Mechanistic studies on the synergistic cytotoxicity of the nucleoside analogs gemcitabine and clofarabine in multiple myeloma: relevance of p53 and its clinical implications

Structural and pharmacological insights into cordycepin for neoplasms and metabolic disorders

Cytotoxic adenosine analogues were among the earliest chemotherapeutic agents utilised in cancer treatment. Cordycepin, a natural derivative of adenosine discovered in the fungus Ophiocordyceps sinensis, directly inhibits tumours not only by impeding biosynthesis, inducing apoptosis or autophagy, regulating the cell cycle, and curtailing tumour invasion and metastasis but also modulates the immune response within the tumour microenvironment. Furthermore, extensive research highlights cordycepin's significant therapeutic potential in alleviating hyperlipidaemia and regulating glucose metabolism. This review comprehensively analyses the structure-activity relationship of cordycepin and its analogues, outlines its pharmacokinetic properties, and strategies to enhance its bioavailability. Delving into the molecular biology, it explores the pharmacological mechanisms of cordycepin in tumour suppression and metabolic disorder treatment, thereby underscoring its immense potential in drug development within these domains and laying the groundwork for innovative treatment strategies.

Targeting cancer via ribosome biogenesis: the cachexia perspective

Cancer cachexia afflicts many advanced cancer patients with many progressing to death. While there have been many advancements in understanding the molecular mechanisms that contribute to the development of cancer cachexia, substantial gaps still exist. Chemotherapy drugs often target ribosome biogenesis to slow or blunt tumor cell growth and proliferation. Some of the most frequent side-effects of chemotherapy are loss of skeletal muscle mass, muscular strength and an increase in fatigue. Given that ribosome biogenesis has emerged as a main mechanism regulating muscle hypertrophy, and more recently, also implicated in muscle atrophy, we propose that some chemotherapy drugs can cause further muscle wasting via its effect on skeletal muscle cells. Many chemotherapy drugs, including the most prescribed drugs such as doxorubicin and cisplatin, affect ribosomal DNA transcription, or other pathways related to ribosome biogenesis. Furthermore, middle-aged and older individuals are the most affected population with cancer, and advanced cancer patients often show reduced levels of physical inactivity. Thus, aging and inactivity can themselves affect muscle ribosome biogenesis, which can further worsen the effect of chemotherapy on skeletal muscle ribosome biogenesis and, ultimately, muscle mass and function. We propose that chemotherapy can accelerate the onset or worsen cancer cachexia via its inhibitory effects on skeletal muscle ribosome biogenesis. We end our review by providing recommendations that could be used to ameliorate the negative effects of chemotherapy on skeletal muscle ribosome biogenesis.

Potential and promising anticancer drugs from adenosine and its analogs

In recent years, many studies have shown that adenosine has efficacy for treating cancer. More importantly, some adenosine analogs have been successfully marketed to fulfill anticancer purposes. In this review, we summarize the anticancer effects of adenosine and its analogs in clinical trials and preclinical studies, with focus on their anticancer mechanisms. In addition, we link the anticancer activities of adenosine analogs with their structures through structure-activity relationship (SAR) analysis, and highlight additional promising anticancer drug candidates. We hope that this review will be of help in understanding the importance of adenosine and its analogs with anticancer activities and directing future research and development of such compounds.

Busulfan, melphalan, and bortezomib compared to melphalan as a high dose regimen for autologous hematopoietic stem cell transplantation in multiple myeloma: long term follow up of a novel high dose regimen

Melphalan at a dose of 200 mg/m² (MEL200) remains the standard high dose therapy before autologous stem cell transplantation (ASCT) for multiple myeloma (MM). Intensifying the high dose regimen has shown promising results. We report here 7-year follow up of our novel high dose regimen of busulfan and melphalan followed by bortezomib (BuMelVel). Forty-three MM patients received BuMelVel high dose therapy with pharmacokinetic adjusted busulfan. Outcomes were compared to a matched control cohort from the CIBMTR database (n = 162) receiving MEL200. The primary endpoint was progression free survival. Five year PFS was 47% v 30% (95% CI; 32-62) in favor or the BuMelVel group (95% CI; 23-37) (p = 0.05). In multivariate analysis for PFS, BuMelVel (HR 0.65; 95% CI 0.44-0.97)(p = 0.036) was predictive. Similar to recent reports of double alkylator therapy, although depth of response was similar between the BuMelVel group and MEL200, the BUMELVEL group experienced an improved PFS.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

Network modeling of kinase inhibitor polypharmacology reveals pathways targeted in chemical screens

Small molecule screens are widely used to prioritize pharmaceutical development. However, determining the pathways targeted by these molecules is challenging, since the compounds are often promiscuous. We present a network strategy that takes into account the polypharmacology of small molecules in order to generate hypotheses for their broader mode of action. We report a screen for kinase inhibitors that increase the efficacy of gemcitabine, the first-line chemotherapy for pancreatic cancer. Eight kinase inhibitors emerge that are known to affect 201 kinases, of which only three kinases have been previously identified as modifiers of gemcitabine toxicity. In this work, we use the SAMNet algorithm to identify pathways linking these kinases and genetic modifiers of gemcitabine toxicity with transcriptional and epigenetic changes induced by gemcitabine that we measure using DNaseI-seq and RNA-seq. SAMNet uses a constrained optimization algorithm to connect genes from these complementary datasets through a small set of protein-protein and protein-DNA interactions. The resulting network recapitulates known pathways including DNA repair, cell proliferation and the epithelial-to-mesenchymal transition. We use the network to predict genes with important roles in the gemcitabine response, including six that have already been shown to modify gemcitabine efficacy in pancreatic cancer and ten novel candidates. Our work reveals the important role of polypharmacology in the activity of these chemosensitizing agents.

Ribonucleotide Reductase Catalytic Subunit M1 (RRM1) as a Novel Therapeutic Target in Multiple Myeloma

Purpose: To investigate the biological and clinical significance of ribonucleotide reductase (RR) in multiple myeloma.Experimental Design: We assessed the impact of RR expression on patient outcome in multiple myeloma. We then characterized the effect of genetic and pharmacologic inhibition of ribonucleotide reductase catalytic subunit M1 (RRM1) on multiple myeloma growth and survival using siRNA and clofarabine, respectively, in both in vitro and in vivo mouse xenograft models.Results: Newly diagnosed multiple myeloma patients with higher RRM1 expression have shortened survival. Knockdown of RRM1 triggered significant growth inhibition and apoptosis in multiple myeloma cells, even in the context of the bone marrow microenvironment. Gene expression profiling showed upregulation of DNA damage response genes and p53-regulated genes after RRM1 knockdown. Immunoblot and qRT-PCR analysis confirmed that γ-H2A.X, ATM, ATR, Chk1, Chk2, RAD51, 53BP1, BRCA1, and BRCA2 were upregulated/activated. Moreover, immunoblots showed that p53, p21, Noxa, and Puma were activated in p53 wild-type multiple myeloma cells. Clofarabine, a purine nucleoside analogue that inhibits RRM1, induced growth arrest and apoptosis in p53 wild-type cell lines. Although clofarabine did not induce cell death in p53-mutant cells, it did trigger synergistic toxicity in combination with DNA-damaging agent melphalan. Finally, we demonstrated that tumor growth of RRM1-knockdown multiple myeloma cells was significantly reduced in a murine human multiple myeloma cell xenograft model.Conclusions: Our results therefore demonstrate that RRM1 is a novel therapeutic target in multiple myeloma in the preclinical setting and provide the basis for clinical evaluation of RRM1 inhibitor, alone or in combination with DNA-damaging agents, to improve patient outcome in multiple myeloma. Clin Cancer Res; 23(17); 5225-37. ©2017 AACR.

The PARP inhibitor olaparib enhances the cytotoxicity of combined gemcitabine, busulfan and melphalan in lymphoma cells

The combination of gemcitabine (Gem), busulfan (Bu), and melphalan (Mel) is a promising regimen for autologous stem-cell transplantation (SCT) for lymphomas. To further improve the efficacy of [Gem + Bu + Mel], we added poly(ADP-ribose) polymerase (PARP) inhibitor olaparib (Ola). We hypothesized that Ola would inhibit the repair of damaged DNA caused by [Gem + Bu + Mel]. Exposure of J45.01 and Toledo cell lines to IC_10-20 of individual drug inhibited proliferation by 6-16%; [Gem + Bu + Mel] by 20-27%; and [Gem + Bu + Mel + Ola] by 61-67%. The synergistic cytotoxicity of the four-drug combination may be attributed to activation of the DNA-damage response, inhibition of PARP activity and DNA repair, decreased mitochondrial membrane potential, increased production of reactive oxygen species, and activation of the SAPK/JNK stress signaling pathway, all of which may enhance apoptosis. Similar observations were obtained using mononuclear cells isolated from patients with T-cell lymphocytic leukemia. Our results provide a rationale for undertaking clinical trials of this drug combination for lymphoma patients undergoing SCT.

Drugs acting on homeostasis: challenging cancer cell adaptation

Cancer treatment aims to exploit properties that define malignant cells. In recent years, it has become apparent that malignant cells often survive cancer treatment and ensuing cell stress by switching on auxiliary turnover pathways, changing cellular metabolism and, concomitantly, the gene expression profile. The changed profile impacts the material exchange of cancer cells with affected tissues. Herein, we show that pathways of proteostasis and energy generation regulate common transcription factors. Namely, when one pathway of intracellular turnover is blocked, it triggers alternative turnover mechanisms, which induce transcription factor proteins that control expression of cytokines and regulators of apoptosis, cell division, differentiation, metabolism, and response to hormones. We focus on several alternative turnover mechanisms that can be blocked by drugs already used in clinical practice for the treatment of other non-cancer related diseases. We also discuss paradigms on the challenges posed by cancer cell adaptation mechanisms.

Drug resistance in multiple myeloma: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective therapeutic protocols, multiple myeloma still tends to be a hard-to-treat hematologic cancer. This hallmark of the disease is in fact a sequel to drug resistant phenotypes persisting initially or emerging in the course of treatment. Furthermore, the heterogeneous nature of multiple myeloma makes treating patients with the same drug challenging because finding a drugable oncogenic process common to all patients is not yet feasible, while our current knowledge of genetic/epigenetic basis of multiple myeloma pathogenesis is outstanding. Nonetheless, bone marrow microenvironment components are well known as playing critical roles in myeloma tumor cell survival and environment-mediated drug resistance happening most possibly in all myeloma patients. Generally speaking, however; real mechanisms underlying drug resistance in multiple myeloma are not completely understood. The present review will discuss the latest findings and concepts in this regard. It reviews the association of important chromosomal translocations, oncogenes (e.g. TP53) mutations and deranged signaling pathways (e.g. NFκB) with drug response in clinical and experimental investigations. It will also highlight how bone marrow microenvironment signals (Wnt, Notch) and myeloma cancer stem cells could contribute to drug resistance in multiple myeloma.

Cell cycle kinetics, apoptosis rates, DNA damage and TP53 gene expression in bladder cancer cells treated with allyl isothiocyanate (mustard essential oil)

Allyl isothiocyanate (AITC) is present in plants of the cruciferous family and is abundant in mustard seed. Due to its high bioavailability in urine after ingestion, AITC has been considered a promising antineoplastic agent against bladder cancer. Because TP53 mutations are the most common alterations in bladder cancer cells and are frequently detected in in situ carcinomas, in this study, we investigated whether the AITC effects in bladder cancer cells are dependent on the TP53 status. Two bladder transitional carcinoma cell lines were used: RT4, with wild-type TP53; and T24, mutated TP53 gene. AITC was tested at concentrations of 0.005, 0.0625, 0.0725, 0.0825, 0.0925, 0.125 and 0.25 μM in cytotoxicity, cell and clonogenic survival assays, comet and micronucleus assays and for its effects on cell cycle and apoptosis by flow cytometry and on TP53 gene expression. The data showed increased primary DNA damage in both cell lines; however, lower concentrations of AITC were able to induce genotoxicity in the mutant cells for the TP53 gene. Furthermore, the results demonstrated increased apoptosis and necrosis rates in the wild-type cells, but not in mutated TP53 cells, and cell cycle arrest in the G2 phase for mutated cells after AITC treatment. No significant differences were detected in TP53 gene expression in the two cell lines. In conclusion, AITC caused cell cycle arrest, increased apoptosis rates and varying genotoxicity dependent on the TP53 status. However, we cannot rule out the possibility that those differences could reflect other intrinsic genetic alterations in the examined cell lines, which may also carry mutations in genes other than TP53. Therefore, further studies using other molecular targets need to be performed to better understand the mechanisms by which AITC may exert its antineoplastic properties against tumor cells.

Synergistic cytotoxicity of gemcitabine, clofarabine and edelfosine in lymphoma cell lines

Treatments for lymphomas include gemcitabine (Gem) and clofarabine (Clo) which inhibit DNA synthesis. To improve their cytotoxicity, we studied their synergism with the alkyl phospholipid edelfosine (Ed). Exposure of the J45.01 and SUP-T1 (T-cell) and the OCI-LY10 (B-cell) lymphoma cell lines to IC₁₀–IC₂₀ levels of the drugs resulted in strong synergistic cytotoxicity for the 3-drug combination based on various assays of cell proliferation and apoptosis. Cell death correlated with increased phosphorylation of histone 2AX and KAP1, decreased mitochondrial transmembrane potential, increased production of reactive oxygen species and release of pro-apoptotic factors. Caspase 8-negative I9.2 cells were considerably more resistant to [Gem+Clo+Ed] than caspase 8-positive cells. In all three cell lines [Gem+Clo+Ed] decreased the level of phosphorylation of the pro-survival protein AKT and activated the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) stress signaling pathway, which in J45.01 cells resulted in the phosphorylation and heterodimerization of the transcription factors ATF2 and c-Jun. The observed rational mechanism-based efficacy of [Gem+Clo+Ed] based on the synergistic convergence of several pro-death and anti-apoptotic signaling pathways in three very different cell backgrounds provides a powerful foundation for undertaking clinical trials of this drug combination for the treatment of lymphomas.

Clofarabine, a novel adenosine analogue, reactivates DNA methylation-silenced tumour suppressor genes and inhibits cell growth in breast cancer cells

Clofarabine (2-chloro-2'-fluoro-2'-deoxyarabinosyladenine, ClF) is a second-generation 2'-deoxyadenosine analogue that is structurally related to cladribine (2-chloro-2'-deoxyadenosine, 2CdA) and fludarabine (9-beta-d-arabinosyl-2-fluoroadenine, F-ara-A). It demonstrates potent antitumour activity at much lower doses than parent compounds with high therapeutic efficacy in paediatric blood cancers. Our previous studies in breast cancer cells indicate that 2CdA and F-ara-A are involved in epigenetic regulation of gene transcription. We therefore investigated whether ClF influences methylation and expression of selected tumour suppressor genes, such as adenomatous polyposis coli (APC), phosphatase and tensin homologue (PTEN), and retinoic acid receptor beta 2 (RARbeta2), as well as expression of p53, p21 and DNA methyltransferase 1 (DNMT1) in MCF-7 and MDA-MB-231 breast cancer cell lines with different invasive potential. Promoter methylation and gene expression were estimated using methylation-sensitive restriction analysis (MSRA) and real-time PCR, respectively. ClF demonstrated potent growth inhibitory activity in MCF-7 and MDA-MB-231 cells after 96h treatment with IC50 determined as equal to 640nM and 50nM, respectively. In both breast cancer cell lines, ClF led to hypomethylation and up-regulation of APC, PTEN and RARbeta2 as well as increase in p21 expression. Only in non-invasive MCF-7 cells, these changes were associated with down-regulation of DNMT1. Our results provide first evidence of ClF implications in epigenetic regulation of transcriptional activity of selected tumour suppressor genes in breast cancer. It seems to be a new important element of ClF anticancer activity and may indicate its potential efficacy in epigenetic therapy of solid tumours, especially at early stages of carcinogenesis.