Clinical and biological relevance of the transcriptomic-based prostate cancer metastasis subtypes MetA-C

To improve treatment of metastatic prostate cancer, the biology of metastases needs to be understood. We recently described three subtypes of prostate cancer bone metastases (MetA-C), based on differential gene expression. The aim of this study was to verify the clinical relevance of these subtypes and to explore their biology and relations to genetic drivers. Freshly-frozen metastasis samples were obtained as hormone-naive (n = 17), short-term castrated (n = 21), or castration-resistant (n = 65) from a total of 67 patients. Previously published sequencing data from 573 metastasis samples were also analyzed. Through transcriptome profiling and sample classification based on a set of predefined MetA-C-differentiating genes, we found that most metastases were heterogeneous for the MetA-C subtypes. Overall, MetA was the most common subtype, while MetB was significantly enriched in castration-resistant samples and in liver metastases, and consistently associated with poor prognosis. By gene set enrichment analysis, the phenotype of MetA was described by high androgen response, protein secretion and adipogenesis, MetB by high cell cycle activity and DNA repair, and MetC by epithelial-to-mesenchymal transition and inflammation. The MetB subtype demonstrated single nucleotide variants of RB transcriptional corepressor 1 (RB1) and loss of 21 genes at chromosome 13, including RB1, but provided independent prognostic value to those genetic aberrations. In conclusion, a distinct set of gene transcripts can be used to classify prostate cancer metastases into the subtypes MetA-C. The MetA-C subtypes show diverse biology, organ tropism, and prognosis. The MetA-C classification may be used independently, or in combination with genetic markers, primarily to identify MetB patients in need of complementary therapy to conventional androgen receptor-targeting treatments.

An open label phase I study of ABR-215050 in patients with prostate cancer refractory to hormone therapy and with rising PSA for determination of MTD and long-term tolerability and safety

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Background: Preclinical studies have demonstrated that ABR-215050, an orally active 3-quinoline-carboxamide derivative with anti-angiogenic abilities, consistently inhibits growth of established prostate cancer in rodent and human xenografts model systems. Tumor vessel density was inhibited by 44–65% consistent with the 41–78% inhibition in tumor weights. The anti-angiogenic response was correlated with an increase in both tumor hypoxic and apoptotic fraction. Based upon these results, ABR-215050 is now tested in the clinical setting. Methods: Cohorts of 6 patients (pts) with hormone refractory prostate cancer and rising PSA were to receive escalating doses of ABR- 215050 (0.5, 1.0, 2.0 and 3.0 mg daily) for 28 days in addition to the androgen ablative therapy. Pts showing stable disease at day 28 were offered to enter a one year extension period at the MTD level to assess long-term tolerability and safety. The primary endpoint in the 28-day study was determination of MTD. Secondary endpoints included changes in PSA levels. Results: Two DLTs (sinus tachycardia and amylase, G3) occurred in the 1.0 mg cohort. The MTD was therefore set to 0.5 mg. Additional 11 pts were enrolled at the MTD level. A total of 17 pts received 0.5 mg and 7 pts 1.0 mg of ABR-215050 once daily. The most frequently related AEs reported during the first 28 days were muscle or joint pain, nausea and fatigue, all of which being mild and transient. Laboratory changes were also seen, such as a transient increase in CRP and amylase. Fifteen out of 17 pts continued into the extension period. Fourteen out of 15 pts remained on treatment = 4 months. The AE profile in the extension period was similar to that reported during the first 28 days of treatment. Nine out of 14 pts had a >50% decrease in PSA velocity at 4 months compared to the pre-treatment period. Six of these pts exhibited a decrease in PSA from baseline, ranging from 8% to 58% (mean 29%). Conclusions: ABR-215050 0.5 mg is well tolerated with manageable side effects. In addition available PSA results suggest stabilization/lowering of the PSA levels.

No significant financial relationships to disclose.

Role of transforming growth factor-beta1 in prostate cancer

TGF-beta1 is an important regulator of the normal and malignant prostate. In the non-malignant prostate, TGF-beta1 stimulates cell differentiation, inhibits epithelial cell proliferation, and induces epithelial cell death. TGF-beta1 is secreted into semen where it is an important immunosuppressive factor. Prostate cancer cells express high levels of TGF-beta1, which seems to enhance prostate cancer growth and metastasis by stimulating angiogenesis and by inhibiting immune responses directed against tumour cells. Prostate cancer cells frequently lose their TGF-beta receptors and acquire resistance to the anti-proliferative and pro-apoptotic effects of TGF-beta1. Accordingly, high expression of TGF-beta1 and loss of TGF-beta receptor expression have been associated with a particularly bad prognosis in human prostate cancer patients. TGF-beta1 also seems to be a mediator of castration-induced apoptosis in androgen dependent normal and malignant prostate epithelial cells. The ability of some prostate tumours to avoid castration-induced apoptosis may not, however, be simply due to loss of TGF-beta receptor type I or type II expression in the tumour cells. It may also be related to an inability of these cells to up-regulate TGF-beta receptor levels in response to castration or possibly due to defects downstream of the receptors. Short-term therapy-induced changes in the TGF-beta system in prostate tumours can probably be used to predict the long-term response to androgen ablation treatment. Further investigations into the TGF-beta system in the prostate are needed, however, to elucidate how alterations in this system affect the behaviour of prostate tumours, and whether this system can be manipulated for therapeutical purposes.

A putative mechanism for the non-specific uptake of intact radiolabelled monoclonal antibodies in the testes and prostate

Non-specific testicular accumulation of radiolabelled intact anti-CEA monoclonal antibody (MAb), (A431/26, Behringwerke AG) was observed in 11 out of 12 patients with the testes and prostate included in the examination field at radioimmunoscintigraphy (RIS). Previous studies have shown that placental alkaline phosphatase (PLAP) serves as an Fc-receptor, mediating IgG transport through the placenta. A closely related protein, the germ cell alkaline phosphatase (GCAP), is expressed in the testes. The testicular uptake of IgG is observed only when intact but not fragmented MAbs are used, indicating involvement of Fc-receptors. MDCK cells (dog kidney cell line) transfected with the plasmid pSVT7 containing the GCAP gene were shown to acquire the capacity to both express membrane bound GCAP and to bind IgG on the cell surface. This might indicate that GCAP is responsible for the non-specific accumulation of intact MAb in the testes and prostate often observed when intact murine MAbs are used for radioimmunolocalization (RIL).