Chemical dissection of the cell cycle: probes for cell biology and anti-cancer drug development

Cancer cell proliferation relies on the ability of cancer cells to grow, transition through the cell cycle, and divide. To identify novel chemical probes for dissecting the mechanisms governing cell cycle progression and cell division, and for developing new anti-cancer therapeutics, we developed and performed a novel cancer cell-based high-throughput chemical screen for cell cycle modulators. This approach identified novel G1, S, G2, and M-phase specific inhibitors with drug-like properties and diverse chemotypes likely targeting a broad array of processes. We further characterized the M-phase inhibitors and highlight the most potent M-phase inhibitor MI-181, which targets tubulin, inhibits tubulin polymerization, activates the spindle assembly checkpoint, arrests cells in mitosis, and triggers a fast apoptotic cell death. Importantly, MI-181 has broad anti-cancer activity, especially against BRAF^V600E melanomas.

Abstract 5015: TCR usage analysis in blood reveals different mechanisms of action of CTLA-4 and PD-1 blockade in patients

Immune-checkpoint blockade therapies are providing long-lasting responses in a subset of patients with malignant metastatic melanoma. In an effort to better understand the underlying mechanism, the T-cell population in peripheral blood mononuclear cells (PBMCs) was characterized. The complementarity determining region 3 (CDR3) of the rearranged T cell receptor variable ß chain genes (TCR Vß) was sequenced. This was performed using gDNA extracted from the PBMCs of twenty-one patients that were treated with antibody to Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4) (tremelimumab) and seven patients that were treated with antibody to the Programmed Death-1 (PD-1) blockade (MK-3475) at baseline and at day 30-60 post first treatment. Four healthy donors were also sequenced as controls. Control PBMCs displayed random distribution with three patients showing a decrease and one showing an increase in the number of unique productive sequences (UPS) from baseline to the time after first cycle. In PBMCs from patients receiving the CTLA-4 antibody, two out of 21 samples showed a decrease in total number of UPS, while 19 out of 21samples experienced an increase. In PBMCs from patients receiving PD-1 antibody, the reponse was more similar to healthy donors as 5 out of 7 (71%) displayed a decrease and 2 out 7 (29%) an increase in total UPS from the pre to post timepoint. There was an increase in the absolute lymphocyte count (ALC) after CTLA-4 blockade therapy (p=0.03), but not in the samples from patients treated with PD-1 antibody (p=0.53). A direct correlation between ALC increase and increase in UPS for CTLA-4 blockade was ruled out (p=0.1 Spearman Correlation). When analyzing according to clinical response status, all responders to CTLA-4 blockade (4 out of 19) experienced an increase in the number of circulating clones. However, samples from clinical responders to PD-1 blockade showed an increase (2 out of 5) or decrease (1 out of 2) in the circulating pool. Considering the concerning toxicity profile for CTLA-4-blockade versus the mild toxicity for PD-1 antibodies, this data supports a model where CTLA-4 blockade induces a non-specific systemic expansion of T cells, while PD-1 blockade may have more specific effects directly in the tumor.

Citation Format: Lidia Robert, Christina L. Harview, Ryan Emerson, Stephen Mok, Blanca Homet, Begonya Comin-Anduix, Richard C. Koya, Harlan Robins, Paul C. Tumeh, Antoni Ribas. TCR usage analysis in blood reveals different mechanisms of action of CTLA-4 and PD-1 blockade in patients. [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 5015. doi:10.1158/1538-7445.AM2014-5015

Distinct immunological mechanisms of CTLA-4 and PD-1 blockade revealed by analyzing TCR usage in blood lymphocytes

Targeting immune inhibitory receptors has brought excitement, innovation and hope to cancer patients. Our recent work revealed the immunological effects of blocking the CTLA4 and PD-1 immune checkpoints on T cell receptor usage among peripheral blood cells, and further uncovers how the expansion of the T cell repertoire matches the immunotoxicity profile of the therapy.

CTLA4 blockade broadens the peripheral T-cell receptor repertoire

PURPOSE

To evaluate the immunomodulatory effects of cytotoxic T-lymphocyte-associated protein 4 (CTLA4) blockade with tremelimumab in peripheral blood mononuclear cells (PBMC).

EXPERIMENTAL DESIGN

We used next-generation sequencing to study the complementarity-determining region 3 (CDR3) from the rearranged T-cell receptor (TCR) variable beta (V-beta) in PBMCs of 21 patients, at baseline and 30 to 60 days after receiving tremelimumab.

RESULTS

After receiving tremelimumab, there was a median of 30% increase in unique productive sequences of TCR V-beta CDR3 in 19 out of 21 patients, and a median decrease of 30% in only 2 out of 21 patients. These changes were significant for richness (P = 0.01) and for Shannon index diversity (P = 0.04). In comparison, serially collected PBMCs from four healthy donors did not show a significant change in TCR V-beta CDR3 diversity over 1 year. There was a significant difference in the total unique productive TCR V-beta CDR3 sequences between patients experiencing toxicity with tremelimumab compared with patients without toxicity (P = 0.05). No relevant differences were noted between clinical responders and nonresponders.

CONCLUSIONS

CTLA4 blockade with tremelimumab diversifies the peripheral T-cell pool, representing a pharmacodynamic effect of how this class of antibodies modulates the human immune system.

The era of oral drugs in oncology: What do patients think about their efectiveness?

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Background: With the growing number of drugs available for the treatment of cancer, most of them of oral administration, some aspects of the everyday clinical practice are changing. Interesting is the opinion of the patients (pts) about oral therapy. Methods: We researched differences in preference, tolerance, effectiveness, and safety by means of the delivery of a survey to (pts) who had received oral and intravenous (IV) treatment. One hundred and ninety (pts) were enrolled from September to November 2008. Results: Seventy percent of the (pts) studied were women, the median age at diagnosis was 60 years (range, 28 - 91 years). Fifty percent had gynaecologic tumors; thirty percent digestive; eighteen percent lung cancer and two percent other tumors, with a median of 3 different lines of therapy (range, 1 to 9). Patients preferred the oral route over the IV (76% vs. 20% respectively; P<0.001) and four percent had no preference. Tolerance was better with oral therapy (64%) than with (IV) chemotherapy (CT) (36%; P<0.001). When the (pts) were asked for effectiveness, sixty percent of them considered the (IV) chemotherapy more effective, while eleven percent chose oral therapy and twenty-nine percent found both equally effective (p<0.001). Sixty one percent of the (pts) evaluated as more secure (IV) chemotherapy, while eight percent did so with oral therapy and thirty one percent did not think that differences existed with one or another route of administration (p< 0.001). Conclusions: The constant evolution in cancer therapy and the increasing participation of (pts) in therapeutic decisions makes it imperative to know the opinion of (pts) on these new treatments. When patients are asked for tolerance or preference, the majority of them choose the oral route. However, when asked about important issues such as effectiveness or safety that offers a treatment, most of them prefer the intravenous route.

No significant financial relationships to disclose.