Discovery of a novel DNA polymerase inhibitor and characterization of its antiproliferative properties

PARP inhibitor resistance mechanisms and PARP inhibitor derived imaging probes

INTRODUCTION

Poly(ADP-ribose) polymerase 1 (PARP1) inhibition has become a major target in anticancer therapy. While PARP inhibitors (PARPi) are approved for homologous recombination (HR) deficient cancers, therapeutic resistance is a challenge and PARPi are now being investigated in cancers lacking HR deficiencies. This creates a need to develop molecular and imaging biomarkers of PARPi response to improve patient selection and circumvent therapeutic resistance.

AREAS COVERED

PubMed and clinicaltrials.gov were queried for studies on PARPi resistance and imaging. This review summarizes established and emerging resistance mechanisms to PARPi, and the current state of imaging and theragnostic probes for PARPi, including fluorescently labeled and radiolabeled probes.

EXPERT OPINION

While progress has been made in understanding PARPi therapeutic resistance, clinical evidence remains lacking and relatively little is known regarding PARPi response outside of HR deficiencies. Continued research will clarify the importance of known biomarkers and resistance mechanisms in patient cohorts and the broader utility of PARPi. Progress has also been made in PARPi imaging, particularly with radiolabeled probes, and both imaging and theragnostic probes have now reached clinical validation. Reducing abdominal background signal from probe clearance will broaden their applicability, and improvements to molecular synthesis and radiation delivery will increase their utility.

Synthesis, molecular modeling simulations and anticancer activity of some new Imidazo[2,1-b]thiazole analogues as EGFR/HER2 and DHFR inhibitors

New imidazo[2,1-b]thiazole analogs were designed, synthesized, and biologically evaluated as anticancer agents. In vitro biological evaluation of the anticancer properties of the compounds was performed against different cancer cell lines. Compounds 23 and 39 showed remarkable broad -spectrum cytotoxic potency on most of the tested cell lines. Compounds 23 and 39 exhibited potent activity against the MCF-7 breast cancer cell line, with IC50 values of 1.81 and 4.95 μM, respectively, compared to DOX and SOR (IC50 values of 4.17 and 7.26 μM, respectively). An enzyme inhibition assay was carried out to clarify the possible mode of action of the tested compounds. Compounds 23 and 39 were identified as possible EGFR, HER-2, and DHFR inhibitors. Cell cycle arrest results indicated that compound 23 caused cell cycle arrest at the G0/G1 phase in the MCF-7 cells and at the G2/M phase in the Hep G2 cells. Compound 39 induced cell cycle arrest at the G2/M phase in Hela cells. In vivo testing of the anticancer activity of the two most promising molecules in this study was conducted, and the results indicated that they possess considerable in vivo anticancer activity in mice. Data obtained from the molecular modeling simulation study were consistent with the biological evaluation results.

New thiazole-based derivatives as EGFR/HER2 and DHFR inhibitors: Synthesis, molecular modeling simulations and anticancer activity

New series of thiazole and imidazo[2,1-b]thiazole derivatives were synthesized and tested for their in vitro anticancer activity. Compounds 27, 34, 39 and 42-44 showed the best anticancer activity against the tested cancer cell lines with high safety profile and selectivity indices, especially MCF-7 breast cancer, compared to sorafenib. As an attempt to reveal their mode of cytotoxicity, EGFR, HER2 kinase and DHFR inhibition assays were performed. Compounds 39 and 43 were the most potent dual EGFR/HER2 kinase inhibitors, with IC₅₀ values of 0.153 (EGFR), 0.108 (HER2) and 0.122 (EGFR), 0.078 (HER2) μM, respectively. 39 and 42 were the best DHFR inhibitors showing IC₅₀ 0.291 and 0.123 μM, respectively. 39 and 43 induced their cytotoxicity via cell cycle arrest at G1/S and G1 phases, respectively, and apoptosis rather than necrosis in the MCF-7 breast cancer cell line. In vivo anti-breast cancer assay of 39 and 43 showed significant tumor volume reduction with recovered caspase-3 immunoexpression. Modeling study results proved the importance of the 5-(4-substituted phenyl)-imidazo[2,1-b]thiazole moiety and the hydrazide side chain for the anticancer activity. The most potent compounds showed good drug-likeness features and could be used as prototypes for further optimization. 39 could be an example of a multi-targeting anticancer agent that acts by inhibiting EGFR/HER2 kinase, DHFR enzymes and cellular apoptosis.

Exploiting DNA Replication Stress as a Therapeutic Strategy for Breast Cancer

Proliferating cells rely on DNA replication to ensure accurate genome duplication. Cancer cells, including breast cancer cells, exhibit elevated replication stress (RS) due to the uncontrolled oncogenic activation, loss of key tumor suppressors, and defects in the DNA repair machinery. This intrinsic vulnerability provides a great opportunity for therapeutic exploitation. An increasing number of drug candidates targeting RS in breast cancer are demonstrating promising efficacy in preclinical and early clinical trials. However, unresolved challenges lie in balancing the toxicity of these drugs while maintaining clinical efficacy. Furthermore, biomarkers of RS are urgently required to guide patient selection. In this review, we introduce the concept of targeting RS, detail the current therapies that target RS, and highlight the integration of RS with immunotherapies for breast cancer treatment. Additionally, we discuss the potential biomarkers to optimizing the efficacy of these therapies. Together, the continuous advances in our knowledge of targeting RS would benefit more patients with breast cancer.

Precision Oncology with Drugs Targeting the Replication Stress, ATR, and Schlafen 11

Precision medicine aims to implement strategies based on the molecular features of tumors and optimized drug delivery to improve cancer diagnosis and treatment. DNA replication is a logical approach because it can be targeted by a broad range of anticancer drugs that are both clinically approved and in development. These drugs increase deleterious replication stress (RepStress); however, how to selectively target and identify the tumors with specific molecular characteristics are unmet clinical needs. Here, we provide background information on the molecular processes of DNA replication and its checkpoints, and discuss how to target replication, checkpoint, and repair pathways with ATR inhibitors and exploit Schlafen 11 (SLFN11) as a predictive biomarker.

Genomic profiling of platinum-resistant ovarian cancer: The road into druggable targets

Ovarian cancer is the most lethal gynecologic cancer. High-grade serous carcinoma (HGSC) is the most frequent histologic subtype and while it is a highly platinum-sensitive cancer at initial treatment, nearly 90 % of stage IIIC patients recur in 5 years and eventually become resistant to platinum treatment. Historically, the definition of platinum-resistant disease is based on the time interval between last platinum therapy and recurrence shorter than 6 months. Nowadays the use of sophisticated imaging techniques and serum markers to detect recurrence makes the accuracy of this clinical definition less clear and even more debatable as we begin to better understand the molecular landscape of HGSC and markers of platinum resistance and sensitivity. HGSC is characterized by a low frequency of recurrent mutations, great genomic instability with widespread copy number variations, universal TP53 mutations, and homologous recombination deficiency in more than 50 % of cases. Platinum agents form DNA adducts and intra- and inter-strand cross-links in the DNA. Most of DNA repair pathways are involved at some point in the repair of platinum induced DNA damaging, most notably homologous recombination, Fanconi Anemia, and nucleotide excision repair pathways. Mechanisms of platinum resistance are related mostly to the limitation of platinum-DNA adduct formation by changing cellular pharmacology, and to the prevention of cell death after DNA damage due to alterations in DNA repair pathways and cell cycle regulation. Understanding these mechanisms of sensitivity and resistance may help to define the utility of platinum re-challenge in each situation and guide new therapeutic opportunities. Moreover, the discovery of mechanisms of synthetic lethality related to alterations in DNA repair and cell cycle regulation pathways has opened up a new avenue for drug therapy in the last decade. In the present article, we review pathways involved in platinum-induced DNA damage repair and their relationship with genomic alterations present in HGSC. Moreover, we report new treatment strategies that are underway to target these alterations.

PARP inhibitor resistance: the underlying mechanisms and clinical implications

Due to the DNA repair defect, BRCA1/2 deficient tumor cells are more sensitive to PARP inhibitors (PARPi) through the mechanism of synthetic lethality. At present, several PAPRi targeting poly (ADP-ribose) polymerase (PARP) have been approved for ovarian cancer and breast cancer indications. However, PARPi resistance is ubiquitous in clinic. More than 40% BRCA1/2-deficient patients fail to respond to PARPi. In addition, lots of patients acquire PARPi resistance with prolonged oral administration of PARPi. Homologous recombination repair deficient (HRD), as an essential prerequisite of synthetic lethality, plays a vital role in killing tumor cells. Therefore, Homologous recombination repair restoration (HRR) becomes the predominant reason of PARPi resistance. Recently, it was reported that DNA replication fork protection also contributed to PARPi resistance in BRCA1/2-deficient cells and patients. Moreover, various factors, such as reversion mutations, epigenetic modification, restoration of ADP-ribosylation (PARylation) and pharmacological alteration lead to PARPi resistance as well. In this review, we reviewed the underlying mechanisms of PARP inhibitor resistance in detail and summarized the potential strategies to overcome PARPi resistance and increase PARPi sensitivity.

Precision medicine in pancreatic cancer: treating every patient as an exception

Patients with pancreatic cancer have not benefited from recent improvements in overall survival brought about by precision medicine in other malignancies. This failure is not due to a dearth of precision-medicine research in pancreatic ductal adenocarcinoma (PDAC), the main type of pancreatic cancer. In fact, the stalled progress in precision therapies for this type of cancer is due to the absence of agents that are able to target the common genetic alterations in PDAC. Several studies have attempted to phenotypically stratify PDAC at the transcriptional level. However, the value of such classifications will only be revealed through prospective studies and, crucially, only after development of new treatment options for this disease. Therefore, it is essential to learn from breakthrough discoveries in other cancer types that could benefit subpopulations of patients with PDAC and convert them from ordinary to exceptional responders. Identifying these exceptional patients will help to bring PDAC in line with other cancer types in terms of availability of precision therapies. Thus, the true challenge to precision medicine for PDAC might be the poor consensus on which genetic and phenotypic alterations across the spectrum of this disease are actionable; not the absence of actionable variables themselves. To reach consensus, knowledge and tools must be developed and disseminated for individuals who provide pancreatic cancer care, to enable the real-time identification of exceptional patients, more precise subgroup classifications, and effective disease management strategies; all informed by immediate feedback from clinical outcome data.