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Poly ( ADP) ribose polymerase ( PARP) plays a key role in DNA repair and is highly expressed in small cell lung cancer ( SCLC). We investigated the therapeutic impact of PARP inhibition in SCLC. In vitro cytotoxicity of veliparib, cisplatin, carboplatin, and etoposide singly and combined was determined by MTS in 9 SCLC cell lines (H69, H128, H146, H526, H187, H209, DMS53, DMS153, and DMS114). Subcutaneous xenografts in athymic nu/nu mice of H146 and H128 cells with relatively high and low platinum sensitivity, respectively, were employed for in vivo testing. Mechanisms of differential sensitivity of SCLC cell lines to PARP inhibition were investigated by comparing protein and gene expression profiles of the platinum sensitive and the less sensitive cell lines. Veliparib showed limited single-agent cytotoxicity but selectively potentiated (≥50% reduction in IC50) cisplatin, carboplatin, and etoposide in vitro in five of nine SCLC cell lines. Veliparib with cisplatin or etoposide or with both cisplatin and etoposide showed greater delay in tumor growth than chemotherapy alone in H146 but not H128 xenografts. The potentiating effect of veliparib was associated with in vitro cell line sensitivity to cisplatin ( CC = 0.672; P = 0.048) and DNA- PKcs protein modulation. Gene expression profiling identified differential expression of a 5-gene panel ( GLS, UBEC2, HACL1, MSI2, and LOC100129585) in cell lines with relatively greater sensitivity to platinum and veliparib combination. Veliparib potentiates standard cytotoxic agents against SCLC in a cell-specific manner. This potentiation correlates with platinum sensitivity, DNA- PKcs expression and a 5-gene expression profile. [ABSTRACT FROM AUTHOR]

Background: SCLC has limited treatment options and inadequate preclinical models. Promising activity of arsenic trioxide (ASO) recorded in conventional preclinical models of SCLC supported the clinical evaluation of ASO in patients. We assessed the efficacy of ASO in relapsed SCLC patients and in corresponding patient-derived xenografts (PDX).Methods: Single arm, Simon 2-stage, phase II trial to enroll patients with relapsed SCLC who have failed at least one line of therapy. ASO was administered as an intravenous infusion over 1-2 h daily for 4 days in week 1 and for 2 days in weeks 2-6 of an 8-week cycle. Treatment continued until disease progression. Pretreatment tumor biopsy was employed for PDX generation through direct implantation into subcutaneous pockets of SCID mice without in vitro manipulation and serially propagated for five generations. Ex vivo efficacy of cisplatin (3 mg/kg i.p. weekly) and ASO (3.75 mg/kg i.p. every other day) was tested in PDX representative of platinum sensitive and platinum refractory SCLC.Results: The best response in 17 evaluable patients was stable disease in 2 (12 %), progressive disease in 15 (88 %) patients and median time-to-progression of seven (range 1-7) weeks. PDX was successfully grown in 5 of 9 (56 %) transplanted biopsy samples. Serially-propagated PDXs preserved characteristic small cell histology and genomic stability confirmed by immunohistochemistry, short tandem repeat (STR) profiling and targeted sequencing. ASO showed in vitro cytotoxicity but lacked in vivo efficacy against SCLC PDX tumor growth.Conclusions: Cisplatin inhibited growth of PDX derived from platinum-sensitive SCLC but was ineffective against PDX from platinum-refractory SCLC. Strong concordance between clinical and ex vivo effects of ASO and cisplatin in SCLC supports the use of PDX models to prescreen promising anticancer agents prior to clinical testing in SCLC patients. Trial Registration The study was registered at http://www.clinicaltrials.gov (NCT01470248). [ABSTRACT FROM AUTHOR]

Summary Platinum-based chemotherapeutics represent a mainstay of cancer therapy, but resistance limits their curative potential. Through a kinome RNAi screen, we identified microtubule-associated serine/threonine kinase 1 (MAST1) as a main driver of cisplatin resistance in human cancers. Mechanistically, cisplatin but no other DNA-damaging agents inhibit the MAPK pathway by dissociating cRaf from MEK1, while MAST1 replaces cRaf to reactivate the MAPK pathway in a cRaf-independent manner. We show clinical evidence that expression of MAST1, both initial and cisplatin-induced, contributes to platinum resistance and worse clinical outcome. Targeting MAST1 with lestaurtinib, a recently identified MAST1 inhibitor, restores cisplatin sensitivity, leading to the synergistic attenuation of cancer cell proliferation and tumor growth in human cancer cells and patient-derived xenograft models. [ABSTRACT FROM AUTHOR]