Fanconi anemia D2 protein confers chemoresistance in response to the anticancer agent, irofulven

LP-184, a Novel Acylfulvene Molecule, Exhibits Anticancer Activity against Diverse Solid Tumors with Homologous Recombination Deficiency

Homologous recombination (HR)-related gene alterations are present in a significant subset of prostate, breast, ovarian, pancreatic, lung, and colon cancers rendering these tumors as potential responders to specific DNA damaging agents. A small molecule acylfulvene prodrug, LP-184, metabolizes to an active compound by the oxidoreductase activity of enzyme prostaglandin reductase 1 (PTGR1), which is frequently elevated in multiple solid tumor types. Prior work demonstrated that cancer cell lines deficient in a spectrum of DNA damage repair (DDR) pathway genes show increased susceptibility to LP-184. Here, we investigated the potential of LP-184 in targeting multiple tumors with impaired HR function and its mechanism of action as a DNA damaging agent. LP-184 induced elevated DNA double-strand breaks in HR deficient (HRD) cancer cells. Depletion of key HR components BRCA2 or ataxia telangiectasia mutated (ATM) in cancer cells conferred up to 12-fold increased sensitivity to the LP-184. LP-184 showed nanomolar potency in a diverse range of HRD cancer models, including prostate cancer organoids, leiomyosarcoma cell lines, and patient-derived tumor graft models of lung, pancreatic, and prostate cancers. LP-184 demonstrated complete, durable tumor regression in 10 patient-derived xenograft (PDX) models of HRD triple-negative breast cancer (TNBC) including those resistant to PARP inhibitors (PARPi). LP-184 further displayed strong synergy with PARPi in ovarian and prostate cancer cell lines as well as in TNBC PDX models. These preclinical findings illustrate the potential of LP-184 as a pan-HRD cancer therapeutic. Taken together, our results support continued clinical evaluation of LP-184 in a large subset of HRD solid tumors.

SIGNIFICANCE

New agents with activity against DDR-deficient solid tumors refractory to standard-of-care therapies are needed. We report multiple findings supporting the potential for LP-184, a novel alkylating agent with three FDA orphan drug designations, to fill this void clinically: strong nanomolar potency; sustained, durable regression of solid tumor xenografts; synthetic lethality with HR defects. LP-184 adult phase IA trial to assess safety in advanced solid tumors is ongoing.

Preclinical Efficacy of LP-184, a Tumor Site Activated Synthetic Lethal Therapeutic, in Glioblastoma

PURPOSE

Glioblastoma (GBM) is the most common brain malignancy with median survival <2 years. Standard-of-care temozolomide has marginal efficacy in approximately 70% of patients due to MGMT expression. LP-184 is an acylfulvene-derived prodrug activated by the oxidoreductase PTGR1 that alkylates at N3-adenine, not reported to be repaired by MGMT. This article examines LP-184 efficacy against preclinical GBM models and identifies molecular predictors of LP-184 efficacy in clinical GBM.

EXPERIMENTAL DESIGN

LP-184 effects on GBM cell viability and DNA damage were determined using cell lines, primary PDX-derived cells and patient-derived neurospheres. GBM cell sensitivities to LP-184 relative to temozolomide and MGMT expression were examined. Pharmacokinetics and CNS bioavailability were evaluated in mice with GBM xenografts. LP-184 effects on GBM xenograft growth and animal survival were determined. Machine learning, bioinformatic tools, and clinical databases identified molecular predictors of GBM cells and tumors to LP-184 responsiveness.

RESULTS

LP-184 inhibited viability of multiple GBM cell isolates including temozolomide-resistant and MGMT-expressing cells at IC50 = approximately 22-310 nmol/L. Pharmacokinetics showed favorable AUCbrain/plasma and AUCtumor/plasma ratios of 0.11 (brain Cmax = 839 nmol/L) and 0.2 (tumor Cmax = 2,530 nmol/L), respectively. LP-184 induced regression of GBM xenografts and prolonged survival of mice bearing orthotopic xenografts. Bioinformatic analyses identified PTGR1 elevation in clinical GBM subtypes and associated LP-184 sensitivity with EGFR signaling, low nucleotide excision repair (NER), and low ERCC3 expression. Spironolactone, which induces ERCC3 degradation, decreased LP-184 IC50 3 to 6 fold and enhanced GBM xenograft antitumor responses.

CONCLUSIONS

These results establish LP-184 as a promising chemotherapeutic for GBM with enhanced efficacy in intrinsic or spironolactone-induced TC-NER-deficient tumors.

Conditional Dependency of LP-184 on Prostaglandin Reductase 1 is Synthetic Lethal in Pancreatic Cancers with DNA Damage Repair Deficiencies

The greater efficacy of DNA-damaging drugs for pancreatic adenocarcinoma (PDAC) relies on targeting cancer-specific vulnerabilities while sparing normal organs and tissues due to their inherent toxicities. We tested LP-184, a novel acylfulvene analog, for its activity in preclinical models of PDAC carrying mutations in the DNA damage repair (DDR) pathways. Cytotoxicity of LP-184 is solely dependent on prostaglandin reductase 1 (PTGR1), so that PTGR1 expression robustly correlates with LP-184 cytotoxicity in vitro and in vivo. Low-passage patient-derived PDAC xenografts with DDR deficiencies treated ex vivo are more sensitive to LP-184 compared with DDR-proficient tumors. Additional in vivo testing of PDAC xenografts for their sensitivity to LP-184 demonstrates marked tumor growth inhibition in models harboring pathogenic mutations in ATR, BRCA1, and BRCA2. Depletion of PTGR1, however, completely abrogates the antitumor effect of LP-184. Testing combinatorial strategies for LP-184 aimed at deregulation of nucleotide excision repair proteins ERCC3 and ERCC4 established synergy. Our results provide valuable biomarkers for clinical testing of LP-184 in a large subset of genetically defined characterized refractory carcinomas. High PTGR1 expression and deleterious DDR mutations are present in approximately one third of PDAC making these patients ideal candidates for clinical trials of LP-184.

Differential operation of MLH1/MSH2 and FANCD2 crosstalk in chemotolerant bladder carcinoma: a clinical and therapeutic intervening study

We aimed to understand the crosstalk between mismatch repair (MMR) and FA-BRCA pathway in primary bladder carcinoma (BlCa) samples as well as in chemotolerant cell line. We analysed the genetic alterations of MLH1 and MSH2 (MMR-related genes) and after that we correlated it with the nuclear translocation of FANCD2 protein. Next, we evaluated this crosstalk in T24 BlCa cell line in response to doxorubicin treatment. In primary BlCa tumors, infrequent genetic deletion (17-20%) but frequent promoter methylation (28-55%) of MLH1 and MSH2 was observed, where MLH1 was significantly (p < 0.05) more methylated among the early staged samples (NMIBC). However, MSH2 was significantly more altered among the NMIBC samples, signifying the importance of MMR pathway during the early pathogenesis of the disease. Furthermore, BlCa samples with underexpressed MLH1/MSH2 protein possessed cytoplasmic FANCD2 protein; encouraging that inefficiency of MMR proteins might restrict FANCD2 nuclear translocation. Next, we analysed publicly available data in GEO2R tool where we observed that in response to chemotherapeutic drugs, expression of MLH1, MSH2 and FANCD2 were diminishing. Validating this result in doxorubicin tolerant T24 cells, we found that expression of MLH1 and MSH2 was gradually decreased with increasing dose of doxorubicin. Interestingly, FANCD2 mono-ubiquitination (L-form) was also reduced in chemotolerant T24 cells. The crosstalk between MMR and FA-BRCA pathway was substantiated in the primary BlCa tumors. Further, in response to doxorubicin, this crosstalk was found to be hampered due to under-expression of MLH1 and MSH2 gene, thereby rendering chemotolerance.

The Chemotherapeutic Potentials of Compounds Isolated from the Plant, Marine, Fungus, and Microorganism: Their Mechanism of Action and Prospects

Research on natural products mainly focuses on developing a suitable drug to treat human disease. There has been a sharp increase in the development of drugs from natural products. Most of the drugs that are available are from the terrestrial origin. Marine natural products are less explored. Oceans are considered as a vast ecosystem with a wide variety of living organisms and natural products that are unexplored. Large numbers of antitumor drugs are from natural sources such as plants, marine, and microorganisms. 80% new chemical entities that were launched over the past 60 decades were from a natural source. In this article, the anticancer potential from the natural source such as plants, fungi, microorganisms, marine, and endophytes has been reviewed. Emphasis is given on the compound from the marine, plant, and of bacterial origin. Finally, we consider the future and how we might achieve better sustainability to alleviate human cancer suffering while having fewer side effects, more efficacies, and causing less harm than the present treatments.

RFWD3 and translesion DNA polymerases contribute to PCNA modification-dependent DNA damage tolerance

DNA damage tolerance pathways are regulated by proliferating cell nuclear antigen (PCNA) modifications at lysine 164. Translesion DNA synthesis by DNA polymerase η (Polη) is well studied, but less is known about Polη-independent mechanisms. Illudin S and its derivatives induce alkyl DNA adducts, which are repaired by transcription-coupled nucleotide excision repair (TC-NER). We demonstrate that in addition to TC-NER, PCNA modification at K164 plays an essential role in cellular resistance to these compounds by overcoming replication blockages, with no requirement for Polη. Polκ and RING finger and WD repeat domain 3 (RFWD3) contribute to tolerance, and are both dependent on PCNA modifications. Although RFWD3 is a FANC protein, we demonstrate that it plays a role in DNA damage tolerance independent of the FANC pathway. Finally, we demonstrate that RFWD3-mediated cellular survival after UV irradiation is dependent on PCNA modifications but is independent of Polη. Thus, RFWD3 contributes to PCNA modification-dependent DNA damage tolerance in addition to translesion DNA polymerases.

GLI1-targeting drugs induce replication stress and homologous recombination deficiency and synergize with PARP-targeted therapies in triple negative breast cancer cells

Triple negative breast cancer (TNBC), an aggressive and highly metastatic subtype of breast cancer. Glioma-associated oncogene 1 (GLI1) is a transcription factor and effector of the Hedgehog (Hh) signaling pathway, and is predictive of poor survival for TNBC patients. A nanostring DNA Damage Response (DDR) mRNA panel was used to identify GLI1-induced regulation of DDR genes. Western blots, immunohistochemistry and immunofluorescence were used to evaluate protein expression. Colony assays and mammosphere formation assays were utilized to assess survival of cancer cells. Flow cytometry analyses were employed to evaluate changes in the cell cycle profile, and DNA fiber assays were used to analyze alterations in replication dynamics in TNBC cells. The UALCAN portal and Ensemble programs were used for computational analysis of TCGA data. CompuSyn software was used to calculate combination index (CI) values to assess synergism in drug combination experiments. Inhibition of GLI1 in TNBC cells transcriptionally downregulate expression of FANCD2 and its foci formation, and causes a homologous recombination repair (HR) deficiency. As HR-deficient cancer cells are sensitive to PARP-targeted therapies, we evaluated a combination of the GLI1 inhibitor, GANT61, and a PARP inhibitor (olaparib) in TNBC cells. Combination of GANT61 and olaparib elevated DNA damage levels and these drug combinations caused synergistic lethality to TNBC cells. Aberrantly activated GLI1 regulates HR-mediated DNA repair by transcriptionally regulating FANCD2 to overcome chemotherapy-induced replication stress and DNA damage, and it contributes to resistance of TNBC cells to therapeutics.

Hedgehog/GLI1 Transcriptionally Regulates FANCD2 in Ovarian Tumor Cells: Its Inhibition Induces HR-Deficiency and Synergistic Lethality with PARP Inhibition

Ovarian cancer (OC) is one of the most lethal type of cancer in women due to a lack of effective targeted therapies and high rates of treatment resistance and disease recurrence. Recently Poly (ADP-ribose) polymerase inhibitors (PARPi) have shown promise as chemotherapeutic agents; however, their efficacy is limited to a small fraction of patients with BRCA mutations. Here we show a novel function for the Hedgehog (Hh) transcription factor Glioma associated protein 1 (GLI1) in regulation of key Fanconi anemia (FA) gene, FANCD2 in OC cells. GLI1 inhibition in HR-proficient OC cells induces HR deficiency (BRCAness), replication stress and synergistic lethality when combined with PARP inhibition. Treatment of OC cells with combination of GLI1 and PARP inhibitors shows enhanced DNA damage, synergy in cytotoxicity, and strong in vivo anticancer responses.

The forkhead box M1 (FOXM1) expression and antitumor effect of FOXM1 inhibition in malignant rhabdoid tumor

PURPOSE

Malignant rhabdoid tumor (MRT) is a rare, highly aggressive sarcoma with an uncertain cell of origin. Despite the existing standard of intensive multimodal therapy, the prognosis of patients with MRT is very poor. Novel antitumor agents are needed for MRT patients. Forkhead box transcription factor 1 (FOXM1) is overexpressed and is correlated with the pathogenesis in several human malignancies. In this study, we identified the clinicopathological and prognostic values of the expression of FOXM1 and its roles in the progression of MRT.

METHODS

We investigated the FOXM1 expression levels and their clinical significance in 23 MRT specimens using immunohistochemistry and performed clinicopathologic and prognostic analyses. We also demonstrated correlations between the downregulation of FOXM1 and oncological characteristics using small interfering RNA (siRNA) and FOXM1 inhibitor in MRT cell lines.

RESULTS

Histopathological analyses revealed that primary renal MRTs showed significantly low FOXM1 protein expression levels (p = 0.032); however, there were no significant differences in other clinicopathological characteristics or the survival rate. FOXM1 siRNA and FOXM1 inhibitor (thiostrepton) successfully downregulated the mRNA and protein expression of FOXM1 in vitro and the downregulation of FOXM1 inhibited cell proliferation, drug resistance to chemotherapeutic agents, migration, invasion, and caused the cell cycle arrest and apoptosis of MRT cell lines. A cDNA microarray analysis showed that FOXM1 regulated FANCD2 and NBS1, which are key genes for DNA damage repair.

CONCLUSION

This study demonstrates that FOXM1 may serve as a promising therapeutic target for MRT.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

Subcellular localization of FANCD2 is associated with survival in ovarian carcinoma

Objective: Ovarian cancer is a leading cause of death from gynecological cancers. Late diagnosis and resistance to therapy results in mortality and effective screening is required for early diagnosis and better treatments. Expression of the Fanconi Anemia complementation group D2 protein (FANCD2) is reduced in ovarian surface epithelial cells (OSE) in patients with ovarian cancer. FANCD2 has been studied for its role in DNA repair; however multiple studies have suggested that FANCD2 has a role outside the nucleus. We sought to determine whether subcellular localization of FANCD2 correlates with patient outcome in ovarian cancer.

Methods: We examined the subcellular localization of FANCD2 in primary OSE cells from consenting patients with ovarian cancer or a normal ovary. Ovarian tissue microarray was stained with anti-FANCD2 antibody by immunohistochemistry and the correlation of FANCD2 localization with patient outcomes was assessed. FANCD2 binding partners were identified by immunoprecipitation of cytoplasmic FANCD2.

Results: Nuclear and cytoplasmic localization of FANCD2 was observed in OSEs from both normal and ovarian cancer patients. Patients with cytoplasmic localization of FANCD2 (cFANCD2) experienced significantly longer median survival time (50 months), versus patients without cytoplasmic localization of FANCD2 (38 months; p < 0.05). Cytoplasmic FANCD2 was found to bind proteins involved in the innate immune system, cellular response to heat stress, amyloid fiber formation and estrogen mediated signaling.

Conclusions: Our results suggest that the presence of cytoplasmic FANCD2 modulates FANCD2 activity resulting in better survival outcome in ovarian cancer patients.

Anticancer Agents from Diverse Natural Sources

This review attempts to portray the discovery and development of anticancer agents/drugs from diverse natural sources. Natural molecules from these natural sources including plants, microbes and marine organisms have been the basis of treatment of human diseases since the ancient times. Compounds derived from nature have been important sources of new drugs and also serve as templates for synthetic modification. Many successful anti-cancer drugs currently in use are naturally derived or their analogues and many more are under clinical trials. This review aims to highlight the invaluable role that natural products have played, and continue to play, in the discovery of anticancer agents.

BRCA2 affects the efficiency of DNA double-strand break repair in response to N-nitroso compounds with differing carcinogenic potentials

The tumor suppressor gene breast cancer susceptibility gene 2 (BRCA2) is frequently mutated or epigenetically repressed in human cancer and has a significant role in the homologous recombination (HR) of DNA double-strand breaks (DSBs). Although N-nitrosodiethylamine (NDEA), N-nitrosodiethanolamine (NDELA) and N-nitrosodipropylamine (NDPA) have similar chemical structures and are able to induce DNA damage, they have varying carcinogenic risks. We hypothesized that the DNA damage repair pathways that are induced by these N-nitroso compounds (NOCs) may differ and that this may contribute to the genotoxic-carcinogenic effect of the NOCs. The present study aimed to characterize the formation of DSBs by NDEA, NDELA and NDPA and also to investigate whether BRCA2 is involved in the DNA damage response. The NOCs were observed to time-dependently induce DSBs and the expression of γ-H2AX in gastric cancer SGC7901 cells. It was observed that the DNA damage induced by NDEA, the most potent carcinogen, was not repaired as efficiently as that caused by NDELA or NDPA. The expression of BRCA2 and RAD51 was demonstrated to be inhibited by NDEA treatment but upregulated by NDELA or NDPA treatment. Furthermore, the knock down of BRCA2 expression impaired the DNA damage repair induced by NDELA or NDPA. The cells with this knock down exhibited an increased sensitivity to NDELA or NDPA treatment, but not to NDEA. These findings suggest that a BRCA2-mediated pathway contributes to differential DSB repair and sensitivity in response to NOC exposure and that it may be associated with the genotoxic-carcinogenic potential of NOCs.

Assessment of FANCD2 nuclear foci formation in paraffin-embedded tumors: a potential patient-enrichment strategy for treatment with DNA interstrand crosslinking agents

A major mechanism of DNA repair related to homologous recombination is the Fanconi anemia (FA) pathway. FA genes collaborate with BRCA genes to form foci of DNA repair on chromatin after DNA damage or during the S phase of the cell cycle. Our goal was to develop a method capable of evaluating the functional status of the pathway in patients' tumor tissue, which could also be practically incorporated into large-scale screening. To develop this method, we first used Western immunoblot to detect FANCD2 protein monoubiquitination in fresh tumor specimens of patients with ovarian cancer undergoing surgery and stained formalin-fixed paraffin-embedded tumor tissue simultaneously with 4',6-diamidino-2-phenylindole, FANCD2, and Ki67 antibodies, eventually extending this method to other solid tumors. This triple stain permitted evaluation of the presence, or lack thereof, of FANCD2 subnuclear repair foci in proliferating cells by immunofluorescence microscopy. Overall, we evaluated 156 formalin-fixed paraffin-embedded tumor samples using the FA triple-staining immunofluorescence method. The ratios of FANCD2 foci-negative tumors in ovarian, lung, and breast tumor samples were 21%, 20%, and 29.4%, respectively. Our studies have led to the development of a suitable method for screening, capable of identifying tumors with somatic functional defects in the FA pathway. The use of paraffin-embedded tissues renders the reported method suitable for large-scale screening to select patients for treatment with DNA interstrand crosslinking agents, poly ADP-ribose polymerase inhibitors, or their combination.

Tumour regression and ERCC1 nuclear protein expression predict clinical outcome in patients with gastro-oesophageal cancer treated with neoadjuvant chemotherapy

Aims:

Neoadjuvant chemotherapy followed by surgery is the standard of care for patients with gastro-oesophageal adenocarcinoma. Previously, we validated the utility of the tumour regression grade (TRG) as a histopathological marker of tumour downstaging in patients receiving platinum-based neoadjuvant chemotherapy. In this study we profiled key DNA repair and damage signalling factors and correlated them with clinicopathological outcomes, including TRG response.

Methods and results:

Formalin-fixed human gastro-oesophageal cancers were constructed into tissue microarrays (TMAs). The first set consisted of 142 gastric/gastro-oesophageal cancer cases not exposed to neoadjuvant chemotherapy and the second set consisted of 103 gastric/gastro-oesophageal cancer cases exposed to preoperative platinum-based chemotherapy. Expressions of ERCC1, XPF, FANCD2, APE1 and p53 were investigated using immunohistochemistry.

In patients who received neoadjuvant chemotherapy, favourable TRG response (TRG 1, 2 or 3) was associated with improvement in disease-specific survival (P=0.038). ERCC1 nuclear expression correlated with lack of histopathological response (TRG 4 or 5) to neoadjuvant chemotherapy (P=0.006) and was associated with poor disease-specific (P=0.020) and overall survival (P=0.040).

Conclusions:

We provide evidence that tumour regression and ERCC1 nuclear protein expression evaluated by immunohistochemistry are promising predictive markers in gastro-oesophageal cancer patients receiving neoadjuvant platinum-based chemotherapy.

Enantioselective total synthesis of (-)-acylfulvene and (-)-irofulven

We report our full account of the enantioselective total synthesis of (-)-acylfulvene (1) and (-)-irofulven (2), which features metathesis reactions for the rapid assembly of the molecular framework of these antitumor agents. We discuss (1) the application of an Evans Cu-catalyzed aldol addition reaction using a strained cyclopropyl ketenethioacetal, (2) an efficient enyne ring-closing metathesis cascade reaction in a challenging setting, (3) the reagent IPNBSH for a late-stage reductive allylic transposition reaction, and (4) the final RCM/dehydrogenation sequence for the formation of (-)-acylfulvene (1) and (-)-irofulven (2).

Molecular mechanisms of human papillomavirus-induced carcinogenesis

Approximately 20% of all cancers are associated with infectious agents. Among them, human papillomaviruses (HPVs) are very common and are now recognized as the etiological agent of cervical cancer, the second most common cancer in women worldwide, and they are increasingly linked with other forms of dysplasia. Carcinogenesis is a complex and multistep process requiring the acquisition of several genetic and/or epigenetic alterations. HPV-induced neoplasia, however, is in part mediated by the intrinsic functions of the viral proteins. In order to replicate its genome, HPV modulates the cell cycle, while deploying mechanisms to escape the host immune response, cellular senescence and apoptosis. As such, HPV infection leads directly and indirectly to genomic instability, further favouring transforming genetic events and progression to malignancy. This review aims to summarize our current understanding of the molecular mechanisms exploited by HPV to induce neoplasia, with an emphasis on the role of the 2 viral oncoproteins E6 and E7. Greater understanding of the role of HPV proteins in these processes will ultimately aid in the development of antiviral therapies, as well as unravel general mechanisms of oncogenesis.

BRCA-FA pathway as a target for anti-tumor drugs

Promising research on DNA repair signaling pathways predicts a new age of anti-tumor drugs. This research was initiated through the discovery and characterization of proteins that functioned together in signaling pathways to sense, respond, and repair DNA damage. It was realized that tumor cells often lacked distinct DNA repair pathways, but simultaneously relied heavily on compensating pathways. More recently, researchers have begun to manipulate these compensating pathways to reign in and kill tumor cells. In a striking example it was shown that tumors derived from mutations in the DNA repair genes, of BRCA-FA pathway, were selectively sensitive to inhibition of the base excision repair pathway. These findings suggest that tumors derived from defects in DNA repair genes will be easier to treat clinically, providing a streamlined and targeted therapy that spares healthy cells. In the future, identifying patients with susceptible tumors and discovering additional DNA repair targets amenable to anti-tumor drugs will have a major impact on the course of cancer treatment.