Iniparib (BSI-201)

Iniparib, previously named BSI-201, is an intravenously administered PARP1 inhibitor, which either alone or in combination with chemotherapy, has important antitumor activity in studies in vitro and in vivo. It is active against a broad range of cancer cells in culture, including drug resistant cell lines. Iniparib has been reported to be a prodrug whose C-nitroso metabolite, 4-iodo-3-nitrosobenzamide, selectively kills tumor cells by oxidizing the zinc finger of PARP-1 resulting in ejection of zinc and inhibition of PARP activity.

Reference

Liang H, Tan AR. Iniparib, a PARP1 inhibitor for the potential treatment of cancer, including triple-negative breast cancer. IDrugs. 2010 Sep;13(9):646-56.

Xuesong Liu, Yan Shi, David X. Maag, Joann P. Palma, Melanie J. Patterson, Paul A. Ellis, Bruce W. Surber, Damien B. Ready, Niru B. Soni, Uri S. Ladror, Allison J. Xu, Ramesh Iyer, John E. Harlan, Larry R. Solomon, Cherrie K. Donawho, Thomas D. Penning, Eric F. Johnson,  Alexander R. Shoemaker. Iniparib Nonselectively Modifies Cysteine-Containing Proteins in Tumor Cells and Is Not a Bona Fide PARP Inhibitor. Clinical Cancer Research. January 15, 2012 18; 510.

S. Kopetz, M. M. Mita, I. Mok, K. K. Sankhala, J. Moseley, B. M. Sherman, C. R. Bradley and A. W. Tolcher. First in human phase I study of BSI-201, a small molecule inhibitor of poly ADP-ribose polymerase (PARP) in subjects with advanced solid tumors. Journal of Clinical Oncology. (Meeting Abstracts) May 2008 vol. 26 no. 15_suppl 3577

PET of Poly (ADP-Ribose) Polymerase Activity in Cancer: Preclinical Assessment and First In-Human Studies.[Pubmed:27841728]

Radiology. 2017 Feb;282(2):453-463.

Purpose To demonstrate that positron emission tomography (PET) with fluorine 18 ((18)F) fluorthanatrace (FTT) depicts activated poly (adenosine diphosphate-ribose)polymerase (PARP) expression and is feasible for clinical trial evaluation. Materials and Methods All studies were conducted prospectively from February 2012 through July 2015 under protocols approved by the local animal studies committee and institutional review board. The area under the receiver operating characteristic curve (AUC, in g/mL. min) for (18)F-FTT was assessed in normal mouse organs before and after treatment with olaparib (n = 14), a PARP inhibitor, or iniparib (n = 11), which has no PARP inhibitory activity. Murine biodistribution studies were performed to support human translational studies. Eight human subjects with cancer and eight healthy volunteers underwent imaging to verify the human radiation dosimetry of (18)F-FTT. The Wilcoxon signed rank test was used to assess for differences among treatment groups for the mouse studies. Results In mice, olaparib, but not iniparib, significantly reduced the (18)F-FTT AUC in the spine (median difference before and after treatment and interquartile range [IQR]: -17 g/mL. min and 10 g/mL . min, respectively [P = .0001], for olaparib and -3 g/mL . min and 13 g/mL . min [P = .70] for iniparib) and in nodes (median difference and interquartile range [IQR] before and after treatment: -23 g/mL . min and 13 g/mL . min [P = .0001] for olaparib; -9 g/mL . min and 17 g/mL . min [P = .05] for iniparib). The effective dose was estimated at 6.9 mSv for a 370-MBq (18)F-FTT dose in humans. In humans, the organs with the highest uptake on images were the spleen and pancreas. Among five subjects with measurable tumors, increased (18)F-FTT uptake was seen in one subject with pancreatic adenocarcinoma and another with liver cancer. Conclusion The results suggest that (18)F-FTT uptake reflects PARP expression and that its radiation dosimetry profile is compatible with those of agents currently in clinical use. ((c)) RSNA, 2016 Online supplemental material is available for this article.

Myc mediates cancer stem-like cells and EMT changes in triple negative breast cancers cells.[Pubmed:28817737]

PLoS One. 2017 Aug 17;12(8):e0183578.

Women with triple negative breast cancer (TNBC) have poor prognosis compared to other breast cancer subtypes. There were several reports indicating racial disparity in breast cancer outcomes between African American (AA) and European American (EA) women. For example, the mortality rates of AA breast cancer patients were three times higher than of EA patients, even though, the incidence is lower in AA women. Our in vitro studies indicate that cancer stem-like cells (CSCs) derived from AA TNBC cell lines have significantly higher self-renewal potential (mammosphere formation) than CSCs derived from EA cell lines. TNBC tumors express high levels of Myc compared to luminal A or HER2 expressing breast cancers. We studied the effects of c-Myc overexpression on CSCs and chemotherapy in AA, and EA derived TNBC cell line(s). Overexpression of c-Myc in AA derived MDA-MB-468 (Myc/MDA-468) cells resulted in a significant increase in CSCs and with minimal changes in epithelial-to-mesenchymal transition (EMT) compared to the control group. In contrast, overexpression of c-Myc in EA derived MDA-MB-231(Myc/MDA-231) cells led to increased epithelial-to-mesenchymal transition (EMT), with a minimal increase in CSCs compared to the control group. Myc/MDA-468 cells were resistant to standard chemotherapeutic treatments such as iniparib (PARP inhibitor) plus cisplatin, / iniparib, cisplatin, paclitaxel and docetaxel. However, Myc/MDA-231 cells, which showed EMT changes responded to iniparib with cisplatin, but were resistant to other drugs, such as iniparib, cisplatin, paclitaxel and docetaxel. Collectively, our results indicate that intrinsic differences in the tumor biology may contribute to the breast cancer disparities.

Homologous Recombination Deficiency (HRD) Score Predicts Response to Platinum-Containing Neoadjuvant Chemotherapy in Patients with Triple-Negative Breast Cancer.[Pubmed:26957554]

Clin Cancer Res. 2016 Aug 1;22(15):3764-73.

PURPOSE: BRCA1/2-mutated and some sporadic triple-negative breast cancers (TNBC) have DNA repair defects and are sensitive to DNA-damaging therapeutics. Recently, three independent DNA-based measures of genomic instability were developed on the basis of loss of heterozygosity (LOH), telomeric allelic imbalance (TAI), and large-scale state transitions (LST). EXPERIMENTAL DESIGN: We assessed a combined homologous recombination deficiency (HRD) score, an unweighted sum of LOH, TAI, and LST scores, in three neoadjuvant TNBC trials of platinum-containing therapy. We then tested the association of HR deficiency, defined as HRD score >/=42 or BRCA1/2 mutation, with response to platinum-based therapy. RESULTS: In a trial of neoadjuvant platinum, gemcitabine, and iniparib, HR deficiency predicted residual cancer burden score of 0 or I (RCB 0/I) and pathologic complete response (pCR; OR = 4.96, P = 0.0036; OR = 6.52, P = 0.0058). HR deficiency remained a significant predictor of RCB 0/I when adjusted for clinical variables (OR = 5.86, P = 0.012). In two other trials of neoadjuvant cisplatin therapy, HR deficiency predicted RCB 0/I and pCR (OR = 10.18, P = 0.0011; OR = 17.00, P = 0.0066). In a multivariable model of RCB 0/I, HR deficiency retained significance when clinical variables were included (OR = 12.08, P = 0.0017). When restricted to BRCA1/2 nonmutated tumors, response was higher in patients with high HRD scores: RCB 0/I P = 0.062, pCR P = 0.063 in the neoadjuvant platinum, gemcitabine, and iniparib trial; RCB 0/I P = 0.0039, pCR P = 0.018 in the neoadjuvant cisplatin trials. CONCLUSIONS: HR deficiency identifies TNBC tumors, including BRCA1/2 nonmutated tumors more likely to respond to platinum-containing therapy. Clin Cancer Res; 22(15); 3764-73. (c)2016 AACR.

A Comparative Oncology Study of Iniparib Defines Its Pharmacokinetic Profile and Biological Activity in a Naturally-Occurring Canine Cancer Model.[Pubmed:26866698]

PLoS One. 2016 Feb 11;11(2):e0149194.

Development of iniparib as an anti-cancer agent was hindered in part by lingering questions regarding its mechanism of action, the activity of its metabolites, and their potential accumulation in tumors. Due to strong similarities in metabolism of iniparib between humans and dogs, a veterinary clinical trial in pet dogs with spontaneous cancers was designed to answer specific questions pertaining to pharmacokinetic exposures and tolerability of iniparib. Dogs were treated with iniparib alone and in combination with carboplatin chemotherapy. Iniparib doses ranged between 10-70 mg/kg intravenously (IV). Plasma, tumor and normal tissue samples were collected before and at various time points scheduled after exposure for pharmacokinetic and biologic analysis. The primary endpoints included characterization of dose-limiting toxicities (DLT) and determination of the drug exposures that could be achieved in both normal and tumor tissues. Nineteen dogs were treated. DLT included fever, anorexia, diarrhea, neutropenia, and thrombocytopenia; most effects were attributable to carboplatin based on the timing of adverse event onset. The maximum tolerated dose (MTD) of iniparib was not identified. Moderate to high variability in plasma exposure was noted for iniparib and all metabolites between animals. When quantifiable, iniparib and metabolite plasma:tumor ratios were < 0.088 and <1.7, respectively. In this study, iniparib was well tolerated as a single agent and in combination with carboplatin over a range of doses. However, clinically relevant concentrations of the parent drug and selected metabolites were not detectable in canine tumor tissues at any studied dose, thus eliminating expectations for clinical responses in dogs or humans. Negative clinical trials in humans, and the uncertainties of its mechanism of action, ultimately led to the decision to stop clinical development of the drug. Nevertheless, the questions that can be asked and answered within the comparative oncology approach are evident from this successfully executed comparative clinical trial and exemplify the value of such studies in drug development.

Tumor BRCA1 Reversion Mutation Arising during Neoadjuvant Platinum-Based Chemotherapy in Triple-Negative Breast Cancer Is Associated with Therapy Resistance.[Pubmed:28087643]

Clin Cancer Res. 2017 Jul 1;23(13):3365-3370.

Purpose: In germline BRCA1 or BRCA2 (BRCA1/2) mutation carriers, restoration of tumor BRCA1/2 function by a secondary mutation is recognized as a mechanism of resistance to platinum and PARP inhibitors, primarily in ovarian cancer. We evaluated this mechanism of resistance in newly diagnosed patients with BRCA1/2-mutant breast cancer with poor response to neoadjuvant platinum-based therapy.Experimental Design: PrECOG 0105 was a phase II neoadjuvant study of gemcitabine, carboplatin, and iniparib in patients with stage I-IIIA triple-negative or BRCA1/2 mutation-associated breast cancer (n = 80). All patients underwent comprehensive BRCA1/2 genotyping. For mutation carriers with moderate or extensive residual disease after neoadjuvant therapy, BRCA1/2 status was resequenced in the residual surgical breast tumor tissue.Results: Nineteen patients had a deleterious germline BRCA1/2 mutation, and four had moderate residual disease at surgery. BRCA1/2 sequencing of residual tissue was performed on three patients. These patients had BRCA1 1479delAG, 3374insGA, and W1712X mutations, respectively, with LOH at these loci in the pretreatment tumors. In the first case, a new BRCA1 mutation was detected in the residual disease. This resulted in a 14-amino acid deletion and restoration of the BRCA1 reading frame. A local relapse biopsy 4 months later revealed the identical reversion mutation, and the patient subsequently died from metastatic breast cancer.Conclusions: We report a BRCA1 reversion mutation in a patient newly diagnosed with triple-negative breast cancer that developed over 18 weeks of platinum-based neoadjuvant therapy. This was associated with poor therapy response, early relapse, and death. Clin Cancer Res; 23(13); 3365-70. (c)2017 AACR.

Differential effects of poly(ADP-ribose) polymerase inhibition on DNA break repair in human cells are revealed with Epstein-Barr virus.[Pubmed:22493268]

Proc Natl Acad Sci U S A. 2012 Apr 24;109(17):6590-5.

Poly(ADP-ribose) polymerase (PARP) inhibitors can generate synthetic lethality in cancer cells defective in homologous recombination. However, the mechanism(s) by which they affect DNA repair has not been established. Here we directly determined the effects of PARP inhibition and PARP1 depletion on the repair of ionizing radiation-induced single- and double-strand breaks (SSBs and DSBs) in human lymphoid cell lines. To do this, we developed an in vivo repair assay based on large endogenous Epstein-Barr virus (EBV) circular episomes. The EBV break assay provides the opportunity to assess quantitatively and simultaneously the induction and repair of SSBs and DSBs in human cells. Repair was efficient in G1 and G2 cells and was not dependent on functional p53. shRNA-mediated knockdown of PARP1 demonstrated that the PARP1 protein was not essential for SSB repair. Among 10 widely used PARP inhibitors, none affected DSB repair, although an inhibitor of DNA-dependent protein kinase was highly effective at reducing DSB repair. Only Olaparib and Iniparib, which are in clinical cancer therapy trials, as well as 4-AN inhibited SSB repair. However, a decrease in PARP1 expression reversed the ability of Iniparib to reduce SSB repair. Because Iniparib disrupts PARP1-DNA binding, the mechanism of inhibition does not appear to involve trapping PARP at SSBs.

Iniparib nonselectively modifies cysteine-containing proteins in tumor cells and is not a bona fide PARP inhibitor.[Pubmed:22128301]

Clin Cancer Res. 2012 Jan 15;18(2):510-23.

PURPOSE: PARP inhibitors are being developed as therapeutic agents for cancer. More than six compounds have entered clinical trials. The majority of these compounds are beta-nicotinamide adenine dinucleotide (NAD(+))-competitive inhibitors. One exception is iniparib, which has been proposed to be a noncompetitive PARP inhibitor. In this study, we compare the biologic activities of two different structural classes of NAD(+)-competitive compounds with iniparib and its C-nitroso metabolite. EXPERIMENTAL DESIGN: Two chemical series of NAD(+)-competitive PARP inhibitors, iniparib and its C-nitroso metabolite, were analyzed in enzymatic and cellular assays. Viability assays were carried out in MDA-MB-436 (BRCA1-deficient) and DLD1(-/-) (BRCA2-deficient) cells together with BRCA-proficient MDA-MB-231 and DLD1(+/+) cells. Capan-1 and B16F10 xenograft models were used to compare iniparib and veliparib in vivo. Mass spectrometry and the (3)H-labeling method were used to monitor the covalent modification of proteins. RESULTS: All NAD(+)-competitive inhibitors show robust activity in a PARP cellular assay, strongly potentiate the activity of temozolomide, and elicit robust cell killing in BRCA-deficient tumor cells in vitro and in vivo. Cell killing was associated with an induction of DNA damage. In contrast, neither iniparib nor its C-nitroso metabolite inhibited PARP enzymatic or cellular activity, potentiated temozolomide, or showed activity in a BRCA-deficient setting. We find that the nitroso metabolite of iniparib forms adducts with many cysteine-containing proteins. Furthermore, both iniparib and its nitroso metabolite form protein adducts nonspecifically in tumor cells. CONCLUSIONS: Iniparib nonselectively modifies cysteine-containing proteins in tumor cells, and the primary mechanism of action for iniparib is likely not via inhibition of PARP activity.