In the search for highly effective modulators addressing ABCG2mediated MDR, 23 pyrimidines were synthesized and biologically assessed. Seven derivatives with (a) nitrogen-and/or halogen-containing residue(s) had extraordinary potencies against ABCG2 (IC 50 < 150 nM). The compounds competitively inhibited ABCG2-mediated Hoechst 33342 transport but were not substrates of ABCG2. The most potent MDR reverser, compound 19, concentration-dependently increased SN-38-mediated cancer cell death at 11 nM (EC 50 ), time-dependently doubled SN-38 toxicity in a period of 7 days at 10 nM, and half-maximally accelerated cell death combined with SN-38 at 17 nM. No induction of ABCG2 was observed. Furthermore, 11 pyrimidines were revealed as triple ABCB1/ABCC1/ABCG2 inhibitors. Five possessed IC 50 values below 10 μM against each transporter, classifying them as some of the 50 most potent multitarget ABC transporter inhibitors. The most promising representative, compound 37, reversed ABCB1-, ABCC1-, and ABCG2-mediated MDR, making it one of the three most potent ABC transporter inhibitors and reversers of ABC transporters-mediated MDR.

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Low molecular weight heparin (LMWH), the guideline based drug for prophylaxis and treatment of cancer-associated thrombosis, was recently shown to sensitize cisplatin resistant A2780cis human ovarian cancer cells for cisplatin cytotoxicity upon 24 h pretreatment with 50 μg × mL−1 of the LMWH tinzaparin in vitro, equivalent to a therapeutic dosage. Thereby, LMWH induced sensitization by transcriptional reprogramming of A2780cis cells via not yet elucidated mechanisms that depend on cellular proteoglycans. Here we aim to illuminate the underlying molecular mechanisms of LMWH in sensitizing A2780cis cells for cisplatin. Using TCF/LEF luciferase promotor assay (Top/Flash) we show that resistant A2780cis cells possess a threefold higher Wnt signaling activity compared to A2780 cells. Furthermore, Wnt pathway blockade by FH535 leads to higher cisplatin sensitivity of A2780cis cells. Glypican-3 (GPC3) is upregulated in A2780cis cells in response to LMWH treatment, probably as counter-regulation to sustain the high Wnt activity against LMWH. Hence, LMWH reduces the cisplatin-induced rise in Wnt activity and TCF-4 expression in A2780cis cells, but keeps sensitive A2780 cells unaffected. Consequently, Wnt signaling pathway appears as primary target of LMWH in sensitizing A2780cis cells for cisplatin toxicity. Considering the outstanding role of LMWH in clinical oncology, this finding appears as promising therapeutic option to hamper chemoresistance.

Tumor cell binding to microenvironment components such as collagen type 1 (COL1) attenuates the sensitivity to cytotoxic drugs like cisplatin (CDDP) or mitoxantrone (MX), referred to as cell adhesion mediated drug resistance (CAM-DR). CAM-DR is considered as the onset for resistance mutations, but underlying mechanisms remain elusive. To evaluate CAM-DR as target for sensitization strategies, we analyzed signaling pathways in human estrogen-positive MCF-7 and triple-negative MDA-MB-231 breast cancer cells by western blot, proteome profiler array and TOP-flash assay in presence of COL1. β1-Integrins, known to bind COL1, appear as key for mediating COL1-related resistance in both cell lines that primarily follows FAK/PI3K/AKT pathway in MCF-7, and MAPK pathway in MDA-MB-231 cells. Notably, pCREB is highly elevated in both cell lines. Consequently, blocking these pathways sensitizes the cells evidently to CDDP and MX treatment. Wnt signaling is not relevant in this context. A β1-integrin knockdown of MCF-7 cells (MCF-7-β1-kd) reveals a signaling shift from FAK/PI3K/AKT to MAPK pathway, thus CREB emerges as a promising primary target for sensitization in MDA-MB-231, and secondary target in MCF-7 cells. Concluding, we provide evidence for importance of CAM-DR in breast cancer cells and identify intracellular signaling pathways as targets to sensitize cells for cytotoxicity treatment regimes.

Although the androgen receptor (AR) is a validated target for the treatment of prostate cancer, resistance to antiandrogens necessitates the development of new therapeutic modalities. Exploiting the ubiquitin-proteasome system with proteolysistargeting chimeras (PROTACs) has become a practical approach to degrade specific proteins and thus to extend the portfolio of small molecules used for the treatment of a broader spectrum of diseases. Herein, we present three subgroups of enzalutamide-based PROTACs in which only the exit vector was modified. By recruiting cereblon, we were able to demonstrate the potent degradation of AR in lung cancer cells. Furthermore, the initial evaluation enabled the design of an optimized PROTAC with a rigid linker that degraded AR with a DC 50 value in the nanomolar range. These results provide novel AR-directed PROTACs and a clear rationale for further investigating AR involvement in lung cancer models.