crucial roles in the survival, migration, and drug resistance of prostate cancer cells.

2. Celastrol Enhances Olaparib Effects: The addition of Celastrol notably enhanced the anti-cancer effects of Olaparib, marked by significant declines in cell proliferation, migration, and survival rates. This combination achieved synergistic inhibition of cancer cells through enhanced DNA damage effects.

3. Inhibition of PI3K/AKT Signaling Pathway: The addition of Celastrol effectively downregulated the activity of the PI3K/AKT pathway, suggesting that its inhibition may reduce resistance to Olaparib, thereby enhancing the effects of combination therapy.

4. Validation of In Vivo Anti-tumor Effect: In mouse xenograft models, the combination treatment group showed significantly reduced tumor growth rates, with no significant toxic reactions, indicating strong in vivo anti-tumor effects.

Conclusion and Significance

This study revealed the synergistic action of HSP90AB1 and PARP1 in prostate cancer cells. The combined therapy of Celastrol and Olaparib achieves multi-pathway inhibition of cancer cell proliferation and survival, particularly enhancing DNA damage and inhibiting the PI3K/AKT pathway, demonstrating significant synergistic effects. Compared to single Olaparib treatment, the combination therapy shows stronger anti-cancer effects, providing a new targeted approach for prostate cancer treatment, especially for cells resistant to single-drug treatment.

Research Highlights

• This study systematically demonstrated the synergistic therapeutic potential of HSP90AB1 and PARP1 in prostate cancer for the first time.
• The combination of Celastrol and Olaparib, by various mechanisms, enhanced sensitivity in cancer cells, effectively inhibiting tumor growth.
• The significant inhibitory effect on the PI3K/AKT pathway in combination therapy provides important insights for developing anti-resistance drugs.

Summary

The combination of Celastrol and Olaparib exhibits significant potential in prostate cancer therapy. The study results offer new insights into targeted therapy for prostate cancer, aiding in the design of combined therapy strategies based on HSP90 and PARP1 to tackle drug resistance in single therapies and improve clinical outcomes for prostate cancer patients.