Subcutaneous transplantation of as few as 200 HCKs expressing E6E7 and HRAS(G12V) resulted in tumor formation within 2 months.
Dissecting RAS signaling pathways, constitutively active forms of AKT1 or MEK1 did not result in tumor formation with E6E7, but tumorigenic transformation was induced with addition of MYC. Increased MYC expression endowed resistance to calcium- and serum-induced terminal differentiation and activated the mammalian target of rapamycin (mTOR) pathway.
An mTOR inhibitor (Rapamycin) and MYC inhibition a level not affecting proliferation in culture both markedly suppressed tumor formation by HCKs expressing E6E7 and HRAS(G12V). These results suggest that a single mutation of HRAS could be oncogenic in the background of deregulated expression of E6E7 and MYC plays a critical role in cooperation with the RAS signaling pathways in tumorigenesis.
Thus inhibition of MYC and/or the downstream mTOR pathway could be a therapeutic strategy not only for the MYC-altered but also RAS-activated cancers.