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ATP-binding cassette C-family drug membrane transporters play an important role in local pharmacokinetics,i.e., drug concentration in cellular compartments. From the structural point of view, only the bovine ortholog of the multidrug-resistance associated protein 1 (bMRP1) has been resolved. We here used μs-scaled molecular dynamics simulations to investigate the structure and dynamics ofbMRP1 in pre- and post-hydrolysis functional states. The present work aims to examine the slight but likely relevant structural differences between pre- and post-hydrolysis states of outward-facing conformations as well as the interactions between MRP1 and the surrounding lipid bilayer. Global conformational dynamics show unfavourable extracellular opening associated with nucleotide binding domain dimerization indicating that the post-hydrolysis state adopts a close-cleft conformation rather than an outward-open conformation. Our present simulations also highlight persistent interactions with annular cholesterol molecules and the expected active role of lipid bilayer in the allosteric communication between distant domains of MRP1 transporter.

Multidrug resistance-associated proteins are ABC C-family exporters. They are crucial in pharmacology as they transport various substrates across membranes. However, the role of the degenerate nucleotide-binding site (NBS) remains unclear likewise the interplay with the surrounding lipid environment. Here, we propose a dynamic and structural overview of MRP1 from ca. 110 μs molecular dynamics simulations. ATP binding to NBS1 is likely maintained along several transport cycles. Asymmetric NBD behaviour is ensured by lower signal transduction from NBD1 to the rest of the protein owing to the absence of ball-and-socket conformation between NBD1 and coupling helices. Even though surrounding lipids play an active role in the allosteric communication between the substrate-binding pocket and NBDs, our results suggest that lipid composition has a limited impact, mostly by affecting transport kinetics. We believe that our work can be extended to other degenerate NBS ABC proteins and provide hints for deciphering mechanistic differences among ABC transporters.

Retrospective series suggest that bevacizumab-induced hypertension (HTN) is a prognostic and potentially predictive biomarker of efficacy of the antiangiogenic drug in the upfront treatment of metastatic colorectal cancer (mCRC) patients. The immortal-time bias and the effect of pre-existing HTN might affect these findings. We conducted a pooled, post hoc analysis of 2 prospective randomized trials of chemotherapy plus bevacizumab in mCRC, and performed a systematic review of the available literature focusing on how the immortal-time bias was taken into account and how pre-existing HTN potentially requiring the use of antihypertensive drugs was managed.The pooled-analysis included patients enrolled in the phase III TRIBE and TRIBE-2 studies that compared upfront FOLFOXIRI + bevacizumab to FOLFIRI or FOLFOX + bevacizumab, respectively. Association between HTN and survival outcomes was assessed by incorporating a time-dependent Cox regression model to consider the time-dependency of the probability of HTN onset during the treatment. The systematic review was conducted according to PRISMA guidelines.The systematic review retrieved 14 eligible and highly heterogeneous studies. A positive prognostic impact of bevacizumab-induced HTN was reported in the 58% of the analyses reporting Progression Free Survival (PFS) and in the 54% of the analyses reporting Overall Survival (OS) data. Immortal-time bias was incorporated in 4 studies (28%). In TRIBE and TRIBE-2 study populations (N = 1175), patients experiencing ≥ G2 HTN during first-line bevacizumab administration showed longer PFS (median: 14.7 versus 10.3 months, p 0.001) and OS (median: 31.7 versus 24.2 months, p 0.001). The association with OS retained statistical significance after correction for time-dependency (p = 0.003) and was confirmed in the multivariable model including HTN as a time-dependent variable (p = 0.02). Moreover, in patients with pre-existing HTN, no difference in terms of PFS and OS was observed compared with the subgroup of patients who never experienced ≥G2 HTN (HR 1.01, p = 0.86 and HR 1.02, p = 0.78 respectively.Bevacizumab-induced HTN during the first-line treatment of mCRC is an independent prognostic factor, also adopting a time-dependency correction. Toxicity should be interpreted as a time-dependent variable when exploring its association with clinical outcome.

164 Background: ARSI [enzalutamide (ENZA) and abiraterone (ABI)] demonstrated to be efficacious as a first-line therapy for mCRPC, showing a median progression-free survival of 16 and 20 months (mos) in pivotal trials, respectively. Nevertheless, some pts of daily clinical practice show exceptionally prolonged disease control with very long duration of treatment. The present study aimed at identifying the characteristics of LTR pts who received one ARSI as a first-line for mCRPC. Methods: We retrospectively reviewed the clinical records of a consecutive series of 647 pts treated in the daily clinical practice with one ARSI as first-line mCRPC in four Italian high-volume Institutions. Pts who had previously received docetaxel in castration-sensitive setting were excluded. Pts received standard AA or ENZA doses (1,000 mg po daily plus prednisone 10 mg po daily or 160 mg po daily, respectively). ARSI were administered until progression and were followed according to each Institution policy. For each pt we recorded pre and post-ARSI clinical history, baseline characteristics, treatment details and clinical outcomes. Pts were considered as LTR in presence of an ARSI exposure ≥ 36 mos. LTR were compared to the progressed pts with an ARSI exposure < 36 mos. On-treatment pts with an ARSI exposure < 36 mos were not considered. Results: We identified 81 LTR pts (53 treated with ENZA and 28 treated with ABI). The median age was 76 yrs (range 56-89). The median treatment duration was 46.1 mos (range 36.4-88.6) and 52 pts were still on treatment. LTR were compared to no-LTR 415 pts (233 treated with ENZA and 182 treated with ABI). Compared to no-LTR, LTR pts showed longer PSA doubling time (PSADT) (PSADT) (p = 0.001) and time to mCRPC (p < 0.0001), lower levels of basal PSA (p = 0.01), and alkaline phosphatase (ALP) (p = 0.01), better ECOG PS (p = 0.01), lower Gleason score (p = 0.01), and less pain level (p = 0.04). ECOG PS, ALP, time to mCRPC and PSADT were all identified as independent predictors of time to treatment interruption in multivariate analysis. LTR showed an 89% decreased risk of death compared to no-LTR (HR = 0.11 IC95% 0.06-0.18). Conclusions: In our experience, several variables, which are usually considered as having a prognostic value, demonstrated to be able to predict the probability of prolonged disease control in mCRPC pts treated with first-line ARSI.