Nitu Bansal

Enrichment of human prostate cancer cells with tumor initiating properties in mouse and zebrafish xenografts by differential adhesion

Prostate tumor‐initiating cells (TICs) have intrinsic resistance to current therapies. TICs are commonly isolated by cell sorting or dye exclusion, however, isolating TICs from limited primary prostate cancer (PCa) tissues is inherently inefficient. We adapted the collagen adherence feature to develop a combined immunophenotypic and time‐of‐adherence assay to identify human prostate TICs.

Tumor Initiating Cells

Cancer Stem cells (CSC) are defined as a population of cells found within a tumor that have characteristics similar to normal stem cells. Like normal stem cells they have the potential to self renew and differentiate. The cellular origin of these cancer stem cells--whether they originate from stem cells that have lost the ability to regulate proliferation, or they arise from more differentiated population of progenitor cells that have acquired abilities to self-renew is still unclear. Investigators have reported isolation of cancer stem cells or tumor initiating cells using techniques developed for isolating hematopoietic stem cells and assays that identify a small subset of tumor initiating cells. The TICs are thought to play an important role in tumor development, progression as well response to therapy and relapse. Strategies that combine conventional therapies with newer approaches that target the TICs may be more effective in tumor cell kill are discussed.

NAD+ Kinase as a Therapeutic Target in Cancer

NAD+ kinase (NADK) catalyzes the phosphorylation of nicotinamide adenine dinucleotide (NAD+) to nicotinamide adenine dinucleotide phosphate (NADP+) using ATP as the phosphate donor. NADP+ is then reduced to NADPH by dehydrogenases, in particular glucose-6-phosphate dehydrogenase and the malic enzymes. NADPH functions as an important cofactor in a variety of metabolic and biosynthetic pathways. The demand for NADPH is particularly high in proliferating cancer cells, where it acts as a cofactor for the synthesis of nucleotides, proteins, and fatty acids. Moreover, NADPH is essential for the neutralization of the dangerously high levels of reactive oxygen species (ROS) generated by increased metabolic activity. Given its key role in metabolism and regulation of ROS, it is not surprising that several recent studies, including in vitro and in vivo assays of tumor growth and querying of patient samples, have identified NADK as a potential therapeutic target for the treatment of cancer. In this review, we will discuss the experimental evidence justifying further exploration of NADK as a clinically relevant drug target and describe our studies with a lead compound, thionicotinamide, an NADK inhibitor prodrug. Clin Cancer Res; 22(21); 5189–95. ©2016 AACR.

BMI-1 targeting interferes with patient-derived tumor-initiating cell survival and tumor growth in prostate cancer

Purpose: Current prostate cancer management calls for identifying novel and more effective therapies. Self-renewing tumor-initiating cells (TICs) hold intrinsic therapy resistance and account for tumor relapse and progression. As BMI-1 regulates stem cell self-renewal, impairing BMI-1 function for TIC-tailored therapies appears to be a promising approach. Experimental Design: We have previously developed a combined immunophenotypic and time-of-adherence assay to identify CD49bhiCD29hiCD44hi cells as human prostate TICs. We utilized this assay with patient-derived prostate cancer cells and xenograft models to characterize the effects of pharmacologic inhibitors of BMI-1. Results: We demonstrate that in cell lines and patient-derived TICs, BMI-1 expression is upregulated and associated with stem cell–like traits. From a screened library, we identified a number of post-transcriptional small molecules that target BMI-1 in prostate TICs. Pharmacologic inhibition of BMI-1 in patient-derived cells significantly decreased colony formation in vitro and attenuated tumor initiation in vivo, thereby functionally diminishing the frequency of TICs, particularly in cells resistant to proliferation- and androgen receptor–directed therapies, without toxic effects on normal tissues. Conclusions: Our data offer a paradigm for targeting TICs and support the development of BMI-1–targeting therapy for a more effective prostate cancer treatment. Clin Cancer Res; 22(24); 6176–91. ©2016 AACR.

Darinaparsin Inhibits Prostate Tumor–Initiating Cells and Du145 Xenografts and Is an Inhibitor of Hedgehog Signaling

Prostate cancer is the leading cause of cancer-related death in men in the United States. A major cause of drug resistance in prostate and other epithelial tumors may be due to the presence of a fraction of tumor cells that retain the ability to initiate tumors and hence are termed tumor-initiating cells (TIC) or cancer stem cells. Here, we report that darinaparsin, an organic derivative of arsenic trioxide, is cytotoxic to prostate cancer cell lines as well as fresh prostate cancer cells from patients at low micromolar concentrations, and importantly inhibits the TIC subpopulations. It also inhibits growth of the castrate-resistant Du145 prostate tumor propagated as xenograft in mice and inhibits the tumor-initiating potential of prostate cancer cells. Although the mechanism by which darinaparsin acts is not completely known, we show that it kills prostate cancer cells by blocking cells in the G2–M phase of the cell cycle and inhibits Hedgehog signaling by downregulating Gli-2 transcriptional activity. These data provide a rationale for evaluating darinaparsin in patients with castrate-resistant prostate cancer. Mol Cancer Ther; 14(1); 23–30. ©2014 AACR.

Species-Specific Differences in Translational Regulation of Dihydrofolate Reductase

We have observed that rodent cell lines (mouse, hamster) contain approximately 10 times the levels of dihydrofolate reductase as human cell lines, yet the sensitivity to methotrexate (ED50), the folate antagonist that targets this enzyme, is similar. Our previous studies showed that dihydrofolate reductase protein levels increased after methotrexate exposure, and we proposed that this increase was due to the relief of feedback inhibition of translation as a consequence of methotrexate binding to dihydrofolate reductase. In the current report, we show that unlike what was observed in human cells, dihydrofolate reductase (DHFR) levels do not increase in hamster cells after methotrexate exposure. We provide evidence to show that although there are differences in the putative mRNA structure between hamster and human mRNA in the dihydrofolate reductase binding region previously identified, “hamsterization” of this region in human dihydrofolate reductase mRNA did not change the level of the enzyme or its induction by methotrexate. Further experiments showed that human dihydrofolate reductase is a promiscuous enzyme and that it is the difference between the hamster and human dihydrofolate reductase protein, rather than the DHFR mRNA, that determines the response to methotrexate exposure. We also present evidence to suggest that the translational up-regulation of dihydrofolate reductase by methotrexate in tumor cells is an adaptive mechanism that decreases sensitivity to this drug.

Small molecule inhibitors block Gas6-inducible TAM activation and tumorigenicity

TAM receptors (Tyro-3, Axl, and Mertk) are a family of three homologous type I receptor tyrosine kinases that are implicated in several human malignancies. Overexpression of TAMs and their major ligand Growth arrest-specific factor 6 (Gas6) is associated with more aggressive staging of cancers, poorer predicted patient survival, acquired drug resistance and metastasis. Here we describe small molecule inhibitors (RU-301 and RU-302) that target the extracellular domain of Axl at the interface of the Ig-1 ectodomain of Axl and the Lg-1 of Gas6. These inhibitors effectively block Gas6-inducible Axl receptor activation with low micromolar IC50s in cell-based reporter assays, inhibit Gas6-inducible motility in Axl-expressing cell lines, and suppress H1299 lung cancer tumor growth in a mouse xenograft NOD-SCIDγ model. Furthermore, using homology models and biochemical verifications, we show that RU301 and 302 also inhibit Gas6 inducible activation of Mertk and Tyro3 suggesting they can act as pan-TAM inhibitors that block the interface between the TAM Ig1 ectodomain and the Gas6 Lg domain. Together, these observations establish that small molecules that bind to the interface between TAM Ig1 domain and Gas6 Lg1 domain can inhibit TAM activation, and support the further development of small molecule Gas6-TAM interaction inhibitors as a novel class of cancer therapeutics.

Abstract 223: Generation of single cell-derived normal, benign and cancer mini-prostates from primary patient-derived tissues

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PAnnClinically effective next generation androgen deprivation therapy (ADT) and androgen receptor (AR)-directed therapies have been developed to treat castration-resistant prostate cancer (CRPC). However, disease progression inevitably occurs, and majority of relapsed tumors continue to overexpress AR. AR mutations and constitutively active AR splice variants (AR-Vs) are detected during ADT and may lead to drug resistance. Therefore, there is dire need to develop models that provide a better understanding of AR signaling and determine markers of ADT resistance in prostate cancer patient cells. Mouse models and existing human prostate cancer cell lines have inherent limitations for deciphering mechanisms of therapy resistance. Unlike the recently reported prostate tissue organoids that were derived at a low efficiency from 7/49 metastatic prostate cancer samples, we have developed a novel and exciting technology to generate normal, benign prostatic hyperplasia (BPH) and cancer “mini-prostates” from both early-stage and advanced prostate cancer patient samples. We have successfully rederived mini-prostates from 17 out of 19 primary prostatectomy tissues. We incorporated developmental epithelial and mesenchymal signals, stem-like cells and growth requirements in 3D cultures for maintaining primary normal, BPH and prostate cancer patient-derived cells as stem-like cell-derived organoids. Our preliminary data show the establishment of patient- single cell-derived normal, BPH and cancer mini-prostates comprised of organoids with glandular tissues that have a thick basement membrane, an outer mesenchymal and inner epithelial cells conveying AR signaling, expressing cytokeratins and secreting PSA. RNA sequencing, expression profiling and ADT revealed that mini-prostate cells maintain the genetic, chemoresistance, and growth rate features of the primary prostate. To model tumor heterogeneity, prostate cells from surgical tissues were isolated upon digital imaging and tissue mapping in mirror sections for AMACR, AR, AR-Vs, p63, Ki67, ERG expression and FISH analysis for TMPRSS2-ERG fusion. Living cells from mapped BPH and cancer clones are being utilized to derive single cells into mini-prostates. Our studies generated novel therapy sensitivity and drug discovery models that would allow for precision medicine and coclinical approaches to be enlisted to reveal chemo- or hormonal-resistance profiles in genetically defined mini-prostates, apply combinatory-targeted therapies and study therapy-induced clonal selection processes to ultimately guide future clinical trials.nnCitation Format: Monica Bartucci, Michele Patrizii, Eric Huselid, Shamila Yussuf, Nitu Bansal, Kathleen Flaherty, Denis Tolkunov, Hua Zhong, Mark N. Stein, Joseph Bertino, Robert DiPaola, Isaac Kim, Hatem E. Sabaawy. Generation of single cell-derived normal, benign and cancer mini-prostates from primary patient-derived tissues. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 223. doi:10.1158/1538-7445.AM2015-223

Modeling and antitumor studies of a modified L–penetratin peptide targeting E2F in lung cancer and prostate cancer

E2F1-3a overexpression due to amplification or to mutation or loss of the retinoblastoma gene, induces genes involved in DNA synthesis and leads to abnormal cellular proliferation, tumor growth, and invasion. Therefore, inhibiting the overexpression of one or more of these activating E2Fs is a recognized target in cancer therapeutics. In previous studies we identified by phage display, a novel 7-mer peptide (PEP) that bound tightly to an immobilized consensus E2F1 promoter sequence, and when conjugated to penetratin to increase its uptake into cells, was cytotoxic to several malignant cell lines and human prostate and small cell lung cancer xenografts. Based on molecular simulation studies that showed that the D-Arg penetratin peptide (D-Arg PEP) secondary structure is more stable than the L-Arg PEP, the L-Arg in the peptide was substituted with D-Arg. In vitro studies confirmed that it was more stable than the L- form and was more cytotoxic as compared to the L-Arg PEP when tested against the human castrate resistant cell line, DU145 and the human lung cancer H196 cell line. When encapsulated in PEGylated liposomes, the D-Arg-PEP potently inhibited growth of the DU145 xenograft in mice. Our findings validate D- Arg PEP, an inhibitor of E2F1and 3a transcription, as an improved second generation drug candidate for targeted molecular therapy of cancers with elevated levels of activated E2F(s).

Abstract 348: Small molecule Axl Ig1-Gas6 inhibitors block Gas6-inducible Axl signaling and suppress tumorigenicity

TAM receptors (Tyro-3, Axl, and Mer) are a family of three homologous receptor tyrosine kinases (RTKs) expressed predominantly on myeloid-derived hematopoietic cells and epithelial cells which function as inhibitory receptors that dampen inflammatory responses and maintain tissue tolerance. Additionally, all three TAMs have been implicated in various human malignancies, where level of expression is often associated with more aggressive staging of the cancers, poorer predicted patient survival, as well as drug-resistant cancers. Over the past several years, considerable effort has been made to generate small molecule tyrosine kinase inhibitors and biological therapeutics (such as monoclonal antibodies and soluble extracellular receptor traps) targeting TAM receptors in human cancers. Early preclinical studies show promising anti-tumor activities using either kinase inhibitors or monoclonal antibodies against Axl and Mer, although cross-reactivity with other tyrosine kinase inhibitors is associated with off-target specificities. Here, we report the development and characterization of a series of small molecule inhibitors that target the interface between the Ig1 domain of Axl and Gas6, and inhibit native receptors and Axl reporter lines with sub-micro-molar affinities. Additionally, these compounds inhibit Gas6 inducible motility and invasion in Axl-expressing cell lines, and suppress tumor growth in xenograft models of non small cell lung cancer. Together, these observations demonstrate that Axl can be targeted by small molecules that bind to the Ig1 domain/Gas6 interaction, and validate Ig1 inhibitors as novel agents for treatment of cancer. Citation Format: Nitu Bansal, Stanley Kimani, Kamlendra Singh, Thomas Comollo, Sushil Kumar, Vladyslav Kholodovych, Youyi Peng, William Welsh, Bertino Joseph, Raymond B. Birge. Small molecule Axl Ig1-Gas6 inhibitors block Gas6-inducible Axl signaling and suppress tumorigenicity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 348.