Regulation of docetaxel resistant cancer stem-like cells by RENCA macrobeads

Despite the initial efficacy of chemotherapy, resistant cells often persist and are thought to contribute to disease relapse. Resistant cells, characterized by stem-like properties, exhibit numerous survival mechanisms, making eradication of these rare cells a significant clinical challenge. We have previously shown that murine renal adenocarcinoma (RENCA) cells encapsulated in agarose macrobeads (MB) form tumor colonies over several months that secrete diffusible factors, which regulate their own growth as well as the growth of freely growing tumor cells outside the macrobead. Young RENCA MBs produce factors necessary for growth and differentiation while mature macrobeads secrete tumor inhibitory proteins. In the current study, we evaluated the effect of young and mature RENCA MBs on the in vitro regulation of docetaxel (DTX) resistant cell populations and in vivo on tumor burden in BALB/cJ mice induced with DTX resistant cells. RENCA MBs were exposed to DTX (5 μg/mL) and maintained in culture for 6 wks to establish resistant cells, followed by culture alone (control) or co-cultured with young (3 wks) or mature (>18 wks) normal RENCA MBs. Incidence and time of macrobead tumor recurrence were evaluated. Also, six weeks following DTX treatment, 10 resistant cells recovered from RENCA MBs were embedded in a fibrin clot and placed under the kidney capsule along with abdominal implantation of young or mature macrobeads. Animals that did not receive macrobeads served as the control. In vitro, 21.5% of macrobeads treated with DTX developed recurrent tumor colonies by 24 weeks (control group) with first evidence at 12 weeks. Following co-culture with young RENCA MBs, 86.8% of macrobeads showed evidence of recurrence with earliest indication at 4 weeks. Culture with mature RENCA MBs significantly reduced the incidence of macrobead tumor recurrence to 1.1% with first evidence noted at 22 weeks. Consistent with in vitro data, 4 of 10 mice in the control group developed palpable tumors 27-29 days following tumor induction while 8 of 10 mice showed evidence of tumors with young macrobead implantation. Remarkably, to date (36 days), none of the mice implanted with mature RENCA MBs developed tumors. Preliminary data suggests that mean tumor volumes (cm3) were smaller (2.6 ± 0.8) in the control group vs. the young macrobead implanted group (6.3 ± 2.3). Furthermore, metastases were localized to the abdomen in the control group (1 of 4 mice) while they were diffuse and prevalent in the abdominal cavity, liver, diaphragm and lungs following implantation of young macrobeads (4 of 4 mice). These data support the notion that RENCA macrobeads function as a biological system that could be utilized as a novel tool to eradicate or maintain dormancy of resistant cancer cell populations. Phase 2 clinical trials of RENCA macrobeads for the treatment of resistant colorectal cancer have been completed (Trial Nos. NCT01053013 and NCT02046174) with a Phase 3 trial planned. Citation Format: Prithy Caroline Martis, Atira T. Dudley, Pradeep R. Dumpala, Hunter L. Gazda, Melissa A. Bemrose, Barry H. Smith, Lawrence S. Gazda. Regulation of docetaxel resistant cancer stem-like cells by RENCA macrobeads [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1285.