Purpose Mutations in KRAS are considered to be the main drivers of acquired resistance to epidermal growth factor receptor (EGFR) blockade in patients with metastatic colorectal cancer (mCRC). However, the potential roles of other genes downstream of the EGFR signaling pathway in conferring acquired resistance has not been extensively investigated. Experimental Design Using circulating tumor DNA (ctDNA) from patients with mCRC and with acquired cetuximab resistance, we developed a targeted amplicon ultra-deep sequencing method to screen for low-abundance somatic mutations in a panel of genes that encode components of the EGFR signaling pathway. Mutations with significantly increased variant frequencies upon disease progression were selected by using quartile analysis. The functional consequences of the identified mutations were validated in cultured cells. Results We analyzed 32 patients with acquired cetuximab resistance in a development cohort. Of them, 7 (22%) carried five novel PIK3CA mutations, whereas 8 (25%) carried previously reported KRAS mutations. Functional studies showed that novel PIK3CA mutations (all in exon 19; p.K944N, p.F930S, p.V955G, p.V955I, and p.K966E) promote cell viability in the presence of cetuximab. Only one novel PIK3CA mutation (p.K944N) was verified in one of the 27 patients with acquired resistance in a validation cohort, simultaneous KRAS and PIK3CA hotspot mutations were detected in 2 patients. Among the above 59 acquired resistance patients, those with PIK3CA or RAS mutations detected in ctDNA showed a pronounced decrease in progression-free survival than patients with no mutation. Conclusions The PIK3CA mutations may potentially contribute to acquired cetuximab resistance in patients with mCRC.

Sulfatinib is a small molecule kinase inhibitor that targets tumor angiogenesis and immune modulation. This phase I study (NCT02133157) investigated the safety, pharmacokinetic characteristics, and preliminary anti-tumor activity of sulfatinib in patients with advanced solid tumors. The study included a dose-escalation phase (50-350 mg/day, 28-day cycle) with a Fibonacci (3+3) design, and a tumor-specific expansion phase investigating the tumor response to treatment. Two sulfatinib formulations were assessed: formulation 1 (5, 25, and 50 mg capsules) and formulation 2 (50 and 200 mg capsules). Seventy-seven Chinese patients received oral sulfatinib; the maximum tolerated dose was not reached. Dose-limiting toxicities included abnormal hepatic function and coagulation tests, and upper gastrointestinal hemorrhage. The most common treatment-related adverse events were proteinuria, hypertension and diarrhea. Among 34 patients receiving sulfatinib formulation 2, one patient with hepatocellular carcinoma and eight with neuroendocrine tumors exhibited a partial response; 15 had stable disease. The objective response rate was 26.5% (9/34) and the disease control rate was 70.6% (24/34). Pharmacokinetic, safety, and efficacy data supported continuous oral administration of sulfatinib at 300 mg as the recommended phase II dose. Sulfatinib exhibited an acceptable safety profile and encouraging antitumor activity in patients with advanced solid tumors, particularly neuroendocrine tumors.