Weighing the Addition of Androgen Suppression Therapy to Radiotherapy Dose Escalation for Intermediate-Risk Prostate Cancer

Overcoming chemoresistance and radio resistance in prostate cancer: The emergent role of non-coding RNAs

Prostate cancer (PCa) continues to be a major health concern worldwide, with its resistance to chemotherapy and radiation therapy presenting major hurdles in successful treatment. While patients with localized prostate cancer generally have a good survival rate, those with metastatic prostate cancer often face a grim prognosis, even with aggressive treatments using various methods. The high mortality rate in severe cases is largely due to the lack of treatment options that can offer lasting results, especially considering the significant genetic diversity found in tumors at the genomic level. This comprehensive review examines the intricate molecular mechanisms governing resistance in PCa, emphasising the pivotal contributions of non-coding RNAs (ncRNAs). We delve into the diverse roles of microRNAs, long ncRNAs, and other non-coding elements as critical regulators of key cellular processes involved in CR & RR. The review emphasizes the diagnostic potential of ncRNAs as predictive biomarkers for treatment response, offering insights into patient stratification and personalized therapeutic approaches. Additionally, we explore the therapeutic implications of targeting ncRNAs to overcome CR & RR, highlighting innovative strategies to restore treatment sensitivity. By synthesizing current knowledge, this review not only provides a comprehension of the chemical basis of resistance in PCa but also identifies gaps in knowledge, paving the way for future research directions. Ultimately, this exploration of ncRNA perspectives offers a roadmap for advancing precision medicine in PCa, potentially transforming therapeutic paradigms and improving outcomes for patients facing the challenges of treatment resistance.

DNA Damage- But Not Enzalutamide-Induced Senescence in Prostate Cancer Promotes Senolytic Bcl-xL Inhibitor Sensitivity

Cellular senescence is a natural tumor suppression mechanism defined by a stable proliferation arrest. In the context of cancer treatment, cancer cell therapy-induced senescence (TIS) is emerging as an omnipresent cell fate decision that can be pharmacologically targeted at the molecular level to enhance the beneficial aspects of senescence. In prostate cancer (PCa), TIS has been reported using multiple different model systems, and a more systematic analysis would be useful to identify relevant senescence manipulation molecular targets. Here we show that a spectrum of PCa senescence phenotypes can be induced by clinically relevant therapies. We found that DNA damage inducers like irradiation and poly (ADP-ribose) polymerase1 (PARP) inhibitors triggered a stable PCa-TIS independent of the p53 status. On the other hand, enzalutamide triggered a reversible senescence-like state that lacked evidence of cell death or DNA damage. Using a small senolytic drug panel, we found that senescence inducers dictated senolytic sensitivity. While Bcl-2 family anti-apoptotic inhibitor were lethal for PCa-TIS cells harboring evidence of DNA damage, they were ineffective against enzalutamide-TIS cells. Interestingly, piperlongumine, which was described as a senolytic, acted as a senomorphic to enhance enzalutamide-TIS proliferation arrest without promoting cell death. Overall, our results suggest that TIS phenotypic hallmarks need to be evaluated in a context-dependent manner because they can vary with senescence inducers, even within identical cancer cell populations. Defining this context-dependent spectrum of senescence phenotypes is key to determining subsequent molecular strategies that target senescent cancer cells.

Radiation Attenuates Prostate Tumor Antiviral Responses to Vesicular Stomatitis Virus Containing IFNβ, Resulting in Pronounced Antitumor Systemic Immune Responses

Vesicular stomatitis virus (VSV) expressing IFNβ induces apoptosis in multiple tumor models while maintaining an excellent safety profile. VSV-IFNβ is oncoselective due to permissive replication in cells with an altered IFN pathway. The human VSV-IFNβ (hIFNβ) vector is currently used in clinical trials as a standalone therapy; however, we hypothesized that oncolytic virotherapy might be more effective when used in combination with radiotherapy (RT). We investigated the synergistic effects of RT and VSV-hIFNβ in the subcutaneous PC3 and orthotopic LNCaP prostate xenograft models and a syngeneic RM9 prostate tumor model. VSV-IFNβ combined with RT amplified tumor killing for PC3 and LNCaP xenografts, and RM9 tumors. This was attributed to the induction of proapoptotic genes leading to increased VSV-IFNβ infection and replication, VSV expression, and oncolysis. In the RM9 tumors, combination therapy resulted in a robust antitumor immune response. Treated RM9 tumor-bearing mice demonstrated an increase in CD8⁺ and CD4⁺ T-cell numbers, 100% resistance to tumor rechallenge, and reduced resistance to reimplantation challenge with CD8⁺ knockdown. RT enhanced the activity of VSV-mediated oncolysis via attenuation of the innate antiviral response, resulting in increased VSV replication and the generation of an adaptive immune response earmarked by an increase in CD8⁺ lymphocyte numbers and antitumor activity. Local tumor irradiation combined with VSV-IFNβ affects tumor cell death through direct and systemic activity in conjunction with pronounced antitumor immunity. IMPLICATIONS: Radiotherapy enhances VSV-mediated oncolysis and anti-tumor immunity, indicating that the ombination has promise for very high risk prostate cancer.

Phase I Trial of MRI-Guided Prostate Cancer Lattice Extreme Ablative Dose (LEAD) Boost Radiation Therapy

PURPOSE

A phase I clinical trial was designed to test the feasibility and toxicity of administering high-dose spatially fractionated radiation therapy to magnetic resonance imaging (MRI)-defined prostate tumor volumes, in addition to standard treatment.

METHODS AND MATERIALS

We enrolled 25 men with favorable to high-risk prostate cancer and 1 to 3 suspicious multiparametric MRI (mpMRI) gross tumor volumes (GTVs). The mpMRI-GTVs were treated on day 1 with 12 to 14 Gy via dose cylinders using a lattice extreme ablative dose technique. The entire prostate, along with the proximal seminal vesicles, was then treated to 76 Gy at 2 Gy/fraction. For some high-risk patients, the distal seminal vesicles and pelvic lymph nodes received 56 Gy at 1.47 Gy/fraction concurrently in 38 fractions. The total dose to the lattice extreme ablative dose cylinder volume(s) was 88 to 90 Gy (112-123 Gy in 2.0 Gy equivalents, assuming an α-to-β ratio of 3).

RESULTS

Dosimetric parameters were satisfactorily met. Median follow-up was 66 months. There were no grade 3 acute/subacute genitourinary or gastrointestinal adverse events. Maximum late genitourinary toxicity was grade 1 in 15 (60%), grade 2 in 4 (16%), and grade 4 in 1 (4%; sepsis after a posttreatment transurethral resection). Maximum late gastrointestinal toxicity was grade 1 in 11 (44%) and grade 2 in 4 (16%). Two patients experienced biochemical failure.

CONCLUSIONS

External beam radiation therapy delivered with an upfront spatially fractionated, stereotactic high-dose mpMRI-GTV boost is feasible and was not associated with any unexpected events. The technique is now part of a follow-up phase II randomized trial.

miR-191 promotes radiation resistance of prostate cancer through interaction with RXRA

Radiation therapy is a common treatment for prostate cancer, however recurrence remains a problem. MicroRNA expression is altered in prostate cancer and may promote therapy resistance. Through bioinformatic analyses of TCGA and CPC-GENE patient cohorts, we identified higher miR-191 expression in tumor versus normal tissue, and increased expression in higher Gleason scores. In vitro and in vivo experiments demonstrated that miR-191 overexpression promotes radiation survival, and contributes to a more aggressive phenotype. Retinoid X receptor alpha, RXRA, was discovered to be a novel target of miR-191, and knockdown recapitulated radioresistance. Furthermore, treatment of prostate cancer cells with the RXRA agonist 9-cis-retinoic acid restored radiosensitivity. Supporting this relationship, patients with high miR-191 and low RXRA abundance experienced quicker biochemical recurrence. Reduced RXRA translated to a higher risk of distant failure after radiotherapy. Notably, this miR-191/RXRA interaction was conserved in a novel primary cell line derived from radiorecurrent prostate cancer. Together, our findings demonstrate that miR-191 promotes prostate cancer survival after radiotherapy, and highlights retinoids as a potential option to improve radiotherapy response.

Effects of dose-escalated radiotherapy in combination with long-term androgen deprivation on prostate cancer

OBJECTIVE

We aimed to examine the effects of a dose escalation for prostate cancer patients receiving long-term androgen deprivation therapy (ADT).

METHODS

A retrospective analysis of 605 patients treated with radiotherapy (RT) and long-term ADT (National Comprehensive Cancer Network criteria-defined intermediate-risk, minimum 10 months; high-risk and very-high-risk, minimum 20 months) was performed. The median ADT time was 31 months. Cox's proportional hazards models were used to compare biochemical disease-free survival (bDFS), clinical relapse-free survival (cRFS) and overall survival (OS) between the ≥70, <78 Gy group and 78 Gy group in a univariate analysis and to assess the effects of the dose escalation on bDFS in a multivariate analysis.

RESULTS

After a median follow-up of 70 months, 5-year bDFS was significantly better in the 78 Gy group than in the ≥70, <78 Gy group [96 vs 83%; hazard ratio 3.6 (95% confidence interval 2.2-6.1); p < 0.001]. 5-year cRFS and OS were similar between the two groups. The multivariate analysis showed that RT dose was still an independent prognostic factor of bDFS (p = 0.005).

CONCLUSION

The results of the present study suggest that dose escalations result in significant improvements in bDFS, even when used in combination with long-term ADT. A longer follow-up is needed to clarify the effects of dose escalations on cRFS and OS. Advances in knowledge: It remains unclear whether high-dose RT is necessary for improving the outcomes of patients receiving long-term ADT. The results suggest that dose escalations result in significant improvements in biochemical control.

High-intermediate prostate cancer treated with low-dose-rate brachytherapy with or without androgen deprivation therapy

PURPOSE

To describe outcomes of men with unfavorable (high-tier) intermediate risk prostate cancer (H-IR) treated with low-dose-rate (LDR) brachytherapy, with or without 6 months of androgen deprivation therapy (ADT).

METHODS AND MATERIALS

Patients with H-IR prostate cancer, treated before 2012 with LDR brachytherapy without external radiation are included. Baseline tumor characteristics are described. Outcomes between groups receiving ADT are measured by Phoenix (nadir +2 ng/mL), and threshold 0.4 ng/mL biochemical relapse definitions (bNEDs), as well as clinical end points. Standard descriptive and actuarial statistics are used.

RESULTS

Two hundred sixty men were eligible, 139 (53%) did not receive ADT and 121 (47%) did. Median follow-up was 5 years. Men treated with ADT had higher T stage and percent positive cores but lower pathologic grade group. bNED rates with and without ADT at 5 years are 86% and 85% (p = 0.52) with the Phoenix definition, and 83% and 78% (p = 0.13) with the threshold definition. Local recurrence or metastasis were rare in both groups (<5%, p = not significant). Death from prostate cancer only occurred in 4 patients, 2 in each group. Overall survival was 85% in those treated with ADT and 93% without at 8 years, p = 0.15.

CONCLUSIONS

The addition of 6 months of ADT to LDR brachytherapy for H-IR prostate cancer does not improve 5 year prostate specific antigen control, and we no longer routinely recommended it.