Biomedical subjects

Adam I Marcus

Publications and source records attributed to Adam I Marcus.

7 recordsLinked to original sources

PubMed2025

Suppression of LKB1-mutant lung adenocarcinoma by natural killer cells from females.

BACKGROUND: This study addressed the enigma of sex differences in smoking-related lung cancer, particularly focusing on the low LKB1 mutation frequency in female patients with lung adenocarcinoma. METHODS: Sex bias was studied with a genetically engineered mouse model and various tail-vein injection models. Immune cells were analyzed by antibody-depletion study, flow cytometry, and immunofluorescence. The relevance of our findings to human disease was validated by evaluating various lung adenocarcinoma datasets. All statistical tests are 2-sided. RESULTS: A statistically significant percentage of females are resistant to LKB1-mutant tumor formation in our models, reflecting this sex difference in humans. Natural killer (NK) cells were identified as a critical factor in this sex-biased response. This sex difference was observed primarily in LKB1-mutant lung adenocarcinoma, probably due to their low major histocompatibility complex class I level, making them the ideal target for NK cells through the missing-self recognition. Although females resistant to LKB1-mutant lung adenocarcinoma formation did not have enhancement of any specific NK subpopulation, our immunofluorescence analysis revealed high numbers of NKs in female lungs even with the presence of LKB1-mutant lung adenocarcinoma. Our gene set enrichment analysis of The Cancer Genome Atlas-lung adenocarcinoma dataset also showed that female LKB1-mutant lung adenocarcinoma patients have a stronger NK-mediated response after adjusting for other male-female differences using the LKB1 wild-type lung adenocarcinoma dataset. CONCLUSION: Females have a stronger NK-mediated response against LKB1-mutant lung adenocarcinoma, which was present in our mouse model and the human lung adenocarcinoma dataset. This study revealed a novel role of NK cells in suppressing LKB1-mutant lung adenocarcinoma in females, which should be assessed in the clinical setting in the future.

Killer Cells, Natural↗

PubMed2006

Farnesyltransferase inhibitors reverse taxane resistance.

The combination of farnesyltransferase inhibitors (FTIs) and taxanes has been shown to result in potent antiproliferative and antimitotic synergy. Recent phase I and II clinical trials have shown that this combination shows clinical activity in taxane-refractory or taxane-resistant cancer patients. To understand the mechanism behind these clinical observations, we used a cancer cell model of paclitaxel resistance and showed that the FTI/taxane combination retains potent antiproliferative, antimitotic, and proapoptotic activity against the paclitaxel-resistant cells, at doses where each drug alone has little or no activity. To probe the mechanistic basis of these observations, paclitaxel activity was monitored in living cells using the fluorescently conjugated paclitaxel, Flutax-2. We observed that all FTIs tested increase the amount of microtubule-bound Flutax-2 and the number of microtubules labeled with Flutax-2 in both paclitaxel-resistant and paclitaxel-sensitive cells. Importantly, we observed a consequential increase in microtubule stability and tubulin acetylation with the combination of the two drugs, even in paclitaxel-resistant cells, confirming that the enhanced taxane binding in the presence of FTI affects microtubule function. Furthermore, this mechanism is dependent on the function of the tubulin deacetylase, HDAC6, because in cells overexpressing a catalytically inactive HDAC6, FTIs are incapable of enhancing Flutax-2-microtubule binding. Similar results were obtained by using an FTI devoid of farnesyltransferase inhibitory activity, indicating that functional inhibition of farnesyltransferase is also required. Overall, these studies provide a new insight into the functional relationship between HDAC6, farnesyltransferase, and microtubules, and support clinical data showing that the FTI/taxane combination is effective in taxane-refractory patients.

Antineoplastic Agents↗

PubMed2006

Arl2 and Arl3 regulate different microtubule-dependent processes.

Arl2 and Arl3 are closely related members of the Arf family of regulatory GTPases that arose from a common ancestor early in eukaryotic evolution yet retain extensive structural, biochemical, and functional features. The presence of Arl3 in centrosomes, mitotic spindles, midzones, midbodies, and cilia are all supportive of roles in microtubule-dependent processes. Knockdown of Arl3 by siRNA resulted in changes in cell morphology, increased acetylation of alpha-tubulin, failure of cytokinesis, and increased number of binucleated cells. We conclude that Arl3 binds microtubules in a regulated manner to alter specific aspects of cytokinesis. In contrast, an excess of Arl2 activity, achieved by expression of the [Q70L]Arl2 mutant, caused the loss of microtubules and cell cycle arrest in M phase. Initial characterization of the underlying defects suggests a defect in the ability to polymerize tubulin in the presence of excess Arl2 activity. We also show that Arl2 is present in centrosomes and propose that its action in regulating tubulin polymerization is mediated at centrosomes. Somewhat paradoxically, no phenotypes were observed Arl2 expression was knocked down or Arl3 activity was increased in HeLa cells. We conclude that Arl2 and Arl3 have related but distinct roles at centrosomes and in regulating microtubule-dependent processes.

ADP-Ribosylation Factors↗

PubMed2005

Cyclostreptin (FR182877), an antitumor tubulin-polymerizing agent deficient in enhancing tubulin assembly despite its high affinity for the taxoid site.

Cyclostreptin (FR182877), a bacterial natural product, was reported to have weak paclitaxel-like activity with tubulin but antitumor activity in vivo. We used synthetic cyclostreptin in studies of its mechanism of action. Although less potent than paclitaxel in several human cancer cell lines, cyclostreptin was active against cells resistant to paclitaxel and epothilone A. At equitoxic concentrations with paclitaxel, cyclostreptin was more effective in arresting MCF-7 cells in mitosis and equivalent in bundling microtubules in PtK(2) cells. Tubulin assembly with paclitaxel occurs at low temperatures and in the absence of GTP or microtubule-associated proteins (MAPs). Brisk assembly with cyclostreptin required MAPs, GTP, and higher reaction temperatures. On the basis of turbidimetry, cyclostreptin-induced microtubules were more stable in the cold than the paclitaxel-induced polymer. Moreover, at 37 degrees C cyclostreptin was a strong competitive inhibitor of the binding of radiolabeled paclitaxel to tubulin polymer, with an apparent K(i) value of 88 nM. Competition studies versus a fluorescent taxoid across a temperature range, in comparison with paclitaxel and docetaxel, showed that only the binding of cyclostreptin to microtubules was markedly reduced at 4 degrees C versus temperatures over 30 degrees C. The binding of cyclostreptin to microtubules was characterized by a relatively greater endothermic and entropic profile as compared with those of the taxoid binding reactions, which are characterized more by exothermic and enthalpic interactions. Molecular modeling showed that cyclostreptin formed a pharmacophore with taxoids but formed hydrogen bonds only with the S9-S10 and M loops in the taxoid site. Initial studies also indicate that, relative to paclitaxel, cyclostreptin is more deficient in nucleation than elongation of polymer.

Animals↗

PubMed2005

The synergistic combination of the farnesyl transferase inhibitor lonafarnib and paclitaxel enhances tubulin acetylation and requires a functional tubulin deacetylase.

Farnesyl transferase (FT) inhibitors (FTI) are anticancer agents developed to target oncogenic Ras proteins by inhibiting Ras farnesylation. FTIs potently synergize with paclitaxel and other microtubule-stabilizing drugs; however, the mechanistic basis underlying this synergistic interaction remains elusive. Here we show that the FTI lonafarnib affects the microtubule cytoskeleton resulting in microtubule bundle formation, increased microtubule stabilization and acetylation, and suppression of microtubule dynamics. Notably, treatment with the combination of low doses of lonafarnib with paclitaxel markedly enhanced tubulin acetylation (a marker of microtubule stability) as compared with either drug alone. This synergistic effect correlated with FT inhibition and was accompanied by a synergistic increase in mitotic arrest and cell death. Mechanistically, we show that the combination of lonafarnib and paclitaxel inhibits the in vitro deacetylating activity of the only known tubulin deacetylase, histone deacetylase 6 (HDAC6). In addition, the lonafarnib/taxane combination is synergistic only in cells lines expressing the wild-type HDAC6, but not a catalytic-mutant HDAC6, revealing that functional HDAC6 is required for the synergy of lonafarnib with taxanes. Furthermore, tubacin, a specific HDAC6 inhibitor, synergistically enhanced tubulin acetylation in combination with paclitaxel, similar to the combination of lonafarnib and paclitaxel. Taken together, these data suggest a relationship between FT inhibition, HDAC6 function, and cell death, providing insight into the putative molecular basis of the lonafarnib/taxane synergistic antiproliferative combination.

Acetylation↗

PubMed2005

Mitotic kinesin inhibitors induce mitotic arrest and cell death in Taxol-resistant and -sensitive cancer cells.

Taxanes are powerful chemotherapy agents that target the microtubule cytoskeleton, leading to mitotic arrest and cell death; however, their clinical efficacy has been hampered due to the development of drug resistance. Therefore, other proteins involved in spindle assembly are being examined as potential targets for anticancer therapy. The mitotic kinesin, Eg5 is critical for proper spindle assembly; as such, inhibition of Eg5 leads to mitotic arrest making it a potential anticancer target. We wanted to validate Eg5 as a therapeutic target and determine if Eg5 inhibitors retain activity in Taxol-resistant cells. Using affinity chromatography we first show that the compound HR22C16 is an Eg5 inhibitor and does not interact with other microtubule motor proteins tested. Furthermore, HR22C16 along with its analogs, inhibit cell survival in both Taxol-sensitive and -resistant ovarian cancer cells with at least 15-fold greater efficacy than monastrol, the first generation Eg5 inhibitor. Further analysis with HR22C16-A1, the most potent HR22C16 analog, showed that it retains efficacy in PgP-overexpressing cells, suggesting that it is not a PgP substrate. We further show that HR22C16-A1 induces cell death following mitotic arrest via the intrinsic apoptotic pathway. Interestingly, the combination of HR22C16-A1 with Taxol results in an antagonistic antiproliferative and antimitotic effect, possibly due to the abrogation of Taxol-induced mitotic spindles by HR22C16-A1. Taken together, our results show that Eg5 inhibitors have promising anticancer activity and can be potentially used to overcome Taxol resistance in the clinical setting.

Antineoplastic Agents↗

PubMed2002

Arabidopsis thaliana protein, ATK1, is a minus-end directed kinesin that exhibits non-processive movement.

The microtubule cytoskeleton forms the scaffolding of the meiotic spindle. Kinesins, which bind to microtubules and generate force via ATP hydrolysis, are also thought to play a critical role in spindle assembly, maintenance, and function. The A. thaliana protein, ATK1 (formerly known as KATA), is a member of the kinesin family based on sequence similarity and is implicated in spindle assembly and/or maintenance. Thus, we want to determine if ATK1 behaves as a kinesin in vitro, and if so, determine the directionality of the motor activity and processivity character (the relationship between molecular "steps" and microtubule association). The results show that ATK1 supports microtubule movement in an ATP-dependent manner and has a minus-end directed polarity. Furthermore, ATK1 exhibits non-processive movement along the microtubule and likely requires at least four ATK1 motors bound to the microtubule to support movement. Based on these results and previous data, we conclude that ATK1 is a non-processive, minus-end directed kinesin that likely plays a role in generating forces in the spindle during meiosis.

Arabidopsis↗