ADC Activity Research Articles

Abstract 4892: MMAE drives immunomodulatory changes in a preclinical xenograft model that are distinct from other clinical-stage ADC payloads

Abstract Monomethyl auristatin E (MMAE), the payload delivered by vedotin ADCs, exerts its cytotoxic effects via microtubule disruption and induction of ER stress, leading to apoptosis and tumor cell death. In addition, MMAE also has the ability to induce immunogenic cell death (ICD) and immune modulation in the tumor microenvironment (TME) (Liu, 2020; Gray, 2020). Other clinical-stage and approved ADCs incorporate payloads that also cause microtubule disruption (DM1, DM4), or that drive DNA damage through topoisomerase I inhibition (exatecan) as the primary mechanism of action (MOA). While ADCs with different linker payloads produce clinical benefit, their long-term impact on survival and how they pair with PD(L)1 agents may differ based on their ability to elicit immune modulation. In this study we have investigated how these payloads compare to MMAE in their ability to drive immune changes in the TME and describe how these changes could support anti-tumor immunity and improve outcomes in the clinic.Building upon an initial in vitro assessment in which we observed superior induction of ICD markers and underlying ER stress with an MMAE ADC, we utilized a B7H4-expressing MDA-MB-468 xenograft model of triple-negative breast cancer to further characterize the ICD properties of ADC payloads. Tumor-bearing mice were treated with a single dose of B7H4-targeted antibody conjugated to either MMAE, DM1, DM4 or exatecan. Tumors were harvested seven days after treatment and processed for immunohistochemistry (IHC) to assess changes in immune cell infiltration and analyzed by RNA-seq to determine alterations in gene expression. Payload-driven anti-tumor activity was observed with all ADC treatments, each leading to a similar reduction in tumor volume compared to vehicle or unconjugated antibody. IHC staining of tumor sections for F4/80, a mouse macrophage marker, revealed that of the microtubule-disrupting agents, only MMAE significantly increased F4/80+ macrophage infiltration in both the tumor nests and stroma. Increased F4/80+ macrophages in tumor nests and stroma was also observed as a result of B7H4-exatecan ADC treatment. RNA-seq analysis revealed a unique profile for the MMAE conjugate, with an increase in human transcripts encoding cytokine and type I interferon response genes. In summary, the anti-tumor activity of the B7H4-MMAE ADC resulted in recruitment of mouse innate immune cells to the xenograft tumors. Importantly, immune response genes related to ICD were increased following B7H4-MMAE treatment compared to DM1, DM4, and exatecan conjugates. Together, these data suggest that treatment with vedotin ADCs results in robust immunomodulatory changes in vivo that are distinct from other clinical ADC payloads. Citation Format: Michelle Ulrich, Kerry Klussman, John J. Gosink, Sean Allred, Kelly Hensley, Piper M. Treuting, Nikhil J. Parekh, Elizabeth E. Gray, Shyra J. Gardai. MMAE drives immunomodulatory changes in a preclinical xenograft model that are distinct from other clinical-stage ADC payloads. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4892.

Discovery of ancestral L-ornithine and L-lysine decarboxylases reveals parallel, pseudoconvergent evolution of polyamine biosynthesis

Polyamines are fundamental molecules of life, and their deep evolutionary history is reflected in extensive biosynthetic diversification. The polyamines putrescine, agmatine, and cadaverine are produced by pyridoxal 5′-phosphate-dependent L-ornithine, L-arginine, and L-lysine decarboxylases (ODC, ADC, LDC), respectively, from both the alanine racemase (AR) and aspartate aminotransferase (AAT) folds. Two homologous forms of AAT-fold decarboxylase are present in bacteria: an ancestral form and a derived, acid-inducible extended form containing an N-terminal fusion to the receiver-like domain of a bacterial response regulator. Only ADC was known from the ancestral form and limited to the Firmicutes phylum, whereas extended forms of ADC, ODC, and LDC are present in Proteobacteria and Firmicutes. Here, we report the discovery of ancestral form ODC, LDC, and bifunctional O/LDC and extend the phylogenetic diversity of functionally characterized ancestral ADC, ODC, and LDC to include phyla Fusobacteria, Caldiserica, Nitrospirae, and Euryarchaeota. Using purified recombinant enzymes, we show that these ancestral forms have a nascent ability to decarboxylate kinetically less preferred amino acid substrates with low efficiency, and that product inhibition primarily affects preferred substrates. We also note a correlation between the presence of ancestral ODC and ornithine/arginine auxotrophy and link this with a known symbiotic dependence on exogenous ornithine produced by species using the arginine deiminase system. Finally, we show that ADC, ODC, and LDC activities emerged independently, in parallel, in the homologous AAT-fold ancestral and extended forms. The emergence of the same ODC, ADC, and LDC activities in the nonhomologous AR-fold suggests that polyamine biosynthesis may be inevitable.

Combinatorial approach for improved production of whole-cell 3-aminopropionic acid in recombinant Bacillus megaterium: codon optimization, gene duplication and process optimization.

The online version contains supplementary material available at 10.1007/s13205-021-02885-7.

Development of a dual-fluorescence reporter system for high-throughput screening of L-aspartate-α-decarboxylase.

β-Alanine (3-aminopropionic acid) holds great potential in industrial application. It can be obtained through a chemical synthesis route, which is hazardous to the environment. It is well known that l-aspartate-α-decarboxylase (ADC) can convert l-aspartate to β-alanine in bacteria. However, due to the low activity of ADC, industrial production of β-alanine through the green biological route remains unclear. Thus, improving the activity of ADC is critical to reduce the cost of β-alanine production. In this study, we established a dual-fluorescence high-throughput system for efficient ADC screening. By measuring the amount of β-alanine and the expression level of ADC using two different fluorescence markers, we can rapidly quantify the relative activity of ADC variants. From a mutagenesis library containing 2000 ADC variants, we obtained a mutant with 33% increased activity. Further analysis revealed that mutations of K43R and P103Q in ADC significantly improved the yield of β-alanine produced by the whole-cell biocatalysis. Compared with the previous single-fluorescence method, our system can not only quantify the amount of β-alanine but also measure the expression level of ADC with different fluorescence, making it able to effectively screen out ADC variants with improved relative activity. The dual-fluorescence high-throughput system for rapid screening of ADC provides a good strategy for industrial production of β-alanine via the biological conversion route in the future.

Controlled coupling of an ultrapotent auristatin warhead to cetuximab yields a next-generation antibody-drug conjugate for EGFR-targeted therapy of KRAS mutant pancreatic cancer

BackgroundAntibody-drug conjugate (ADC) construction poses numerous challenges that limit clinical progress. In particular, common bioconjugation methods afford minimal control over the site of drug coupling to antibodies. Here, such difficulties are overcome through re-bridging of the inter-chain disulfides of cetuximab (CTX) with auristatin-bearing pyridazinediones, to yield a highly refined anti-epidermal growth factor receptor (EGFR) ADC.MethodsIn vitro and in vivo assessment of ADC activity was performed in KRAS mutant pancreatic cancer (PaCa) models with known resistance to CTX therapy. Computational modelling was employed for quantitative prediction of tumour response to various ADC dosing regimens.ResultsSite-selective coupling of an auristatin to CTX yielded an ADC with an average drug:antibody ratio (DAR) of 3.9, which elicited concentration- and EGFR-dependent cytotoxicity at sub-nanomolar potency in vitro. In human xenografts, the ADC inhibited tumour growth and prolonged survival, with no overt signs of toxicity. Key insights into factors governing ADC efficacy were obtained through a robust mathematical framework, including target-mediated dispositional effects relating to antigen density on tumour cells.ConclusionsTogether, our findings offer renewed hope for CTX in PaCa therapy, demonstrating that it may be reformatted as a next-generation ADC and combined with a predictive modelling tool to guide successful translation.

Characterization of cysteine sulfinic acid decarboxylase from Tribolium castaneum and its application in the production of β-alanine.

β-alanine is a precursor for the production of pharmaceuticals and food additives that is produced by chemical methods in industry. As concerns about the environment and energy are increasing, biocatalysis using L-aspartate-α-decarboxylase (ADC) to convert L-aspartate to β-alanine has great potential. Many studies have focused on the catalytic activity of ADC, but these researches were limited to the prokaryotic enzymes. In this study, the gene encoding cysteine sulfinic acid decarboxylase from Tribolium castaneum (TcCSADC) was synthesized and overexpressed in Escherichia coli, and the enzyme was purified and characterized for the first time. It could use L-aspartate as its substrate, and the specific activity was 4.83 μmol/min/mg, which was much higher than that of ADCs from prokaryotes. A homology modeling assay indicated that TcCSADC had a dimer structure. Based on the evolutionary information from thermophilic bacteria, twenty-three variants were constructed to attempt to improve its abilities that transform L-aspartate to β-alanine. One mutant, G369A, was screened that had improved thermal stability. An analysis of the suitability of the catalytic process showed that the up to 162 g/L β-alanine could be produced using cells expressing the recombinant G369A variant, which is the highest yield to date. The CSADC from T. castaneum has important value for studies of the mechanism of ADCs and CSADCs from eukaryotes, and the engineered strain containing the G369A variant has great potential for the industrial production of β-alanine.

Involvement of polyamines in sucrose-induced tolerance to atrazine-mediated chemical stress in Arabidopsis thaliana

Treatment of Arabidopsis thaliana seedlings with the PSII-inhibiting herbicide atrazine results in xenobiotic and oxidative stress, developmental arrest, induction of senescence and cell death processes. In contrast, exogenous sucrose supply confers a high level of atrazine stress tolerance, in relation with genome-wide modifications of transcript levels and regulation of genes involved in detoxification, defense and repair. However, the regulation mechanisms related to exogenous sucrose, involved in this sucrose-induced tolerance, are largely unknown. Characterization of these mechanisms was carried out through a combination of transcriptomic, metabolic, functional and mutant analysis under different conditions of atrazine exposure. Exogenous sucrose was found to differentially regulate genes involved in polyamine synthesis. ARGININE DECARBOXYLASE ADC1 and ADC2 paralogues, which encode the rate-limiting enzyme (EC 4.1.1.19) of the first step of polyamine biosynthesis, were strongly upregulated by sucrose treatment in the presence of atrazine. Such regulation occurred concomitantly with significant changes of major polyamines (putrescine, spermidine, spermine). Physiological characterization of a mutant affected in ADC activity and exogenous treatments with sucrose, putrescine, spermidine and spermine further showed that modification of polyamine synthesis and of polyamine levels could play adaptive roles in response to atrazine stress, and that putrescine and spermine had antagonistic effects, especially in the presence of sucrose. This interplay between sucrose, putrescine and spermine is discussed in relation with survival and anti-death mechanisms in the context of chemical stress exposure.

Antrodin C, an NADPH Dependent Metabolism, Encourages Crosstalk between Autophagy and Apoptosis in Lung Carcinoma Cells by Use of an AMPK Inhibition-Independent Blockade of the Akt/mTOR Pathway.

The current study aims to explore the possible anti-lung carcinoma activity of ADC as well as the underlying mechanisms by which ADC exerts its actions in NSCLC. Findings showed that ADC potently inhibited the viability of SPCA-1, induced apoptosis triggered by ROS, and arrested the cell cycle at the G2/M phase via a P53 signaling pathway. Interestingly, phenomena such as autophagosomes accumulation, conversion of the LC3-I to LC3-II, etc., indicated that autophagy could be activated by ADC. The blockage of autophagy-augmented ADC induced inhibition of cell proliferation, while autophagy activation restored cell death, indicating that autophagy had a protective effect against cell death which was induced by ADC treatment. Meanwhile, ADC treatment suppressed both the Akt/mTOR and AMPK signaling pathways. The joint action of both ADC and the autophagy inhibitor significantly increased the death of SPCA-1. An in vitro phase I metabolic stability assay showed that ADC was highly metabolized in SD rat liver microsomes and moderately metabolized in human liver microsomes, which will assist in predicting the outcomes of clinical pharmacokinetics and toxicity studies. These findings imply that blocking the Akt/mTOR signaling pathway, which was independent of AMPK inhibition, could activate ADC-induced protective autophagy in non-small-cell lung cancer cells.

In vitro and in vivo mechanisms of ADC disposition and activity

In vitro and in vivo mechanisms of ADC disposition and activity

Co-production of AmpC and extended spectrum beta-lactamases in cephalosporin-resistant Acinetobacter baumannii in Egypt.

Acinetobacter baumannii is an opportunistic pathogen that has been held responsible for a lot of infections worldwide. Infections caused by this pathogen are difficult to control because of the widespread of antimicrobial resistance mechanisms. The aim of the present study is to assess the prevalence of extended spectrum β-lactamases (ESBLs) and AmpC β-lactamases among isolates of A. baumannii collected from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has demonstrated elevated resistance level to β-lactams, quinolones and aminoglycosides. All isolates were sensitive to colistin and polymyxin B. ESBL activity was detected in 86% of the isolates. Among the tested ESBL encoding genes, blaTEM gene was the most prevalent gene as it was detected in 52% of the isolates. While blaPER, blaSHV and blaVEB were detected in 12%, 4%, and 2%, respectively. AmpC activity and blaADC gene were detected in 90% of the tested isolates. Insertion sequence ISAba1 was located 9bp upstream of blaADC gene in 88.9% of the ADC-expressing isolates providing a potent promoter activity for its expression. To our knowledge this is the first report of loss of intrinsic ADC activity, in 10% of the tested isolates, as a result of insertional inactivation by an element belonging to IS5 family transposase. Co-expression of both ESBLs and AmpC β-lactamases was detected in 78% of the isolates. The study demonstrates high prevalence of resistance to β-lactam antibiotics through ESBLs and AmpC β-lactamases production among A. baumannii clinical isolates. Prevalence of β-lactamases should be detected routinely and reported in hospitals to avoid inappropriate use of antibiotics and therapeutic failure.

Abstract LB-053: Towards new cryptophycins as promising payloads for ADC

Abstract Cryptophycins are a class of macrocyclic depsipeptides produced as secondary metabolites by cyanobacteria of the genus Nostoc and were found to bind to microtubules at the vinca site. The natural product C-1 isolated in 1990 and the synthetic derivative C-52 displayed potent in vitro and in vivo antitumor activity in preclinical models. Cryptophycin C-52 (LY355703) produced marginal antitumor activity at MTD in two phase II lung cancer trials and was therefore discontinued. Considering its higher potency versus other tubulin binders such as maytansine and auristatin, this chemical series was selected for an ADC approach. Several conjugates were evaluated in vitro and in vivo based on the conjugation of C52 derivatized at the para-benzylic position of the macrocycle. As described in this study, this optimization led to the discovery of cryptophycin ADC which displayed potent antitumor activity in vivo. However, these conjugates were found unstable in mice plasma while being stable in the plasma of non-rodent species. This species-dependent instability was shown to be the result of a mice plasmatic metabolization of C52 macrocycle once conjugated to the antibody. We therefore designed and synthesized new cryptophycin ADC which exhibited improved plasmatic stability when tested in mice and enhanced therapeutic index in comparison with C52 ADC. In conclusion, these data demonstrated the potent in vitro and in vivo antitumor activity of these new cryptophycin ADC and warrant further development of this cytotoxic payload for an ADC approach. Citation Format: Marie-Priscille Brun, Hervé Bouchard, François Clerc, Jidong Zhang, Pierre-Yves Abecassis, Céline Amara, Eric Beys, Florence Efremenko, Céline Nicolazzi, Marie-Hélène Pascual, Olivier Pasquier, Alain Krick, Pierre-François Berne, Laurence Gauzy, Nathalie Karst, Sylvain Huille, Christophe Henry, Anne-Marie Lefebvre, Ingrid Sassoon. Towards new cryptophycins as promising payloads for ADC. [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 LB-053.

PSMA ADC for progressive glioblastoma: Phase II Brown University Oncology Research Group Study.

2065Background: Antiangiogenic agents targeting new blood vessel formation are approved to treat progressive glioblastoma (GBM), but limited data are available on the activity of vascular disrupting agents targeting established blood vessels in these tumors. Prostate specific membrane antigen (PSMA) is a transmembrane peptidase upregulated on endothelial cells of solid tumors including GBM, making it a potential therapeutic target. A PSMA-targeted monoclonal antibody conjugated with microtubule disrupting agent monomethyl auristatin E (MMAE) is undergoing evaluation in advanced prostate cancer (PSMA ADC, Progenics Pharmaceuticals). Unconjugated MMAE has demonstrated activity against GBM cell lines. Methods: We investigated the activity of PSMA ADC in a single arm Phase II study in progressive GBM patients following prior treatment with radiation, temozolomide and bevacizumab. 2.5 mg/kg PSMA ADC was administered intravenously every 3 weeks until disease progression, unacceptable toxicity or removal from st...

An anti-HER2 antibody conjugated with monomethyl auristatin E is highly effective in HER2-positive human gastric cancer

ABSTRACTAntibody-drug conjugate (ADC) is a novel class of therapeutics for cancer target therapy. This study assessed antitumor activity of ADC with an antimitotic agent, monomethyl auristatin E (MMAE) and a humanized monoclonal anti-HER2 antibody, hertuzumab, in gastric cancer. The efficacy of hertuzumab-MC-Val-Cit-PAB-MMAE (hertuzumab-vcMMAE) on human epidermal growth factor receptor 2 (HER2) positive human gastric cancer cells, NCI-N87, was evaluated in vitro and in vivo. The cytotoxicity of hertuzumab was significantly enhanced after conjugation with MMAE. Compared to trastuzumab, hertuzumab had a higher affinity to HER2 and had more potent antibody-dependent cell-mediated cytotoxicity (ADCC) activity in vitro. After conjugation with MMAE, the binding specificity for HER2 was not affected. Furthermore, the internalization of hertuzumab-vcMMAE in HER2 positive gastric cancer cells was verified. Although the conjugation of hertuzumab and MMAE decreased the ADCC effect, the overall cytotoxicity was dramatically increased in HER2 positive gastric cancer cells. In vitro data on this hertuzumab-vcMMAE has exerted much stronger antitumor activity compared to trastuzumab-DM1 in HER2 positive gastric cancer cells. A single administration of hertuzumab-vcMMAE at 5 or 10 mg/kg showed high potency and a sustained tumor inhibitory effect on NCI-N87 xenografts in mice. In conclusion, hertuzumab-vcMMAE conjugate is a highly effective anti-HER2 targeted therapy for HER2-positive gastric cancer.

Wounding induces changes in tuber polyamine content, polyamine metabolic gene expression, and enzyme activity during closing layer formation and initiation of wound periderm formation

Tuber wound-healing processes are complex, and the associated regulation and modulation of these processes are poorly understood. Polyamines (PA) are involved in modulating a variety of responses to biotic and abiotic plant stresses and have been suggested to be involved in tuber wound responses. However, the time course of wound-induced changes in tuber PA content, activity of key biosynthetic enzymes and associated gene expression has not been determined and coordinated with major wound-healing processes. The objective of this study was to determine these wound-induced changes and their coordination with wound-healing processes. Wounding induced increases in putrescine (Put) and spermidine (Spd), but had only minor effects on spermine (Spm) content during the 168h time course which encompassed the initiation and completion of the closing layer formation, and the initiation of cell division and wound periderm formation. As determinants of the first committed step in PA biosynthesis, arginine and ornithine decarboxylase (ADC and ODC, respectively) activities were below levels of detectability in resting tubers and expression of genes encoding these two enzymes was low. Within 6h of wounding, increases in the in vitro activities of ADC and ODC and expression of their cognate genes were observed. Expression of a gene encoding S-adenosylmethionine decarboxylase, required for Spd and Spm biosynthesis, was also increased 6h after wounding and remained elevated throughout the time course. Expression of a polyamine catabolic gene, encoding polyamine oxidase, was down-regulated after wounding. Results indicated a rapid wound-induced increase in PA biosynthesis during closing layer formation and the time of nuclei entry and exit from S-phase. PA content remained elevated as wound-induced cells became meristematic and initiated formation of the wound periderm suggesting sustained involvement in wound-healing.

Abstract 2904: SN-38 antibody-drug conjugates as a novel platform for solid cancer therapy: preclinical science

Abstract SN-38 is the active metabolite of the camptothecin prodrug, CPT-11 (irinotecan), which is a solid cancer therapeutic, particularly colorectal cancer (CRC). SN-38 is highly potent (low nM), but its bioavailability is hampered by a low rate of CPT-11 conversion to SN-38 (e.g., <5%), as well as its subsequent detoxification, mainly by UGT1A1 glucoronidation. In an attempt to improve SN-38's bioavailability and therapeutic index, we conjugated it to tumor-targeting humanized monoclonal antibodies (mAbs) using a novel pH-sensitive linker and a maleimide attachment to the mAb's interchain SH groups, achieving a drug-antibody ratio of 7.6. Linker coupling on the 20th position of SN-38 helps maintain SN-38 in the more active lactone form. In human serum, SN-38 is released from the linker with a half-life of ∼24 h, providing ample time for the ADC to localize in tumors. The pH-sensitive linker has the potential to release of SN-38 in the acidic tumor microenvironment by the targeted ADC in the absence of its direct internalization. Studies using two different SN-38-conjugated mAbs targeting CEACAM5 (IMMU-130) and Trop-2 (IMMU-132) show growth inhibition and regression of diverse human solid cancer xenografts in mice given repeated doses (cumulative ≤ 50 mg/kg in mice, or ∼ 4 mg/kg human equivalent dose [HED]), without defining an MTD (CPT-11 conversion is more active in mice, but mice are more tolerant to SN-38 than humans). Dosing regimens using the same total amount of the ADC given once or twice weekly for at least 2 weeks appears to be preferred over the same total amount given once every other week (2 doses). IMMU-130 is a poorly-internalizing mAb that shows good ADC activity in human CRC models expressing CEACAM5, while IMMU-132 internalizes rapidly and is active against CRC, gastric, breast, pancreatic, and prostatic cancers expressing Trop-2; both targets have antigen receptors in the 1 x 10*5 range in most cancer cell lines. Studies to assess tumor and tissue concentrations of SN-38 in xenograft models given the ADC or CPT-11 are ongoing. Toxicity studies performed in relevant animal species found the ADCs were tolerated at HED of up to 60 mg/kg, limited by neutropenia and diarrhea (also dose-limiting for CPT-11 therapy), and with no evidence of selective toxicity to antigen-expressing normal tissues. These results with an ADC having relatively modest toxicity suggest a high therapeutic index. Ongoing Phase I/II clinical trials confirm anticancer activity with a high therapeutic window (less neutropenia and GI toxicity than CPT-11) in cancers expressing the target antigens. Citation Format: David M. Goldenberg, Thomas M. Cardillo, Robert M. Sharkey, William J. McBride, Edmund A. Rossi, Chien-Hsing Chang, Serengulam V. Govindan. SN-38 antibody-drug conjugates as a novel platform for solid cancer therapy: preclinical science. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2904. doi:10.1158/1538-7445.AM2014-2904

Contribution of polyamines and other related metabolites to the maintenance of zucchini fruit quality during cold storage

In order to investigate the contribution of polyamines and related amino acids in the maintenance of zucchini fruit quality during cold storage, two varieties of Cucurbita pepo with different degrees of chilling tolerance were used, Natura (more tolerant) and Sinatra (moresensitive). After harvest, free putrescine levels decreased during storage at 20 °C, whereas in fruit kept at 4 °C this polyamine accumulated in both varieties, but with higher levels in the sensitive variety (Sinatra). This behavior suggests that putrescine is accumulated as a response to low temperature in zucchini fruit by stress-induced chilling injury, and not due to the postharvest storage itself. ADC activity responds quickly to chilling but sharply decreases after 14 days, whereas its expression remains high in both varieties. ODC activity takes over when the cold stress is relatively severe, as this activity was found to be much higher in Sinatra. ODCexpression also correlated with ODC activity. DAO activity increased in Natura fruit, and conversely decreased in Sinatra fruit during storage at 4 °C, whereas the proline content was higher in Natura and lower in Sinatra. Therefore, we suggest that putrescine degradation and proline accumulation contribute to the acquisition of chilling tolerance in zucchini fruit. GABA content decreased in both varieties, with a greater reduction in Natura fruit and less in Sinatra fruit. In addition, GABA transaminase showed a higher activity in Natura fruit than in Sinatra fruit during cold storage, suggesting that GABA catabolism could be involved in the tolerance to postharvest cold storage in zucchini fruit.

Abstract A262: Antiandrogen modulation of prostate-specific membrane antigen (PSMA): Dynamics and synergy with PSMA-targeted therapy.

Abstract Introduction: Recent approvals of new prostate cancer (PCa) drugs and a growing number of pipeline agents have created opportunities for designing rational drug combinations. Potent antiandrogens such as enzalutamide and abiraterone affect expression of numerous androgen-regulated molecules, including PSMA, a well-characterized cell-surface target for PCa therapy. Methods: Cytotoxicity and the kinetics of antigen expression were evaluated in PCa cell lines (LNCaP, C4-2 and 22Rv1) that vary according to androgen dependence and level of PSMA expression. Expression of PSMA and prostate-specific antigen (PSA) was evaluated over time in cells cultured in enzalutamide or abiraterone. Reversibility was examined following drug washout. Cells were tested for susceptibility to antiandrogens used alone and in combination with PSMA ADC, which is a fully human PSMA monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE). Potential drug synergy or antagonism was evaluated using the Combination Index and Bliss independence methods. Results: In androgen-dependent LNCaP cells, enzalutamide and abiraterone exerted antiproliferative effects that were accompanied by a 2- to 3-fold increase in PSMA expression and a decrease in PSA expression. PSMA expression reached maximum levels after four weeks’ culture in enzalutamide and returned to baseline levels within days following enzalutamide removal. In androgen-independent C4-2 cells, enzalutamide and abiraterone increased PSMA expression in the absence of any significant anti-proliferative effect. PSMA ADC exhibited synergistic antitumor activity with both enzalutamide and abiraterone in LNCaP and C4-2 cells. Lesser effects were observed using 22Rv1 cells, an androgen-independent cell line with low basal expression of PSMA. Conclusions: Enzalutamide and abiraterone significantly and reversibly augmented PSMA expression and potentiated the activity of PSMA ADC in androgen-dependent and -independent PCa cell lines in vitro. In androgen-independent cells, the effects on PSMA expression and PSMA ADC activity were uncoupled from any anti-proliferative effect of the antiandrogens. The findings support clinical exploration of regimens that combine potent antiandrogens and PSMA-targeted therapies. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A262. Citation Format: Jose D. Murga, Wells W. Magargal, Sameer M. Moorji, Vincent A. DiPippo, William C. Olson. Antiandrogen modulation of prostate-specific membrane antigen (PSMA): Dynamics and synergy with PSMA-targeted therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A262.

Antiandrogen modulation of prostate-specific membrane antigen (PSMA): Dynamics and synergy with PSMA-targeted therapy.

e16007 Background: Recent approvals of four new prostate cancer (PCa) drugs and a growing number of pipeline agents have created opportunities for designing rational drug combinations. Potent antiandrogens such as enzalutamide and abiraterone affect expression of a host of androgen-regulated molecules, including those that represent targets for therapy. One such target is PSMA, a well-characterized cell-surface antigen abundant on prostate cancer cells. PSMA ADC is a PSMA-targeted antibody-drug conjugate currently in phase II clinical testing, comprised of a fully human IgG1 mAb conjugated to vcMMAE (valine-citrulline monomethylauristatin E). Here we examined the kinetics and reversibility of PSMA induction by potent antiandrogens and their associated effects on the preclinical activity of PSMA ADC. Methods: Androgen-dependent and -independent PCa cell lines with varying basal levels of PSMA expression were cultured for up to one month in the presence of enzalutamide or abiraterone, followed by drug washout. Cells were tested for PSMA expression over time and for susceptibility to cytotoxicity by PSMA ADC. Potential drug synergy or antagonism was evaluated using the combination index method. Results: Enzalutamide (1 mM) increased PSMA expression by approximately 2.5-fold in LNCaP (androgen-dependent) and C4-2 (androgen-independent) cells, with maximal expression observed after approximately 4 weeks’ culture. PSMA expression returned to basal levels within days following removal of enzalutamide from the culture. Enzalutamide and PSMA ADC exhibited synergistic antitumor activity in LNCaP and C4-2 cells (P < 0.05). Similar results were observed for abiraterone in C4-2 cells. Less induction of PSMA expression by antiandrogens and modest effects on cytotoxicity were observed using 22Rv1 cells, an androgen-independent cell line with low basal expression of PSMA. Conclusions: Enzalutamide and abiraterone significantly and reversibly augmented PSMA expression and potentiated the activity of PSMA ADC in PCa cell lines in vitro. The findings support clinical exploration of regimens that combine potent antiandrogens and PSMA-targeted therapies.

Diffusion-weighted imaging of hepatocellular carcinoma for predicting early recurrence and survival after hepatectomy.

The effectiveness of imaging (including apparent diffusion coefficient [ADC] of diffusion-weighted magnetic resonance imaging [DWI]) and laboratory variables for predicting early tumor recurrence and overall survival after surgery in hepatocellular carcinoma (HCC) patients are analyzed. The present study included 116 consecutive patients with HCC who underwent partial hepatectomy. Patients were classified into two groups: patients with and without early recurrence (<1year). Preoperative imaging variables (tumor number, size, shape, capsule, ADC, and venous invasion) and laboratory variables were evaluated to predict early recurrence using univariate and multivariate analyses. Overall survival was calculated using the Kaplan-Meier method. Twenty patients (17%) developed early recurrence after surgery. Multivariate logistic regression analysis showed that tumor ADC (p=0.0002), aspartate aminotransferase (p=0.0121), and serum prothrombin time activity percentage (p=0.0082) were statistically significant for predicting early recurrence. The optimal ADC cutoff value for predicting early recurrence obtained from receiver operating characteristic analysis was ≤0.898×10(-3)mm(2)/s. In patients with ADC ≤0.898×10(-3)mm(2)/s, the 3- and 5-year survival rates (77 and 56%, respectively) were significantly decreased compared with those in patients with ADC >0.898×10(-3)mm(2)/s (97 and 97%, respectively; p=0.0015). Low tumor ADC value by DWI was a risk factor for early postoperative HCC recurrence and was associated with lower patient survival rates.

Effect of exogenous spermidine on polyamine content and metabolism in tomato exposed to salinity–alkalinity mixed stress

We investigated the effects of seeds pretreatment with exogenous spermidine (Spd) on the polyamine content and metabolism in the roots of two cultivars of tomato (Solanum lycopersicum), Jinpengchaoguan and Zhongza No. 9 grown under conditions of mixed salinity-alkalinity stress. These cultivars differ in their tolerance to salinity stress, with the former more tolerant than the latter. PA content, whether in its free forms, soluble conjugated forms, or insoluble bound forms, increased significantly during salinity-alkalinity stress. The activities of S-adenosylmethionine decarboxylase (SAMDC) and diamine oxidase (DAO), concentrations of free Spd, soluble conjugated forms of Spd and spermine (Spm), and insoluble bound form of Spd in the roots were enhanced to a greater extent in cv. Jinpengchaoguan roots than in cv. Zhongza No.9 in response to salinity-alkalinity stress. Interestingly, Spd application to seeds markedly suppressed the accumulation of free Put, but promoted an increase in free Spd and Spm concentrations, as well as soluble conjugated forms of Spd and insoluble bound forms of Put in both cultivars. From these data, we deduced that exogenous Spd promotes the conversion of free Put into free Spd and Spm, and soluble conjugated forms and insoluble bound forms of PAs under salinity-alkalinity stress. Furthermore, under salinity-alkalinity stress conditions, exogenous Spd enhanced the activities of ODC, SAMDC and DAO, and reduced the activities of ADC and polyamine oxidase (PAO) in cv. Zhongza No.9 roots. In addition, exogenous Spd reduced the activities of ADC and ODC, and increased the activities of DAO and SAMDC in cv. Jinpengchaoguan roots under salinity-alkalinity stress conditions. These results suggest that exogenous Spd treatment can regulate the metabolic status of polyamines caused by salinity-alkalinity stress, and eventually enhance tolerance of tomato plants to salinity-alkalinity stress. Additionally, Spd treatments have varying effects on different tolerant tomato cultivars.