A Phase I Study of sequences of the CDK4/6 Inhibitor, Ribociclib Combined with Gemcitabine in Patients with Advanced Solid Tumors.

Background: Based on preclinical data showing addition of CDK4/6 inhibitors to gemcitabine is synergistic, ribociclib was evaluated in combination with gemcitabine to determine the maximum tolerated dose (MTD) and dose limiting toxicities (DLT). Methods: In this single arm multicohort phase I trial, we evaluated the safety and efficacy of Ribociclib plus Gemcitabine in patients with advanced solid tumors. Patients received Gemcitabine intravenously on days 1 and 8 followed by Ribociclib days 8-14, with treatment repeated every 3 weeks. Results: The study enrolled 43 patients between October 2017 and September 2019. The escalation phase (19 patients) determined the MTD and recommended phase II dose (RP2D) to be ribociclib 800mg daily and gemcitabine 1000mg/m2 for the expansion phase (24 patients). One patient experienced Grade 4 thrombocytopenia. Eleven patients experienced Grade 3 adverse events (AE), the most common being neutropenia, thrombocytopenia, and anemia. No partial or complete responses were observed. 15/22 (68%) of efficacy evaluable patients who received the MTD achieved best response of stable disease. Conclusions: The addition of Ribociclib to Gemcitabine was tolerated well and yielded stability of tumors in both cohorts. Ribociclib and gemcitabine could have synergistic activity in certain tumor types, and our data provides support for the combination. Clinical Trial Registration: NCT03237390.

Syk-dependent homologous recombination activation promotes cancer resistance to DNA targeted therapy.

Enhanced DNA repair is an important mechanism of inherent and acquired resistance to DNA targeted therapies, including poly ADP ribose polymerase (PARP) inhibition. Spleen associated tyrosine kinase (Syk) is a non-receptor tyrosine kinase acknowledged for its regulatory roles in immune cell function, cell adhesion, and vascular development. This study presents evidence indicating that Syk expression in high-grade serous ovarian cancer and triple-negative breast cancers promotes DNA double-strand break resection, homologous recombination (HR), and subsequent therapeutic resistance. Our investigations reveal that Syk is activated by ATM following DNA damage and is recruited to DNA double-strand breaks by NBS1. Once localized to the break site, Syk phosphorylates CtIP, a pivotal mediator of resection and HR, at Thr-847 to promote repair activity, particularly in Syk-expressing cancer cells. Inhibition of Syk or its genetic deletion impedes CtIP Thr-847 phosphorylation and overcomes the resistant phenotype. Collectively, our findings suggest a model wherein Syk fosters therapeutic resistance by promoting DNA resection and HR through a hitherto uncharacterized ATM-Syk-CtIP pathway. Moreover, Syk emerges as a promising tumor-specific target to sensitize Syk-expressing tumors to PARP inhibitors, radiation and other DNA-targeted therapies.

Syk-dependent alternative homologous recombination activation promotes cancer resistance to DNA targeted therapy.

Enhanced DNA repair is an important mechanism of inherent and acquired resistance to DNA targeted therapies, including poly ADP ribose polymerase inhibition. Spleen associated tyrosine kinase (Syk) is a non-receptor tyrosine kinase known to regulate immune cell function, cell adhesion, and vascular development. Here, we report that Syk can be expressed in high grade serous ovarian cancer and triple negative breast cancers and promotes DNA double strand break resection, homologous recombination (HR) and therapeutic resistance. We found that Syk is activated by ATM following DNA damage and is recruited to DNA double strand breaks by NBS1. Once at the break site, Syk phosphorylates CtIP, a key mediator of resection and HR, at Thr-847 to promote repair activity, specifically in Syk expressing cancer cells. Syk inhibition or genetic deletion abolished CtIP Thr-847 phosphorylation and overcame the resistant phenotype. Collectively, our findings suggest that Syk drives therapeutic resistance by promoting DNA resection and HR through a novel ATM-Syk-CtIP pathway, and that Syk is a new tumor-specific target to sensitize Syk-expressing tumors to PARPi and other DNA targeted therapy.

DOCK7 protects against replication stress by promoting RPA stability on chromatin.

RPA is a critical factor for DNA replication and replication stress response. Surprisingly, we found that chromatin RPA stability is tightly regulated. We report that the GDP/GTP exchange factor DOCK7 acts as a critical replication stress regulator to promote RPA stability on chromatin. DOCK7 is phosphorylated by ATR and then recruited by MDC1 to the chromatin and replication fork during replication stress. DOCK7-mediated Rac1/Cdc42 activation leads to the activation of PAK1, which subsequently phosphorylates RPA1 at S135 and T180 to stabilize chromatin-loaded RPA1 and ensure proper replication stress response. Moreover, DOCK7 is overexpressed in ovarian cancer and depleting DOCK7 sensitizes cancer cells to camptothecin. Taken together, our results highlight a novel role for DOCK7 in regulation of the replication stress response and highlight potential therapeutic targets to overcome chemoresistance in cancer.

Role of adjuvant therapy in stage IIIC2 endometrial cancer.

OBJECTIVE: The role of the different types of adjuvant treatments in endometrial cancer with para-aortic node metastases is unclear. The aim of this study was to report oncologic outcomes after adjuvant therapy in patients with stage IIIC2 endometrial cancer. METHODS: This retrospective single-institution study assessed patients with stage IIIC2 endometrial cancer who underwent primary surgery from January 1984 to December 2014. All patients had hysterectomy (±salpingo-oophorectomy) plus lymphadenectomy (para-aortic nodes, ±pelvic nodes). We included all patients with stage III endometrial cancer and documented para-aortic lymph node metastases (International Federation of Obstetrics and Gynecologists stage IIIC2). We excluded patients who did not provide consent, who had synchronous cancer, or who underwent neoadjuvant chemotherapy. Follow-up was restricted to the first 5 years post-operatively. Cox proportional hazards models, with age as the time scale, was used to evaluate associations of risk factors with disease-free survival and overall survival. RESULTS: Among 105 patients with documented adjuvant therapy, external beam radiotherapy was administered to 25 patients (24%), chemotherapy to 24 (23%), and a combination (chemotherapy and external beam radiotherapy) to 56 (53%) patients. Most patients receiving chemotherapy and external beam radiotherapy (80%) had chemotherapy first. The majority of relapses had a distant component (31/46, 67%) and only one patient had an isolated para-aortic recurrence. Non-endometrioid subtypes had poorer disease-free survival (HR 2.57; 95% CI 1.38 to 4.78) and poorer overall survival (HR 2.00; 95% CI 1.09 to 3.65) compared with endometrioid. Among patients with endometrioid histology (n=60), chemotherapy and external beam radiotherapy improved disease-free survival (HR 0.22; 95% CI 0.07 to 0.71) and overall survival (HR 0.28; 95% CI 0.09 to 0.89) compared with chemotherapy or external beam radiotherapy alone. Combination therapy did not improve prognosis for patients with non-endometrioid histology (n=45). CONCLUSIONS: In our cohort of patients with stage IIIC2 endometrioid endometrial cancer, those receiving chemotherapy and external beam radiotherapy had improved survival compared with patients receiving chemotherapy or external beam radiotherapy alone. However, the prognosis of patients with non-endometrioid endometrial cancer remained poor, regardless of the adjuvant therapy administered. Distant recurrences were the most common sites of failure.

A microfluidic platform for cultivating ovarian cancer spheroids and testing their responses to chemotherapies.

There is increasing interest in utilizing in vitro cultures as patient avatars to develop personalized treatment for cancer. Typical cultures utilize Matrigel-coated plates and media to promote the proliferation of cancer cells as spheroids or tumor explants. However, standard culture conditions operate in large volumes and require a high concentration of cancer cells to initiate this process. Other limitations include variability in the ability to successfully establish a stable line and inconsistency in the dimensions of these microcancers for in vivo drug response measurements. This paper explored the utility of microfluidics in the cultivation of cancer cell spheroids. Six patient-derived xenograft (PDX) tumors of high-grade serous ovarian cancer were used as the source material to demonstrate that viability and epithelial marker expression in the microfluidic cultures was superior to that of Matrigel or large volume 3D cultures. To further demonstrate the potential for miniaturization and multiplexing, we fabricated multichamber microfluidic devices with integrated microvalves to enable serial seeding of several chambers followed by parallel testing of several drug concentrations. These valve-enabled microfluidic devices permitted the formation of spheroids and testing of seven drug concentrations with as few as 100,000 cancer cells per device. Overall, we demonstrate the feasibility of maintaining difficul-to-culture primary cancer cells and testing drugs in a microfluidic device. This microfluidic platform may be ideal for drug testing and personalized therapy when tumor material is limited, such as following the acquisition of biopsy specimens obtained by fine-needle aspiration.