Deep androgen receptor suppression in prostate cancer exploits sexually dimorphic renal expression for systemic glucocorticoid exposure

BACKGROUND

Enzalutamide and apalutamide are potent next-generation androgen receptor (AR) antagonists used in metastatic and non-metastatic prostate cancer. Metabolic, hormonal and immunologic effects of deep AR suppression are unknown. We hypothesized that enzalutamide and apalutamide suppress 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2), which normally converts cortisol to cortisone, leading to elevated cortisol concentrations, increased ratio of active to inactive glucocorticoids and possibly suboptimal response to immunotherapy. On-treatment glucocorticoid changes might serve as an indicator of active glucocorticoid exposure and resultant adverse consequences.

PATIENTS AND METHODS

Human kidney tissues were stained for AR and 11β-HSD2 expression. Patients in three trials [neoadjuvant apalutamide plus leuprolide, enzalutamide ± PROSTVAC (recombinant poxvirus prostate-specific antigen vaccine) for metastatic castration-resistant prostate cancer (CRPC) and enzalutamide ± PROSTVAC for non-metastatic castration-sensitive prostate cancer] were analyzed for cortisol and its metabolites using liquid chromatography-mass spectrometry (LC-MS/MS). Progression-free survival was determined in the metastatic CRPC study of enzalutamide ± PROSTVAC for those with glucocorticoid changes above and below the median.

RESULTS

Concurrent AR and 11β-HSD2 expression occurs only in the kidneys of men. A statistically significant rise in cortisol concentration, cortisol/cortisone ratio and tetrahydrocortisol/tetrahydrocortisone ratio with AR antagonist treatment occurred uniformly across all three trials. In the trial of enzalutamide ± PROSTVAC for metastatic CRPC, high cortisol/cortisone ratio in the enzalutamide arm was associated with significantly improved progression-free survival. However, in the enzalutamide + PROSTVAC arm, the opposite trend was observed.

CONCLUSION

Enzalutamide and apalutamide treatment toggles renal 11β-HSD2 and significantly increases indicators of and exposure to biologically active glucocorticoids, which is associated with clinical outcomes.

Stromal fibroblast-derived miR-409 promotes epithelial-to-mesenchymal transition and prostate tumorigenesis

Tumor-stromal interaction is a dynamic process that promotes tumor growth and metastasis via cell-cell interaction and extracellular vesicles. Recent studies demonstrate that stromal fibroblast-derived molecular signatures can be used to predict disease progression and drug resistance. To identify the epigenetic role of stromal noncoding RNAs in tumor-stromal interactions in the tumor microenvironment, we performed microRNA profiling of patient cancer-associated prostate stromal fibroblasts isolated by laser capture dissection microscopy and in bone-associated stromal models. We found specific upregulation of miR-409-3p and miR-409-5p located within the embryonically and developmentally regulated DLK1-DIO3 (delta-like 1 homolog-deiodinase, iodothyronine 3) cluster on human chromosome 14. The findings in cell lines were further validated in human prostate cancer tissues. Strikingly, ectopic expression of miR-409 in normal prostate fibroblasts conferred a cancer-associated stroma-like phenotype and led to the release of miR-409 via extracellular vesicles to promote tumor induction and epithelial-to-mesenchymal transition in vitro and in vivo. miR-409 promoted tumorigenesis through repression of tumor suppressor genes such as Ras suppressor 1 and stromal antigen 2. Thus, stromal fibroblasts derived miR-409-induced tumorigenesis, epithelial-to-mesenchymal transition and stemness of the epithelial cancer cells in vivo. Therefore, miR-409 appears to be an attractive therapeutic target to block the vicious cycle of tumor-stromal interactions that plagues prostate cancer patients.

A randomized phase II study of pazopanib in castrate-sensitive prostate cancer: A University of Chicago phase II consortium/DoD Prostate Cancer Clinical Trials Consortium study

170

Background: Intermittent androgen suppression (IAS) has been studied as a way of minimizing toxicity from long term androgen deprivation therapy (ADT). Based on previous studies with similar agents, we hypothesized that inhibition of VEGFR would result in prolonged time to PSA progression (TTPP) and allow for longer periods off ADT.

Methods: Men with biochemically recurrent, progressive prostate cancer and no evidence of macroscopic metastases were enrolled. They received 6 months of ADT. If at the end of that time the PSA was <0.5 ng/mL (with castrate testosterone levels), they were randomized to pazopanib 800 mg/d or observation. The primary outcome was TTPP, defined as time to a PSA >4.0 ng/mL, at which time they were restarted on ADT.

Results: 37 pts met randomization criteria. 18 were randomized to pazopanib. Only 4 pts met the endpoint criteria of TTPP, whereas 13 (72%) pts went off study for other reasons with 1 pt on treatment at study closure. Reasons for discontinuation included drug toxicity (grade 1/2, 9 pts) and patient preference (2 pts). No grade 3/4 toxicity was noted. 1 pt was removed due to pulmonary embolus, 1 pt due to MD discretion and 1 pt due to noncompliance. 19 pts were randomized to observation of which 12 were off treatment when the study was stopped. Only 5 pts met criteria for TTPP, whereas 7 of 12 (58%) dropped out for other reasons, including the frequency of protocol related blood draws and visits (3 pts) and randomization to observation (2 pts), 1 pt was removed per MD discretion and 1 pt transferred care. Due to high dropout rates in both arms, accrual was halted as the primary endpoint could not be measured robustly.

Conclusions: Minimizing the long term toxicities of ADT is an unmet need in prostate cancer therapy. Hence clinical interventions in concert with IAS represent an attractive area for drug development. This trial has outlined several barriers that exist in studying this patient population and might help to optimize future studies. Future trial design in this arena should investigate drugs with minimal toxicity and employ a design that maximizes patient convenience while anticipating the low threshold for patient drop out.

No significant financial relationships to disclose.

Phase II study of AT-101 to abrogate Bcl-2-mediated resistance to androgen-deprivation therapy (ADT) in patients (pts) with newly diagnosed androgen-dependent metastatic prostate cancer (ADMPC)

137

Background: Preclinical studies demonstrate that Bcl-2 is over-expressed in most pts with prostate cancer, causes drug resistance to ADT, and that modulation of Bcl-2 improves sensitivity of tumor cells. We are conducting a phase II study for men with ADMPC to test the hypothesis that AT-101, a small molecule Bcl-2 inhibitor, improves clinical results of pts initiating ADT for metastatic prostate cancer. Building on results from SWOG 9346 (Hussain JCO 2006) demonstrating that PSA nadir after 7 mo of ADT predicts survival, we are using a novel phase II trial design, in which the primary endpoint is the percentage of patients with PSA ≤ 0.2 ng/ml at 7 mo of ADT plus AT-101.

Methods: Pts had ADMPC, PSA > 5.0 ng/ml within 12 wks prior to registration and no prior ADT for metastatic disease. ADT with LHRH agonist and bicalutamide started 6 wks prior to initiation of oral AT-101, 20 mg/day for 21 days of 28 day cycle. Pts received up to 8 cycles of ADT and AT-101. A total of 55 pts were enrolled (to obtain 48 evaluable pts) to in a two stage design with null hypothesis 48% versus alternative 68% with PSA ≤ 0.2 at 7 mo. With α = 0.1 and β = 0.9, > 27 pts meeting this endpoint are required to recommend further study.

Results: 55 pts were enrolled, median age 61.5 y; Gleason score (GS) 6 (5%),GS 7 (30%), GS 8 (24%), and GS 9 (41%). 3 pts had visceral mets and the remaining pts had bone or nodal metastasis. 42 pts have discontinued (9 toxicity, 9 progression, 1 withdrew) or completed (n = 23) 7 mo of treatment. In intention to treat analysis, 11 of 42 pts (26%) met the primary endpoint 10, of 42 (23%) pts had PSA > 0.2 and < 4.0 ng/ml after 7 mo. Grade 1/2 toxicities (%) included fatigue (36/9), nausea (20/9), vomiting (13/7), anorexia (15/2), AST/ALT (25/5), hypercalcemia (9/0), constipation (13/3), dry skin (9/0), anemia (18/0), sensory neuropathy (7/7), vomiting (12/7), hyperglycemia (7/4). Grade 3 toxicities were sensory neuropathy 2 pts, GI obstruction 1 pt, syncope 1 pt.

Conclusions: Although final study results are pending the analysis of pts currently on therapy, 26% of pts achieved an undetectable PSA at 7 mo in a population with aggressive disease (66% GS ≥ 8).

No significant financial relationships to disclose.

Fluorescence-activated cell sorting (FACS) and immunofluorescence (IF) detection and characterization of circulating tumor cells (CTC) from men with castrate-resistant prostate cancer (CRPC)

41

Background: Men with progressive CRPC have identifiable CTC. The currently available technologies for isolation of these CTC are limited by requiring send out to a central lab, high cost, and relative inflexibility with regards to characterization of the CTC. We hypothesized that modern FACS techniques followed by IF could be utilized for point of care isolation and characterization of CTC from men with CRPC.

Methods: Patients (pts) with progressive CRPC according to Prostate Cancer Working Group 2 criteria were eligible. 15mL of whole blood was collected in BD CPT Vacutainer tubes. The mononuclear cell layer was labeled with primary antibodies against CD45 and EpCAM conjugated to separate flours. The EpCAM+/CD45− population was sorted directly onto a chamber slide, fixed and stained for multiplex IF imaging of markers including: pan-cytokeratin (CK), PSA, and the androgen receptor (AR). Imaged cells were considered CTC if were nucleated and PSA or CK positive. The methodology would be considered feasible if ≥ 5 of the first 15 pts had detectable CTC.

Results: 15 pts with progressive CRPC were accrued to the study. Of these, 14 had documented skeletal metastases and 13 had progressed through docetaxel chemotherapy. 13/15 pts had EpCAM+/CD45− events on flow cytometry; median 94 (range 0–1700). Ten patients had CTC imaged after IF staining. A median of 4 (0–25) CTC were detected, but in 7 pts with >100 events by flow, all had detectable CTC with a median 22 (10–25) (p<0.001 vs. # events <100). A total of 9 contaminating cells (nucleus but no CK or PSA) were observed. All CTC stained positive for AR with variable intensity.

Conclusions: FACS followed by IF is feasible for detection of CTC from men with metastatic CRPC. There is considerable loss of CTC during the processing, however, in men with >100 EpCAM+ events, CTC can be imaged and characterized routinely with these methods. This is a promising technique for utilization in translational research given the relative flexibility, ease and cost. Patients are now being enrolled for pre-analytical validation of IF staining for multiple prostate cancer biomarkers including AR.

No significant financial relationships to disclose.

A phase II trial of gemcitabine(G), capecitabine (C), and bevacizumab (B) in patients (pts) with metastatic renal cell carcinoma (RCC)

e16072

Background: RCC is resistant to most traditional DNA and DNA repair targeted chemotherapy; although modest response rates to nucleotide analog based therapy, including GC, have been reported. Bevacizumab has activity in RCC. We thus performed a single center phase II trial of GCB in pts with metastatic RCC. Methods: Eligibility included clear cell or unclassified histologies, performance status 0–1, measurable disease, normal organ function and no prior treatment with VEGF binding agents or pyramidine analogs. Following significant hematotoxicity in the first 7 of 8 pts, chemotherapy was modified to G 1,000 mg/m2 (days 1, 8), C 1,000 mg po bid (days 1–14) and B 15 mg/kg (day 1) on a 21 day cycle with disease re-evaluation every 3 cycles. Primary endpoint was objective response rate (ORR) using a Bayesian continuous reassessment method designed to detect an improvement in the ORR from a 15% historical rate to 27%. Maximum planned enrollment = 55. Results: 30 pts enrolled from March 2005-May 2008 of which 29 were evaluable: 1 never treated. Pt characteristics: male 83%, median age 58 (36–82), prior nephrectomy 83%, prior radiation 52%, prior cytokine therapy 28%, prior VEGFR tyrosine kinase inhibitor 69%. MSKCC prognostic group: good 24%, intermediate 66%, poor 10%. 7 pts had a partial response (24%). Median overall and progression free survival were 9.8 mo (95%CI: 6.2, 14.9) and 5.3 mo (95%CI: 3.9, 9.9). Grade 3 or 4 toxicities: leucopenia 17%, neutropenia 31%, thrombocytopenia 7%, anemia 14%, proteinuria 3%, rash/hand foot syndrome 7%, fatigue 21%. Average change in mean arterial pressure after 2 cycles: 5.6 (p = 0.040). Serious adverse events: bowel perforation resulting in death 1 pt (3%), sepsis 1 pt (3%), PE/DVT 3 pts (10%), seizure 1 pt (3%). Conclusions: The trial was terminated early despite not meeting protocol criteria for success or futility due to slow accrual and the fact that the historical response rate on which the trial was based became irrelevant with emerging data using sequential VEGF pathway directed therapies. Nevertheless, the observed progression free and overall survival compare favorably to other phase II trials in this population.

[Table: see text]

A phase I study of testosterone in patients (pts) with early castrate resistant prostate cancer (CRPC)

15584

Background: Transition to the castrate resistant state may be due, in part, to the development of a more sensitive and promiscuous androgen receptor (AR) pathway. Androgen therapy of CRPC leads to growth arrest and tumor shrinkage in preclinical models. Historical studies of exogenous testosterone in pts is limited. This study was designed to determine toxicity of a transdermal testosterone therapy (Androderm [A]) in early CRPC. Methods: Pts with progressive PSA increases following androgen ablation and antiandrogen therapy with minimal or no bone metastases (Bone Scan Index of < 1.4%) and no visceral metastases were eligible. Pts were randomized to treatment with 2.5, 5.0, or 7.5mg/day of A and LHRH agonist treatment was maintained. Toxicity was evaluated every 2 weeks and all subjects underwent laboratory, quality of life (UCLA Prostate Cancer Index), and hand grip strength testing at baseline and week 6. Treatment was discontinued for severe toxicity, radiologic progression, or a 3-fold increase in PSA. Results: To date fourteen men were enrolled. Median baseline PSA was 10.9ng/mL (Range:5.3–63.6). Eight pts had no radiologic evidence of disease. Median on therapy testosterone levels (ng/dL) were 216 (n=4), 308 (n=5), 325 (n=5) for 2.5, 5.0, 7.5mg/day dose levels, respectively. Toxicities included grade 2 rash (n=1, dose 7.5), grade 2 hypertension (n=1, dose 7.5), grade 2 hypoglycemia (n=1, dose 5), and grade 2 anorexia (n=1, dose 5). In 29% of pts (n=4), there was a decrease in PSA (max decrease = 43%) from baseline lasting from 4 - 36 weeks; two sustained an initial rise before PSA decline. All other subjects required discontinuation of therapy due to PSA increase and/or radiological progression within 2–13 weeks; none of these patients sustained symptomatic progression of disease and PSA decreased in 8/11 pts with available data after therapy discontinuation. In this small sample, there were no significant differences between baseline and 6-week QOL and hand-grip scores. Conclusion: Testosterone treatment in early CRPC is feasible and safe, although use of PSA to assess anti-tumor effects is difficult. Further evaluation would require a randomized trial to evaluate time to progression and QOL endpoints.

No significant financial relationships to disclose.

Bony metastatic disease responses to sorafenib (BAY 43–9006) independent of PSA in patients with metastatic androgen independent prostate cancer

4506

Background: Sorafenib is a novel bis-aryl urea, multi-kinase inhibitor, approved for the treatment of advanced renal cell carcinoma. It inhibits b- and c-Raf kinase, PDGFR, c-kit, VEGFR, Flt-3 and p38 and demonstrates anti-proliferative and anti-angiogenic activity. Studies have shown a role for anti-angiogenic therapy for androgen-independent prostate cancer (AIPC). Evidence suggests that the Ras-Raf-MAPK-ERK signaling pathway is dysregulated in AIPC and might be targeted by sorafenib. Methods: 22 patients (pts) with progressive metastatic AIPC enrolled in an open-label, single arm phase II study. The primary objective was to determine if sorafenib is associated with a 50% 4 month probability of progression free survival as determined by clinical, radiographic, and PSA criteria. Sorafenib was given continuously at a dose of 400 mg orally twice daily in 28-day cycles. Clinical assessment and PSA measurement occurred every cycle with radiographic measurements every 2 cycles. Results: Baseline patient characteristics included a median (range) age of 64 (51–78), Gleason 8 (6–9), PSA 226.4 ug/l (2–1905), Alk Phos 108 u/l (48–259), Hb 12.7 g/dl (10.2–15.1). 60% of patients had received one prior chemotherapy regimen. Of the 19 pts with progressive disease, 10 progressed only by PSA criteria in the absence of evidence of clinical and radiographic progression. Two pts were found to have dramatic disappearance of bone metastatic lesions as demonstrated by bone scan, even though they met PSA progression criteria at the time the scans were obtained. Toxicities likely related to treatment include: one grade 3 hypertension and hand-foot syndrome; grade 1/2 toxicities: fatigue, anorexia, hypertension, skin rash, nausea, and diarrhea. Conclusion: Sorafenib in AIPC is relatively well tolerated with 2 patients demonstrating evidence of improved bony metastatic lesions. Interpretation of this study is complicated by discordant radiographic and PSA responses. PSA may not be an adequate biomarker for monitoring sorafenib activity. Further study of sorafenib in metastatic AIPC using clinical and radiographic endpoints is warranted.

No significant financial relationships to disclose.

Increased efficacy and toxicity with combination anti-VEGF therapy using sorafenib and bevacizumab

3004

Background: The multikinase inhibitor, sorafenib (sor), targets raf-kinase and vascular endothelial growth factor receptor 2 (VEGFR2). Bevacizumab (bev) is a monoclonal antibody against VEGF. We theorized that combining the two agents would have synergistic therapeutic effects. Methods: Eligible pts had advanced solid tumors, good end organ function, and PS ≤ 1. A phase I dose-escalation study (cohort 1) used sor 200 mg po BID, and bev 5 mg/kg q2 wks IV (dose level, DL1) or 10 mg/kg (DL2). After DLT was reached, DL4 was added to cohort 1 which tested sor 200 mg po BID on days 1–5 q wk with bev IV 5 mg/kg q 2 wks in an attempt to minimize toxicity. Cohort 2 is an expansion phase at MTD (DL1: sor 200 mg po BID daily with bev IV 5 mg/kg), randomized to start with single drug for 4 wks. Cohort 2 has extensive translational endpoints, including imaging. Results: 34 pts have enrolled, 16 in cohort 1 and 18 in cohort 2. Tumor types include ovarian cancer (13), melanoma (4), and renal cell carcinoma (3). The median age was 58 yrs (30–76); pts received a median of 6.5 (1–15) prior regimens. In cohort 1, 3/16 pts had PR (19%; duration 4, 5+, 12+ mos), all with ovarian cancer, and 11/16 had stable disease (SD; 69%; 3+ - 13+ mos). 10/13 assessable cohort 2 pts had SD (77%; 3+ - 6.5+ mos). The most common DL1 AEs Gr ≥ 2 were hypertension (HTN; 6/6) and hand-foot syndrome (4/6). Other Gr 3 AEs in DL1 were leukopenia and infection (2; 2). DLT was reached at DL2 when 2/6 patients developed Gr 3 proteinuria (4, 5 gm/24 hr) and 3/6 developed uncontrolled Gr 3 HTN. Dose reduction on daily sor (DL1 and DL2) occurred for 11/12 pts at a median of 2 cycles, but is delayed on the intermittent schedule (DL4). In all pts, common Gr 1–2 AEs were elevated AST/ALT (18), rhinorrhea (12), fatigue (10), and anorexia (4). 4 pts developed Gr 2–3 diarrhea and 4 Gr 2–3 nausea/vomiting. Gastrointestinal fistulae occurred in two pts with PR, occurring within 4 wk of initiation of therapy, both in areas of tumor regression. Serial PET and DCE-MRI results and proteomic signal pathway analysis will be reported. Conclusions: The combination of sorafenib and bevacizumab appeared to increase both clinical effect and toxicity at below recognized single agent doses. Sor 200 mg po BID d1–5 qwk and bev of 5 mg/kg q2 wks is suggested for further study, pending further dose escalation.

No significant financial relationships to disclose.

A phase II study of ixabepilone (BMS 247550) in metastatic renal cell carcinoma

14646

Introduction Ixabepilone (BMS) is a semi-synthetic analog of Epothilone B that functions as a microtubule stabilizer and has anti-cancer effects in several cancers including renal cell carcinoma (RCC) (Zhuang, ASCO 2004). The initial phase II study in RCC utilized a difficult and unconventional dosing schedule (6 mg/m2 IV days 1–5 every 21 days). Hence, this phase II study in RCC was designed to verify previous observations and to test the safety, feasibility, and activity of administering BMS once every 3 weeks- a schedule used in other malignancies. Methods Treatment consists of BMS 40 mg/m2 IV on day 1 every 3 weeks. Eligibility included metastatic RCC with clear or non-clear cell histology, no limits on the number of previous treatments, performance status 0–2, and normal organ function. The primary endpoint is the overall response rate by RECIST criteria on radiologic evaluation conducted every 9 weeks. Accrual to the full planned 41 patients (pts) will proceed provided that 2 or more responses are observed in the first 21 pts. Results Ten pts have enrolled (4 clear cell) with 1 declining participation prior to receiving any treatment. Eight pts have completed at least 3 cycles. Grade 3–4 toxicities include lymphopenia-2, diarrhea-2, alopecia-1, and infection-1. Grade 1–2 toxicities seen in more than 50% of pts include alopecia, neuropathy, nausea, fatigue, anemia, and lymphopenia. We have observed 1 unconfirmed partial response of short duration and 1 pt exhibited stable disease with a minor response but discontinued treatment due to excessive neurotoxicity. Three pts continue on treatment. Conclusions Toxicity at 40 mg/m2 IV on day 1 every 3 weeks is higher than previously reported with the daily x 5 schedule. While lymphopenia, diarrhea, neuropathy, and fatigue are all expected adverse events, the rates of toxicity across all grades is higher than previous reports. VHL mutation analysis is planned and will be correlated with response to therapy. Accrual and pt follow up continue.

No significant financial relationships to disclose.

Proteomic analysis for the early detection and rational treatment of cancer--realistic hope?

Proteomics is an emerging field in medical science focused on the library of proteins specific to a given biosystem, the proteome, and understanding relationships therein. This field incorporates technologies that can be applied to serum and tissue in order to extract important biological information to aid clinicians and scientists in understanding the dynamic biology of their system of interest, such as a patient with cancer. These tools include laser capture microdissection, tissue lysate arrays and mass spectrometry approaches. These new technologies are more potent coupled with advanced bioinformatics analysis. They are used to characterize the content of, and changes in, the proteome induced by physiological changes, benign and pathologic. The application of these tools has assisted in the discovery of new biomarkers and may lead to new diagnostic tests and improvements in therapeutics. These tools additionally can provide a molecular characterization of cancers, which may allow for individualized molecular therapy. Understanding the basic concepts and tools used will illustrate how best to apply these technologies for patient benefit for the early detection of cancer and improved patient care.

Chaotic oscillations in cultured cells: rat prostate cancer

Normal prostate epithelial cells exhibit uniformity of structure, function, and DNA content. This uniformity is dramatically perturbed in cancer with the development of variance associated with tumor cell heterogeneity. The development of this kind of diversity is paralleled in models of chaotic oscillators that produce multiple pseudosteady states. We have tested prostatic cancer cells in culture for the presence of chaos by comparing the micromotion of two related rat prostate cancer cell lines that exhibited large differences in motility and metastatic potential. In these extremes of cancer cell types, our data suggest that the three criteria which characterize a chaotic oscillation are fulfilled by their cellular micromotions: (a) absence of defined regularity in the time series as evidenced using Fourier analysis and visual inspection; (b) determinism as evidenced by attractor reconstruction; and (c) sensitive dependence on initial conditions as evidenced by a positive Lyapunov exponent. Cellular motion was studied by using an electronic cell impedance sensor which records, in real time, the fluctuations in the resistive and capacitive properties of cells cultured on recording electrodes. Our data and a preliminary screen of other cell types support a model of established cell lines in culture as chaotic oscillators.

Synthesis and characterization of putrescine-based poly(phosphoester-urethanes)

A novel set of putrescine-based segmented polyurethanes was synthesized using 1,4-butane-diisocyanate and phosphoester diols, and was characterized for its potential as a degradable biomaterial. These poly(phosphoester-urethanes) (PPU) were flexible polymers with ultimate tensile strength (UTS) from 2 to 3 MPa, elongations up to 80% and tan delta near 0.15. The incorporation of phosphoester bonds in the backbone of the polymer by using bis(2-hydroxyethyl)phosphite (BGP) and bis(6-hydroxyhexyl)phosphite (BHP) as chain extenders resulted in hydrolytic degradation which was evaluated in vitro. By varying the content of the phosphoester diol BGP, degradation rate, as followed by mass loss and GPC, could be modulated. Polymers based on the more hydrophobic monomer, BHP, showed slower degradation than corresponding BGP based polymers. Tensile properties of PPU-B2 after 22 days in vitro degradation show more than a 50% drop in UTS and ultimate elongation, likely caused by void spaces left behind in the polymer after mass loss and swelling. The attachment of a drug, PAS, pendant to the phosphoester group of the PPU was demonstrated. PAS was linked via the spacer 4-hydroxybenzaldehyde, and free, intact drug was released in about 5 h from a thin film.