Following are public and technical abstracts for the PARP-1 Inhibitors project funded by the Department of Defense Kidney Cancer Research Program (KCRP) for 2017.
Principal Investigator: Vladimir Kolenko
Institution: Institute for Cancer Research
Funding Mechanism: Idea Development Award — Established Investigator
Award Amount: $566,149
Public Abstract
Recent advances in cancer biology and drug discovery provided the foundation for the development of targeted agents. Targeted therapeutics act on specific molecular factors and pathways involved in tumor development and progression and, therefore, they selectively affect cancer cells while sparing normal cells and tissues. The clinical potential of poly(ADP-ribose) polymerase 1 (PARP-1) inhibitors has been increasingly recognized over the last years, prompting intensive research on their therapeutic applications. While PARP-1 plays a key role in repairing DNA damage in tumor cells, recent findings indicate that it also serves as a potent transcriptional modulator of various tumor-promoting genes. In clear cell renal cell carcinoma (ccRCC) PARP-1 regulates the expression of hypoxia-inducible factor alpha subunits (HIF-1alpha and HIF-2alpha), the most common driving factors in renal carcinogenesis. PARP-1 also functions as a transcriptional coactivator of nuclear factor-kappaB. Enhanced NF-kappaB activity is closely associated with ccRCC tumor progression, metastatic spread, and clinical drug resistance. However, the therapeutic utility of known PARP-1 inhibitors is limited by their non-specific activity. The clinical use of these agents is associated with frequently reported adverse events, including nausea, vomiting, diarrhea, fatigue, and headache. Hematological toxicities such as anemia, lymphopenia, and thrombocytopenia are the most common dose-limiting toxicities of conventional PARP-1 inhibitors. These clinical setbacks can be explained by the fact that all known PARP-1 inhibitors were developed by targeting PARP-1 activation via interaction with Nicotinamide Adenine Dinucleotide (NAD). NAD is utilized by many proteins other than PARP-1. Therefore, inhibiting PARP-1 by competing with NAD tends to affect a number of other metabolic processes and results in multiple off-target effects.
Importantly, all of the clinically relevant PARP-1 inhibitors such as olaparib, veliparib, and rucaparib, as well as those in exploratory stages of research elsewhere, also act by blocking the NAD binding site on PARP-1 and therefore display promiscuous inhibitory activity. To address these limitations, we have developed a novel class of PARP-1 inhibitors by targeting the histone-dependent route of PARP-1 activation, a mechanism that is unique to PARP-1, thus minimizing the off-target effects and ensuring greater specificity (patents US 2016/ 0097083 and WO 2016/054237 A3). Our preliminary studies demonstrate that histone-dependent PARP-1 inhibitors are highly specific for PARP-1 and do not affect the activity of other enzymes. Importantly, novel inhibitors demonstrate superior in vitro and in vivo antitumor activity compared with olaparib (FDA-approved PARP-1 inhibitor) and sunitinib (tyrosine kinase inhibitor approved for the treatment of advanced ccRCC). Our published and preliminary findings fortify the role of histone-dependent PARP-1 inhibitors as effective therapeutic agents for the treatment of kidney cancer. To evaluate the therapeutic potential of novel PARP-1 inhibitors and investigate the molecular mechanisms underlying their antitumor activity, we propose the following Specific Aims: (1) Evaluate the in vitro antitumor activity of histone-dependent PARP-1 inhibitors; (2) Examine ADME and PK properties of histone-dependent PARP-1 inhibitors; (3) Determine the in vivo efficacy of histone-dependent PARP-1 inhibitors using patient-derived xenograft models of human ccRCC.
Technical Abstract
Background: Recent advances in cancer biology and drug discovery provided the foundation for the development of targeted agents. Targeted therapeutics interfere with molecules involved in tumor development and progression and, therefore, they specifically affect cancer cells while sparing normal cells and tissues. There is clear promise of poly(ADP-ribose) polymerase 1 (PARP-1) inhibitors for the treatment of solid and hematological malignancies harboring mutations in DNA damage-repair genes. Apart from its role in DNA repair, PARP-1 has been demonstrated to exert key roles in transcriptional regulation of pro-tumorigenic genes in cancer cells of various origins. In clear cell renal cell carcinoma (ccRCC) PARP-1 enhances the stability and accumulation of hypoxia-inducible factor alpha subunits (HIF-1alpha and HIF-2alpha), arguably the most common driving factors in renal carcinogenesis. The therapeutic utility of known PARP-1 inhibitors has been limited by their non-specific activity. All conventional PARP-1 inhibitors have been designed as Nicotinamide Adenine Dinucleotide (NAD) mimetics. Therefore, such compounds also inhibit other enzymes that use NAD, affecting a number of metabolic processes and producing various off-target effects. To address these limitations, we have developed a novel class of PARP-1 inhibitors by targeting the histone-dependent route of PARP-1 activation, a mechanism that is unique to PARP-1. Our preliminary studies demonstrate that histone-dependent PARP-1 inhibitors are exquisitely specific for PARP-1. These compounds are also highly effective in targeting both DNA repair and transcriptional functions of PARP-1. Importantly, novel inhibitors demonstrate superior antitumor activity compared with olaparib and sunitinib in a xenograft model of human ccRCC.
Area of Emphasis: Targeted Therapies
Hypothesis and Objective: Our studies have led to the identification of a novel class of histone-dependent small-molecule PARP-1 inhibitors targeting both DNA repair and transcriptional functions of PARP-1. Our published and preliminary findings fortify the role of histone-dependent PARP-1 inhibitors as effective therapeutic agents for the treatment of kidney cancer. The overall objective of our proposal is to validate the therapeutic potential of novel PARP-1 inhibitors using clinically relevant cell and animal models of human ccRCC and investigate the molecular mechanisms underlying their antitumor activity.
Specific Aims: (1) Evaluate the in vitro antitumor activity of histone-dependent PARP-1 inhibitors; (2) Examine ADME and PK properties of histone-dependent PARP-1 inhibitors; (3) Determine the in vivo efficacy of histone-dependent PARP-1 inhibitors using patient-derived xenograft models of human ccRCC.
Study Design
Aim 1. These experiments will be performed using a lead group of histone-dependent PARP-1 inhibitors. All these agents show a strong capacity to inhibit PARP-1 activity. We will examine the antitumor activity of these agents using a panel of patient-derived ccRCC cell lines. The proposed experiments will also examine synthetic lethality of histone-dependent PARP-1 inhibitors with mutations in the PBRM1, SETD2, and BAP1 genes.
Aim 2. In order to qualify advanced leads for in vivo characterization in Aim 3, selected compounds must first meet desirable ADME (Absorption, Distribution, Metabolism, and Excretion) criteria. As the project advances, additional characterization will occur, including evaluation of potential off-target effects. Advanced leads will also be subject to in vivo pharmacokinetic (PK) testing.
Aim 3. We will examine the antitumor efficacy of histone-dependent PARP-1 inhibitors using patient-derived xenograft (PDX) models of human ccRCC. We will conduct a full dose response analysis using different dosing regimens and routes of administration, as appropriate.
Innovation: We developed a novel screening assay to identify agents targeting the histone-dependent route of PARP-1 activation (Patent US 2016/0097083). By using our proprietary screening assay, we identified a novel class of histone-dependent PARP-1 inhibitors targeting a mechanism unique to the PARP-1 activation pathway (Patent WO 2016/054237 A3). Novel histone-dependent PARP-1 inhibitors have no obvious structural homologues among components of eukaryotic enzymatic pathways.
Impact: Development of new therapeutic strategies for the treatment of advanced ccRCC represents an urgent clinical necessity. The proposed studies will provide proof-of-principle evidence that ccRCC can be safely, specifically, and effectively targeted with histone-dependent PARP-1 inhibitors. The proposed studies will also generate new data of interest to a broad community of scientists and clinicians studying kidney cancer biology and developing new treatment options to improve the outlook for people diagnosed with this deadly disease.