Mechanisms Of Anticancer Drug Resistance Research Articles

Abstract 2525: A novel splicing factor, SPF45/RBM17, might influence 5-FU resistance of gastric carcinoma

Abstract Background: SPF45/RBM17 was identified as a factor required for splicing of short introns in mRNA precursors transcribed from DNA. SPF45 is also thought to be related to anti-cancer drug resistance, suggesting that the SPF45 molecule has a different resistance mechanism from the conventional mechanism of anticancer drug resistance. In this study, we investigated the relationship between SPF45 expression and anticancer drug sensitivity in gastric cancer. Materials and Methods: A total of 654 gastric cancer cases were used in this study. SPF45 expression was examined using immunohistochemistry. The correlation between SPF45 expression and clinicopathological factors was evaluated. Results: Of the 654 gastric cancer cases, 240 were positive for SPF45 expression and 414 were negative for expression. There was no significant difference in age and gender between the two groups, but SPF45-positive cases were significantly more frequent in patients with undifferentiation (p = 0.004), lymphatic invasion (p = 0.013) and venous invasion (p < 0.001). As for anticancer drug therapy, 215 of the 654 patients with gastric cancer who underwent radical surgery were treated with adjuvant chemotherapy and 94 patients with advanced recurrent gastric cancer were treated with chemotherapy. 75 SPF45-positive-patients who received 5FU-based adjuvant chemotherapy (S-1, UFT, 5-DFUR) after surgery had significantly worse recurrence-free survival (RFS) than 140 SPF45-negative-patients (p=0.027). 102 SPF45-positive-patients who didn’t receive adjuvant chemotherapy was no significantly different in RFS from 203 SPF45-negative-patients. In the 215 patients who received adjuvant chemotherapy, 81 DPD-positive patients had significantly worse RFS than DPD-negative patients (p=0.043). In the 305 patients who didn’t receive adjuvant chemotherapy, there was no significant difference in RFS between DPD-positive patients and DPD-negative patients (p=0.880). SPF45-positive cases were significantly more frequent in patients with DPD expression (p < 0.001).In 94 patients with advanced recurrent gastric cancer treated with chemotherapy, there were 42 recurrent patients and 52 stage IV patients. 50 of SPF45-positive patients had significantly worse progression-free survival than 44 of SPF45-negative patients (p < 0.001). Regarding overall response, SPF45-positive-patients had worse response rate than SPF45-negative-patients (p=0.016). In SPF45 positive group, 20.0% responded (CR in 0% and PR in 20%) and 80.0% did not respond (SD in 52% and PD in 28%). In SPF45 negative group, 42.6% responded (CR in 0% and PR in 42.6%) and 57.4% did not respond (SD in 46.8% and PD in 10.6%) Conclusion: Our results suggest that the splicing factor SPF45 influences anticancer drugs such as 5-FU resistance in gastric cancer. Acknowledgments: We thank Kazuhiro Fukumura and Akila Mayeda, Fujita Health University. Citation Format: Koji Maruo, Masakazu Yashiro, Takashi Sakuma, Gen Tsujio, Yasuhiro Fukui, Hiroaki Kasashima, Kiyoshi Maeda. A novel splicing factor, SPF45/RBM17, might influence 5-FU resistance of gastric carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2525.

COX2-Inhibitory and Cytotoxic Activities of Phytoconstituents of Matricaria chamomilla L.

Chamomile tea is a popular beverage and herbal remedy with various health benefits, including antioxidant and antimicrobial activities and beneficial effects on metabolism. In this study, we investigated the inhibitory activities of secondary metabolites from Matricaria chamomile L. against COX2, an enzyme involved in inflammation and linked to cancer development. The cytotoxicity of the compounds was also evaluated on a panel of 60 cancer cell lines. Myricetin, one of the COX2-inhibiting and cytotoxic compounds in chamomile tea, was further studied to determine a proteomic expression profile that predicts the sensitivity or resistance of tumor cell lines to this compound. The expression of classical mechanisms of anticancer drug resistance did not affect the responsiveness of cancer cells to myricetin, e.g., ATP-binding cassette (ABC) transporters (ABCB, ABCB5, ABCC1, ABCG2), tumor suppressors (p53, WT1), and oncogenes (EGFR, RAS), whereas significant correlations between myricetin responsiveness and GSTP expression and cellular proliferation rates were observed. Additionally, Kaplan–Meier survival time analyses revealed that high COX2 expression is associated with a worse survival prognosis in renal clear cell carcinoma patients, suggesting a potential utility for COX2 inhibition by myricetin in this tumor type. Overall, this study provides insight into the molecular modes of action of chamomile secondary metabolites and their potential as cancer-preventive or therapeutic agents.

In vitro effects of ascorbic acid on viability and metabolism of patients' osteosarcoma stem cells.

Stagnation in novelties of osteosarcoma (OS) treatment indicates the need for new therapeutic methods. OS cancer stem cells (OS-CSC) are taught to have the ability to self-renew and develop mechanisms of anticancer drug resistance, and this is why it is difficult to eradicate them. Their metabolism has been recognized as a potential target of therapeutic action. Ascorbic acid (AA) is considered to act pro-oxidative against OS-CSC in vitro by oxidative effect and by inhibition of glycolysis. This study examined an in vitro impact of AA on OS-CSC metabolism isolated from patients' biopsies, with the aim of better understanding of OS-CSC metabolism and the action of AA on OS-CSC. OS-CSC were isolated using a sphere culture system and identified as stem cells using Hoechst 33342 exclusion assay. Determination of the dominant type of metabolism of OS-CSC, parental OS cells, human mesenchymal stem cells (hMSC) and U2OS OS lineage before and after AA treatment was done by Seahorse XF (Agilent). Cytotoxicity of high-dose AA was confirmed by the MTT test and was proven for all the examined cell types as well as HEK293. Seahorse technology showed that OS-CSC can potentially use both glycolysis and oxidative phosphorylation (OXPHOS), and can turn to glycolysis and slow metabolic potential in unfavorable conditions such as incubation in AA.

LncRNAs Roles in Chemoresistance of Cancer Cells.

Cancer is an important health issue worldwide. Cancer therapy is multifaceted, and drug resistance is still the major limiting factor in the treatment of patients with this disease. Although the mechanisms of anticancer drug resistance have been broadly investigated, a massive biological signal pathway of Non-coding RNAs (ncRNAs) involved in this process has not been completely understood. Long noncoding RNAs (lncRNAs) are a kind of transcripts with a minimum length of 200 nucleotides in size, which have a limited potential for coding proteins. The roles of these RNA molecules have been evaluated in relation to several pathological processes, including tumor formation and progression. Increasing evidence has recently reported that non-coding RNAs (ncRNAs), particularly long non-coding RNAs, have significant roles in many cellular and genomic processes, and because of their potential in regulation specific genes, they are also involved in drug resistance. In this review, we review the literature on the features of lncRNA, their regulation roles in the gene expression related to chemo resistance, and the potential of these RNAs as targeted therapies for personalized treatment in cancers.

Potential of the miR-200 Family as a Target for Developing Anti-Cancer Therapeutics.

MicroRNAs (miRNAs) are small non-coding RNAs (18–24 nucleotides) that play significant roles in cell proliferation, development, invasion, cancer development, cancer progression, and anti-cancer drug resistance. miRNAs target multiple genes and play diverse roles. miRNAs can bind to the 3′UTR of target genes and inhibit translation or promote the degradation of target genes. miR-200 family miRNAs mostly act as tumor suppressors and are commonly decreased in cancer. The miR-200 family has been reported as a valuable diagnostic and prognostic marker. This review discusses the clinical value of the miR-200 family, focusing on the role of the miR-200 family in the development of cancer and anti-cancer drug resistance. This review also provides an overview of the factors that regulate the expression of the miR-200 family, targets of miR-200 family miRNAs, and the mechanism of anti-cancer drug resistance regulated by the miR-200 family.

Functions of Yes-association protein (YAP) in cancer progression and anticancer therapy resistance

The Hippo pathway, a highly conserved kinase cascade, regulates cell proliferation, apoptosis, organ size, and tissue homeostasis. Dysregulation of this pathway reportedly plays an important role in the progression of various human cancers. Yes-association protein (YAP), the Hippo pathway’s core effector, is considered a marker for cancer therapy and patient prognosis. In addition, studies have indicated that YAP is involved in promoting anticancer drug resistance. This review summarizes current knowledge on YAP’s role in cancer progression, anticancer drug resistance, and advances in the development of YAP-targeting drugs. A thorough understanding of the complex interactions among molecular, cellular, and environmental factors concerning YAP function in cancer progression may provide new insight into the underlying mechanism of anticancer drug resistance. It might lead to improved prognosis through novel combined therapies.

Glucose deprivation enhances resistance to paclitaxel via ELAVL2/4-mediated modification of glycolysis in ovarian cancer cells.

The dysregulation of glycolysis regardless of oxygen availability is one of the major characteristics of cancer cells. While the drug resistance of ovarian cancer cells has been extensively studied, the molecular mechanism of anticancer drug resistance under low-glucose conditions remains unknown. In this study, we investigated the pathway mediating drug resistance under low-glucose conditions by examining the relationship between embryonic lethal abnormal vision Drosophila homolog-like (ELAVL) protein and glycolysis-related enzymes. Ovarian cancer cells resistant to 2.5 nM paclitaxel were exposed to low-glucose media for 2 weeks, and the expression levels of ELAVL2, ELAVL4, glycolytic enzymes, and drug resistance-related proteins were elevated to levels comparable to those in cells resistant to 100 nM paclitaxel. Gene silencing of ELAVL2/4 using small interfering RNA prevented the upregulation of glycolysis-related enzymes, reduced lactate production, and sensitized 2.5 nM paclitaxel-resistant ovarian cancer cells to anticancer agents under hypoglycemic conditions. Furthermore, pharmacological inhibition of glycolytic enzymes with 2-deoxyglucose, a specific inhibitor of glycolysis, triggered caspase-dependent apoptosis, reduced lactate generation, and blocked the expression of drug resistance-related proteins under low-glucose conditions. These results suggest that the level of ELAVL2/4 is responsible for the development of chemoresistance through activation of the glycolysis pathway under glucose deprivation conditions.

Roles of CYP3A4, CYP3A5 and CYP2C8 drug-metabolizing enzymes in cellular cytostatic resistance

Metabolic deactivation by cytochrome P450 (CYP) is considered a potential mechanism of anticancer drug resistance. However, this hypothesis is predominantly based on indirect pieces of evidence and/or is influenced by interfering factors such as the use of multienzymatic models. Thus, an experimental approach for its verification is needed. In the present work, we employed HepG2 cells transduced with CYP enzymes involved in docetaxel, paclitaxel and vincristine metabolism to provide mechanistic evidence on their possible roles in resistance to these chemotherapeutic agents. Using MTT proliferation tests, we showed that overexpression of CYP3A4 resulted in decreased antiproliferative activity of 1 μM docetaxel (by 11.2, 23.2 and 22.9% at 24, 48 and 72 h intervals, respectively), while the sensitivity of CYP3A4-transduced cells was restored by co-administration of ketoconazole. Paclitaxel exhibited differential efficacy in CYP2C8- and empty vector-transduced cells (significant differences between 10.9 and 24.4% for 0.01, 0.1 and 1 μM concentrations), but neither montelukast nor clotrimazole was capable of affecting this asymmetry. Finally, the pharmacological activity of vincristine was not influenced by CYP3A4 or CYP3A5 overexpression. In the follow-up caspase activation assays, docetaxel was confirmed to be a victim of CYP3A4-mediated resistance, which is, at least partly, brought by impaired activation of caspases 3/7, 8 and 9. In summary, our data demonstrate that CYP3A4-mediated metabolic deactivation of docetaxel might represent a significant mechanism of pharmacokinetic resistance to this drug. In contrast, the possible role of CYPs in resistance to paclitaxel and vincristine has been disconfirmed. Importantly, the expression of CYP3A4 in HepG2_CYP3A4 cells is comparable to that in primary hepatocytes and HepaRG cells, which suggests that our results might be relevant for in vivo conditions, e.g., for hepatocellular carcinoma. Thus, our data may serve as a valuable in vitro background for future in vivo studies exploring the area of intratumoural metabolism-based drug resistance.

3,3'-Diindolylmethane Promotes Gastric Cancer Progression via β-TrCP-Mediated NF-κB Activation in Gastric Cancer-Derived MSCs.

Gastric cancer is a malignant tumor characterized by high morbidity and invasion. Surgery combined with chemo-radiotherapy is the most common treatment for gastric cancer, while multiple drug resistance always results in treatment failure. Once the anti-tumor drugs enter the tumor foci, tumor cells as well as those found in the microenvironment are affected. However, the effects of drugs on tumor microenvironment (TME) are easily overlooked. In this study, we investigated the effects of the anti-cancer drug 3,3’-diindolylmethane (DIM) on gastric cancer-derived mesenchymal stem cells (GC-MSCs) and their subsequent impact on cancer progression. Surprisingly, we found that the therapeutic concentration of DIM upregulated the expression level of tumor-related factors such as CCL-2, IL-6, and IL-8 in GC-MSCs. The conditioned medium of DIM-treated GC-MSCs promoted the proliferation, invasion, and migration of gastric cancer cells in vitro and tumor growth in vivo. Mechanistically, DIM enhanced the expression of β-TrCP, an E3 ubiquitin ligase leading to IκBα degradation and NF-κB activation in GC-MSCs. The β-TrCP knockdown partially eliminated positive results caused by DIM. Our results showed that the therapeutic dosage of DIM induced cell death in cancer cells, while enhancing MSC paracrine functions in the stroma to offset the original DIM effect on cancer cells. These findings provide a new mechanism of anti-cancer drug resistance and remind us to adjust the chemotherapeutic scheme by combining the anti-cancer drug with an appropriate signaling pathway inhibitor to block the side effects of drug on targeted TME cells.

Microengineered 3D Tumor Models for Anti-Cancer Drug Discovery in Female-Related Cancers.

The burden of cancer continues to increase in society and negatively impacts the lives of numerous patients. Due to the high cost of current treatment strategies, there is a crucial unmet need to develop inexpensive preclinical platforms to accelerate the process of anti-cancer drug discovery to improve outcomes in cancer patients, most especially in female patients. Many current methods employ expensive animal models which not only present ethical concerns but also do not often accurately predict human physiology and the outcomes of anti-cancer drug responsiveness. Conventional treatment approaches for cancer generally include systemic therapy after a surgical procedure. Although this treatment technique is effective, the outcome is not always positive due to various complex factors such as intratumor heterogeneity and confounding factors within the tumor microenvironment(TME). Patients who develop metastatic disease still have poor prognosis. To that end, recent efforts have attempted to use 3D microengineered platforms to enhance the predictive power and efficacy of anti-cancer drug screening, ultimately to develop personalized therapies. Fascinating features of microengineered assays, such as microfluidics, have led to the advancement in the development of the tumor-on-chip technology platforms, which have shown tremendous potential for meaningful and physiologically relevant anti-cancer drug discovery and screening. Three dimensional microscale models provide unprecedented ability to unveil the biological complexities of cancer and shed light into the mechanism of anti-cancer drug resistance in a timely and resource efficient manner. In this review, we discuss recent advances in the development of microengineered tumor models for anti-cancer drug discovery and screening in female-related cancers. We specifically focus on female-related cancers to draw attention to the various approaches being taken to improve the survival rate of women diagnosed with cancers caused by sex disparities. We also briefly discuss other cancer types like colon adenocarcinomas and glioblastoma due to their high rate of occurrence in females, as well as the high likelihood of sex-biased mutations which complicate current treatment strategies for women. We highlight recent advances in the development of 3D microscale platforms including 3D tumor spheroids, microfluidic platforms as well as bioprinted models, and discuss how they have been utilized to address major challenges in the process of drug discovery, such as chemoresistance, intratumor heterogeneity, drug toxicity, etc. We also present the potential of these platform technologies for use in high-throughput drug screening approaches as a replacements of conventional assays. Within each section, we will provide our perspectives on advantages of the discussed platform technologies.

Functional dissection of the KRAS G12C mutation by comparison among multiple oncogenic driver mutations in a lung cancer cell line model

The development of molecular targeted therapy has improved clinical outcomes in patients with life-threatening advanced lung cancers with driver oncogenes. However, selective treatment for KRAS-mutant lung cancer remains underdeveloped. We have successfully characterised specific molecular and pathological features of KRAS-mutant lung cancer utilising newly developed cell line models that can elucidate the differences in driver oncogenes among tissues with identical genetic backgrounds. Among these KRAS-mutation-associated specific features, we focused on the IGF2-IGF1R pathway, which has been implicated in the drug resistance mechanisms to AMG 510, a recently developed selective inhibitor of KRAS G12C lung cancer. Experimental data derived from our cell line model can be used as a tool for clinical treatment strategy development through understanding of the biology of lung cancer. The model developed in this paper may help understand the mechanism of anticancer drug resistance in KRAS-mutated lung cancer and help develop new targeted therapies to treat patients with this disease.

Putative molecular determinants mediating sensitivity or resistance towards carnosic acid tumor cell responses

BackgroundCarnosic acid (CA) is one of the main constituents in rosemary extract. It possesses valuable pharmacological properties, including anti-oxidant, anti-inflammatory, anti-microbial and anti-cancer activities. Numerous in vitro and in vivo studies investigated the anticancer profile of CA and emphasized its potentiality for cancer treatment. Nevertheless, the role of multidrug-resistance (MDR) related mechanisms for CA's anticancer effect is not yet known. PurposeWe investigated the cytotoxicity of CA against known mechanisms of anticancer drug resistance (P-gp, ABCB5, BCRP, EGFR and p53) and determined novel putative molecular factors associated with cellular response towards CA. Study designCytotoxicity assays, bioinformatic analysis, flow cytometry and western blotting were performed to identify the mode of action of CA towards cancer cells. MethodsThe cytotoxicity to CA was assessed using the resazurin assays in cell lines expressing the mentioned resistance mechanisms. A pharmacogenomic characterization of the NCI 60 cell line panel was applied via COMPARE, hierarchical cluster and network analyses. Flow cytometry was used to detect cellular mode of death and ROS generation. Changes in proteins-related to apoptosis were determined by Western blotting. ResultsCell lines expressing ABC transporters (P-gp, BCRP or ABCB5), mutant EGFR or p53 were not cross-resistant to CA compared to their parental counterparts. By pharmacogenomic approaches, we identified genes that belong to different functional groups (e.g. signal transduction, regulation of cytoskeleton and developmental regulatory system). These genes were predicted as molecular determinants that mediate CA tumor cellular responses. The top affected biofunctions included cellular development, cellular proliferation and cellular death and survival. The effect of CA-mediated apoptosis in leukemia cells, which were recognized as the most sensitive tumor type, was confirmed via flow cytometry and western blot analysis. ConclusionCA may provide a novel treatment option to target refractory tumors and to effectively cooperate with established chemotherapy. Using pharmacogenomic approaches and network pharmacology, the relationship between cancer complexity and multi-target potentials of CA was analyzed and many putative molecular determinants were identified. They could serve as novel targets for CA and further studies are needed to translate the possible implications to clinical cancer treatment.

Towards the overcoming of anticancer drug resistance mediated by p53 mutations.

Cancer continues to be a leading threat to human health and life. Resistance to anti-cancer drugs is a major impediment towards efficacious cancer treatment. p53 mutations play an important role in cancer cell resistance to chemotherapeutic drugs. The frequency of p53-based chemoresistance is highly associated with the chemical properties of the anticancer drug, the cellular drug target, the biological function being blocked by the chemotherapeutic agent, the genomic instability and alterations of the tumor, as well as its differentiation state. The p53-based molecular mechanisms of anticancer drug resistance are insufficiently understood. With a clear focus on the role of p53 mutations in anticancer drug resistance, the present article reviews the biological structure and function of p53, its regulatory mechanisms, as well as the molecular mechanisms underlying p53 mutation-dependent chemoresistance and possible modalities to surmount this drug resistance. We specifically discuss the roles of p53 in the development of chemoresistance to classical cytotoxic agents including for example cisplatin, doxorubicin, 5-fluorouracil, temozolomide, and paclitaxel. It is expected that the clinical manifestation of drug resistance can be integrated with data obtained from molecular multi-omics analyses addressing the alterations provoked by p53-driven resistance to discover the altered networks in these drug resistant tumors. Thus, novel drugs targeting mutant p53 or mutant p53-based dysregulated pathways, could be developed that may overcome well-defined mutant p53-mediated chemoresistance. Thus, an in-depth understanding of the p53-driven resistance modalities could facilitate the development of novel targeted antitumor drugs and strategies aimed at enhancing the efficacy of current cancer therapeutics.

Non-coding RNA in drug resistance of gastric cancer.

Gastric cancer (GC) is the third leading cause of cancer-related mortality worldwide. The poorly prognosis and survival of GC are due to diagnose in an advanced, non-curable stage and with a limited response to chemotherapy. The acquisition of drug resistance accounts for the majority of therapy failure of chemotherapy in GC patients. Although the mechanisms of anticancer drug resistance have been broadly studied, the regulation of these mechanisms has not been completely understood. Accumulating evidence has recently highlighted the role of non-coding RNAs (ncRNAs), including long non-coding RNAs and microRNAs, in the development and maintenance of drug resistance due to their regulatory features in specific genes involved in the chemoresistant phenotype of GC. We review the literature on ncRNAs in drug resistance of GC. This review summarizes the current knowledge about the ncRNAs’ characteristics, their regulation of the genes involved in chemoresistance and their potential as targeted therapies for personalized treatment in resistant GC.

The multi-factorial nature of clinical multidrug resistance in cancer.

Curative cancer therapy remains a major challenge particularly in cancers displaying multidrug resistance (MDR). The MDR phenotype is characterized by cross-resistance to a wide array of anticancer drugs harboring distinct structures and mechanisms of action. The multiple factors involved in mediating MDR may include host factors, tumor factors as well as tumor-host interactions. Among the host factors are genetic variants and drug-drug interactions. The plethora of tumor factors involves decreased drug uptake primarily via impaired influx transporters, increased drug efflux predominantly due to the overexpression of MDR efflux transporters of the ATP-binding cassette superfamily or due to drug efflux mediated by extracellular vesicles (EVs) or drug-loaded lysosomes undergoing exocytosis, deregulation of cell death mechanisms (i.e. anti-apoptotic modalities), enhanced DNA damage repair, epigenetic alterations and/or deregulation of microRNAs. The intratumor heterogeneity and dynamics, along with cancer stem cell plasticity, are important tumor factors. Among the tumor-host interactions are the role of the tumor microenvironment, selective pressure of various stressor conditions and agents, acidic pH and the intracellular transfer of traits mediated by EVs. The involvement of these diverse factors in MDR, highlights the need for precision medicine and real-time personalized treatments of individual cancer patients. In this review, written by a group of researchers from COST Action STRATAGEM "New diagnostic and therapeutic tools against multidrug resistant tumors", we aim to bring together these multidisciplinary and interdisciplinary features of MDR cancers. Importantly, it is becoming increasingly clear that deciphering the molecular mechanisms underlying anticancer drug resistance, will pave the way towards the development of novel precision medicine treatment modalities that are able to surmount distinct and well-defined mechanisms of anticancer drug resistance.

Mechanisms of Anticancer Drug Resistance in Hepatoblastoma.

The most frequent liver tumor in children is hepatoblastoma (HB), which derives from embryonic parenchymal liver cells or hepatoblasts. Hepatocellular carcinoma (HCC), which rarely affects young people, causes one fourth of deaths due to cancer in adults. In contrast, HB usually has better prognosis, but this is still poor in 20% of cases. Although more responsive to chemotherapy than HCC, the failure of pharmacological treatment used before and/or after surgical resection is an important limitation in the management of patients with HB. To advance in the implementation of personalized medicine it is important to select the best combination among available anti-HB drugs, such as platinum derivatives, anthracyclines, etoposide, tyrosine-kinase inhibitors, Vinca alkaloids, 5-fluorouracil, monoclonal antibodies, irinotecan and nitrogen mustards. This requires predicting the sensitivity to these drugs of each tumor at each time because, it should be kept in mind, that cancer chemoresistance is a dynamic process of Darwinian nature. For this goal it is necessary to improve our understanding of the mechanisms of chemoresistance involved in the refractoriness of HB against the pharmacological challenge and how they evolve during treatment. In this review we have summarized the current knowledge on the multifactorial and complex factors responsible for the lack of response of HB to chemotherapy.

Abstract 2186: Drug treatment induces phenotypic switch and stemness during acquisition of drug resistance

Abstract The breast tumor heterogeneity and development of drug resistance has become a challenge for anti-cancer therapy. Tumor cells acquire resistance due to intra-tumor heterogeneity imposed by epithelial to mesenchymal transition. The drugs which target epithelial cells may fail to target mesenchymal and the intermediate phenotypes due to which the cancer cells acquire drug resistance. This concept provoked us to understand the phenotypic diversity among the tumor heterogeneity which might lead to drug resistance. Hence the aim of our study is to identify the mechanisms of anti-cancer drug resistance which would ultimately help in identification of new clinical targets. Treatment of breast cancer cell lines MCF7 and MDA MB 231 with Doxorubicin showed a loss of epithelial markers and gain of mesenchymal markers in MCF7 cells, and vice versa in MDA MB 231 cells, thereby shifting them into an intermediate phenotype. Moreover, Doxorubicin treatment of MDA MB 231-Nanog stable cells led to an increase in Nanog positive cells confirming that the treatment-induced increase in stemness property of cancer cells. We predict that phosphoproteomic dataset of the anti-cancer drug-resistant cells let us analyze the possible molecular players involved in the phenotypic switch and hence drug resistance (work in progress). Thus, our current data suggest that the anti-cancer therapy induces cancer cells to undergo a phenotypic switch and increases the stemness property which might be responsible to gain resistance. Identification of the critical regulators of the phenotypic switch by phosphoproteomics analysis is likely to help us investigate the possible mechanisms underlying anti-cancer drug resistance. Previous reports also suggest that conventional therapies fail to eliminate cancer stem cells thereby allowing tumor relapse. These results suggest that understanding the protein abundance and phosphorylation state of key signaling molecules would elucidate specific signaling interactions or/and pathways differentially active in drug-resistant tumors would help us predict novel kinases, and hence identify drug targets. Citation Format: Santhalakshmi Ranganathan, Annapoorni Rangarajan. Drug treatment induces phenotypic switch and stemness during acquisition of drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2186.

Novel Mechanisms of Resistance to Investigational Molecularly Targeted Drugs.

Drug resistance is a critical problem inhibiting the effective use of targeted molecular cancer therapies. Investigators have revealed a variety of resistance mechanisms, including alterations in drug targets, activation of pro-survival pathways, and the ineffective induction of cell death. The key alterations driving this resistance are likely condition-dependent, and a detailed analysis would be required to characterize these diverse alterations under a variety of conditions in order to facilitate practical precision medicine for treating individual cancer patients. We have been investigating the molecular mechanisms of anti-cancer drug resistance, and analyzed our original resistant cells against anti-mitotic kinase inhibitors. This study suggests that novel mechanisms reduce cytokinetic dysregulation caused by those inhibitors, and anti-apoptotic activities are associated with resistant phenotypes. These observations suggest that the activation of various bypass mechanisms may allow cancer cells to avoid the selective antiproliferative effect of molecularly targeted drugs, and such bypass activation mechanism would thus be a critical target for designing combination chemotherapy to overcome non-genetic drug resistance.

Abstract 1292: Camalexin, an indole phytoalexin from Arabidopsis thaliana, displays activity against ovarian cancer stem cells

Abstract Ovarian cancer is the most lethal of all gynecological cancers. Current treatment of advanced ovarian cancers, which includes debulking surgery and chemotherapy, is initially effective in majority of patients; however, 70-90% of them eventually develop disease recurrence with limited treatment options. This recurrence can be attributed to therapy-resistant cancer stem cells (CSC), which represent a subset of all malignant cells that form the bulk of ovarian cancers. CSC may remain as a minimal residual disease after the bulk of ovarian tumor mass has been removed by surgery and/or chemotherapy; therefore, there is considerable current interest in the development of new therapies that can effectively target this insidious subpopulation of tumor cells. Here we report on the anticancer activity of camalexin, a major indole phytoalexin of Arabidopsis thaliana, against ovarian cancer stem cells. We demonstrate that camalexin inhibits proliferation and induces cell death in ovarian cancer stem cells that exhibit various molecular mechanisms of anticancer drug resistance. Furthermore, we present the mode of action of this prospective anticancer agent identified by combined approach that included in silico predictions, comprehensive analysis of whole-genome gene expression data and target-specific assays. Lastly, we demonstrate the relevance of the identified mode of action in context of ovarian cancer cell signaling. Citation Format: Roman Mezencev, John F. McDonald. Camalexin, an indole phytoalexin from Arabidopsis thaliana, displays activity against ovarian cancer stem cells. [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 1292.

How can nanomedicines overcome cellular-based anticancer drug resistance?

Despite the great progress in the field of cancer research, complete remission of cancer patients is a rarely seen outcome in clinics. The failure of a plethora of promising anticancer drugs is mostly due to the insurgence of multidrug resistance (MDR) phenomena with various factors, both physio-pathological and cellular, being responsible for their development. Over the past 40 years, the impressive progress in the nanotechnology field and its application in medicine (i.e., nanomedicine) enabled the development of novel cancer treatments with improved specificity and efficacy, mainly referring to the possibility to overcome MDR. However, the emergence of many nanomedicines defined in the literature as "overcoming the resistance" has resulted in very few of them eventually being approved for clinical application and reaching the marketplace (liposomal formulation of doxorubicin (Myocet®, Caelix®) and paclitaxel nanoparticles (Abraxane®), for instance). The capacity of nanomedicines to overcome physio-pathological-based resistance by enhancing drug accumulation at the tumor site via passive and ligand-mediated targeting has been largely reviewed in the past few years. This review will specifically focus on the cellular mechanisms involved in the MDR, which will be discussed with respect to the cellular site in which their action is exerted (that is, membrane, cytoplasm or nucleus). A complete overview of various nanomedicines designed to bypass or directly inhibit each of these specific resistance mechanisms will be offered.