LB-100

LB-100 sensitizes hepatocellular carcinoma cells to the effects of sorafenib during hypoxia by activation of Smad3 phosphorylation.[Pubmed:26666823]

Tumour Biol. 2016 Jun;37(6):7277-86.

Hepatocellular carcinoma (HCC) is a common cancer with poor prognosis. The multikinase inhibitor sorafenib is the only clinically proved systematic treatment for HCC. However, few patients respond to sorafenib. Hypoxic microenvironments contribute to sorafenib resistance. LB-100, a serine/threonine protein phosphatase 2A (PP2A) inhibitor was previously found to be a chemosensitizer in HCC. Here, we tested whether LB-100 could sensitize HCC to the effects of sorafenib. Intriguingly, LB-100 enhanced the effects of sorafenib in HCC cells only during hypoxic environments. LB-100 dramatically increased intracellular p-Smad3 level, which was responsible for the effect of LB-100 as a sensitizer. LB-100 downregulated Bcl-2 expression and enhanced sorafenib-induced apoptosis in HCC cells. We further proved that PP2A mediated LB-100-induced p-Smad3 overexpression. In addition, p38 mitogen-activated protein kinase pathway was activated in hypoxic conditions, and enhanced p-Smad3-dependent Bcl-2 inhibition and consequent apoptosis. In conclusion, LB-100 sensitized HCC cells to sorafenib in hypoxic environments. This effect was mediated by inactivation of PP2A, resulting in enhanced level of p-Smad3. Increased p-Smad3 downregulated Bcl-2, causing increased apoptosis of HCC cells.

Safety, Tolerability, and Preliminary Activity of LB-100, an Inhibitor of Protein Phosphatase 2A, in Patients with Relapsed Solid Tumors: An Open-Label, Dose Escalation, First-in-Human, Phase I Trial.[Pubmed:28039265]

Clin Cancer Res. 2017 Jul 1;23(13):3277-3284.

Purpose: To determine the MTD and to assess the safety, tolerability, and potential activity of LB-100, a first-in-class small-molecule inhibitor of protein phosphatase 2A (PP2A) in adult patients with progressive solid tumors.Experimental Design: LB-100 was administered intravenously daily for 3 days in 21-day cycles in a 3 + 3 dose escalation design.Results: There were 29 patient entries over 7 dose escalations. One patient stopped treatment after one dose because of an acute infection and was reenrolled after recovery; each course was analyzed as a separate patient entry. Two patients had dose-limiting toxicity (reversible increases in serum creatinine or calculated serum creatinine clearance) at the 3.1 mg/m(2) level. Probable or possible study drug-related grade 3 adverse events occurred in 6 (20.7%) patients [anemia (n = 2), decreased creatinine clearance, dyspnea, hyponatremia, and lymphopenia]. Ten (50%) of 20 response-evaluable patients had stable disease for four or more cycles. One patient with pancreatic adenocarcinoma had a partial response noted after 10 cycles, which was maintained for five additional cycles. The other patients achieving stable disease had one of the following: fibrosarcoma, chondrosarcoma, thymoma, atypical carcinoid of lung, or ovarian, testicular, breast (n = 2), and prostate cancer. The recommended phase II dose of LB-100 is 2.33 mg/m(2) daily for 3 days every 3 weeks.Conclusions: The safety, tolerability, preliminary evidence of antitumor activity, and novel mechanism of action of LB-100 support its continued development alone and in combination with other therapies. Clin Cancer Res; 23(13); 3277-84. (c)2016 AACR.