Circulating microRNAs are associated with docetaxel chemotherapy outcome in castration-resistant prostate cancer

Background:

Docetaxel is the first-line chemotherapy for castration-resistant prostate cancer (CRPC). However, response rates are ∼50% and determined quite late in the treatment schedule, thus non-responders are subjected to unnecessary toxicity. The potential of circulating microRNAs as early biomarkers of docetaxel response in CRPC patients was investigated in this study.

Methods:

Global microRNA profiling was performed on docetaxel-resistant and sensitive cell lines to identify candidate circulating microRNA biomarkers. Custom Taqman Array MicroRNA cards were used to measure the levels of 46 candidate microRNAs in plasma/serum samples, collected before and after docetaxel treatment, from 97 CRPC patients.

Results:

Fourteen microRNAs were associated with serum prostate-specific antigen (PSA) response or overall survival, according to Mann–Whitney U or log-rank tests. Non-responders to docetaxel and patients with shorter survival generally had high pre-docetaxel levels of miR-200 family members or decreased/unchanged post-docetaxel levels of miR-17 family members. Multivariate Cox regression with bootstrapping validation showed that pre-docetaxel miR-200b levels, post-docetaxel change in miR-20a levels, pre-docetaxel haemoglobin levels and visceral metastasis were independent predictors of overall survival when modelled together.

Conclusions:

Our study suggests that circulating microRNAs are potential early predictors of docetaxel chemotherapy outcome, and warrant further investigation in clinical trials.

Circulating microRNAs associated with docetaxel-resistant castration resistant prostate cancer

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Background: Despite a range of new treatments, docetaxel (DTX) remains the first-line chemotherapy for castration-resistant prostate cancer (CRPC). However, only 50% of patients respond to docetaxel at the cost of potentially significant toxicity. Therefore, there is a need for new biomarkers to identify early response to therapy. This study aims to determine if circulating microRNAs are associated with DTX chemotherapy outcome in CRPC. Methods: Global microRNA profiling was performed on DTX-resistant and sensitive cell lines to identify candidate circulating microRNA biomarkers. Custom Taqman Array MicroRNA cards measured the levels of 46 candidate microRNAs in plasma/serum from 97 CRPC patients, collected pre- and three weeks post-cycle one of DTX. Responses were defined by the PCWG1 serum prostate-specific antigen (PSA) response criteria; partial response (PR), stable disease (SD), progressive disease (PD). Multiple T-test, Mann-Whitney U, Kaplan-Meier, Receiver Operating Characteristic (ROC), and Cox regression analyses were used to assess the associations between microRNA levels and clinical outcomes. Results: Eighteen microRNAs were associated with PSA response or overall survival (p<0.05). DTX non-responders (PD+SD) and patients with shorter survival had high pre-DTX levels of miR-200 family members (miR-200a, miR-200b, miR-200c, miR-429; p<0.05), or decreased/unchanged post-DTX levels of miR-17 family members (miR-19b, miR-20a, miR-20b; p<0.05). The combined levels of miR-20a, miR-146a, miR-200b, miR-200c, miR-222, and miR-301b predicted PSA response (ROC AUC 0.74, 95% CI 0.64-0.84). Pre-DTX miR-200a levels (HR 3.0, 95%CI 1.6-5.8; p=0.001) and post-DTX change in miR-20a (HR 3.4, 95%CI 1.8-6.3; p=0.0002) were independent predictors of overall survival when modeled with hemoglobin levels (HR 2.6, 95%CI 1.4-5.1; p=0.02), PSA response (HR 2.1, 95%CI 1.1-3.9; p=0.03), and visceral metastases (HR 2.0, 95%CI 1.1-3.5; p=0.03). Conclusions: Circulating microRNAs are potential early predictors of DTX chemotherapy outcome and may be useful in stratifying patients in future clinical trials. These microRNAs may also be involved in DTX resistance and represent potential therapeutic targets.

Accumulation of dephosphorylated 4EBP after mTOR inhibition with rapamycin is sufficient to disrupt paracrine transformation by the KSHV vGPCR oncogene

Dysregulation of the PI3K/Akt/mTOR pathway is one of the most frequent events in human cancer. However, the clinical benefits of PI3K/Akt/mTOR inhibitors have not yet achieved their predicted potential in many of the most prevalent human cancers. Of interest, treatment of Kaposi's sarcoma (KS) patients with rapamycin provided the first evidence of the antineoplastic activity of mTOR inhibitors in humans, becoming the standard of care for KS arising in renal transplant patients. Thus, the study of KS may provide a unique opportunity to dissect the contribution of specific mTOR downstream targets to cancer development. The KS-associated herpesvirus (KSHV) is the etiological agent for KS, and the KSHV-encoded oncogene viral-G protein-coupled receptor (vGPCR) promotes the potent activation of the PI3K-Akt-mTOR pathway by both direct and paracrine mechanisms. We focused on a direct target of mTOR, EIF4EBP1/2/3 (4EBP), which inhibits the translation of eukaryotic initiation factor 4E (eiF4E)-bound mRNAs. 4EBP phosphorylation by mTOR relieves its inhibitory activity, hence resulting in increased eiF4E-dependent mRNA translation. We developed a paracrine transformation model, recapitulating the cellular composition of KS lesions, in which vGPCR-expressing cells promote the rapid proliferation of endothelial cells, thus expressing KSHV-latent genes by the release of growth factors. Using this model, we show here that the accumulation of dephosphorylated 4EBP in response to rapamycin or by the expression of an mTOR-insensitive mutant of 4EBP1 is sufficient to disrupt the eiF4E function downstream of mTOR to a similar extent than the mTOR catalytic inhibitor Torin2 and to halt KS development. We also provide evidence that eiF4E contributes to paracrine neoplastic, signaling through the release of pro-angiogenic factors that are acting on endothelial cells, expressing KSHV-latent genes. These findings may provide a preclinical platform and the rationale for the development of novel mTOR, inhibiting agents that may selectively disrupt the mTOR-4EBP interaction for the treatment of KS and other tumor lesions, exhibiting hyperactive mTOR pathway function.